United States Environmental Protection Agency Risk Reduction Engineering Laboratory Cincinnati, OH 45268 Research and Development EPA/600/M-91/022 July 1991 ENVIRONMENTAL RESEARCH BRIEF Waste Minimization Assessment for a Manufacturer of Printed Circuit Boards F. William Kirsch and Gwen P. Looby* Abstract The U.S. Environmental Protection Agency (EPA) has funded a pilot project to assist small- and medium- size manu- facturers 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 Minimization Opportunity Assessment Manual (EPA/625/7- 88/003, July 1988). The WMAC team at Colorado State University inspected a plant producing printed circuit boards — a plant that already had taken steps to control its hazardous wastes. Producing a circuit board involves many major pro- cesses and subprocesses: preparing the board; depositing copper en the board by electroless plating; applying dry film; electrolytically plating copper; electrolytically plating tin; etch- ing and stripping; applying solder; and, perhaps, plating gold on connectors. Each of these steps produces hazardous wastes, e.g., electrolytic copper plating results in acid soap dumps, copper and tin drag-out, and sulf uric acid. The main sources of metallic contamination (copper [both dissolved and metallic], tin, lead, gold) are the rinses after scrubbing, plating, and etching. Although the greatest amount of waste can be reduced by reusing effluent from the MEMTEK f (with some further treatment), the greatest dollar savings can be found by chang- ing the dry film developer. The present brand adheres strongly to the unexposed film and requires an aggressive acid soap; a less aggressive, nonhazardous soap could be used with a less- adhering dry film developer. This Research Brief was developed by the principal inves- tigators and EPA's Risk Reduction Engineering Laboratory, Cincinnati, OH, to announce key findings of an ongoing re- search 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 manufac- turers and an additional stress on the environment. One solu- tion 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 manu- facturers who want to minimize their formation of hazardous waste but lack the inhouse expertise to do so. Under agree- ment with EPA's Risk Reduction Engineering Laboratory, the Science Center has established three WMACs. This assess- ment 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 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 for the assessment, each client must fall within University City Science Center, Philadelphia, PA 19104 Mention of trade names or commercial products does not constitute endorsement or recommendation for use. Printed on Recycled Paper ------- persons, and lack mhouse expertise in waste minimization ment without more regulations and higher costs for manufactur- ers Methodology Of Assessments 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. Fi- nally, a confidential report that details the WMAC's findings and recommendations (including cost savings, implementation costs and payback times) is prepared for each client. ' _. A _ , Plant Background This plant typically operates about 4,500 hr/yr to turn out printed circuit boards, which are distributed regionally Like the plants of some other small and medium-size manufacturers this one had taken several steps on its own initiative to control hazardous waste emissions. It presented a challenge to the in their 8fforts to idenwy addifonai Manufacturing Operations The lami'nated flat sheets of nonconducting material are A thin layer of copper is deposited by electroless platinq on boards that are first cleaned and rinsed and then coated wrth a catalyst for the reduction of the copper To apply the circuit pattern, a dry film process is used — laminating a photosensitive polymer resist, covering parts of the board with the printed circuit design mask before exposure to ultraviolet liqht develooina with sod'um carbonate, and eventually rinsing with' tap water .-. Electrolytic plating of copper occurs on the circuit design developed in the preceding series of operations Then tin is electronically plated on the^copper to protect the circuft deSgn A the alkahne etchant used to strip away the plating resist. A"y.coPPe[ not Protected by tin is also etched away by an aiKalin® solution. Finally, an ammonium bifluoride-hydrogen pero*lde s°'utl?n removes the tin to complete the electronic circuitry on the board- whlch IS then water-rinsed and air-dried. The plant had already taken these kinds of actions to reduce hazardous waste: Using dry film photoresist to eliminate chlorinated solvents associated with silk screen application. Substituting tin for lead solder after electrolytic areas, which are the portions of the boards not coated by an epoxy solder mask, which also functions as an insulator Then a eutectic solder is coated on the surface not covered by the mask. 7 To meet certain customers' specifications, connectors are sometimes gold plated before solder mask application. Combining an automated electroless plating machine with countercurrent rinsing to cut down drag-out of plating solution and to reduce the quantity of rinse water. Agitating these rinse tanks with compressed air to get better rinsing in a given tank volume . Most of the hazardous waste generated in this plant occurs m various liquid streams. These major waste streams, together with their treatment, disposal, and recycling costs are given in Table 1 • Tnnirttha*!