Tin-bismuth plating for component finishes

With the transition to lead-free, the electronics industry has widely adopted matte Sn for use component surface finishes. However, it is well know that plated Sn finishes can result in Sn whisker formation. After significant work by numerous researchers, the exact mechanism for Sn whisker growth is still unknown. While industry standard test have been developed, there are no acceleration factors to correlate the laboratory test results to field life. Furthermore, testing (JESD22A121) of components with industry accepted mitigation strategies has still shown whisker growth in excess of allowable standards (JESD201A). The addition of bismuth, to Sn plating reduces whisker growth length. Sn whisker growth, solder wetting, backward compatibility and reliability are discussed.