Microstructures and Drop Impact Test of SAC305, Sn58%Bi and Epoxy Sn58%Bi Solder Joint on the OSP Surface Finished PCB Substrate

Lead free Sn3.0%Ag0.5%Cu(SAC305) solder and low temperature Sn58%Bi solder have been widely used to replace lead based solder alloys.Because Sn58%Bi solder has poor ductility and shock absorbance ability, previous researches have tried to improve its mechanical properties by adding additional elements, reinforcements, carbon nano tube (CNT) and polymer.The bonding strength and drop impact reliability of SAC305 solder, Sn58%Bi and epoxy contained Sn58%Bi solder (epoxy Sn58%Bi solder) assembled on the OSP surface finished PCB substrate were investigated using low speed shear and board drop impact tests.After soldering, Cu6Sn5 intermetallic compound (IMC) was formed in the solders and OSP surface finished PCB substrate joints.Bonding strength and drop reliability of epoxy Sn58%Bi solder had superior mechanical properties than those of SAC305 solder and Sn58%Bi solder.The crack in the solder joint of SAC305 after board drop impact testing takes place within the IMC layer.However, the crack at the solder joint of the Sn58%Bi after board drop impact testing occurred on the interface between IMC layer and Sn58%Bi solder and the crack in the solder joint of the epoxy Sn58%Bi presented within the solder, respectively.