v>EPA
United States
Environmental Protection
Agency
Research and Development
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
EPA/600/S-92/033 Sept. 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a
Manufacturer Producing Printed Circuit Boards
Harry W. Edwards and Michael Kostrzewa"
Phylissa S. Miller"
Abstract
The U.S. Environmental Protection Agency (EPA) has funded
a pilot project to assist small- and medium-size manufacturers
who want to minimize their generation of waste but who lack
the expertise to do so. Waste Minimization Assessment Cen-
ters (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 performed an
assessment at a plant which manufactures single-sided, double-
sided, and multilayer printed circuit boards — approximately
259,000 sq ft/yr. In general, circuit art work is received and
digitized. The circuit design film template is laser generated
from the digitized artwork. In addition copper/epoxy laminates
and copper foil (the inner layer's material for multilayer boards)
are cut into blank boards and layers with hydraulic shears.
Component holes are cut by drilling machines. Drilled boards
are mechanically scrubbed to prepare for plating. Circuit pat-
terns are created on the boards and foil layers with a dry-film
photoresist process and the multilayer boards are built up. The
actual copper circuit pattern is generated by a series of photo-
lithographic and plating processes. Final processing includes
legend application, routing, rinsing, electrical testing, inspections,
packing, and shipping. The team's report, detailing findings
and recommendations, indicated that the majority of waste was
generated in the plating lines and that the greatest savings
could be obtained by installing a spray rinse and electrowinning
system on the first rinse tank of the electrolytic copper plating
line to reduce both copper plating rinse water (88%) and
plating sludge (80%) due to drag-out in the first rinse tank.
' Colorado State University, Department of Mechanical Engineering
" University City Science Center, Philadelphia, PA
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cin-
cinnati, OH, to announce key findings of an ongoing research
project that is fully documented in a separate report of the
same title available from the University City Science Center.
Introduction
The amount of waste generated by industrial plants has become
an increasingly costly problem for manufacturers and an addi-
tional stress on the environment. One solution to the problem
of 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 manufacturers
who want to minimize their formation of waste but who lack the
inhouse expertise to do so. Under agreement with EPA's Risk
Reduction Engineering Laboratory, the Science 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 consider-
able direct experience with process operations in manufactur-
ing plants and also have the knowledge and skills needed to
minimize waste generation.
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
annual sales not exceeding $75 million, empby no more than
500 persons, and lack inhouse expertise in waste minimization.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers, and
reduced waste treatment and disposal costs for participating
Printed on Recycled Paper
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plants. In addition, the project provides valuable experience for
graduate and undergraduate students who participate in the
program, and a cleaner environment without more regulations
and higher costs for manufacturers.
Methodology of Assessments
The waste minimization assessments require several site visits
to each client served. In general, the WMACs follow the pro-
cedures outlined in the EPA Waste Minimization Opportunity
Assessment Manual (EPA/625/7-88/003, July 1988). The WMAC
staff locate the sources of 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 supporting tech-
nological and economic information is developed. Finally, a
confidential report that details the WMAC's findings and rec-
ommendations (including cost savings, implementation costs,
and payback times) is prepared for each client.
Plant Background
The plant produces single and multilayer printed circuit boards.
The plant operates 4,100 hr/yr to produce approximately 259,000
sq ft of printed circuit board.
Manufacturing Process
This plant manufactures single-layer and multilayer printed
circuit boards. Raw materials for board production include
copper/epoxy laminates and copper foil. Process raw materials
include both dry-film and positive-image photoresist, copper
etchant, black oxide reagents, B-stage resin, copper plating
reagents, tin plating reagents, photodeveloper, photofixer,
stripping and etching solutions, tin/lead solder, and gold-tab
plating reagents.
The following steps are involved in making the boards:
• Circuit information is received from customers as blue-
prints, films, computer floppy diskettes, or some combina-
tion of these. Circuit information received as artwork is
digitized and stored in a computer. Working film, a tem-
plate for the circuit design, is laser generated from the
customer's circuit information.
• Laminates and foil are cut into blank boards and layers
with hydraulic shears. Component holes are then gener-
ated in the blank boards with high-speed, numerically-
controlled drilling machines. Drill programs are generated
digitally and provide drilling instructions for the drilling
machines. Drilled boards are mechanically scrubbed to
prepare for plating.
