&EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/M-91/021 July 1991
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for Multilayered
Printed Circuit Board Manufacturing
F. William Kirsch and Gwen P. Looby*
Abstract
The U.S. Environmental Protection Agency (EPA) has
funded a pilot project to assist small- and medium- size manu-
facturers who want to minimize their generation of hazardous
waste but lack the expertise to do so. Waste Minimization
Assessment Centers (WMACs) were established at selected
universities and procedures were adapted from the EPA Waste
Minimization Opportunity Assessment Manual(EPA/625/7-88/
003, July 1988). The WMAC team at Colorado State University
inspected a plant manufacturing multilayered circuit boards.
This complex operation has seven key elements: preparing
individual layers of boards; transferring circuit patterns to these
layers and forming copper oxide castings; bonding to form
multiple layers; applying copper (electroless plating) to ensure
electrical contact; applying photoresist to define the area on
which copper circuits are to be plated; applying copper electro-
lytically to establish circuit patterns on outer board surfaces
followed by tin or tin/lead plating to protect the circuits; and
applying solder and final cleanup after selectively removing
protective tin layers. All these elements of the manufacturing
process generate hazardous waste, e.g., electrolytic applica-
tion of copper generates sulfuric acid; propylene glycol methyl
ether; copper-laden deionized water and rinse water; ethoxylated
octylphenol; copper-free drag-out-laden water; and copper
sulfate. The plant had already instituted waste minimization
techniques; the team's report, detailing findings and recom-
mendations, indicated that additional reductions and savings,
although not as great, were still possible. The greatest reduc-
tion would come from separating liquid wastes into four streams
containing differing amounts of waste. Copper-containing
streams could be further treated and reused in process rinses
and baths. Spent process solutions could be stored for recycling
and reclaiming.
This Research Brief was developed by the principal inves-
tigators and EPA's Risk Reduction Engineering Laboratory,
Cincinnati, OH, to announce key findings of an ongoing re-
search project that is fully documented in a separate report of
the same title available from the authors.
Introduction
The amount of hazardous waste generated by industrial
plants has become an increasingly costly problem for manufac-
turers and an additional stress on the environment. One solu-
tion to the problem of hazardous waste is to reduce or eliminate
the waste at its source.
University City Science Center (Philadelphia, PA) has
begun a pilot project to assist small- and medium- size manu-
facturers who want to minimize their formation of hazardous
waste but lack the inhouse expertise to do so. Under agreement
with EPA's Risk Reduction Engineering Laboratory, the Sci
ence Center has established three WMACs. This assessment
was done by engineering faculty and students at Colorado State
University's (Fort Collins) WMAC. The assessment teams have
considerable direct experience with process operations in manu-
facturing plants and also have the knowledge and skills needed
to minimize hazardous waste generation.
•University City Science Center. Philadelphia, PA 19104
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The waste minimization assessments are done for small-
and medium-size manufacturers at no out-of-pocket cost to the
client. To qualify for the assessment, each client must fall within
Standard Industrial Classification Code 20-39, have gross an-
nual sales not exceeding $50 million, employ no more than 500
persons, and lack inhouse expertise in waste minimization.
The potential benefits of the pilot project include minimiza-
tion of the amount of waste generated by manufacturers, re-
duced waste treatment and disposal costs for participating
plants, valuable experience for graduate and undergraduate
students who participate in the program, and a cleaner environ-
ment without more regulations and higher costs for manufactur-
ers.
Methodology of Assessments
The waste minimization assessments require several site
visits to each client served. In general, the WMACs follow the
procedures outlined in the EPA Waste Minimization Opportunity
Assessment Manual (EP A/625/7- 88/003, July 1988). The WMAC
staff locates the sources of hazardous waste in the plant and
identifies the current disposal or treatment methods and their
associated costs. They then identify and analyze a variety of
ways to reduce or eliminate the waste. Specific measures to
achieve that goal are recommended and the essential support-
ing technological and economic information is developed. Fi-
nally, a confidential report that details the WMAC's findings and
recommendations (including cost savings, implementation costs,
and payback times) is prepared for each client.
Plant Background
This plant manufactures multilayered circuit boards from
thin, flat sheets of combined epoxy resin and fiber glass upon
which thin layers of copper have been laminated on both sides.
Afterthe circuit has been developed on each sheet, the multilay-
ered board is produced by stocking the sheets through a
bonding process using heat and pressure. Then the external
circuits must also be created.
As in all circuit board manufacture, the processes in this
plant are complex, but certain key elements must be described
to make the results of a WMAC assessment understandable
when they are being summarized. These are the key elements
in this plant's operations:
preparing boards of individual layers, including
the drilling of tooling holes,
transferring circuit patterns to layers and forming
copper oxide castings,
bonding to form multiple layers,
applying copper by electroless plating to provide
a continuous electrical path covering the entire
external surface and drilled holes,
applying photoresist techniques to define the area
on which copper circuits are to be electrolytically
plated,
applying copper electrolytically to establish external
circuit patterns of multiple layers, followed by tin or
tin/lead plating to protect the circuits when
extraneous copper's removed, and
applying solder and final cleanup after selectively
removing protective tin layers.
