Evolutions of the interface and shear strength between SnAgCu-xNi solder and Cu substrate during isothermal aging at 150 degrees C
The interfacial evolution and shear strength of Sn3.8Ag0.7Cu–xNi composite solders on organic solderability preservative (OSP) finished pad were investigated at a temperature of 150 °C aging for 0–1000 h. It was found that all aged joints exhibited a duplex intermetallic compounds (IMCs) structure; i.e. a layer of (CuNi)6Sn5 close to the solder and a layer of Cu3Sn adjacent to the Cu substrate. The growth of the Cu3Sn layer was suppressed significantly after Ni particles addition, and the scallop-shape IMC with the composition of (CuNi)6Sn5 could be examined at the interface of all solder joints. In comparison with the non-composite joint, the IMC grain was refined significantly at the interface of composite joints. In addition, the mean thickness of interfacial IMC layers increased linearly with the square root of the aging time for all the diffusion couples. The Cu3Sn layer shows the fastest growth rate at the interface of non-composite. The fracture after the ball shear test occurred in the bulk solder for all as-reflowed joints and the aged SAC and SAC–0.5Ni joints. The fracture mode of SAC–1Ni and 2Ni joints transferred from an initial ductile type to a mixed type near the interface with the partial brittle fracture after 50 h aging.