A Cooperative Project
between the
U.S. Environmental
Protection Agency
and PWB
Manufacturers
Nationwide
 September 1996
EPA 744-F-95-009
                                                                            PRINTED WIRING BOARD CASE STUDY 3
                      U.S.EPA*
                                     PRINTED WIRING
                                      BOARD PROJECT
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                                  Opportunities  for
                                Acid Recovery and
                                      Management
                               /"  I  1he Design for the Environment (DfE)
                                  I   Printed Wiring Board Project is a volun-
                                -I-  tary, cooperative effort between the
                               printed wiring board (PWB) industry, the U.S.
                               Environmental Protection Agency (EPA), and
                               other stakeholders dedicated to helping PWB
                               manufacturers reduce risk to their workers
                               and the environment in cost-effective ways.
                               One of the goals of this project is to provide
                               PWB manufacturers with pollution prevention
                               information specific to the PWB industry, so
                               that they are better equipped to incorporate
                               environmental concerns into day-to-day busi-
                               ness decisions.
                                  This case study highlights the pollution
                               prevention efforts of a medium-sized PWB
                               manufacturer whose experience shows that
                               implementing viable pollution prevention
                               alternatives can result in economic as well as
                               environmental benefits.  In particular, this case
                               study illustrates:
                                • How acid recycling and recovery can
                                   reduce process wastes,  chemical costs,
                                   and occupational exposure, and improve
                                   process control.
  • How working together with employees in
    the facility and with equipment vendors
    and chemical suppliers can improve the
    potential for pollution prevention success.
  • How the complexity of pollution preven-
    tion efforts can range from simple
    improvements in operation and mainte-
    nance to researching and developing a
    unique in-process recycling unit.
   In support of EPA's pollution prevention
hierarchy, recycling strategies described in this
case study should be investigated only after
every attempt has been made to implement
source reduction options such as changes in
materials, processes, practices, or products.

Company Background

   Located in Woburn, Massachusetts, Printed
Circuit Corporation (PCC) is a manufacturer of
double-sided and multilayer printed wiring
boards for the electronics industry. PCC
employs 300 people and produces 1.8 million
surface square feet of board per year in its
100,000 ft2 manufacturing facility.
   PCC, one of the first companies to join
EPA's 33/50 Program, has been active in the
area of pollution prevention for many years.
As part of this program, the company elimi-
nated methylene chloride in 1990 and 1,1,1-
trichloroethane in 1993 through chemical
substitution. More recently, PCC  has begun to
regenerate ammoniacal etchant, recycle rinse
water, and recover copper using an on-site
etchant regeneration system.  (For more infor-
mation on etchant regeneration,  refer to PWB
Case Study 2.)
   Motivated by the desire to reduce waste,
save money, and meet requirements of the
Massachusetts Toxics Use Reduction Act
(TURA),  PCC continues to look for pollution
prevention opportunities. TURA requires facili-
ties that use listed chemicals in quantities
above certain thresholds to inventory those
chemicals and prepare plans on how to
reduce or eliminate their use or generation  as
hazardous byproducts. Sixteen states have
similar pollution prevention planning laws.  In

