Addition of porous Cu interlayer to Sn-3.0Ag-0.5Cu lead-free solder joint for high temperature application

The microstructural and mechanical properties of Sn-3.0Ag-0.5Cu lead-free solders added with a porous Cu interlayer were investigated. Two types of porous Cu, P15 and P25 with the diameter of φ1.7 mm and φ1.0mm respectively were used in this study. The porous Cu was arranged in a sandwich-liked layer in between Sn-3.0Ag-0.5Cu solder alloys with rod Cu as a substrate metal. Solder joint without porous Cu interlayer were also prepared as the control sample. Three soldering temperatures of 267°C, 287°C and 307°C with soldering time of 5 minute were applied. Tensile test was performed to evaluate the joint strength of the solder alloy. The result shows that the joint strength increased proportionately with increasing soldering temperature and smaller pore size of porous Cu. Microstructure and fracture surface were observed by using optical microscopy (OM) in order to understand the failure behavior of the joint. It is found that penetration of molten solder alloy into the various pore sizes of porous Cu interlayer significantly influenced fracture morphology and strength of the joint.