A Cooperative Project
between the
U.S. Environmental
Protection Agency
and PWB
 September 1996
 EPA 744-F-96-003
                                                                            PRINTED WIRING BOARD CASE STUDY 4
                                     PRINTED WIRING
                                      BOARD PROJECT
                                  Plasma Desmear:
                                       A Case Study
                               ~\~\7"7"ast:e' To a manufacturing operation,
                                 \ \ / waste points to parts of the produc-
                               .  T V  tion process where resources are
                               not being fully utilized, where money is lost,
                               and, in many cases, where an environmental
                               burden is generated. Like most companies,
                               the management of Circuit Center, Inc. (CCI),
                               a manufacturer of double-sided and multilayer
                               printed wiring boards (PWBs), is always look-
                               ing for ways to reduce the waste the company
                               generates. And their efforts to improve their
                               environmental performance go beyond waste
                               reduction. They seek reductions in toxic mate-
                               rials used, occupational hazards, and toxic
                               byproducts generated.

                               Several years ago, CCI's efforts led them to
                               examine their desmear operations. With waste
                               disposal related to this process accounting for
                               over 13% of the plant's environmental man-
                               agement costs, their permanganate desmear
                               process was a likely target for investigation. At
                               the same time, process engineers were exam-
                               ining product quality problems related to their
                               permanganate line. After some research into
      techniques for improving the efficiency of their
      permanganate process, CCI's focus turned to
      not just improving the line, but replacing it
      with a completely different desmear technolo-
      gy called the plasma process. CCI's research
      indicated that, by using a plasma desmear,
      they could reduce the waste from this process
      dramatically (thereby reducing costs) and
      improve product quality. With further investi-
      gation, the company decided to give it a try. In
      this case study, they share their experience in
      implementing their plasma desmear process.
      What is the Design for the Environment
         (DfE) Printed Wiring Board Project?
         Representatives  of the printed wiring
         board industry and other stakeholders
         entered into  a  partnership with the
         Environmental  Protection Agency
         (EPA) called the Design for the Envi-
         ronment PWB Project. This is a cooper-
         ative, non-regulatory effort where EPA,
         industry, and other  interested parties
         are  working together to develop  tech-
         nical information on pollution preven-
         tion technologies specific to the  PWB
         industry. This information includes
         comparative data on the risk,  perfor-
         mance, and cost of  alternative manu-
         facturing options.

         To date, the DfE Project has focused on
         conducting a comprehensive evaluation
         of alternative  technologies for making
         through-holes conductive.  By publish-
         ing the results of these evaluations, DfE
         is able to provide PWB manufacturers
         with the information they need to
         make informed business decisions that
         take human health and environmental
         risk  into consideration, in addition to
         performance and cost. The Project is
         also identifying  and publicizing other
         pollution prevention opportunities in
         the industry through the development
         of PWB case studies such as this one.

Why Pollution Prevention?
Located in Dayton, Ohio, Circuit Center, Inc., manufactures
approximately 375,000 surface square feet of printed wiring
board annually. With 130 employees, CCI specializes in small
quantity orders of primarily prototype boards. The nature of
this market requires that they routinely process many types of
substrates. In die 1980s, CCI started pursuing pollution pre-
vention opportunities more aggressively. Through some initial
successful projects, they found that preventing pollution,
rather Uian treating wastes after they were created, not only
improved the environment, but  could also improve their
product quality and bottom line.
   CCI Benefits from Eliminating Permanganate

One of their early pollution prevention efforts was to replace
their electroless copper line with a formaldehyde-free, non-
copper direct metallization line. Although they are a relatively
small shop, they were able to justify this type of capital-
intensive project through savings from, their reduction in
chemical use, waste treatment costs, water use, and their
improved product quality.

Investigating the
Desmear Process
With the change to direct metallization successfully complet-
ed, CCI process engineers were able to  concentrate on other
parts of the manufacturing process. After the electroless line
was replaced with the more efficient direct metallization
process, it became clear the heavy copper deposition of the
electroless copper process had been masking manufacturing
inconsistencies caused by the permanganate desmear. These
inconsistencies, especially pink ring and voids, were a partic-
ular problem on panels with high aspect ratios. In addition to
uncovering quality issues, the dean and efficient direct metal-
lization line also highlighted the waste associated with the
neighboring permanganate line. It was clear that changes had
to be made to the desmear process to improve quality and to
reduce waste.
The Most Common Desmear Technique
Smear is caused by the heat generated during drilling, which
can melt the resin, depositing it on the interconnects as the
drill bit retracts from the hole wall. This smear has to be
removed to provide good plating adhesion to the epoxy,
glass, and copper constituents of a drilled hole.

