Advances in Industrial Energy-Efficiency Technologies
Prepared for:
U.S. Department of Energy
Office of Industrial Technologies
Washington, DC 20585
Produced by:
National Renewable Energy Laboratory
Golden, Colorado 80401-3393
In conjunction with:
Energetics, Inc.
Columbia, Maryland 21046
DOE/CH10093-137
DE92001229
December 1992
The manufacture of circuit boards and other electronic assemblies involves numerous soldering operations to attach the various components. Conventional soldering leaves an acidic residue that, if left untreated, dramatically increases the likelihood of failure of the assembly. To avoid this, soldering residues are currently cleaned using chlorofluorocarbon (CFC) solvents. However, CFCs are very damaging to our environment, contributing to the destruction of the protective ozone layer. The use of these solvents also creates large volumes of waste requiring treatment and disposal.
By signing the Montreal Protocol in the 1980s, the United States, in cooperation with countries around the world, has agreed to eliminate production of CFCs by 2000. In addition to this international agreement, the use of CFCs in the United States between now and 2000 has been further restricted by a 1990 amendment to the Clean Air Act. Consequently, if the U.S. electronics manufacturing industry is to survive, a fundamental change in the way electronic assemblies are produced must be developed in the next few years. Although various alternatives to the CFC cleaning have been proposed, none has emerged as the optimum choice for all applications.
As part of its Industrial Waste Reduction Program, the U.S. Department of Energy (DOE) is working with Sandia National Laboratories, Motorola, Inc., and Los Alamos National Laboratories, Motorola, Inc., and Los Alamos National Laboratory to develop a new, no-clean soldering process that eliminates the need for any type of post-soldering cleaning. Besides the environmental benefits, eliminating the use of cleaning solvents will conserve energy by saving the distillate fuel used to make the solvents and by saving the electricity used during cleaning.
Motorola is committed to implementing the process throughout its corporate manufacturing structure. With DOE's assistance, the process can be moved more quickly from the development stage to commercialization for use throughout the electronics manufacturing industry. Sandia brings to the project decades of experience in designing electronic assemblies for nuclear weapons and in analyzing the reliability of electronic systems.
Photo: In the traditional process, the rosin flux must be chemically cleaned with CFC solvents. With the no-clean process, the circuit board is ready to use after soldering. [provided in source document]
The new no-clean soldering process works by utilizing two dilute acidic solutions to prevent the buildup of oxidation residues during soldering. An adipic acid flux remove residue prior to soldering. During the soldering operation, the application of a formic acid solution in a nitrogen-cover blanket effectively inhibits oxidation. These two acid solutions leave no residues themselves; the adipic acid evaporates during soldering, and the formic acid is converted to carbon dioxide and water.
The collaboration between DOE, Sandia, Los Alamos, and Motorola on the project began in 1991. Motorola installed and is operating the no-clean soldering equipment along with conventional soldering and cleaning equipment to establish a baseline for comparison. Sandia designed reliability tests for the electronic assemblies and is performing post-test failure mode analysis. Los Alamos performed surface chemical analysis at the completion of environmental testing. Motorola assembled the reliability test hardware supplied by Sandia. To date, electrical testing of an IPC B-24 circuit board, a FMU-139 printed wire board, and a Motorola test board has been completed.
The no-clean soldering process is applicable to all wave-soldering machines that use either of two CFCs - Freon TMS or 1,1,1 trichloroethane - as the cleaning solvent. Currently, about on-third of all wave-soldering machines used in the United States (about 900 out of 2500 machines) are candidates for the new process.
Assuming the new technology is adopted by 90% of the potential market, the annual energy savings could be 20 petajoules (18 trillion Btu). The new process should also reduce CFC-11 equivalent emissions by about 16,000 metric tons annually by 2010.
Testing of the non-clean soldering process and subsequently analysis of the test results were completed in December 1992. Project team members completed surface analyses of the test boards and compared the reliability of the electronic boards assembled using the new method with military specifications.
The no-clean soldering process provides Motorola with an effective way to eliminate the need for solvent-based cleaning during the manufacture of electronic assemblies. Motorola and DOE are sharing the results of this work with other electronics manufacturers, some of whom are trying to solve similar solvent-cleaning problems. The new solvents soldering process will not only save energy and help preserve our environment, but will also help prevent the erosion of yet another major U.S. industry to foreign competition.
For More Information:
Industrial Waste Reduction Program
CE-222
Office of Industrial Technologies
U.S. Department of Energy
1000 Independence Ave., SW
Washington, DC 20585
(202) 586-9496
Last Updated: February 13, 1996