Preparation and microstructure of functionally gradient diamond/SAC composite solder bumps

With the method of copper-coating 100μm Diamonds was added into Sn3.0Ag0.5Cu(SAC305) solder to acquire Diamond/SAC305 composite solder bumps on Cu pad, which is considered to be a potential material to improve the thermal management of HB-LEDs, on account of the favorable conducting property of diamonds. Not only was a relatively high (7 wt. %) and controllable addition amount of diamonds achieved, but also a much better outlook of the solder bumps was observed. What´s more, spreading areas of the new solder were calculated and shear strengths of the bumps were measured. Spreading area went up and down respectively before and after the diamond additions was 3wt%. Meanwhile the shear strength fluctuated with peaks at 1wt% and 7wt%. The distribution of diamonds was observed as centralizing mainly at the interface between the solder and the Cu pad, making up a special enhanced interface character as a kind of functionally gradient (FG) solder bump.