06.08.2005 12:00 AM

Georgia Tech Studies Alternatives to Tin-Lead Solder
You may find it more difficult to locate lead-based solder in the future. Although lead-based solder for electronics has yet to be outlawed in the United States, many manufacturers are looking at alternatives. One concern is the amount of lead deposited in landfills when consumer electronic devices are disposed. Researchers at Georgia Tech are studying alternatives to lead solder. "Though many challenges remain to be addressed, both lead-free solders and conductive adhesives show much promise as a means of replacing conventional solder materials. But before these alternatives become truly viable, we must develop conductive adhesives that can carry high currents, and lead-free solders that have low processing temperatures, high reliability and good thermal-mechanical properties," said C.P. Wong, a Regents Professor in Georgia Tech's School of Materials Science and Engineering.

One widely accepted lead-free solder is made from an alloy consisting mostly of tin, to which silver and copper have been added. However, the melting point of this solder is about 30 degrees (Celsius) hotter than tin-lead solder, which can stress circuit boards and electronic components and reduce their reliability. Electrically conductive adhesives are another option being studied at Georgia Tech. Wong said while conductive adhesives have a lot of advantages, there are a few challenges.

"After you attach a component to a board with conductive adhesives and then cure it, you must test the connections under conditions of high humidity and heat. When you do that, electrical resistance in the joint increases and conductivity drops. That is a major problem for the industry." These problems have limited use of conductive adhesives mostly to low power applications such as connections to LCD displays.

Wong and colleagues at the National Science Foundation-sponsored Microsystems Packaging Research Center found that galvanic corrosion, not oxidation, was the main reason conductive adhesives have problems. Wong explained, "By understanding this galvanic corrosion, we can develop improved materials that use an inhibitor such as acid to protect the contacts from corrosion, and we can use an oxygen scavenger to grab the oxygen required for corrosion to take place. We can also include a sacrificial material with a lower potential metal that is attacked by the corrosion process first, sparing the conductive materials."

For information on other alternatives to lead-based solder for electrical connections, see the Georgia Tech news release Getting the Lead Out: Alternatives to Conventional Solder Offer New Choices for Electronics Manufacturers.


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