United States Air and EPA-430-B-93-005
Environmental Protection Radiation October 1993
Agency (6205J)
svEPA No-Clean Soldering To
Eliminate CFC-113 and Methyl
Chloroform Cleaning of Printed
Circuit Board Assemblies
Printed on Recycled Paper
-------
ICOLP*
NO-CLEAN SOLDERING TO ELIMINATE CFC-113 AND
METHYL CHLOROFORM CLEANING OF PRINTED CIRCUIT
BOARD ASSEMBLIES
by
James Attpeter
Stephen O. Andersen
Mike Cooper
Carl Eckersley
Larry Ferguson
Leslie Girth (Chair)
Larry Ucntenberg
James McNeil, Jr.
Waft Pillar
Irene Sterian
Richard Szymanowski
Rick Wade
Michael Zatz
Stephen O. Andersen, Project Director
Nina Bonnelycke, Solvent Substitutes Manager
U.S. Environmental Protection Agency
Stratospheric Protection Division
* ICOLP is the Industry Cooperative for Ozone Layer Protection. ICOLP corporate member companies include AT&T, British
Aerospace. Compaq Computer Corporation, Digital Equipment Corporation, Ford Motor Company, Hitachi Limited, Honeywell, IBM,
Matsushita Electric Industrial, Mitsubishi Electric Corporation, Motorola, Northern Telecom, Texas Instruments and Toshiba Corporation.
Industry association affiliates include American Electronics Association, Association Pour la Research et Development des Methodes et
Processus Industriels, Electronic Industries Association, Halogcnated Solvents industry Alliance (U.S.), Japan Electrical Manufacturers
Association, and Korea Specialty Chemical Industry Association. Government organization affiliates include the City of Irvine, California,
the Russian Institute of Applied Chemistry, the Swedish National Environmental Protection Agency, the U.S. Air Force, and the U.S.
Environmental Protection Agency. Other organization affiliates include Center for Global Change, Industrial Technology Research
Institute of Taiwan, Korea Anti-Pollution Movement, National Academy of Engineering, and Research Triangle institute.
James Altpeter is employed by Ford Motor Company; Stephen Andersen is employed by the U.S. Environmental Protection Agency; Mike
Cooper is employed by NCR Corporation; Carl Eckersley is employed by Compaq Computer Corporation; Larry Ferguson and James
McNeil, Jr., are employed by the U.S. Air Force; Leslie Guth is employed by AT&T; Larry Lichtenberg is employed by Motorola; Walt
Pillar is employed by GE Aerospace; Irene Sterian is employed by IBM; Richard Szymanowski is employed by Northern Telecom; Rick
Wade is employed by UDS/Motoroia; and Michael Zatz is employed by ICF Incorporated. We would like to thank the many individuals
and companies that provided insight and information thai helped produce this manual. This manual was funded by the U.S. EPA and
ICOLP.
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-------
Hi
Disclaimer
The U.S. Environmental Protection Agency (EPA), the Industry Cooperative for Ozone Layer
Protection (ICOLP), the ICOLP committee members, and the companies that employ the
ICOLP committee members do not endorse the cleaning performance, worker safety, or
environmental acceptability of any of the technical options discussed. Every cleaning
operation requires consideration of worker safety and proper disposal of contaminants and
waste products generated from the cleaning processes. Moreover, as work continues,
including additional toricity testing and evaluation under Section 612 (Safe Alternatives
Policy) of the Clean Air Act Amendments of 1990 and elsewhere, more information on the
health, environmental, and safety effects of alternatives will become available for use in
selecting among the alternatives discussed in this document.
EPA and ICOLP, in furnishing or distributing this information, do not make any warranty
or representation, either express or implied, with respect to its accuracy, completeness, or
utility; nor does EPA and ICOLP assume any liability of any kind whatsoever resulting from
the use of, or reliance upon, any information, material, or procedure contained herein,
including but not limited to any claims regarding health, safety, environmental effects or fate,
efficacy, or performance, made by the source of the information.
Mention of any company or product in this document is for informational purposes only, and
does not constitute a recommendation of any such company or product, either express or
implied by EPA, ICOLP, ICOLP committee members, and the companies that employ the
ICOLP committee members.
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IV
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Table of Contents
List of Exhibits ix
Technical Advisors and Reviewers xi
Foreword 1
The Montreal Protocol 1
U.S. Clean Air Act Amendments 2
Acceleration of ODS Phaseout 6
Excise Tax 6
Other International Phaseout Schedules 6
Cooperative Efforts 7
Structure of the Manual .. 9
Methodology for Selecting a Cleaning or No-Clean Process 11
Technical 11
Economic 13
Summary Charts 15
Cleaning Options . . .. 15
Summary Matrix . . . 15
Introduction to No-Clean Options 19
No-Clean Wave Solder Fluxes 19
Low-Solids No-Clean Fluxes 20
High-Solids No-Clean Fluxes 20
No-Clean Solder Pastes 22
Controlled Atmosphere Soldering 22
Process Details 25
No-Clean Wave Soldering 25
No-Clean Wave Soldering in Air 25
Retrofitting Existing Equipment for Controlled Atmosphere Soldering . 28
New Equipment Options for Controlled Atmosphere Soldering ...... 28
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vi
Table of Contents (Continued)
No-Clean Reflow Soldering 29
No-dean Reflow Soldering in Air 30
Retrofitting Existing Equipment for Controlled Atmosphere Soldering . 30
New Equipment Options for Controlled Atmosphere Soldering 30
Qualification of No-Clean Materials and Processes 31
Material Screening 31
Process Qualification 32
Economics of No-Clean Processes 35
No-Clean Wave Soldering 35
No-Clean Wave Soldering in Air 35
Retrofitting Equipment for Controlled Atmosphere Soldering 35
New Equipment Options 36
No-Clean Reflow Soldering 36
Retrofitting Equipment for Controlled Atmosphere Soldering 36
New Equipment Options 38
Environmental, Health, and Safely Issues 39
Environmental Issues 39
Volatile Organic Compounds (VOCs) '. 39
Waste Disposal 39
Health and Safety 40
Formic Acid 40
Flux Exposure Issues 40
Reduced Oxygen Atmosphere 40
Manual Summary 41
-------
vii
Table of Contents (Continued)
Case Studies ,of Industrial Practices 43
Case Study #1: No-Clean Wave Soldering in a Controlled Atmosphere
Environment 45
Case Study #2: An Alternative Testing Method To Qualify No-Clean
Processes 50
Case Study #3: Evaluation of No-Clean Processes at AT&T ... 54
Case Study #4: Flux Selection Criteria 57
Case Study #5: Spray Fluxing for Today's Soldering Processes 59
Case Study #6: Choice of a No-Clean Process at NCR 61
References 67
List of Vendors for No-Clean Process Equipment and Materials to Replace
CFC-113 and Methyl Chloroform , 69
Glossary 73
Appendix A: Industry Cooperative for Ozone Layer Protection 77
Appendix B: The IPC Phase-3 Testing Program 79
Appendix C: Patents Relevant to Controlled Atmosphere Soldering 85
Appendix D: Solder Fluxes and Pastes Evaluated by Northern Telecom 87
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viii
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IX
List of Exhibits
Exhibit 1 Parties to the Montreal Protocol (May 1993) 2
Exhibit 2 Ozone-Depleting Solvent Corporate Phaseout Dates 3
Exhibit 3 Excise Tax on Ozone-Depleting Solvents 6
Exhibit 4 Cleaning Options to Replace CFC-113 and Methyl
Chloroform ; 16
Exhibit 5 Summary Matrix Comparing No-Clean Processes 17
Exhibit 6 Composition of Traditional and Low-Solids Flux 21
Exhibit 7 Wetting Comparison Between Nitrogen and Air With
Activated Rosin Flux 24
Exhibit 8 Performance Characteristics of Flux Application Methods 26
Exhibit 9 Comparison of IPC and Bellcore SIR Testing Procedures 33
Exhibit 10 Total Process Material Cost Breakdown for a Traditional
Soldering Process 37
Exhibit 11 SIR Values of Boards from DOE Cells 47
Exhibit 12 Ionic Cleanliness 48
Exhibit 13 Schematic of Dust Box Testing Machine 51
Exhibit 14 Average Ionic Cleanliness of Test Samples 81
Exhibit 15 Average SIR Data from Condensing Atmosphere Tests 82
Exhibit 16 Average SIR Data from Noncondensing Atmosphere Tests 83
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XI
Technical Advisors and Reviewers
The committee thanks the following individuals for providing valuable input during the preparation
of this manual. The committee also expresses its appreciation to their employers for allowing these individuals
the time to review drafts and provide general information to be used in the manual.
Name
Dr. Husamuddin Ahmadzai
Mr. W. Baca
Mr. David Bergman
Mr. David Dodgen
Mr. Donald Elliott
Mr. Joe Felry
Mr. An FitzGerald
Ms. Kathi Johnson
Mr. Sudhakar Kesavan
Ms. Cheryl Lechok
Mr. Jonathon Linton
Mr. James Mertens
Mr. Terry Munson
Mr. Bob Phal
Mr. Ralph Ponce de Leon
Dr. Wallace Rubin
Ms. Laura Turbini
Mr. Yi
Affiliation
Environmental Protection Agency (Sweden)
U.S. Department of Defense
Institute for Interconnecting and Packaging Electronic Circuits (IPC)
Multicore Solders Incorporated
Electrovert Limited (Canada)
Texas Instruments
Northern Telecom Limited (Canada)
Hexacon Electric Co.
ICF Incorporated
Praxair Incorporated
Environmental Design Incorporated
Dow Chemical U.S.A.
Contamination Studies Laboratory Incorporated
Motorola
Motorola
Multicore Solders Limited (United Kingdom)
Georgia Institute of Technology
U.S. Department of Defense
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xii
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FOREWORD
This manual has been prepared jointly by the U.S.
Environmental Protection Agency (EPA) and the
Industry Cooperative for Ozone Layer Protection
(ICOLP1) to aid the electronics industry in its
phaseout of ozone-depleting solvents. It will prove
useful to both large and small- manufacturing
facilities because the processes described are
applicable to a wide range of manufacturing
applications. The manual has been prepared by a
committee of experts from industry, the US. EPA,
and the U.S. Air Force.
In 1987, the U.S. EPA, the Department of
Defense, and the Institute for Interconnecting and
Packaging Electronic Circuits (IPC) formed an Ad
Hoc Solvents Working Group. This working
group concluded that military standards and
specifications inadvertently discouraged and/or
prohibited the use of no-clean processes by
prescribing the flux and solvents that must be used
in specific manufacturing operations. The working
group felt that these constraints were slowing the
rate of technological progress and prohibiting
manufacturers from considering all alternatives to
ozone-depleting solvents. DOD agreed with the
committee's recommendation to switch from
prescriptive standards to performance standards in
a three-phase strategy:
• Phase 1 - Perform a CFC cleaning test to be
used as a benchmark against which other
alternatives would be compared.
• Phase 2 - Evaluate alternative cleaning
formulations against the benchmark and
approve those which clean equal to or better
than the benchmark.
• Phase 3 - Evaluate no-clean controlled
atmosphere soldering processes (See Appendix
B for additional details).
In 1990, the U.S. EPA, ICOLP, and IPC helped
catalyze interest in perfecting no-clean technology.
1 Appendix A presents more detailed information
about ICOLP.
Key manufacturing companies participating in the
efforts included AT&T, Ford, General Electric,
Motorola, and Northern Telecom. This new group
of technical experts and the market clout of the
ICOLP companies helped to quickly commercialize
and implement no-clean technologies. These
cooperative efforts have helped to introduce new
technologies with rapid market penetration and
competitive prices. Many of the experts who
contributed to these achievements are the authors
of this report or are listed in the
acknowledgements.
The Montreal Protocol
The 1987 Montreal Protocol on Substances that
Deplete the Ozone Layer and subsequent 1990 and
1992 amendments and adjustments control the
production and consumption of ozone-depleting
chemicals. At the most recent meeting in
Copenhagen in November 1992, chemicals
including chloroQuorocarbon l,l,2-trichloro-l,2,2-
trifluoroethane (commonly referred to as CFC-
113) and 1,1,1 -trichloroethane (commonly referred
to as methyl chloroform or MCF) were scheduled
for a complete phaseout in developed countries by
the year 1996. The phaseout schedule for
developing countries was unchanged from the
London meeting of Panics (2010 for CFC-113 and
2015 for 1,1,1-trichloroetnane) with a vote on
further acceleration scheduled for 1995. In
addition, the 1992 amendments include a control
schedule for hydrochlorofluorocarbons (HCFCs),
with a production freeze in 1996, reductions in
2000,2010, and 2020, and a complete phaseout in
developed countries by 2030. HCFCs are not yet
controlled for developing countries.
Exhibit 1 lists the countries that have ratified the
Montreal Protocol as of May 1993. In addition,
many companies worldwide have corporate policies
to expedite the phaseout of ozone-depleting
chemicals. Exhibit 2 presents the corporate
phaseout policies for some of these companies. In
addition to providing regulatory schedules for the
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r
Exhibit 1
Algeria
Antigua and Barbuda
Argentina
Australia
Austria
Bahamas
Bahrain
Bangladesh
Barbados
Belarus
Belgium
Botswana
Brazil
Brunei Darussalatn
Bulgaria
Burkina Faso
Cameroon
Canada
Central African
Republic
Chile
China
Congo
Costa Rica
Cote d'lvoire
Croatia
Cuba
Cyprus
Czech Republic
Denmark
Dominica
Date: May, 1993
PARTIES TO THE
Ecuador
Egypt
El Salvador
EEC
Fiji
Finland
France
Gambia
Germany
Ghana
Greece
Grenada
Guatemala
Guinea
Hungary
Iceland
India
Indonesia
Iran
Ireland
Israel
Italy
Jamaica
Japan
Jordan
Kenya
Kiribati
Kuwait
Lebanon
Libyan Arab
Jamahiriya
MONTREAL PROTOCOL
Liechtenstein
Luxembourg
Malawi
Malaysia
Maldives
Malta
Marshall Islands j
Mauritius
Mexico
Monaco
Morocco
Netherlands
New Zealand
Nicaragua
Niger
Nigeria
Norway
Pakistan
Panama
Papua New Guinea
Paraguay
Peru
Philippines
Poland
Portugal
Romania
Republic of Korea
Russian Federation
St. Kitts and Nevis
Samoa
Saudi Arabia
Senegal
Seychelles
Singapore
Slovakia
Slovenia
South Africa
Spain
Sri Lanka
Sudan
Swaziland
Sweden
Switzerland
Syrian Arab Republic
Tanzania
Thailand
Togo
Trinidad & Tobago
Tunisia
Turkey
Uganda
Ukraine
United Arab
Emirates
United Kingdom
United States
Uruguay
Uzbekistan
. Venezuela
Yugoslavia
Zambia
Zimbabwe
phaseout of ozone-depleting chemicals, the
Montreal Protocol established a fund that will
finance the incremental costs of phasing out
ozone-depleting substances by qualifying
developing countries that are Party to the Protocol.
U.S. Clean Air Act
Amendments
The 1990 U.S. Clean Air Act (CAA) amendments
contain several provisions pertaining to
stratospheric ozone protection. Section 602 of the
CAA lists the ozone-depleting substances that are
restricted. These ozone-depleting substances are
defined as Class I and Class II substances. Class I
substances include all fully balogenated
chlorofluorocarbons (CFCs), including CFC-113,
three batons, MCF, and carbon tetrachloride.
Class I! substances are defined to include 33
hydrochlorofluorocarbons (HCFCs). The sections
of the CAA that are of importance to users of this
manual are discussed below.
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Exhibit 2
OZONE-DEPLETING SOLVENT CORPORATE PHASEOUT DATES
Successful Pnaseouto
A-dec
ADC Telecommunications
Advanced Micro Devices
Alcatel Network Systems
Apple Computer
Applied Magnetics
AishinSciki
Alps Electric
AT&T
Cadillac Gage
Calsonic
Canon
Corbin Russwin Hardware
Casio Computer
Chip Supply
Clarion
Compaq Computers
Conner Peripherals
Commins Engine
Diatek
Fuji Photo Film
Fujitsu
Harris Semiconductors
Hewlett Packard
IBM
ITT Cannon
Japan Aviation Electronics
Kilovac
Kyocera
Mabuchi Motor
Matsushita
MDM
Minebea
Minolta Camera
Mitsui High-tech
Motorola
Murata Erie N.A.
Murata Manufacturing
National Semiconductor
NEC
Ninon Dempa Kogyo
Nissan
Northern Telecom
NRC
Iki Electric
Omrbn
OTC/SPX Pacific Scientific EKD
Ricoh
Rohm
Sanyo MEG
Sanyo Energy .
Seagate Technology
Seiko Epson
Seiko-sba
Sharp
Shin-etsu Polymer
SMC
Sony
Stanley Electric
Sun Microsystems
Symmons Industries
Taliey Defense Systems
Thomson Consumer Electronics
3M
Toshiba
Toshiba Display Devices
Toyota Motor
Unisia JECCS
Yokogawa Electric
Future Phaseout:
Citizen Watch - 12/93
Funac - 12/93
Hitachi - 12/93
Hitachi Metals - 12/93
Isuzu Motors - 1993
Konyo Seiko - 12/93
Mitsubishi Electric - 12/93
Mitsubishi Heavy Industry - 12/94
Mitsubishi Motors - 8/93
NHK Spring - 1293
Nissan Diesel Motor - 1994
NSK - 12/93
Olympus Optical - 12/93
Sumitomo Electric - 12/93
Sumitomo Special Metals - 12/93
Suzuki Motor - 1994
Taiyo Yuden - 12/93
Victor Japan - 11/93
Yamaha - 12/93
Zexel - 8/93
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Sect/on 604 and Section 605:
Phaseout of Production and
Consumption of Class I and Class II
Substances.
Sections 604 an3 605 of the CAA present phaseout
schedules for Class I and Class II substances. The
phaseout schedule which applies for any ozone-
depleting substances listed in the CAA and in the
Montreal Protocol is the more stringent of the
two. The CAA is currently being amended to
reflect the changes in the phaseout schedule made
in Copenhagen. Other substances with ozone-
depleting potential are also regulated under the
.Montreal Protocol and the CAA. While they are
not used in solvent cleaning applications, these
substances are used in other applications. Section
60S of the CAA specifies provisions for the
phaseout of HCFCs. The CAA freezes the
production of HCFCs in 2015 and phases them out
by 2030. The U.S. EPA has announced that the
phaseout schedule for these chemicals will be
accelerated to the dates prescribed in the Montreal
Protocol. Since these restrictions limit production,
any HCFCs recovered or recycled may be used in
commercial operations after the applicable
phaseout date.
Section 608: National Emissions
Reduction Program
Section 60S directs EPA to promulgate regulations
by July 1992 requiring that emissions from all
refrigeration and cooling equipment (except mobile
air conditioners that are covered in Section 609)
be reduced to their "lowest achievable levels."
While this is not of direct importance in the use of
ozone-depleting solvents, it has implications for
facilities in which refrigeration and/or air
conditioning equipment is used. This section will
require air conditioning and refrigeration
technicians to be certified to ensure that
technicians are familiar with proper recycling and
recovery practices. This section also prohibits any
person from knowingly venting any of the
controlled substances, including HCFCs, during
servicing of refrigeration or air conditioning
equipment (except cars) beginning July 1, 1992,
and requires the safe disposal of these compounds
by that date. A "Notice of Proposed Rulemaking"
was published in ithe Federal Register in December
1992, and the Final Rule was published on May 14,
1993.
Sect/on 670: Ban of Nonessential
Uses
Section 610 of the CAA directs EPA to
promulgate regulations that prohibit the sale or
distribution of certain "nonessential" products that
release Class I and Class II substances during
manufacture, use, storage, or disposal. In the
CAA,Congress defined several products as
nonessential, including CFC-containing cleaning
fluids for noncommercial electronic and
photographic equipmentand CFC-propelled plastic
party streamers and noise horns. In addition,
Congress established guidelines so that EPA may
determine that additional products are
nonessential. Regulations banning nonessential
products that release Class I substances were
published on January 15, 1993. The CAA also
bans the sate and distribution of certain products
releasing Class II substances, including aerosol
products, pressurized dispensers, and most foam
products after January 1,1994. Regulations to ban
these products are currently being developed by
EPA.
Section 611: Labeling
Section 611 of the CAA directs EPA to
promulgate regulations by May 15,1992 requiring
labeling of products that contain or were
manufactured with Class I substances and
containers of Class I or Class II substances. The
label will read "Warning: Contains or
manufactured with [insert name of substance], a
substance which barms public health and
environment by destroying ozone in the upper
atmosphere." The label must clearly identify the
ODS by chemical name for easy recognition by
average consumers.
On February 11,1993, the EPA. published in the
Federal Register a Final Rule for the labeling
section of the CAA. The CAA defines three types
of products that must be labeled and specifies the
time frame by which these products must be
labeled as follows:
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• Effective May 15, 1993, containers in which a
Class I or Class II substance is stored or
transported, and products containing Class I
substances must be labeled
•• Effective May, 15,1993, products manufactured
with Class I substances must be labeled.
However, products manufactured with Class I
substances can be temporarily exempted from
the labeling requirements of this section if EPA
determines that there are no substitute products
or manufacturing processes that (a) do not rely
on the use of the Class I substance, (b) reduce
the overall risk to human health and the
environment, and (c) are currently or potentially
available. If EPA temporarily exempts products
manufactured with Class I substances from the
labeling requirement based on the lack of
substitutes, the products must be labeled by
January 1, 2015. Manufacturers that can show
that they have reduced their consumption of
Class 1 substances by greater than 95 percent
from 1986 levels are exempt from the product
labelling requirements.
• No later than January 1, 2015, products
containing or manufactured with a Class II
substance must be labeled.
The CAA allows for petitions to be submitted to
EPA to apply the labeling requirements to
products containing Class II substances or a
product manufactured with Class I or II substances
which are not otherwise subject to the
requirements. This petition process will operate
between May 15, 1993 and January 1, 2015. For
products manufactured with Class I substances, a
successful petition would result in the labeling of
a product previously determined by EPA to be
exempt. For products containing or manufactured
with Class II substances, the petition process could
lead to labeling of a product that had been left
unlabeled by default.
Section 612: Safe Alternatives Policy
Section 612 establishes a framework for evaluating
the environmental impact of current and future
alternatives. Such regulation ensures that the
substitutes for ozone-depleting substances wilt
themselves be» environmentally acceptable.
Provisions of Section 612 require EPA to:
-• Issue rales which make it unlawful to replace
any Class I and Class II substances with a
substitute that may present adverse effects to
human health and the environment where EPA
has identified an available or potentially
available alternative that reduces the overall risk
to human health and the environment
• Publish a list of prohibited substitutes,
organized by use sector, and a list of the
acceptable alternatives
• Accept petitions to add or delete a substance
previously listed as a prohibited substitute or an
acceptable alternative
• Require any company which produces a
chemical substitute for a Class I substance to
notify EPA 90 days before any new or existing
chemical is introduced into commerce as a
significant new use of that chemical. In
addition, EPA must be provided with the
unpublished health and safety studies/data on
the substitute.
To implement Section 612, EPA will (1) conduct
environmental risk screens for substitutes in each
end use and (2) establish the Significant New
Alternatives Program (SNAP) to evaluate future
introduction of substitutes for Class I substances.
EPA is working with the National Institute for
Occupational Safety and Health (NIOSH),
Occupational Safety and Health Administration
(OSHA), and other governmental and
nongovernmental associations to develop a
consensus process for establishing occupational
exposure limits for the most significant substitute
chemicals.
The environmental risk screens for the substitutes
will be based on a number of environmental
criteria, including OOP, toxicity, and likely human
exposure. Economic factors will also be
considered. EPA will organize these assessments
by use sector (i.e. solvents, refrigeration, etc) and
will either list a substitute as acceptable, or will
restrict uses that adversely affect human health and
the environment. Petitioners will have the burden
of proof to change a substance's status.
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6
EPA published a 'Notice of Proposed Rulemaking*
in the Federal Register on May 12, 1993. The
Final Rule is scheduled to be published early in
1994.
SNAP will routinely evaluate substitutes not
covered in the Final Rule and will classify them
based on the results of the risk screens.
Acceleration of ODS
Phaseout
All production of Class I substances - CFCs,
halons, methyl chloroform, and carbon
tetrachloride - will be eliminated by January 1,
1996. Limited exemptions for essential uses and
for servicing certain existing equipment will be
granted as the result of a petition process. At the
request of former President George Bush, U.S.
producers of these substances reduced the
production of ODSs by SO percent of 1986 levels
by the end of 1992. The U.S. is also re-examining
the phaseout schedule set forth in the amended
Protocol for HCFCs and is evaluating the possible
need for controls on the use of methyl bromide.
Excise Tax
Effective in 1991, the U.S. Congress placed an
excise tax on ozone-depleting chemicals
manufactured or imported for use in the United
States. This tax provides a further incentive to use
alternatives and substitutes to CFC-113 and MCF.
The tax amounts, shown in Exhibit 3, are based on
each chemical's ozone-depleting potential and
apply to purchased chemicals as well as floor stock.
Other International Phaseout
Schedules
European Community Directive
Under the Single European Act of 1987, the 12
.members of the European Community (EC) are
now subject to various environmental directives.
Exhibits
Excise Tax on Ozone-Depleting Solvents
Calendar Year
1991
1992
1993
1994
1995
Tax Amount
Per Pound
CFC-113 MCF
$1.096
$1.336
$2.68
$3.48
$4.28
$0.137
$0.167
$0.211
$0.435
$0.535
Effective January 1,1993, taxes on
ozone-depleting chemicals were
increased by a provision in the Energy
Policy Act of 1992.
The members of the EC are Belgium, Denmark,
Germany, France, Greece, Great Britain, Ireland,
Italy, Luxembourg, the Netherlands, Portugal, and
Spain. Council Regulation number 594/91 of
March 4, 1991 provides regulatory provisions for
the production of substances that deplete the
ozone layer. The EC phaseout schedule for CFC-
113 production is more stringent than the
Montreal Protocol. It calls for an 85 percent
reduction of CFC-113 by January 1, 1994 and a
complete phaseout by January 1,1995. For MCF,
the production phaseout schedule calls for a 50
percent cut in production by January 1,1994 and
a complete phaseout by January 1,1996. While all
members must abide by these dates, Council
Regulation number 3322/88 of October 31, 1988
allows EC members to take even more stringent
measures to protect the ozone layer.
Other Legislation
Several other countries have adopted legislation
that is more stringent than the terms of the
Montreal Protocol. Environment Canada, the
federal environmental agency responsible for
environmental protection in Canada, has proposed
-------
a more stringent reduction program. Under the
proposed schedule, all production, import, and
export of CFCs for use in Canada must be reduced
75 percent by January 1, 1994 and eliminated by
January 1, 1996. Environment Canada has also
announced a series of target dates for the phaseout
of CFCs in specific end uses. For solvent cleaning
applications such as metal and precision cleaning,
it mandates a phaseout of CFC-113 by the end of
1994. The production, import, and export of
halons and carbon tetrachloride in Canada is to be
eliminated by January 1,1994, and'January 1,1995,
respectively. Methyl chloroform production,
import, and export will follow the following
phaseout schedule: 50 percent reduction by
January 1, 1994; 85 percent reduction by January
1, 1995, and 100 percent reduction by January 1,
1996.
Japan has also ratified the revised Montreal
Protocol. The recent Ozone Layer Protection Act
gives the Ministry of International Trade and
Industry (MFTI) the authorization to promulgate
ordinances governing the use of ozone-depleting
compounds. MITI and the federal Environmental
Agency have established the "Guidelines for
Discharge Reduction and Use Rationalization."
Based upon these guidelines, various government
agencies provide administrative guidance and
advice to the industries under their respective
jurisdictions. Specifically, Mm prepares and
distributes manuals and encourages industry to
reduce the consumption of ozone-depleting
compounds through economic measures such as tax
incentives to promote the use of equipment to
recover and reuse solvents. On May 13, 1992,
MITI requested its 72 Industrial Associations to
phase out CFC and MCF use by the end of 1995.
The EFTA (European Free Trade Agreement)
countries (i.e., Austria, Finland, Iceland, Norway,
Sweden, and Switzerland) have each adopted
measures to completely phase out fully
halogenated ozone-depleting compounds. Some of
the EFTA countries have sector-specific interim
phaseout dates for certain solvent uses. Norway
and Sweden have eliminated their use of CFC-113
in all applications except textile dry cleaning by
July 1 and January 1, 1991, respectively. In
addition, Austria will phase out CFC-113 in some
solvent cleaning applications by January 1, 1994.
Austria, Finland, Norway, and Sweden will
completely phase out their use of CFC-113 in all
applications by January 1,1995. Sweden also plans
an aggressive phaseout date of December 31,1994
for MCF.
Cooperative Efforts
TheU.S. Environmental Protection Agency (EPA)
works with industry to disseminate information on
technically feasible, cost effective, and
environmentally acceptable alternatives to ozone-
depleting substances. As pan of this effort, the
U.S. EPA and ICOLP are preparing a series of
manuals providing technical information on
alternatives to CFC-113 and MCF. Based on
actual industrial experiences, the manuals aid users
of CFC-113 and MCF worldwide in implementing
alternatives.
The first manuals in the series are:
• Conservation and Recycling Practices for CFC-
113 and Methyl Chloroform
• Aqueous and Semi-Aqueous Alternatives to
CFC-113 and Methyl Chloroform Cleaning of
Printed Circuit Board Assemblies
• Alternatives for CFC-113 and Methyl
Chloroform in Metal Cleaning
• Eliminating CFC-113 and Methyl Chloroform in
Precision Cleaning Operations
• No-Clean Soldering to Eliminate CFC-113 and
Methyl Chloroform Cleaning of Printed Circuit
Board Assemblies
• Eliminating CFC-113 and Methyl Chloroform in
Aircraft Maintenance Procedures.
This manual describes a simply structured program
to help eliminate the use of CFC-113 and/or MCF
in an electronics manufacturing facility. The
manual presents "no-clean" soldering processes
available for the electronics industry. The typical
product being manufactured will be printed circuit
board assemblies that consist of a rigid epoxy glass
resin laminate with through-hole components and
bottom and/or top-side surface mount technology.
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8
The manual:
* ProvKjes a methodology to select a "no-clean"
prr,..»vs
-• Includes summary charts that present an
overview of the'no-clean'processes discussed in
this manual
• Details characteristics of "no-clean* soldering
processes
• Outlines the process and equipment
characteristics of these alternatives
• Discusses the costs associated with each "no-
clean" process
• Presents detailed case studies on industrial
applications of these technologies.
This manual will benefit all users of CFC-113 and
MCF in the electronics industry. Ultimately,
however, the success of any CFC-113 and MCF
elimination strategies will depend upon how
effectively reduction and elimination programs are
coordinated within a facility or organization. The
development and implementation of alternatives to
CFC-113 and MCF for electronics cleaning present
a demanding challenge to any organization. The
rewards for successfully implementing these
procedures are the contribution to global
environmental protection and the increase in
industrial efficiency.
-------
STRUCTURE OF THE MANUAL
This manual is divided into the following sections:
• METHODOLOGY FOR SELECTING A CLEANING OR 'NO-CLEAN* PROCESS
This section discusses technical and economic issues that should be considered when selecting a
cleaning process.
• SUMMARY CHARTS
This section presents two summary charts that match cleaning and no-clean processes with a variety
of evaluation criteria.
• INTRODUCTION TO NO-CLEAN OPTIONS
This section presents three no-clean choices: no-clean fluxes, no-clean pastes, and controiie
atmosphere soldering to enhance process results.
• PROCESS DETAILS
This section describes the equipment that is typically associated with no-clean processes.
• QUALIFICATION OF NO-CLEAN MATERIALS AND PROCESSES II
This section lists information on material and process requirements as well as the test methods used!
to qualify a no-clean process. I]
• ECONOMICS OF NO-CLEAN PROCESSES
This section details the costs associated with implementing each of the no-clean options discussed in
the manual.
• ENVIRONMENTAL, HEALTH, AND SAFETY ISSUES
This section discusses issues associated with no-clean processes which might affect human at!
environmental health and safety.
• CASE STUDIES OF INDUSTRIAL PRACTICES
This section provides specific examples of actual industrial applications of no-clean soldering
processes.
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10
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11
METHODOLOGY FOR SELECTING A CLEANING
OR NO-CLEAN PROCESS
The methodology used to select a no-clean process
for printed circuit boards (PCBs) must take into
account a number of important, considerations.
These can be grouped into two categories:
technical and economic
Technical
The factors that determine technical
feasibility include:
• Compliance with specifications
• Defect rate
• Customer return issues
• Industry direction
• Cosmetic appearance of the PCBs
• Ability of supplier to meet
specifications
• Process flexibility
• Process control
• Process throughput
• Time scale
• Health, safety, and environmental
concerns
• Future costs
• Availability of the process
• Process installation
• Process compatibility
• Floor space requirements
• Operating and maintenance
requirements
• Other selection criteria related to the
specific application
Compliance With Specifications. Military or
civilian contracts or specifications may strictly
define process parameters and performance.
For example, military and other high reliability
specifications frequently require conformal
coatings. Excessive residue often causes surface
defects such as vesication. A military contractor
may have to ensure that the chosen process will
decrease or eliminate this type of defect,
whereas this would not be a concern for other
types of electronic products without conformal
coating. Before selecting any new process,
current and future customer requirements
should be considered.
Defect Rate. This is defined as the rate at which
parts fail to meet quality standards. The impact
of any cleaning or no-clean process on
downstream processes such as testing, post-wave
assembly and, subsequent hardware
requirements must be evaluated for their effects
on defect rate. Consider the possibility that
using a new cleaning or no-clean process may
require the purchase of new components that
are compatible with the new process.
Customer Return Issues. This factor is concerned
with the percent of units returned, how easily
returned units can be repaired, and how well
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12
repairs and modifications can be done in the
field.
Industry Direction. Investing in a process that is
supported by industry direction may decrease
costs. Unlike standard equipment, specialized
equipment frequently means higher costs for
parts and service, limited reliable sources for
providing technical assistance, and higher risks.
Cosmetic Appearance of the PCBs. Although
visual appearance unrelated to- performance is
becoming less important, some customers still
demand visual standards of cleanliness for
electronic components.
Ability of Suppliers to Meet Specifications. The
quality of incoming boards and components is
critical to the success of a no-clean process. It
is essential that suppliers deliver boards free
from oxidation and other contaminants since
there will be no further cleaning during the
manufacturing process. In cases where boards
will be cleaned using an alternative process,
incoming board cleanliness is less of a concern.
Process Flexibility. This factor is defined by the
number of different types of technology that can
be efficiently soldered with the new process. It
also considers compatibility with typical
materials.
Process Control Process control refers to the
ease of operation and manipulation of a
soldering or cleaning process. Simple processes
are often better from the standpoint of process
control. A second part of this issue involves the
tools and techniques that insure the process is
operating as expected. A process that cannot be
easily controlled or audited is not desirable.
Process Throughput. Throughput is more
important to the success of a no-clean process
than it is to an alternative cleaning process.
No-clean soldering may not be applicable for
some low-volume manufacturing processes or
for shops using a large number of different
components. Low-volume shops often buy
small quantities of components which may sit
for several years in inventory. While the
components may arrive clean from the supplier,
they are iikely to become contaminated while in
storage — a factor which adversely affects
solderability.r In high-volume shops,
components move quickly out of inventory and
are less likely to become contaminated.
• Time Scale. The conversion of an existing
process may require the removal of old
equipment, the installation of new equipment,
connecting the services, performing acceptance
trials, establishing manufacturing protocols, and
implementing them into production. It may be
necessary to begin with zero planned production
initially, and then slowly ramp-up to full
production.
• Health, Safety, and Environmental Concerns. The
U.S. EPA is conducting an overall risk
characterization for substitutes under Section
612: Safe Alternatives Policy of the Clean Air
Act of 1990. This involves a comprehensive
analysis based on ozone-depletion potential,
flammability, toxicity, exposure effects, energy
efficiency, degradation impacts, air, water, solid
waste/hazardous waste pollution effects,
environmental releases, and global warming
potential.
• Future Costs. This consideration requires
evaluating conditions such as escalating waste
disposal costs and major expenditures associated
with pending control legislation.
• Availability of Process. "Availability* is different
from "industry direction." "Availability*
concerns whether vendors can provide the
equipment and supplies for the process to be
implemented. For example, some alternatives
might be available only from a few vendors in
specific geographic areas.
• Process Installation. This is the work that will be
required to put the system into production and
includes physical installation of the process,
material handling considerations, and employee
training.
• Process Compatibility. The fewer the number of
changes caused by the proposed process, the
more likely that the changeover will be
successful. Upstream and downstream process
adjustments required for a changeover should
be considered.
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13
Floor Space Requirements. The total amount of
space available and its value have a significant
impact on process selection. In some instances
permits may be required before installing a new
process. When compared to traditional vapor
degreasing, no-clean processes will require less
floor space while most alternative cleaning
processes will require more floor space.
Operating and Maintenance Requirements, Each
new process will require the development of
operating and maintenance procedures. In
some instances a new process might require
additional labor to operate and may require
special operator training, while in others, the
amount of necessary labor may decrease.
Economic
The factors that determine the economic
feasibility include:
• Cleaning process and equipment
• Waste stream
• Plant size considerations
• Process time
• Process material consumption
• Labor
• Utility costs
expense and environmental risk previously
associated with disposal of the solvent.
• Plant Size Considerations. An increase in
necessary floor space may require expansion or
remodeling of a manufacturing facility.
•• Process Time, The amount of time which it takes
to produce a finished board may have a direct
impact on the cost associated with a particular
board assembly process. In most cases, it takes
less time to solder a board using a no-clean
process than it does to solder, clean, and dry
boards in a traditional process. In general, the
longer it takes to produce a board the higher
the overall cost of the process will be.
• Process Material Consumption. The amount of
raw materials consumed in the production
process will greatly affect process costs. Raw
materials to consider include flux, solder, and in
some cases, nitrogen. Solvent costs are
eliminated in no-clean processes.
