&EPA
United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S-92/008 May 1992
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Printed
Circuit Board Manufacturer
Gwen P. Looby and F. William Kirsch*
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 the University of Tennessee performed an
assessment at a plant manufacturing printed circuit boards for
television sets—approximately 4.3 million sq ft of finished boards
per yr. To make printed circuit boards, the plant begins with
making screens as all printing is accomplished using silk-
screening techniques. The circuit boards undergo several op-
erations including punching, scrubbing, printing, etching, and
soldering. Finished boards are inspected, deslugged, electri-
cally tested, packed,, and shipped, the team's report, detailing
findings and recommendations, indicated that the majority of
waste was generated in the circuit board production lines but
that the greatest savings could be obtained by installing a
closed-loop cooling water system to reduce (60%) excess
water usage in the UV-light curing ovens after screen printing
and the cooling of the cupric chloride etch tanks.
This Research Brief was developed by the principal investiga-
tors and EPA's Risk Reduction Engineering Laboratory, Cincin-
nati, OH, to announce key findings of an ongoing research
project that is fully documented in a separate report of the
same title, which is available from the authors.
*University City Science Center, Philadelphia, PA 19104.
Introduction
The amount of waste generated by industrial plants has be-
come an increasingly costly problem for manufacturers and an
additional stress on the environment. One solution to the prob-
lem 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
in-house 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 the University of
Tennessee's (Knoxville) 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 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 $50 million, employ no more than
500 persons, and lack in-house expertise in waste minimiza-
tion.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers, reduced
waste treatment and disposal costs for participating plants,
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 proce-
Pnnted on Recycled Paper
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dures outlined in the EPA Waste Mmimizatiorr Opportunity?
Assessment Mawa/(EPA/625/7-88/003, July 1988). TheWMAC
staff locales 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 detailing WMAC's findings and recommen-
dations (including cost savings, implementation costs, and
payback times) is prepared for each client.
Plant Background
The plant produces printed circuit boards for use in television
sets. The plant operates 5,760 hr/yr to produce approximately
4.3 million sq ft of finished boards.
Manufacturing Process
The various manufacturing processes used in this plant, along
With the wastes that are generated, are described below.
Screen Production
Screens, whfch are used to transfer ink patterns to the circuit
boards, are produced using photographic film sheets,, Kodak
developer, glue, methyl ethyl ketone (MEK), polyester mesh
fabric, screen emulsion, and tape.
Designs for the circuit boards are transmitted from corporate
headquarters via modem to the plant's computer system. A
laser printer prints the pattern on film sheets to 0.7 millimeter
accuracy. The film sheets are developed in a Kodak develop-
ing solution and manually water rinsed. Spent, water and devel-
oper are dumped into the sewer.
In a separate operation, polyester mesh fabric is pneumatically
stretched over and glued onto metal frames using screen glue
thinned by MEK. Next, emulsion is manually spread onto the
screen and allowed to dry for one hour.
The film sheet is then manually taped to the screen, and the
unit is exposed to ultraviolet light to transfer the film pattern to
the emulsion coating. A water rinse removes the exposed
emulsion, leaving the inverse of the circuit pattern on the
screen. The emulsion is then electrically heat-cured in an oven
for approximately 8 hr at 100"F. Finished screens are stored or
transferred to production as needed. The screen production
process is illustrated in Figure 1.
Circuit Board Production
Raw materials for this process include pre-sized zinc/copper
coated f&erglass panels and screen-printing inks. Operations
occur on two separate production lines that are identical except
for their capacities.
Sk to ten reference holes are initially punched into the panels
for alignment purposes. A conveyor then transports the panels
to a mechanical wet scrubbing: operation that uses nylon brushes
and spray-rinsing to remove a protective zinc layer from the
copper coating. (The zinc coating prevents oxidation of the
copper during shipment to the plant.) Rinse water containing
zinc, copper, and brush particles is filtered before being pumped
to the plant's water treatment system. Paper filters containing
copper, zinc, and brush particles are disposed of in a local
landfill. Panels are then dried; in a- hot-air electric1 dryer &t
130°F.
The panels are stacked and; manually transported to one of
three screen-printing machines where they are printed with
etch resist ink. The etch resist ink prevents the etchant from
removing, the copper on the board that will form the circuit
pattern. The panels are visually inspected and continue to the
etching process that is described on page 4. Any rejected
panels are processed through the stripping etch resist tank
(described in the etching process) and reprinted with the etch:
resist ink.
After etching, the panels are screen printed with a solder mask
ink, then cured in a UV oven at 300°F. This mask prevents the
solder or "SealBrite" from adhering to undesired areas. Panels
are then screen printed with a legend in white ink on top; of the
solder mask to identify the board type, After UV curing ait
300°F,. the panels are screen printed with legend in black ink.
on the under side of the board to identify circuit components.
