Phase Analysis in the Solder Joint of Sn-Cu Solder/IMCs/Cu Substrate

A joint assembly of solder/IMCs/copper was prepared and experienced a thermal aging test for 50, 100, 400, and 600 hours at 150°C. The morphology at the interface of the assembly was investigated with an optical microscope (OM) to measure the thickness of the intermetallic layer, and with secondary electron images (SEI) to evaluate the interfacial microstructure. X-ray color mappings using an electron probe microanalyzer (EPMA) of copper and tin were also applied to study the concentration variations near the interfaces in the joint assembly. According to the intensities of Cu and Sn, collected by color mapping, software was employed to construct series of statistical graphs, and the detailed concentration profiles at the interfaces of the assembly were investigated from these graphs. Two important results were derived. The first, is that analyses of the interfacial profiles exhibit Cu3Sn-rich, Cu6Sn5-rich, and tin-rich phases, which match with the boundaries of solder/Cu6Sn5, Cu6Sn5/Cu3Sn, and Cu3Sn/copper, respectively. The second, is that the semi-quantitative measurements with a peak-fitting model employed suffices to evaluate the interfacial concentration profiles with a statistical variation less than 5 mol %.