Strong grain size effect on the liquid/solid reactions between molten solder and electroplated Cu

Electrodeposition of Cu metallization and its soldering reaction with solder alloy are of technological significance in microelectronic packaging industry. This study aims to investigate the effect of Cu grain size on the liquid/ solid reactions between molten Sn-3 wt% Ag-0.5 wt% Cu (SAC305) solder alloy and electroplated Cu. Two Cu electroplated films, denominated as fine-grained Cu (FG-Cu) and coarse-grained Cu (CG-Cu), are prepared and reacted with SAC305 at 260 degrees C for 5-20 min. Microstructural characterization shows that the Cu6Sn5 6 Sn 5 intermetallic compound (IMC) is formed in these two solder joints, while that in the FG-Cu solder joint grows at a faster rate than that in the CG-Cu solder joints. The Cu6Sn5 6 Sn 5 IMC in the FG-Cu solder joint exhibits a slender column-like grain morphology, unlike the common scallop-like grain morphology in the CG-Cu solder joints. The strong grain size effect is rationalized by comparing the contribution of two fluxes of ripening and interfacial reaction to the growth of Cu6Sn5. 6 Sn 5 .