Influence of solder layer thickness on the interfacial reaction in Ni/Sn/Cu system

In this paper, we reported a study on the effect of solder volume on the intermetallic layer morphology and thickness in the Ni/Sn/Cu system wi th 10µm, 20µm, 40µm Sn layer. The content of Cu and Ni in the solder increased wi th the reducing of solder volume. In the aging process, the IMCs at Cu/Sn boundary remained stable with nearly constant thickness in 10µm and 20µm Sn layer diffusion couples, of which the scallop-shaped IMCs at Sn/Ni side transformed into rod-shaped, and tended to connect mutually after 24 hours aging, while in 40µm the IMC layer continued to grow at a fast rate, and the IMCs of (Cu, Ni)6Sn5 at Sn/Ni boundary transformed rapidly into planar after 96h aging. Lower volume of solder may lead to increasing density of (Cu, Ni)6Sn5 rods and formation of Kirkendall voids at Cu/ IMC interface, which is a reliability concern. For the addi tion of Ni prevents the formation of Cu3Sn, no visible Cu3Sn was detected at the Sn/Ni boundary.