Morphology evolution and grain orientations of intermetallic compounds during the formation of full Cu3Sn joint

The morphological evolution and grain orientations of intermetallic compounds (IMCs) were investigated during the formation of full Cu3Sn joints at two soldering temperatures (310 and 430 °C). The mechanical properties of both types of full Cu3Sn joints were then analyzed. The experimental results showed that the morphology of interfacial IMCs varied significantly at two temperatures. At 310 °C, scallop-like Cu6Sn5 grains became larger but were fewer in number and the top of the scallops became rough due to the grain ripening effect. With the increase in the soldering temperature to 430 °C, Cu3Sn no longer grew uniformly as observed during soldering at 310 °C, but exhibited various growth rates. Furthermore, some η-Cu6Sn5 transformed into η′-Cu6Sn5 during cooling, and the following orientation groups between η′-Cu6Sn5 and η-Cu6Sn5, i.e., {102}η′ and {112‾0}η, {112}η′ and {101‾0}η, and {2‾01}η′ and {0001}η, were found to be near-parallel. The Cu3Sn grains were preferably oriented with [203] and [100] crystal orientations parallel to transverse direction (TD) at both temperatures. Noteworthy, the Cu3Sn grains with [203]//TD and [010]//ND grew much faster than those with other orientations at 430 °C. Moreover, molecular dynamics simulation showed that the diffusion coefficients of atoms in Cu3Sn crystals along [203] direction were significantly greater than those in other low-index crystal directions. After soldering, two types of full Cu3Sn joints obtained at different temperatures exhibited different shear strength and fracture mechanisms.