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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. In an effort to assist these manufacturers Waste Minimization Assessment Centers (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). That document has been superseded by the Facility Pollution Prevention

Guide (EPA/600/R-92/088, May 1992). The WMAC team at

Colorado State University performed an assessment at a plant

that manufactures printed circuit boards. Templates for the

circuit design are generated from customer-supplied circuit

information. Copper/epoxy laminates and copper foil are cut

into blank boards and layers. Circuit patterns are generated

through a series of photolithographic and plating processes.

The team’s report, detailing findings and recommendations,

indicated that the onsite ion-exchange treatment of metalcontaining rinse water generates regenerant solutions that could

be further treated by electrowinning to recover metals and to

achieve significant cost savings.

This Research Brief was developed by the principal investigators and EPA’s National Risk Management Research Laboratory, Cincinnati, OH, to announce key findings of an ongoing

research project that is fully documented in a separate report

of the same title available from University City Science Center.

Introduction

The amount of waste generated by industrial plants has become an increasingly costly problem for manufacturers and an

additional stress on the environment. One solution to the

problem of waste generation 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 generation of waste but who lack

the in-house expertise to do so. Under agreement with EPA’s

National Risk Management Research 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 considerable direct experience with process operations in

manufacturing plants and also have the knowledge and skills

needed to minimize waste generation.

The pollution prevention opportunity 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, employ no more

than 500 persons, and lack in-house expertise in pollution

prevention.

The potential benefits of the pilot project include minimization

of the amount of waste generated by manufacturers, and

reduction of waste treatment and disposal costs for participating 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.

Pollution Prevention Assessment for a

Printed Circuit Board Plant

ENVIRONMENTAL

RESEARCH BRIEF

Harry W. Edwards*, Michael F. Kostrzewa*,

and Gwen P. Looby**

* Colorado State University, Department of Mechanical Engineering

* University City Science Center, Philadelphia, PA

United States

Environmental Protection

Agency

National Risk Management

Research Laboratory

Cincinnati, OH 45268

Research and Development EPA/600/S-95/020 September 1995
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Methodology of Assessments

The pollution prevention opportunity assessments require several site visits to each client served. In general, the WMACs

follow the procedures 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

identify 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 technological and economic information is developed. Finally, a confidential report that details the WMAC’s findings

and recommendations (including cost savings, implementation

costs, and payback times) is prepared for each client.

Plant Background

This plant manufactures printed circuit boards. It operates

approximately 4700 hr/yr to produce about 100,000 ft2 of product annually.

Manufacturing Process

The plant, which functions as a job- and small-productionshop, produces single-sided, double-sided, and multi-layer circuit boards.

Circuit information is received from customers as blueprints,

films, computer diskettes, or computer-generated artwork. Circuit information that is received as artwork is digitized and

computer-stored. The template for the circuit design, known as

the working film, is laser-generated from the customer’s circuit

information. Programs that provide drilling instructions for the

computer-controlled drilling machines are generated digitally.

The raw materials for printed circuit boards include copper/

epoxy laminates and copper foil. Laminates and foil are cut

into blank boards and layers using hydraulic shears. Component holes are then generated in the blank boards using highspeed, numerically-controlled drilling machines. The drilled

boards are mechanically scrubbed in preparation for plating.

Circuit patterns are created on the individual layers of multilayer boards with dry-film, positive-image photoresist. The first

step in transferring the electrical circuit design to the individual

layers is 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 and exposing the film to UV

light. Exposed film is polymerized and protects the underlying

copper circuitry and unexposed photoresist is removed with an

aqueous developing solution and rinse. Unwanted copper is

then removed with an ammonia/hydrogen peroxide etchant.

The remaining protective film is removed with an alkaline resist

stripper leaving the desired copper circuitry. 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 multi-layer panels, and

the holes are cleaned with a sulfuric acid-based de-smear

solution. Further processing of multi-layer boards is identical

to that of single and double-sided boards.

The circuit patterns for single and double-sided boards, and

the outer layers of the multi-layer boards are generated by a

series of photolithographic 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 electrolytically plated with tin/lead solder to protect

the copper circuity during subsequent steps to remove the

resist film and unwanted copper. The tin/lead 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 the customer with a surface for mounting electrical components. Additional processing involves conditioning of

the soldered surfaces, cleaning, rinsing, and inspecting the

finished circuit boards. Final processing includes silk-screen

application of a legend, routing, rinsing, electrical testing, inspections, packaging, and shipping.

An abbreviated process flow diagram for the production of

printed circuit boards is shown in Figure 1.

Existing Waste Management Practices

This plant already has implemented the following techniques to

manage and mint flowing rinses.

Pollution Prevention Opportunities

The type of waste currently generated by the plant, the source

of the waste, the waste management method, the quantity of

the waste, and the waste management cost for each waste

stream identified are given in Table 1.

