Effective Vacancy Research Articles

Effect of Cu grain size on the voiding propensity at the interface of SnAgCu/Cu solder joints

Effect of Cu grain size on void formation at the interface of SAC305 (Sn3.0Ag0.5Cu)/Cu solder joint was studied. The joints with ED CCL (Electrodeposited Copper Clad Laminate) substrates exhibited a strong voiding tendency. But this tendency was significantly reduced after annealing treatment at 150°C for 1000h. At the same time, no voids were found at the interface of SAC305/HPOFC (High Purity Oxygen Free Copper, 99.9999wt%) plate. It was found that the grain size of annealed ED CCL increased by two orders of magnitude than that of ED CCL, but it was just about half of the grain size of HPOFC plate. The smaller grain size of Cu could increase the amount of grain boundaries, thus increasing the amount of effective vacancies (EVs). Under gradient of concentration, these EVs would coalesce to form voids at the interface of Cu3Sn/Cu. Therefore, to lower the tendency of void formation at the interface, increasing the size of grain is an effective way.