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 That document has been superseded by the Facility Pollution Prevention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 microelectronic components. Thin-film circuitry is generated on sheet-alumina substrates using photolithography for pattern generation and vacuum-chamber vapor

deposition to form circuit components. Integrated circuits and

other components are attached to the ceramic substrates. The

team’s report, detailing findings and recommendations, indicated that the waste streams generated in the greatest quantities are rinse water and waste developer and that significant

cost savings could be realized by installing flow meters and

flow reducers in certain production areas.

This Research Brief was developed by the principal investigators and EPA’s Risk Reduction Engineering 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, Philadelphia, PA.

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 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 Risk Reduction Engineering 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 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 $75 million, employ no more than

500 persons, and lack in-house expertise in waste minimization.

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.

Waste Minimization Assessment for a Manufacturer

of Microelectronic Components

United States

Environmental Protection

Agency

Risk Reduction

Engineering Laboratory

Cincinnati, OH 45268

Research and Development EPA/600/S-94/015 September 1994

Harry W. Edwards*, Michael F. Kostrzewa,

and Gwen P. Looby**

E AP ENVIRONMENTAL

RESEARCH BRIEF

* Colorado State University, Department of Mechanical Engineering, Fort Collins,

CO

** University City Science Center, Philadelphia, PA
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Methodology of Assessments

The waste minimization 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 monolithic and hybrid amplifiers and

integrated circuit assemblies. Over 100,000 assemblies are

produced by the plant during approximately 5,000 hr/yr of

operation.

Manufacturing Process

Thin-film circuitry is generated on sheet-alumina substrates

using photolithography for pattern generation and vacuumchamber vapor deposition to form circuit components. Photoresist is applied to the substrate, dried, exposed to ultra-violet

light, and developed to leave polymerized material on areas to

be protected during subsequent vapor deposition. Remaining

photoresist is removed with a resist stripper. These process

steps may be repeated several times to add circuit elements in

a sequential manner. Resistors are trimmed to specifications

using laser cutting machines.

Assembly of the products involves attaching integrated circuits

and other components to the ceramic substrates. Much of the

process is automated. The resulting products are tested, inspected, packaged, and shipped.

An abbreviated process flow diagram for this plant is shown in

Figure 1.

Existing Waste Management Practices

This plant already has implemented the following techniques to

manage and minimize its wastes:

• Waste acetone from the stagnant bath for photoresist removal is reused in the ultrasonic acid bath in the same line.

• Waste tri-iodide stripping solution is shipped offsite for gold

recovery.

• Water-based solder fluxes are replacing solvent-based solder fluxes.

• A closed-loop rinse is used for the cleaning that follows

stripping and etching.

• Acetone and isopropyl alcohol baths and waste drums are

kept covered to reduce evaporation.

Waste Minimization 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 annual waste management cost for each

waste stream identified are given in Table 1.

Table 2 shows the opportunities for waste minimization that the

WMAC team recommended for the plant. The minimization

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 financial savings of the minimization

opportunities result from the need for less raw material and

from reduced present and future costs associated with waste

management. 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

reflect the savings achievable when implementing each waste

minimization opportunity independently 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, three additional measures were considered.

These measures were not analyzed completely because of

insufficient data, minimal savings, implementation difficulty, or

a projected lengthy payback. Since one or more of these

approaches to waste reduction may, however, increase in

attractiveness with changing conditions in the plant, they were

brought to the plant’s attention for future consideration.

• Reuse the laser cooling water instead of sewering it after use.

• Use deionized water and a hot air dryer to replace acetone

and isopropyl alcohol used for drying wafers after initial

cleaning.

• Continue to use the tri-iodide gold stripper for a longer period

of time before disposal.

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. Environmental Protection Agency. The EPA Project Officer was Emma

Lou George.
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Alumina sheets

Initial

cleaning

Vapor

deposition Photolithography

Die

attaching

Die

cutting

Stripping

and

etching

Cleaning Testing Inspection

Completed microcircuits

packaged and shipped

Figure 1. Abbreviated process flow diagram.

Table 1. Summary of Current Waste Generation

Waste Management Annual Quantity Annual Waste

Waste Stream Generated Source of Waste Method Generated (lb) Management Cost*

Waste acetone Initial cleaning of thin-film substrate Shipped offsite for incineration 740 $720

Evaporated acetone Initial cleaning of thin-film substrate Evaporates to plant air 100 80

Waste isopropanol Initial cleaning of thin-film substrate Shipped offsite for incineration 380 460

Evaporated isopropanol Initial cleaning of thin-film substrate Evaporates to plant air 330 260

Waste developer Photolithography Shipped offsite for incineration 2,180 1,360

 (aqueous sodium hydroxide)

Waste photoresist Stripping following photolithography Shipped offsite for incineration 01 01

Waste acetone Stripping following photolithography Shipped offsite for incineration 370 420

Evaporated acetone Stripping following photolithography Evaporates to plant air 470 370

Waste hydrogen peroxide Etching following photolithography Shipped offsite for incineration 02 02

Tri-iodide stripper/gold Stripping following photolithography Shipped offsite for gold recovery 1,830 650

Rinse water Various operations Sewered 37,800,000 7,660

* Includes waste treatment, disposal and handling costs, and applicable raw material costs.

1 No waste was shipped offsite during the previous yr; waste is accumulating onsite. No estimate of the quantity of accumulated waste was available. 2 No waste was shipped offsite during the previous yr; waste is accumulating onsite. Fifty-five lb of waste had accumulated at the time of the assessment.
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Table 2. Summary of Recommended Waste Minimization Opportunities

Annual Waste Reduction

Net Annual Implementation Simple

Minimization Opportunity Waste Stream Reduced Quantity (lb) Per cent Savings Cost Payback (yr)

Neutralize waste developer and heat in an Waste developer —-1 —- $940 $2,800 3.0

 evaporator to reduce the water content

 of the waste shipped offsite.

Install flow meters and flow reducers to re- Rinse water 4,540,000 12 920 400 0.4

 duce water usage in the production areas

 of the plant.

Extend the length of usage of the acetone Waste acetone 500 45 850 0 Immediate

 and isopropanol in the initial cleaning baths Waste isopropanol 250 66

 and of the acetone in the baths of the photo-

 resist removal process.

Replace acetone in the initial cleaning bath Waste acetone 190 26 225 90 0.4

 with a nonhazardous cleaner. Distill and Evaporated acetone 50 50

 reuse the replacement solvent cleaner.

 (A negligible amount of still bottoms will

 be generated.)

Reuse acetone from the initial cleaning Waste acetone 370 50 420 0 Immediate

 bath for photoresist removal.

1 This opportunity does not reduce the quantity of waste generated, but it does offer a cost benefit to the manufacturer.
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BULK RATE

POSTAGE & FEES PAID

EPA

PERMIT No. G-35

United States

Environmental Protection Agency

Center for Environmental Research Information

Cincinnati, OH 45268

Official Business

Penalty for Private Use

$300

EPA/600/S-94/015