In January, 1990, Texas Instruments' Defense Systems and Electronics Group (DSEG) announced it will eliminate all ozone depleting solvents (ODS) in its assembly cleaning processes by the end of 1994. At the time of DSEG's announcement, the Montreal Protocol called for only a 50 percent reduction in production of CFCs by the year 2000, and there was an anticipated phaseout of 1,1,1-trichloroethane. The U.S. government has since pushed forward the deadline for the complete production phaseout of both solvents to December 31, 1995. While the Montreal Protocol applies to the production ODS, the DSEG accelerated phaseout is one year ahead of this deadline. DSEG uses in-line degreasers with CFC-based FREON TMS® cleaning agent or 1,1,1-trichloroethane in its assembly operations at several locations in Dallas, Texas. A team of technical personnel was formed to find alternatives for the ODSs in all of DSEG's internal printed wiring assembly operations.
The team members evaluated the specific cleaning requirements of each contract assembly area. They researched various alternative technologies including: HCFCS; water-soluble flux; batch degreasing with non-ozone-depleting solvents, such as isopropyl alcohol (IPA); controlled atmosphere soldering (CAS); and semi-aqueous cleaning with hydrocarbons. At first, the team wanted to use HCFC technology and worked with a DuPont defense systems expert to develop an HCFC cleaning process. They scrapped the project when studies by DuPont and the Environmental Protection Agency showed that HCFCs have a higher toxicity than was first suspected and their ozone-depleting potential is equivalent to 1,1,1-trichloroethane. Water soluble flux for electronics soldering has been used in commercial operations for years. There is a significant cost savings associated with this process since only water is necessary to clean off any post soldering residues. Recently a citric acid based flux became commercially available that was successfully use on deliverable electronic assembly hardware manufactured for the Department of Defense (DoD) . Extensive testing on the citric acid based flux with involvement from the Naval Air Warfare Center has provided results that have enabled a full scale production readiness assessment on a major DSEG program. Solvent cleaning is necessary for assemblies that are not compatible with the other suggested DSEG alternative technologies. TI limited the solvents for electronic assembly cleaning to non-ozone depleting solvents. After a risk assessment it was determined that an intrinsically safe machine for use with a flammable solvent, specifically IPA, was a potential alternative process. After an extensive supplier search, a U.S. supplier was selected which has significant experience manufacturing cleaning systems compatible with flammable solvents. Preliminary testing indicates that an IPA degreaser should provide a process that can clean a variety of products that are not suitable with other alternative technologies. The first unit is scheduled for implementation the later part of 1993. DSEG has been involved in several evaluations of no clean technology since 1991. The majority of TI's effort has been focused on a new mass wave soldering process know as controlled atmosphere soldering (CAS) . This process requires soldering to be accomplished in an inert, nitrogen environment. Use of an inert soldering environment allows the utilization of new flux chemistries that leave minimal, benign flux residues which do not require subsequent cleaning. Elimination of cleaning is an obvious benefit of this technology. In addition, CAS reduces lead solder dross formation significantly. Furthermore, volatile organic compound (VOC) emissions are reduced with the spray flux application system used as it applies less flux than conventional systems. DSEG is participating with external organizations such as the Institute for Interconnection and Packaging Electronics Circuits (IPC) , Department of Energy (DoE), Sandia National Laboratories and other defense contractors to evaluate CAS technology. After considerable testing, semi-aqueous technology was selected as one of the viable alternatives for DSEG's use in board-level assembly operations and hand-soldering processes. The team members confirmed the compatibility of the semi-aqueous material on various components, hardware and laminates. In-line equipment was procured to utilize the semi-aqueous material in further evaluations. Equipment optimization indicated optimal cleaning with slow conveyor speed and high spray pressures. Ionic cleanliness testing, residual rosin and ion liquid chromatography tests on printed wiring assemblies indicated semi-aqueous cleaning was comparable to 1,1,1-trichloroethane cleaning. TI worked with the U.S. Air Force to perform four environmental qualification tests based on MIL-STD-810. The tests were Thermal Shock, Temperature/Altitude, Temperature/Altitude/Humidity and Salt Fog. In addition a "Life Test" provided by the Naval Air Warfare Center was completed. All qualification tests were successful. TI is scheduled to implement semi-aqueous technology on a U.S. Air Force program.
Implementation of the aforementioned technologies can eliminate the use of ozone depleting substances in electronics assembly operations.
Details of Reductions
Additional Information :
The cost savings has not been quantified at this time. Some of the alternative technologies will require significant capital expenditures.
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