• Circuit patterns are created on the board and layers with
dry-film photoresist. For the individual inner layers of the
multilayer boards, the circuit pattern is generated with
positive-image photoresist. The electrical circuit design is
transferred to the individual layers by first laminating a UV-
sensitive dry-film photoresist to the layers. An image of the
design is generated by placing a template of the circuit
over the film, exposing the film to UV light, and developing
the photoresist. Unexposed photoresist is removed, but
exposed film is polymerized and protects the underlaying
copper circuitry. Unwanted copper is removed with an
ammonia etchant. The remaining protective film is re-
moved, and exposed copper circuitry is oxidized and
cleaned. Oxidation assures good interlayer bonding be-
tween panels in the multilayer array. Fiberglass-weave
sheets impregnated with resin are placed between each
layer, and the array is heated and bonded in a hydraulic
press. Component holes are then drilled in the multilayer
panels. Further processing of multilayer boards is identical
to that of single and double-sided boards.
• The circuit pattern is generated by a series of photolitho-
graphic and plating processes. First, the surfaces are
copper plated in an electroless plating process. This process
deposits copper on all exposed surfaces, including the
surfaces of drilled holes. Photoresist is then laminated to
the board surfaces. Additional copper is electrolytically
plated on the surface circuit patterns. After cleaning, the
pattern is plated with tin to protect the copper circuitry
during subsequent steps to remove the resist film and
unwanted copper. The tin layer is removed following resist
stripping and copper etching. A solder mask is silk-screened
and thermally cured to the board surfaces prior to dipping
the boards in molten tin/lead solder. The solder layer
provides a surface for mounting electrical components.
Additional processing involves conditioning of the soldered
surfaces, cleaning, rinsing, and inspecting the finished
circuit boards. Connector tabs can be gold plated in sub-
sequent processes if requested by the customer.
• Final processing includes silk-screen application of a leg-
end, routing, rinsing, electrical testing, quality assurance
inspections, packing, and shipping.
An abbreviated process flow diagram is shown in Figure 1.
Existing Waste Management Practices
This plant already has implemented the following techniques to
manage and minimize its wastes:
• Tin plating is used to provide a protective mask for the
circuit image during photoresist stripping and copper etch-
ing. Unalloyed tin plating replaces traditional tin/lead sol-
der, thereby reducing lead contamination. Tin/lead solder
is still used as a final circuit coating.
• Bright tin plating has been replaced by matte tin plating.
The matte tin is less dense and provides a greater topog-
raphy than the bright tin. Thus, the matte tin requires less
tin stripper and generates less spent tin stripper.
• Dry film used as plating resist eliminates chlorinated sol-
vents frequently used in silkscreening operations.
Silkscreening is still used to apply wet resist solder masks
and circuit legends.
• Deburrers and scrubbers using water replace more tradi-
tional solvent-based drying.
• The water supply to the electroless copper plating, electro-
lytic copper plating, black oxide, and gold tab plating lines
has been divided so that each line has a separate supply
valve. In the past, the water supply to all of these lines
was controlled by one valve. By separating the water
supply, less water is wasted when a given line is not in
use.
• Counterflow rinses and flow reducers are used in plating
operations to reduce rinse water usage. Still drag-out tanks
are used following electrolytic copper and tin plating to
reduce contamination of subsequent flowing rinses.
• An automated plating machine is used on the electroless
copper plating line. Automation reduces excess rinse wa-
ter contamination by providing consistent residence and
drainage times.
• Loss of gold in rinse water has been reduced with an ion
exchange resin on the gold plating rinse.
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Film Application
and Development
Water to Sewer
Studge to Shelter
Spent Reagent
Batch Treatment
- Water to Sewer
- Sludge to Shelter
Electrolytic Plating,
Etching, Stripping
Solder, Routing,
Plating, Packaging
• Scrap gold, solder, and aluminum are shipped offsite for
recycling.
Waste Minimization Opportunities
The type of waste currently generated by the plant, the source
of the waste, the quantity of the waste, and the annual man-
agement costs are given in Table 1.
