OL1.OCT–Sandia–Sept–SC
CFC-less soldering process exceeds military requirements
The major contributor to generating chlorofluorocarbons (CFCs) in the
electronics industry is the solvents used to remove flux residue after
wave soldering. Sandia National Laboratories, of Albuquerque, NM, is out
to do away with CFCs. In a joint program with Motorola's Government
Electronics Group (Scottsdale, AZ) and Los Alamos National Laboratory (Los
Alamos, NM), Sandia has developed and successfully demonstrated a new
soldering process that uses adipic acid in place of pine rosin flux as the
wetting agent. At present, the most stringent soldering standards in the
electronics industry are those dictated by MIL-STD-2000. Even commercial
enterprises base their own soldering standards on these benchmarks.
According to Ron Iman, project manager of Sandia's Manufacturing Systems
Reliability Modeling Dept., the joint research effort will hopefully
spearhead an industry-wide effort to convince the military establishment
to adopt no-clean soldering processes into MIL-STD-2000. Adipic
acid–also known as hexanedioic acid–is a compound that has long been
used by the food industry to give tartness to gelatin. More recently,
companies like Motorola and Ford have successfully adopted the compound
for their soldering processes. Unlike pine rosin, which leaves behind a
corrosive, sticky residue that must be removed with solvents, adipic acid
requires no such cleaning step. It is applied with an ultrasonic nozzle as
the pc board passes through the flux chamber. So far, test results for the
no-clean soldering process look promising. In tests conducted by both
Motorola and Sandia, pc boards soldered through the no-clean process
exceed all the standards outlined in MIL-STD-2000, including visual
defects, ionic cleanliness, electrical resistance, mechanical pull,
surface electrical resistance, and long-term storage performance. For
instance, resistors soldered to the board required 65 lb of pull force to
remove them–although the military requires just 4 lb of pull force. The
boards also survived long-term storage tests that simulated 20 years of
storage, whereas the military requires boards to survive for only 10
years. Sandia's no-clean process uses a sealed chamber containing
nitrogen and formic acid (a substance found in ants and plants that breaks
down into carbon dioxide and water) for soldering. Adding a sealed
nitrogen chamber to the existing soldering equipment increases the cost of
soldering by $25,000. However, according to Sandia's Iman, the process
repays for itself by eliminating the need for a cleaning machine and its
related maintenance, utility, and labor costs–typically $100,000 to $200,
000 a year. –Spencer Chin
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