Effect of Kaolin Geopolymer Ceramics Addition on the Microstructure and Shear Strength of Sn-3.0Ag-0.5Cu Solder Joints during Multiple Reflow.

Solder interconnection in three-dimensional (3D) electronic packaging is required to undergo multiple reflow cycles of the soldering process. This paper elucidates the effects of multiple reflow cycles on the solder joints of Sn-3.0Ag-0.5Cu (SAC305) lead (Pb)-free solder with the addition of 1.0 wt.% kaolin geopolymer ceramics (KGC). The samples were fabricated using powder metallurgy with the hybrid microwave sintering method. Apart from using conventional cross-sectioned microstructure imaging, advanced synchrotron real-time in situ imaging was used to observe primary IMC formation in SAC305-KGC solder joints subjected to multiple reflow soldering. The addition of KGC particles in SAC305 suppressed the Cu 6 Sn 5 IMC's growth as primary and interfacial layers, improving the shear strength after multiple reflow soldering. The growth rate constant for the interfacial Cu 6 Sn 5 IMC was also calculated in this study. The average growth rate of the primary Cu 6 Sn 5 IMCs decreased from 49 µm/s in SAC305 to 38 µm/s with the addition of KGC particles. As a result, the average solidified length in the SAC305-KGC is shorter than SAC305 for multiple reflow soldering. It was also observed that with KGC additions, the growth direction of the primary Cu 6 Sn 5 IMC in SAC305 changed from one growth to two growth directions. The observed results can be attributed to the presence of KGC particles both at grains of interfacial Cu 6 Sn 5 IMCs and at the surface of primary Cu 6 Sn 5 IMC.