This plant had already established several waste minimiza-
tion techniques:
using dry-film photoresist to eliminate the
chlorinated solvents associated with silk-screen
photoresist;
substituting tin for tin/lead solder on a majority of
the circuit boards;
spray-rinsing circuit boards laden with copper
before bath-rinsing to differentiate rinses according
to copper concentration;
treating effluents before discharge to the sewers
by:
- adjusting pH of those free of copper, and
- ion-exchanging and electrowinning copper-
containing solutions;
air-agitating the plating tanks to improve mixing
and the rinse tanks to reduce the amount of rinse
water needed;
deionizing water to eliminate calcium and
magnesium sludge formation in a variety of tanks;
mechanically scrubbing the boards and then air-
drying them after plating and stripping to avoid
using solvent;
recirculating and filtering rinse water from the
scrubbing operations;
plastic-coating racks used in the plating operations
to reduce the amount of hazardous rack-stripping
solution needed; and
recycling much metallic waste, especially copper.
The scope and variety of these measures presented a
challenge to the WMAC's efforts to reduce still further the
emission of hazardous waste. All quantities of waste stated are
to be considered in proportion to the operational level of about
1000 printed circuit boards/wk.
Manufacturing Operations
Operating for a total of 5,148 hr/yr, this plant makes about
1000 printed circuit boards/wk, many of which are prototypes
designed according to a customer's performance specifica-
tions. One of the plant's principal strengths is its capability to
produce multilayered circuit boards, which lead to larger and
more powerful circuits compressed into compact spacing. Fig-
ure 1 presents a schematic arrangement of the manufacturing
operations.
Circuit patterns, after being transferred to each layer, are
developed by etching unprotected copper from these layers.
Individual layers, each with its specific circuit, are etched after
oxidation to ensure good bonding among them. A heated
hydraulic press supplies the compression. Electroless copper
plating ensures electrical contact whenever it is designed, and
electrolytic copper plating establishes circuit patterns on outer
board surfaces according to a prior design and after photoresist
application and development. Tin plating is applied to preserve
the desired external circuit when the exposed photoresist is
stripped away. Then the tin is removed before final application
of a solder mask and solder, and finally the last rinsing and
electrical testing are done.
Hazardous Waste Generation
The variety, interdependence, and complexity of the manu-
facturing operations in this printed circuit board plant lead to
numerous sources of hazardous waste, which vary widely in
quantity and in quality. Table 1 summarizes the principal sources,
their amounts, the management method applied, and the asso-
ciated costs.
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Board
Preparation
Cutting
Drilling
Scrubbing
Rinsing
Drying
Dry-Film
Photoresist
Positive image-
exposure
Developing
Copper Removal
and
Resist Strip
Removing copper
Neutralizing
Rinsing
Stripping
Copper
Oxidation
Cleaning
Etching
Oxidizing
Rinsing
Laminating
Pressing
Baking
Drilling
Etching
>
Electroless
Copper Plating
Conditioning
Etching
Cleaning
Accelerating
Plating
Rinsing
Dry-Film
Photoresist
Cleaning
Scrubbing
Rinsing
Negative image-
exposure
Developing
Electrolytic
Copper Plating
Cleaning
Plating
Rinsing
Tin Plating
Cleaning
Plating
Resist
Strip
Stripping
Rinsing
>
Tin Removal
Stripping
Rinsing
Scrubbing
Drying
Solder
Application
Solder masking
Cleaning
Soldering
Rinsing
Drying
Finishing and
Testing
Figure 1. Sequence of Manufacturing Operations
The principal volumes of liquid hazardous waste are attrib-
utable to rinses and drag-outs. The highest cost, however, is
associated with recycling 5085 gal/yr of ammoniacal copper
chloride solution ($19,800/yr). Many liquid waste streams incur
little or none of these costs because they involve only pH
adjustment before disposal.
Summary of Recommended Waste Minimization
At this plant, total hazardous waste management costs,
which had already been brought down to $46,880/yr by 10
separate measures, can be further reduced by $14,080/yr
(30%) on the basisof 6 waste minimization opportunities (WMOs)
identified and recommended by the WMACteam.
The greatest cost reduction would result from a proposal to
segregate four liquid wastes and, by further cleaning of some,
allow them to be reused and eventually sewered. Five of the
WMOs recommended have simple paybacks of less than 2 yr.
Cost savings to be achieved with each of the six WMOs are
summarized in Table 2, together with the waste reductions and
associated costs. All savings are calculated for each WMO
independently so that each can be evaluated on its own merits.
Actual experience, however, will probably reveal some interde-
pendence and lead to new cost-saving data. All data in this
summary ought to be considered in relation to the operational
levels stated for this plant.
This Research Brief summarizes a part of the work done
under Cooperative Agreement No. CR-814903 by the University
City Science Center under the sponsorship of the U.S. Environ-
mental Protection Agency. The EPA Project Officer was Brian A
Westfall.
The EPA contact, Emma L. George, can be reached at:
Pollution Prevention Research Branch
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
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•&U.S. GOVERNMENT PRINTING OFFICE: 1991 - 548-028/40029
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United States Center for Environmental Research BULK RATE
Environmental Protection Information POSTAGE & FEES PAID
Agency Cincinnati, OH 45268 EPA PERMIT NO. G-35
Official Business
Penalty for Private Use $300
EPA/600/M-91/021
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