• Labor. Changes in the amount or skill level of
labor required to perform a particular assembly
process may affect process costs. In no-ciean
processes, the labor costs associated with
operation of the cleaning equipment are
eliminated.
• Utility Costs. The price and consumption of
electricity, water, and waste disposal to public
utilities should be considered in evaluating a
process.
Cleaning Process and Equipment. The cost
associated with retrofitting or purchasing new
equipment as well as the savings realized by
eliminating other equipment should be
considered.
Waste Stream. The type and quantity of waste
generated as a byproduct from a manufacturing
process can impact overall costs. Eliminating
the solvent cleaning process will eliminate the
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14
-------
SUMMARY CHARTS
15
This section focuses on two charts which highlight
technology applicable to specific requirements.
The remainder of the manual provides additional
detail about the various options.
Cleaning Options
The cleaning options chart shown in Exhibit 4
presents a range of fluxing and cleaning
combinations that may be used successfully with
different types of products. Reviewing these
combinations is a first step in selecting a process.
When rosin fluxes are used, cleaning with
hydrocarbon/surfactants or with saponifiers may be
necessary. With water soluble flux/paste, plain
water cleaning is preferred although aqueous
saponified or semi-aqueous cleaning are also
applicable. No-clean processes may be applicable
for rosin-based flux formulations used with
through-hole, surface mount and mixed component
single- and double-sided boards.
Summary Matrix
The second chart, shown in Exhibit 5, provides
brief, relevant comments on the costs, applicability,
strengths, and weaknesses associated with
equipment configurations of six no-clean processes
discussed in this manual.
A brief explanation of some of the criteria
displayed in Exhibit 5 follows:
Component Issues. Issues of concern include
corrosion, failure of seal, effects on plastics, effects
on functional performance, removal of markings,
and the potential to trap flux residues.
Defect Kate. This concern refers to the soldering
defect rate associated with a no-clean process
relative to traditional soldering processes.
Waste Stream Issues. Process control, volume, local
regulations, and management decisions influence
this highly localized issue. Waste stream
reductions are realized with no-clean processes
since disposal of spent solvent is eliminated. In
addition, there are no wastewater issues as there
are 'in aqueous and semi-aqueous cleaning
processes. When soldering is performed in a
controlled atmosphere, less lead/tin solder dross is
formed.
Health and Safety Issues. These issues include
toxicity, flammability, odor, VOC concerns, and
occupational exposure to hazardous chemicals used
in no-clean processes.
Idle Time Cost. Since soldering equipment is often
used less than 100 percent of the time, factoring in
the cost of ventilation, nitrogen flow (for
controlled atmosphere systems) is important.
Process Cost. The associated cost per square meter
of product is determined by a number of variables
at the local level. The chart, however, presents a
likely reduction in cost by implementing a no-clean
process.
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16
Exhibit 4
CLEANING OPTIONS TO REPLACE
CFC-1 1 3 AND METHYL CHLOROFORM
!
I Kt»r:
PTH Plated Through Hole
SM Surface Mount
L========±======
/ // / / & / j// / //
PTH Rosin Rux
PTH Water-Soluble Flux
PTH Synthetic Activated
Flux
SM Rosin Rux
SM Water-Soluble Paste
Mix Rosin Rux
Top & Bottom
SM&PTH
Mix Water-Soluble Rtw
Top ft Bottom
SM&PTH
•No-Clean* Flux and Paste
Controlled Atmosphere Soldering
with No-Clean Flux and Paste
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
•
X
X
X
X
ram*
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17
su
1 Due to i
: Depend!
*Dencndc
4 For men
sDependc
Exhibits
MMARY MATRIX COMPARING NO-CLEAN PROCESSES
"f2
-------
18
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19
INTRODUCTION TO NO-CLEAN OPTIONS
Successful implementation of no-clean soldering
processes requires a detailed understanding of both
the soldering process and the materials used in the
no-clean process. As with traditional assembly
processes, the selection of fluxes and equipment
will continue to be an area in which there are a
wide variety of available options, so users must
consider all of the properties, capabilities, and
limitations associated with each no-clean option.
When considering the use of a no-clean flux, no-
clean paste, or controlled atmosphere, select
materials and equipment with care since the
variability associated with no-clean processes is
greatly reduced relative to traditional soldering
operations. To fully take advantage of this new
technology, users must acquire new knowledge and
must form sound judgements based upon
engineering data and experience.
Switching to a no-clean processes will sometimes
require a shift in thinking on the pan of engineers,
management, and/or customers, due to the small
amount of harmless residue which may remain on
a PCB that is no longer cleaned after soldering.
While the residue may be benign and cause no
damage to the functional quality of the board,
cosmetic quality may be lowered. In any case, each
potential no-clean user must weigh for themselves
the importance of cosmetics in their final product.
Eliminating post-solder cleaning necessitates that
greater attention be paid to the boards and
components used in the manufacturing process.
Boards and components must be sufficiently clean
prior to the soldering process, since residues will
no longer be removed in a post-solder cleaning
step. Many of the residues found on boards after
testing of a no-clean system can be attributed to
the boards and components arriving at the plant
uncleaned. Users of no-clean systems must ensure
that their suppliers can meet the cleanliness
requirements associated with the no-clean
soldering process. In addition, proper handling of
boards and components prior to soldering becomes
more vital when using a no-clean process.
There are several options available to
manufacturers which will allow for soldering
without subsequent cleaning. These are:
• Continue normal soldering using an RMA flux
or paste, but eliminate post-solder cleaning
• Use a low-residue type flux or paste and
eliminate the cleaning process
• Change the method of flux application for wave
soldering so that the amount and placement of
flux is more precisely controlled and the
cleaning step is eliminated.
In addition, some manufacturers may choose to
carry out the soldering operation in a controlled
atmosphere to reduce the level of oxygen present
during soldering. Benefits associated with this
switch include better cosmetics, better solder
wetting characteristics, improved solder joint
quality, and reduced solder dross. Potential
drawbacks associated with the use of a controlled
atmosphere include increased bridging, which is
often related to board design. However, as more
sophisticated equipment is introduced, the
incidence of bridging in controlled atmosphere
soldering will decrease.
This section provides a brief overview of the use of
alternative flux and paste materials as well as
describes soldering in a controlled atmosphere.
No-Clean Wave Solder
Fluxes
If soldering with a traditional flux and simply
eliminating the cleaning process yields
unsatisfactory results, consideration should be
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20
given to changing the flux formulation. No-clean
is the classification given to fluxes whose residues
are benign and may be left on a printed circuit
board (PCS) after the soldering operation is
completed. Thus, no post-solder cleaning
operation is required and the use of CFC-113 or
methyl chloroform (MCF) is eliminated. There are
two general types of no-clean wave solder fluxes
available at the present time: low-solids no-clean
fluxes and the less frequently used high-solids no-
clean fluxes. In addition, a new generation of
water-based low-residue fluxes is- currently being
developed. If successfully developed, water-based
low-residue fluxes will be useful in meeting
stringent VOC requirements in many
nonattainment areas.
Low-Solids No-Clean Fluxes
A typical low-solids, low-residue flux will contain
0.5 to 4 percent solids, while traditional rosin
fluxes contain 15 to 40 percent solids. Exhibit 6
shows a typical chemical composition of a
traditional flux and a low-solids flux. The reduced
solids content results in less post-solder residue
remaining on the board, ideally eliminating the
need for cleaning.
Due to the decreased solids content of the flux,
flux placement on the board becomes extremely
important in ensuring that an adequate solder joint
will be formed and in achieving acceptable
cosmetic appearance.. Enough flux must be
Deposited on the board to facilitate the formation
of a good quality solder joint, but excess flux will
result in increased residues, thereby possibly
interfering with bed-of-natls testing and/or
adversely affecting board cosmetics. For this
reason, traditional foam and wave fluxing methods
may be considered unsatisfactory as they can result
in an excessive amount of flux being deposited on
the PCB. Therefore, manufacturers using low-
solids fluxes often opt for the use of an alternative
flux delivery method. Spray fluxers are a popular
alternative because the amount and pattern of flux
delivered can be closely controlled. Spray fluxing
will be discussed in greater detail in the ponton of
this manual devoted to equipment requirements.
Low-Solids No-Clean Fluxes
• Contain only 0.5 to 4 percent solids
• Eliminate the need for post-solder
cleaning for cosmetic purposes
because their reduced solids content
results in less residue
• Can be used in existing wave soldering
machines
• May be applied with a variety of
fluxing methods (foam, wave, and
spray)
• May affect solderabtlity and board
cosmetics
• May require adjustment of the
amount and pattern of flux deposited
• May leave flux residue that can make
product testing more difficult,
especially in cases where "bed-of-nails"
testing is conducted.
High-Solids No-Clean Fluxes
High-solids fluxes are the other no-clean flux
option. They are similar in nature to their low-
solids counterparts, but with solids contents in the
range of 15 to 40 percent. High-solids no-clean
fluxes have been used in Europe for several years,
but they have failed to gain widespread acceptance
in the U.S., primarily due to cosmetic preferences
of PCBs. The higher concentration of flux residue
which remains on the board may also result in
increased tackiness, test probe penetration
problems, electrical problems, and reduced
aesthetics. These residues, however, lock corrosive
residues in a safe matrix, thereby providing a
method for controlling long-term corrosion caused
by stronger activation packages.
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21
Exhibit 6
Composition of Traditional and Low-Solids Flux
Solvents 60%
Activator 5%
Rosin 35%
Solvents 97%
Activator < 2%
Surfactant/
Inhibitor < 1%
Traditional: Total Solids = 40%
Low Solids: Total Solids = 0.5 - 4%
Source: Adapted from "Circuits Manufacturing," April, 1990
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22
High-Solids No-Clean Raxes
• Contain 15 to 40 percent solids.
•• Used in-Europe and Japan, but not
widely in the U.S.
• May result in increased tackiness,
reduced testability, and electrical
problems. These factors may
necessitate changes in the test probe
and clamp used.
• May produce boards that appear to be
unclean but which meet all test
criteria.
No-Clean Solder Pastes
The simplest way in which a reflow soldering
process can be convened to no-clean is to continue
soldering using a traditional RMA paste and
simply eliminate the post-solder cleaning step. In
cases where this switch does not result in a
satisfactory board, however, manufacturers may
choose to switch to a low-residue no-clean solder
paste. These pastes can be left on the board,
thereby eliminating the need for solvent cleaning
using CFC-113 or MCF after reflow soldering.
After reflow, no-clean pastes leave a small amount
of residu~ on the board which is usually not
visually detectable by the naked eye.
Low-Residue No-Clean Solder Pastes
• Eliminates need for cleaning after
reflow soldering processes
• Leave harmless residue which is not
visible with the naked eye
• May require use in a controlled
atmosphere to produce adequate
solder joints.
Controlled Atmosphere
Soldering
In most cases, excellent soldering results can be
achieved in a no-clean process conducted in an air
atmosphere. However, soldering in a controlled
atmosphere will improve solder joint quality,
increase yield as a result of reduced wetting
defects, improve cosmetic appearance by reducing
post-solder residue, and significantly reduce the
waste stream as less solder dross is produced.
In a controlled atmosphere soldering process, an
inert gas, usually nitrogen, is pumped into the
soldering chamber in order to reduce the level of
oxygen present at the time the soldering operation
takes place. Soldering in a controlled atmosphere
may reduce the amount of flux required to produce
an acceptable solder joint. This reduction, in turn,
can reduce post-solder residue and eliminate the
need for post-solder cleaning.
Potential users of controlled atmosphere soldering
should be aware of several U.S. patents which
apply to soldering processes carried out in a
controlled atmosphere. These patents (see
Appendix C for the complete text) are held by the
Linde Division of Union Carbide Industrial Gases:
• Patent #5121875 - Wave Soldering Under
an Inert Atmosphere
• Patent #4821947 - Soldering Without Flux
• Patent #5071058 - Control of Oxygen in a
Soldering Process
• Patent #4823680 - Laminar Diffusers
Additional patents are held by other equipment
manufacturers and gas suppliers, and licensing
charges may apply with the use of controlled
atmosphere soldering.
As a result of the switch to a controlled
atmosphere, several changes in the soldering
process occurred. In the case of wave soldering,
the controlled atmosphere can reduce the need for
flux if a sufficiently low level of oxygen can be
achieved in the soldering module. In some
instances, manufacturers will be able to eliminate
the use of a traditional or a no-clean flux in favor
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23
of what is commonly referred to as a preparation
fluid (normally a solution of 1 to 2 percent adipic
acid in alcohol). Formic acid, injected as a gas,
has been used in some applications to reduce dross
on the solder wave and to promote solder wetting.
»
Another benefit provided by soldering in a
controlled atmosphere is improved solder wetting.
One supplier of industrial grade nitrogen
conducted extensive studies in which the wetting
force over time was measured in air and nitrogen
atmospheres using a wetting balance! The tests
were conducted using copper wires which had been
dipped into activated rosin flux. Exhibit 7 presents
the results of the study and shows that, not only is
the wetting force for copper greater in a nitrogen
atmosphere, but the wetting time is approximately
32 percent shorter as well.
Controlled Atmosphere Soldering
• Reduces oxygen levels in the solder
area significantly by using nitrogen;
levels below 10 ppm are possible
• Can be used in conjunction with no-
clean fluxes and no-clean solder pastes
• Can be used in both wave and reflow
. soldering processes
• May completely eliminate the need for
flux
• Can be easily adapted to existing
equipment by the use of several
available retrofit options
• Improves joint quality and reduces
wetting defects'and solder dross
• May result in increased bridging.
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24
150
100
50
0
•SO
-100
• 150
-200
•250
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Source:
«
Wetting Con
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Nitrogan
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-------
PROCESS DETAILS
25
As mentioned earlier, switching to a no-clean
soldering process can be accomplished through
several process changes, including the removal of
the cleaning step, changing the 'method of flux
application in wave soldering, changing the flux or
paste formulation, and soldering in a controlled
atmosphere. Deciding which of these options is
most beneficial depends on a number of factors
which are specific to each manufacturing facility.
This section describes these options as they apply
to both wave soldering and reflow soldering. In
addition, a detailed discussion of equipment and
process modifications is presented for each option.
No-Clean Wave Soldering
Traditional wave soldering operations consist of
two primary pieces of equipment: a conveyorized
wave solder machine and a solvent cleaning
machine. No-clean wave soldering operations
require only the conveyorized wave solder machine.
Although these machines may differ in size, all
have the same basic modules.
The primary considerations in switching to a no-
clean wave soldering process include the flux
selection, the method of flux application, and the
process profile. This section describes no-clean
wave soldering operations and discusses the critical
process details which affect the success of a no-
clean operation.
No-Clean Wave Soldering in Air
Wave soldering without cleaning can be performed
in an air atmosphere in a variety of ways. The first
is to continue'using traditional fluxes while simply
eliminating the cleaning process. This is the
simplest method and should be tested before any
investments are made in equipment retrofits or
No-Clean Wave Soldering
• Can be performed in an air or
controlled atmosphere
• Can often be implemented using
existing equipment and no-clean fluxes
with little or no retrofit
• Requires little additional worker
training because Operation is similar
to traditional soldering
• Eliminates costs associated with
purchase, operation, and maintenance
of cleaning equipment
purchases. In most cases, the results of such a test
will be excessive residue and/or testability issues
which are unacceptable to the manufacturer and/or
the customer. As a consequence, additional
process changes may be required to convert to a
no-clean process.
The logical next step is to change the flux
formulation and possibly the method of flux
application. A change in flux formulation usually
means a switch to either a low-solids no-clean flux
or a high-solids no-clean flux. Numerous
formulations of these fluxes are currently available
on the market, so manufacturers are able to test a
large number in their current equipment.
A change in the method of flux application
involves the addition of a stand-alone fluxing
module or retrofit of the existing soldering
machine. There are three types of flux application
methods which have proven successful in no-clean
applications:, foam, wave, and spray. General
performance characteristics of each of the flux
application methods are shown in Exhibit 8. The
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26
Exhibits
PERFORMANCE CHARACTERISTICS OF FLUX
APPLICATION METHODS
I (•Mill
i SOL
.<*.«*»,_«-
«U»BMk*MM
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27
following is a summary of each method, how it
works, and issues associated with its use.
•• Foam Flwdng. Foam fluxing has traditionally
been the most widely used method of flux
application in, the electronics industry. In this
process, flux is bubbled up to a foamy head by
forcing air through one or more porous stones
or tubes located under the flux bath. The PCB
then passes over the foam head and flux is
deposited on the board. To reduce safety
hazards, it is possible to substitute nitrogen for
air in this application method.
The benefits associated with the use of foam
fluxing include its current widespread use, the
absence of any uncontrollable health or safety
impacts, and its relatively low cost Drawbacks
of using foam fluxing center on the
characteristics of flux deposition. When using
a foam fluxer, controlling the amount of flux
deposited on a board is difficult. In addition, it
is possible to deposit flux on the top side of the
board. This can have significant implications in
a no-clean process because it results in more
flux residue, which can cause subsequent
cosmetic and/or testing problems.
• Wave Fluxing. Wave fluxing is similar to wave
soldering in that the PCB passes over a wave of
flux, just as it later passes over the solder wave.
Wave fluxing is considered versatile because
most liquid fluxes can be applied in this
manner. As with foam fluxing, the major
difficulties in wave fluxing are controlling the
amount of flux deposited, and controlling the
tendency to deposit flux on the top side of the
board. Maintaining the proper wave height is
vital to avoid applying too much or too little
flux. Some new wave fluxing equipment reliably
controls the amount of flux deposited. Other
manufacturers, however, are still working to
achieve this control in their equipment.
• Spray Flwdng. In some cases, the traditional
methods of flux application - foam and wave
fluxing - are not used in no-clean wave
soldering because they may apply too much flux.
Instead, many users are opting for spray fluxing,
a method in which a thin layer of flux is applied
through a finely controlled mist. Spray fluxers
have the advantage of being able to consistently
apply the same amount of flux in the same
pattern while *also reducing flux consumption.
In addition to maintaining consistency, spray
fluxers allow deposit rates to be varied easily
and closely controlled. Recently, a new type of
spray fluxer was introduced to the market. This
fluxer is based on precision microjets of flux
which are triggered on and off as the flux
applicator moves quickly under the board. This
equipment can achieve flux deposition thickness
of 600 micrograms per square inch and higher.
In addition, the application device exhibited no
problems with clogging during development and
testing.
While all flux application methods have safety
risks associated with them, these risks are often
greater with spray fluxers. Since fluxes
traditionally contain significant amounts of
flammable solvents, special safety measures are
needed to reduce both flammability risks and
odors associated with the flux vapor. The
flammability and vapor exposure risks are
generally higher in spray fluxing than in foam or
wave fluxing. These increased risks necessitate
that spray fluxing take place in well-ventilated
areas which are equipped with sufficient fire
control devices.
If spray fluxing is selected, the fluxing module
on the soldering machine can be replaced with
a spray unit Another option for convening to
spray fluxing is to purchase a new fluxing unit
which can be placed before the soldering
machine as a new module. Several companies
manufacture stand-alone spray fluxers which can
be installed on an existing production line.
These units usually consist of a short conveyor
with a spray unit mounted under the conveyor
and a hood mounted above the conveyor.
Proper ventilation and fire control devices are
required.
With the exception of the possibility of a new flux
application method, the remaining steps in the
soldering process are the same for no-clean
processes as for traditional soldering operations.
However, the process window (a measure of the
flexibility of a soldering process) is reduced when
using a no-clean process.
After the flux has been applied to the PCB by
foam, wave, or spray fluxing, the board moves into
the preheat zone of the wave soldering machine.
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Preheating of the board is an important part of the
soldering process as it performs several vital
functions:
• • reduces the risk of thermal shock which can
damage Jhe board and/or components
•• removes flux volatiles
-• activates the flux chemistry
•• removes the oxide layer on the board.
The more volatile no-clean flux chemistry results in
a process window much smaller than that
associated with conventional fluxes. As a result,
specific preheat temperatures and solder contact
angles are vital to ensure proper flux activation
and the formation of good quality solder joints.
Under- or over-heating of the board must be
avoided as the flux may either not activate or may
burn. Production engineers should work with the
flux manufacturer to determine the optimum
soldering process profile.
No-Clean Wave Soldering in Air
• Three options: 1) existing equipment
with existing flux, 2) substitute a no-
clean flux, 3) substitute an alternative
flux application method
• Can be performed with foam, wave, or
spray fluxing
• Spray fluxing can be implemented
relatively cheaply due to reduced
operating costs
• Process window becomes smaller than
in traditional soldering.
Retrofitting Existing Equipment for
Controlled Atmosphere Soldering
No-clean soldering in air frequently does not
produce the highest quality, the most satisfactory
cosmetics, and the desired waste stream
characteristics. Consequently, some manufacturers
choose to perform the wave soldering operation in
a controlled atmosphere. In many cases it is
possible to retrofit existing wave solder machines
for controlled atmosphere soldering.
For operation with a controlled atmosphere,
traditional wave soldering machines must be
retrofitted with a hood to control the oxygen
content in the soldering module. The hood seals
a portion of the machine so that nitrogen can be
pumped in and oxygen displaced. At the present
time, at least two manufacturers offer nitrogen
retrofit packages. Regardless of the retrofit
chosen, users should be aware that there are at
least four patents (see Appendix C for copies of
these patents) owned by a major supplier of
industrial gases which apply to the use of
controlled atmospheres in soldering processes.
One type of retrofit which facilitates using a
controlled atmosphere is a hood which is placed
only over the solder pot area only. This is a
simple retrofit which can be completed in a short
amount of time in the manufacturing facility.
Although it is the least expensive available retrofit
for soldering in a controlled atmosphere, it is also
the least gas efficient The other retrofit is a hood
which covers both the preheat modules and the
solder pot. This retrofit results in low oxygen
levels, while using less nitrogen than the solder-
pot-only retrofit Due to the size of the "long"
hood, this retrofit is sometimes installed by the
wave soldering equipment manufacturer. The
installation procedure may require that the entire
wave soldering machine be shipped to its
manufacturer.
New Equipment Options for Controlled
Atmosphere Soldering
Three types of specially designed equipment are
available for no-clean soldering operations. The
first, an open-tunnel machine, allows an
uninterrupted flow of boards to be soldered in a
controlled atmosphere. The second, a sealed-
tunnel machine, can achieve extremely low levels
of oxygen in the solder area but does not allow an
uninterrupted flow of boards. A third option uses
a partially-closed tunnel with carefully focused
nitrogen injected to reduce oxygen concentration
using less nitrogen than other methods. These
machines differ significantly in mechanical design.
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Open-TumuL An open-tunnel wave soldering
machine has curtains at the entrance to the
preheat module and at the exit of the solder
module to trap nitrogen in the machine and to
prevent significant amounts of oxygen from
entering the machine. However, because the
curtains on these machines are limited in their
ability to trap sufficient nitrogen within the
tunnel, open-tunnel machines may require a
significant amount of nitrogen to achieve
sufficiently low oxygen levels. Despite the fact
that open-tunnel machines may consume more
nitrogen than sealed-tunnel machines, they are
popular because they allow continuous high-
volume processing of boards or pallets.
Seaied-TunneL For operations which require
strict control of the atmosphere in the preheat
and solder modules, a sealed-tunnel wave
soldering machine is currently available on
world markets. In these machines, entrance to
and exit from the controlled atmosphere area of
the machine is made through a vacuum
chamber. The principle behind this procedure
is similar to that of an airlock. The product
(board or pallet) moves into the entrance
vacuum chamber and all of the oxygen in the
chamber is removed. Pumps then fill the
chamber with nitrogen and the chamber is
opened to allow the product to move to the
preheat module. After the product passes over
the solder wave, it moves into the exit vacuum
chamber. Nitrogen is then removed from the
exit vacuum chamber before the product exits.
These vacuums ensure that little oxygen enters
the machine, thereby providing strict control of
the atmosphere. The major drawback
associated with these machines is their relatively
low throughput compared to that of their open-
tunnel counterparts.
Partialfy-CIosed Tunnel A third type of
controlled atmosphere soldering system has
recently been developed which combines a dual
wave with a focused nitrogen supply in a
partially closed tunnel. Unlike the other
machines, the nitrogen gas is not captured
around the solder pot. Rather, it is introduced
from focused slots immediately ahead of and
immediately after each solder wave. The
focused use of nitrogen results in a significantly
lower nitrogen consumption when compared
with the open- and sealed-tunnel equipment.
Users of this third design have reported
satisfactory soldering with a decrease in solder
bridging. This type of focused nitrogen system
can also be installed as a retrofit on existing
soldering equipment with relatively little
difficulty. The safety of this design is
comparable to that of other nitrogen soldering
systems. However, since there is no actual
tunnel, safety enhancements should include
special ventilation for fumes and solder spatter
shields.
In the case of either the open-, sealed-, or
partially-closed tunnel machines, if the objective is
to minimise oxygen levels, special attention must
be given to the location(s) where the oxygen
concentration levels are measured. In order to
make an accurate comparison between the three
types of machines, oxygen levels on each machine
must be measured using the same oxygen meter at
a similar location. The use of formic and other
acids in flux formulations may adversely affect the
performance of some oxygen analyzers. Care must
be taken in the selection and operation of the
analyzer.
No-Clean Reflow Soldering
The simplest way to convert from traditional
reflow soldering with a standard RMA paste to a
no-clean reflow process is to leave the soldering
process unchanged and eliminate the post-solder
cleaning step. To clean stencils, a number of
cleaning processes can be used in place of CFC-
113 or MCF. These include isopropyl alcohol,
semi-aqueous cleaners, and other cleaners. Many
manufacturers have been successful in phasing out
CFC-113 and MCF cleaning in this manner.
However, if this simple modification does not
provide adequate board quality characteristics, a
switch to a low-residue no-clean solder paste may
be warranted. As with wave soldering, additional
cosmetic quality can be achieved by conducting the
soldering operation in a controlled nitrogen
atmosphere.
While the low-residue paste can often be
substituted for the traditional RMA paste in
existing equipment, soldering in a controlled
atmosphere requires either the retrofit of existing
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30
reflow ovens or the purchase of a specially
.designed nitrogen-capable oven. If a controlled
atmosphere is introduced, it may be possible to use
either a traditional RMA paste or a low-residue
no-clean solder paste. In either case, it is
important to ensure that the paste chosen is
compatible with the atmosphere in which the
soldering operation will be carried out, be it air or
nitrogen.
Retrofitting 'Existing Equipment
Controlled Atmosphere Soldering
tor
No-Clean Reflow Soldering '
• Can be implemented in most existing
equipment
• Eliminates the need for extensive
worker re-training
• Eliminates relatively expensive
cleaning costs
• Is enhanced when performed in an
inert atmosphere.
No-Clean Reflow Soldering In Air
The selection of a no-clean solder paste entails the
consideration of several factors. The slump, tack,
and deposition characteristics may be different
from the current paste, thereby requiring nev,
stencils of a different thickness or opening to
deposit the same amount of paste. In addition, the
reflow process window is smaller in a no-clean
process. As is the case with wave soldering, the
temperature profile may need to be changed to
ensure proper activation of the flux, removal of
votatiles, and minimization of thermal shock.
Consult with the paste manufacturer to verify the
recommended thermal profile for each solder
paste. Large boards with high heat sinking
capability may pose a particular challenge. All of
these process changes, however, can usually be
accommodated in existing equipment.
Most existing reflow ovens can be retrofitted for
such operations. Some reflow ovens, however, are
too open and consequently cannot be used for
controlled atmosphere soldering. With such use,
nitrogen would leak out of the oven at a rate
which is too high to adequately carry out the
soldering procedure to desired results. Therefore,
new equipment will be required to replace these
ovens.
Retrofitting reflow machines so that they can
maintain a nitrogen atmosphere involves several
procedures. First, the machine should be checked
thoroughly for leaks and all leaks should be sealed
to ensure that oxygen does not enter the machine.
Second, nitrogen supply lines must be added to
introduce gas into the preheat and reflow modules
of the oven. These supply lines should also be
checked for leaks. Third, an oxygen monitor
should be installed to allow workers to keep track
of the amount of oxygen present during soldering.
Finally, curtains must be installed at the entrance
to the preheat zone and at the exit from the reflow
zone to reduce air penetration into the machine
and to trap nitrogen inside.
New Equipment Options for Controlled
Atmosphere Soldering
Although it is usually not necessary to invest in
new equipment in order to implement a no-clean
reflow soldering process, soldering in a controlled
atmosphere may require new equipment. This
need arises when the existing oven is not able to
be adequately sealed to hold nitrogen. Since
traditional ovens are not designed to enclose a gas
within the preheat and solder modules, significant
leaks may occur when attempting to seal these
areas. No-clean reflow soldering machines are
similar to conventional reflow ovens but have an
open-tunnel with curtains at the entrance and exit
to allow the use of a controlled atmosphere. In
these machines, the curtains enclose the preheat,
ramp-up, and solder modules and trap the nitrogen
gas in the machine.
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QUALIFICATION OF NO-CLEAN MATERIALS
AND PROCESSES
The evaluation of a no-clean process involves both
materials qualification and process qualification.
Materials qualification includes not only testing the
flux or paste for adequacy but considering
numerous other factors, including solder joint
quality, reliability, interaction with solder mask,
long-term corrosion, cosmetics, and solder balling.
Process qualification involves analyzing the board
after soldering. Numerous factors can affect the
quality and reliability of a solder joint, including
material compatibility, component cleanliness, and
soldering process variables. This section describes
both the major considerations in qualifying no-
clean fluxes and solder pastes and the
recommended test methods and results required
for qualifying a no-clean process. The flux testing
results obtained by one telecommunications
manufacturer are presented in Appendix D.
Material Screening
The qualification of a no-clean wave or reflow
soldering process begins with a thorough screening
of the materials (flux or paste). An preliminary
screening is performed to determine whether or
not the flux or paste will solder the components in
question. This simple preliminary screening
ensures that poor candidates are eliminated as
early in the qualification process as possible,
thereby eliminating unnecessary testing.
After the preliminary screening is completed, the
manufacturer should be left with a small,
manageable number of candidates. The next step
in the materials screening process is to perform a
variety of standard tests which have been designed
to evaluate the effect of fluxes, pastes, and their
residues on PCBs.
A large number of standard tests can be performed
in order to screen out unacceptable materials. The
recommended tests and required results differ
depending on the application and the quality
standards which apply. However, the following five
tests are usually considered sufficient for qualifying
most materials:
• Copper Mirror
• Silver Chromate
• Corrosion
• Surface Insulation Resistance (SIR)
• Electromigration.
There are two generally accepted sources for these
test procedures. The first is the IPC-TM-650 test
methods manual, published by the Institute for
Interconnecting and Packaging Electronic Circuits
(fPC). The second is Issue 3 (December 1991) of
the Bellcore specification TR-NWT-QOQ078.
To achieve the highest possible reliability, a flux or
paste should achieve satisfactory results in each of
these tests.
Copper Mirror TtsL The copper mirror test is
recommended as a test for the short-term
corrosrviry of a flux. Specifically, it is used to
determine the level of copper removal caused by a
flux. The test should be performed according to
the methods described in IPC-TM-650, test method
13.32.
After the test is completed, the uncoated glass
panel is visually inspected to determine the extent
to which the flux induced corrosion of the copper.
If there is any instance of complete copper removal
on the test panels, the flux has failed the test.
Silver Chromate. The silver chromate test is the
recommended test for determining the presence of
halides (chlorides and bromides) in a flux. This
test for halide content should be performed
according to the procedures outlined in IPC-TM-
650, test method 2.3.33. Test results are evaluated
by visually inspecting the test paper to determine
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32
if any color change has occurred. If halides are
present, the color of the test paper will change to
off-white or yellow-white.
Corrosion Tea. The flux corrosion test is
recommended ia order to determine the corrosive
propenies of flux residues which remain on the
PCB after the soldering operation. While the
copper mirror and silver chromate tests are
chemical tests of the flux itself, the corrosion test
evaluates the effect of the flux residue remaining
after soldering. This test, which should be carried
out in accordance with the procedures outlined in
IPC-TM-650, test method 2.6.15, is especially
useful for evaluating the corrosrvity of flux residues
under extreme environmental (temperature and
humidity) conditions. In order to analyze the test
results, the test specimens are examined under 20X
magnification. The presence of a green-blue
discoloration indicates corrosion. Other changes
in color, however, do not necessarily indicate
corrosion.
Surface Insulation Resistance (SIX) Test. The SIR
test should be performed as pan of the flux or
paste qualification process to determine its long*
term electronic reliability. SIR testing involves
exposing standard test boards to temperature,
humidity, and an electrical bias in order to
determine board resistance. The test should be
carried out in accordance with the procedure
outlined in IPC-TM-650, number 2.633, or
according to paragraph 13.1.4 of Bellcore
specification TR-NWT-000078. To evaluate the
acceptability of the results, they are compared to a
standard value. Too low an SIR value indicates
that long-term operation may cause circuit failure
due to shorts.
As shown in Exhibit 9, the primary differences
between the IPC and Bellcore SIR tests are the
temperature settings and the length of time after
which readings are taken. In the IPC test,
measurements of the insulation resistance are
taken after 1, 4, and 7 days at conditions of 85'C
and 85 percent relative humidity. The test results
are evaluated using the 4- and 7-day
measurements. In the Bellcore test, measurements
are taken after 1 and 4 days at 35°C and 90 percent
relative humidity, with the 4-day result being used
to classify the flux or paste.
While the IPC lest does not specify exact minimum
SIR values as pass/fail criteria, the Bellcore
specification does. In the case of a test pattern
with 0.050 inch spacing, a minimum resistance of
1 x 10s megohms is required to qualify the flux or
paste. If the IPC-B-25 board is used (spacing of
0.0125 inches), a minimum resistance value of 2 x
104 megohms must be achieved.
Electromigration. The electromigration test should
be carried out as described in the Bellcore
document TR-NWT-00078, Issue 3. After the test
is completed, the test samples are examined
visually using back-lighting and 10X magnification.
The product is said to pass the test if there is no
evidence of electromigration that reduces
conductor spatings by more than 20 percent. The
test is considered a failure if heavy corrosion
occurs, although minor discoloration is considered
acceptable.
Process Qualification
The qualification of a no-clean wave soldering
process depends on a wide variety of factors,
including:
Solderability
Quality
Cosmetics
Testability
Repeatability.
Since u is highly unlikely that a single flux will be
superior in all of these categories, tradeoffs must
be made selecting the correct flux for a given
process.
SoUenbUity. Solderability is the ability of a flux to
aid in the formation of a solder joint Solderability
is not usually a significant problem when
substituting a no-clean flux or paste for a
traditional flux or paste, provided that soldering
process parameters are correctly adjusted and
adequately monitored.
Just as important as the flux and paste is the
Solderability of the components which are being
soldered to the board. In order to maintain board
cleanliness and overall Solderability, all
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33
Exhibit 9
Comparison of (PC and Bellcore SIR Testing Procedures
Parameter
Test Pattern
Temperature
Humidity
Testing intervals
Passing results
1 Class III only.
2 Classes I and II.
IPC-SF.818
IPC-B-25, B comb
2ec1/50»c2
85 percent1/^ percent2
24, 96, and 168 hours
IxlO2 megohms
Bellcore TR-NWT-000078
(Issue 3)
IPC-B-25, B comb (0.0125
inch spacing), or 0.050 inch
spaced board
35"C ± 2°C
90 percent
24 and 96 hours
IPC-B-25: 2X104 megohms
0.050 in: IxlO5 megohms
components and the board itself must be clean.
Due to the reduced solids content of the flux used
in a no-clean process, pre-solder cleanliness of
components becomes a major factor in maintaining
the solderability of the board. You must ensure
that your suppliers provide you with sufficiently
clean and solderable components since they will
not be cleaned later in the assembly process.
Quality. The quality of a soldered board is a
measure of the defect rate and is obviously the
most important consideration in qualifying a no-
clean wave or reflow soldering process. Bridges,
skips, webbing, and other defects should be closely
monitored in qualifying a process and in normal
operations.
Cosmetics. The overall visual appearance of a
board after soldering is an important consideration
in qualifying a no-clean Dux. Cosmetic appearance
does not affect the reliability or quality of a
soldered board.
However, cosmetics are the primary reason for
some manufacturer's choice not to switch to a no-
dean flux. In the case of high-solids no-clean
fluxes, cosmetics are the major factor contributing
to their lack of large-scale penetration into the
American manufacturing market Conversely,
these fluxes have gained widespread acceptance in
Europe. While the use of no-clean fluxes may
leave a visible residue on the board, the residues
are most often benign and, given good flux
selection, do not affect board performance or
reliability. Controlling the amount of flux applied
to the board impacts the amount of final residue.
Thus, proper application can minimize the amount
of residue.
Testability. Testability is a measure of the ability to
accurately ,test the electrical performance
characteristics of the board after assembly and
soldering. Testability often depends on clean
solder connections if pin-test Gxturing Is used.
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34
Repeatability. The term repeatability refers to the
ability to produce the same quality of board
regularly with few modifications to process
parameters. Repeatability is essential in
maintaining efficiency in the soldering process. A
soldering process which varies regularly will
require that production be stopped frequently to
adjust the appropriate parameters and re-test the
operation.
Repeatability will often be more difficult to obtain
with a no-clean process than with a traditional
soldering process because of two factors. These
include:
• the small process window within which the
no-clean process is carried out
• the frequent monitoring and process
auditing required because of the
components' sensitivity to change.
These audits, however, ensure that all applicable
parameters are at optimal levels to cany out the
soldering operation.
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35
ECONOMICS OF NO-CLEAN PROCESSES
Each of the no-clean processes described in this
manual has associated costs (both fixed and
variable) and offsetting benefits. This section
describes, for each no-clean process, the average
cost of implementing the process as well as any
benefits which might result from its use.
Regardless of the no-clean process which is
utilized, the largest benefits realized occur from
the complete elimination of the cleaning process.
Thus, facilities which switch to a no-clean soldering
process save both the capital cost of cleaning
equipment and floor space, and the material and
operating costs associated with the use of the
cleaner, including the elimination of solvent
disposal.
