Detrimental Effects of Excessive Gold Plating on Lead-Free Solder Joints

This article presents two case histories that shed light on the role of gold in lead-free solder joint failures and the damage mechanisms involved. One of the failures, a brittle fracture of the solder joint, is attributed to the synergistic effects of voids, intermetallic compounds, and CTE mismatch. The investigation of the other failure revealed evidence of tin-whisker formation. As the author explains, the growth of tin whiskers is due to compressive stress in the tin solder material caused by diffusion of end-cap metals (Ni and Cu) and the formation of Sn-Ni-Au intermetallics. In both cases, the failures can be prevented by limiting the thickness of gold on all components.