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addition to investigating and implementing chemical substitu-
tion and other source reduction options, PCC has promoted
environmental protection through acid recovery and
improved acid management practices, the focus of this case
study.
        very of Methane Sulfonic
              Strip
   As a surface finish, PCC uses solder-mask-over-bare-cop-
per with hot-air-solder-leveling. This outer layer finish pre-
vents copper oxidation and facilitates solderability during the
assembly process. Before panels can then undergo
nickel/gold tab plating (also called finger plating, connector
plating, or microplating) for electrical conductivity and envi-
ronmental resistance, the tin/lead solder must be stripped
from the panel. In the stripping process, PCC uses methane
sulfonic acid (MSA) and applies a reverse electrical current to
dissolve tin and lead from die boards.
   In the past, PCC changed the acid every 30,000 "ends"
(one pass of a circuit panel), or approximately every 6 weeks
depending on production schedules. MSA is a very expensive
acid (~$21/gal), and  accounted for an average of
$17,000/year in raw material costs. Spent solution was sent
off-site for disposal at a cost of approximately $5,600/year.
PCC recognized an opportunity to conserve acid, prevent
hazardous waste generation, and lower employee exposure
to corrosive materials using a relatively simple and efficient
in-process recycling technology called diffusion dialysis.
   Diffusion dialysis is a technology that uses an anion
exchange membrane allowing anions and the hydrogen ions
(due to their small size and mobility) to pass through into a
water stream that is running counter current to the flow of the
spent acid. The acid (e.g., HC1, H2SO^> is reconstituted on the
water side of the membrane and is  directed back to the
process tank. The metal-rich, acid-depleted stream can be
sent to on-site waste treatment or shipped off-site for treat-
                                         ment. Fresh acid
                                         in proportion to
                                         the unrecovered
                                         amount is added
                                         to the bath to
                                         maintain the
                                         concentration
                                         within the cor-
                                         rect operating
                                         window. In addi-
                                         tion to MSA tab
                                         strip recovery,
                                         diffusion dialysis
                                         has potential
                                         applications in
                                         plating or other
                                         wet processing
                                         operations such
                                         as rack strip,
                                                        plating bath pre-dip, and microetch that is treated on-site.
                                                          At PCC, the diffusion dialysis recycling unit is hard-piped
                                                        to the MSA tab stripping bath. The company first evaluated a
                                                        5 gallon/day recycling unit in an off-line pilot test. They
                                                        assessed parameters such as acid recovery and metal rejection
                                                        rates, as well as the stripping rate  of the recovered acid. PCC
                                                        then proceeded to evaluate the system on-line. After work-
                                                        ing with the vendor to fine-tune metal rejection and acid
                                                        recovery rates, PCC was able to maintain a constant solution
                                                        level in the stripping  bath.
                                                          Based on the project's costs and savings, as outlined
                                                        below, the payback on the investment was approximately
                                                        6 to 7 months.

                                                        Annual Savings:
                                                           Process chemicals    $14,500
                                                           Waste disposal        $5,600

                                                        Other Benefits:
                                                         •  Reduces long-term liability associated with hazardous
                                                            waste shipments.
                                                         •  Reduces employee exposure associated with bath
                                                            dumping.

                                                        Capital Costs:
                                                           Pure Cycle AJ-10     $10,800
                                                           Acid Recycling System

                                                        Concerns/Disadvantages:
                                                         •  Metals stripped from the board must still be either sent
                                                            off-site in a low acid matrix (same volume), or treated in
                                                            the on-site wastewater treatment facility. Based on the
                                                            total volume of strip generated and the metal content of
                                                            the spent material, the background lead concentration in
                                                            the influent to the treatment facility rose <1 ppm; howev-
                                                            er, PCC's treatment facility is able to treat this increase
                                                            such that the discharge still meets regulatory standards.
                                                         •  Labor costs will actually increase slightly because the solu-
                                                            tion must be analyzed and additions made, if necessary.

                                                        Payback:
                                                           Approximately 6-7 months
                                                                tetchant Regeneration
Acid - Out
   Microetching is a ubiquitous process found as a preclean
step for many of the stages of PWB manufacturing.
Microetching removes anywhere from 10 - 70 microinches of
copper to rid the panels of oxidation prior to the subsequent
process, such as pattern plate, soldermask application, or hot-
air-solder-leveling. PCC generally uses a sulfuric acid/hydro-
gen peroxide solution as the microetchant.
   PCC had been decanting 138 gallons of spent microetch
solution per week from the electroless copper line and 35 gal-
lons/week from the black oxide line.  This spent solution was
being sent off-site for recycling.  In order to conserve sulfuric
acid and prolong bath life, PCC and a chemical vendor
worked together to install an electrolytic plate-out cell to plate
          Diffusion Dialysis Cell Pair

