9th ANNUAL AEROSPACE HAZARDOUS MATERIALS MANAGEMENT CONFERENCE SEPTEMBER 28-30,1994 DENVER, COLORADO

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1 9th ANNUAL AEROSPACE HAZARDOUS MATERIALS MANAGEMENT CONFERENCE SEPTEMBER 28-30,1994 DENVER, COLORADO TECHNICAL PAPER COVER SHEET Paper Title: Martin Marietta Control Systems - ODC Elimination Program for Manufacturing Processes Number of Pages: - 8 Primarv Author: Joseph E. Kane Martin Marietta Control Systems Johnson City, NY Presenter:, Co-Authors: Same Melonie M. Sviatyla Environmental, Health and Safety Leader Martin Marietta Control Systems

2 Martin Marietta Control Systems ODC Elimination Program For Manufacturing Processes Joseph E. Kane Senior Process Engineer & Melanie M. Sviatyla Environmental, Health, And Safety Leader Martin Marietta Control Systems Johnson City, New York Abstract For cleaning electronics in low-to-medium volume production, few processes have proven as flexible or easy to implement as vapor degreasing. As a result, many users looking to eliminate ozone depleting chemicals have been forced to reexamine virtually all aspects of electronics assembly and soldering. Even shops with a modest product mix often need completely different process solutions for cleaning at component prep, wave and ref1 ow sol der i ng, hand sol der touchup, conformal coat, cable and harness assembly, chassis wiring, and test rework. This is especially true for military contractors, who have fewer process options than their commerci a1 cousins. Many equipment suppliers have concentrated on the high end of the market, developing expensive in-1 ine equipment for high volume businesses. Effective batch systems are available, but some needs continue unmet, forcing smal 1 er shops to devel op home-grown sol uti ons. This presentation will outline the ODC elimination efforts at one medium-volume supplier of flight-critical electronics. Special attention will be given to two important but frequently neglected topics: cleaning of individual circuit card assemblies after hand solder touchup or modification, and cleaning of large chassis assemblies with a motherboard wired to a front-panel interface. Introduction Significant ODC elimination efforts began at MMCS in As the project progressed, news of the environmental threat grew more and more alarming, 1 eading to increasing regulatory pressures, shortened government phaseout schedules, and skyrocketing solvent prices. MMCS established a goal to beat the Montreal Protocol and Bush Administration deadlines by completely eliminating usage of CFC-113 and 1,l.l trichloroethane by Final efforts were successful in avoiding consequences of the "Label Law" provisions of the Clean Air Act Amendments, which went into effect in May Of 7

3 During early phases of the project, usage reductions were achieved with existing cleaning processes by improving vapor degreasers, operator techniques, and recycll ing equipment. Efforts were coordinated by a smal 1 team of design, process, and environmental engineers. In 1991, 1,1,1 trichloroethane reductions from Machine Floor outsourcing were offset by the new BSY-2 product line, which added 5 new degreasers, including a high capacity in-line unit. In early 1992, the focus shifted to development and implementation of a1 ternati ve cl eani ng processes. To mobi 1 i ze resources and promote ownership on the factory floor, the project was expanded and reorganized. A multi-functional Leadership Team coordinated the contributions of about 50 participants on the Solvent Elimination CPI Team, which included Tiger Teams in 8 process areas. Tiger Teams included salaried contributors and hourly participants. Process development was compl icated by the re1 atively immature state of alternative cleaning technologies. Solvent and equipment options were few, poorly understood, and distrusted by military customers. Many new processes had to be homegrown. Process Development : CFC-113 and 1,1,1 trichloroethane share special properties: they are non-flammable, have low toxicity and moderate boiling points, form stable mixtures with other solvents, and clean a wide range of organic and inorganic soils. Direct replacement compounds are not yet available. Dur i ng devel opment of new cl eani ng processes and equi pment, product materials and finishes were tested for compatibility, and some compounds were found to degrade urethane conformal coatings. Best results have been obtained with a1 coho1 and terpene based sol vents, though they requi re speci a1 care due to their fl ammabi 1 i ty/combusti bi 1 i ty. Much progress was achieved by changing the nature of the soils; processes were modified to eliminate the source of contamination, or to substitute fluxes and other process compounds which are easier to clean. Solderi nq Processes: RMA solder fluxes were retained. Low-residue ( no clean ) solder fluxes are not approved for use on military hardware. 2 Of 7