No-Clean Wave Soldering
Each of the options for instituting a no-clean wave
soldering operation (eliminate cleaning, .change
flux, change flux application method) at the least
eliminates entirely the post-solder cleaning step,
resulting in savings in equipment expenditures,
solvent purchases, and solvent disposal costs. This
section describes the costs associated with each of
the no-clean wave soldering options presented
earlier in the Process Details section of this
manual.
No-Clean Wave Soldering In Air
No-clean fluxes (low- or high-solids formulations)
can sometimes be substituted directly for
traditional fluxes with no additional process
changes. In this case, an overall savings usually
results since both the solvent and cleaning
equipment costs are eliminated.
In instances where a manufacturer wishes to
retrofit existing wave soldering equipment for use
with a spray fluxer, there is a cost associated with
the purchase of this new equipment. Spray fluxers
are produced as stand-alone units by several
manufacturers and costs range from approximately
$4,500 to 120,000. There are additional benefits
associated with the use of a spray fluxer because,
due to the controlled nature in which a spray
fluxer applies flux to a board, a smaller quantity of
flux is consumed over any given period of time.
One manufacturer, for instance, has seen a flux
savings of 68 percent by switching to a spray fluxer.
In addition, many spray fluxers eliminate the use of
flux thinners.
Retrofitting Equipment for Controlled
Atmosphere Soldering
No-Clean wave soldering in a controlled
atmosphere may be accomplished by retrofitting
existing equipment with a device such as a hood or
other innovative technique which permits nitrogen
inerting.
Depending on the type of hood chosen, the capital
cost of retrofitting existing equipment typically
totals between $10,000 and $30,000 for the
addition of a nitrogen hood. The lower cost is
associated with a nitrogen hood that covers the
solder pot area only, while a hood which covers
the preheat and solder areas brings the cost to the
higher end of the range. Additional costs arise in
the installation of piping to cany the nitrogen to
the soldering machine. Installed piping costs an
average of $30 per foot, but can range from $15 to
$50 per foot. The total cost of piping depends on
the distance which the nitrogen is piped.
* j
Purchasing nitrogen is another cost which
primarily depends on the size of the area to be
controlled as well as the amount of time during
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36
which the machine is operational. The amount of
nitrogen required in these machines is usually in
the range of 1500 to 2000 cubic feet per hour (cfh)
and the cost of industrial grade nitrogen purchased
in bulk ranges from approximately $0.12 to 50.50
per 100 cubic feet (note that this cost varies with
the grade purchased and the country in question).
In some newly designed retrofit packages, the
amount of nitrogen required has been as low as
300-600 cfh.
Economic benefits from retrofitting existing
equipment for no-clean wave soldering in a
controlled atmosphere include the elimination of
the cleaning process as well as the potential for
substantial savings in flux and solder usage. The
experience of several manufacturers has shown that
flux and thinner savings in the range of 50 to 70
percent are possible with the addition of a spray
fluxer and soldering in a controlled atmosphere.
In addition, a 50 percent reduction in the amount
of solder used is also feasible since solder dross is
often greatly reduced. A breakdown of traditional
soldering costs by component is shown in
Exhibit 10.
New Equipment Options
The purchase of new equipment which is specialty
designed for controlled atmosphere wave soldering
will be significantly more costly than retrofitting
existing equipment. As mentioned earlier, two
types of equipment are available — open-tunnel
a,,J sealed-tunnel machines. A typical open-tunnel
wave solder machine has a capital cost of $80,000
to 5300,000. The range in cost is due to the large
number of options available, including spray
fluxing modules, extra preheaters, computer
controls, oxygen analyzers, and bar code scanners.
Nitrogen usage in open-tunnel machines is
generally between 700 and 2400 cfh.
A sealed-tunnel wave solder machine will often be
more expensive than an open-tunnel machine.
Unlike open-tunnel machines, there are very few
manufacturers of fully enclosed soldering
equipment. A typical model, which costs in the
neighborhood of $300,000, consists of a spray
fluxing module, preheaters, a solder module, and
entrance and exit vacuum chambers. Additional
options for these machines such as oxygen
analyzers and bar code scanners can add
approximately £30,000 to the capital cost.
Nitrogen usage in a sealed-tunnel machine ranges
from 100 to 700 cfh.
The benefits which can be achieved from
conducting soldering operations in a controlled
atmosphere include the costs associated with the
cleaning process which would have otherwise been
required as well as flux and solder savings. In the
case of both the open-tunnel and sealed-tunnel
machines, flux savings can be as high as 70 percent
(depending on the flux application method used),
and solder savings can be as high as 50 percent.
No-Clean Reflow Soldering
The most cost effective method for converting a
traditional reflow soldering operation to a no-clean
operation is to use traditional pastes without post-
solder cleaning. In this case, there are no
additional costs incurred, and the expenses
associated with the purchase and operation of
cleaning equipment are saved. If this change does
not produce acceptable results, the implementation
of a low-residue paste may affect the process cost.
The cost of a low-residue paste may be higher than
that of conventional pastes because it is produced
in smaller quantities. In addition, new stencils may
be required for use with low-residue pastes.
Retrofitting Equipment for Controlled
Atmosphere Soldering
A controlled atmosphere can often be employed in
existing reflow ovens by performing retrofits to
ensure that nitrogen is adequately confined to the
soldering area within the oven. This retrofit
involves ensuring that the equipment is leak-free as
well as installing nitrogen supply pipes from a tank
to the soldering machine. Depending on the size
of the oven, the cost of such a retrofit can range
from $20,000 to $100,000.
In general, it takes approximately one week to
retrofit an oven so that it can accommodate a
controlled atmosphere. An oven which has been
retrofitted typically consumes approximately 2400
cfh of nitrogen and can achieve an oxygen level of
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37
Exhibit 10
Total Process Material Cost Breakdown
For a Traditional Soldering Process
Solder 46%
Flux & Thinner 13%
Cleaning Solvent 41%
Source: "Printed Circuit Assembly," March, 1989
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38
less than 500 ppm, although actual nitrogen
consumption and oxygen levels will depend on the
degree to which the tunnel has been successfully
sealed as well as the flux or paste being used. The
work atmosphere must maintain a sufficiently high
level of oxygen to ensure worker safety.
New Equipment Options
In cases where it is not possible to retrofit existing
ovens to adequately seal nitrogen within the
tunnel, a nitrogen-dedicated oven can be
purchased. These ovens are specially designed for
use with a controlled atmosphere and therefore
consume less nitrogen while achieving lower levels
of oxygen. The cost of a new oven with nitrogen
capabilities can range from approximately $75,000
to $175,000. These ovens consume approximately
2000 cfh of nitrogen and can limit oxygen levels to
less than 20 ppm.
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39
ENVIRONMENTAL, HEALTH, AND SAFETY
ISSUES
Several issues relating to the environment, human
health, and. safety must be considered when
evaluating the various no-clean soldering processes
available. These are:
• Volatile organic compound (VOC) emissions
• Waste disposal
• Worker comfort and safety
Regardless of the process used, the primary
environmental benefit realized is the elimination of
CFC-113 and methyl chloroform (MCF). Not only
will the reduced use of CFC-113 and MCF have a
significant effect on ozone layer depletion, but,
since these compounds are greenhouse gases, their
elimination will help to mitigate potential global
warming problems. Other environmental, health,
and safety issues depend on the soldering process
chosen.
Environmental Issues
in addition to the effects of eliminating the
impacts of CFC-113 and MCF on ozone depletion
and global warming, there are additional
environmental issues to consider including
emissions of volatile organic compounds and waste
disposal.
Volatile Organic Compounds (VOCs)
VOCs are gases released into the atmosphere at
normal use temperatures during the soldering
process. VOCs contribute to the formation of
ground-level ozone (smog). When compared with
a traditional soldering and solvent cleaning
operation, a no-clean soldering process results in
an overall reduction in VOC emissions. VOC
emissions are increased from the use of low-solids
fluxes which contain 0.5 to 5 percent solids as
opposed to nearly 40 percent solids in traditional
fluxes. The remainder of the low-solids
formulation is approximately 1 percent activator
and the balance is comprised of alcohol (usually
isopropyl alcohol). Therefore, depending on the
alcohol used in a given flux formulation, VOC
emissions from low-solids no-clean fluxes may be
higher than those from traditional flux. However,
the elimination of the CFC-113 and MCF solvent
cleaning process will result in an overall reduction
of VOC emissions from board assembly processes
since both have traditionally been combined with
an alcohol. In addition, the use of a spray fluxer
and/or a controlled atmosphere may decrease flux
usage by approximately 50 percent, thereby
reducing VOC emissions. The net reduction in
VOC emissions will depend on the solids content
of the flux and the cleaning process being
eliminated.
Waste Disposal
The U.S. Environmental Protection Agency (EPA)
classifies solder dross as a hazardous waste under
the Resource Conservation and Recovery Act
(RCRA). When compared with conventional wave
soldering operations, using no-clean fluxes results
in little change in the amount of solder dross
produced. In the case of controlled atmosphere
soldering, however, the reduced concentration of
oxygen present during the soldering operation
results in the formation of substantially less solder
dross, thereby reducing the amount of hazardous
waste produced.
In addition to a reduction in solder dross waste,
the elimination of the post-solder cleaning
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40
processes will further reduce waste disposal needs
for assembly plants by eliminating disposal of spent
solvents or wastewater.
Health and Safety
There are several issues associated with no-clean
soldering processes which may affect the health
and safety of workers. These include formic acid
usage in some controlled atmosphere processes,
prolonged exposure to high-alcohol content fluxes,
and reduced oxygen atmospheres.
Formic Acid
Formic acid is currently used as a reducing agent
in a small number of controlled atmosphere
soldering processes, often those where strict
soldering standards exist Formic acid can have
potentially serious health effects for workers.
Therefore, the U.S. Occupational Health and
Safety Administration (OSHA) has set a
mandatory Permissible Exposure Limit (PEL) of 5
ppm for formic acid. The careful handling of
formic acid is critical. Spills may result in the
need to evacuate the manufacturing facility,
resulting in a work stoppage that may last for
several hours. Besides the hazard of formic acid
itself, metal formates are produced as a by-product
of the use of formic acid in soldering processes.
These waste products require that workers clean
the soldering equipment regularly, the>*.by
increasing their exposure to lead and requiring that
ail work be stopped during the cleaning process.
While the cleaning of equipment is more frequent
when formic acid is used than when it is not, the
frequency of cleaning when formic acid is used is
still over 50 percent less than in machines used to
solder in air atmospheres. In any processes where
formic acid is handled or used, safety showers, eye
wash stations, and respiratory protection must be
available.
contained under«an exhaust hood. The fumes from
excess flux, if not properly recovered, can cause
heart irritation and lung damage as well as
headaches and upset stomachs. Spray fluxers are
generally equipped with a timer and sensor which
switch the spray on when a board arrives, and turn
the spray off as the board leaves the fluxing zone.
This mechanism helps to minimize overspray and
reduces the hazards posed by flux exposure. In
addition, because of their high alcohol content,
liquid fluxes are often extremely irritating to the
eyes and skin with repeated or prolonged contact.
In order to protect against these hazards, the use
of protective gloves and safety goggles is
recommended.
Regardless of the flux application method
employed, workers on production lines which
utilize no-clean flux formulations may experience
discomfort due to odor. The high alcohol content
of no-clean fluxes contributes to this strong odor.
Adequate workplace ventilation is required to
ensure worker safety and comfort.
Reduced Oxygen Atmosphere
Another worker safety issue results from the use of
controlled atmosphere soldering equipment. If not
properly controlled, the presence of nitrogen
results in a deficiency of oxygen, thereby posing
potential danger to workers near the machine.
Workers must be sure that they do not place their
heads inside machinery where a nitrogen
atmosphere is being maintained. Doing so could
result in the worker receiving insufficient oxygen
and blacking out. Potential users of controlled
atmosphere soldering should consult with the
nitrogen supplier as well as the equipment
manufacturer concerning the possible hazards
associated with the handling and use of nitrogen.
In addition, facilities must ensure that adequate
ventilation is present in the area in which the
nitrogen atmosphere is to be used.
Flux Exposure Issues
In facilities where production lines are modified
for the use of spray fluxers, precautions must be
taken to ensure that any overspray of flux is
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41
MANUAL SUMMARY
This manual provides a structured program to evaluate the feasibility of a change to a no-
clean soldering process. It also provides a methodology for evaluating a variety of no-clean
soldering options. This information includes:
An overview of the currently available no-clean technologies
Major characteristics of the various types of no-clean soldering processes
Detailed information on procedures to determine the applicability of a no-
clean option in a specific manufacturing process
Data on the cost of implementing the various no-clean options
Information on environmental, health, and safety issues associated with no-
clean processes.
The next section builds on this basic understanding of no-clean soldering processes and
presents detailed case studies of these applications as they are implemented in industry.
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42
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43
CASE STUDIES OF INDUSTRIAL PRACTICES
The following section presents actual industrial experiences with some of the alternative
technologies discussed earlier in this manual.
Mention of any company or product in this document is for informational purposes only and
does not constitute a recommendation of any such company or product, either expressed or
implied by EPA, ICOLP, ICOLP committee members, and the companies that employ the
ICOLP committee members.
Case Study #1: No-Clean Wave Soldering in a Controlled Atmosphere
Environment
Case Study #2: An Alternative Testing Method To Qualify No-Clean Processes
Case Study #5: Evaluation of No-Clean Processes at AT&T
Case Study #4: Flux Selection Criteria
Case Study #5: Spray Fluxing for Today's Soldering Processes
Case Study #6: Choice of a No-Clean Process at NCR.
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44
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45
CASE STUDY #1:
"NO-CLEAN" WAVE
SOLDERING IN A CON-
TROLLED ATMOSPHERE
ENVIRONMENT
Motorola (Government Electronics Group) joined
in a Cooperative Research and Development
Agreement with Sandia National Laboratories and
Los Alamos National Laboratory to evaluate a no-
clean solder materials system for military
applications. The study evaluated the physical,
chemical, electrical, and long term aging effects of
the no-clean system under varying environmental
conditions and using various materials and
concentrations. After evaluating systems, the
research group proposed using low-solids adipic
acid and gaseous formic acid materials as an
alternative for the rosin flux process which
required cleaning after wave soldering.
The adipic and formic acid materials system has
been used successfully as a no-clean application in
many commercial installations. Although
Motorola has six machine/material installations
similar to the one described here, none of the
installations has been evaluated for use in military
applications.
In this study, tests to evaluate ionic cleanliness,
chemical residues, and surface insulation resistance
(SIR) were performed on three different printed
wiring board (PWB) designs. These designs also
included a group of electronically functional boards
that were subjected to an accelerated aging test to
simulate 20-year long-term storage conditions.
The IPC B-24 comb pattern circuit board served as
the SIR test vehicle; a general purpose Motorola
Test Board (MTB) designed for through-hole
assembly served as a vehicle for ionic cleanliness as
well as chemical and physical testing; and a high-
volume production FMU-139 bomb fuse board
served as the functional vehicle for long-term
storage testing.
A series of designed experiments subjected the test
boards to a broad array of process variables,
including normal process conditions and
concentrations of adipic and formic acids.
Evaluation of the Effects of
Wave Solder Machine
Parameters
The wave soldering machine used during this
program has several key features, including three
independent conveyors (flux, preheat, and solder),
a dual wave (turbulent chip and laminar), and an
ultrasonic spray head for the adipic acid flux. The
extent to which the various tests could be
controlled allowed the research group to
methodically evaluate the machine parameter
effects. The soldering process has many different
controllable parameters that influence the visual
solder quality and ionic cleanliness of the PWB.
AU of these parameters were evaluated with the
designed experiments. The parameters include:
• Flux conveyor speed
• Preheat conveyor speed
• Solder conveyor speed
• Solder pot temperature
• Wave angle
• Turbulent wave on/off
• Adipic acid percentage
• Formic-nitrogen flow.
Experiments
The effects of machine parameters were evaluated
to determine their contribution to PWB cleanliness
and electrical , performance. Because of the
complexities of the PWB design, no single setting
for machine parameters will provide uniformly
high visual quality for all products. To evaluate as
broad a group of settings as possible, the
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46
experiments were designed to use a realistic range
of ievels for machine parameters. . The levels
evaluated represented the extreme. levels that
wouid potentially be used in processing PWBs.
Hie effect of each of the designed experiments
were analyzed, and the subsequent experimental
design was based upon this analysis. With the
exception of the initial screening experiment, two
PWBs per cell were used in all of the tests. This
format not only allowed the research group to
evaluate a broad range of machine parameters, but
also yielded a significant amount of information on
the process and material effects.
The study assessed three different PWB designs.
The factors and extreme levels for alt of the
parameters evaluated in the experiments are
presented in the following table:
Factors Low
Flux conveyer speed 0.8
Preheat temperature 80
Time in solder pot 1
Adtpic acid concentration t
Nitrogen flow in formic acid None
Wave angle S
Solder pot temperature 245
Hieh
1.4 meter/minute
130 degrees C
4 seconds
2 percent
7 liier/ain.
nitrogen
9 degrees
260 degrees C
The low and high levels of the factors shown above
are composites of all the levels evaluated. An
RMA flux was used as a control for this series of
experiments.
Specific test objectives were to demonstrate that
the process could produce hardware that:
• meets the military specification limits for ionic
cleanliness and SIR
• does not degrade during typical environmental
conditioning
• does not degrade with long-term storage.
Experiment Designs
The initial experiment consisted of a half fraction
2A5 screening experiment to evaluate the impact of
process parameters on solder joint quality and
ionic cleanliness. The FMU-139 bomb fuse PWBs,
which were used to run this initial test are double-
sided, 0.092 inch thick boards for solder joint
quality and had their contamination levels
measured in a Model 500R ionograph. The results
from the initial screening were analyzed and
provided inputs for additional work evaluating
long-term storage characteristics.
The data from the first experiment provided
direction to form the basis for setting the levels for
the Long-Term Storage (LTS) test conditions.
This experiment used machine parameters that
produced low (3 to 5 micrograms sodium ton
equivalent), medium (5 to 7 micrograms sodium
equivalent), and high (20 to 30 micrograms sodium
equivalent) tonic contamination on FMU-139
bomb fuse boards.
The FMU-139 bomb fuse boards were electrically
functional and used to evaluate the effects of
cleanliness on degradation of electrical
performance in LTS conditions. In this portion of
the evaluation, three different machine parameters
were used to run the boards over the wave.
Control boards for the long-term storage test used
an RMA flux as a control. The boards from this
experiment were subjected to an environmental
stress test to simulate 20 years in storage - 80°C at
40 percent humidity for 2522 hours.
The second experiment used the MTB as the test
vehicle. The MTB is a double-sided, 0.062 inch
thick PWB, designed for through-hole components
such as axial, DIP, TO-99 components, and
connectors. The MTB has dry film solder mask on
both sides and was specifically designed to support
wave soldering process development. A 2A5 full
factorial experiment, which gave a 64 cell
experiment with two boards per cell, was used
during this ponton of the testing.
After running through the ceils in the experiment,
the MTB boards were subjected to ionograph
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47
testing and visual examination. After
environmental conditioning, the components on
the MTB were tested electrically and mechanically.
The third experiment evaluated the effects of
machine setting-on two PWB designs used in this
series of testing - MTB and IPC-B-24 boards. In
this experiment, the boards were subjected to ionic
cleanliness testing, visual inspection, chemical
surface analysis via high pressure liquid
chromatography (HPLC), electron microprobe
analysis (EMPA), scanning Auger microscopy
(SAM), secondary ion mass spectroscopy (SIMS),
and Fourier transform infrared spectroscopy
(FTIR).
Results
The results from the testing show that the no-clean
soldering process is capable of producing reliable
hardware whose visual quality is equivalent to that
achieved with the existing rosin-based flux followed
by cleaning.
The results from these tests were obtained from
experiments designed to incorporate a wide range
of machine control parameter settings. The levels
evaluated represent the extreme limits of those
that could potentially be used in processing PWBs.
The data from each of the experiments support
these conclusions with very few anomalies. The
results from the testing were reproducible and
predictable. Level settings for factors were
adjusted based upon statistical evaluations of test
data with the subsequent PWBs having levels as
clean as those obtained using rosin-based flux
processes.
SIR testing on separate groups of boards (85°C/85
percent relative humidity and 50°C/90 percent
relative humidity for 21 days each). Exhibit 11
shows SIR data from day seven of the SIR test.
Exhibit 11
SIR Values of Boards from DOE Cells
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Exoerimental Gel
The results from the SIR testing indicate that
there is a sensitivity to machine parameters and
that the boards soldered and not cleaned using
adipic and formic acid materials provide SIR
results as good as or better than PWBs soldered
with an RMA flux and cleaned with methyl
chloroform. A MTB was run using the same
soldering conditions as each IPC B-24 board. This
"witness" MTB provided the relative ionic
cleanliness for the B-24 boards run in each DOE
experiment cell. Thus, the research group was able
to link the SIR test data with ionic cleanliness data
for each of the cells.
SIR
The standard SIR test as described in the IPC Test
Method 650 Number 2.6.3.3 was used for this
evaluation.
A total of 95 IPC B-24 boards from eight cells
were subjected to SIR testing, with only six boards
having low SIR values after 4 to 7 days of testing.
Two temperature/humidity profiles were run in the
Ionic Conductivity
The MTB tests provided data for ionic conductivity
by acting as a common vehicle to assess tonic
cleanliness in all experiments. The MTB provided
a common reference point for review of data from
experiment to experiment and cell to cell.
Additional ionic conductivity verification testing
was performed by the Navy EMPF facility in
Indianapolis, IN. The results from this testing
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48
indicate that the conditions under which the wave
soldering machine operates can radically affect the
resultant cleanliness of a PWB. The testing
conducted by the EMPF for the ionic conductivity
readings verified the results obtained by Motorola.
The results observed in this portion of the test
indicated that ionic cleanliness varied from an
average of near 3 micrograms equivalent sodium
ion to a high of near 25. The results were both
predictable and reproducible. This data is shown
in Exhibit 12.
Exhibit 12
Ionic Cleanliness
The Naval Weapons Center at China Lake, CA ran
independent FITR testing on samples and
concluded that there appeared to be no significant
residues present on the boards.
Temperature-Humidity and
Temperature-Cond/t/on/ng Test Results
No corrosion was observed when the boards were
subjected to visual inspection under 10X
magnification. Solder joints were evaluated for
corrosion or cracking by four point Kelvin
measurement No significant shifts in the
resistance values of the solder joints were
observed.
«*>
8 6
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Experimental CeD
Chemical Surface Contamination
Analysis
The IPC Honeywell 355 HPLC procedure was
modified to analyze the surfaces of the PWBs for
traces of adipic and formic acid residues or their
salts. The modified test was sensitive to as low as
approximately 40 micrograms per square
centimeter of adipic acid or its salts. Barely
detectable trace amounts of adipate salts were
found on the board. Subsequent FITR and SIMS
analysis also confirmed very low levels of residue.
Long-Term Storage Electrical Function
Forty of the FMU-139 bomb fuse boards were
subjected to the long-term storage testing (30 from.
the adipic/formic add process and 10 from the
control group — rosin flux process). The boards
were placed in an environment of 80"C and 40
percent relative humidity for a total of 2^22 hours.
These conditions simulate a 20-year long-term
storage of these boards. The boards were pulled
from the test chamber for verification of electrical
function at discrete intervals of 126, 1,260, 1,639,
and 2422 hours. All boards tested functionally
operable up to the 1,639 hour point (equivalent
life of 133 years in storage). Some time after the
1,639 hour samples were pulled and tested, the
environmental chamber control failed and the
humidity in the chamber went to 100 percent.
This caused water to drip down into the chamber
on several of the boards at a continuous rate. It is
estimated that, at this point, the life stress testing
exceeded well over 100 years of storage. This
overstress resulted in three boards from the adipic
acid group failing the final electrical test and two
rosin fluxed boards showing substantial visual
corrosion damage. All of the boards that failed
during the last portion of the test had water stains,
attesting to the fact that they were directly under
the leak in the chamber. The cause of the failure
in these boards could be traced to the same
mechanism: a specific single ceramic-bodied diode
whose leads corroded and whose lead seal failed
and allowed moisture into the diode cavity in the
package. No other components failed or showed
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49
evidence of any problems. Even with the
significant environmental overstress, the test
results, based on the results obtained from the
remaining boards that were not directly under the
leaking reservoir, provided valuable positive
information regarding the benign nature of the
adipic/formic acid process.
Conclusion
The results from this series of tests are clear:
adipic and formic acids are materials that are safe
and beneficial to the wave soldering process and
do not require cleaning after solder assembly. The
products soldered with the adipic and formic acid
materials exceeded the product design criteria by
more than a 30 percent margin. The use of a
controlled nitrogen atmosphere provides an
environment where adipic acid can successfully and
safely serve as a no-clean flux. This conclusion is
supported by all of the data from the ionic
conductivity test results to the SIR and long-term
storage test results. The solder joints obtained
with the adipic/formic acids have the same high
quality visual appearance of solder joints formed
with RMA fluxes. In addition, the adipic/formic
materials do not degrade circuit performance and
the residues do not require cleaning.
For Further Information
Mr. Larry Lichtenberg
Principal Process Engineer
Motorola
Government Electronics Group
8220 E. Roosevelt St.
Scottsdale, AZ 85252
Tel: 602-441-6858
Fax: 602-441-7020
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50
CASE STUDY
AN ALTERNATIVE
TESTING METHOD TO
QUALIFY NO-CLEAN
In late 1991, Northern Telecom announced that it
had eliminated the use of ozone-depleting solvents
from its manufacturing facilities worldwide. This
case study describes a unique testing method
developed at one of Northern Telecom's facilities
and its use as an audit tool for a specific no-clean
process.
The Problem
In an effort to eliminate the use of ozone-depleting
substances (ODSs) in solvent cleaning applications,
the research team at Northern Telecom's Research
Triangle Park (RTF), NC facility elected to
implement a no-clean soldering process. In
convening to the no-clean process, engineers at
RTF were faced with the task of choosing an
appropriate tow-solids flux to be used in place of
their conventional flux. The identification of an
acceptable flux involved two stages - the flux
selection and flux testing/qualification.
While flux selection criteria assured that the flux
used was totally safe, problems with the Final
inspection Quality Group (FIQC) often developed.
The most frequent problem identified by the FIQC
involved the amount of residue left on the wave
soldered boards after using the low-solids flux.
The amount of residue was significant enough to
leave an easily perceivable tack. Different
engineers, using different process parameters and
taking samples at different times, achieved varying
results when performing post-solder quality testing.
These differing results proved to be very disruptive
to the production process.
The Solution
In an effort to design a test for board tack which
would produce reliably repeatable results, John
Peterson, the senior chemist at the RTF facility,
constructed a patented "dust box machine.* It was
decided that the most accurate way to measure the
tack of a board is to determine the amount of
powder that would stick to a sample board after
wave soldering with a given quantity of flux.
The dust box, shown in Exhibit 13, is a device
which applies a fine spray of powder to the surface
of a printed circuit board. The device is comprised
of several parts: an enclosed test chamber, a
mechanism. to introduce the powder into the
chamber, and a fan to disperse the powder.
Selecting an appropriate powder was a unique
challenge in and of itself - weight, safety, and
adhesion to board surfaces all posed problems.
Calcium carbonate was eventually chosen. Pass-fail
criteria were determined by a general consensus of
manufacturing and quality engineers after they
were presented with a wide variety of test samples.
The Test Process
A test coupon made of normal production board
material with solder mask applied is precleaned,
run through the normal manufacturing process
(including fluxing, preheating, and wave soldering),
and weighed. The weight is recorded and the test
coupon is placed in the dust box machine for
exactly two minutes, during which time the fan
blows the calcium carbonate dust onto the test
coupon at a constant rate. The test coupon is then
removed from the chamber and re-weighed to
determine whether the amount of powder that has
stuck to the board is acceptable. The exact test
procedure is as follows:
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51
Exhibit 13
Schematic of Dust Box Testing Machine
Source: Northern Telecom
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52
Dust Box Test Procedure
1. Clean an IPC-B-25 test coupon with solder
mask with an alcohol rinse
2. Run the clean coupon through the current
production process with the solder mask
side down
3. Weigh the coupon after processing
4. Record the weight (Wl)
S. Place the coupon into the dust box with
the flux side facing the fen
6. Close the dust box door and turn on the
switch
7. Run the fan for two minutes
8. Remove the coupon from the dust box and
record its weight (W2)
9. Calculate percentage weight gain as:
<[(W2-W1)/W1] x 100}.
In order to determine the acceptable amount of
flux residue which could be allowed to remain on
the boards after soldering, the boards were run
using differing degree of flux concentration.
Results must be related to a flux type and specific
quality criteria. The Northern Telecom levels for
one flux are as follow::
Percent Weight Gain Classification
0.0% - 0.5%
0.51% - 0.8%
0.81% - higher
Pass
Marginal Pass
Fail
Acceptability criteria such as these were
determined for each manufacturing line depending
on the product and quality control requirements of
the line.
The total cost of the dust box testing is
approximately $3,500 ($1,000 for the dust box and
52,500 for a laboratory scale). Both are one-time
capital costs.
Results and Benefits
Seve:a; benefit -.ere realized by using the dust box
as a tool to measure board tack. First, the tests
yielded quantitative, repeatable results when
compared with the previous subjective evaluations.
Second, by achieving an accurate measure of board
tack, the wave solder parameters could be
accurately adjusted to result in fewer flux-related
soldering problems. Finally, for the specific flux
tested, Northern Telecom found that traditional
SIR test results correlated well with the tack
results produced by the dust box.
The correlation of dust box test results with results
from SIR tests may be of particular interest to
small manufacturers, many of whom cannot afford
the expensive equipment necessary to perform tests
such as SIR. Throughout the implementation of
the no-clean processes at the RTP facility, seven
production lines were monitored for several
months, and the correlation between board tack,
SIR, ionic contamination, and flux deposition rate
was analyzed. Any one of the tests could be used
as a stand-alone method to audit process control
while using no-clean -fluxes. Because of the
relatively low cost of the equipment used in two of
the tests, overlapping tests were run to increase the
confidence of the results.
Deposit rate testing, which is no more than
calculating the weight difference in flux solids left
on a mylar sheet, correlated well with solvent
extract testing. Flux deposit testing can easily be
done by production staff, with a laboratory scale
costing less than S3,000. Mylar sheets are
inexpensive, and a test can be completed in less
than five minutes.
Using the dust box, SIR testing can be correlated
to a specific flux type and to a board tackiness.
SIR tests require expensive environmental
chambers, time, and specially trained staff. The
dust box test method, whose equipment can be
purchased for under $3,500, can be run in under 15
minutes by machine operators or lab technicians.
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• 53
Conclusions
In the process of converting from soldering with
solvent cleaning to a no-clean soldering process,
Northern Telecom designed two inexpensive but
effective audit methods to predict board quality.
The dust box is a product quality audit tool and
the flux deposit testing is a process audit tool.
Once correlated to a given flux, both devices
quickly and easily predict production quality. The
simplicity of the tests allows them to be conducted
as often as needed at little cost Although not a
replacement for typically used SIR tests, they have
proven to be very predictable for specific fluxes.
For Further Information
Mr. Richard Szymanowski
Manufacturing Engineer
Northern Telecom Incorporated
P.O. Box 13010
4001 East Chapel Hill-Nelson Highway
Research Triangle Park, NC 27709
Tel: 919-992-5000
Fax: 919-992-3998
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54
CASE STUDY #3:
EVALUATION OF
NO-CLEAN PROCESSES
ATAT&T
At AT&T, materials used in soldering processes
are carefully evaluated to ensure product reliability
and compatibility with manufacturing processes.
AT&T tests fluxes, pastes, and their residues to
determine their ability to corrode copper mirrors
or plates and their halide content, pH level, and
conductivity. In addition, AT&T evaluates liquid
fluxes and solder pastes for soldering performance
and also tests solder pastes for rheology,
printability, and slump resistance.
No-Clean Solder Paste and
Reflow
In 1988, AT&T started to evaluate low-residue
solder pastes in controlled reflow atmospheres.
While the physical and Theological properties of
these early materials were far from ideal, AT&T
could reflow them in atmospheres with various
reactive additives to produce good solder joints
and small amounts of residue. Results from
reliability tests showed that these residues were
noncorrosive and nouumductive. AT&T obtained
a patent that covers this reactive-atmosphere
soldering method.
For general applications, a controlled atmosphere
is greatly preferred to one that incorporates
reactive species. Thus, our focus turned to the
evaluation of paste materials that would reflow in
nitrogen and were compatible with AT&T's
reliability and process requirements. The physical,
rheological, thermal, electrical, and chemical
properties of more than 25 materials from 10
vendors were evaluated. By the end of 1990,
AT&T had identified several materials that met its
requirements.
thermal profile rand the oxygen content of the
reflow environment AT&T obtained thermal
profiles on assembled printed wiring boards, typical
of those soldered in production, and performed
oxygen mapping under loaded production
conditions.
Several commercially available ovens met the
thermal requirements. The best ovens were those
that incorporated forced convection to promote
temperature uniformity. Nearly all the ovens from
major vendors could maintain less than 100 parts
per million (ppm) of oxygen (Oj) and the most
gas-tight systems could maintain less than 10 ppm
throughout their length.
Next, to determine oxygen window or range of
oxygen concentrations that gave favorable results,
a metered air leak (about 20-percent oxygen) was
introduced into the nitrogen source line that fed
the heated zones of the oven. Low-residue solder
pastes were evaluated in atmospheres that had up
to 10, 100, 500, 800, 1000, and 1500 ppm of
oxygen. The results suggested that up to 500 ppm,
compared to less than 10 ppm of oxygen, neither
decreased the visible quality of the solder joint nor
increased the visible paste residue left on the
board after reflow.
In some instances, a level of 800 ppm of oxygen
did not cause severe problems with joint quality,
biit tended to cause more solder balls to form and
unprotected copper to oxidize. Therefore, the
maximum oxygen level that can be tolerated was
determined, not by the oxygen sensitivity of the
solder paste, but rather by the need to minimize
oxidation to preserve solderability for later
operations.
In early 1991, AT&T conducted a factory trial at
AT&T's Shreveport Works in Louisiana. Reflow
soldering was conducted in nitrogen with less than
100 ppm of oxygen. The soldering results were
good, with solder defects of less than 15 ppm. As
a result, in September, 1991, the process was
implemented at AT&T's Columbus Works in Ohio.
Since then, most AT&T surface-mount assembly
factories have purchased nitrogen-capable reflow
equipment.
As a parallel effort to evaluation of pastes, AT&T
evaluated nitrogen-capable reflow ovens for their
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55
No-Clean Flux and Wave
Soldering
Post-solder cleaning can be eliminated only if the
flux residues tHat remain on the board do not
affect performance, testability, or reliability. Flux
manufacturers have formulated low-solids fluxes to
completely eliminate cleaning operations.
However, accelerated aging tests of circuit boards
uncovered long-term corrosion problems. When
these aging tests were repeated with new boards
exposed to less low-solids flux (LSF), there were
no failures. Experiments showed that the surface
insulation resistance (SIR) decreased as the
amount of flux applied was increased, suggesting
that excessive flux residues may compromise the
circuit's integrity. Most of the SIR testing was
done at extreme performance conditions (i.e., 35°
C and 90 percent relative humidity). Pollutants in
the air, higher temperatures, and relative
humidities could exacerbate an electrical integrity
problem.
To date, over 60 formulations of LSF have been
received from 14 different vendors. The
dependence of SIR on flux quantity has been
demonstrated for most of the formulations that
passed the prescreening tests (i.e., pH, haltde, and
copper mirror).
The discovery of the inverse relationship between
flux quantity and SIR revealed the need to apply
the flux in a carefully controlled way, so that only
the amount required to ensure a good solder
connection was applied to the board. It is also
important to insure that the flux is applied
uniformly and the process can be consistently
repeated.
In addition, AT&T found that partially heated flux
residue which did not come into contact with the
solder wave caused more damage than the fully
heated residue that came into contact with the
wave. Thus, flux residue that remains on the top
side of a circuit board (i.e., the component side)
was potentially more detrimental to circuit-board
reliability than the residue on the bottom side (i.e.,
the circuit side). This means that application
methods that deposited excessive amounts of flux
on the top side of the board were not desirable.
Because of the >extremely low solids content of
these fluxes, traditional flux-monitoring techniques
are not accurate enough. Typical application
methods require monitoring because they use open
reservoirs which allow the main constituent of a
flux (i.e., alcohol) to evaporate and absorb water.
Accordingly, a closed flux reservoir and delivery
system are beneficial because they prevent
compositional changes and negate the. need for
monitoring.
Moreover, significant savings in time and expense
are realized with a closed system. For example,
when the cost to dispose of 5 gallons of spent flux
each day is included, the closed system of AT&Ts
patented spray fluxer (the LSF-2000), when
compared to an open system, can save 520,000 per
year in costs for monitoring, additional flux and
alcohol, and disposal.
Development of a Low-Solids
Spray Fluxer
Because of the characteristics of LSFs, the
following application properties are considered
preferable:
• Uniform, controlled flux application
• Minimal flux residue on the top side of a circuit
board
• Closed system (to avoid evaporation and water
absorption).
To address these needs, AT&T in 1988 developed
a low-solids spray fluxer. This spray fluxer used an
ultrasonic atomization system to deposit flux on
circuit boards. AT&T was granted patents that
cover both the methods and the apparatus.
The first generation spray fluxer helped to
successfully eliminate the need for post-solder
cleaning. But after extended field experience with
it, users demanded more efficient performance and
a wider range of features, including better
uniformity in flux disposition, wider spray
capability, and decreased maintenance.
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56
In 1990, the second generation low-solids spray
fluxer was developed. It uses a pressure-assisted,
airless spray system that is mounted on a traversing
mechanism. A spray nozzle passes back and forth
beneath the circuit boards on the conveyor and
releases four overlapping coats of flux material,
which results in a highly controlled and uniform
layer of flux. With specially designed board
sensors, exhaust system, and self-cleaning nozzle,
the system ensures high solder quality and efficient
use of flux material.
During the summer of 1990, a prototype of the
LSF-2000 was tested successfully at AT&Ts facility
in Mesquite, TX and at the Columbus Works. A
production model was installed in Columbus in
September 1990. The LSF-2000 system has now
been deployed in many AT&T factories and has
also been made available to industry in general.
