United States
                          Environmental Protection
                                     Risk Reduction
                                     Engineering Laboratory
                                     Cincinnati OH 45268
                         Research and Development
                                     EPA/600/S-92/008 May 1992
                     Waste Minimization Assessment for a Printed
                                Circuit Board Manufacturer

                                   Gwen P. Looby and F. William Kirsch*
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 setsapproximately 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.
                         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-

                         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

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

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 300F. 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
300F,. 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 300F. Panels are then air cooled,
stacked, and allowed to stabilize dimensionally for 8 hr until
their temperature reaches 85F.

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 300F 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

       Designs Sent


        Metal Frames

        Mesh Fabric

  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 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 130F 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 110F. 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

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 130F. 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



Oven Curs

and Oven Cure

Oven Cure
                                                      Micro-Etch and

      Figure 2.  Circuit Board Production.
Solder Coating
with Punching



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 100F 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  360F
and are roll-coated with tin/lead solder at 510F. 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 130F 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 (100F) 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
130F 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  250F 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

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

   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
It should be noted that the economic savings of the minimiza-
tion opportunity,  in most cases, result from the need for less

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
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
2,700 Ib
48,000 rags
192,000 gal

120 gal
17,860 ft1
165 gal
275 gal
23,000,000 gal
38,000 Ib
Annual Waste
Management Cost ($)

 "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.

Table 2^ Summary of Recommended Waste Minimization: Opportunities
Waste Stream
                                      Annual Waste Reduction
Minimization Opportunity
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
                                          67,200 gal     35
                                            2,590lb      96
                                                                                    GOVERNMENT PRINTING OFFICE: 1992-648-080/40259

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Research Information
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