4 Water soluble fluxes are now permitted, but bring along their own compl ete set of process chal 1 enges, and unl i ke rosin- based fl uxes, incomplete removal from tight spaces has serious consequences for product reliability. Rosin based fluxes are difficult to remove, but residues are virtually inert. Hand soldering poses special problems. Military requirements call for removal of flux shortly after soldering. Since hand soldering operations cannot be held to a fixed schedule, most large batch-style cleaners are unsuitable because of high cycle times. Soldering techniques have much to do with cleanabil ity. Operators commonly use more flux than is necessary by employing it as a heat transfer medium., Training school practices were updated, and process speci a1 i sts were en1 i sted to coach operators on proper techniques. RMA solder fluxes differ in cleanability, and most are available in different concentrations. Most soldering had been performed with fluxes containing 35% solids, but 15% and 25% versions are now used as well. Thinner fluxes work very well for surface mount touchup, but do not have "staying power" on large terminals. In some cases, substituting higher flux content P3 cored solder wire for P2 has eliminated the need for added liquid flux. Pen-type flux dispensers were introduced for better control, and flux dispenser bottles were fitted with flow restrictors. At wave solder, top-side fluxing was used on most large motherboards. Tests revealed that the resulting mess was not justified by improved solder quality, and the practice was discontinued. Cleanins Durinq and After Hand Soldering: Hand soldering operators were encouraged to adopt a "clean as you go1' approach, breaking up concentrations at the workbench while flux is still relatively soft. Hand-held solvent dispensers from 4 different manufacturers were tested, and one was selected for introduction into every shop area. Dispensers attach to spray cans and control the flow of solvent through a cleaning brush or needle. A trigger grip controls the flow. A wide selection of brushes and needles is available, and units are ESD safe. Isopropanol had been used for many years for defluxing, but often left "white residue" which is difficult to remove. This problem has been virtually eliminated by substituting a commercial blend of IPA, methanol, and ethanol, which is available in spray cans or bulk. To remove burned-on or hardened flux, a terpene solvent is used, either in aerosol. - cans, pump top bottles, or speci a1 pen-type dispensers. 3 Of 7

5 Benchtop C1 eani ng Cleaning at the workbench is essential to break up flux concentrations, but flux is actually "spread out" rather than removed. Another process is needed to flush residues from surfaces. The process must be readily available to the individual operator, without the long waits for access associated with larger batch cleaners. The cycle time must be reasonable, and equipment should be portable and easy to set up and control. The ideal system would be optimized for cleaning individual assemblies. Small, inexpensive units could be installed throughout the shop, just like the vapor degreasers they replace. Small ultrasonic tanks fit this description, but ultrasonics have been strictly prohibited for cleaning military electronics due to a history of component damage. Recent studies in England and in this country suggest that newer ultrasonic equipment can be used safely by limiting frequencies and energy densities. MMCS tested systems from several manufacturers, and ultrasonic processes were implemented in several shop areas in Ultrasonic cleaning was not found to be as effective as had been hoped fop cleaning under surface mounted components, and government approval has not yet been sought for use on active electronic devices. Most inexpensive ultrasonic systems can only be used safely with aqueous solutions, usually of saponifiers, which break down flux rosin by chemically changing it into a water soluble soap. Several different saponi f i ers were tested at various temperatures and concentrations, and an ultrasonic process was implemented in the Solder Training School. It was also necessary to develop a primary rinse with another saponifier to remove a defoaming residue from the first solution. An automatic lifting arm was developed which lowers the assembly into the tank, and lifts it out after a preset time has elapsed. Another ultrasonic system is used to clean connectors after pretinning, where flux flows into small areas in and around the pins. JetCl ean Since ultrasonics were ruled out for cleaning circuit card assembl i es, and no other options were commerci a1 ly avai 1 ab1 e, a benchtop cleaning system was developed in-house. JetClean features a smal 1 cleaning chamber sized for individual circuit card assemblies, with submerged nozzles for spray-under-immersion cleaning. The unit is self-contained and fits on any workbench, sets up in minutes without tools, is easily maintained, and requires only a compressed air line and ground connection for service. 4 Of 7

