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Georgia Tech in the US is investigating conductive adhesives as part of its programme to develop alternatives to tin-lead solder.

Adhesives could replace solder

“In certain applications that require high current densities, conductive adhesives still do not measure up to metallic solders,” said Professor CP Wong at the university’s school of materials science. “However, progress is being made at improving the properties of these materials.”

Conductive adhesives are essentially glue filled with metal powder, and one avenue to reduced electrical resistance, said Georgia, is self-assembling molecular conductors that provide a direct connection through the adhesive.

“Recent studies show that with incorporation of these self-assembled mono-layers, the electrical conductivity and current-carrying capability of conductive adhesives could compete well with traditional solder joints,” Wong said. “This could be a significant advance in improving these materials.”

Another issue with adhesives is decreasing performance with long-term exposure to high humidity and heat. “Electrical resistance in the joint increases and conductivity drops. That is a major problem for the industry,” said Wong.

Oxidation has been blamed for this change, but Wong claims galvanic corrosion, caused by contact between dissimilar metals in the adhesive and contact is the real culprit.

“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,” he said. “We can also include a sacrificial material with a lower potential metal that is attacked by the corrosion process first, sparing the conductive materials.”


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