Abstract: The indentation creep behavior of the bulks of Cu/SAC305/Cu, Cu/SAC0705/Cu and Cu/SAC0705BiNi/Cu lead-free micro solder joints are comparatively investigated at different maximum load by nanoindentation method. And the Bi, Ni concentration on the creep behavior of the bulks of Cu/SAC0705/Cu micro solder joints are analyzed and discussed. The mode of loading-unloading is adopted. Here the holding time is 180 s and the maximum load is 20 mN, 30 mN, 40 mN, and 50 mN, respectively. The indentation morphologies of the bulks of the micro solder joints at different maximum load are observed by FEI SIRION scanning electron microscopy (SEM). The results indicate that the creep depth and indentation size of the bulks of Cu/SAC0705BiNi/Cu are smaller than that of Cu/SAC305/Cu and Cu/SAC0705/Cu at the same maximum load and holding time. Compared with the bulks of Cu/SAC0705/Cu micro solder joints, at four different maximum loads, the indentation creep rate (C_IT) of the bulks of Cu/SAC0705BiNi/Cu micro solder joints are declined 11.883%, 16.059%, 8.815 7%, and 12.891%, respectively. The creep stress exponent of the bulks of Cu/SAC0705/Cu micro solder joints increases 32.175 % by adding Bi and Ni elements. The addition of Bi and Ni elements can effectively improve the creep resistance of the bulks of low-Ag Cu/SAC0705/Cu micro solder joints.

Key words: creep resistance, creep stress exponent, nanoindentation, micro solder joint