United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S-94/015 September 1994
ENVIRONMENTAL
RESEARCH BRIEF
Waste Minimization Assessment for a Manufacturer
of Microelectronic Components
Harry W. Edwards*, Michael F. Kostrzewa,
and Gwen P. Looby**
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 manufactur-
ers, Waste Minimization Assessment Centers (WMACs) were
established at selected universities, and procedures were
adapted from the EPA Waste Minimization Opportunity As-
sessment Manual (EPA/625/7-88/003, July 1988). That docu-
ment has been superseded by the Facility Pollution Prevention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 cir-
cuitry is generated on sheet-alumina substrates using photoli-
thography 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, indi-
cated that the waste streams generated in the greatest quanti-
ties 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 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 available from University City Science Center, Phila-
delphia, PA.
* Colorado State University, Department of Mechanical Engineering, Fort Collins,
CO
"University City Science Center, Philadelphia, PA
Introduction
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
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 Reduc-
tion Engineering Laboratory, the Science Center has estab-
lished 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 ex-
perience 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 minimiza-
tion.
The potential benefits of the pilot project include minimization
of the amount of waste generated by manufacturers and re-
duction 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.
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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 proce-
dures 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 tech-
nological and economic information is developed. Finally, a
confidential report that details the WMAC's findings and recom-
mendations (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 vacuum-
chamber vapor deposition to form circuit components. Photore-
sist 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, in-
spected, 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 re-
moval 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 sol-
der 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 pos-
sible 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 in-
clude a wide variety of possible future costs related to chang-
ing 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 du-
plication 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. Environmen-
tal Protection Agency. The EPA Project Officer was Emma
Lou George.
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Alumina sheets
Initial
cleaning
Die
attaching
Cleaning
Vapor
deposition
Photolithography
Die
cutting
Stripping
and
etching
Testing
Figure 1. Abbreviated process flow diagram.
Inspection
Completed microcircuits.
packaged and shipped
Table 1. Summary of Current Waste Generation
Waste Stream Generated
Source of Waste
Waste Management
Method
Annual Quantity
Generated (Ib)
Annual Waste
Management Cost*
Waste acetone
Evaporated acetone
Waste isopropanol
Evaporated isopropanol
Waste developer
(aqueous sodium hydroxide)
Waste photoresist
Waste acetone
Evaporated acetone
Waste hydrogen peroxide
Tri-iodide stripper/gold
Rinse water
Initial cleaning of thin-film substrate
Initial cleaning of thin-film substrate
Initial cleaning of thin-film substrate
Initial cleaning of thin-film substrate
Photolithography
Stripping following photolithography
Stripping following photolithography
Stripping following photolithography
Etching following photolithography
Stripping following photolithography
Various operations
Shipped offsite for incineration 740
Evaporates to plant air 100
Shipped offsite for incineration 380
Evaporates to plant air 330
Shipped offsite for incineration 2,180
Shipped offsite for incineration O1
Shipped offsite for incineration 370
Evaporates to plant air 470
Shipped offsite for incineration O2
Shipped offsite for gold recovery 1,830
Sewered 37,800,000
$720
80
460
260
1,360
O1
420
370
O2
650
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 Ib 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
Minimization Opportunity
Neutralize waste developer and heat in an
evaporator to reduce the water content
of the waste shipped offsite.
Install flow meters and flow reducers to re-
duce water usage in the production areas
of the plant.
Extend the length of usage of the acetone
and isopropanol in the initial cleaning baths
and of the acetone in the baths of the photo-
resist removal process.
Replace acetone in the initial cleaning bath
with a nonhazardous cleaner. Distill and
reuse the replacement solvent cleaner.
(A negligible amount of still bottoms will
be generated.)
Reuse acetone from the initial cleaning
bath for photoresist removal.
Waste Stream Reduced
Waste developer
Rinse water
Waste acetone
Waste isopropanol
Waste acetone
Evaporated acetone
Waste acetone
Quantity (Ib)
1
4,540,000
500
250
190
50
370
Per cent
~
12
45
66
26
50
50
Savings Cost Payback (yr)
$940 $2,800 3.0
920 400 0.4
850 0 Immediate
225 90 0.4
420 0 Immediate
This opportunity does not reduce the quantity of waste generated, but it does offer a cost benefit to the manufacturer.
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United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/S-94/015
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