Conclusions
The most promising alternatives for no-clean
soldering are modified processes, not simple
substitutions of material. Controlled atmosphere
reflow processes that use low-residue solder pastes
have been shown to produce minute amounts of
benign residue. With the improved solder pastes
now available, this process can provide the reflow
capability needed for total no-clean, surface mount
assembly.
AT&T has defined a production prams that can
be implemented with equipment that is
commercially available. Further optimization will
be done as AT&T gains experience with, the system
in its factories and as improved materials become
available.
Before fluxes are used in production, proper
evaluation is imperative. AT&T found that some
LSFs are better than others. For all LSFs, SIR
testing confirmed the theory that arose from
accelerated aging studies. That is, large quantities
of post-solder LSF residues can be detrimental to
the circuit. This work points out the need for the
appropriate qualification of materials and the use
of proper application equipment.
The equipment developed and used by AT&T
maintains the original flux composition and
controls the quantity of flux applied. This system
has been successfully deployed at AT&T
manufacturing locations. By using low-residue.
solder paste materials and processes and by using
low-solids fluxes with the appropriate process,
AT&T has eliminated the need for cleaning and is
making progress toward its environmental goals.
For Further Information
General
Dr. Leslie Guth
Supervisor
Environmental Materials and Processes
AT&T Bell Labs
Engineering Research Center
Room 2-2041
P.O. Box 900
Princeton, NJ 08540-0900
Tel: 609-639-3040
Fax: 609-639-2851
Solder Paste
Mr. John Morris
Member of Technical Staff
AT&T Bell Labs
Engineering Research Center
P.O. Box 900
Princeton, NJ 08540-0900
Tel: 609-639-2671
Low-Solids Flux
Mr. John Sohn
Member of Technical Staff
AT&T Bell Labs
Engineering Research Center
P.O. Box 900
Princeton, NJ 08540-0900
Tel: 609-639-2368
Fax: 609-639-2851
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57
CASE STUDY #4:
FLUX SELECTION
CRITERIA
When Northern Telecom, Ltd. decided to phase
out its use of CFC-113 and methyl chloroform
ahead of the mandated phaseout schedule,
engineers made the decision to replace
conventional soldering operations with no-clean
processes, in order to implement the no-clean
wave soldering process, it was necessary to
extensively test candidate fluxes to determine their
applicability to no-clean applications.
Initially, there was no significant doubt that no-
clean fluxes could solder, but the long-term
resultant quality was questioned within Northern
Telecom as well as by influential customers. The
initial task in convening to a no-clean soldering
process was a three-step program to evaluate
candidate fluxes. The three steps were:
• Evaluate the long-term reliability of components
after they have been exposed to the flux
• Determine whether flux residues were active or
inactive
• Evaluate the processed PCB for reliability after
extended environmental stressing.
It was decided that a flux and all components must
pass all of these tests before any of the materials
could be run in production. Production was the
fourth step in the process change-over.
Virtually all tests were based on stressing the
product by three to five times the severity
commonly seen in a production cell. This was
done to provide a high confidence level even if
irregularities in the process took place.
Test #1 •> Component
Reliability
The first test in choosing a flux for use in the no-
clean wave soldering process was designed to
evaluate the long-term reliability of components
after they had been exposed to the flux. A single
comprehensive screening test was designed and
implemented to facilitate this evaluation. By
immersing a component in flux and subsequently
aging the part in an environmental chamber under
conditions of 85°C and 85 percent relative
humidity for 10 days, five potential problems could
be discovered:
Breakdown of seals
Deterioration of plastics
Deterioration of markings
Corrosion
Changes in performance.
In order to ensure that a wide variety of
components was tested while not performing
excessive testing, several hundred discrete
components were categorized into 13 general
component families. Testing was reduced by using
a few parts from a given family and designating
them as being representative of the group.
Parts, as received in a normal fashion, were
electrically tested to the facility's incoming
inspection standard for the part, visually inspected,
and weighed. The pan was then immersed for IS
minutes in a room temperature beaker of the no-
clean flux. At the end of the IS minutes, the pan
was removed, air-dried, re-weighed, re-tested, and
visually re-inspected. The pan was then place in
the environmental chamber for 10 days, at which
time all of the tests were repeated. The significant
failure noted during this test was copper corrosion,
with few failures in the other four potential
problem categories.
Test #2 - Flux Residue
Activity
The second test used by Northern Telecom in the
evaluation of no-clean fluxes was designed to
determine if a flux candidate contained active
residues. The presence of these active residues
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58
might adversely affect the performance of a
product several years after delivery of the products
to a customer.
The standard IPC-B-25 comb pattern test panel
was the primary tool used in this test, although for
a part of the test a plain copper pattern was used.
In the second pan of the test, a striped solder
mask pattern was imposed on the combs. A bias
voltage was used in both tests. This modification
tested any interaction between flux, mask, and
substrate as well as the potential of the flux to
cause circuit changes after years of use. The
surface insulation resistance and electromigration
tests were used to determine reliability with one
significant change from the standard procedures
used for these tests. The key difference in the
Northern Telecom test was that the comb pattern
was fluxed, air dried, and tested in a comb-up
position. Approximately 90 percent of all flux
candidates failed this test, even though many had
passed similar tests as presented in the Bellcore
TSY-000078 specification.
For Further Information
Mr. Richard Szymanowski
Manufacturing Engineer
Northern Telecom Incorporated
P.O. Box 13010
4001 East Chapel Hill-Nelson Highway
Research Triangle Park, NC 27709
Tel: 919-992-5000
Fax: 919-992-3998
Test #3 - PCB Reliability
The third test used by Northern Telecom in
evaluating candidate no-clean fluxes was designed
to determine the long-term reliability of the
assembled no-clean PCB under extreme
environmental conditions. This test involved
taking a printed circuit assembly which had been
processed in a no-clean manner and stressing that
unit for an extended length of time in an
environmental chamber.
Chamber parameters were 3S°C and 90 percent
relative humidity, and the test was extended to
approximately 1,000 hours. The logic in this test
plan was that discrete components were carefully
screened for use in the process, as were the flux,
board substrate, and solder mask. The interactions
of the common denominator had been tested, and
any product, having passed this environmental
stress test, could be used with predictable long-
term performance.
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59
CASE STUDY #5:
SPRAY FLUXING FOR
TODATS SOLDERING
PROCESSES
Spray fluxing technology is currently receiving a
considerable amount of attention by some
progressive electronic manufacturers. Using a
spray application method to coat the bottom of a
printed circuit board with flux is not a new process
for printed circuit assembly operations. What is
new are the vast improvements in spray fluxing
equipment that can improve quality, increase
efficiency, and lower manufacturing costs for
companies using low solids "no clean" fluxes in
their soldering processes.
These improvements have been substantiated
through practical application at the UDS
subsidiary of Motorola located in Huntsville, AL.
This case study describes the need, acceptance
criteria and benefits realized by implementing a
spray fluxing system in an operational printed
circuit assembly soldering process. If companies
are to successfully pursue defect reduction
programs, Just-In-Time manufacturing, and CFC
elimination, k is essential that they continuously
improve -the soldering process. One of the more
critical elements in a wave soldering process is the
flux formulation that L> used, especially for
operations using low solids fluxes. The impact of
a flux formulation on the solder defect rate for
printed circuit assemblies can be significant
Some of the soldering fluxes available on today's
market considerably reduce solder defects, but can
emit offensive vapors into the work environment.
Keeping the assembly line operators' well-being in
mind makes it more difficult to select defect-
reducing fluxes. For this reason, an enclosed spray
fluxing system is very advantageous. If the proper
system is implemented, the vapors will be
restricted to and contained within the area of the
actual fluxing operation. This allows the use of
any low solids flux without fear of operator
irritation.
Advanced technology spray fluxing systems not
only improve the quality of the soldering process,
but can also eliminate the need for some process
control requirements. The traditional fluxing
systems such as foam, wave, and conventional spray
fluxers require titration and/or specific gravity
measurements to properly control the chemical
balance of the flux. When using these types of
fluxing systems, it is necessary to regularly
compensate for evaporation of the flux solvent by
manual and/or automatic methods.
Recent advancements in spray fluxing equipment
by some equipment manufacturers, however, have
eliminated the need for these process controls.
The liquid flux is totally enclosed in a pressurized
vessel, eliminating concerns about solvent
evaporation and water absorption from the
atmosphere. Titration, specific gravity, and solvent
compensation are no longer important aspects of
the wave soldering operation.
Substantial material savings will be realized with
the implementation of this new equipment
technology. In the case of the UDS subsidiary of
Motorola, a 68 percent reduction in flux and 100
percent elimination of solvent usage were noted.
These savings were accomplished by the
intermittent operation of the spray fluxer. The
flux spray is activated only when a printed circuit
board enters the area of the fluxing operation. In
most conventional operations, the flux is pumped
in a continuous flow, creating enormous waste.
There are several spray fluxing units currently on
the market UDS/Motorola analyzed four different
units Cram four different equipment manufacturers
for a single soldering operation at UDS. The
equipment was evaluated according to seven
general categories:
1. Uniformity and consistency of flux deposition
2. Ventilation and safety
3. Maintenance
4. Ease of operation
5. Equipment reliability
6. Equipment compatibility with a high product
mix and low volume operation
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60
7. Enclosed flux reservoir.
As a result of these considerations, the field of
possible candidates narrowed quickly to two
equipment manufacturers, because of
noncompliance gf the other systems with the above
criteria. Further evaluation and testing of the
remaining two spray fluxing units was then
performed using the same criteria.
After careful evaluation of the results, it was
obvious that the low-solids- spray fluxer
manufactured by AT&T (LSF-2000) was the best
choice for the type of soldering operation that was
required. The matrix shows a comparison between
the AT&T unit and the competitive unit, which is
labeled unit "B."
This information .was collected by observing both
units in operation. The consistency of flux
. deposition was measured by processing test printed
circuit board samples through each separate fluxing
unit. The test samples were weighed before the
application of flux, processed through each fluxing
unit, allowed to dry, and then weighed again to
determine the amount and consistency of flux
applied to each sample.
This test concluded that process variation with the
AT&T unit could be expected to vary with +. 10
percent and unit "B" was within the range of +, SO
percent. With fine tuned adjustments, however,
the AT&T unit during actual production showed
variation of only +. 5 percent.
The AT&T unit's dual ventilation system, with
amplifiers to exhaust the vapors of the flux spray
quickly and restrict the fumes to the immediate
processing area, satisfies the UDS ventilation and
safety concerns. The unit includes a flame detector
system that senses a fire up to 35 feet away. If a
flame is detected, the entire system shuts down
instantly and automatically.
With the proper equipment options, the unit self-
adjusts the width of the flux spray for the width
sizes of various printed circuit boards. This
eliminates the need for special set-up
considerations for the unit during multiple product
line changeovers. None of the other low-solids
spray fluxers analyzed and evaluated offered all of
these special operating features.
Recent improvements in low solids spray fluxing
technology offer a viable means for electronics
assemblers to enhance soldering processes, improve
quality levels, and lower manufacturing costs.
With the enclosed reservoir and improved
ventilation systems, a wider selection of defect-
reducing fluxes are available for use. Reductions
in total chemical usage of as much as 85 percent
can be realized by implementing spray fluxing
technology. Spray fluxing technology for low-solids
no-clean applications works extremely well in any
wave soldering environment.
For Further Information
Mr. Rick Wade
Advanced Manufacturing Technology
Manufacturing Engineer
Motorola/UDS
5000 Bradford Drive
Huntsvttle, AL 35805
Tel: 205-430-8952
Fax: 205-430-8975
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CASE STUDY #6:
CHOICE OF A NO-CLEAN
PROCESS AT NCR
Previous Process
NCR, Workstation Products Division (WPD)
Clemson designs and assembles medium to high-
end computer workstations. In 1987 the Clemson
plant installed an SMT circuit board assembly line
to enhance the plant's high volume production
capability. The process flow of this initial SMT
line is: STENCIL PRINT -SMTPLACEMENT-
REFLOW - HAND ASSEMBLY - WAVE
SOLDER - INLINE CLEAN - POST SOLDER
INSPECTION - TEST. Up to the present
phaseout of CFCs, Clemson SMT Operations used
rosin chemistry solder paste, convection reflow, SA
flux wave solder and in-line CFC-113 clean.
Alternatives Considered
In February 1991, WPD Clemson received
corporate approval to install a second SMT
production line to meet the increased production
demands that resulted from new products and
increased orders. An equipment selection team,
made up of manufacturing engineers, was formed
to evaluate state-of-the-art SMT soldering
technology and to determine the layout and
strategy of the new line.
In May 1990, NCR formed a corporate-wide Ozone
Depleting Substances (ODS) phaseout team to
establish the NCR corporate schedule for ODS
elimination. At its first meeting, the ODS team
set the end of 1992 as the deadline for all NCR
plants to eliminate CFCs in circuit board cleaning
operations for bareboard and board assembly
operations.
In light of the corporate CFC phaseout deadline,
the equipment selection team was forced to face
the CFC issue head-on and select equipment and
process strategies accordingly. Whatever decision
was made for the new SMT line would also be
implemented on the existing line.
The options considered were:
1. Convert from CFC-113 to an HCFC solvent
2. Convert from CFC-113 cleaning to aqueous-
saponifier cleaning and continue with rosin flux
chemistry
3. Convert from CFC-113 cleaning to water-only
cleaning and use OA flux chemistry
4. Convert from CFC-113 cleaning to semi-
aqueous-aqueous cleaning, i.e., terpene, and
continue with rosin chemistry
5. Eliminate the need for cleaning by converting to
a no-clean process.
The following actions were undertaken after
preliminary evaluation of each of these options.
Option #1. Immediately dropped because of the
price of HCFC solvents, incompatibility with
existing in-line cleaning machine, and fear of a
future ozone-related ban.
Option #2. Initially seen as attractive because it
would allow NCR to continue using rosin solder
pastes and wave solder flux and avoid the pains of
weaning from rosin chemistry. Also, aqueous
cleaning with saponifier is an old and proven
process in through-hole assembly. NCR decided
against this option for several reasons:
• The uncertainty of ability to dean under the
tight spacings found in SMT
• The requirement of major facilities work to
install floor drains and water treatment system
• Saponifier concentration/foaming issues and
odors.
• Uncertainty as to future EPA legislation on
water and water emissions.
Option #3. Considered very seriously because of
the relative simplicity of the cleaning process.
Several site visits were made to evaluate various
equipment. Also, OA flux would enhance
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62
solderabiliry and lower solder DPM. However, this
option was dropped because:
• • NCR did not want the reliability risk of OA flux
being left on boards
4»
• Major work on facilities would be required to
install floor drains and water treatment system
* Uncertainty as to future EPA legislation on
water and water emissions.
• Unavailability then of a water soluble solder
paste that met NCR processing requirements
for printability and reflow.
Option #4, Much has been written about semi-
aqueous terpene cleaning and the ability of the
terpene process to exceed the cleanliness of CFC-
113 cleaning. This option was attractive.
However, NCR looked at terpene equipment at
several trade shows and decided that the
equipment was too expensive and complex. NCR
also did not want to have to pacify angry operators
who might be irritated by orange/citrus-odors.
Option #5. In light of the dissatisfaction with
options 1-4, NCR decided that the best long-term
strategy was to eliminate the need for cleaning
altogether. There are definite challenges to
implementing a no-clean process, but it poses the
least threat to the environment and involves the
lowest volume of chemicals and effluents.
• Wave Solder »
-• Touchup and Repair
Stencil Print
With regard to stencil printing, the primary
decision is what paste to use -- no-clean/low solids
paste or continued use of the RMA paste. The
concern here was that the stencil printing process
had been set up using RMA paste. Initial testing
of no-clean and low solids solder pastes was
discouraging because the pastes lacked the same
printability and tackiness characteristics as the
RMA paste. The team did not want to sacrifice its
low printing DPM level nor the reliability of an
RMA paste. One engineer on the equipment team
was assigned to focus on solder pastes at the
NEPCON show.
Reflow
NCR had been successfully reflowing RMA solder
paste with an SPT convection reflow oven. To
implement no-clean soldering, the team was not
sure if it would have to purchase controlled
atmosphere reflow equipment. One engineer on
the team focused on reflow equipment at the show.
Wave Solder
Evaluation of the No-Clean
Option
In February 1991, the NCR Clemson equipment
selection team attended the NEPCON West trade
show to evaluate SMT equipment for the second
line. At the time, both the no-clean and water-
only cleaning options were very serious contenders.
Prior to the NEPCON show, the team held many
discussions as to the particular no-clean strategy
which should adopted, should no-clean be the final
choice. In these discussions, the team realized that
there were three .hurdles to overcome in attaining
no-clean status:
• Stencil Print/Reflow
Up to this point, NCR had been using an
Electrovert Century 2000 wave solder machine with
a foam fluxer, using an SA flux. The team realized
that there were several paths to achieving no-clean
wave soldering. One was to simply put a 2-5
percent solids no-clean flux in the fluxer and foam
it onto the board. This requires modifying the
wave soldering parameters (no-clean fluxes
generally require a higher topside board preheat
temperature). Also, the no-clean flux requires acid
titration rather than specific gravity to maintain
the proper flux-to-solids percentage.
Another path was to use the same wave solder
equipment but add on a more controlled method
of applying the no-clean flux - namely a spray
fluxer. This is accomplished by either upgrading
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63
the fluxer in the machine itself or by purchasing a
stand-alone spray fluxer module.
The third path was the controlled atmosphere
option. This is accomplished by either retrofitting
an existing wave, solder machine with a hood (long
hood enclosing preheat and solder pot; short hood
enclosing the solder pot only) or purchasing a new
nitrogen wave solder machine. One engineer on
the equipment selection team focused on wave
soldering equipment selection.
Touch-Up and Repair
Touch-up and repair initially did not come up in
the team's discussions, but no-clean hand soldering
and repair may pose the greatest challenge. The
other processes involve equipment which can be
controlled to accomplish no-clean soldering. Hand
soldering involves people; specifically, people
trained to solder with RMA flux. This is raised as
an issue because RMA flux, unlike no-clean fluxes,
is actually very forgiving and allows for deviation
in the hand soldering process with regard to tip
temperature and tip contact time. Operators with
marginal soldering skills usually can mask their
deficiencies with RMA flux.
The team had already obtained no-clean flux
samples, and as an experiment gave various
samples to hand sotderers in place of RMA flux at
the bench. The results were obvious. The no-
clean fluxes are primarily alcohol and evaporate
almost immediately upon solder tip contact Tip
temperature has to be controlled, time on the
connection has to be minimal, and initial
component solderability is critical. Instead of a 5
second wetting window as with RMA flux, the
operator using no-clean flux now has only a 1-2
second window. In addition, the no-dean samples
tested left some residue after hand soldering.
When operators are accustomed to a CFC-113
cleaning culture where any residue can and should
be washed off, the appearance of residue is difficult
to accept. Thus, an entire change in attitude
towards residues is necessary. The NCR team used
the NEPCON show to meet with flux vendors and
attend technical sessions in the hope of learning
from the experience of others in this area.
The Selection Process
The 1991 NEPCON West show proved an
excellent catalyst for a decision by the equipment
selection team. The team was so favorably
impressed with no-dean technology (particularly
controlled atmosphere technology) that the water
dean option was dropped and the focus was shifted
totally on no-clean soldering.
The NCR team's selection of a specific no-clean
process and its evaluation of each of the available
technologies is discussed in detail below.
Stencil Print/Reflow
The team dedded to pursue controlled atmosphere
reflow and was impressed with most vendors at the
show. The engineer focusing on reflow prepared
a comparison matrix and, based on cost and design
of equipment, narrowed the selection down to five
key vendors. Evaluation trips were then taken and,
based on reflow performance and cost, the decision
was made to purchase a Watkins Johnson
controlled atmosphere convection oven. Though
NCR has achieved satisfactory reflow results in its
conventional reflow oven, the incited oven gives
cosmetically smoother and shinier joints with
better classical wetting traits - using the same
RMA paste. Based on information gathered at
NEPCON technical sessions and experience
gathered during vendor evaluations, the team
dedded that the controlled atmosphere during
reflow would at least enhance the process,
especially the reflow of no-clean pastes. The
controlled atmosphere reflow oven has been in
operation on the second SMT line since January
1992. NCR continues to run RMA solder paste in
production but has been seriously testing no-clean
pastes, and with good results. While the team
completes its no-dean paste testing, NCR
continues to use an in-line CFC-113 cleaner even
though earlier tests by various NCR plants have
shown that RMA paste residues can be safely left
on. WPD changed to a no-dean solder paste in
Summer 1992.
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64
Wave Solder
The team left the NEPCON West show having
tentatively decided on controlled atmosphere wave
soldering, though not clear on whether to pursue
a machine with-a "retrofit" hood or a new-design
nitrogen machine. Prior to NEPCON, the team
had already conducted tests with no-clean fluxes in
the Century 2000 machine, utilizing a foam fluxer.
The results were discouraging, for several reasons:
• Amount of flux applied with a foam fluxer could
not be controlled
* Residues could not be totally eliminated.
Though benign, they interfered with incircuit
bed-of-nails testing and resulted in many
Quality Assurance battles
• Flux balance could not be adequately controlled
with specific gravity or titration methods
• Wave soldering yields were inconsistent due to
battles with solder balls, shorts, and webbing.
The team had not yet totally discounted this
option, though with the above results in mind, it
decided to aggressively evaluate controlled
atmosphere equipment. At the time of the 1991
NEPCON West show, there were three primary
suppliers of controlled atmosphere wave solder
equipment --SEHO (a German-based company
was first to market), Soltec (based in Holland), and
Electrovert. Electrovert had already introduced
and implemented a "retrofit" hood for its
Econopak line, had a proposed design for a hood
for the Ultrapak line, and was showing the
prototype new-design ATMOS machine. The team
was impressed with all three for various reasons.
Team members were further encouraged to pursue
controlled atmosphere wave soldering because the
sister NCR WPD plant in Augsburg, West
Germany had been using a SEHO machine for
over a year with very good results. Two members
of the equipment selection team traveled to
Oosterhout, Holland (Soltec), NCR Germany,
Kreuzwertheim, Germany (SEHO) and Montreal,
Canada (Electrovert) to test solder boards on each
system.
The results of the trip were encouraging for
controlled atmosphere wave soldering on the
whole. Each vendor's machine performed equally
well with regard to soldering and no-clean results
on the NCR production boards used for the
testing. With the controlled atmosphere
technology, a 1 percent adipic acid "preparation
fluid" is often used in lieu of a traditional flux.
Since it was recommended by each manufacturer
during the testing, it was used for each test. It
should be noted that at the Electrovert facility
both the new ATMOS controlled atmosphere
machine and an existing model Electrovert
machine retrofitted with a full-length hood were
evaluated.
The SEHO and Soltec machines are designed as
nitrogen machines (not retrofits). The Electrovert
and SEHO machines are "open tunnel" designs in
that each end of the tunnel is open and metal
doors or curtains are placed throughout the tunnel
to baffle air flow. The Soltec machine is the only
"closed tunnel" design, utilizing vacuum lock
chambers at the entrance and exit of the tunnel to
completely seal the tunnel. The SEHO and
Electrovert machines use an ultrasonic spray fluxer.
The Soltec machine uses a drum spray fluxer.
Electroven also offers a drum spray fluxer. Since
all three machines soldered the test boards equally,
other criteria were used to make a final selection.
The criteria used were:
Soldering performance
Absence or presence of visible residues
Nitrogen consumption
Maximum conveyor width
Production rate
Local US. support
Soldering Performance
Each machine soldered equally well, and solder
wetting under nitrogen was better than could be
achieved in air. Two negatives, however, were
encountered with each system. Each machine
produced solder shorts only on specific through-
hole connectors. This was determined to be due to
a change in the surface tension of solder under
nitrogen. The shorts occurred consistently,
regardless of machine or soldering parameters
(including flux). As demonstrated at NCR
Germany with over a year's experience with
nitrogen wave soldering, eliminating the shorts
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65
requires redesign of the particular problem areas
to change tbe spacing of the leads and/or the
length of the leads. The other problem
encountered consistently was solder balls clinging
to the bottom side solder resist The balls in all
cases could be easily brushed off. This seems to be
an effect of the nitrogen atmosphere and tbe no-
dean flux.
Visible Residues
wanted to be able to run existing pallets .in
whatever machine was purchased. At the time of
evaluation, the Soltec machine could not handle
the 18 inch width. New pallets for bigger boards
would need to be purchased, clip stiffeners would
be needed, or boards would have to be run without
pallets. The SEHO machine available at the time
required tbe use of special SEHO pallets which
greatly added to the cost of the system. The
Etectrovert machines utilized traditional finger
type conveyors at widths up to 20 inches.
The team was very impressed that with each
system, boards were clean and dry upon exiting the
machine. Each vendor's fluxer performed
adequately in depositing consistent and controlled
amounts of flux. The team could create visible
residues with the 1 percent adipic acid solutions by
applying heavy amounts, but excellent soldering
occurred using only a tight mist. One benefit of
the controlled atmosphere is that small amounts of
very low-solids fluxes can be used.
Nitrogen Consumption
Each machine was evaluated as to the nitrogen
flow rate in cubic feet per hour (cfh) required to
maintain 10 ppm oxygen over the solder pot. The
Soltec and SEHO machines consumed the least
nitrogen -- about 700 cfh. The Soltec accomplishes
this by completely sealing off the tunnel with the
vacuum locks. The SEHO minimizes nitrogen
consumption by effective use of flap doors through
the tunnel. The Electrovert ATMOS machine
consumed around 1400 cfh of nitrogen. This is
primarily because it has a larger 20" width tunnel
and minimally baffles air flow with rubber curtains.
The Electrovert retrofit hood consumed the most
nitrogen - 2,000 cfh or higher, mainly because of
its design. The "nitrogen" machines are designed
to hold the nitrogen blanket by "humpbacking* the
tunnel in the solder pot section. The retrofit
hoods are straight with the high point being the
exit end. There is little to hold the nitrogen in.
Maximum Conveyor Width
NCR produces boards ranging in widths from 4.8
inches to IS inches. The larger boards are run in
18-inch wide picture frame pallets. Team members
Production Rate
Production rate requirements vary in real life
production. The Clemson wave solder machines
are fed by a hand assembly conveyor, with the rate
depending on the size of the board and the
number of through-hole components that have to
be hand placed. Quite a few smaller plug-in
boards with very few through-hole parts are also
run. Hand assembly feeds them as fast as the wave
solder machine will accept them. The team did
not want to have to limit speed if at all possible.
Tbe Soltec machine could only take a board every
20-30 seconds because of tbe processing time of
the vacuum locks. The SEHO machine was
limited because of the timing of the pallets
through the flap doors. The Electrovert machines
had no limitation because there are no chambers
or flap doors.
Local U.S. Support
The team wanted evidence from each vendor that
it could adequately support this equipment in the
U.S. (NCR Clemson does not stock large
inventories of spares and relies on overnight
shipments and quick response Meld service). At
the time of initial evaluation, Soltec and SEHO
had very limited resources in the U.S. Electrovert
maintains two facilities in the U.S. and a factory in
Canada.
Tbe initial recommendation after the evaluation
trip was to purchase an Electrovert Ultrapak
machine with a full-length nitrogen hood.
Electrovert had not yet produced an Ultrapak with
a hood, but it was a proven machine in the field
and would handle Clemson width and production
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66
requirements. This recommendation was based on
successful results with an Econopak with a hood at
the Eiectrovert factory (the Econopak would not
handle the NCR width requirement). The overall
cost of an Ultrapak with a hood and all of the
necessary optiens was around US$150,000.
Because of the relatively low system cost, and with
the cost of nitrogen at about $0.20 per 100 cubic
feet, the Ultrapak option was very attractive
despite the anticipated nitrogen consumption rate
of 2,000 cfh. However, after further discussion and
cost analysts, it was decided that the 2,000 cfh
consumption rate was too high and the Ultrapack
style machine did not fit the streamlined, state-of-
the-art image the team wished to portray with its
new line. Next in line was the new Eiectrovert
ATMOS. Though it was a new model, the team
felt comfortable in its rugged design, the use of
existing solder pot and software control packages,
and the conveyor width of 20 inches. An ATMOS
with all the options is twice the cost of the
Ultrapak system - around USS300,000. This was
still cheaper than a Soltec or SEHO with
equivalent options and its nitrogen consumption
rate of 1,500 cfh was considered reasonable. Also,
the low-profile streamlined design of the ATMOS
was very well received by NCR managers attending
the 1992 Nepcon West show. Based on the above
discussion, the team chose the Electroven ATMOS
controlled atmosphere wave solder machine. NCR
Clemson has purchased one machine for its new
SMT line and one to replace its old Century 2000
on the existing SMT line. Both systems have been
in full production use since January 1992.
Hand Soldering/Repair
This area poses the most challenge in NCR-
Clemson's operation. From Nepcon technical
sessions and conversations with other NCR plants
and other companies, it was learned that no-clean
hand soldering techniques are available and do
work. What the team currently faces is final
material selection and the learning curve. SMT
manufacturing associates are all required to go
through an initial in-house 40-hour solder training
program and receive yearly certification after that.
Current activity is to modify the training
curriculum to reflect the use of no-clean flux and
core solder and to teach stricter techniques -
namely the need for lower tip temperatures and
very strict adherence to a 2 second soldering
window. Part of the challenge is that it is often
very frustrating for the hand soldering operator
when he or she cannot make picture perfect solder
joints within 2 seconds using no-clean flux.
Another pan of the challenge is accepting, both
internally and externally, visible residues from the
no-clean flux. SIR and analytical chemical testing
are being done at NCR's Manufacturing
Technology Research Center to support safely
leaving the residues on the board.
Conclusions
NCR eliminated CFC usage in the U.S. for PCB
assembly in early 1993. To date, Clemson has fully
achieved no-clean status in the wave solder process
by implementing controlled atmosphere no-clean
technology. Problems encountered as a result of
implementing this technology are solder shorts and
solder balls. Board design is being changed where
appropriate and when possible to eliminate the
shorting issue. Engineers are also working with
Electroven on some developments to the
equipment, as well as with bareboard vendors on
changes to the solder mask to try to eliminate the
solder balls. On the positive side, NCR Clemson
has realized the following benefits:
1. Greatly enhanced solder wetting
2. 75 percent reduction in solder dross
3. 50 percent reduction in flux consumption
4. Reduced chemical inventory
5. Savings of S2300/barrel of CFC-113 solvent.
For Further information
Mr. Michael Cooper
Process Engineer
NCR Corporation
E&M Clemson
7240 Moorefield Hwy.
Liberty, SC 29657
Tel: 803-843-1892
Fax: 803-843-1841
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REFERENCES
Altpeter, James*E. 1990 (November). Inert Gas Wave Soldering Evaluation. Presented at the International
Conference on CFC and Halon Alternatives, Baltimore, Maryland.
Andrews, GJ. 1990 (March). Evaluation of the Corrosion and Reliability Aspects of Printed Circuit Boards
Flow Soldered Using 'No Clean' Fluxes. Circuit World: 11-12.
AT&T. Corporate Literature.
Bandyopadhyay, N. and J. Morris. 1990 (February). No-Clean Solder Paste Reflow Processes. Printed Circuit
Assembly: 26-31.
BCM Engineers. 1990 (October). Emissions Characterization of Wave Soldering Machine. Prepared for Ford
Electronics and Refrigeration Corporation, Dearborn, Michigan.
Brammer, Dieter. 1991 (June). No-Clean Processes Yield Top-Quality SMAs. Circuits Assembly. 37-45.
Chamberland, R. Evaluation of Controlled Atmosphere Reflow Soldering of No-Clean Solder Pastes. Union
Carbide Industrial Gases Inc. Tarrytown, NY.
Electrovert Corporation. Corporate Literature.
Elliott, D.A. and LJ. Turbini. Characterizing Residues From Controlled Atmosphere Wavesoldering.
Electrovert Corporation and Georgia Institute of Technology.
Guth, Leslie A. and John R. Morris. 1992 (March/April). No-Clean Soldering Processes. AT&T Technical
Journal: 37-44.
Hwang, Jennie S. 1990 (July). Controlled-Atmosphere Soldering: Principle and Practice. Printed Circuit
Assembly: 30-38.
Institute for Interconnecting and Packaging Electronic Circuits (IPC). 1992 (March). Cleaning and
Cleanliness Testing Program: Phase 3 - Controlled Atmosphere Soldering.
Kester Solder. Corporate Literature.
Kocka, D.C. 1990 (June). No-Clean Fluxes Are a Viable Alternative to CFC Cleaning. Electronic Packaging
and Production: 95-97.
Liyanage, N. 1990 (April). The Reality of No-Clean Fluxes. Circuits Manufacturing: 58-64.
Manko, Howard H. 1990. Advantages and Pitfalls of "No-Clean" Flux Systems. Presented at NEPCON West,
Anaheim, CA.
Mead, MJ. and M.S. Nowotarski. 1988 (January). The Effects of Nitrogen for IR Reflow Soldering. Union
Carbide Industrial Gases Inc. Linde Division, Tarrytown, NY.
Phillips, Barbee B. 1989. Process Considerations When Using "No-Clean" Flux. Presented at NEPCON East.
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Rubin, W. and M. Warwick- 1990 (May). Low Solids Fluxes for No-CleanrSoldering. Electronic Production:
25-29.
Schouten, G. 1991. Benefits of Inert Gas Soldering in Reducing Soldering Defects. Presented at NEPCON
West, Anaheim, CA.
Schouten, G. 1989 (September). No Fluxing, No Cleaning: Inert-Gas Wave Soldering. Circuits
Manufacturing-. 50-53.
Taylor, Simon. 1991 (October). Complex Synthetic Fluxes Offer Enhanced No-Clean Performance. Soldering
Technology: 27-29.
Toubin, A. 1989. Low Solids Content Fluxes. Circuit World: Vol. IS, No. 2.
Trovato, R. 1991 (April). Inciting the Soldering. Circuits Assembly: 48-52.
Trovato, R. 1990 (April). Soldering Without Cleaning. Circuits Manufacturing: 66-67.
United Nations Environment Programme (UNEP). 1991 (December). 1991 Solvents, Coatings, and Adhesives
Technical Options Report.
Wade, Richard L. 1989 (March). A View of Low-Solids Fluxes. Printed Circuit Assembly. 31-34.
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LIST OF VENDORS FOR NO-CLEAN PROCESS EQUIPMENT AND MATERIALS
TO REPLACE CFC-113 AND METHYL CHLOROFORM
Controlled Atmosphere Soldering
Equipment
Dover Soltec
7 Perimeter Road
Manchester, NH 03103
Tel: (603)647-6005
Fax: (603)647-6501
Electrovert Limited (International Sales)
1305 Industrial Blvd.
LaPrairie, Quebec J5R2E4
Canada
Tel: (514)659-8901
Fax: (514)659-2759
SMT-Automation, Inc.
325-L Hill Caner Parkway
Ashland, VA 23005
Tel: (804)798-6000
Fax: (804) 798-5933
No-Clean Fluxes and Pastes
AIM Products Inc.
9-T Rocky Hill Road
Smithfield, RI 02917
Tel: (401)232-2772
Fax: (401)232-2802
Cramco
80 Sinnott Rd.
Scarborough, Ontario MIL 4M7
Canada
Tel: (416)757-3667-
Fax: (416) 757-5530
Indium Corporation of America
1676 Lincoln Avenue
Utica, NY 13502
Tel: (315)768-6400
Fax: (315) 768-6362
Electrovert USA Corp. (North American Sales)
805 W.N. Carrier Pkwy.
Suite 200
Grand Prairie, TX 75050
Tel: (214)606-1900
Fax: (214)606-1700
Hollis Automation, Inc.
15-T Charron Avenue
Nashua, NH 03063
Tel: (603)889-1121
Fax: (603)880-0939
Alpha Metals
600 Route 440
Jersey City, NJ 07304
Tel: (201)434-0098
Fax: (201)434-2529
Hi-Grade Alloy Corp.
17425-T S. Laflin Avenue
P.O. Box 155
East Hazel Crest, IL 60429
Tel: (708)798-8300
Fax: (708)798-8924
Kester Solder
515 East Touhy Ave.
Des Plaines, IL 60018-2675
Tel: (708)297-1600
Fax: (708)390-9338
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London Chemical Co., Inc.
240 Foster Avenue
Bensenville, IL 60106
Tel: (312)766-5902
Fax: (312)860-1218
*
Senju Pastes
Christopher Associates
2601 S. Oak Street
Santa Ana, CA 92707
Tel: (714)979-7500
Multicore Soldeis, Inc.
1751 Jay EU Dr.
Richardson, TX 75081
Tel: (214)238-1224
Fax: (214)644-9309
Spray Fluxing Equipment
AT&T
P.O. Box 900
569 Carter Road
Princeton, NJ 08542-0900
Tel: (609)639-2232
Fax: (609)639-2818
Electrovert Limited (International Sales)
1305 Industrial Blvd.
LaPrairie, Quebec J5R 2E4
Canada
Tel: (514)659-8901
Fax: (514)659-2759
Process Control Technologies, Inc.
9100 West Piainfield Road #12
Brookfield, IL 60513-2422
Tel: (708)387-0906
Fax: (708)387-0937
Sonatech, Inc.
702 Botello Road
Goleta, CA 93017
Teh (805)967-0437
Electrovert USA Corp. (North American Sales)
805 W.N. Carrier Pkwy.
Suite 200
Grand Prairie, TX 75050
Tel: (214)606-1900
Fax: (214) 606-1700
Precision Dispensing Equipment, Inc (microjets)
P.O. Box 40370
Bay Village, OH 44140-0370
Tel: (216)899-9911
SEHO
SMT-Automation, Inc.
325-L Hill Carter Parkway
Ashland, VA 23005
Tel: (804)798-6000
Fax: <804) 798-5933
Wenesco, Inc.
6423-T N. Ravenswood Avenue
Chicago, IL 60626
Tel: (312) 973-4430 ext 65
Fax: (312)973-5104
Industrial Grade Nitrogen
AGA Gas, Inc.
6225 Oaktree Boulevard
Cleveland, Ohio 44131
Tel: (216) 642-6600
Fax: (216)642-6746
Air Products & Chemicals, Inc.