Table 2 shows the opportunities for pollution prevention that

the WMAC team recommended for the plant. The opportunity,

the type of waste, the possible waste reduction and associated

savings, and the implementation cost along with the simple

payback time 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 the economic savings of the opportunities, in most cases, results from reduction in raw material and

costs associated 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 also should be noted that the

savings given for each opportunity that pollution prevention

opportunity alone and do not reflect duplication of savings that

may result when the opportunities are implemented in a package.

This research brief summarizes a part of the work done under

Cooperative Agreement No. CR-819557 by the University City

Science Center under the sponsorship of the U. S. Environmental Protection Agency. The EPA Project Officer was Emma

Lou George.
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Circuit Design

Copper/Epoxy Laminates,

Copper Foil

Laser Generation

of Working Film

Dry Film Application,

Exposure, and

Development

Cutting and

Drilling

Copper Etch and

Resist Stripping

Baking and

Bonding of Layers

Electroless Copper

Plating

Dry Film Application

and Development

Cleaning

Electrolytic Tin/Lead

Plating

Resist Strip and

Copper Etch

Solder Stripping

Solder Reflow

Silkscreening

Routing Electrolytic Copper

Plating

Circuit Boards Packaged and

Shipped to Customers

Figure1. Abbreviated process flow diagram for circuit board production.
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Table 1. Summary of Current Waste Generation

Annual Quantity Annual Waste

Waste Stream Generated Source of Waste Waste Management Method Generated (lb/yr) Management Cost

De-smear solution Electroless copper plating Shipped off-site as hazardous waste for

recovery or disposal 2,290 $2,120

Conditioner solution Electroless copper plating Shipped off-site as hazardous waste fo

recovery or disposal 2,290 4,050

Pre-dip solution Electroless copper plating Shipped off-site as hazardous waste for

recovery or disposal 15,580 2,710

Microetch solution (copper sulfate solution) Electroless copper plating Shipped off-site as hazardous waste for

recovery or disposal 5,500 1,490

Microetch solution (copper sulfate crystals) Electroless copper plating Shipped off-site as hazardous waste for

recovery or disposal 2,750 470

Rinse water Electroless copper plating Treated in on-site ion-exchange columns;

sewered 19,364,000 5,740

Organic cleaner Electrolytic copper plating Shipped off-site for incineration 11,910 10,060

Copper plating solution Electrolytic copper plating Shipped off-site for copper recovery 3,210 6,070

Rinse water Electrolytic copper plating Treated in on-site ion-exchange columns; sewered 19,364,000 5,740

Pre-dip solution Electrolytic tin/lead plating Shipped off-site as hazardous waste for

recovery or disposal 7,330 1,000

Rinse water Electrolytic tin/lead plating Treated in on-site ion-exchange columns;

sewered 9,682,000 2,870

Copper etchant Copper etching Shipped off-site for copper recovery 24,740 17,530

Tin/lead stripper Solder stripping Shipped off-site for tin and lead recovery 4,120 6,860

Solder brightener/conditioner Solder reflow Shipped off-site as hazardous waste for

recovery or disposal 5,040 2,490

Copper regenerant solution Ion-exchange treatment Shipped off-site for copper recovery 20,620 6,260

Copper precipitate Ion-exchange treatment Shipped off-site for copper recovery 8,250 3,430

Tin/lead regenerant solution Ion-exchange treatment Shipped off-site for tin/lead recovery 6,870 2,080

Screen washing solution Cleaning of silk screens Shipped off-site for incineration 1,170 2,920

Rack stripping solution Stripping of racks Shipped off-site for copper recovery 11,910 3,130

Copper scrap Board trimming Shipped off-site as municipal trash 4,520 0
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Table 2. Summary of Recommended Pollution Prevention Opportunities

Annual Waste Reduction

Net Annual Implementation Simple

Pollution Prevention Opportunity Waste Stream Reduced Quantity (lb/yr) Per Cent Savings Cost Payback (yr)

Install an electrowinning system in conjunction Copper regenerant solution 20,620 100 $ 6,640 $ 24,360 3.7

with the ion-exchange systems on the copper- Tin/lead regenerant solution 6,870 100

bearing and tin/lead-bearing rinse water streams

to recover dissolved metals from the regenerant

solutions. Sell the recovered metals to a recycler.

A total of 309 lb/yr of scrap metal will be shipped

to the recycler.

Use polyethylene plating racks in the electrolytic Rack stripping solution 8,910 75 2,350 4,030 1.7

copper plating bath to reduce the need for subsequent stripping of unwanted copper from the

metal plating racks.

Install flow meters, flow reducers, and contact Rinse water (electroless copper plating) 2,904,600 15 2,150 2,560 1.2

switches to reduce water usage by process Rinse water (electrolytic copper plating) 2,904,600 15

rinses. Rinse water (electrolytic tin/lead plating) 1,452,300 15
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BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

National Risk Management Research Laboratory (G-72)

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/S-95/020