Shear strength and fracture surface analysis of lead-free solder joints with high fraction of IMCs

The effects of high fraction of intermetallic compounds (IMCs) on the shear strength and fracture mechanism of Cu/Sn3Ag0.5Cu/Cu solder joints were investigated. Reflowing at 250 degrees C up to 60 min, then isothermal aging was conducted at 150 degrees C with multiple aging time. The results showed that the thickness of Cu3Sn IMC gradually increased with the extending of reflowing time and aging time. In addition, the shear strength of solder joints decreased with increasing reflowing time and aging time, which was due to the excessive growth of the interfacial IMC layer. From the fractography, the brittle fracture mode was observed because of the Cu6Sn5 and Cu3Sn appeared on each fracture surface in all of shear samples. Furthermore, the area ratio of Cu3Sn on the fractured surfaces increased with the increment of reflowing time and aging time. In addition, the hardness and the Young's modulus of Cu3Sn decreased initially and then increased with increased reflowing time.