7201 Hamilton Blvd.
Allentown, PA 18195
Tel: (215)481-4911
Fax: (215)481-5900
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Airco Gases MG Industries r
575 Mountain Avenue 2460A Boulevard of the Generals
Murray Hill, NJ 07974 P.O. Box 945
Tel: (201)464-8100 Valley Forge, PA 19482
Fax: (201)464-3379 Tel: (215)630-5400
Fax: (215)630-5600
Liquid Air Corp. Union Carbide Industrial Gases Inc.
2121-T N. California Blvd. Linde Division
Walnut Creek, CA 945% 39 Old Ridgebury Rd.
Tel: (415) 977-6500 Danbury, CT 06817-0001
Fax: (415) 977-6840 Tel: (800) 521-1737
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GLOSSARY
CFC - An abbreviation for chlorofluorocarbon.
CFC-113 - A common name for the most popular CFC solvent — l,l,2-trichloro-l,2,2-trifluoroethane - with
an ODP of approximately 0.8.
Chlorofluorocarbon - An organic chemical composed of chlorine, fluorine and carbon atoms, usually
characterized by high stability contributing to a high ODP.
Conformal coating - A protective material applied in a thin, uniform layer to all surfaces of a printed wiring
assembly including components.
Controlled atmosphere soldering - A soldering process done in a relatively oxygen-free atmosphere. The
process greatly reduces oxidation of the solder, contributing to better solder joint metallurgy and less dross
formation.
Deflindng - The removal of flux residues after a soldering operation. Defluxing is a pan of most high-
reliability electronics production.
Flux - An essential chemical employed in the soldering process to facilitate the production of a solder joint.
It is usually a liquid material, frequently based on rosin (colophony).
Formic acid - A substance which is sometimes used in conjunction with no-clean wave soldering to reduce
the level of oxygen present in the soldering chamber. Formic acid can cause human health threats and has
an exposure limit of 5 ppm.
Greenhouse effect - A thermodynamic effect whereby energy absorbed at the earth's surface, which normally
radiates back out to space in the form of long-wave infrared radiation, is retained by gases in the atmosphere,
causing a rise in temperature. The gases in question are partially natural, but manmade pollution is thought
to increasingly contribute to the effect. The same CFCs that cause ozone depletion are known to be
"greenhouse gases,* with a single CFC molecule having the same estimated effect as 10,000 carbon dioxide
molecules.
High-solids no-clean Dux - A flux which contains more solid matter than traditional fluxes.
Low-residue solder paste - A solder paste containing less solids than a traditional paste. The decreased solids
content allows for the elimination of post-solder solvent cleaning.
Low-solids no-clean flux - A flux which contains little solid matter, thereby leaving less post-solder residue
and usually eliminating the need for cleaning. See no-clean flux
Methyl chloroform (MCF) - A designation for a popular solvent called 1,1,1-trichioroethane. Methyl
chloroform has an ODP of 0.12.
No-clean flux » A flux whose residues do not have to be removed from an electronics assembly; therefore, no
cleaning is necessary. This type of flux is usually characterized by low quantities of residues. It may be a low-
or high-solids formulation.
OOP - An abbreviation for ozone-depletion potential.
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74 '
Ozone - A gas formed when oxygen is ionized by, for example, the action of ultraviolet light or a strong
electric field. It has the property of blocking the passage of dangerous wavelengths of ultraviolet light.
Although it is a desirable gas in the stratosphere, it is toxic to living organisms at ground level (see volatile
organic compound).
Ozone depletion, ~ Accelerated chemical destruction of the stratospheric ozone layer by the presence of
substances produced, for the most part, by human activities. The most depleting species for the ozone layer
are the chlorine and bromine free radicals generated from relatively stable chlorinated, fluorinated, and
brominated products by ultraviolet radiation.
Ozone-depletion potential - A relative index indicating the extent to which a chemical product may cause
ozone depletion. The reference level of 1 is the potential of CFC-11 and CFC-12 to cause ozone depletion.
If a product has an ozone-depletion potential of 0.5, a given weight of the product in the atmosphere will, in
time, deplete half the ozone that the same weight of CFC-11 will deplete. The ozone-depletion potentials are
calculated from mathematical models which take into account factors such as the stability of the product, the
rate of diffusion, the quantity of depleting atoms per molecule, and the effect of ultraviolet light and other
radiation on the molecules.
Ozone layer - A layer in the stratosphere, at an altitude of approximately 10-50 km, where a relatively strong
concentration of ozone shields the earth from excessive ultraviolet radiation.
PCB - An abbreviation for printed circuit board.
Printed circuit - A printed circuit is an electronic component designed for interconnecting the other
components. It usually consists of a metallic conductor pattern on an insulating substrate. After fabrication,
it is known as a printed circuit board (PCB); after assembly where components are added, it is known as a
printed wiring assembly (PWA).
Process Window - A term used to describe the range of settings for various soldering parameters at which
satisfactory soldering results will occur. Process parameters include preheat temperature, conveyor speed, and
solder wave height. A small process window implies that strict control needs to be maintained over the
process parameters.
PWA - An abbreviation for printed wiring assembly.
Reflow soldering - A method of electronics soldering commonly used with surface mount technology, in which
a paste formed of solder powder and flux suspended in an organic vehicle is melted by the application of
external heat.
Rosin - A solid resin obtained from pine trees which, in a pure form and usually with additives, is frequently
used as a flux.
Rosin flux - A flux whose main nonvolatile constituent is rosin. There are several categories of rosin flux,
often designated by the codes R (pure rosin), RMA (rosin, mild activation), RA (rosin, activated usually with
free chloride ions), RSA (rosin, super activated), SA (synthetic resin, activated).
Solvent — Although not a strictly correct definition, in this context a product (aqueous or organic) designed
to clean a component or assembly by dissolving the contaminants present on its surface.
Surface mount technology (SMT) - A technique of assembling surface mount devices or surface mount
components on the surface of PCBs and PWAs, as opposed to wiring them through holes. Surface mount
technology offers a number of important advantages such as miniaturization, but also some disadvantages such
as difficulty in defluxing under certain types of SMD.
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Surface mount component (device) - A component capable of being attached to (device) a PCB by surface
mount technology. The device may be either leaded or leadless.
Vesication - A blistering defect which may occur on boards with confonnal coatings when excessive residues
are present
•
Volatile organic compound (VOC) - These are constituents that will evaporate at their temperature of use
and which, by a photochemical reaction, will cause atmospheric oxygen to be converted into potential smog-
promoting tropospheric (ground-level) ozone under favorable climatic conditions.
Wave soldering - Also known as flow soldering, a method of mass soldering electronics assemblies by passing
them, after fluxing and pre-heating, through a wave of molten solder.
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APPENDIX A
INDUSTRY COOPERATIVE
FOR OZONE LAYER PROTECTION
The Industry Cooperative for Ozone Layer
Protection (1COLP) was formed by a group of
industries to protect the ozone layer. The primary
role of ICOLP is to coordinate the exchange of
nonproprietary information on alternative
technologies, substances, and processes to
eliminate ozone-depleting solvents. By working
closely with solvent users, suppliers, and other
interested organizations worldwide, ICOLP seeks
the widest and most effective dissemination of
information harnessed through its member
companies and other sources.
ICOLP corporate, affiliate, and associate
members include:
AT&T
British Aerospace
Compaq Computer Corporation
Digital Equipment Corporation
Ford Motor Company
Hitachi Limited
Honeywell
IBM
Matsushita Electric Industrial
Mitsubishi Electric Corporation
Motorola
Northern Telecom
Texas Instruments
Toshiba Corporation
In addition, ICOLP has a number of industry
association and government organization affiliates.
Industry association affiliates include American
Electronics Association (AEA), Association Pour
la Research et Development des Metbodes et
Processus Industriels, Electronic Industries
Association, Halogenated Solvents Industry
Alliance, Japan Electrical Manufacturers
Association, and Korea Specialty Chemical
Industry Association. Government organization
affiliates include the City of Irvine (California), the
Russian Institute of Applied Chemistry, the
Swedish Environmental Protection Agency, the
U.S. Air Force, and the U.S. Environmental
Protection Agency (EPA). Other organization-
affiliates are the Center for Global Change
(University of Maryland), Industrial Technology
Research Institute of Taiwan, Korea Anti-Pollution
Movement Association, National Academy of
Engineering, and Research Triangle Institute. The
American Electronics Association, the Electronic
Industries Association, the Japan Electrical
Manufacturers Association, the Swedish National
Environmental Protection Agency, the U.S. EPA,
the U.S. Air Force, and the U.S.S.R. State Institute
of Applied Chemistry have signed formal
Memorandums of Understanding with ICOLP.
ICOLP will work with the U.S. EPA to
disseminate information on technically feasible,
cost effective, and environmentally sound
alternatives for ozone-depleting solvents.
ICOLP is also working with the National Academy
of Engineering to hold a series of workshops to
identify promising research directions and to make
most efficient use of research funding.
The goals of ICOLP are to:
• Encourage the prompt adoption of safe,
environmentally acceptable, nonproprietary
alternative substances, processes, and
technologies to replace current ozone-depleting
solvents
-------
78
• Act as an international clearinghouse for
information on alternatives
• Work with existing private, national, and
international trade groups, organizations, and
government bodies to develop the most efficient
means of creating, gathering, and distributing
information on alternatives.
One example of ICOLP's activities is the
development and support of an alternative
technologies electronic database "OZONET."
OZONET is accessible worldwide through the
United Nations Environment Program (UNEP)
database "OZONACTION,11 and has relevant
information on the alternatives to ozone-depleting
solvents. OZONET not only contains technical
publications, conference papers, and reports on the
most recent developments of alternatives to the
current uses of ozone-depleting solvents, but it also
contains:
• Information on the health, safety, and
environmental effects of alternative chemicals
and processes
• information supplied by companies developing
alternative chemicals and technologies
* Names, addresses, and telephone numbers for
technical experts, government contacts,
institutions and associations, and other key
contributors to the selection of alternatives
• Dates and places of forthcoming conferences,
seminars, and workshops
• Legislation that has been enacted or is in place
internationally, nationally, and locally.
Information about 1COLP can be obtained from:
Mr. Andrew Mastrandonas
1COLP
2000 L Street, N.W.
Suite 710
Washington, D.C. 20036
Tel: (202)737-1419
Fax: (202)296-7442
-------
79
APPENDIX B
THE IPC PHASE III TESTING PROGRAM
Introduction
The institute for Interconnecting and Packaging
Electronics Circuits (IPC) Phase III Controlled
Atmosphere Soldering (CAS) program was
initiated to evaluate the effects of nitrogen as an
inciting atmosphere for a wave solder process
utilizing low residue fluxes in a no-clean
application. The use of inert atmosphere soldering
had been introduced and used by many different
companies as an early alternate to cleaning circuits
after wave soldering. The IPC CAS study
examined two independent variables - atmosphere
and flux materials - as they relate to wave solder
processing to determine if there are any significant
problems which arise when using either the Duxes
or the inerting process. The results of this study
provide data on the effect of an inert atmosphere
in wave soldering, as well as on no-clean
alternatives to standard wave soldering using rosin
based fluxes and post-solder solvent cleaning.
Structure of Study
The study used surface insulation resistance (SIR)
testing as a primary indicator of flux/cleanliness
effects. The study was further supported with ionic
cleanliness testing and surface chemical analysis to
provide additional data for assessing the relative
effects of the materials and processes used in the
test. The Phase III CAS program used IPC B-24
SIR test boards for the study, which have served in
several other previous IPC studies gathering
similar data. Five B-24 boards were used in each
test cell.
The control materials for this study were rosin
based RA and RMA flux formulations whose
characteristics had been evaluated in previous IPC
testing. The test fluxes evaluated were a 2 percent
solution of adipic acid in isopropyl alcohol, and a
commercially available low-solids flux formulation.
These materials were subjected to a series of tests.
These tests examined the materials in an array of
process configurations involving different fluxes,
board placement, and cleaning options.
The series of tests included the following
combinations:
Blank
Control
Adipic/Up/NC
Adipic/Down/NC
LSF/Up/NC
LSF/Down/NC
Adipic/Up/C
Adipic/Down/C
LSF/Up/C
LSF/Down/C .
RA
RMA
Where the test legend is as follows:
Adipic 2 percent adipic acid in anhydrous
isopropyl alcohol
LSF Commercially available low solids flux.
Down B-24 test board run circuit side down in
wave solder
Up B-24 test board run circuit side up in
wave solder - no solder of test contacts
NC Not cleaned
C Cleaned in a batch non-saponified
deionized water cleaner
RA Control flux-solvent cleaned (methyl
chloroform)
RMA Control flux-solvent cleaned (methyl
chloroform)
-------
80
The tests evaluated the B-24 board in both face up
(circuit side up) and face down (circuit side down)
formats. This provided a direct comparison to
assess the effects of normal processing in
comparison to a worst case scenario with flux
deposition on the top side of the board where the
flux would not be subjected to the full effects of
molten solder. Low residue fluxes were applied
using an ultrasonic spray fluxer for those circuits
that were processed in the face down position. For
circuits that required face up processing, the low
residue fluxes were applied to those boards with
manual spray application using pump-spray bottles
until the board was saturated with flux. The rosin-
based RA and RMA control fluxes were applied
using standard foam fluxing techniques. A new
foam stone was used with each material to prevent
cross contamination of flux materials.
During the soldering process the average oxygen
content in the wave section ranged between 5 and
14 ppm of O2, with an average of about 10 ppm.
The control samples using RA and RMA fluxes
were run in an ambient atmosphere. All other test
fluxes and conditions were run using the inert
atmosphere.
The Phase III CAS program evaluated these
processes for use in both military and commercial
electronic assemblies with the primary concern
being cleanliness of the boards after wave
soldering. Two different types of Ionic Cleanliness
checking machines were used in the CAS program
- an lonograph 500 and two Omegameter 600
SMD machines. Pric: to initiation of the testing,
all of the boards were visually examined, serialized,
electrically checked, cleaned in the Omegameter
600 SMD machines to a baseline reading, dried in
nitrogen and sealed in individual Kaypak bags.
Process travelers accompanied each board through
the production process to track the board and its
process flow.
After the boards were passed through the wave
soldering machine, they were inspected for visual
defects, sealed again in individual Kaypak bags, and
routed to other testing procedures. The additional
testing procedures included ionic cleanliness, SIR
testing (using two different profiles ~ Standard
Navy • Condensing Atmosphere Profile and the
Modified Navy Profile - Noncondensing
Atmosphere Profile), and evaluation by high-
pressure liquid chromatography (HPLC) and ionic
chromotography (1C) to determine ionic
contamination levels. During the processing all
boards were handled with clean white gloves to
help minimize extraneous contamination.
The results from the ionic cleanliness testing are
presented in Exhibit 14. The results of the
condensing atmosphere SIR testing are presented
in Exhibit 15. The results of the noncondensing
atmosphere SIR testing are presented in Exhibit
16.
Conclusions
Based upon the results obtained from the ionic
cleanliness and SIR testing, the low-solids fluxes
provided results equal to or better than the solvent
cleaned rosin-based controls.
HPLC and 1C test results indicate a similar level of
organic and inorganic residue present on the
surface of the boards. These test results are
consistent with values observed in other IPC tests
as well as those observed in industry. The test
results indicate that low-solids fluxes can be
effectively used in controlled atmosphere soldering
applications when used with appropriate materials,
proper handling, and proper operating procedures.
No negative effects were observed that could be
attributed to the reduction of oxygen in the solder
wave area. In addition, no solderability issues were
observed in running the boards across the wave
solder machine and nothing was found in the
cleanliness or SIR testing. It should be noted that
components were not soldered to these test boards.
The effect of the reduced oxygen levels in the wave
soldering zone can be observed in the visual
inspection of through-hole solder joints. However,
facilities using nitrogen incited wave soldering in
conjunction with low-solids fluxes routinely report
low defect levels (less than 200 ppm) for processes
that are running under proper control. Therefore,
considering all of the information gathered in this
study, it has been demonstrated that the
combination of low-solids fluxes with a controlled
atmosphere offers an effective alternative to
cleaning after wave soldering and can significantly
reduce waste streams in manufacturing.
-------
81
Exhibit 14
AVERAGE IONIC CLEANLINESS OF TEST SAMPLES
Machine 1-600
Machine 2-600
UMd to Solder Ckcufe
Key: AA = Adipic Acid
LSF = Low-solids flux
U = Board face up
D m Board face down
NC = Board not cleaned
C = Board cleaned in nonsaponified deionized water cleaner
RA = Activated rosin control flux cleaned in methyl chloroform
RMA = Rosin mildly activated control flux cleaned in methyl chloroform
-------
82
Exhibit 15
AVERAGE SIR DATA FROM CONDENSING
ATMOSPHERE TESTS
100000000
24 96 168 336 504 672
HounofSlRTMtTIm*
673 697
Key: AA = AdipicAcid
LSF - Low-solids flux
U — 3oard face up
D = Board face down
NC = Board not cleaned
C = Board cleaned in nonsaponified deionized water cleaner
RA = Activated rosin control flux cleaned in methyl chloroform
RMA = Rosin mildly activated control flux cleaned in methyl chloroform
•A-U-KC
•A-D-NC
•A-U-C
'A-D-C
1L-U-HC
• L-D-NC
•L-U-C
•L-D-C
•HA-D-C
•RMA-D-C
•CCaiTROL
•BLANK
-------
83
Exhibit 16
AVERAGE SIR DATA FROM NONCONDENSING
ATMOSPHERE TESTS
1.QOE+15
l.OQE+14
I l.OOE+13
l.OOE+08
24 96 166 336 504
HoutsofTMtTbvw
672 674
Key: AA = AdipicAcid
LSF = Low-solids flux
U = Board face up
D = Board face down
NC = Board not cleaned
C = Board cleaned in nonsaponified deionized water cleaner
RA = Activated rosin control flux cleaned in methyl chloroform
RMA = Rosin mildly activated control flux cleaned in methyl chloroform
-------
84
-------
85
APPENDIX C
PATENTS RELEVANT TO CONTROLLED
ATMOSPHERE SOLDERING
-------
86
-------
United States Patent
NowotmU
5,071*058
H5] Pate 9f Patent; Dec. 10,1991
[54] PROCESS FOM JOINING/COATING USING
AN ATMOSPHERE HAVING A
CONTROLLED OXIDATION CAPABILITY
Inveator MarkS.
N.Y.
[21] AppLNo: 41138
[22] Fikd: Ott.lB.IMf
US.
PU
[32]
us. a.
22S/42; 427/432
221/119.211.179; IMll.
22S/1MU. 37.42,223. 219. 221; 427/432
[MJ
US. PATENT DOCUMENTS
9/1975
3.900.191 t/1979
4.121.790 10/1971
4J694U 1/I9U
4,444.114 4/19*4
4431.797 9/1919
440M93 S/19M ChnaophetaL
4410391 9/19M
221/320
/219
i/iaai
/219
FOREIGN PATENT DOCUMENTS
99894 S/197S «T— *»«/»i«
129M10 tO/1971 tMad rjajllnai 22S/219
2171042 7/1917 IMMd
OTHER PUBLICATIONS
Chip » Smtacnte » O»-
". IBM Tecbx • j»l Dado-
rare Balkan. voL 20, No. 6, Now. 1977. p.,
-FSp
the 21st
Mayl971.pe.27S-3S4.
I ML Mcouncii
. «r Am—Alvm H. Fntachler. Peter
ABSTRACT
to a method of eoodoctini a joi-
1ST]
of
n
[63] ConiiMirina of Scr. No. 29U59. Sep. 30. IMJ. abm- M
1/219; 221/223; datm
ig atmotpbefe having
that ircfuiifo to
ferjobv
ICMOU-
than that of air. Typically the wo-
of ni-
a set point. The luge of the setpoint
which can
10 ppn to about 100.000
on the application. When a flax is med
• icflow mhkiiiii. the iei-
100 MTBI as teat than abovt y)i.ffft BMP of
300 poo to about 10000 ppn. When
the joinmg techaiqae is wave soider-
UOOOppn to about lOQuOCOppa of oxygen
SQUOOO ffiwit to about JOjOOft ffPBii
a Jiiiaint'u^iii j tiinntuhfre having a lower
-------
Jrareni
Dec. 10,1991
5,071,1158
12
/ S S / S S ' S S / / / / / A
X\\X\X"V \\XW\Xt
^ii^ii^^^^^^ii ^i^.
FIG. IA
F/G. IB
K>
12
r
FIG. 1C
-------
5.071.038
1
PROCESS FOR JOINI*G/COA1INC USKG AN
ATMOSPHERE HAVING A CONTROLLED
OXIDATION CAPABILITY
M^SS^^*^tiT^flp5lk*lio"Ser- Antowi*«*»"»^^
No. 07/2J1.*59. filed Sept. XX I9SS. and now afaaa- oxygen content. Liquid puttied nitrogen which bis
dcned. . been vapomed it mmnmcndcd as the comroUed atmo-
f-LDOFTHEWVENTTON .» UM^r. ^.d^ Aug.
Thisnventxnratsmtoametbodofjoiamg/coatiBg 19. 1973. dartoiei a method far flux free soldering of
----- ^ --- ._*_*_; — . -- : ----- 1__ . -------- . - ^ — _
, wetting agents are
15 added to the solder. Tbe solder • « aac based solder
US. Pat. No. 4.121.730 to Seboer et aL. dated Oct.
. . _ . , K l>7>. disdann processes and compositions for sol-
Tbe method can be opomiicd to provide improved owing ahumnum containing workpieces. The 757 to Benifer. daieJ Sept. j.
compounds which are detrimental to wettnig of the l9Mdea*e»«™«hodof wave soldering in an enclo-
substrate oartees wbkfa are to be joined or coated. "B^^cb is mbwanrtrily free of oxygen. A gaseous
However, fhuing agents are typically corrosive ami * >*mj°Bg *9e>H «"cfa as hydrogen is added to tbe oxy.
residues mast be removed ftom workpieces after the f«»*«««tmosphere in tbe enclosure to provide a flu>-
joiaing or coaaag operabon. In addmon. should tbe
**" "**•«*** tcToiristopb el aL. dated
UJL Patent No. GB 2171042. to Kamijo
et aL. dated July 1.1987. discloses an apparatus for wire
. an etectric discharge to msh a fine metaJ wire
„ . ec*1 "f™"? into • ban shape: the ball of metal is subsequently
ff ^ MsMmtta^autaf MS^tnaSa* *aVanK4l mm -•* -* •
-_ r *5 ""•»< •» <»* f«»"ncciiem area, wherein the metal
can be welted by the soider/coanag a provided and tbe
-_
an e wee y e soercoanag a provie an tbe ftows nder pressure K> form a bond. It is desired to
soMcr/coaMf .y..-!^.. ts camedom man mnatao. have the metal whicn » pressed im^ U« esmnectiom
sphere, such as an oxygen free atiaoiphera.it is possible area be suNtaaiially fm of c«ides and impurities. This
to solder/coal the metallic substrate without a flux. is accomplished uiag one of two methods: 1) When a
However, fluifan soldering in aa men atmosphere does » tote wire of pure silver is used, the oxygen content of
not alwBM nravide MSCOMM ujiu— • at th» .M-IK* -^- _. —
- , r. — -w .WK *m «• pure iHvcr *» oca, me oxygen content or
not always provide adequate, wetting of the metallic tbe atmosphere surrounding the electric discharge area
wb«r«ie.Thevi»co^«^Hir{»cetartiooofthemet-
« wwm the metal ball is formed is maintained at no
al-comprising filter material causa such material to more tban 100 ppm. or. 2) When the metal wire is not •
form droplets and pull away from the ntftatltc substrate pure Tti* tmt has ****TM<1 metal impurities added to it
whkh must be weU contacted by the metal comprising 33 to increase the wire tensite strength, the oxygen content
filler material to obtain a good bond between such mate- of th* «mM»k«M. «»~..~ii~- >k» _«__^ -i:—•
er matera to otain a goo bond between such mate* of the »«"ift'p>**»* surrounding the electric discharge
rial and tbe substrate, Tbe pulling away of the metal. areaismatmainedat lOOppmioMOppm. In this second
comprising filter material from tbe substrate n fre- method, die metal impurities are deposited as oxides on
queatly referred to as dewenmg. The wetting ability of tbe surface of the molten metal ball, so that when the
the metal comprising filler material has been increased 40 ball is pressed into the connections area, the pure metal
by adding wetting agent* such as bismuth, strontium. inside the ball forms a better bond in tbe contacting
barium. beriUiom. and antimony to the metal-compris- area.
ing filter material However, these wetting agents are The U^. Patents listed above which relate to solder-
expensive, ipmrtinui generate toxic fumes, and en ing either state directly or infer thai the oxygen content
form unricurablf compounds, such as brittle mter-met- u of tbe soldering atmosphere should be free of oxygen
allies, within the solder (which weaken the solder). entirely or that the oxygen concentration should be
Typical of the known an in this area are the follow. reduced to tbe minimum practical, in addition, several
ing UJS. PM. Nos. of the methods described require presence of* reducing
-------
5.071.038
toMering armosphm. or the addition of wetting <
pounds u> the iolder/caatmg material, uuiciuu naara aes»gns ana nux typi .
li would ae an advantage to have a jonmg/oaatmg ami ripi riiiii •miiiii over the 1.000 to 100.000 ppm
method which pn»^iinproved wetting between the oxygen oaaeannMB range will provide an optimum
fowerialandihemetal- 5 oxyEncoacenmuon for a particular a^icatuo.
the production me of When jranrngftriarhtg i« conducted in the absence of
for wave soldering will vary for
meal oauda. and does KM rcqunibeaddt- a Dux, the deared oxygen eoaceatniioo Cm an atmo-
lien of a wetting agent 10 the metal comprising BPerA sphere rrmiiiriiif substantially, of nitrogen and oxygen)
coating material. win decrease and the allowed variability will be less.
SUMMARY OF THE INVENTION 10 BIUEF DESCRIPTION OF THE DRAWINGS
that of or. h
oxides. Typically the
and lae oxygen
The set
The method of the promt invcation couipriiu con- FIGS. 1A-1C show schematics of the dewening of
•boa* in an oxidiriny at- subsgate surface which can occur during reflow solder*
I oxidation .-inability. The sag or after awdcr dipping if the oxygen concentration
? surrounding the solder is 100 ppm, or
FIG. 1A shows a substrate such at copper which has
'and with solder.
FIG. IB shows the structure obtained when an etec-
mate of the type shown iu FIG. IA b
• when the substrate b dipped in solder and
about 10 pamper mulioa(ppm) to about 100X00 ppm the aoBospbere surrounding the soldering operation
(10% by volume). ^^ cinni|ii ii 11 oxygen at a concentration of greater than 100
In Bfl •flMMpQ0a> CBaVISlmVJf CHGDbUiy Of Mi HWrt gfatt p|MnX
and oxygen, the preferred oxygen conwnt for reflow 23 FIG. 1C shows the reflow or solder dip structure
soldering of tkeueuic circuity board*, m the pmunx obtained when the atmosphere surrounding the solder-
of a flux, ranges from gicater than about 100 ppm to las ing operation couipibes oxygen at a concentration of
thaaatomSOXOOppm(5%by volumekoverthbaxy- 100 ppm or has.
SSum^iut Z tte 10 DETAILED DESCRIPTION OF THE
'bavoided. WmtThatt PREFERRED EMBODIMENTS
b a rnirtm commonly remaining on circuit boards after The method of the present invention cempiiiei con-'
cleaning. It it a tin-flux Lamnonnd which forms m the ducting joinmg/coamg operations in an oxidizing ai-
presence of high oxygen UJncaiiUatiom. such as that of mosphue having a Umited and controlled oxidation
J3 capafcihtj. The desired oxidation capability of the atmo-
be used in the sphere in the immediate space suncunding the joining-
hydrogen, /coating operation depends on the typr of joming/coai-
d mUtures ing being carried out. However, m all cases it b impor-
theteof. One of the most piden«d men gases for use m taw that the atmosphere have sufficient oxidation capa-
tbe present invention is nitrogen due to tow cost and «9 bibty to form a hmned number of compounds compris-
ooiHOxichy. The most preferred atmosphere oxygen ing metal comprising filler or metal comprising coating
content for reflow soldering ranges from greater than elements, thus reducing the surface tension of the metal.
about 300 ppm to about 10X00 ppm: over this oxygen comprising filler/coating material and preventing such
conccWFation ranges there B good wetting of the sub- man Mats from puffing into droplets instead of wetting
strate. white haie fottnaion b avoided and the circuit 43 the substrate surface as desired. Sim. Jtaneously. if the
boards (which are typically 40uuy glass laminates) do oxidation capabibty hi too grrat, huge wff*^>nu of com-
net shew dbcotoatkm of the tend which occurs at poundi comprising metal compibiug rOler/coaung ma-
oxygen concntraoons of 30X00 ppm or more. The terial rlrmrnti. snc*» as metal oxides (dross), will he
optimum oxygen concentration for reflow soldering formed, aa^ the presence of targe amounts of such com*
can vary for different board dcagm and flux typo: SO pounds can interfere with wetting of the substrate sur-
however, minimal experimentation over the greater face as well as provide a metal-comprising filler/coai-
than 100 ppm to less than 30X00 ppm oxygen eoncen- mg material composition and joined/coated structures
tration range win provide an optimum oxygen conceit- which do not function at desired.
tration for a particular application. Two commonly used soldering technique? and ex-
In an atmosphere which consists essentially of nttro- 13 amptes of application of the method of the ptesent in-
gen and oxygen, the preferred oxygen content for wave vennon to
-------
5.071.058
5 * o
of ria. loe\ gold, su^cck iadian aad bboutb ia a wide Cwait teattfsooaa|naaagepa«y^laBlaaimaie mate-
range of relative peroentages. Reflow soldering ntypi- rial were aanany etoctroetaied with a 6fc40 ba had
callydooem air at a lena^aiirebgrwtrn shorn 200*0 solder aa top of copper c&canry. The boards were
aad about 230* C: however, reflow soldering has been coated with RMA Oax and heated man oven to a nuuu*
done over a icmuciaiuic range bom about ISO* C to > mm iiai|iiiiiaii Between 220* C and 240* C the
about 500* C Mild acid Caxes are Tamper used to tool taa* far aeatmg and coabag of the tnaids was
dissolve eabtiag i**Hft off of the solder and substrate about S aaaaaas. lac aaaopbere composed dry mtro-
surfaces. A comraoaly used, mildly active flux is resin ^toga^rmnimikMtot* 10 ppm oxygen) with
or RMA Oax; this to r bfcad of alcohol ****> •*** eoatislUd aonooas of oxyaen. Aodmoas of —
(rosiaX and i
slow!
thought that n-
EFFECT OP IEFLOW SOtDEMNO ATMOSPHERE
KTRATUNONSOLXNatDEWETTma
AMB WHITE MATE
by the solder. We
gold, silver.- nickel, or Kavar.
prising nickel aad i
ter Technology Corporation ofl
cuit boards
tammatesori
Reflow soldering I
in air and in
cmic <,ntr
-------
5,071.058
" 8
tratktt. Wave soldering is a process whereby ekaronic TAB
are attiched to a cncailboud by bringing TABLE 2-continned
the component ad the band ia contact with a ^errecnoFW A VE lotDHUNO ATMOsmcmE
solder bath or wave. Typify the component to be
the board aiid the asscnwly is contacted with the solder
bath. The coniponentB held mpoBtm mine board by BUDGES rex DROSS pftotxrcno!
iHtcii n pfirtifg cuiuiBOiift of im? ""*niirrtf m __fgOj _______ BOARD
through hotes in the board or using a glue to attach the »"» o aj*
connectors to the board. The solder bath or wave wets 10 l*2? ' »»
, f , 3JDDD T * A4M
r m [I I •lllliMm Jill**. •^««Smmm«immmmmimmmmmmmmm**VBBjjjjjn>BBA.m^BWWWiB!^
IJMK lOHScr Ouafn ffB^pttuttty • paauagapagg IQ iQfm g •VVBBW^MHHH. . -
wave. If the solder is not pumped, then the proem is _"» »/*•>» per hoard ranged bctmiui 0 and 2 tor
referred to as drag soldering. Wave tirfirfring is also I* ?****_ ****jy.a*°ye *** Pereent (tOOOO ppmX Ti
motrve radiator is«mMiri The method of the -- _
invention on be applied ID meal joining |"-- run of T^?** ? _<°Jl^_*Bgtf' Tne dra>> fonmtion rate
toe type dncribcd above and can be extended to other ™"t"Bt" «B»**7 *om Ml mVhr M 20&QOO ppm
aiipUcation by one stflted m the an. » <20% by voi«ne) oayjia ooncemratwn to aot Ita^ir
UA PW. No. 4.6KU9I w Ae proett iavemor day "MpPp^-Trhe prdemd oxyfra cowcntraiion is.
rtmrrt thit ihrtr irr trih aiUiaiin ' ••>' tlimUinmi i ^a*fa». >tni im •boat JOjOOO ppm «ad 30000 ppm
to wave soldering in a low nijgtn rnnliinim «aw far tha pynpibr .soidering a|iplirnriim; tha oaygen
sphere. One advantage is there is a lower production f01*™11*110" P*^*"** •boot • 90% reduction hi drou
me of dross ia ••••K«-)JT"r* comprising • low oxygen ** formation me without inrfriirj bridging.
concentration. Droas is a munuv of solder oxide and . *^"c °f^"IB °?y concentmion for wave lolder-
solder which is typically contmnaPy iuua»ed hem the mgwfll vary far dilfami board designs and fliu typev
lolder bath and replaced with pure solder, •^rmng ***BOT "^ jf*111'"1 **• ** done *° determitie the
the COM of soldering. One disadvantage of tewoxygm opwn levclk b b eipeend. m view of the proent
Bridging B the oaatended joinia^ c/ad>cent compo- °??? *"•'"" •*•"• ^^ •• "nwrcr. atxxx 1.000 ppm
nent leads by solder. Bridging CM resnhm shorting ovt a-d *** lOftOOO ppm. When no flu is used, the opti-
of the cirenh. VS. PM. Ma <6!O39I describes a pro- f"" oxygen ronfrmntiore may be tubuantially
cess for wave soldering a work piece wherein a portion lower- _
of the w^vg « in frmo^fi t^itt, • ^^^1. aiMMy^^ 35 Tneoxiditing capability of the jommg/coMhig pro-
one percent or lenoiygen by volume, whale a dUfcrent ««» m^ospheKcaa be controlled to the i^aired act
ponion of the wave is in contact with an atmoipbut poiniby nmciMn im, IIIIHIIH.I which would be apparent
contaiamg from about I tpenxn to about SO percent by » one skuledm the art. One of the nwre common lech-
voltme oxygen. It was rtimi»inil upon lutut 1*111 Move* is to control the composition of a gas which
experimentation that there are atmosphere oxygen con* *° P***** (hrougb the pun ruing area* providing the de-
cemrauons for whtch the dram production rate of the sired atmonilmi tuiiimiiiliiigthejemmg/coatingeper-
wr-- could be reduced without causing high bridging ***•
mm*. TIM* H~r**~~y I'T'^lt itt qf a thtgff stmuspuuL As previously <
in contact with the entire soldering wave, thus provid* »»•»««€»*
mg an mipi uvyment over the pieviously
patented method.
rial having through h
locations for bridge (ocnation per b
hi MI Etectroven Econpak ronoi >o - _ __ . ^
chine (of the type available from Etectroven Ltd.. ««»eimteds»tnige«.TneCTygencjmeiasc/tlieseform»
Montreal Canada). An RMAfmi was used. Tbe boards rf •troguirtBge from about IJOOtoabout SOOOOppm
were preheated to about HXT CThesokter wave tern. osygien.-nieieta» two s«iice» c/ nktogen can be
pemure was about 250* C The solder alloy was«2J63 .. ™*T ***.ripf"""1 *•• «»>ogemc nitrogen. If the
by weight ratio of ondendantimony. The results for 5S **»«"* «««O|»» •«»»« does not provide the desired
bridging ratr amt drnn Modactton are summarited hi o»y«f« conceaajnuon. it can be adjusted in a manner
TABLE 2 below. wroch W|M provide the desued oxygen concentration by
___, _, •ddrnf either nitrogen, oxygen, or air to the available
TABLE! nitrogen tanrrp.
EFFECTS OF WAVE SOLDERING ATMOSPHERE M Examples of srfinioMl metal application processes
OXYOEN «>"OHO«.*mWO RATE AND wmch would benefit from use of • procasing atmo-
sphere of controlled mintrimi cipability Jnclude hot air
hjvelhig, which based to cott circuit boards with tol-
MIDGES PER DROSS PRODUCTION ***•. •"* •»!»«•«"•«. «^ tin coating of steel.
JOARD ~ iN'uis7H»"~" M The •bove rtiirlinure illustrates
mum t a«l which demonstrate the method of the pro
tooooo l «>««. The best mode of the invention as presently contem-
a» plated is disclosed. However, one skilled in the an will
-------
5,071.058 .
9 10
: the broad rangec/applicability of the generic reduced dacotonooa aad reduced white hue on saw
concept of the umiuion It i
c«ihediscicaedembodm*«whicbIaUwiihwthespirit (a) providiag a balh of meal-comprising filler mate-
and scope of the invention be included as part of the rial, wherein said filter material is provided at a
invention, as npuiiii! in the appended claims. 9 tmpcratun at which it is sufficiently fluid and
1 claim: . active to bond to said metal-comprising surfaces
1. A method c/apptyd^ a inetalO^**a^ ^^ •nnaj^im^^BW •••WWi**""""*' 41W (Ca^BDCflttanVC WIBCA PCfaWtt •n'OCBttnttlf? DQBQlflF OI
- - , , » . 4»nmm ^•/•mm^^nm VanHfl •ajm»«nnn*»^ njMM *^B ^•^••^*i Wj 4Pmn»jii
slut provided
surfaces to be
filer material in
;sur-
>1fljii-i..^tti<*aiiiil LiminniimMHTmt—"""•' • - »circuit
"^T~Ijr*^ i^gj ggg (ibtnBte ana in a shirty board which method provides good wetting of said
10 ppm to about material used to join said metalif| ctwpnsmg a metai-com- (b) beating said assembly to a temperature at which
mime eeatmn material which ism contact with at said uuial i cmiprhing filter material is sufficiently
!*••••*•• •"^^•^™
least one substrate area to which said metal-corn- fluid and active to join said meial-compnsing sur-
prising coating material is to be bonded: and. faces, wherein said heating is carried out in a single.
