Interfacial reaction, ball shear strength and fracture surface analysis of lead-free solder joints prepared using cobalt nanoparticle doped flux

摘要

In this research study, we investigated the interfacial reaction and fracture modes in BGA solder joints prepared using Co nanoparticles doped flux. Solder joints were formed in a reflow oven at 240 °C for 45s and subsequently aged at 150 °C up to 1008 h. One set of aged solder joints was used in both micro-structural characterization to examine the morphology and growth of interfacial IMC layer and nano-mechanical characterization to determine the hardness and Young's modulus of different phases. Another set was experimented in ball shear test to determine the average shear strength and crack paths in different failure modes. Results showed that the growth of Cu_6Sn_5 enhanced and that of Cu_3Sn suppressed due to the profound stability of Cu_6Sn_5 in the presence of Co atoms. In the case of undoped condition, the direction of crack changed from a ductile failure mode to a brittle failure mode with respect to aging time. No catastrophic brittle failure mode was observed for Co doped solder joints. The mechanisms for the better fracture behavior in Co-doped solder joints are suggested and correlated to Cu_6Sn_5/Cu_3Sn interfacial reaction.