This ink is also UV cured at 300°F. Panels are then air cooled,
stacked, and allowed to stabilize dimensionally for 8 hr until
their temperature reaches 85°F.
Waste ink from all four screen-printing operations (etch resist,
solder mask, white legend, and black legend) is scraped off
screens and machines and is reused. A xylene/propylene spe-
cial-blend solvent is used for cleaning screens and machines.
Rags containing waste ink and solvent from the four screen-
printing operations are recycled offsfte. Broken screens are
landfilled without cleaning, and screens that are still intact: but
no longer needed are cleaned and recycled. The UV ovens, on
all four screen-printing operations are maintained at 300°F via
cooling water.
After air cooling, the panels undergo punching and solder or
SealBrite coating, operations. Panels with boards that will not
support surface-mounted components (approximately 10% of
the product) undergo the micro-etch and solder coating as
described in a separate section. Those panels are then pro-
cessed through a two-stage punching operation. In the first
stage, 1,500-2,000 holes per board are punched into the pan-
els for component wiring. (Each panel contains two to eight
boards, depending on finished board size and original panel
size.) In the second stage, called compound punching, the final
wiring holes are punched and the panels are cut into their
respective boards. Alignment for these punching operations is
accomplished by a printed bar code on the board (provided by
the legend printing process), which is read by the punching
machine. Panel webbing and slugs, amounting to 13% of the
original panel area, are hauled to a local landfill. Boards are
then stacked and ready for inspection.
All panels with boards that have surface-mounted components
(90% of product) undergo two-stage punching operations ex-
actly as described above but on different machines. Panel
webbing and slugs are hauled to a. landfill. Individual boards
are then transferred to the micro-etch and SealBrite coating
process described in a separate process description. After
SealBrite coating, boards are stacked and ready for inspection.
All finished boards are visually inspected. About 4% of the
boards are rejected due to solder mask printing or punching
errors. The satisfactory boards are then desluggsd by manual
insertion of boards over a bed of carefully positioned pins: to
remove any blockage. Next, the boards are hand-fed into an
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Designs Sent
Via
Modem
Metal Frames
Mesh Fabric
Glue
Figure 1. Screen Production.
automatic electrical tester, which rejects approximately 1% of
incoming boards. All rejected boards are landfilled and consti-
tute about 5% of incoming panel area. Finally, the boards are
boxed, bar coded, and shipped. The circuit board production
process is illustrated in Figure 2.
Etching
Etching removes the unnecessary copper coating, leaving the
circuit pattern on the panels. Raw materials for the etching
operation include hydrochloric acid, chlorine gas, caustic soda,
and "Sur-Clean" micro-etch solution.
Panels from screen-printing inspection are conveyed through
etch tanks. The etch solution is composed of hydrochloric acid,
dissolved gaseous chlorine, and recirculated water from the
rinse as needed. The solution is heated by the exothermic
reaction of removing the copper and is maintained at 130°F by
cooling water circulating in jackets around the tanks. Balance of
the system is maintained automatically. Etch chamber solutions
are bled to a storage tank as they become saturated with
copper and are shipped weekly to a recycler. Fumes drawn off
the etch tanks are diverted to a fume scrubber that operates 24
hr/day, 7 days/wk. The scrubber recirculates 20 gal/min of water
with 1.5 gal/min of fresh water and a 1.5 gal/min overflow.
Wastewater is discharged to the municipal sewer. Caustic soda
is also added to the scrubber water.
The primary etch process is follpwed by a four-stage cascade
rinse. Wastewater from this rinsing operation is dumped every 2
hr to the water treatment system. Following rinsing is a stripping
etch resist bath that removes the etch mask from the panels.
The solution is composed of caustic soda beads dissolved in
water that is heated to 110°F. Water from this tank is continu-
ously filtered to remove the stripped etch resist ink particles.
Contaminated paper filters and etch resist sludge are landfilled.
The stripping etch resist solution is dumped twice a week to
the water treatment system. Fumes drawn off of the stripping
etch resist tank are directed to the fume scrubber described
earlier.
Next, the panels are sent through a two-stage countercurrent
rinse. Wastewater from the rinse continually flows to the water
treatment system. Finally, the panels are micro-etched to
remove any oxides present. The micro-etch solution consists
of Sur-Clean 92 solution and water. Spent solution is dumped
twice a week to the water treatment system. Fumes collected
over the micro-etch tanks are directed to the fume scrubber
discussed earlier. Following micro-etch processing, panels
undergo a two-stage countercurrent rinse after which they
pass through a hot-air electric dryer at 130°F. Wastewater
from the rinse continually flows to the onsite water treatment
system. From the dryer, panels are stacked and transferred to
the solder mask screen printing area.
