Surface Precipitation and Growth of Bismuth Particles in Sn-Ag-Cu-Bi Solder Joints

With the advance in heterogeneous integration packaging, there has been a demand for solders with ideal mechanical properties and ideal melting temperatures. Sn-Ag-Cu (SAC) solders provide a reliable alternative to PbSn solders, with ideal mechanical properties and low melting points when alloyed with other elements. SAC-3Bi is observed to have bismuth precipitation at room temperature when aged over a period of time. This is only observed on the exposed surface, as removing the observed surface resets the nucleation and coarsening progress. Once the bismuth phase separates from the beta-Sn matrix, it will coarsen over time. The results show that different cooling rates during the solder solidification will affect the coarsening rates, indicating different diffusion and nucleation rates affected by the cooling process.

Automated summary

With the development of heterogeneous integration packaging, there is a growing demand for solders with ideal mechanical properties and melting temperatures. Sn-Ag-Cu (SAC) solders are a reliable alternative to PbSn solders, offering ideal mechanical properties and low melting points when alloyed with other elements. SAC-3Bi solder is found to have bismuth precipitation at room temperature after being aged, specifically on the exposed surface. Different cooling rates during solder solidification affect the coarsening rates, indicating varying diffusion and nucleation rates influenced by the cooling process.