6 JetClean was designed for safe use with common flammable solvents used at the workbench, including alcohols, terpenes, and esters, but it can be used with aqueous solutions. Compressed air operates a dual -di aphragm pump, which ci rcul ates sol vent from the cleaning chamber through a particle filter and out through the spray nozzles. Compressed air is also diverted into an adjacent chamber to dry the assembly after cl eani ng. About 30 JetClean systems are in operation at MMCS, with primary use being the main assembly area after hand solder touchup, repairss or mods. Other systems in use include small outlying assembly areas and labs, where work volume does not justify installation of more expensive "dishwasher" type cl eani ng systems. JetClean is now available commercially in 2 sizes for cleaning circuit card assemblies and solder stencils, in addition a smaller model with an open basket can be used for cleaning small assemblies or small batches of components after pretinning. C1 eaninq Before Conformal Coat: A mixture of deionized water and isopropanol had been used before conformal coating as a final spray rinse after vapor degreasing. Tests proved that vapor degreasing could be eliminated by cleaning with IPA and water at sufficiently high flow rates. Spray systems from two different manufacturers were tested, and one unit was purchased. The chosen system is a "dishwasher" with counter-rotating spray arms, originally designed to wash with deionized water or saponifier solution, then perform a cleanliness test with alcohol and water. The cleaning cycle has been modified to perform a prerinse with deionized water, followed by a cleaning cycle with 75% isopropanol and 25% deionized water. Board cleanliness is continuously monitored with a conductivity meter, eliminating the need for a separate cleanliness test. Humidity and Omega Meter tests prove that the new process cleans much more effectively than the previous solvent-based process. The system replaces a vapor degreaser and spray booth, and government approval is being sought to el iminate the Omega Meter cl eanl iness test. Cleaninq After Wave and Reflow Soldering: MMCS assemblies were tested and inspected after cleaning in ultrasonic tanks (aqueous and a1 cohol ), aqueous and semi -aqueous i n-1 i ne systems, aqueous and semi -aqueous "di shwashers", a semi -aqueous spray-under-immersion cleaner, and in a spray system containing a 1 ong-chai n a1 cohol sol vent. 5 Of 7

7 Aqueous processes performed poorly, and i n-1 i ne equi pment was rejected due to cost and space limitations. After working with a spray-under-immersion batch system, it became apparent that "dishwasher" type equipment offers higher spray pressures and volumes. MMCS selected a three-stage semi-aqueous process consisting of a primary wash with a hydrocarbon solvent in one machine, followed by a DI water rinse in another, then drying in a separate forced-air oven. A terpene-based solvent proved most effective at removing flux ceramic surfaces, dissolving temporary fixturi ng compounds ("Comp-Hs and penetrating and cleaning in tight spaces (i.e. within connectors under. surface mounted components). The mi 1 d orange-peel odor i s we1 tolerated by our workforce. C1 eani nq At Final Assembly: from The basic MMCS chassis assembly typically consists of a large motherboard wired to connectors in a front-panel assembly, though many are much more complex. Construction includes RTV's and other substances which are not compatible with terpenes and other aggressive solvents. They require considerable hand soldering, and their size, complexity, and tight spaces make them very hard to clean. By minimizing flux usage during soldering and maximizing bench cleaning, the problem was reduced considerably. A final rinse with alcohol/water was found to be safe and effective. A special option was developed for our alcohol/water "dishwashert8 system at conformal coat to allow cleaning of large assemblies. Large wired assemblies over 20" across were cleaned effectively, leading to installation of a second system in the final assembly area. dl7 e Another system was developed in house for especially soiled chassis. It uses an air powered pump and a spray wand to spray pure cleaning solvents, flushing contaminants off surfaces and out of tight spaces. Some features are simi 1 ar to commerci a1 1 y avai 1 ab1 e cl eaners for paint spray guns. and Concl us i ons : 1. In any ODC elimination effort, not all of the answers are available off the shelf. 2. Involvement of the end users is essential, both to tap a creative well and to ensure that new processes transition smoothly to the shop. 3, Success may involve more than a search for solvents and equipment. Some consideration should be given to the soils: creating less of it or making it easier to remove. 6 Of 7

8 FREON USAGE - I GALL0 NS VIRGIN i3sssss RECYC. liizi I Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 1990 THROUGH ,1,1 TCA USAGE GALLONS 2ooo II VIRGIN E3ssss3 RECYC. n 1Q 2Q 3Q 4Q IQ 2Q 3Q 4Q 1Q 2Q 3Q 4Q 1Q 2Q 3Q 1990 THROUGH Of 7