A Comparative Study on the Influence of SAC305 Lead-Free Solder Sandwiched by Sn on the Micromechanical and Electrical Properties of the Joints

Herein, the favorable influence of sandwich-stacked Sn/SAC305/Sn multilayers on the micromechanical and electrical properties of the Cu-Sn/SAC305/Sn-Cu solder joints over Cu-SAC305-Cu joints is reported. Solder joint interface is characterized through X-ray diffraction spectroscopy, scanning electron microscopy, transmission electron microscopy, scanning tunneling microscopy (STM), and nanoindentation studies. The use of Sn multilayers facilitates the formation of more homogeneously distributed intermetallic compounds (IMCs) with smaller crystallite sizes and higher dislocation densities at the joint interface. Nanoindentation test results manifest that the hardness, modulus, and resistance to plastic deformation of the joint interface for the samples prepared with Sn multilayer are 3.26 GPa, 123.3 GPa, and 1.5 x 10(9), respectively, much higher and improved than 0.32 GPa, 41.82 GPa, and 5.28 x 10(5) in turn, found for samples prepared without using Sn multilayers. STM results confirm a much better electron transfer capacity of the solder joint interface that consists of Sn multilayers compared with solder joints produced without incorporation of Sn multilayer. Wherein, Sn multilayer containing solder joint found less prone to be affected by the humid atmosphere compared with nonlayered solder joint, in which, the former is found to be 48% less sensitive toward humidity (85% Rh) than later.

Automated summary

The use of sandwich-stacked Sn/SAC305/Sn multilayers in Cu-Sn/SAC305/Sn-Cu solder joints improves micromechanical and electrical properties compared to Cu-SAC305-Cu joints. Sn multilayers facilitate the formation of more evenly distributed intermetallic compounds and higher dislocation densities. Additionally, the Sn multilayer solder joints exhibit better hardness, modulus, resistance to plastic deformation, electron transfer capacity, and resistance to humidity compared to nonlayered solder joints.