Mechanism of Ag3Sn grain growth in Ag/Sn transient liquid phase soldering

Transient liquid phase (TLP) bonding is a potential high-temperature (HT) electron packaging technology that is used in the interconnection of wide band-gap semiconductors. This study focused on the mechanism of intermetallic compounds (IMCs) evolution in Ag/Sn TLP soldering at different temperatures. Experimental results indicated that morphologies of Ag3Sn grains mainly were scallop-type, and some other shapes such as prism, needle, hollow column, sheet and wire of Ag3Sn grains were also observed, which was resulted from their anisotropic growths. However, the scallop-type Ag3Sn layer turned into more planar with prolonging soldering time, due to grain coarsening and anisotropic mass flow of Ag atoms from substrate. Furthermore, a great amount of nano-Ag3Sn particles were found on the surfaces of Ag3Sn grains, which were formed in Ag-rich areas of the molten Sn and adsorbed by the Ag3Sn grains during solidification process. Growth kinetics of the Ag3Sn IMCs in TLP soldering followed a parabolic relationship with soldering time, and the growth rate constants of 250, 280 and 320 °C were calculated as 5.83×10−15 m2/s, 7.83×10−15 m2/s and 2.83×10−14 m2/s, respectively. Accordingly, the activation energy of the reaction was estimated about 58.89 kJ/mol.