(b) heating said assembly to a temperature at which 39 controlled oiktiring atmosphere having an oxygen
said metal-UMT inismg coating material is suffi* concentration of from about 7.000 ppm to about
ciently fluid and active to bond to said substrate lOOjOOOppm.
area, wherein said heatmgis carried out in a single. 12. The method of daim 10 or claim 11 wherein the
; an oxygen neteng temperature of said metal-comprising filler ma-
of from about 10 ppm to about 40 ttrial is teas than the metong temperature of said at teast
IfXXQOO ppm. ' two metal-comprising surfaces.
3. Tbe method of dacB I or daim 2 wherein said U TT« method of claim 10 or d«cn 11. wherein •
oxygen concKntraoon^is umuoUcd^at a set yamt Una is added to said mtial rompriiing filler material or
4w The method of daim 1 or 2 wncntin a flm 0 prca* 0 flax is TTT***** to at least mtv of said metaJ^omprising
em at the time of ceniaciing said meul
-------
„ 5,071,058
11 12
."^ <*^J*"M ***«* «*«»«" »T»e»«fc*l of claim I wbemn tbe coatnsnate-
^^ am ts GDuroUed from about 10 to about |^ « «PP^ «. «»pewi« of »m than .bout 230«
20. Tbe method oTdatm 11 whema taid i
3 »o nrni mniiH • raier m~t~«^ or a flu a appbcd
JS
43
40
63
-------
United States Patent
Nowotatdd
[il] Patent Number 4,823,680
Apr. 25,1989
(34) WIDE LAMINAR FLUID DOORS
JmntRY.
FOREIGN PATENT DOCUMENTS
&CT333 4/If7T
S4OMI
P3J A«*
PI] ApptNo:
122] roe* DK.7.WT
OTHER PUBLICATIONS
^CIMM! ^\M^>^flHMM^*> *.*— •^ j^>,.
ran uywzncs * Mcunw
flBL Nor Yoik. 196L Swtiw ia pp. I-U ttd ScctkM
VMF9/M
34-34,
M«y 1987, pp.
loyee
UChureh
of an
29IV2I9; 412^4
US. PATENT DOCUMENTS
ftOndtoOow.in
toordiracdyaeRmm
3J2UN
3J3UM
X573JW
XW7JOO
UW.90D
of find tow fact
wtthoftfee
MIU10
4J5UWI
-------
US. Patent Apr.25,w89
4,823,080
12
FIG. IB
-------
US. Patent A|>.25,iM» am 2*3 4,823,680
FIG.2
-------
Apr.2S.lS89 She* 3 of 3 4,8i3,<»»
FIG. 3
56
IG. 3A
-------
4.823,680
US. Pat. No. 4.69*226 to Winner describe
WIDE LAMINAR FLUID DOORS barrier cunani at an aperture in a wall within a duct, as
at the entrance of a furnace. The fluid barrier curtain is
BACKGROUND OF THE INVENTION used to maintain separation of fluids oa opposite sides of
• ci^i ~r-«-- IMMIHIJJLIL • ' * *** haiiiu" cunam. Wttmef dncuitei the importance of
T^t^vSS^LestoamelhodawJtppara- ^.fj?0*"* fe*"* Wang an effective barrier
=^^^-^^^^sl™,ri: w «3^^^H^^i.^EJ
aide of the xone, mcludiag the use of f***" edge vanes
located at the aide of the apparatus from which the fluid
is removed; and, the iHitinmhip between the width of
distance acton which the fluid enter* and exits. e.g. the
gae^aBBe aCVQvV |Q£ c£*»£ajie£a«jpBV 2OflC C8B OC a& ftJtBt 9£
thirty tines the width of the slot in She fluid curtain
to direct the flow of
or to contnllhe comoocoioo of
Several of the geooal prindpab of find dynamic*
20 WUCD provide beckfEQQQd m^™ limntHiyfc related to the
sacst OVCBDOQ Bay be found to Stpeeter« nandboott
of Fluid Dynamka-. McGraw-Hill New York, 1961 in
Section 10. pages 1-13 and m Sectioa 26. pages 1-21.
The dftigii of the apparatus used to pieveiit an exter-
- , _ ,_. ., , , w ual fluid from entering a procus space can vary, as
t treated. Soaieoi toe BKaauaeMappucaDOMOtjias ahntrated by the apparatus 4*R\vn4 m the patents
jets or curtains •" ^ ^ I*"""**1 *^ """ll,^* B«ted above. State of the an technology has permitted
from cuiniiig a procesi space wheretn a conaaaous ^ ^^^^ ^f p^ contaminants within the process
uuuveyor awst uuwc parti iitHmgh the |j«» Jis apace. apace to averaae ".T™9**t*"**7i>t as low as about 100
US.Pwi«dBcn»«^«aeofgBa>en.«a«^ia 30 ^
this latter manner •cnde USL_Pit j*x WjWU to cenlhiidthiwijh openings to the process. The 100 ppm
Colemaa, earitled: APPARATUS FOR KRADIA- coacentmtkmh tbVnonn«l preceas condition, with
TION IN A CONTROLLED ATMOSPHERE; US. rrm^mr »*-fi>™ ocrnrr«g. dm ing which contami-
Pat No. S.807JDS2 to Trow, entitled: APPARATUS _.. concentration can rise as faian as ambient concen-
FOR IRRADIATION OF A MOVING PRODUCT „ „*„ (iO*ppmX
IN AN INERT ATMOSPHERE; US. Pat Na There are tmne applications for which a 100 ppm
3.936.930. lo Tioue, eatitled: METHOD OF INERT- ~»t.,»MrW», u^i. rod p.fri^.u.iy »~4^
ING THE ATMOSPHERE ABOVE A MOVING H Mjt. M io*ppm mult to product defects or rrdnced
PRODUCT; US. P«L Na <29&J41 to Nowadd. cob- -JM c.M.1a>.fffthftfit?HrttHit'.-m H^^rf'*•»»
tied: INDUSTRIAL OVEN HAVING MEANS FOR *> ^^^^.SeaueaaSetarmut^amafmttKfe
MINIMIZING HEAT LOSS; US. PaLNp. 4^448.616. oooTuTa particle-free environment, due tosubnicron '
to Francis. Jr. et aL> cantlea: PROCESS FOR RE- BBC /ttm^MJ^i. jn fhrtrkal ctrcnitn- which can be
DUONG BACKMOONG; and US. Pat No, moered inoperative by the presence of a panicle of
4>69&226 to Wtoer. entitled: FLUID BARRIER dun. Heat^reatmg. joining and formmg of metals re-
CURTAIN SYSTEM. 45 „««» oi»geu4kBe gaseous eavtroaount at elevated
US. Pat No. 3J07J52 to Troue dnciceei a treatment lempuatitft, since pretence ofmygen (even at concen-
endoaurc for the contmuoui in-Une atadiation Meat- natiom as k>w as 10 ppm) can cause pans to discolor so
nim of tesnrtvc of a iiiovmg coated product. The that they matt be reworked or pickled. In the case of
treKmentcnckiHuc includes means for maintaunag the bnziafev presence of oxygen may prevetU jointag from
surface c/a moving coa^prodiKn under a blanket of 30 mxiutingao that the part bnrined. Thick film firing of
neft 0vi flBHB^ we mvoia&oD tveatnieiit theROL Tlooe printed cizcoits fiPBQtte&tiy if^ji'f'T* several difTcieist
> the importance of the following features ie- processing zones in series, with each tone compraiaga
[gMblaaketing: That the men gas flow be dif
r, that there be a long rnliaixr rnnnrt rrom amb*- anch as those used for soldering or galvanizing require
ent air which siu rounds the enclosure to the source of 33 protection from oxygen; current technology requires
the tRRt gas flew and that the ga* flow be directed piacmg aa enclosure over the hath and purging it with
downward toward the surface of the moving coated an men or reducing gas, or placing an men liquid atop
product. • the iff"**"? IT**** surface. These techniques restrict
US. Pat. N0.4.44S.616 to Francis. Jr-etaL relates to accesi to the nx>hennxtal surface, cattsecwuuninatioo
a process for suhatinTialry reducing the h"'""i"»i or n and rrll**M"tMlly JIM u in . the operating' com of the
by process. la addition, tiuie are application* wherein it is
the ia«c/a particular gM jet arnngeaiem and a defined desired to protect a window from obscuration by a diny
gas flow rale, ine gas jet arrangement cotupmes a pipe environment
with holes which produce* a turbulent flow unJermost The known technology, prior to the present rnven-
r onrtiMons of uptrainu^ The hole sate or width of a slot 45 two* permits incursions of the type previously desciibcd
in the gaa distribution conduit is specifically stated not due to u^ of flow stability. The incursions, due to the
-------
4,823.680
of aa opening
r g — ~^^w ^»^"^»J*
with M poiiiuM protected by mother fluid layer. The
10 «. •..;-.- — =-•—• to be mrifprnrtrnt of any
or zones. Different flid com.
be used far ovcrttppm| prtM
COOsBCICfl IflBtt vflft flWCCaUl
It is abo desired
U
plane. Cost, safety, and i
to
Quid compugtion
of ambient iato the preceat
£:.Md*-rt«.d
SUHHARyOTlHEINVENIIOH
There ate abo
6** ««nM« flow*) are not
flew rate of the fluid
fB fioa " aaen^
costly joUuittbere a.
in tenai of procai eco-
e applications for which
i of enenal fhads *?f .•"<»?'•"* iaereatein
by eaaaag a flaid toflow, fa lamiuai ftmu, fa pradarity JO •'^•'•Py mririin ptetectioa and a flow rate a
totfaecnqtaiacdBpao&.Taedq>thortfaickM ****> Tae optoaom flow rate can be detemtaefw
"iniiml qpmimntaiiuii. the Quid at or behind the area
P«» « opoinf to be prateeted b lanpied for the
portoo of drat tart oaenriiihit to be protected, in 33 »«*^*'- l«i^^ty of JateteKaad the fluid flow rate b
the direction of Onidlkw at the ioarce of oriain of the *«•»* *>«"» the Hmitatiota pro: owjy speculed,
of fhdd flow b at leatt fat&m "m obtained at the aanpfed loeatioa.
: ***• rf «*POrtio»of Aaa^heftiB,tiK^OfceNiBBBer-,Fr.i»a.
thediiectioBof Ihadflow. Ia« the«iaaTeroot of the ratio of the moraentum force of
_ , , ,..„..,.. the flmdhiyer at itt source of origin. Fm. to the pressore
»Ibrcerf the Iha^ layer at to source of oriain to the fatce acroas the layer as it passes over the opening or
—re *> defined asthe reaction force of the fluid
m httnnw torn CCK» the soriiaoe.or area plane to be MnJnst in source of oriaja. Far a Qua, thk k *qa*\ tn-
aed> The Hiirtnrai of the protective fluid at to
8 of origia is at least about 005 times the dataaee
i the surface or area plane in the direction of flow
of fluid flow ta at least about at creat as the
• great aatae
Quidl layer an be aatd to protect aevetat
-------
4.823,680
. *
Pmai is the amimnrn pressure difference and across boundaries within which the materials procx *•
Ah il the area of the surface or area plane. ing » takmg,place. The invention is particularly usefu,
If Pmu varies with item, then akvlatknt should be Cor applkabaas wherein it a desired to move solid ma-
based oa the largest expected Pnaz. If Ah varies with terial bemg processed across the sane boundaries from
tine, then calculations ihoald be baaed on the largest 3 which enema! fluids are to be excluded and for applies-
expected Ah. tic«w^»« optical accenacnm the same bc*uidaries is
Fm can be iMuuoUcd IB response to Fp so that Fr dcsiifo
remaoiwithm the desired raiis^ Alternatively, Fm can For example, the invention b useful for applications
be controlled in response to process fluid compoaitioo where it is desired to mamtsin a fluid of a given compo-
measuremeots at a given, sample jpmfrm so that Fr 10 saian. temperature or other set of intensive propenies
remains within the dewed range. oneoe aide of an opening (process environment) to an
As used herein, "fluid How me" means volumetric endosed processing area despite the presence of a fluid
flow rate of the fluid at the Outsource of origin. of » djflcfert conporition, tempetantre or other set of
As nsed benm, laminar" fluid Dow neans that the mtenave propenies on the other side of the opening
TTOtf**"* •f""* ™theiannn»ifliiiiUmtiflmii> the fluid IS (ambient).
Uyer velocity at the sounx of origm of the fluid layer One embodiment of the present invention is shown in
are less than atioutaitmes the aven^ velocity of the FIGS 1 1A and IB to illustrate the general principles
fluid in its direction of flow at itt tflWffy of ongn and involved. A portion of an enclosed processing chamber
that the nncncnaqaare of the sixes of torbokat eddies 2 a shown having opening 4 which mutt be protected
m the fluid teyer at its source of origin are less than 0.1 20 from catty of ambient Quid 6 uiuuit outside processing
tines the thickness of the layer at the source of origin of chamber 2. The processing chamber is filled with envt-
the fluid layer. . fontnent fluid t, which differs bom ambient fluid 6. The
BRaSFDESCRDTIONOFTHEDRAWINOS
FIG. 1 fflnstrates one «*«HiliimfffT of the invention. 25 FIG. IA) having « height H and a length L, across
TfhaTmMfl|rr-^g*""*"M'HttiliH*M'lM*i*r*^**^*rf which the ambient fluid 6 1» to be prevented from trmv-
from the entry of external fluid into the chamber using ding, A Ovid distribution source 12 having an opening
a Uyer of fluid Qowmgfrem a distributioo source post* through which Quid flow 14 ocean, in this case a reel-
boned above the opening, and wherein the opening sice angle of width W and length Displaced on one side of
is the ITHTT as thf crcaaHMCtkwal ana of tihf fm*-l*f*'il 30 thr barrier rrTTingtf 10. In flpfr case, the fluid distribu-
12 is placed outside ime*M'*& chamber 2.
FIG. lAgtestrimabreak^twayaoM sectional view Le, on the ambient side of the barrier rectangle 10. A
of the pcnico of HO. 1 bearing the same numerical and laminar flow of fluid U exits the distribution source 12,
m this oaeparaDel to the barrier rectangle 10.
FIG. IB is 3 schemiticaPy fflaatrated side devation 35 The fluid flow 14 can be at an angte toward cr away
of FIG. 1. showing the feature whereby the angle of from the processing chamber 2 should the application
fluid flow from the fluid distribution source am be requn^ and the a^sirabflity of the flutd flow 14 being »t
adjusted. * such an angle can be determined by sampling at any
FTP f ""•*"•*•• •* •'•''TlintTiH iff fl*" j»-^b-« goat within chamber 2 for the desired intensive proper*
similar to that Omstnted in FIG. i. hot wherein the 40 ties and adjusting the fluid flow 14 direction so as to
dmribo!ic»sauK*oftheflttidlaverisTnBiti^ ' produce the preferred results.
oradjacouuthediamberendoMiremamaanerwhich The width W of the fluid distribution source 12
reduces the opening soe to the chamber. should beat least aboutOOS times height H of opsning
FIG. 2A Olustrate»abreak'away cross sectional view 4.
ofthepcctionofHG.2bearingtbesainenumericaland 49 In practice, it is fluid flow 14 which defines the actual
alphabetical idtniifk aoon. uatnai1 10 which is fm im'il
FIG. 2B is a srhmiaucADy tUustrated aide elevanon The prown cnvnonment a, ambient o and fluid flow
of FIG. 2. thawing the feature whereby the angle of 14 may comprise any fluid composition, temperature.
fluid flow from the fluid distribution source can be density or other set of n
FIG. 3 shows another raihadiuiuit of the invention plasmas, such fluids containing pankuiate mauer. and
ambitnt using a layer of fluid Under some occratmgcondnieos. some of fluid flow
from a dtstribouoo HHUBJ positioned to provide fluid 14 may mix mto pncess environment •. so it is in'efu*-
flow in a direction parallel to the horizontal surface or 99 bk that the fluid comprising fluid flow 14 be inert or
plane- beneficial with lagaid to the prof t is being practiced
FIG. JA is a schematically fflustrated aide elevation wuhm pncess environment ft. Under other operating
of FIG. 3, showing the features whereby the angle of conditions, fluid flow 14 does not mix ouo process envi-
fluid flow from the Quid distribution source can be roument t. so fluid which would be deleterious to the
adjusted and whereby the spat jug or drsfsncp bttwun 60 piucus can be used.
the fluid flow layer and the opening or surface to be Process requirements, safety considerations, physical
protected can be adjusted. ' Imitations, fluid cost, and the judgment of the pract
__________ -i. JLI_ i *%«• -*^w~, _• _ . ___ - , •"•»' of the invention will determine the choice of the
DESCRIPTION OF THE PREFERRED fl_y -__-j^, fluid flow u
UIBO ««*"'imHi »«uia tiow i*.
or orienu-
The present nventkm has broad appucation in mate- tion. The layer of fluid flow 14 can also be of varying
flaUS ptOCCSflBf W&CfCtt It IS OCSRQ tO VBdHCC tDC rtttpftj WEB Of OHCDtBtlOli HTCSpCCtlVC OI UIC StZC*
Amount of external fluid, g*s or liquid, which tnvds or orientition of opening 4» Thin, it is possible to pro-
-------
4,823,680
Force Number which hai
aoc protected. Even in such a cue. however, the
at ^mfrjtn* * farm pr*~n *n"irff"TpfHT t will
fluid layer It Safer geometries win provide
performance at fee sane Fore* Number. Thm, the
performance in a Dew application en be estimated
b»i!donthe
U
of Ibid flow 14 adte
layer.
EXAMPLE 1
or«"llitotbe
For sppirstioos in wfaicfa mote than one Quid flow
! tbe fluid
a Bahtvariate
However, as initial estimate of fluid flow 23
be made imn the method of the pro-
A clear
box 22. having opening 24 was
temperature helium so that box 22
only benum at room temperature The inter-
were 3.5 inches high by
wide, by 70 mehes long. Because the laminar
Btt— dimibiition source 36 was mounted so that it em-
tested downward m ftmt oftbe entrance to bn 22. the
offluMiflowactaaOyasedcanbe 30 •» of *oe opeoiag 24 into box 22 was restricted to
wbereia HBOA 2J inches in height H by about &5 inches in
^•f" L Thin, the barrkrpUwe2t across the opening
"^ a local area of abott2Usouatc inches or about 1.48
E>t •V"*1* &*» The fluid distrQxition source 26 had a
*»**' w«f«*»«OJ iacha««J wMpoiitk»«dK> th*t
._, --
eat tnventica and the prenmpiiaa that each component
flow must provide the total protection for the portion of
the desired barrier plane which it flows
qjiently.the
o/ the
i ate sampled ?*^»»«*i«ig «t^ _ „__„_
and the fluid flow rale from each individual
iVing op the barrier plane is reduced or 39
I tk* overall balance des«d b obtained.
The design of tbe fluid flow components win be a
function of the degree of protection required, the cost
of tbe environment, the coat of the fluid layer compo-
fluid flow from distributor 26 wo?ld be in a direction
downward across opening 24. The OJ inch width of
distribunr M was about O20 times the distance of travel
- _ _„ ^^ tirin;. ,,1ini —j^j- ...—ni^p. , across the opening ^* ^ ***nptr point 30 was located at
'•mf'the jmliTnTfr*rf the pi-"i^—r •rrfrim t1"1 ^* the botnim of the cpenmgm tbe center of dmemiooL.
MI ,rf.>J^~-r~.—.= . -rr*'.-* so that it was j-»««*i«M>iy behind tbe barrier plane 21
which was on the box -22 side of the laminar fluid distri-
iMMVfMk MMMMM ^£ '
The laminar fluid dsnribution sourced device was
fanned by construcong a box which was solid on xl>
sides except the bottom side 25 from which the fluid 27
was to flow. The boftntn side .25 comprised a sheet of
siiilcrcd metal powder with a porosity of about 2 mi-
crons. The fluid 27 used to provide tbe laminar layer
filling bottom 25 of distributor 26 was room tempera-
tve Hrtrftsjjfn The nitrogen. Quid was tnjected mto an
opening 33 in the top of the distributor 24. Tbe size scale
of any tnrhnlfnct in the niuogui fluid 27 flowing from
dsttributor 24 was about equal to the size of porosity
method of the present invention.
The method of the present invention » effectively
used when there is a positive flow rate of fluids from
within process i nvimiiim m g across barrier plane 10.
wboitbaresiiioenvi«)oaemOwexitmg8croaibar-43
rier piane 10, or when there is a negative flow rate
•cross barrier plane 10 (U-. a net inflow of fluid flow
layer 14 acrus barrier plane 10). In the latter ease, the
fund layer 14 mast be men or beneficial to the environ-
nwM a; and the scceptabkaniouDt of net inflow of fluid 50
layer M across barrier plane 10 it proportional to the
width W of Quid layer 14 and cannot exceed the total
flow of fluid flow layer 14.
J1*8,"1^^ Pf^F1**™* "*eution is effective even
when porOMtt of bamtrpUne 10 which fluid flow Uyq- 35
14 « to prowct are blocked by phy«cal item*. One of
the porp^c/ the inethol of the present invention it to
allow physical objects which are to be processed to
ud leave) processenclosaR 2 without allowing
(about 2 mkions) of bottom 25. much smaller than 0.1
of the O3 inch width W of dBtributorM.Vnut. tbe fluid
flow 27 from bottom 2S ofdatribntot 26 was expected
to be laminar in nature. A hot wire anemometerwas
aatd to measuae the velocity fluctuations as tbe nitrogen
ambient^ to enter process enclosure 2. There is, bow- aO c merged from distributor 26. No velocity fluctuations
eve^iUw^efl^ivu«Mc/ ambient «exdnsk» if the were observed. Thus, the nitrogen fluid layer 27 exiling
ject prevents fluid flow 14 from reaching a portion of distributor 2C was laminar m nature,
An extension 34 was added to the aery tic rectangular
box 22 to enhance the effect of the layer of nitrogen
fluid m exdudmg the ambient room temperature air 36
snrour.dmg the box 22. Tbe walls of the extension 34
were 5 J mcne, high. 8 J mcho ia width (equ^tem to
length L) and exnio« c« abc« 2JnSeTpi«b3rie!
10 which protects a portim of opening 4.
Tins problem can be overcome by using more- tbm one
Quid flow couipuueiit so that the comhinsrion of com- 65
the •««• «f *•"" pume 10 from
14 a blocked off. There
-------
4,823,680
9 10
pkae2S of the ooena^ The dteance of the extension may alter Pound the point at which Pau ocean,
OM fh» fl« battier ftefc stow as ^ niFIO. 2, saalng it ncccsauy to nuke pressare measurements at
When there «n no nitrogen flaid layer 27 flowing wioai poina across the Boundary plane to determine
fromdistriDutor2*abebmmparie«irwaidfroejbox p^u..
22 of about 3400 standard c^ feet per boor (SCFH) J Ah is the area opening 24. U8E-1 square ft.
was reamed topivvettanibientan-(mcasaKdasax^ /Thai Fp canals 1.99 E»3 Ib and, the value of the
Ico)inffltr»iiooto«mplepont30.TT»chdnimpBr»e ForeeNnnber.fr. b about OL«.
gas was fed into the center of imanpilar box 21
taraegh • poroo* smtered meal cylinder 37 widen \ EXAMPLE!
rfcc* of bo« a to toe center* «
~m mm —
"».._- - * ~«- -««— - ~ ' mm— DOB mammuT was C4wment to that
BCf tnenwcrnenaBipargeiiowi, u
• -m I -"-mmmm-mfm-.^.^ ^^^^M^HM^^ •• V^BV* W^MMM
j 5J mcbes high. 8J inchet wide and
49 mchts long {between openings). Each distribution
nnnummnTii .~y —...—-....-.--.„.„^-— ^"'^"j**^"T^^^l?^*. •^i_*^^*j^*TTf **^^nr*Y^^
m the hdmm environment e/box 22 wttca could be m daacawana described m Fiampr 1. Thai, thentioof
•^ ^^^ ^P^^"^^"» _ ^nr . . a-*- ._^ * * 4nlMt 1>4^^^ ^V Mft ^l^k ftMtAflU^K m^t tf^tfmti
mmmmmmSmmmmtm^mm. ^.mmtmmtmmm 4^ *^ a^ - «
flniriiniiion souice *» to tne DOttom
««««»« »>«•> —a be reahxed by o*ing n nhrcgcn wafl of chanmto 23 wa» about 0^ satisfying the crite-
wide laminar flaki door to protect a helium environ- ria flat anca ratio be at least 001
meat of a ' nciil IMOCAUL 25 The cflectivencai of the laminar fluid layer doon
The Force Number for thb example can be calco- were enhanced by extending the chamber wall oat past
Uted as follows: the openings at each end of the chamber. The length of
j- _ ( «hnm>gh t""'**^! mttal pyBnder
37, exiting fcom each i?ff"iiiHj| 24> The puige gas wnhm
steaoy.occa»ionBuy.uie
imlk» a» Mgh as
liOOO ppm utygu. and then drop back to its typical
tiie fluid layer over the am of the 2
Ib/cubic foot; and His the height of opening 24. 2M t» . .. , .
B-l It Thus, Pmax eqaab IJ5 E-2 lb/lk». Typically, *^Bju"1 a*lc"rt.P?1 _ . „ .
Pmax will be **»* difference m meuute across »*»• fluid nuregf B to purge sourue J7 located m the center of
^^^^ ^^ ,*^ •««»»*«*p«^^» ^* g.w^»»^^^ mmmm-mmmmf mmmmf mmmmmmf ^ ^^ m^mmmL fSfmmmmmm ^_ , «• .. ^^ W^
ftyi iiitf of f**p controlled ^••niithii»« dating this ex* oxygen clan rnlfation upatu which had occarred at
periment.no winds were present (either from withza the «5 sample point 30 disappeand. The system was nxmi-
enviromncnt imirtr enrkiafd chamber 32. or from ambi- . teredfar M6 bocrsand dumg that time period only 10
winds may be prurntwithm the system and such winds 0.001 per nunatc.
-------
4,823,680 | I
11 r ' ' 12
The Force Nmnber far the abcive system was calcu- twieas as tow as atom 1000 ppmdiie to random fluent-
taedttsia«theiameimhadasprovidedmEXAMPLE atiau »the awoeen flow iwieraaf the opening. Each
I, substituting the appropriate uumfiical values. Uatnar Anid door dotributioa 26 wu fed with 400
SCFH of room tempenrare air white the nitrogen
pj*L25 E-3-shigs per cubic foot. Tie volume flow a purge me at source 37 was auintamed « 600 SCFH,
ra»eofeachlaininarfhiidlayer,V,was4.17E-2aibicft. The osygen tevd at the sample peim decreased to a
per iecoad.Tbe area of each dbtribotor bottom 2Sw*s median rnnmmatinn of 10 ppg The decreased con-
2^ E-2se^iare feel Therefore, Fn far aeb fluid layer centraooa of oxygen fluctuated over a nnge from I to
distributor was 1.32 E* tta. . lOOppadBetBiaodomftnmiiliontintbeflowpaneni
The weight deiu^ of nitrogen, pNjg, is 7.23 E-2Ib 10 atthedoor.TniidCTaMticdtcii.au in corygen content at
per cubic foot. The weight deuriry of air, pig, a 7.49 die sample point upon ate of laminar fluid doors com*
E-2top»o*fcft>ctTheh*igtocfeBchopenmgHwM prising air was unexpected, in view of the approxi-
2M E-l feet Thus, POMI eqaal about 5.16 E-4 Ib/il1. matdy 21% oxygen contrtumico at the sample point
Tie ate* of each opening was about US E-l square wiftc« the laminar fiaid doors (even with the nitrogen
feet. Tins, Fj» for each wide laminar Quid door was 15 purge) and in view of air being the laminar fluid 27.
aboot7.fiZE.Slb. . The Force Nmnher far each laminar Hoid door can
Whetcby Fr eqoab aboot 1 Jl. This Force Nomber DC rtlralatrd ma aaaunersmuTar to the previous caam-
lb within the pnfiened range oral tola pks.
Aa m apparent ftom the previously presented equa- The mm density el the nnm temperature air nssd as
tkai. for a given applicatkiohavmg specific equipment 20 the laminar door fluid was 2J3EJ slugs per cnbfc loot.
and flnid compoaitinni, Fr is conirolkd by controlling The ^olame Ouw fate of each laminar fluid layer. V.
thevoUnneflownte.V.ortheflaidoMdtoptDvidetbe was UU E-l cubic feet per second. The ana of the
fluid layer. The number 31 shownonFIOS. 2,2A and bottom 25 of each distributor 26, Aj. was about 8J3E-2
2B represents a controlled votametnc flow rate. One sc)uare fBet. Thns, the, moBentQtti force. Fin, equated
skilled m the art wfflnnderstaaddiat the means of eon-25 about 143 E-4B» for each jet.
rrol can be any means known in the an and the specific The weight density of nitrogen at about l«TC,pN:
means is not part of the indention g, ttaboatSJB El Ib. per cabic foot The weight den-
PYAMPun sity of ancient air. pag, is 7.49 E-2Ib. per cooic foot.
EXAMn£9 Each openiag heightH was SJ3E-2 feet. Each opening
A conDnnons rornace having two vertical openings. 30 area was about L67 E-l square feet Thus. Fp for each
and having an environment of not nitrogen was pro- miming was about 3.44 E»4 Ib.
ircied from contaminaitttn by ambieni room tempera- The Fmue Nsmoer, ttien> • about IjO and within the
tote air suiiounding the fhmace, asmg a wide laminar preferred range of abouiai to 10.0...
fluid door ajuipiiied of air at loom teuipciaiure. . BVA**wtc*
This exampk flhmrates that Ae bmmar fhnd layer 35 fiXAMFL£4
r of the A hot aoldereavironmem having no purge Hrw was
laminar fluid itself mto das ptucess environment would protected from a room temperature air ambient ming
be deleterious, since the. laminar Quid • air at room room temperature miroyn laminar fluid doors over the
gen. * • 40 FIG.J shows the geometry of die hot solder surface
A horizontal rectangular furnace 22, one end of 40jJ«xectedbyrwobMunarrhiidooorsS6*nd34.The
which is ffluisntedm FIG. 2.2^1 and 28 with openings two laminar fluid doors. 5f and 60, were placed on
tors 26 at the top of each opfnmg The geometry of bath52froaccaMcrnigsurto40ofbothS2aodoiu-
described in EXAMPLE 2, except flat the openings 24 tm and 40 weight peieent lead. The temperature of the
were one mch faigfc Hand 24 iacfaesm length L. and die solder was 260* C The total exposed area of surface 40
disrioutors 26 were OJincba wide Wand 24 inches in of solder bath 52 uiiaiiirid about SJ inches by about 4.2
length. - ' inches. The openis^G to »)der surface 40 was a rect-
height^ 24 mchesmwid^(equivalent to Lin FIG. 2) smaQ distance aeovedKsokte. The purge flow/ate of
by 40 mcbes long (between openings). Toe ratio of **T ••«**•* Thf Q"gh *T*"*^aT ^* *** **** •"***"M¥fMij •""*»«-
laminar door width W to dw distance of travel from eat was zero. The ambient around d» solder bath was
distributor bottom 25 to dw bottom wan of furnace 22 air. The bumnar fluid flow, represented by vectors 42
~ ng the criteria that «uch ratio be at k« 55 and 44.
O05. The distrAutonMaad4O for the lammar fluid were
The performance of the wide laminar fluid doon wai constructed as deacribei in EXAMPLE 1. The 2 mi-
enhanced by fitrading Ac waDs of the furnace out c*onpoio«aiue$4aa4StofeachdhttiflmtorMandCO,
fro»Cfenmg24aotbattheEdhnensMMasiIrastratedm respectively, was positioned so that fluid flow vectors
FIG. 2 was abont 3 inches at each end of funace22. <0 42 and 44 would be parallel to surface 40 of solder bath
A sample point (not shown on FIO. 2) was located at 5X The room tenmerature nitrogen fluid repreiented by
the bottom > ff in i of one m»iung 24, about one mch vectors 42 and 44 was distributed omformly by the 2
back into the furnace environment from opening- 24. ' micron porous sheets 54 and SI ofsintered metal so that
v^th 600 standafo cubic wet per IUMU (SCFH) of hot laminai uyen 01 toom temperature mifugen flowed
(160* C.) nitrogen purge entering through purge source *5 acrontbe tc^ of aoldersur&ce4a The laminar layers
37 in the ffntet of the furnace, the oxygen conotntra- met
-------
4,823,680 .
13 14
capabfe of protcctmg sender surfiace 40 from oxid'aiiaii. The two laminar fliad Uym of the constructed em-
h was discovered that the utt of rwolaininar layers as bodiment described above were opentcd to that the
described above provided hirtfiiril laminar fluid door principai direction of fluid flow from each distribution
stabfliry, substantially reducing or eliminating ambient device at its source of origin was tocated upon the same
wide W and Umcbe* long L. The distance of travdH However, one skated in the an will dearly under-
of each laminar Quid door from each distributor was 2.1 stand that the two laminar fluid flow layer distributors
mches so Jbtt the entire 41 inch dmnciCBVcrf opening 56and Mean be posnfeaed at diffcxtw spacing* above
62 was protecttd. Each door, protected an area IS opeamg or surface 40, aoefa that one fluid flow layer
incheska«Lby rI inches*lengthH.Thus,thenoo 10 operates over an am plane which is parallel to the area
of laaoaar Oow door width W to distance of travel plane of the other fluid flow layer ^paahioucdalontit.TheheigittoflhceiteiisiOttg layer distributor. 96 or O. can conprae a different
was about 1 JO inches above bath sur&ce 40. flindVfcreuniple, a coetrotkd volume of a Tint fluid M
A sample point 4i ws« loaned about tfllS incbes enters distributor device 56 whfle a controlled volume
above the top of the acdder surface in the center of of a second fluid 46 enter* distributor device 40.
'-^-^*----30 EXAMPLES
tors M and M, the oxygen mm.niiraliou at sample The hot solder appfanion described in EXAMPLE
ponu46wnabout21%(equmtttn>totheoxyt^coii- 4 and shown m FIG. 3 was repeated using argon (a gas
oentntion in air). When about 200SCFH of room ten* heavier than air) m the laminar fluid curtain gat. Con-
pcratBR ntragen was caused to flow through each 19 urntionil wisdom suggeso that a very mmjaaal flow of
a heavy a^hlK argon would be required^ exclude air
pie point 44 was reduced to about 03%. When the from the solder surface. The heavy gas, argon, should
nitrogen flow rase wn increased tea total of about 400 settle downward end sit atop the solder surface. Experi-
SCFH from each dsttiibutor, the oxygen utmut iilratiOB, mnitation showed, bowevu, that the argon fluid flow
ataunplepomt46wMiedacedtol6ppm.^ 40 mast satisfy the Force Number roquiiemcnts disclosed
The Poice Number for each distributor en be §p» hcrem.
pnuiaatedmamamiersimiku-totbttusedmtheprevH A fluid flow rate of 140 SCFH of argon was required
ons examples* ' . , for each I*""™** fhud door to f^clitdc air down to a
The mass ueuity or tbt nitrogen lamiuar flmd pj was roiif nmanon of 27 ppm to 77 ppm mganmed at sample
Z25E-3 stags per cubic Coot. The voteme flow rate toe 4S point 44.
each laminar fluid door, V, was &3< E»2 cubic feet per The mast density of arfon,pj,h about 3^1 E-3 slabs
second at about 200 SCFH aad 1.11 E-l cubic feet per per cubic foot The volume flew rate for each laminar
second at about 400 SCFH. The area of the pciious flow door was iJS9 ot standard cubic feet per second.
portion M aad SI of each distributor M and C0.respec- ' The area of each fhuu door, Aj. was S.9 E-2 square feet.
tryely.Aj. was abort J.90E-2«|uare feet Thus. Fm, the SO Thus, Fin, the momentum force for each door was 8J3
1 .18 E-4bat a nitrogen flow me of about 200 SCFH The wdght density of argon, parg. a ljQ3E>l Ibper
and about .4.71 E-4 Ib at a nitrogen flow rate of about cubic foot The dntance across the laminar flow layer,
400 SCFH. ' w, was SJD E-2 feet. The opeamg area protected by
Typically the pressure f one, Fp,b equal to the buoy* J3 each laminar Dow door. Ah, waa I J4 E-l square feet.
ance force across each laminar flow door. The weight Thus, the pressure force. Fp, across each opening was
O^nsiry of nitrogen, pNig, is abow 7.23 E-2 »p« cubic about 2.94 E4 Ib.
foot The weight density of air. pag, is about 7.49 E-2 to The Force Number, Fr, for this example of an trgoii
per cubic foot. The distance across the laminar flow hanmar fluid door ws» about
-------
'4,823,680
ue
in the art more thai
nodule*- 9 14. The
' ' * one of laid more than one
wul if14Mime that jumeroni M»»HH*I««M •MMKK««»- 4 «A Tho mmtm i *JT **.^_ • ...i • < ..
^^ "-•"•-^- •• a*, laemeuoo we jam • whereia the composition
one other of
• 15. TBe IBrthOO of fntnil 1 wneieja said
10
•aid method
fluid to flow, m
19 directly
flak! How protect, u km
<
U whem.
95
l> or claim 9 whenm at least a portion of any of said
I. wherrm rabstMttnlly aU 24. The method of claim W wherein said Force Num.
' J «S ber nates from about 0.1 to about IttO.
t whefdn „„ fluk|
-------
4,823,680
17 18
flow is to lamhwrnwnxwheRm the thickness of the at 34. The hmsllstinn of ciaba 17. claim 32 or claim *.'
least one fluid layer at its source of origin b at least whefemFmbc^ofitioUedmrcspnM to measured vuia-
about OJQS times the distance across the opening to the tionsmFp.
o»t*ined space which bio be pfttected by the at least 38. The umallarinn of daim 17. claim 32. or claim 33
oog fluid Dow layer, ""hfrfin 1*1% lengthwbe dimension ' wherem Fm b controlled m response to a measured
T>f Th* at Iftrfl ffff fhfM liyfr it in SOtitTf of fffig** ** ** cmiiaminant level in said contained space to maintain a
i ^K<» width of fCMtsnunant level below a specified concentration
to protect.
