&EPA United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati, OH 45268 Research and Development EPA/600/M-91/045 Oct. 1991 ENVIRONMENTAL RESEARCH BRIEF Waste Minimization Assessment for a Manufacturer of Prototype Printed Circuit Boards F. William Kirsch andGwen 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 hazardous waste but lack the expertise to do so. Waste Minimization Assessment Centers (WMACs) were established at selected universities and procedures were adapted from the EPA Waste Minimiza- tion Opportunity Assessment Manual (EP A/625/7-88/003 July 1988). The WMAC team at Colorado State University per- formed an assessment at a plant manufacturing prototype printed circuit boards. Various processes are involved including photographic operations, drilling, scrubbing, laminating, etch- ing, and plating. The majority of the waste generated by this plant comes from the plating process. The team's report, detailing findings and recommendations, indicated that the greatest waste reduction and cost savings would result from recovering copper, tin, and lead from the plating wastewater. 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 the authors. Introduction The amount of hazardous waste generated by industrial plants has become an increasingly costly problem for manufacturers 'University City Science Center, Philadelphia, PA 19104. and an additional stress on the environment. One solution to the problem of hazardous waste 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 formation of hazardous waste but lack the inhouse 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 assessmentteams have considerable direct experience with process operations in manufacturing plants and also have the knowledge and skills needed to minimize hazardous 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 forthe assessment, each client must fall within Standard Industrial Classification Code 20-39, have gross annual sales not exceeding $50 million, employ no more than 500 persons, and lack inhouse expertise in waste minimization. The potential benefits of the pilot project include minimization of the amount of waste generated by manufacturers, reduced waste treatment and disposal costs for participating plants valuable experience for graduate and undergraduate students who participate in the program, and a cleaner environment without more regulations and higher costs for manufacturers. ^£/y Printed on Recycled Paper ------- Methodology of Assessments The waste minimization assessments require several s'rte visits to each client served. In general, the WMACs follow the procedures outlined in the EPA Waste Minimization Opportu- nityAssessment Manual(EPA/625/7-88/003, July 1988). The WMAC staff locates the sources of hazardous waste in the plant and identifies 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 support- ing 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 prototype single-sided, double-sided, and multi-layer printed circuit boards, the plant operates 3,500 hr annually to produce approximately 175,000 boards/yr. Manufacturing Process Preproduction Activities The manufacture of circuit boards begins with preproduction activities such as engineering, photographic operations, and programming. Circuit information-is usually received from the customer in the form of diagrams, films, computer-generated artwork, and computerized drill programs. A template for the circuit design (known as the working film) is generated photo- graphfcalJy by the plant from the circuit information supplied. Sheets of copper foil/epoxy/copper foil laminate are cut to size as blank boards. The boards are drilled, scrubbed, and rinsed in preparation for circuit creation. Excess epoxy is removed from the drilled holes by a plasma desmear machine or with concentrated sulfurte acid. Inner Layers The circuit pattern used in creating the individual inner layers of multi-layer arrays is generated with positive-image photoresist. In order to transfer the electrical circuit design to the board, a U V-sens'rtive dry-film photoresist is first laminated to the board. An image of the circuit design is generated on the board by placing a template of the circuit over the film, exposing the film to UV light, and then developing the photoresist. Unexposed photoresist is removed and the exposed photoresist is polymer- ized and remains in order to protect the copper circuitry. A sutfurfc acid-based etchant is then used to remove the unwanted, unprotected copper. The remaining protective film is removed to reveal the copper circuitry that is then oxidized and cleaned. The oxidation process permits effective interlayer bonding between panels in multi-layer arrays. A heated hydrau- lic press is used to form multi-layer arrays from the individual boards. Outer Layers Circuit patterns on the outer surfaces of multi-layer arrays and double-sided boards are generated using a similar process. First the board surfaces are copper-plated using an electroless plating process. Negative-image dry-film photoresist is then applied in order to define the circuit pattern. Additional copper is then electrolytteally plated on the circuit patterns to provide a sturdy substrate for mounting components and connectors. The boards are cleaned and then the circuitry is plated with a tin-lead solder to protect it during the removal of unwanted copper and resist film. Further processing includes the conditioning of soldered sur- faces, cleaning, rinsing, and inspection. The legend is then applied using silk-screening and the boards are routed, rinsed, electrically tested, inspected, packed, and shipped Waste Generation Relatively clean rinses and other wastewater with contaminant levels below