«« *• • . iI5 E "V*u lnformatlon Into Perspective, it is useful to keep - .*•* covered racks tor those excess copper and tin deposits on the racks. • Applying mechanical deburrers, scrubbers, and hot-air dryers to eliminate some hazardous solvents. (The dusts from these operations are collected and sold to a metal reclaimer ) '' The basic operation of the plant consists of a complex series of mechanical and chemical process steps to deposit copper selectively on flat sheets of nonconducting materials formed from resins and fiber glass. Of course, the copper must lines- and in the alkaline "ch and Metallic copper is generated by mechanical cleaning op- orations, drilling and routing operations, and cutting operations . . ' In comes from electrolytic plating and stripping; lead from rinsing and deburring. D- .? streams discharged to the sewer because they are IL considlered hazardous are those from the dry film developer ,8 P03^'830 rinse- the gold plating rinse, and the spent resist sirippor. ------- Board Preparation • Hydraulic shearing • Drilling • Debarring Electroless Copper Plating Hot soap cleaner Rinses Preetch Miaoetch Catalyst predip Catalyst Rinses Accelerator Rinses Electroless copper plating Rinse Neutralizer Rinse Hot air dryer Dry Film Application • Photopolymer lamination • Mask Application • UV exposure • Developer • Rinse Electrolytic Copper Plating Acid soap Cascade and bath rinse Microetch Spray and bath rinse Sulfuric acid predip Electrolytic copper plating Spray Rinse ^- Electrolytic Tin Plating • Sulfuric acid predip • Electrolytic tin plating Etch & Strips Resist stripper Alkaline etch Rinse Tin stripper Rinse Hot air dryer Gold Tab Plating • Mask application • Nickel plating • Rinse • Gold plating • Rinse Solder Application Solder mask application Thermocuring Copper cleaner/rinse Hot air leveling Post clean Fine scrubber Final Processes • Inspection • Labeling • Routing • Packaging • Storage Figure 1. Sequence of Manufacturing Operations. ------- The other rinses and dumps are directed into a large trench with a level controller (but without a sewer connection). The controller activates a pump to transport the liquids to a MEMTEK ultrafiltration system (to 0.1 u.) that uses chemical reactions, precipitation, and membrane filtration. Suspended solids in an associated concentration tank are removed by bleeding a "slip stream" to a settling tank, from which sludge is dewatered to about 60% solids before it is hauled to a solid disposal site for hazardous wastes. As noted in Table 1, some solutions are taken out of the plant for metal recovery and a credit. Summary of Recommended Waste Minimization Eight waste minimization opportunities (WMOs) recom- mended by the WMAC team could cut the annual waste man- agement costs at this plant from $86,850 to $42,225, about a 51% reduction. The largest waste volume is liquid (2.97 million gal/yr), but one recommended WMO could reduce that by 62% through recycling effluent from the MEMTEK filtration unit. Because of the relatively low cost of water supply and sewering, however, this large volumetric reduction will save only about $3,840/yr at the present time. A dry film developer is applied to the circuit boards to remove unexposed photopolymer (under the design mask) and reveal the circuit design. The largest cost saving for a particular WMO ($23,550/yr) is estimated to come from substituting a different developer. The sodium carbonate developer being used requires a very aggressive acid soap to remove it before copper is electrolytically deposited. When this soap is rinsed and the rinsings go to the ultrafiltration unit (MEMTEK), the relatively large soap molecules frequently plug the pores of the filtering membranes in the MEMTEK. With a less adhesive developer, a less aggressive soap solution can be applied, and then the washings can be adjusted for pH and sent directly to the sewer. In addition, the conditioner now used to treat the spent acid soap and rinsings before they go to the MEMTEK can be eliminated. The circuit board manufacturer knew of alternative developers, such as Morton Thiokol's Dynaclean, which reportedly can be cleaned by the MacDermid L5-B that forms a nonhazardous waste. Product names are given to illustrate that such products are commercially available. All eight WMOs are summarized in Table 2, together with their reductions in emissions and the associated savings and costs. The savings are calculated for each WMO independently, but it is obvious that some are related, so that the results from implementing one can affect the results independently calcu- lated for another. 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. Environ- mental Protection Agency. The EPA Project Off icer was Brian A Westfall. at: The EPA contact, Emma L. George, and can be reached Pollution Prevention Research Branch Risk Reduction Engineering Laboratory U.S. Environmental Protection Agency Cincinnati, OH 45268 Table 1. Summary of Current Waste Generation Waste Stream Hazardous Waste Generated Hazardous Liquid Waste A. Electroless copper: Waste rinses Catalyst predip Accelerator B. Electrolytic copper: Acid soap predean Water rinses Copper plating predip Tin plating predip C. Resist strip, copper etch, and tin strip: Water rinses Alkaline etch Tin strip Rack stripper D. Other processes: Deburrer #1 Deburrer #2 Scrubber Hot air leveling Hazardous Solid Waste A. MEMTEK unit Annual Quantity Annual Waste Management Costs Generated Treatment