CCI had been using a permanganate-based process, the most
common desmear method, which typically consists of three
process baths:
1) An alkaline solvent swell facilitates the subsequent removal
of the epoxy-resin smear. The chemistry of this bath is usually
proprietary, but often contains n-methyl pyrrolidone, which is
highly flammable and a skin and eye irritant.
2) A permanganate bath in an alkaline solution heated to
l60°F or higher removes the drill smear. This bath contains
sodium or potassium permanganate in a sodium hydroxide
solution. The occupational health and safety concerns lie in
the high temperature and caustic nature of this bath.
3) An acidic neutralizer, often a sulfuric acid-based chemistry,
removes all traces of alkalinity and the oxidizer from the sur-
face and through-holes. Sulfuric acid is a strong irritant to the
nose, lungs, and skin.

Permanganate Waste Generation
Permanganate desmear waste volumes vary from one facility
to the next; however, they are often a significant portion of a
facility's waste stream. For example, when  CCI examined their
annual desmear-related disposal costs, they found that costs
totaled over $40,000: quite significant (13%) for a facility with
overall annual environmental management costs of $300,000.

A Costly Process
Other costs associated with the permanganate process include
chemical purchases,  energy for the bath pumps and heaters,
extensive labor for testing and maintaining the process baths
within the required parameters, and water costs. In some
parts of the U.S., the costs of water used for the rinses
between baths can be a significant operating expense. For
example, one larger  facility (producing 1.8 million surface ft2
PWB per year) uses  over 3 million gallons of water annually
for their permanganate rinses alone.  The table on the next
page shows the breakdown of the permanganate-related
waste disposal costs  for CCI.

   U.S. EPA
Permanganate Desmear Waste Generation
Process Bath
Hole Swell Bath
Permanganate Bath
Neutralizer Bath
Rinse water
Waste Contents
glycol ethers mixture (30%)
potassium permanganate solution
hydrazine mixture
rinse water and bath dragout

Annual Quantity Generated
592 gal
640 Ib
112 gal
405,660 gal

Annual Costs for Treatment and Disposal
Plasma Possibilities
With the direct metallization line exposing the problems asso-
ciated with the permanganate desmear process, CCI worked
toward improving the efficiency of their desmear line. How-
ever, they found that even with daily lab testing and more
frequent operator monitoring of the desmear baths, they were
still experiencing process inconsistencies and waste. They
then turned their attention to the plasma desmear process.
                Plasma Desmear Unit

The Plasma Technology
Unlike the permanganate series of wet chemical tanks, the
plasma desmear process takes place in a compact, sealed
chamber. Panels are loaded on a rack and placed in the
chamber 'where a vacuum is drawn. Using a radio frequency
(KF) energy generator, a gas plasma is formed that contains
chemically active ions or radicals. A mixture of tetrafluo-
romethane and oxygen is used as the reactive gas. The radi-
cals react with the polymer smear on the board, breaking the
polymer into water vapor, carbon dioxide, and hydrofluoric
acid, all of which are volatile and vaporize at the low pres-
sure. Because the reaction takes place in a vacuum, only
small amounts of process gases are needed to get efficient
reaction rates. The amount of hydrofluoric acid (HF) gas
generated, therefore, is proportionally small and is generated
in a closed system, minimizing potential exposures. Also
note that the HF gas is a process byproduct and is only gen-
erated when the reaction is taking place. However, in the
event of a malfunction, it is possible that the HF could be
released. It is critical, therefore, that the equipment be  prop-
erly and professionally installed.

In contrast to the open, heated baths of the permanganate
process, occupational health and safety issues associated with
the enclosed plasma process are greatly reduced. It should be
noted, however, that the tetrafluoromethane gas is toxic by
inhalation. The small amount of hydrofluoric acid generated
by the process is toxic by inhalation and ingestion and  is
highly corrosive. Equipment manufacturers do offer the
option of an alkaline wet scrubber to neutralize the hydroflu-
oric acid  gas produced. The scrubber can be equipped with a
pH meter to indicate to the operator when additional alkaline
solution should be added.

Plasma Cost Savings
Working  with a plasma equipment manufacturer to identify
the system that would best meet their needs, CCI installed a
plasma desmear unit in the fall of 1992. As soon as the  sys-
tem was in production, CCI noticed a dramatic reduction in
incidences of pink ring and wedge voiding, and, consequent-
ly, in desmear-related scrap.

