Failure mode analysis of lead-free solder joints under differential reflow profiles by high speed impact testing

The aim of this research is to investigate the mechanical behavior of lead-free solder for high speed impact. A high speed impact test was set up to measure the solder joint reliability. Differential impact speed and room temperature aging effect has been studied with Ni/Au substrate. Furthermore, two different solder alloys (96.5Sn-3Ag-0.5Cu, 98.5Sn-1Ag-0.5C) and three different reflow profiles are considered. This paper focuses on failure mode analysis and investigates the failure characteristics of lead-free solder joints, 96.5Sn-3Ag-0.5Cu and 98.5Sn-1Ag- 0.5C, which are aging at room temperature, respectively, then those solder are impacted at shear rates of 0.3 m/s and 1.0 m/s. Four types of failure mode are found in this high speed impact testing result. Mode M1 is the fracture around the interface but not remain the solder on pad. Mode M2 is fracture around the interface and remained the solder on pad. Mode M3 is fracture across the solder ball. Mode M4 is fracture on the substrate with lift the pad. The aging time could increase the interfacial strength, therefore the percentage of M3 and M4 mode failures increases in Ni/Au substrate. According the results, we find that in reflow profile A and reflow profile C, the failure percentage of Mode M2 is increasing; in reflow profile B, the failure percentage of Mode M3 and Mode M4 are large than Mode M1 and Mode M2.The failure mode M2 is the majority in solder alloy 96.5Sn-3Ag- 0.5Cu, and the failure mode M2 and M3 are the majority in solder alloy 98.5Sn-1Ag-0.5C.