Abstract
In this paper, we studied the reliability of Cu joint with a Sn–Ag–Bi–In (SABI) lead-free solder under a high electric current stress with or without trace amounts of Co and/or Ni as grain refiners. Electromigration (EM) caused critical failure of the soldered structure at current densities exceeding 10 kA/cm2, over 100 °C. Because of the anisotropic diffusion coefficients along the a/b and c axis of β-Sn tetragonal crystal, the EM resistance of the joints depended on the grain size and their orientation. The observation of microstructure with electron backscatter diffraction revealed that the grain with the addition Co and/or Ni becomes much finer than that without any additive resulting in, an improved EM resistance. The best alloy in the present our study is SABI containing 0.1 wt% Co, exhibiting a lifetime twice larger than that with SABI. The improvements of EM reliability by these additives are significantly different depending on diffusivity of the refiner elements.
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