While the savings associated with quality improvements alone
were significant, CCI also saw cost savings resulting from the
elimination of wastewater treatment, water use, and off-site
hazardous waste shipments associated with desmear. Addi-
tionally, operating costs were reduced.

All operators received training on using the system computer
to select the appropriate  run cycle for the job and on loading
boards and handling hot racks. After the operators became
accustomed to the system, operating costs for desmearing (for
the chemistry and processing time) decreased from $0.15/ft2

with permanganate to $0.1 I/ft2 with the plasma system. CGI
engineers also point to the labor savings associated with the
reduced need for maintenance, daily lab testing, waste treat-
ment, and constant tinkering to keep the permanganate
chemistries within the required parameters.

Although a quantitative energy analysis has not been con-
ducted, plant engineers estimate that the energy used for the
plasma desmear RF generator is approximately the same as
that used for permanganate bath pumps and heaters. Equip-
ment manufacturers estimate the energy cost is approximately
$0.02/ft2. Overall, plant managers and engineers are confident
that the plasma system is significantly more cost-effective than
the permanganate chemistry for desmearing holes.

Other benefits that are not easily quantified, but that should
also be taken into consideration, include overall reduced
worker exposure, lower environmental liability, and the
space-saving compact packaging of the plasma units.

           Advantages of Plasma Desmear
   "Jljiprovel^product quality* through" better control and
      ""IIMe^cy'oTthe deimear process.
      |;t||patc§ water use™and wastewater treatment.
      'lu^es^gpe^rating costs.	
      r"Wectiye!y"9esrngar feflon1* substrates.	
But Witt It Work For Me?

While many facilities agree that the environmental and prod-
uct quality improvements of plasma desmear are significant,
larger facilities have expressed some doubts regarding
throughput issues. Where lower throughput shops do not
have an issue with the system cycle time (estimated to be 11 -
15 minutes per load), larger facilities may. Conversations with
larger facilities currently using plasma desmear indicate,
however, that throughput is not a problem. Plasma system
manufacturers provide a range of unit sizes. Systems with
larger chamber size, larger power sources, or additional units
are recommended to accommodate higher throughput.

The capital costs of a plasma  desmear unit vary depending on
both throughput requirements and  the number of equipment
options purchased. Typically, the capital costs range from
$65,000 to $150,000. Options  may include higher frequency
RF generators to reduce cycle time, software options, a wet
scrubber, or built-in analytical equipment.

While this case study describes one facility's success with
plasma desmear, it may not be the  best choice for every facil-
ity. Each individual manufacturer must consider its specific
conditions to determine the most appropriate technology for
their facility.
For More Information on
Contact the manufacturers of plasma systems specifically
designed for PWB desmear operations directly for more infor-
mation. The DfE Project partners identified the following two
companies as vendors of plasma equipment:
        Advanced Plasma Systems, St. Petersburg FL
                  Phone: 813-573-4567
            Plasma Etch, Huntington Beach, CA
                  Phone: 714-843-5944

EPA's Design for the Environment Program would like to
thank Circuit Center Inc. for participating in this case study
and DfE PWB Project participants from the following
organizations who provided advice and guidance: Cognis,
Inc., Concurrent Technology Corporation, Continental Circuit
Corp., DuPont Electronic Materials, Hadco Corp.,  Institute for
Interconnecting and Packaging Electronic Circuits, Merix
Corp., National Security Agency, Printed Circuit Corp., and
Massachusetts Toxics Use Reduction Institute.
      Additional Pollution Prevention
      Resources for the PWB Industry

 In addition to this case study, the DfE PWB Project has pre-
 pared other case studies that examine pollution preventioji __
 opportunities for the PWB industry. All case studies IT   "*
 based on the experiences and successes of facilities
 implementing pollution prevention projects.
 study topics  available include:          ,
        Pollution Prevention Wo^J^PjCjncj
             On-site Etchant RegeTjgrajlon
           Acid Management and Re~Soibery^ ,^-—"*}

 These case studies, and other docurnenl^publijEeS. by the ~
 DfE Project,  are available from:  Ipfe.,-,,^
    Pollution Prevention InfomiatioIi;Cle|ring
             U.S. EPA 401 M Strigt, flj
                 Washington, DG-204fe
          Phone: 202-260-102g:;FJxT-2Sl-260-|l7:
              e-mail: PPIC@epairJ|il