the publicly owned treatment works (POTW) limits are discharged directly to the sewer as industrial wastewater. Rinse streams and spent reagent solutions with contaminant levels above the POTW limits are treated onsite in a MEMTEK* uftraf ittration system. Dried sludgef rom the MEMTEK is shipped to a copper smelter for final disposal. Copper sulfate crystals precipitated from the spent copper etching solution and waste etchant are shipped to an offsite recycler for copper recovery. Silver from waste photographic fixer is recovered onsite. Cop- per/epoxy/aluminum dust generated by drilling and debarring operations is disposed of as conventional waste. Aluminum and copper foil scraps are collected and shipped offsite for recycling. Table 1 shows the waste streams generated by this plant, the waste management methods used, and the quantities and costs of wastes disposed. Existing Waste Management Practices This plant has taken the following steps to manage and mini- mize its wastes: • Deionized water is used for makeup thereby reducing sludge formation. • Rinses in the plating process are used only as required. Time-controllers, spray-rinses, and counted low rinses are also used to minimize water consumption. • Mechanical scrubbers are used instead of solvent-based cleaning and solvent-based drying is replaced by hot-air dryers. • The use of dry film plating resist replaces the use of chlorinated solvents in conjunction with silkscreening op- erations. • Water from overflow rinses enters the tanks from the bottom and drains from the top of the tanks thereby improving mixing and reducing water usage. • Scrap aluminum is collected and sold to a recycler. • Silver is recovered onsite from a waste photographic fixer. . Copper-containing sludge is shipped to a smelter for metal recovery. • Copper sulfate crystals are shipped offsite for metal recov- ery. Mention of trade names or commercial products does not constitute endorsement or recommendation for use. ------- Waste Minimization Opportunities Table 2 presents brief descriptions of the waste minimization opportunities (WMOs) recommended forthe plant by the WMAC. The quantities of hazardous 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. ft should be noted that the economic savings of the minimiza- tion opportunity, in most cases, results from the need for less raw material and from reduced present and future costs asso- ciated with hazardous 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 should also be noted that the savings given for each opportunity reflect the savings achiev- able when implementing each waste minimization opportunity independently and do not reflect duplication of savings that would result when opportunities are implemented in a package. Additional Recommendations The WMAC team also investigated several other opportunities for waste minimization that required lengthy paybacks or were considered to be beyond the scope of this program. Those measures are: • Reduce sludge volume through precipitant substitution. • Reuse the MEMTEK effluent that is discharged to the sewer. • Increase drainage times over plating baths. • Install a sludge dryer. • Recover and recycle the copper from the copper/epoxy scrap. This Research Brief summarizes a part of the work done under Cooperative Agreement No. CR-814903 by the University City Science Center underthe sponsorship of the U.S. Environmen- tal Protection Agency. The EPA Project Officer was Emma Lou George. Table 1. Summary of Current Waste Generation Waste Generated Waste Management Method Annual Quantity Generated Annual Waste Management Cost Plating Operations Treated rinse water Untreated rinse water Copper etchant Plating sludge Copper sulfate crystals Other Operations Cooling water Waste photo fixer Copper/epoxy scrap Treated in MEMTEK and sewered Sewered Offsite metal recovery and disposal Shipped to smelter Offsite metal recovery Sewered Silver recovered onsite Offsite landfill 398,700 gal 1,200,200 gal 330 gal 21,97516 9,985 Ib 113,750 gal 35 gal 13,000 Ib $24,630' 1,880' 690 4,900 890 180' 0 0 'Includes raw material costs. Table 2. Summary of Recommended Waste Minimization Opportunities Present Practice Proposed Action Waste Reduction and Associated Savings The current waste management method for plating wastewater and reagent bath dumps involves precipitation and ultra- filtration using a MEMTEK system. This method results in a considerable amount of plating sludge that is shipped to a smelter for copper recovery. Overflow rinse water rates exceed the flow rates required for certain processes. Cooling water from the heated press is sewered after use. Install at ion exchange/electrowinning system to recover copper, tin, and lead from the plating wastewater. The recovered metals can be sold to a recycler and the treated rinse water can be discharged to the sewer as industrial wastewater. Reduce water usage by installing timers, flow reducers, and flow meters. Reuse the cooling water as rinse water in the plating line. Waste reduction = 21,975 Ib/yr Additional waste generated = 1,830 gal/yr Waste management cost savings=$22,070/yr Implementation cost = $60,520 Simple payback = 2.7 yr Waste reduction = 293,000 gal/yr Waste management cost savings = $460/yr Implementation cost = $990 Simple payback = 2.2 yr Waste reduction = 113,750 gal/yr Waste management cost savings = $180/yr Implementation cost = $400 Simple payback = 2.2 yr •ttV.S. GOVERNMENT PRINTING OFFICE: 1991 - S4S-018/40075 ------- United States Environmental Protection Agency Center for Environmental Researqh Information Cincinnati OH 45268 BULK RATE POSTAGE & FEES PAID EPA PERMIT NO. G-35 Official Business Penalty for Private Use $300 EPA/600/M-91/045 ------- |