Disposal Recycling Copper plating and chemical drag-out 916,663 gal Table salt/water dumps 530 gal Copper-laden, dilute hydrochloric acid 530 gal Acid soap dumps 10,189 gal Soap, etch, copper and tin plating drag-out 366^665 gal 10% Sulfuric acid dumps 3,266 gal 2% Sulfuric acid dumps 3^266 gal Etch, resist and tin strips drag-out 549,997 gal Spent ammonium hydroxide 13,950 gal Spent ammonium bifluoride/peroxide 1,450 gal Spent rack stripper 1 [550 gal Copper-laden rinse water 366,665 gal Copper-, tin/lead-, and gold-laden rinse water 366ie65 gal Epoxy-, Copper-, and tin/tead-laden rinse water 183,332 gal Copper-, ferric chloride-, hydrochloric acid-laden rinse 183,332 gal Metal hydroxide sludge 27,700 Ib $10,488 $4,380 $587 $246 $6,285 $352 $45.765 $12,570 $704 $5,471 ------- Table 1. Continued. Waste Stream Hazardous Waste Generated B. Electroless copper: Microetch C. Drilling and routing D. Deburrer #1 E. Shearing F. Filters: Electrolytic copper Post clean Auto tab plater Copper sulfate crystals Copper, aluminum, and gold dust Metallic copper Copper/epoxy laminate dropoffs Nonhazardous filter cake Tin/lead-laden filters Gold-laden resin filter cartridges Annual Quantity Annual Waste Management Costs Generated Treatment Disposal Recycling 2,800 Ib 200 Ib 200 Ib 1,200lb 25 Ib 25 Ib 25 Ib Table 2. Summary of Recommended Waste Minimization Opportunities Present Practice Proposed Action Waste Reduction and Associated Savings All but four rinse streams (dry film developer, post dean, gold plater, spent resist stripper) and process bath dumps go to a common trench and from there to the MEMTEK, in which they are chemically reduced, precipitated, filtered, and settled. The scrubber uses 183,300 gal/yr to rinse particulates from circuit boards—metallic copper, lead, tin, and epoxy. The liquid containing particulates goes to the MEMTEK.from which effluent goes to the sewer. Thorough rinsing is mandatory for many operations in this plant. Observation of the plant revealed operators set flow rates for water excessively high. The particular brand of dry film developer in use adheres so strongly to the unexposed film that an aggressive acid soap is required for removal. This soap presents problems in the MEMTEK and necessitates prior treatment with conditioning agents. Tin is stripped away from the electrolytically deposited copper sites that it protects. A solution of ammonium bifluoride and hydrogen peroxide is the stripping agent. The relatively large quantity of washes is sent off-site for treatment and recovery of tin. Deionized water is used for rinsing on the electrolytic copper and tin plating lines. Its use should be extended to the electroless copper plating line. Reuse the MEMTEK effluent to reduce demand for rinse water. To widen the range of possible uses, some further treatment (e.g., ion exchange, adsorption, and filtration) may be needed. Additional storage tanks, pumps, and piping will be required. Saving occurs in lower water demand and sewer charges. Filter (in a closed loop system) scrubber liquids to remove hazardous particulates and recycle the water for rinsing the scrubber. Dispose of filter cartridge as solid hazardous waste. Install flow reducers or flow meters on the water supply to seven identified manufacturing operations. Waste reduction and cost savings are calculated only for reduced water usage, treatment costs, and sewer costs. Change to another dry film developer, use a less aggressive soap (also nonhazardous), and discharge the liquid to the sewer after pH adjustment. Concentrate the tin stripping solution to reduce hauling and treatment costs. Partial freezing will cost less than evaporation. The metal reclaimer has said the concentrate is acceptable, and there will be no increase in unit costs of hauling and recycling. The separated solid can be melted and sewered. Use deionized water in five baths in the electroless copper plating line, thereby reducing sludge formation and extending the lifetime of the bath. The savings will be achieved in lower cost of treatment chemicals, as well as in lower water and sewer costs. Use an ion-exchange regener- ation system. Waste reduction = 1,833,325 gal/yr Cost reduction = $3,840/yr (net) Implementation cost = $22,000 Simple payback = 5.7 yr Waste reducion = 183,300 gal/yr Cost reduction = $2,150/yr (net) Implementation cost = $650 Simple payback = 4 mo Waste reduction = 440,000 gal/yr Cost reduction = $5,840/yr Implementation cost = $360 Simple payback = less than 1 mo Waste reduction = 13,500 gal/yr Cost reduction = $23,550/yr (based on conditioner use alone) Implementation cost = $0 Simple payback = immediate Waste reduction = 1,650 gal/yr Cost reduction = $4,030/yr (net) Implementation cost = $10,000 Simple payback = 2.5 yr Waste reduction = 1,015 gal/yr Cost reduction = $1,840/yr Ion-exchange saving = $6,500/yr Implementation cost = $9,800 Simple payback = 1.2 yr ------- Table 2. Continued. Present Practice Prooosed Action Wa*Ste Reduction and rroposea Acnon Associated Savings Implementation cost = $0 Simple payback = immediate reagents implementation cost = $200 copper nuggets, and tin anodes will result. Simple payback = 9 mo &U.S. GOVERMMENT PRINTING OFFICE: 1991 548 028/40028 ------- ------- United States Center for Environmental Research BULK RATE Environmental Protection Information POSTAGE & FEES PAID Agency C.ncinnati, OH 45268 E^ PERM^ NO G 35 Official Business Penalty for Private Use $300 EPA/600/M-91/022 ------- |