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     U.S.EPA
out copper from the microetch. Electrolytic recovery has been
used to recover valuable metals from bath rinses, but in this
case, it is the regenerated microetch and the associated sav-
ings that motivated PCC to explore this recycling technique.
   This setup uses dimensionally stable anodes
and cheap scrap laminate as the cathode
onto which the copper is plated. The
pumps are hard-piped for batch transfer
from the microetch process bath to the
electrolytic plate-out cell. PCC chose only
the electroless copper and the black oxide
lines for microetchant regeneration because
other preclean processes do not have high cop-
per concentrations, due to a high rate  of copper dragout.
   The continuous-batch plate-out system allows for better
process control because the copper concentration remains
more stable, which in turn provides for a more stable etching
rate. In addition, the copper ion concentration in the
microetch is lowered to 25 - 45 g/1, from an average of 45 -
80 g/1 by the old decant method. The reduced copper con-
centration has the effect of decreasing the average amount of
copper dragged into the subsequent rinse and then into
waste treatment by about 50%. More importantly, the spent
microetch is no longer decanted from these processes each
week and sent off-site. Not only are disposal and materials
handling costs cut, but employee exposure is reduced.
                 Before Microetch Regeneration
 (g/D
                           Time
 Better Process Control Through Microetch Regeneration


Annual Savings:
 Chemical purchases                     $1,750
 Off-site transportation and recycling      $15,625
 Scrap copper sales                       $3,950

Additional Benefits:
  • Reduced wastewater treatment and sludge disposal costs
    due to decreased copper dragout into rinsewater.
  • Reduced employee exposure associated with bath dump-
    ing.
  • Reduced materials handling/labor time associated with
    bath dumping.
  • Reduced liability associated with shipping spent
    microetch off-site.
                       500 amp rectifier
                       2 double diaphragm pumps
                       4 dimensionally stable anodes

                     Annual Operating Costs:
                       Energy costs
                       Labor (1 hr. every other day)

                     Payback:

                       5 months, with annual operating costs of
                                         $2,500
                                         $1,500
                                         $4,000


                                           $600
                                         $2500
                                         -$3100
Capital Costs:

 200 gallon tank
$1,000
      1LRanel Solder Strip Recycling
      iiiliilii^frf^rv'^aa^ -^.. ^r— —      _ •

   Recycling spent solution is not always as easy as hooking
up a unit and adding fresh solution periodically. It may
require extensive experimentation and teamwork. Under-
standing the chemistries involved in the process is the key to
regenerating bath solutions successfully.
   After outer layer etching, PCC strips the tin/lead etch-resist
with a nitric acid and ferric nitrate solution. The nitric acid is
used to strip the tin/lead layer, and the ferric nitrate compo-
nent is necessary to remove the intermetallic layer that forms
when the tin and copper diffuse into each other. These solu-
tions also contain wetting agents, copper etching inhibitors,
and anti-tarnishing agents.
   PCC currently has a $15,000 grant from Massachusetts Tox-
ics Use Reduction Institute to study the feasibility of recycling
the nitric acid stripping solution using diffusion dialysis. The
project involves the use of diffusion technology to separate
the stripped metals from the stripping solution, rendering it
reusable. This would be a continuous, on-line recycling sys-
tem similar to that used for MSA recovery.
   The major roadblock to this process is the presence of an
iron component in die proprietary stripping solution. This
component is necessary in order to dissolve the intermetallic
layer that forms when the solder (tin/lead) is plated onto the
copper surface of the PWBs. Recall from the discussion of
MSA recycling, however, that the diffusion dialysis process
will reject from the spent solution all metals, including the
iron, which is essential to the stripping process.
   PCC believes it may be possible to determine the rate of
loss of iron from the diffusion dialysis process and replace the
iron with a concentrated replenisher. The difficulties here
include adjusting for the losses of the other components,
since rejection of organics and non-metal inorganic materials
varies, depending on the charge and size.
   In order to make these determinations, PCC contacted its
solder strip chemical vendor. PCC arranged a meeting with
the company's process engineers, representatives from its
chemical vendors, and the diffusion  dialysis equipment ven-
dor. Together they designed an off-line pilot system to test
the acid reclaim efficiencies and metal rejection rates at vari-
ous ratios of virgin to spent solder strip.
   Currently, PCC is awaiting further test results from its
chemical vendor on parameters such as solder stripping rates,
intermetallic removal, copper etching inhibition, and anti-tar-
nish capability. Based on the findings, the chemical vendor

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                                  will be able to deter-
                                  mine the additive pack-
                                  age of chemical
                                  constituents that would
                                  replace the compo-
                                  nents lost from the dif-
                                  fusion dialysis process.
                                    The next step will
                                  be to determine if the
project is technically and economically feasible. PCC will base
its decision on the cost of the chemical vendor's additive
package, the cost savings from the recycling process, and
Other factors such as reduced risk of exposure. If the project
is deemed feasible, the recycling unit would be attached
directly to the solder strip sump. The reclaimed solution from
the unit would be sent back to the sump. The reject would
be plumbed to waste treatment.  PCC would then analyze the
solution regularly, making additions of the package prepared
by the vendor as necessary. Stripping  rate and copper etch
rate would also be monitored, along with nitric acid reclaim
efficiency and metals rejection.
  ?o'jlutfon Prevention Through
       ~ess Control   .

