Grain growth sequence of Cu3Sn in the Cu/Sn and Cu/Sn–Zn systems

Transmission electron microscopy (TEM) technique is used to figure out the growth mechanism of Cu3Sn in the systems of Cu/Sn and Cu/Sn–Zn where Cu is polycrystalline. After reflow in Cu/Sn system, a layer of equiaxed Cu3Sn grains is already present. During solid-state aging initial equiaxed Cu3Sn grains become columnar and newly formed equiaxed Cu3Sn grains nucleate at the triple junction sites of the interfaces between Cu/Cu3Sn and two adjacent Cu3Sn grains. After prolonged aging large columnar and equiaxed Cu3Sn grains are present with several voids near the Cu side. Sn–0.5 wt.%Zn solders are prepared to react with Cu for comparison. The result shows that Cu3Sn grains in this system are constrained to be equiaxed without progressive columnar growth after long time aging.