Dissolution Rate of Electronics Packaging Surface Finish Elements in Sn3.0Ag0.5Cu Solder

Abstract

A clear understanding of the characteristics of solder wetting to component terminations is critical for establishing thermal process profiles that ensure acceptable solder joint integrity. For example, component gold plating thickness as well as the soldering process temperature and time must be carefully controlled to prevent embrittlement by the gold/tin intermetallic compound. The electronics industry has successfully applied the results published in 1969 by W.G. Bader to relate process temperature and time to surface finish dissolution rates in defining acceptable soldering process profiles for tin/lead surface finishes. To date, there is no single comprehensive data set for these materials that is comparable to the Bader work. To address this need, solder dissolution experiments modeled on the Bader work were conducted using Sn3.0Ag0.5Cu (SAC305) solder with gold, silver, palladium, platinum, copper and nickel samples. In these experiments, samples were immersed in a solder pot, and the resulting material dissolution was determined for different solder temperatures and immersion times. This paper describes the test approach for measuring the solder dissolution of these materials and tabulates dissolution rates suitable for optimizing soldering process profiles for electronic assemblies. The dissolution rates of the surface finish materials were found to typically be about 50% higher for the lead-free SAC305 solder than tin–lead solder.