   In focusing on new technologies for recovering spent
materials or other source reduction opportunities, a company
may overlook simple changes in operations and maintenance
that can yield great'benefits. Despite its success with pollution
prevention over the past several years, PCC learned an impor-
tant lesson about the need to understand its processes to
avoid unnecessary waste. PCC's story, which is described
below, illustrates how a thorough process evaluation helped
the company solve problems in its preclean step for primary
image dry-film photoresist lamination.
   In the preclean step,  PCC uses a 10% sulfuric acid spray
and aluminum oxide scrubbing in a conveyorized spray
process. This process accounted for 50% of the sulfuric acid
used at the plant. A PCC environmental engineer initiated an
investigation of the preclean process after the production
manager first asked the  chemistry lab personnel to dump and
replenish the sulfuric acid solution twice a day, then three
times a day, instead of once. Next, the environmental engi-
neer assembled a team consisting of the plant engineer, the
area process engineer, and the production supervisor to dis-
cuss the role of sulfuric  acid in the preclean step and to iden-
tify the conditions that precipitated the requests for more
frequent bath changes.
   The primary reason for requesting more frequent bath
dumps was staining on  the panels. The process engineers
were concerned that the staining would interfere with adhe-
sion to the dry-film. They decided that every time the staining
occurred, they would investigate the process in an attempt to
identify the root cause of the problem. To their surprise, the
cause of the problem was not the chemistry; instead, the
problem was caused by plugged nozzles and rinses that
either did not operate properly or were not turned on.
   By correcting the mechanical failures, increasing the main-
tenance schedule, and improving training of the line opera-
tors, PCC was actually able to reduce the number of bath
dumps required to once a week. Not only was the bath
dumped less frequently, but through these simple improve-
ments, PCC has also cut its sulfuric acid usage by more than
85% for the process. This translates to a savings of over 26
tons of sulfuric acid per year and over $12,000 in chemical
costs.  Thus, by working together and understanding the
chemical and mechanical components involved in any
process, the chances for pollution prevention success
improve dramatically.

The Design for  the  Environment
(DfE)  Approach	
   This case study describes how teamwork and thorough
process evaluations helped one company reduce waste,  save
money, and improve process control through acid recovery
and improved acid management. The EPA's Design for the
Environment Program encourages you to evaluate systemati-
cally the technologies, practices, and procedures in your facil-
ity that may affect the environment. Our goal in working with
the PWB manufacturers is to help you to make informed
choices, now and in the future, by promoting the search for
and evaluation of cleaner alternatives.

Acknowledgments

   EPA's Design for the Environment Program would like to
thank Printed Circuit Corporation for participating in this case
study and PWB DfE Project participants from the following;
organizations who provided advice  and guidance: rirmit,  W^ff
Center Inc., EPA - New England, Institute 1
and Packaging Electronic Circuits, Morton Internaji§nal,;
National Security Agency.
   Mention of product trade names doe|noi
ment or recommendation of use.
                                   -  *«.T-*,>
   The DfE Program wants your feedback. If you
email at oppt.dfeQepamail.epa.gov
                                  -, .„      , sp^lKI,
to pollution prevention in the PWB7jfod;us*t£y, aQd^mpre infigr-/*"
                                            - *     • t£ii '&
   For additional PWB case studie|^oth^
mation on EPA's Design for
DfE Printed Wiring Board Project,
   Pollution Prevention Informatii
            U.S. EPA, 401 M Streel
                 Washington, DC
         Phone: 202-260-1023
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              e-mail: PPIC@epamail.epgggv; x
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          4§\  Recycled/Recyclable
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        Printed with Soy/Canola Ink on paper that contains
        at least 50% recycled fiber.

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