Table 2 shows the opportunities for waste minimization that the
WMAC team recommended for the plant. The type of waste,
the minimization opportunity, the possible waste reduction and
associated savings, and the implementation cost along with the
payback times are given in the table. The quantities of waste
currently generated by the plant and possible waste reduction
depend on the production level of the plant. All values should
be considered in that context.
It should be noted that, in most cases, the economic savings of
the minimization opportunities result from the need for less raw
material and from reduced present and future costs associated
with waste treatment and disposal. Other savings not quantifi-
able by this study include a wide variety of possible future
costs related to changing emissions standards, liability, and
employee health. It should also be noted that the savings given
for each opportunity reflect the savings achievable when
implementing each waste minimization opportunity indepen-
dently and do not reflect duplication of savings that would
result when the opportunities are implemented in a package.
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. Environmental
Protection Agency. The EPA Project Officer was Emma Lou
George.
Figure 1. Abbreviated process flow diagram.
Table 1. Summary of Current Waste Generation
Waste Generated Source of Waste
Cuposit reagents
Cuposit rinse water
Oxide/desmear reagents
Oxide/desmear rinse water
Copper plating reagents
Copper plating rinse water
Spent copper etchant
Spent tin stripper
Gold-tab reagents
Gold-tab rinse water
Spent nickel plating solution
Spent solvent (TCA)
Press cooling water
Developer rinse water
Waste photo fixer
Spent rack stripper
Plating sludge
Copper scrap (dropoffs)
Solder dross
Electroless copper plating line
Electroless copper plating line
Black oxide/desmear line
Black oxide/desmear line
Electrolytic copper and electrolytic tin plating line
Electrolytic copper and electrolytic tin plating line
Enclosed closed-loop etching machine on the
electrolytic copper and electrolytic tin plating
Two-step tin removal tanks on the electrolytic
copper and electrolytic tin plating
Gold-tab plating line
Gold-tab plating line
Gold-tab plating line
Gold-tab plating line (to remc
adhesive residue during wt
Multilayer circuit board press
Photoresist developer rinse
Photoresist and film developing
Rack stripping operation
All plating lines
Circuit board routing and,
Hot-air leveling
Annual Quantity
Generated
Annual Waste
Management Cost
22,050 gal
1,117,200 gal
38,963 gal
705,600 gal
108,800 gal
3,823,470 gal
22,330 gal
5,795 gal
$ 3,714
9,354
6,563
5,908
47,420
37,361
88,813
81,024
1 Plant personnel report no incremental cost associated with present disposal to POTW.
*Plant personnel report no incremental cost associated with present disposal in municipal waste.
e masking tape
7i/humid weather)
7
ing operations
765 gal
3,034,080 gal
165 gal
110 gal
282,240 gal
1,1 28,960 gal
30 gal
1,348 gal
1 16,900 Ib
8,575 Ib
6,500 Ib
129
1 1,804
570
980
893
3,572
O1
22,326
24,257
O2
23,230
. GOVERNMENT PRINTING OFFICE: I9M - S50-067/80172
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Table 2. Summary of Recommended Waste Minimization Opportunities
Annual Waste Reduction
Waste Generated
Spent rack stripper
Plating sludge 1
Copper plating rinse
water
Plating sludge 2
Minimization Opportunity
Use polyethylene plating racks
in the electrolytic copper plating
bath to reduce the need for
stripping solution.
Install a spray rinse and electro-
winning-system to replace the
first rinse in the electrolytic
copper plating line.
Quantity
101 8 gal
448 Ib
328, 300 gal
14,240 Ib
Percent
75.5
75.5
88
80
Net Implementation
Annual Savings Costs
$16,951 $28,300
14,453 4 17,433
Payback
Years
1.7
1.2
Plating sludge3
Oxide/desmear rinse
water
Increase drain times over the 4,450 Ib
electrolytic copper plating tanks
to reduce drag-out.
Install contact switches on the 183,750 gal
rinses in the desmear/etchback
line to reduce water consumption.
25
69
12,237
581
1 Plating sludge results from treatment of spent stripper.
2Plating sludge results from drag-out on first electrolytic copper plating line rinse tank.
3Plating sludge results from drag-out on electrolytic copper plating line.
4This figure includes copper recycling credit, increased electricity consumption, and cathode replacement cost.
1,000
645
0.08
1.1
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
EPA/600/S-92/033
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
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