Wetting behavior and elastic properties of low alpha SAC105 and pure Sn solder

The issue of soft error in microelectronics packaging have necessitated the development of low alpha (LA) activity solders as, as solders are found to be major sources of radiation in electronic devices that causes soft error. Low alpha ray emitter Sn and Sn-1.0 %Ag-0.5 %Cu (SAC105) solders were prepared and their alpha activity was measured using Ultra Low Background Alpha Particle Counting Systems. The solders are confirmed to be low alpha solders having activity less than 0.005 α/h/cm² (LC3 Grade). Microstructure of the LA SAC105 and Sn are characterized using scanning electron microscopy. Wetting balance tests are conducted to assess their solderability at different temperatures. Elastic properties i.e. Young Modulus and hardness were determined using Vickers hardness test and Nanoindentation technique. All the solders show good wettability and solderability having zero cross time less than 1.5 s. The wettability of low alpha solders is better as compared to the normal ones. Hardness results show the reduction in hardness of the LA solders as compared to normal ones. This is attributed to removal of radioactive trace impurities as the latter results in high hardness due to solid-solution hardening mechanism. Nanoindentation results shows the scatter in the values of hardness and Young's Modulus for different IMCs phases found in solder joint with Cu and in bulk.