Solder Coating
As mentioned earlier, the solder coating process is applied to
approximately 10% of the product. This 10% is generally
composed of boards that do not have surface-mounted com-
ponents. The solder protects the copper that has leads at-
tached. This process is outdated and has been replaced by
the SealBrite process; however, the line is currently being
used to reduce the load on the SealBrite line. Raw materials
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Panels
^
*•
Punching
w.
Scrubbing
^
Printing
and
Oven Curs
Etching
w
Sb/cfer
Mask
Printing
and Oven Cure
b-
Legend
Printing
and
Oven Cure
Micro-Etch and
r
Figure 2. Circuit Board Production.
Solder Coating
with Punching
Punching
w
Inspection
Debugging
Testing
Boxing
Shipping
for this process include an acidic etch solution called Sur-
Cfean 92 solution, Organo Flux, roll salts, and solder.
Panels from the legend-printing process undergo a micro-etch
solution spray consisting of Sur-Clean 92 solution and water.
The micro-etch solution removes any oxides present and pre-
pares the surface for soldering. Waste solution is dumped to
the water treatment system. Panels are rinsed in a two-stage
countercurrent spray system; water is continuously discharged
to the water treatment system. Next, the panels are conveyed
through a hot-air electric dryer at 100°F and through a flux
tank in which Organo Flux is roll-coated onto the panels to
promote solder adhesion. No waste is generated from the flux
operation. Panels are preheated in an electric oven at 360°F
and are roll-coated with tin/lead solder at 510°F. Roll salts are
used to remove impurities from the solder bath. Waste "dross"
(contaminated solder) is minimal and is disposed of in the
municipal trash. After solder coating, the panels undergo a
three-stage spray rinse. Fresh water enters the third tank and
ts recirculated into the first tank. The second tank water level
Is maintained by drag-out from the first tank. Wastewater is
discharged to the water treatment system. Finally, the panels
are conveyed through a hot-air electric dryer at 130°F and on
to the punching operations described earlier in the description
of Circuit Board Production.
SealBrite Coating
SealBrite coating is applied to 90% of the product. SealBrite
compound functions similarly to solder, as a base for compo-
nent attachment. Raw materials for this process include sulfu-
ric acid, hydrogen peroxide, SealBrite, and SealBrite thinner.
Isopropyl alcohol is used for cleaning the SealBrite tank.
Boards from the punching operations described under Circuit
Board Production are micro-etched in a tank with a heated
solution (100°F) consisting of sulfuric acid, hydrogen peroxide,
and water. The etch removes any oxides that are present and
prepares the surface for the SealBrite coating. The micro-etch
tank is cleaned twice a year; bottoms are drained to the water
treatment system. Cooling water circulates through a jacket
around the tank and is added to a high-pressure spray rinse
that follows the micro-etch. That rinse is followed by a four-
stage cascade rinse; this water is added to the high-pressure
spray rinse along with fresh water. Wastewater from the high-
pressure spray rinse is sent to the water treatment system.
The boards are conveyed through a hot-air vacuum dryer at
130°F and then through the SealBrite tank. SealBrite is roll-
coated onto the boards. Thinner is added manually to the tank
as needed. Isopropyl alcohol is used to clean the SealBrite
roller periodically. Spent SealBrite solution is collected and
shipped offsite as a hazardous waste. The coating is cured in
an infrared oven at 250°F and then air cooled. Evaporated
thinner from the oven is ducted to the outside atmosphere.
After SealBrite processing, boards are: then transported for
inspection as previously described.
Wastewater Treatment System
Wastewater from various production processes is collected in
a 500-gal holding tank. The initial pH of the mixed wastewater
in the holding tank is in the approximate range of 7 to 8. From
the holding tank, water is pumped into a 2,000-gal central tank
for pH adjustment to 9 to 10 by addition of caustic liquid
(sodium hydroxide). After pH adjustment, water is pumped at a
rate of 45 gal/min through two electrochemical cells in series.
These cells contain iron plates that convert copper salts to iron
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salts. The plates are.periodically washed down with hydrochlo-
ric acid to prevent copper buildup and are changed every
month. Hydrogen gas and hydrochloric acid exiting the tank
are recirculated into the central tank, along with any copper
ions washed from the plates. Water then flows through two
degassing .tanks in series that allow trapped hydrogen gas_to
be vented to the outside atmosphere. Wastewater is then
pumped to a clarifier where floe and dispersant are added to
promote sludge precipitation. Sludge is pumped to a :sludge
thickening tank for further settling and on to one of two filter
presses. Decanted water from both operations is returned to
the clarifier. Sludge is removed to the local landfill. The water
from the clarifier is pumped to a mixing tank where plant
cooling water, water from the fume scrubber, and water from
the SealBrite line, which is collected separately in a holding
tank, are mixed with the treated water and discharged to the
municipal sewer.
