As of July 1, 2006, the European Union will mandate all semiconductor packages be lead-free. Most chip packages shipped today use a layer of tin and lead over copper. Lead-free substitutes will likely use tin over copper and will be processed by higher temperatures (owing to the higher reflow profiles of lead-free solder pastes).

Research at Agere has shown that tin-copper packaging meet current standard tests developed for leaded product. However, when using the products like the customer uses them, Agere has observed that commercially available tin-copper packaging form tin whiskers, which are known to cause electrical shorts and other system failures.

Three tests proposed by the Jedec Solid State Technology Association with guidance from the National Electronics Manufacturing Initiative effectively screen for susceptibility to tin whiskers. Of the three tests, two display no discernable difference between matte-tin on copper and nickel undercoated matte-tin on copper. According to Agere, a layer of nickel between the copper and tin provides "dramatic improvements" using real-world environment.

Agere evaluated semiconductor packages from multiple sources using various tin plating processes. Agere observed tin whiskers would grow on semiconductor packages after the packages had gone through a lead-free assembly process onto boards that used tin plating (instead of tin-lead).

Adding a layer of nickel between the layers of tin and copper mitigated tin whisker growth, Agere found.

"We are unveiling these findings in hopes that the electronics industry will adopt our approach to avoid the problems Agere observed in currently accepted copper and tin packages," said Dr. Melissa Grupen-Shemansky, director of packaging and interconnect technology. "We evaluated multiple options being used by other semiconductor companies in a scientifically valid study over a prolonged timeframe and found that Agere's tin-nickel-copper combination resolved the tin whisker problem seen after high-temperature, high-humidity storage."

Early results from an independent study conducted by NEMI corroborate the Agere findings on whiskers found on commercially available tin over copper packages, Agere said.

NEMI will publish its own findings next year.