Micromechanical and microstructure evolution of leaded (SnPb) and lead-free (SAC305 and SnCu) mixed solder joints during isothermal aging

This paper studies how isothermal aging affects the micromechanical and structural properties of mixed solder joints made of 60Sn-40Pb (SnPb) with Sn-3.0Ag-0.5Cu (SAC305) and SnPb with Sn-0.7Cu (SnCu). The nanoindentation test was done to measure the micromechanical properties of SnPb/SAC305 and SnPb/SnCu mixed solder joints. These properties are hardness, reduced modulus, and stress exponent. Scanning electron microscopy (SEM) was used to look at the microstructure of a cross-section of mixed solder joints. The micrographs that were taken were then examined with open-source image processing software called ImageJ. It was found that the rate and distribution of intermetallic compound (IMC) formation and the reduction of Sn-rich phase grain size affect how the hardness and stress exponent values of mixed solder joints change after 1000 h of high temperature storage (HTS). ImageJ analysis shows that the Pb-rich phase particle count and distribution can be used to figure out how mixed solder joints respond to indentation creep and how that relates to isothermal aging. Using ImageJ, it’s clear that the indentation creep behavior of the GBS mechanism of an as soldered SnPb/SnCu mixed solder joint is caused by the highest number and size of Pb-rich phase particles that are not well distributed across the dendritic area of Sn-rich phase grain boundaries.