Qoid asms «t least oae fluid flow layer, wherein
t V A LKA^A ^^MA f^^MH^ft MWH ^UMMkM IMMWMBV fflllMTj BHIMf WM... V^MP «B^H^ v«*pw ^r «.• ^^""B^^^™ »«.»^^^ ww«awi*weM •••w •*PB^>.»~
W ^. -.!.».»«. .. IMM MM <*«_« fhrid « a«» of tl«i« least loneftaidh^^
is at lecst about ftft? *»•«•• the «*«••.•««• •**»pgf thf sur-
IS ace or ana plane to be protected by the at least one
the at least one flmd layer at its toy ice of origin is at
_..__, ... _,. leastabout equal to the lengthwbe dimension of the
(c>me^ for conmJlmgilmnowrfsa^ chosen Bad ^rfaee or aiS|*nnewhicntoflnid layer b to protect.
from said device so that md Had uowtsammai; 20 ^ wherem die it least one fhnd flow has a "orce
(d)means for controlling tike tow dimensions of said Number ranging from about O05 to about 30.0. said
cboten find from said at least one device to that in«anatk>o imprbmg:
the depth or thickness of each fluid flow^layer w ^ feast one device from which laminar fluid flow
Qown^ from esch of said at least one device bat etnanatn. m proaamity to or directly across said at
least about OJBunes the distance m the principal -3 tent a portion of said at least one surface or area
dnectiao of flow from sttteadi device acron said plane;
atka«aporraofsaidatleastonet>pemngmthe (b) means for supplying a chosen fluid to said at least
orindpal doecaon of tow from aaid each device; one device;
(e) means for controlling the momentum force, Fm, (c) mram far controlling the flew rate of said chosen
of each said fluid flow layer ao that n Force Nmn- jo .fluid from aaid at least one device so that said fluid
ber. Fr. b generated far arid each fluid tow layer flow b laminar;
which ranges between about O05 and SOLO; and, ' (d) means for controlling the flow dimensions of said
(0 means for -"-"**••. said at least one device in chosen Quid from said at least one device so that
prbxantty to said at least one opening so that « the depth or thickness of each fluid flow layer
susanatica^ component flows from said at least 15 flowing from each said at least one device b about
one device extends in pronmity to or directly OuOS times the distance in the pnucipal direction of
acroai at least one area having '"••>"••!<•••> as large tow from said each device across said ail least a
as said at least* portion of snU at least one opening portion of said at least one surface or ana plane;
to be piutfiflfl - (*•) means for controlling the momentum force, Fm.
ja Tfrf installation of daim 27 wherein taM at trftft ^ ' of each said fluid flow layer so that a Force Nunv
oocrlrriCTBmtrBr'-^-^»'^T^ri* T.i»»l. j|. iflMimfry fff nf dJrt*Slty «gm«« •« !*•*«
one fluid flow devices are used and wherem at least one n or tten ohnie to be nioteeted.
* • j ^—.^.^^ •%>^^ «^ik^ «n^^uu>^^ •• ^^*mfm^*^*t »** •!*•• •••^C ^^ ^^ ^^^^» V*^^B^M Mr «^v BJP—^F^^^"^^^^
2Si^lSSnfrr^iS^£i^tai^f 37.Themstall«tioncfclahn3t »m,4jt nHm~»f>«l direction of*
open^whik^^pr«c^dJnKtk»rfOw«anoUier flow fron, any of snid at lt^ot« devices b parallel w
of satd more than one devices is at an angle to the same aav of said «t least one siirlacecTawa plane.
said at lent one openmg. J5 j|.Ttain«»Ibt«ofdnm»»wbeTem
3i. The mstallatinn of claim 27 wherem more than gnpdtvicf bmmmwl •»*!«•* ttkl priiff^**1 «>«»»^««i« ft
one flmd flow device b used and wherem the principal Qow from any of ***** at *••** one drvi*'*** b at an angle
directions of flow of said more than one fhnd flows at |Q »«iy of ««fr[ ^ frrt! me Tnrfarr or area plane.
thetf source of origm are psraHrt or on the same area. 39. The installation of *»*•»»•• 36 wherein more than
plane- M one devices are mounted ao that said principal direction
3X The imtallatkM of daba 27 wherem said means of of flow from at least one of said more than one devices
control in step (e) b capable of continuing Fm so that b parallel to any of said at least one said surface or area
Fr b mamtamrd at or near a setpoint ranging from plane while said principal direction of flow from any
about 0.05 to 90. other one of said more than one devices bat an angle to
33. Tbetnttallaoon of claim 32 wherem s*^ means of «s another at least one surface or area plane.
ccotrol m step (e) b capable of controlling Fmso that 40. The installation of claim 96 wherem more than
Fr B «.MiitM««H at or near a setpoint ranging from one fluid flow devices are used and wherein at least one
about 0.1 to 10. of said more than one devices b mounted so that said
-------
4,823,680
principal diitoioa of flow ftooitafcl at lean one devise
20
ofclaiai3«,cl«on41 orctaiin42
aid more than one devices is at aa angle to the
mrfaceof area plain u> be
4LTnenttallationemnsaidnieaBiof
control in step
-------
United States Patent
Nowotmki
(ill Patent Number:
(45] Date of Patent:
4,821,947
Apr. 18, 2989
154] PLOTLESS APPLICATION OP A
METALXXNtfPRISING COATING
WJ
Dmbury, Cona.
{22}
Feb. 8, DM
B23K.1/M; B23K. 33/3*
HQ5K3/34
, 228/219; 228/180.1;
198]
Filed:
te.0.*
US.GL.
228/205; 228/206; 228/224; 228/37; 228/2*0;
228/2*2; 427/311; 427/329; 427/432; 427/43*
FltUofSMKfc 22«/Hai. 205.206,
228/208.214,211-221.223.224,2*0, 262.37;
427/293,311,312,329,432.434
.22S/37
VJS. PATENT DOCUMENTS
1,709,457 12/1972 TnOMkarl '
WK7I1 1/197« KkamktctaL.
440M07 J/1919 Aadeom.lr.«taLm.
4430457 7/1919 DOM
4J3J.757 9/I9S9 B
06MW 2/19M ~
4.606.4W
.231/123
.23S/1KL1
-^tWMWIV^^W ^"r »wwrw- • iMMrpnBP nv
4.610J91 9/1W4 ftoiWManld
•1917
FOREIGN PATENT DOCUMENTS
246711 4/1917
221/223
99D4 vim
S296S 4/l«M
Japi
2*OM I2/19M Jap
22I/J19
221/221
,221/37
90210 «/I97T "««•
,221/21*
OTHER PUBLICATIONS
t_Revauim£>_IBM Teeenial ..Dnciasore
voL 11. No. 12. p. 1617. May 1969.
Newitudd ct «L. The Effect of t Nitrogen Atmo-
ipbefc oa the W»ve Tmning of Compooent Lads".
Haadoos and PmentttioB tt NEPOON WEST, Feb.
23.1986.
•NicholM P. Godki
M.H«nrich
Attuimf. AfHA or firm Shifky L. Church
ABSTRACT
.221/37 *F
iluf luwsdOB rpittei to MI unproved procen for tpplt*
HUOP of • tBftil-cftinpnitm ffr***^j to & neul^ooo*
pnb)( soffiMe withoot omf • ihn. The metal-cooiprn-
•I Mifftrr Bntt K wcftihic by Of loffniiir wettibte-
coattct with a bath of the|metaienttrtBchiiiDCftitla«withnapecttothe.coil-
•t auuowl dnriBf the time period of itt kppliodoB to
B« mritee. nd BfcfenMy iaett with
iSv;!! ns|iecxtobaOitb£CoattBf naterialaodtJbenetal-oom-
•UUl/JlI* „. .„!> - • . _*- ... ... "BPt-fc. * -^ . -*- - ----- _^—J __. •.
The Best mwimrmrtit temper Mure il
flfiUEe it dtyitff to ttif oietai*
tnrtKx utd no dtnuy! B done to otter
•BlctMbadjaoeat to the tnettUoompriiint surface.
» Oabaa, 1 Dimtaf Shettt
-------
US. Patent Apr.18,1989 Sheetlof2 4,821,947
X
FIG. I
-------
US* Patent Apr 18,1989 Sheet 2 of 2 4,821,947
CVJ
d
u.
-------
4,821,947
surfaces will exhibit the same temperature as the t>Rtal-
FLUXLESS APPLICATION OF A comprising surface.
METAL-COMPRISING COATING The cmnpmmih detrimental to wetting can be re-
acted or dissolved and washed away bom the meta!-
BACKGROUND OF THE INVENTION 3 cnoipihrng stniace or from the surface of a metai-corn-
1 Field of the Invention prising coating bath using a fluxing agent Fluxing
This invention relates to an improved process for a*atti «• *• •°* commonly used method of obtain-
appticatioo of a metal-comprising coating to a metal* ing a wettabk pan inrfaoe at the tinie of application of
comprismc "Hae. More particularly, a method is dis- .„ *• nxtaJ^rmprismg coating. However, fluxing agents
do*edw1uchenaolesaf^4ic*rJoa of the coating witboot tie typically uuiusive and residaes must be removed
use of a flu in contact with the metal-comprising sur- fr"*1 ••* P"* after coating. In addition, should the
face. The coating • applied in an atmosphere which b «w»at of flax be insufficient, the solder or coating
inert at least with respect to the coating material during material can fonn kacles on the pan as the pan is re-
thetime period of its application. .. «oved from the coating bath; wetting time may be
2. Background of the Invention madcquatr within the process so that poor bonding
Soldering and brazing are weO known methods of between pan and coating occurs; and, dross production
joining metallic items to each other. Both involve wet- during processmg may be high, hading to heavy main-
ting metal pans with a liquid "finer* metal at elevated tenance requirements.
temperature and then allowing the parts to cool below— Amethodof soldering without a flux b disclosed in
the solidus of the filler metaL When the filler metal Japanm- patent application No. 9.756/77 of K. Noboku
solidifies, the pans are joined. « aL. filed Feb. 2,1971, Noboku et si bring the article
Tinning and galvanizing are well known processes to be soldered into contact whh a molten solder bath to
whereby parts comprising a metal are given a prouc- WBKB ultrasonic vibration is applied. The ultrasonic
tive metal coating by dipping the pans into a molten M vacation is disclosed as causing cavhatioa which breaks
bath of the metal which is to provide the protective up the oxidized metal on the pan to expose an active.
coating. soMerable surface. The major disadvantage of ultra-
Soldering, tinning, f^vaiimiig a^ sonOar processes ionic soldering is the potential for damage to the stnic-
which involve the wetting of a sobd. metal comprised tural integrity of the pan exposed to the ultrasonic
surface with a liquid metal-comprising coating require x vibration. In addition, ultrasonic soldej jtg a geometri-
that the surface and the coating be dean and free from cally dependent The cavitating effect cannot reach
compounds which prevent wetting daring application tome pan areas such at the inside of small, plated holes
of the coating, hfoimd handbag of the meuU-conipris- of printed cucait boards.
ing pans and the oietal-co«bprising coating often results There is a need in many soldering or metal coating
inthefonniuionoCTMipo^odswhkfaarecletrimuitalto 35 operations, and particularly within the electronics in-
wetting, such as metal oxides. In addition, the environ- dastty, for an application method which does not re-
ment of the coating application ptoom itself frequently outre the ing of high ptocenuig temperature* which can
causes the formation of such OBnipmimii. Other com- damage the part, which does not require the use of a
pounds typically formed during processmg which are flux, and which does not require mechanical vibration
harmful to good wetting include chJmida, suhldes. 40 which can harm pan structural integrity.
^r^^aDdtrtl^ ionic, covaletu^ organic com- SUMMARY OF THE INVENTION
To obtain good wetting, and thus good bonding of The present im>ciiti0u lonccms a method of fluxless
coating to surface, such compounds must be reduced soldering or fluxless coating with a metal-comprising
back to a metal, reacted to form another compound 43 coating, wherein the pan to be coated is not exposed to
which is not detrimental to wetting, or removed by a temperature which banns the pan or components
techniques such as dissolution or •"*rfMi»trtJ "'—'"»g thereof. Tha pan is contacted with a bath or wave
ILS. Pat. No. 4.33S.757 to Bertiger. dated Sept 3, comprising the coating or solder material The coating
1915, discloses a method of wave soldering man atmo- material b capable of forming compounds which can be
sphere comprising a gatfotu reducog agent (hydro- 30 detrimental to welting during die (me peimd the coat-
gen). However, practical experience has indicated the ing n applied tote pan surface. Fomation of the com-
bydrogen reacts with metal oxides etc. at temperatures pounds detrimental to wetting is prevented hy use of an
greater than about 600* C. Many of the plastics and inert environment in cootact with the solder or metal
resins comprising an ekctrcnic device such as a printed comprised coating material as the coating material is
circuit board melt, degrade or change from their in- 33 applied to the pan surface.
tended dimensions at the temperatures required to re- The part to be soldered or coated must have a wew-
duce oxides to a metallic-state. Me surface. Le. a surface which can be wetted by the
U.S. Fat No. 4,606.493 to Chriuoph et aL. dated solder or metal-comprising coating material. Since the
Aug. 19. 1986, discloses a method and apparatus for pan surface may form compounds detrimental to wet-
soldering plate shaped circuit carriers whereby heated 69 ting upon exposure to the process environment, the
reducing gas (at about 600* C.) is used to reduce oxides preferred inert environment a inert with respect to both
at the solder side of the earrieri. The high temperature the pan wettable surface and to the solder or coating
gas boaly briefly impinged upon the sower side of the material. The men environment may be men with re-
carrier so that other materials comprising me'board are spect to the bath of solder or coating material also.
not affected by the exposure to the high temperature (3 The environment is men with respect to the coating
gas. However, te is impractical to apply individual jets material if a continuous solid is not formed on the metal
to heat only the metal-comprising surfaces of the car- comprised coating during its application to the pan
rier. and the areas adjacent to the metal-comprising surface.
-------
4,821,947
3 . 4
The environment is men with respect to the put, coning provided they melt, vaporize, or undergo- *
wcniMr infftrr If • mnthinmn snftl h imf fnrmnl nrn chemical change to fbfm. at last substantially, • liquid
the wettahk surface during exposure of the wettabk or vapor upon contaawto the inetal-omnprismgcomt-
tuffiCT to the pimm cnviiOBHMti. ing bath* Inorganic materials cut be wed is protective
The cnvixonnMai a mm with rcspea to the coating 3 catting* provided they vaporize, indu or undergo a
material bath if a cccumuouBsofid a not formed on the chemical change to a vapor, Squid, or material which is
contact surface of the bath within the time period dor- solubk » the metal-comprising coatiag upon contact
iaVt "which the Dflui is Qpcfittooi^ •» INHDOBH toBpow™ ^u^ tog RMHUBL
tare, pressure aod Oath flow pattern characteristics. The pert itself may comprise a material which does
The inert environment can comprise any Onid which 10 not form significant amounts of compounds daring stor-
compliet with the above applkable definition. The mert age or processing. The smmce of the part then retnains
a partial vtcanm wherein the remaining fluid complies When the metal-comprtiing pan safacs is not coaled
with the •hove applicable defmilinn by a protective coating and is not at least substantially
|0 ||»g £|g£tf*30|Ct ffgjfjgfy m JT"l>g>l>l|ilj |ajgff 0|8M^ IS najgff ^m^ fCSpCCt tO CDC pFOCCJHI CBVITOQflMOt SOT tAC
spheres or environments can be provided using flnids thne period of pnceaexpoevre. Unnecessary to sekct
such as nitrogen, argon, hydrogen, and natures a different process environment which it inert to both
behavior if they are present fa low enough concentre- prising coating material. If the metal-comprising pan
tions. For rr"T**T oxygen, COj, and HjO are an oxi- 20 surtace does not enter the process in a dean, wettabk
domgtotm4eadsoldmat2f»rC300*CIftbeyare form, it must be cleaned and the metal-comprising coat-
presentatcono . . _ ..
100% by volume, respectively, however, they wfll not which prevent wetting, or it must be cleaned and pbceo
form continuota oxides on the weoabkpm surface nor in an environment inert to the metal-comprising sur-
onthesoloerasaaappboitothewettabkpmsurface. 23 bees of the part prior to contact with the coating mate-
When a partial vacuum provides the ixcrt atmosphere rial bath. The cleaning may be accomplished by chemi-
and oxygen is present, the oxygen partial pressure cal or oechamcal means, so the resulting pan surfaces
should be below about k or rettooabk
immefsed m the metal^ompramg ooatmg matenaL The to have the entire soldei or coating bath prot^ctfld by a
protective ooatmg can also be any material which is fluid which a inert to the metal-comprising coating
wettabk by the metal-comprising coating and which 30 material, flux can be used on the solder or coating bath
can remain on the part after application of the metal- surface so long as it does not enter ths area of the bath
rising coating without affecting the intended use w-m^^^jy --..i./-^ »h- «~«««M» pn mrfkg^ The
of the pan. flux dissolves or reacts with the undesirabk compounds
lit f f*^*"TT^* •*M*i>***y *M****j*^g, f*"*T^'T**T ^"""''^g* so they are removed and do not buOd up withm the b**n
can be provided using materials such at tin, lend, bis- 33 over tm^Pnaence of the Qux on the solder or coating
moth, indium, cxhnimn and alloys thereof, which melt bath surface at a location outside of the pan contact
at solder tonperatures, washing away any surface conn area assists in removal of the compounds from the bath
pounds or dirt from the wettabk surface. Examples of in genenl, reducing the probability that such corn-
other protective coating materials, which typically do pounds wiB enter the-contact area of the bath.
not form compounds deuiiuenial to wetting, include to The method of the present invention discloses a pro-
gold, silver, platinum and palladium, These protective cess which can be used for soldering or for coating of
coating materials may melt or may remain on the part metal-comprising pans, whereby there is no need to use
surtace, depending on the metal^ompnamg coating lempcmturcs which arc harmful to the metal^ompris-
appbcanoo temperature. Since they are adeouate con- nig part surfaces or which are harmful to other maten*
doctors, for many electronic applications gold, silver, 63 aU adjacent to the metal-comprising pan surfaces. Typi-
after soldering without aflecong the intended use of the- above the temperature of the solder or metal-cpmpris-
—t. Organic matrriab can be used as the protective ing bath. The most commonly used solders require bath
-------
4,821,947
5 o
430* C and preferably below metaKcomprisjg sarface daring the proc»a exposure
•bout 300* Claaddnioa, there is BO needtousereduc- time period.
tag gases, fluxes or ultrasonic vibration to achieve good Apia, the proem environment which is inert with
bonding of the solder er metat-coropr'ning coating to respect to the metal-comprising coating during the lime
the metal-comprising pan. 3 of its applkatkia niay not be sufficiently inert to the
Thus, a rypicslexainpte of the nietbod of the present wetttbfepwinifaeetoprevait the formation of coot-
invention foUowc poods detrimental » wetting of the put surface. In
A method of bonding together at km two metal- neb cases, it wig be necessary to apply a protective
comprisiag surfaces, compiiiing the Kept ofc "naiuig to the wtttable pan surface, or to select a differ-
_ (a) providing at least two metal-ooeflpris^ surfaces 10 cot eByvoonwot which i> tnen with respect to both the
be bonded a a weoi^te nriK« or a sariace which be> -..,.,,„„.._._„
-ttabte upon contact with - —*.!-«—««• DEFINITIONS
bath; Wettable surface as wed in the specification and
(b) providini a bath which comprises a mcial rum IS cttavherem mem a sarface which can be wet by the
prising coating capable of forming at least one com- Bolder or omal-campriug coating material.
pouaddetrimfflUl towcoiagofthe wettabksar&ct. Metal ooimpremg pan «riaocwn»ed in the ipedfic.-
wherein at katt a portion of the bath ii protected from fen sad chums herein meam a surface comprising a
the formation of said at la* one cxm^ouiid using an metal aietal alloy, or mixture of metals.
envinmmcat which a inert with rapcct to at leait the 20 Mtul toinpriiiiiji, bath as used in the specification
nietal-coeapriiiag coating daring the time period of in nd dans herein means a fluid at process conditions,
application; which comprises a metal, metal altoy or mixture of
(c) coBtaf***! the metal-compnbag snruoes to be metah.
bonded with the bath at a Jocarioa withm the oath inert enviioumciu as ssed m the teecificitioa and
which it protected by the inert euvifooment, whcicui 2S daimi Hf*'1) i> iHfimM n> thr Stanmary of thf Inveo-
the |iroceu environment temperature it uiflicieBtry low non with raptct to etal^»nprifinicoatia«iab. wlwa mete, vuorbvs. oriamleVe* ebenu^ebange
lequent to contact with tbebath. so that the metai-com- »mlio>kl«avmiKic.«we«ttaawtotheinetalan.
prevent the formation of umi|MiMnili detmeatal to R«»m^mth«spWificatioeihefem means a mate-
wetting oo the pan saface. In sach case n a necessary « ^ ^^^ „ , Hmrffl st thr until cnmnriiini bath ton
to apply a protective coating to the wcttabte part sur- ^.^^^ which material a^solva^mpounds detri-
removed, rfneoemry.mxome of
contact with the solder w loetal-CTmpramg bath, er
with eoe^ounds de*riaw«al to or whkh prevent wet-
pan »mm»«" auu 10 ise-soiocr or
prisiiig coaling material.
Another esample of the method of the present myen- BRIEF DESCRIPTION OF THE DRAWINGS
tJOTfoUowi: RQ.1 shows a scaematiclbr vertical bMing of ekse-
prising surfiKv which is wettable by a metal-comprisnig
coatiag material or which becomes wettable on contact
with a i»th of a**ul-«»praia» coating material: S3 DESCRIPTION OF THE PREFERRED
(b) providing a bath which comprises a metalxxxn- EMBODIMENTS
prmng coating material capable of forming at kast one EXAMPLE l
compound dttiiinfti'nl to wetting of the part sarface. KAAnu-bc i
wherein at least a portion of the bath a protected from It is often desirable m the ckcuunio industry to coat
the formation of said at least one compound using an 60 component leads with solder prior to assembly into the
environment which a inert with respect to at least the final circuit. The leads may be coated with solder to
metal-comprising coating during the time period of its protect the lead surfaces from oxidation during long
application; and, term storage. Fresh solder may be applied to the surface
(c) contacting the metal-comprtsmg surface with the of the leads juu prior to soldering of the leads into the
bath at a location within the bath which is protected by 63 desired electronic component or configuration. The
the men environment, wherein the process environ- solder coaling on the lead* will melt and flow upon
mem temperature is sufficiently low that no damage is subsequent soldering, washing away any compounds
done to the part, including -it***™1* adjacent to the detrimental to wetting which may have fanned on the
-------
4,821,9*7 '
solder-coated leads. As a result, there are fewer unset- Without the use of nitrogen environment 4 over the
~ 1 assembly soldering. The solder surface of bath 2, kicks and bridging of coating oc-
3 the leads in a caned on the coated leads. If desired, when the leads
> the solder, and are aowcd by a protective coating or do not form
.
iBi.e.f,««hiiig.tlienui»die«. 5 detrimental compound* jdwrf process exposure time
P"« «° costing. t would be possible to Bike men only
the Rgioa of die wider tatb at which the contact with
e i. - wave 10 wherein application of the
j«e the lads ML solder to the leads ocean. If this were done, oxide 14
the solder ww applied sad the solder woold farm oc the bsth surface areas not protected by
showmt the proem b provided in the inenaanosphere and make tt more nesesssry to use
TOLeSS-sirio^by^^ fluxlatoremoveoi^whtt
«Soa«ttt4/Se solder 4 comprised about 60* by form during the soldenng operation.
weight tin sad about 40% by weight lead. The solder « IS EXAMPLE?
Wave «Jderi« h a eo.«» method of formmg
C Tlie solder 6 was recirculaied solder &*t co* ** cuaib tnc* m
by pumping it through a tube 8 so that h ^ •ore.!
they m to
10 wa, .^^«o^with.^prd^to.bo« 10
-------
4.821,947
10
wherein at Ion m po-jon or said bath is
However, when thecnntponent kadi nm iiimniliiilu protected from Ihe fermatijo of said at tent
the tin lad coated mrtaflaed bole* within CBCab - onmponnd oang m cnviraamaH wbidi is men
bonds, Ac solder did not always wet completely, op with respect to at least the axtal-comprismg cow-
through the hoto the kadi were m. Cemptoai wetting 3 tag material during the time period of in applica-
tion of arena bond 30 at it paiied through eootaet (e) ooataetiBf aid inctat-compristng suffice to be
point 33 of solder wave 2S. Compfrtr wetting up bonded with said bath at a location within said bath
through Ihe holes was ate arhifurdIwhea the orcmt which a csMaoally flux-free aad which is pro-
t boards and conipcmcot leads WCTB etched .with glacial iO _ iHitfJ oy.s aid mert cpyuoument. aad wherem said
acetic acid m an air caviionmrn*! at HMMII tfinprnumc. cu^uuiirrifiit tuupeiature t> sufficiently low that no
wore noted and dntd ta an* at toon tcnpenmc aad dsniagf is done to said netat-compriflag suffices
wen coatat^ with the solder bath within a time per* aad no damage is done to other materials adjacent
hrf of >» than abcrot 2 mnuaaaftg drying. to said meuladta the aalder wave. ing sariaoe is coated with a protective coating which is
was washed away DOB the metaQued fiivtbil boaid removed upon contact with said bath.
soldering sites upon contact with the soldering wave. *>.1*-e jnetBod °* ***** * wherein said protective
23 coattuc la adettad ^rum IBB CVBUB coBusttfic 011
^» "™^^^™^ ^f »^^*^^^w^ •—w «••«* ^pww^v W«**WMM^ w» '
; iggjs and the tm lead plated fitrait composed coatings which meh upon contact with said
board soldering sitei. bath; toetal-comprised coatings which dissolve in said
Thea«*hcdoffJtepfeietttayfem1eBptDvto bath at said bath tempeiaiuic; inorganic coatings which
which is soluble in the
mg pans. Use of OKtBetbodenmtBates the mamlenaoce pritMg coating upon contact wnh said hath; and organic
atMl dean up problems asaocialed with the use of a fhn. coatings which matt, vapocue or uadergo a chemical
Use of the method nas been shown to preveat formation change to fonn, at least suhManrially. a vapor or liquid
parts are removed from the coaling hath, due to contia* IS 5. The method of chum > •
vons Qiion prHfnt on the a>i*'*ffg surfafr. use of the face is a TnftiWionipnied mrfarc which does sot torn
the awtal oomprised sarfaees. providing a general m- «. The method of ctaim 1
of solder* face is generated by chemical or mrchstacal cleaning
mg or coating. The ability to accomplish all of the 40 which b done sufficiently close to the time of contact
t^o-vt at temper-uurea which tuTiaot detrimental to the wh^satfbaththatrJiewetlabieaatiiseettaiaittssubstan-.
pans to be coated or soldered and without the use-of Ttslrjr frrf in ftffTfffTlt tfniiiiip"1" *** -*j*>*'*ig •* *•*
integrity subitaiuiaDy aad |>aniciihtt1ybeBetod^ 7. The atahod of daim 1 wherem said wettabie ur-
wettabte surtace is mihrfaincrt io a
Bnvnonmeat untO tune of contact with
bath that said wettabie surface remairu suUstan-
broad iruge of applicability, however, uid is susceptible SO time of contact with said bath.
fmliftfiimntadhcioaed. Cqnirqqtntly.itis not intended meat is men with respect to both said wettabie surface
tt..t tK» f^eenmA >«h^.-M«t. -^ f. ii»;..tw^ pf fti. aad nid metal-coiupriiiBg coating material.
invention. On the contrary, the intent b to include aD t. The method of chum 1. chum 2, claim 3. claim 4.
die spirit and scope of the invention as expressed in the cuvuuiuuent b adeeted frc^c the group consisting of
appended chests. • nitrogen, argon, hydrogen, nuuiuci thereof, substantial
What b churned b: varimiiii aad partial vacuums comprising nitrogen, ar-
TL A method of bonding together at least two metal- goo, hydrogen and mixtures thereof.
comprising swCsces. comprising the steps of: CO 10, The method of chum 1, claim 2, claim 3, claim 4,
(a) pfuviding at kast two essentially nut-free, metal- chum S, cfaum 4* chum 7, or chum S, wherein said inert
coHipflsmg sufnces to be ponded, wherem said cnwonaMmt compnses aa oaidttmg agent, but wnereui
raetal-ornprhagsurfaoebawetttbtesiirfaceora the concentration of said oxidizing agent is such that
surfsce which becomes wettabie upon contact with under process cecditiaus there b no substantial forma-
a metal-comprising bath; 69 tioaof compoimds &triineatal to wetOBg with respect
(b) providing a bath which comprises a metal-corn- to at Irast the metal comprising coating material during
prising coating capable of forming at least one' the period of its application to each metal-comprising
compound detrimental to wcttmg of said wettabie mrfice-
-------
4.821,947
.11 . 12
1L The n»ethed of dam 10 wfamhi said environment bath at said bath temperature; inorganic coatings, which
m selected from'the group consisting of environments melt, vaporiae or undergo chcmfcal change to a liquid.
comprising oxygen at concentrations less than about vapor, or material which is soluble in the metal-com-
1% by volume, carbon dioxide at concentrations less prmng coaling upon contact with said bath; and organic
than 100% by vc4ume. water at concentrations less than 3 coatings which mdt. vaporize or undergo a chemical
100% by volume, partial vacuums comprising oxygen change tb fenn. at least substantially, a vapor or liquid
at a psrtidpresstarrffag than about O01 atmospheres. upon contact with said bath.
partial vacuums comprising car^ dioxide, partial vac- a. Tbe method of claim M wherein said wenable
warn comprising water airi mixtures thereof. surface is generated bjr chemical or mechanical cleaning
IZTbetnetbodafdaimlwheremsaidinenenviron- 10 wnkb b done sufficiently dose to the time of contact
mcottemperamre is no higher wan said metatcompris- with said bath that tb wenable sunace remains substan*
ing bath temperature. _ tiaOy free of compounds detrimental to wetting at the
U. Tbe nxtbod of daimlwfaerein said men environ- time of contact with said bath.
ment temperature is less than about 430* C 33. The method of chum M wherein said wettable
14 The method of date Iwherem a Dux is applied to IS mrf.^ » f^^mt^ h» A-^.ig.1«- ™~K...^I ,-u«.;.,e
sndbath at a localk»notwithmsaU contacting area of .fter wnicb said wettabk sisrface is maintained in a
•aid bath. ^'^ , sofoaentry iam envooonientunnltinie of contact with
13_ The tnf*^***^ «••» i mil* mm «»ia jmniingr mat^ asid *"'** *fc«t **^\ ^i^mihtf nirftrT remains substan*
tiai or said suftsoBS^P be joined aie vibrated at ireijutu- riffly *Vr* 5*^ '^^pfHimh dftrimn"** t? ""TWing •* *****
cies leu than Wracydes per second » time c/e«ttact with said bath.
16. A metbod of applying a metalHwnpmn^ coating 23. Tbe nwJhod of dam M wherein said inert envi-
toatleast*p«^c/themettl«mBpnsmgsiirfsce*or „„„& * jaen whb ropect to both said wettabte sur-
a part, compnsmg the steps of: _^ frpp fft^ ^.^ metal-com^niig coating material.
(a) providing apart having at least one metal-cam- 24V Tbe in«bodflf claim I6\ claim 17, dain'18. claim
fknimff surface which o wf naMf by a metal^om- 23 «» _.•_;_ «fi ^« * •« • - M ..^ Mi«^ ^> « .. * _
. r^ • . * kSok ii«i linn i mjiii_ * c"**** "> ^^^ *l» cuum 22, or ciaun u wnerein
EI^^S^^^h^cfnSSDriiiM said inert eBvironment is selected from the group con-
~' " • "TUT™ Ku^-r. ^ fj«*«^g of mtiogcn, argon, hydrogen, mixtures thereof,
which j-n-mniU"* • ">^*«t-coin- Hihatantial "tTimiHi and partial vacuums comprising
prising ecitiiignwerialcal-«K^rfle*miiig at least JO "i2t*Si2^1LSfSSf« eUi.
oTc^DOUDddetrn^tal to wetting of said «r- J^S^fS^S^^xK^
bee. wherein at least a portion of said bathb pro- 11 c-tern 28. cla« 21, claim ft « clami 23 wherein
iccted from the formation of said at least one com-
pound using an environment which n men with
during the t"nf ppriod of its application; and, l"' fo*B*»tion of compounds detrimental to wetting
(c) conucting saidmetal-connritingsu&ce with ***» respe6* to at least the metatcomprising coating
said bath at a location whhin said bath which b material during the period of its application to each
essentiaUyfhu-^ree and which b protected by said m^lcomprismg:ntH*ce.
iamenvironnwst.airdwlKremsaidimKMenvi.40 »• The method of claim 23 wherein said men envn
ronment temperature is sufficiently low that no ronmsnt a selected from the group consisting of envt-
rtnn"fp b donf to **M imtsVcotnpp"**! sgrfrtn, • ronmcnts cnoi prising oxygen at concentrations less than
ms^4 BO damage b *HTIT to *»''T> materials adjacent about 1% by volume, carbon dioxide at concentrations
to said octal-comprising surfaces during the pro- *• ***» 10°* °y volume, water at concentrations teas
cess exposure time period. 49 tblul l°°* °y volume, partial vacuums comprising
17 The mffh"^ «*• "'•i— «* ;-^i~<~g thf additmial oxygen at a partial pressure of kas than about 0.01 atrao-
Jtep.' spheres; partial vacuums comprising carbon dioxide.
(d) permittmg said metal-comprising coating to cool Barual vacuums comprising water, and mixtures
below its solidus subsequent to its application to thereof..
laid metal-comprising surface. SO 27. Tbe metbod of claim M wherein said men envi-
18. The method of dam Wwherem said nwtal-com- ronment temperature b no higher than said metal-corn-
pi iiing surface does not fenn nrniprHnHtr which are prising bath temperature.
detrimental to wetting when exposed to said process 28. The method of chum 16 wherein said inert envi-
environment. ronment temperature b lea than about 450* C.
19. Tbe nwtbcd of claim 16 wherem said metal-corn- 3) ». The method of claim 16 wherein a flux is applied
prising surface b coated with a protective coating ;o said bath at a location not within said contacting area
which b removed upon contact with said bath. of said bath.
20. The metbod of dam 19 wherein said protective 30. The method of claim 16 wherein said coating
coating b selected from the group consisting of metal material or said surfaces are vibrated at frequencies less
comprised coatings which melt upon contact with said CO than 20.000 cycles, per second.
bath; metal comprised coatinp which dissolve m said • * • * *
-------
United States Patent
Hatertjr et al.
IIWA
pi] Patent Norn CR
HSJ Date
-------
ILS. Patent June 16,1992 sbMtiors 5,121,875
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U.S. Patent
Jme 16,1992
Sheet 2 of 5
5,121,875
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U.S. Patent Ju»u,i*92 steer a or» 5,121,875
-------
U.S. Patent
Jane 16, 1992
Sheet 4 of 5
5,121,875
Fig. 4
100000
10000
1000
100
10
\
UNCURTAINED HEIGHT
O 10.2 CM
A 7.6 CM
D 5.1 CM
I J I Ni I
OXYGEN RANGE
10
10
I I I I I
10
20
30
40
60
NITROGEN PURGE GAS FLOW/
UNCURTAINED AREA {cm* /sec/cm* )
70
-------
U.S. Patent
Jane 16,1992
Sheet 5 af S
5,121,875
OO OS
14 15 2J> 2£ 10
RMA FLUX THICKNESS (mteTOlMttrt)
Fig. 5
-------
5,121.875
WAVE SOLDERING IN A PROTECTIVE
ATMOSPHERE ENCLOSURE OVER A SOLDER
POT
This application b • division of prior U.S. application
Ser. No. 07/660.415 filed Feb. 22. 1991.
TECHNICAL HELD
This invention pertains to a wave soldering machine
and process for producing soldered connections on a
printed circuit board carrying electronic components.
BACKGROUND
Wave soldering b a common method of forming
solder joints between electronic components and circuit
traces on a printed circuit board. Electronic cornpo-
10
15
unintended, thereby causing a short: Still another n
failure of the solder to fill a metallized hole in the board
To eliminate post-soldering cleaning and false pin
testing results, no-clean fluxes and special flux applica-
tion techniques have been developed. A no-clean flux is
a flux that after solder contact leave* a tow level of
residue which b noncorrosive and nonconductive. Pref-
erably a no-clean flux contains little or no halide. but
preferably a non-corrosive, non-conductive or-
acid dissolved in a solvent such as ethanol or
Common RMA flux b a no-clean flux
a mixture of rosin (abietic acid), activator
(danetbyuunme hydreehloride) and solvent (alcohol).
