Anisotropic grain growth and crack propagation in eutectic microstructure under cyclic temperature annealing in flip-chip SnPb composite solder joints

The evolution of eutectic structure under temperature cycling tests (TCTs) in SnPb composite solder joints has been investigated. After 500 cycles of TCT, the Sn grains coarsened and developed anisotropic stripes close to the necking site in the solder joint because of stress-induced atomic migration. Then, cracks triggered by thermal stress were observed to propagate along the Sn stripe interfaces. After a prolonged 14,410 cycles of TCT, the cracks expanded across the entire solder joint and led to electrical open failure.