Nanoindentation properties of as-soldered low-Ag SAC-Bi-Ni/Cu

In this study, the nanoindentation properties of the as-soldered low-Ag SAC-Bi-Ni solder alloys on Cu substrate were characterized. The overall evaluations on the elastic modulus, hardness, and creep properties of the new solder alloys were proposed based on the comparisons with low-Ag solder SAC0307, SAC0705, and high-Ag solder SAC305. Experimental results indicated that the hardness of the SAC solders without Bi and Ni addition varied from 127MPa to 196MPa. Meanwhile, the elastic modulus was between 29-36GPa, and the creep stress sensitivity was from 15 to 19. However, the hardness of low-Ag SAC-Bi-Ni solders was between 305-403MPa. Additionally, with Bi and Ni elements addition, the elastic modulus of SAC0705 increased to 35-63GPa, and the value of creep stress sensitivity reached to 25-45. It is clear that the addition of Bi and Ni in low-Ag SAC solder greatly improved its nanoindentation properties, which were critical for the solder joint reliability.