Another no-clean flux b adrpic acid (1% by weight) in
ethyl or bopropy) alcohol. To avoid false pin test re-
sults, known as contact defects, no-clean flux desirably
is applied in a thin layer. The following table shows the
acuu *i
-------
5,121,875'
3 w
A protective atnatphcre under which wave solder- led to obtain the benefits of soldering machines de-
ing is performed with the benefits mentioned comprise* signed to operate under a protective atmosphere.
a non-oxidizing gas and not more than S percent oxy* It is also an object of this invention to provide aa
gen. preferably not more than 100 ppm oxygen, and economical design for new wave soldering machines
most preferably not more than 10 ppm oxygen. Nitn> 3 initially intended to operate under a protective atmo-
gen b a satisfactory non-oxidizing gas in which to per- sphere.
form the contacting with solder, and became of its low It b a feature of thb invention that only the solder pot
cost, nttrogerf is a preferred non-oxidizing gas. and the immediate space over the solder pot need be
To achieve and maintain the protective atmosphere. provided with a protective atmosphere, allowing flua-
the various operations are conducted in a long conttnu- 10 ing. preheating and cooling to be performed in air.
out enclosure or series of joined tunnels. Typical appa- It is another feature of this invention that the protec-
ratus is described in US. Pat. No. 4.921,136 to Hohner- tive atmosphere used may contain up to 3% oxygen in
lein. The protective atmosphere n introduced into the the solder contacting region.
tunnel enclosing tee solder pot and flows out through It is an advantage of this invention that the retrofh of
the work entrance tunnel and the work egress tunnel. 13 wave soldering marhmei designed to operate m air is
To restrict the escape of protective atmosphere, seal economical and speedy to accomplish.
flaps are provided in the tunnels. Toe flaps are tilted It is a further advantage that low soldering defect
open in the transport direction by a passing workpiece tales are achieved with reduced usage of flux which
and clos: thereafter. Thus Hohnerlein's fluxing, pre- ebmnates the need for cleaning of circuit boards after
hearing, solder artachinenu detachment, and cooling are 20 soldering.
under a protective atmosphere. It is another advantage of this invention that the prc-
Allematively. gas jets have been used to form gas lective atmosphere may be generated by separation of
curtains and provide gas flow barriers at specific loca- air by membrane or pressure swing adsorption, or by
tions in tumwlt us described in U.S. Pat No. 4,538.737 partial combustion of air.
Still another technique, described by Scnouten in SUMMARY OF THE INVENTIO?:
Cimiia Manufaniirinf. September 1989 pages 31-33. The invention provides a hood to enclose and pro-
has been to provide chambers mine entrance tunnel and vide a protective atmosphere over the solder wave in
the egress tunnel. Boards pass intermittently through the solder pot of a wave soldering machine while kav.
the chambers which open and close. Within a chamber. 10 ing the other operative areas exposed to a non-protec-
when closed, a vacuum is drawn. The chamber is then live atmosphere. By non-protective atmosphere is
filled and flushed with a protective atmosphere. This meant any gas mixture having an oxygen concentration
process is repeated allowing the oxygen content in the of, or oxidizing capability equivalent to, 3 volume per*
soldering zone to be kept b-low 10 ppm. The protective cent or greater, an example being air. The hood has an
atmosphere used is nitrogen. JS opening for an inlet on one side and an opening for an
Many wave soldering machines designed for use in outlet on another side for the passage of a circuit board
air are in operation in industry. Despite thr benefits of conveyer over the solder wave. Optionally a short duct
soldering under a protective atmosphere, it is difficult extending from a hood side may be provided for a hood
for a circuit board manufacturer to justify the replace* tnki o outlet. The lower extremity of the hood fits
meni of an existing machine designed to solder in air 40 around and is sealed on three sides to the upper extrcm-
with a new machine designed to solder under a proiec- hy of the solder pot by an ebmomeric seal. The remain*
tive atmosphere. The operating savings that might be. htg side of the hood carries an elastomeric sea! and buns
realized would take several years to off-set the cost of up against an upright bulkhead having it* tower extrem*
•toe new machine. hy immersed in the solder and seated to the inside watts
An alternative to a new soldering machine designed 43 of the solder pot. The elevation of the pot b adjustable
to solder in a protective atmosphere is to retrofit an while the sealing b maintained. Also the pot and its
existing machine so that it can be operated in a protec* bulkhead may be withdrawn laterally from under the
tive atmosphere. Heretofore, wave soldering machines hood.
initially designed to solder primed circuit boards under Air b restricted from entering the inlet and outlet
a protective atmosphere have provided a protective 50 openings of the hood by curtains of thin solid material
atmosphere for all the functions of fluxing, preheating. cut into vertical strips. The curtain material b ekctri*
contacting with solder, separation from solder and cool- caUy conductive to avoid the build up of static charge
tag of the board. It has been believed that a protective by rubbing on a ctrcttit board as it passes through the
atmosphere for all these functions was necessary to curtain.
achieve the benefits of soldering in a protective atmo- 95 Protective atmosphere b introduced by one or more
sphere as enumerated earlier. However, to provide a distributors under the hood. A preferred embodiment
protective atmosphere for all these sections of a conven- uses three gas distributors. One distributor b located
tiona) air soldering machine b significant in terms of directly over the solder wave and over the path of the
cost, additional complexity and retrofit time. conveyer. Another distributor'»located on, the forward
Thus there b a need for an apparatus for retrofitting 60 aide of the solder wave under the path of the conveyer.
an air soldering machine which minimizes the amount The third gas distributor b located on the rearward aide
of additional installation required. A method and appa- of the solder wave under the path of the conveyer. The
rani* requiring a protective atmosphere only over the distributors are porous tubes of sintered metal allowing
soldering ponton of thr machine itself would be very the protective gas to be introduced in a laminar flow.
attractive. 65 Around the pump shaft which produces the solder
It ban object of this invention to provide a method wave b a cover with its lower extremity extending into
and apparatus whereby existing wave soldering ma- the solder in the pot to form a seal. Outside the hood.
chines originally designed to operate in air are retrofit- over the inlet opening and the outlet opening are cotlec*
-------
5.121,875
5 6
tor ducts for collecting the exhaust gas emanating from ponion of ibe shaft b driven by a motor or by a belt. To
the hood through ibeie opening*. The process employs prevent the ingestkm of air into the solder around the
a no-clean flu and allows up to 5% oxygen content in pump shaft IS. the shaft is provided with an inverted
the protective atmosphere. It products low levels of cup-shaped cover. The lower, open ponion of the cup is
soldering defects on circuit boards, low levels of pin 5 immersed in the solder to provide a seal. An inlet is
testing defects and etiaiinatesposi-soldehng cleaning of provided for a protective atmosphere to be supplied
boards. under or into the cover. A small hole is also provided in
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an overall view of a soldering aacame 10 vine (not shown).
equipped with the apparatus provided by this invention. A vertical bulkhead 26 located towards the rear of
FIG. 2 is a side view of a cross-section taken through the solder pot has its lower edge immersed into the
the center of the hood provided by this invention with solder. The bulkhead tide edges which extend into the
the solder pot partially withdrawn from wader the solder pot are scaled by an dastoneric material to the
hood. • 15 inside walls of the solder pot. The bulkhead has a veni-
FIG. 3 is a front view of a cross-section of the hood caJ front extension 2S.
and toe upper ponion of the solder pot. Over the solder pot 10 ban enclosure or hood 30 for
FIG. 4 is a graphical representation of the oxygen retaining a controlled or a protective atmosphere over
concemruion in the protective atmosphere under a the solder pot The hood has a fust or front side 32
hood fabricated pursuant to this invention as a function 30 facing where an operator usually would stand, a second
of inen gas flow and uncurtained opening heights. or entrance side 34 facing the advancing conveyer, a
FIG. § b a graphical representation of the effect upon third or exit side 36 facing the retreating conveyer and
solder bridging of oxygen concentration in the zone of a fourth or rear side 3$ opposite the front side 32.
detachment of the workpiece from molten solder. On the entrance side 34 of the hood is an opening 40
*
EMBODIMENTS transporting circuit boards passes in an upward inctina-
Showrt in the figures are the pertinent elements of a tion through the entrance in the hood, over the solder
wave soldering machine equipped with a preferred wave and emerats through the exit in the hood. Option-
embodiment of this invention. The machine comprises a 30 ally the entiaace and/or exit for the boarris may include
frame (not shown) on which is mounted a conveyer 2 a shon duct (not shown) extending from the hood side.
for transporting printed circuit boards 4. After being The tower extremities of the front side 32. entrance
loaded with a circuit board, the conveyer carries the side 34 and exit side 36. except for the conveyer en-
circuit board through a flc\ applicator 6 which is in an trance 40 and exit openings 42, fit around and are sealed
ambient air atmosphere. 35 to the outside upper extremities of the solder pot 10 by
Flux for use in this invention b no-clean flux. A pre- an elastomeric sea) 44. The rear side 31 of the hood
ferred no-clean flux b 1% by weight of adipic acid carries an elasiomeric seU 46 and buns against the front
dissolved in ethanol or bopropanol. vertical extension 21 of the bulkhead 26. The solder pot
In practice, the flux b applied to the bottom of the with the bulkhead b movable vertically without break-
board by common techniques to provide after the evap- 40 ing the seals to adjust the elevation of the pot. The
oratfoa of solvents a layer with a thickness of 4 microns solder pot also can be withdrawn rearwards from under
or less, preferably 2 microns or less. The use of a flux the hood to facilitate maintenance.
allows soldering materials with poor wetabUHy and The top of the hood has a polycarbonate window <8
solderability. such as oxidized copper, and allows good for viewing of the solder wave. One edge of the win-
filling with solder of plated or metallized notes in the 43 dow b attached to a hinge allowing the window to be
circuit board. With the thin layer of no-clean flux used opened. Edges of the window when closed are sealed
in this invention, cleaning of boards after soldering b by an dastomeric gasket. The front side 32 of the hood
unnecessary m most cases. also has a polycarbonate window SO for viewing of the
The conveyer 2 next passes the circuit board over a depth of solder contact by the circuit boards into the
preheater • where the board b heated in an air anno- 50 solder wave as they pass across the wave. Poiycarbon-
sphere to a temperature between 70* C. and the meltmg ate window material b selected for its lightness, non-
point of the solder used. Typically the preheat tempera- braakabiUty and machmabUity. The totter property al-
ture b 100* C to 160*C The flux solvent b evaporated lows the Polycarbonate to be drilled to provide holes
upon reaching 70* C m the preheater. for attachment to supporting structure.
Next on the machine frame in the line of travel of the 93 The useabihty of polycarbonate, which softens at a
conveyer b an often solder pot 10 or tank. While the temperature of 140* C. b surprising considering the
process b not touted to a given solder composition, a proximity of the polycarbonate window to the high
solder alloy typically used b 623% tin. 37% lead and temperature solder. White not wishing to be held to this
0.3% antimony by weight. Solder bath temperatures explanation, the laminar introduction of protective at-
range typically between 190* and 300* C. most typi- to mospbere apparently results in low transfer of heat from
eally between 240* C to 260* C. the molten solder to the window.
The solder pot 10 has a-generaUy rectangular or "L" Within the hood, the atmosphere b controlled. The
shape when viewed from above. The pot contains mol- attachment of a circuit board to the solder b performed
tea solder 12. a means 14 for pumping the solder into a ma protective atmosphere. A protective atmosphere b
wave and a wave flow guide 16. The pumping means 14 63 cc«nptbedofanofHOxidizinggasandnotmorethanS%
comprises a shaft II partially immersed in the solder. oxygen by volume, preferably not more than 100 ppm
The immersed portion of the shaft has an impeller 20 for oxygen and most preferably not more than 10 ppm
pumping the molten solder. The uaimmened upper oxygen. The non-oxidizing gas must have an oxygen
-------
5.121,875 ';
7 8
content MM f rener than the oxygen level daired in the molten wider and during detachment from the wider.
protective atmosphere. Preferably the tuMvoxidizing Thu» the oxygen concentration in the detachment re-
gas has not more than one-half the oxygen concentra* gkm can be established independently at an optimum
lion desired in the protective atmosphere. level to obtain a minimum bridging rate for a given flux
Nitrogen is a preferred non-oxidizing fa* because of 3 composition and flux layer thickness. For example.
its low cost and availability. Other gases also useful for RMA flux 3 microns thick yield* tow bridging rates
this purpose an carbon dioxide, argon, water vapor, with oxygen concentrations of 5 to 21%.
hydrogen and other non-oxidizing gases and mixtures with a protective atmosphere over the solder sur-
thereof. Optionally, gaseous formic acid or other reac- ttcn, BO oxide layer forms on the solder surfaces.
live gas. ifc, other gaseous mono-caitoxyUc acid, nay 10 Hence flowing solder surfaces forming the wave art
be supplied with, or introduced into, (be protective gas susceptible 10 attainment of hood gas as minute bub-
in concentrations of lOppato 10% by volume, prefer* btet -r^ bubbles rise to the surface of the solder and
My 100 ppm to 1%. and most preferably 300 ppm to bn« rekasing minute frajmenu of soWer into the pro-
5.000 ppm. The added reactive gas removes oxides tectrve iipwiphffrf. These fragments form minute
which msy not have been removed by the flux from the IS ipheresorbaUs,mtheorderof0.2to05minindimme.
oietaliwiiionionsoftheboixdortbecomiKMiemieads. ^ |fci| mv^ throughout the atmosphere under the
Addittonaliy.sttCh reactive gases allow a higher ^oxygen ^ ^ depoA „ .,, ^p^ ^^^ p^^^
content m the protective atmosphere without deteten- brushing removes the balls. Downward solder flows
ous effects. Thus nitrogen conuJnmg ftom ttOlto 5* from tl« wave m faovkted with a guide or chute to
by volume of oxygen, as obtained from air by tneav 20 ^vce egtnianent of gas into the soMer
branesefuraticm.isiisaMetoprovideapiDtecirveatnio. preferraWy gas is supplied at a fanned rate to issue
sphere. j^ |w, djHributon j, a laminar flow. Laminar flow is
* here ' Usuall thTdetachmem b * " eonsidered to exist when the root mean square of ran-
Gas. 10 pmvde the desired atmosphere is preferably 30 1*™"°* • *•«« «««Ph"« which mmmuzet the
mtrodiicedufidertheboodthroughdistribiiionmone. »«"»*•! °f 5**1? "* {"TtS?* <**"****
two or preferably three locations. The distributors are Menwnration or air through the hood opciungv
porous, sintered metal tubes having a diameter of 10 mm ^pooa^ itower/*""Bty *** my te * W" ™
and a length approximately equal to the length of the Ule "PP6* distributor (above the conveyer), and a higher
hood inlet and outlet openmgTThey have a pore size of 33 *•*» £» *"» **to**r distributors Cbelow the con-
about 0.0005 mm to 0.05 mm. preferably 0.002 to 0.005 ***«>• T** «*bw densny g« will occupy tbehood
mm ' space mostly below the conveyer and the tower density
I*ch distributor extends horizontally normal to the f« «be hood space mostly above the conveyer. Such
direction of travel of the conveyer!. The first dtstribu- «* * •*«** of different denstoes reduces the infiltration
tor S2 in the direction of travel of a dram board is 40 of w into the hood allowing lower levels of oxygen
located below the conveyer in front of the solder wave. concentration to be achieved with tower overall con-
The second distributor 54 is located over the conveyer sumption of supplied gases.
ewer the solder wave. The third distributor Mis located The inlet and outlet opewnn 40. 42 to the hood are
below the conveyer after the solder wave. preferably rectangular and are provided with curtains
The two lower distributors 52. 56 are each camilev. 49 *• of a solid material to restrict air from entering the
ered in a horizontal attitude from respective vertical gas bood. The curtains are a thin, flexible material cut into
supply tubes which enter through and are supported vertical strips to mmmiie the drag forces exerted on
frmthetopofthebulMieadHandaieiidlmizontaUy ««J electiiMl components as they enter and exit through
under the bulkhead extension »- The depth of penetra. <»«e openings. Preferred thidmessrs range from 0.1 to
tion of each gas supply tube is adjustable allowing each SO 0-2 mm. Overly thin curtains are Mown open by the
tower distributor to be positioned below the top edge of exhaust flow. Overly thick curtains displace compo-
the solder pot and close to the solder surf ace. The upper »*»«* from desired positions on the cucuh board.
distributor Mis supported in a liorixontal atthnde by a To m>wid»buiM up of stalk charge by rubbing of the
gas supply tube entering the top of the bood. curtains on the circuit boards, the curtain material is
With the hood enclosing only the solder pot. the SS electrically conductive and electrically grounded. A
hood b so short thai the leading portion of a circuit static charge may destroy the functionality of electrical
board may contact the solder wave white the trailing components on UK board.
portion protrudes from the entrance opening. Thus the In addition, the curtains do not shed fibers onto the
first and second gas distributers 52. 54 mainly supply arcuit board, are resistant to chemical attack by the flux
gases providing the atmosphere for the bottom and top to and solder fumes, are tolerant of temperatures to 265* C.
of an entering board and attaching to the wave. Simi- and withstand physical brushing to remove the minute
larly. the leading portion of a board may protrude out of solder balls which deposit in the enclosed soldering
the exit opening white its trailing portion is m the solder environment. A suitable material is silicon* rubber
wave. Thus the second and third distributors 94. 56 loaded with graphite fibers.
mainly supply gases providing the atmosphere for the A3 In the apparatus embodiment described, a circuit
top and bottom of a leaving board and detaching from board detaches from the solder wave in a protective
the wave. This configuration allows different oxygen atmosphere and immediately begins 10 cool. Because of
coDcemnbons to be achieved during attachment to the the shortness of the bood, a board leaving the wave
-------
5,121,875
9 10
quickly emerges from the eiit opening in the hood nd In * hood configured pursuant 10 this invention, bav-
coolsinair. ing intel and cut openings *0.7 em wide by 10 3cm high
Using • tow-residue, noncorrosive. nonconductive obscured with strip curtains through which circuit
flux allow* pon-soldering cleaning to be obviated. Eke* boards were conveyed. 1 1 normal cubic centimeters per
trica! inspection, is required is performed upon the 3 second of nitrogen (having not more than 10 ppm of
cooled boards with a low incidence of contact defects oxygen) per square centimeter of hood opening distrib-
(fabv open measurements). oted tinder the hood ff"*""«~«'« oxygen concentration
In view of the use of a sbonbood allowing a circuit in the hood at 100 ppm. A normal volume of gas as used
board attaching or detaching from the sower wave to htiriu df noigs an aiMHiiiit of gf* TIT*** to the volume of
protrude through a hood opening, it is surprising that I0 the gas at 25* C and i atmosphere. Benefits of protec-
the benefits of protective atmosphere soldering an icd* tive annosphere soldering are achievable in hoods eon-
ixable, and particularly with reasonable supplied gas KgattA pursuant to tins invention with non-oxidizing
Hows. This surprising result n attributed m varying consumptions ranging from 5 to SO normal cubic
degrees to the c^auu, U* suppbed gas dmnbutor eeatiaeun ^^ „,,.« ««„»«„ of hood
configuration, the gas distributor locations, and the "
o exhaust gis Witb "* ""^ over the mkt and outlet opening.
menu since, in most instances, it has insufficient oxygen EXAMPLE I
for respiration and contains noxious flux fumes. A col- ^^ _ .
lector is a U-shaped duct with hs openmc facing the „ * ". *** rfbne««' «* operated in accordance
hood opening. Alternatively, a collector nay comprise * wllb.Uw mv**™ ^ "" «"«« and «u
a tube with perforations facing the hood opening. Each openings ««" «°-7 em wide by 102 cm high. The hood
collector leads to its own closed exhaust duct «. ft to wa» P0*!" *«• «trogen «"» *» oxygen content of
earn away the collected exhaust g«~ Optionally. abcmt I ppm. The nitrogen was initially at room temper-
collecion are additionally or exclusively provided „, «ure •"«« the «older *»ve «** « 260' C. The oxygen
along the bottoms of the hood openings. ***** over *« *older *»* ** measured versus nitro-
ln each exhaust duct is a valve «, 70 to control the fen flow rate for different levels of uncurtained opening
amount of exhaust gas which is collected by hs com- height Uncurtained opening height is the distance from
spending collector. By adjusting the valves in the the bottom of the curtains to the bottom of an entrance
closed ducts leading from the collectors, the exhaust „ or exit opening. The openings often have a significant
flow captured by each collector may be controlled. By uncurtained height in order to prevent the jostling of
this means the distribution of gas exhausting through ' tall unstable parts.
the hood inlet opening and through the hood outlet An advantage of this invention is that tow oxygen
opening may be controlled to a large degree: The ad- levels can be obtained even with relatively large uncur-
justment of the valves in the exhaust ducts may be used 40 tained opening heights. Thus circuit boards with tall
also to counter a pressure distribution created outside unstable parts can be processed without resorting to
one or both of the openings in the hood. Such a pressure mechanical doors which must open and shut to prevent
uistribution may be a draft created by a fan which may «r infiltration.
biou on. across, or away from one of the openings. |n order to omit oxygen levels in the hood to a de-
A soldering machine originally designed with fluxer, 45 ^red maximum level, the non-oxidizing gas flow per
preheater and solder poi to operate in air usually has a „& ^e, of uncurtained opening must have a certain
liftabie cover over these components. Tne cover usu- „„„,,„, v^ na 4 thow, the mytga fevei, ^
ally «. provided with at ta« one exhaust port mam- «rved versus sillied g«s flow per unit are* of uncur.
tuned at a slight vacuum to draw off noxious fumes ttmed ope^xtg (m 3 diflefcnt uncurtained heights. IOJ
«*n«ted mthae operations. Hence when a protective 50 cm, 7.6 cm. and S.I COL Tne uncurtained heights were
atmosphere hood is retrofitted over the solder pot. it is
not obvious thai exhaust collectors over the hood open-
• *
have sufficient capacity and is not appropriately located 33
10 withdraw tts gas difcharcet from the hood. u Sf ^^ ffm oj.j
ine |ti£icii44l epvOv***1**1* includes several safety
features. A safety shut-off valve operated by a solenoid . Vfftr Umu ffm O}»<«a/j)10
is provided in the protective gas supply line. This shut-
off valve is maintainfd rlosed under twoconditions One to where
k when a contact switch irnif i that the top window on •^ g ^ fjg^ pg, mfa uncurtained area in normal
the hood is open. Another is when a differential ores- ^pic centimeters per second per square centimeter of
sure sensor determines that the pressure tn the exhaust uncurtained orming By uncanained opening is meant
-------
II
5,121,875
The above empirical relationships can to rewritten to
yield the following relationship for calculating the total
now required for a given hood
ftl
*c
12
hid ialei aad ait openings 40.7 cm long by 10.3 em
high. Extending normally from each hood opening for
23 cm and mtegnl with the hood was a sheet metal duct
cross-tection identical to the opening. At the end
,.,,,.1, tfuct pBojpjetely covering iu opening was. a
ter that varies between 40 and 60. The units for "A" are
normal cubic centimeters per second per square centi-
meter. "B** is the tfcul unrunamrd area in square cenb-
"Ppm Oi" is the difference between the maw-
I0
over the solder
tilers per second of nitro-
aot more than 10 ppm oxygen. This
the oxygea concentration in the
mum wygaleveJ desired ai the solder wave and the
oiygen content of the supplied gas. "C*k the nitrogen
flow rcqiiired when the tnicwiained area is zero. "C" is
about 2jOOO normal cubic centimeters per MCTBfJ for
reasonably tight hoods.
The values for "A~ and *^ given above ar suitable
for all gases with a denary whbjn 10 percent of that of
nitrogen. Low density gasses such as hydrogen will
have larger values for the parameters "A" aad "C*.
High density gases such as carbon dioxide and argon
will have lower values by about one-half for the paranv
eten "A" and "C".
An alternative method for estimating the gas flow
required when the uncurtained area is small or is not
known is to use the relationship:
wav«iiBo^ihebOOTCOBveycraiidadawtca 1.57 nor-
mal users per arfond of nitrogen contamiiig. levels from
0.01% 10 20% oxygen at desired m the several test runs.
A sheet metal deflector directed this flow at the region
when boards detached from the solder wave. A probe
m this detachment region measured the oxygen conceit-
traboa. After detachment from the solder, boards
emerged through the exit opening in the hood and
cooled in air.
The top of the hood bad a polycarbonate window
above the solder wave for viewing the wave. The win.
dow did not soften or "g Its outside temperature WAS
about 40* C
Result* of the tests are depicted graphically in FIG. S.
-E- ban empirical parameter. For nitrogen and gases »
with a density within 10% of nitrogen. TT has a value
between 3 and SO cm Vsec/cm'.-E" preferably bin the
ranee of S to 20 cmVsec/cm1. "Total opening area" is
theiun>ofthecuTUinedanduncurun»edare.ofboth
the entrance and exit and any other opening. M
Low density gases such as hydrogen will have larger
value* for ~E". High density gases such as carbon dwx-
Ue and argon will have lower values by about oiwbalf
for the parameter "E~-
Another alternative method for estimating the gas *>
flow required when the opening area is not known is:
« « *
*
were obtained.
However, with a
ery tow bri
flux thirknrn of 2J microns or
da^gimtes of one per board were
in the detachment
no.i*«w*i-F
„ . . .
uanempirpa«metCT.For
dga»es 45
with a density withm 10% of mtrogen. "F" has a value bomn, ^
ide and argon will have tower values by about one-half
obtained whb oxyg
«»* of 3% and 30% oxygen. A higher, but moderate
bridging rate of 6 per board was obtained wHhanoxy-
gen concentration of OJ* in the detachment sone.
For all three of these oxygen concentrations tested,
the number of open defects including unfilled holes was
sere per board. With the low RMA flux thickness used
of 2J microns, the rate of contact defects expected m
electrical testing was tow.
Simitar experiments without any flux produced a
r«e of 7 |w board, sevefii open defects per
bomn, ^ bote ^^ gt^n., exeerimentt usini
I% *** S» •*» «teolK4 ^mBedTpwduce a
m the detachment tone of from
EXAMPLE 2
Circuit boards with 120 closely spaced potential
bridging shes were fluxed with a spray fluxer. The
applied flux was MnOr.de 7M manufactured by Hi-
Grade Alloy Corp. East Hazelcrest. OL Hi43nde 7M is
an RMA flux which leaves noncorrosrve and noncon-
ductive rendues The m**^ww of flux arfrftfd to ***** cir*
out boards was controlled by varying the duration of
the spray. The thickness of the flux was calculated from
the weight of the flux deposited on the circuh board and
the density of thf flm (08 gm/cc). The circuit boards
were then passed over a preheater which heated them
to about 70* C. in the air.
The boards then entered a solder pot hood with a
general configuration as described earner. The hood
85
40
65
est thicknesses of no-clean flux, allows wave aolderiag
^ _•"*•*!. «MI.of •^d?*» •"*"""SL <|^BCti'
«»w»ation of cleanag. moderate consumption of pro-
tecnveatmoaphere g«t and low apparatus c«t.
Although th^mvenuon^as been «»e«erU»ed with ref.
e|en**ito specific embodtmmts as examples, it wiu be
appreciated that to is intended to covn all modiliratiofts
•** eouivmlaiu whhin the scope of the appended
ebons.
What is claimed i*
1- A method for wave soldering metal comprising
surfaces on a printed circuit board, said method corn-
prising:
(a) applying no-clean flux to the board in air;
(b) preheating the board in air;
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13
5,121,875
14
(c) attaching the baud to • lolder wave in a proicc-
live atmosphere;
(d) detaching the board from the lolder wave in a
controlled atmosphere;
2. The invention as in claim 1 wherein the flux is
applied to provide a layer efflux not more than 4 mi-
crons thick after evaporation of solvents from the flux.
J The invention as,in claim 1 wherein the flux com-
prises a di-omic acid in solvent.
4 The invention as in claim 1 wherein the flax com-
prises adipk acid in a solvent.
5.Tl*»ventiei»asmcJaimlwl>ere«thefliaoom-
pises adipic acid in ethyl alcohol or nopropyl alcoboL
tThetoveBtionasmelatolwbe«miheboanlis
Cheated to a tempmttina the nage from *TC to
the melting porat of the tower nsed.
I0
17. The invention as in claim 1 wherein said atmo-
spheres an provided by fupplying carbon dknide or
argon gas or nwtum thereof coniararag not men than
one-half the maximum oiygen concentration desired in
aaid atmospheies at a flow rate (in normal cubic centi-
neten per second) of between 2.000 and 20.000.
M. The invention as in claim I wherein said steps for
attaching to and detaching from a solder wave are per-
formed by adorning the board through an inlet imp a
*°°& enclosing not more than a solder pot containing
the »eJdcr wave anacaing the baart to and dctachmg
the board from the aolder wave wilhm said hood;
egieasmg^ bosrt through an exit in aaid hcod.
»• Tte tnvwtwn « nctoim 1 kwbena said atmo-
.
«
iefionof anactan«t
bo«dtohe
comprise* a non-uuduing gas and not more than J%
bv volume
gas and not mon than 100
wherein theatmoiphere
j,:mnvention « m claim II wherein said atmo-
n
compraes a rwn^wdtung gas and not more than 10
ppm oxygen oy volume.
10. The invention as m claim 1 wherein said atmo- 3,,
sphere for atu« .nng to the sower wave compraa a
non-oudutng gas and not more than 5% oxygen and
laid atmosphere for detaching from the solder wave
comprises a non-oxidizing gas and from 5 to 10% oxy.
**"* __ , . ........ M
II. The invention as m claim 1 wherein said atmo*
ipnere for attaching to the solder wave comprises .-
non-oxidizing gas and not more than 100 ppm oxygen
snd said atmosphere for detaching from the solder wave
comprises a non-oxidizing gas and from 5 to 10% oxy- 40
lm-
12. The invention as hi claim 1 wherein said atmo-
rphere for attaching to the solder wave comprises a
x>n-oxidizing gas and not more than 10 ppm oxygen
utd said atmosphere for detaching from thetowerwave 4$
ximprises a non-oxidizing gas and from 3 to 10% oxy-
(en.
13. The invention as in claiml wherein the protective
itmnsphere for attaching to the solder includes a mono-
arboxylk acid. 90
14. The invention as in claim 1 wherein the protective
ionosphere for attaching to the solder includes formic
cub
Bni
sam
per tccwid) of between 5 and
^ ^m^f*^ ^ uncurtained areas (in square
ood enttince awl exit and any
penings tndudmg leakage openmg*
* *^ ^ ^ "^
21 The invention as in "'-<-• It wherein said atmo-
^^^j „, f,^)^^ ^ wpplying carbon dioxide or
"fgon gas or mixrores thereof containing not more than
one-half the maximum oxygen concentration desired in
IS. The invention as in claim I wherein the atmo-
inhere maintained above the board has a lower density 93
ban the atmosphere maintained below the board.
1». 'I he invention as in claim 1 wherein said atmo-
pberes an provided by supplying nitrogen gas contain-
ng not more than one-half the maihnum oxygen con-
ientration desired in said atmospheres at a flow rate (in 60
tormal cubic centimeters per second) of between 4.000
ind 40.000. "
at a flow rate (in normal cubic ceati-
per s«x»d) of bwween Z5 «d 25 um» the
curtained and uncurtained anas (in square centimeters)
of both the hood entrance and exit and any other uncnr-
tamed openings including leakage openings in said
hood.
23. The invention as in claim 18 wherein said atao-
spheres an provided by supplying nitrogen gas at a
flow rue (m normal cubic centimetm per second) of
7/XK>p|OT^gr«»'ftH40aml
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87
APPENDIX D
SOLDER FLUXES AND PASTES EVALUATED
BY NORTHERN TELECOM
Following extensive research, Northern Telecom
has chosen "no clean* assembly materials as the
preferred alternative to the use of CFC-113
solvents in the manufacture of printed circuit
assemblies. In the course of its three-year program
to switch to "no dean," many solder fluxes and
pastes were evaluated. The following fluxes and
pastes meet Northern Telecom's material
requirements including Bellcore standard TR-
NWT-000078, issue 3. Provision of this
information in no way constitutes endorsement of
a supplier or supplier's material. Manufacturers of
printed circuit assemblies and electronic products
should conduct their own investigations of
soldering fluxes and pastes to ensure compatibility
with their processes.
compatibility with the solder mask used on the
printed circuit board. Table 2 includes the solder
masks that were found acceptable with each of the
pastes.
No Clean Solder Fluxes
Table 1 lists the "no clean* solder fluxes which,
through lab testing and process application, meet
Northern Telecom's material requirements when
tested with specific solder masks. The table also
lists the compatible masks for each of the fluxes.
These solder masks also meet Northern Telecom's
material requirements. Note: not all
combinations of fluxes and masks were tested.
Solder Pastes
Table 2 lists the solder pastes which, through lab
testing and process application, meet Northern
Telecom's material requirements including Bellcore
TR-NWT-000078, issue 3. Before a solder paste is
used in assembly, it must be tested for
-------
88
TABLE t
LIQUID SOLDERING FLUXES
No Clean Flux
Supplier
Alpha Metals
Alpha Metals
Fry Metals
Product
SM387
Teleflux
NR 100A
Compatible Masks
Supplier
PC
DuPont
DuPont
DuPont
Enthone
Talyo
PC
Taiyd
Talyo
Taiyo
DuPonl
DuPont
DuPonl
Enthone
Probimer
PC
Taiyo
Taiyo
TaJyo
DuPonl
DuPont
W.R. Grace
Product
401
930
Valu 8030
Valu 8200 series
DSR 3241
PSR-4000
401
222-401
222-401
PSR-4000
8130
930
Valu 8030
DSR 3241
52
401
222-401
222-404
PSR-4000
Valu 8030
Valu 8200 series
CM -1000
No Clean Flux
Supplier
Hi-Grade
Kester Solder
Kester Solder
Product
3549-HF
924 FB
9SOE
Compatible. Masks
Supplier
Taiyo
Taiyo
Probimer
PC
PC
Taiyo
Taiyo
Taiyo
DuPont
DuPont
DuPont
Dynachem
Probimer
W.R. Grace
Dexter Hysol
Coales
PC
Enthone
Taiyo
Probimer
DuPont
Coates
Probimer
Product
222-401
PSR-4000
52
401
501
222-401
222-404
PSR-4000
8130
930
Valu 8200 series
EPIC SP-100
52/52M
CM- 1000
SR1000
IMAGECURE
401
ESR 3241
PSR-4000
52
Valu 8200 series
IMAGECURE
52M
-------
89
TABLE 1
UQUIiJ SOLDERING FLUXES
No Clean Flux
Supplier
Kester Solder
Kesier Solder
Multicore
Solder
Product
923
951
X33/03
Compatible Masks
Supplier
PC
Taiyo
Taiyo
Taiyo
DuPonl
DuPont
DuPont
Enihone
Probimer
Probimer
W.R. Grace
Dexter Hysol
Coates
PC
PC
Taiyo
Taiyo
Enthone
Probimer
W.R. Grace
Dynachem
Dexter Hysol
Coates
DuPont
Taiyo
Taiyo
Probimer
Product
401
222-401
222-404
PSR-4000
8130
930
Valu 8200 series
DSR 3241
52
52M
CM-1000
SR1000
1MAGECURE
401
501
222-401
PSR-4000
DSR 3241
52/52M
CM-1000
EPIC SP-100
SRIOOd
IMAGECURE
Vacrei 8130
222-401
PSR-4000
52
No Clean Flux
Supplier
Lonco
Multicore
Solder
Product
11W
X33
Compatiblo Masks
Supplier
PC
Taiyo
Taiyo
Taiyo
DuPont
DuPont
DuPont
DuPont
Enthone
Probimer
W.R. Grace
Taiyo
Taiyo
Probimer
Probimer
PC
Coates
Product
401
222-401
222-404
PSR-4000
8130
930
Valu 8030
Valu 8200 series
DSR 3241
52
CM-1000
222-401
PSR-4000
52
52M
501
IMAGECURE
-------
90
TABLE 1
LIQUID SOLDERING FLUXES
No Clean Flux
Supplier
MuMicore
Solder
Mulilcore
Solder
MuUicore
Solder
Product
X33/04
X32/FQ1
X32/FM
Compatible Masks
Supplier
PC
PC
Talyo
Taiyo
W.R. Grace
DuPont
PC
Taiyo
Taiyo
Taiyo
DuPont
DuPont
DuPont
Enthone
Probimer
W.R. Grace
PC
Taiyo
Taiyo
W.R. Grace
Product
401
501
222-401
222-404
CM- 1000
Valu 8200 series
401
222-401
222-404
PSR-4000
8130
Valu 8030
Valu 8200 series
DSR 3241
52
CM-1000
401
222-401
222-404
CM-1000
No Clean Flux
Supplier
Mullicore
Solder
Product
EA0037
!
Compatible Masks
Supplier
PC
Taiyo
Taiyo
DuPont
Enthone
W.R. Grace
Product
401
222-401
PSR-4000
Valu 8030
DSR 3241
CM-1000
V
-------
91
TABLE 2
SOLDER PASTES
No Clean Flux
Supplier
Alpha Metals
f
Alpha Metals
Kester Solder
Kester'Solder
Product
LR4001
390-DH4
243F
243
Compatible Masks
Supplier
Taiyo
Taiyo
Probimer
Taiyo
Taiyo
Probimer
PC
Taiyo
Taiyo
Taiyo
DuPont
DuPont
DuPont
DuPont
Enthone
Probimer
W.R. Grace
Taiyo
Taiyo
Probimer
Dynachem
Product
222-401
PSR-4000
52
222-401
PSR-4000
52
401
222-401
222-404
PSR-4000
8130
930
Valu 8030
Valu 8200 series
DSR 3241
52
CM- 1000
222-401
PSR-4000
52
EPIC SP1-00
No Clean Flux
Supplier
Indium Corp.
Mullicore
Solder
.
Multicore
Solder
SCM
Product
SMQ51
NC40
RM-92
X63PNCR
Compatible Masks
Supplier
PC
PC
Taiyo
Taiyo
DuPont
DuPont
Enthone
Probimer
Dynachem
PC
Taiyo
DuPont
Coates
Probimer
PC
Taiyo
Taiyo
DuPont
DuPont
Probimer
Coates
Taiyo
Taiyo
Probimer
Product
401
501
222-401 :
PSR-4000
Valu 8030
Vacrel 8130
DSR 3241
52/52M
EPIC SP-100
401
PSR-4000
Vaiu 8200 series
IMAOECURE
S2M
401
222-401
PSR-4000
Valu 8030
Valu 8200 series
52/52M
IMAGECURE
222-401
PSR-4000
52
-------
92
TABLE 2
SOLDER PASTES
No Clean Flux
Supplier
Multicore
Solder
Mitsui Corp.
Product
NO-
361/RM32
Senju 7U2C
Compatible Masks
Supplier
Taiyo
Taiyo
Probimer
Taiyo
Probimer
Dynachem
Product
222-401
PSR-4000
52
222-401
52
EPIC SP-100
No Clean Flux
Supplier
Mitsui Corp.
Product ;
Senju 201C
Compatible, Masks
Supplier
Taiyo
Taiyo
Probimer
Product
222-401
PSR-4000
52
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