Existing Waste Management Practices
• A computer-controlled regeneration system has been in-
stalled to .maintain cupric chloride etch solution.
• Excess ink collected on screens in the screen-printing
operations is manually scraped off and returned to the ink
reservoir.
• Filter presses are used to reduce the volume of waste-
water sludge shipped offsite.
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 time are also given in Table 2.: 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.
raw material and from reduced present and future costs asso-
ciated with waste, treatment and disposal. Other savings not
quantifiable 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.
Additional Recommendations
In addition to the opportunities recommended and analyzed by
the WMAC team, four additional measures were considered.
These measures were not completely analyzed because of
insufficient data or minimal savings as indicated below. They
were brought to the plant's attention for future reference, how-
ever, since these approaches to waste reduction may increase
in attractiveness with changing plant conditions.
• Install an enclosed solvent cleaning system for the clean-
ing of screens to minimize the evaporation of solvent.
Minimal savings and high capital costs are projected for
this recommendation.
• Use reusable filters to remove ink from the stripping etch-
resist caustic solution in place of paper filters. Minimal
savings are projected for this recommendation.
• Replace the cupric chloride etch solution with a sulfuric
acid/hydrogen peroxide etch solution. The proposed etch
solution would generate considerably less waste and that
waste would be more easily recoverable. A lengthy payback
for this recommendation is predicted.
• Investigate the possibility of recovering the cupric chloride
etch solution onsite.
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. Environmen-
tal Protection Agency. The EPA Project Officer was Emma Lou
George.
It should be noted that the economic savings of the minimiza-
tion opportunity, in most cases, result from the need for less
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Tib!* 1. Summary of Current Waste Generation
Waste Generated
Fittors containing copper and zinc
Regs containing Ink andxytene blend
Pofyostar scraon mesh containing
emulsion coating
Rojoctod circuit boards
Panel wobbfag and slugs
Spent Btchant
Etch resist sludge
Contaminated paper filters
containing etch resist
Spent SealBrita solution
Evaporated SealBrita thinner
Process wastawater
Wastewator sludge
Source of Waste
Mechanical wet scrubbing operation in the
circuit board production line.
Cleaning of screens and machines in the four
screen-printing operations in the circuit
board production line.
Screen-printing operations in the circuit
board production line.
Inspection process in the circuit board
production line.
Punching process in the circuit board
production line.
Etch chambers associated with the etching
process.
Filtering of solution from the stripping etch
resist bath.
Filtering of solution from the stripping
etch resist bath.
SealBritB coating process.
SealBrite coating process.
Various production processes, fume
scrubber, and equipment cooling.
Onsita wastewater treatment system.
Annual Quantity
Generated
2,700 Ib
48,000 rags
23,880ft2
247,500ft2
643,500ft2
192,000 gal
120 gal
17,860 ft1
165 gal
275 gal
23,000,000 gal
38,000 Ib
Annual Waste
Management Cost ($)
1,730"
21,890
1,730"
2,080"
35,600*
110,530
1,730"
1,900"
7,330
0"*
56,750
14,160"
"Does not Include the total cost of$720/yr for municipal landfill disposal. This charge is assessed regardless of the quantity of waste.
"Plant personnel report no costs associated with the management of this waste. There is a replacement cost associated with the evaporation.
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Table 2^ Summary of Recommended Waste Minimization: Opportunities
Waste Stream
Reduced:
Annual Waste Reduction
Minimization Opportunity
Quantity
Percent
NetAnnual implementation Payback
Savings, $ Cost; $ Years
Wastewater Install a closed-looped, chilled water
system, including an electric
chiller, an outdoor condenser, and a
storage tank, in order to use
recirculated water for cooling the UV
curing^ ovens and the etch tanks:
Spentetchant Install a steam generation system to
heat the spent etch solution as it is
transported from the etch tank to the
storage tanks to drive off a> portion
of the water and thereby reduce the
volume of waste shipped offsite. The
steam produced should be directed to
the plant's fume scrubber.
Filters- containing Use reusable polymer membrane
copper and: zinc- filters instead of paper filters: for
filtering copper and zinc
from the wastewaterofthe
mechanical wet scrubbing operation.
Particles collected on the new
filters should be scraped off and
sold for recycle.
14:iOOO,000:gal 60
4Q.QQO
76,640;
1.9
67,200 gal 35
33,510
28,180
0.8
2,590lb 96
3,100
7,700
2.5
7
GOVERNMENT PRINTING OFFICE: 1992-648-080/40259
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United States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
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EPA/600/S-92/008
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