Effect of nickel (Ni) on the growth rate of Cu₆Sn₅ intermetallic compounds between Sn–Cu–Bi solder and Cu substrate

Abstract

In this work, the lead-free composite solder was fabricated by mixing Ni element with Sn–0.7Cu–10Bi solder. The effect of nickel (Ni) addition on the growth behavior of intermetallic compounds (IMCs) between Sn–0.7Cu–10Bi–xNi (x = 0, 0.05, 0.10, 0.15 and 0.20, in wt%) solder and Cu substrate during the soldering process was studied. The microstructure and the IMCs growth of the solder joints under thermal aging were systematically investigated. The results shown that the addition of Ni element has a slightly influence on melting point of the solder. Moreover, the addition of Ni element can change Cu₆Sn₅ shape from scalloped-like structure into flat-like one. Moreover, the results reveal that Ni can considerably inhibit the growth and reduce the thickness of Cu₆Sn₅. The thickness of Cu₆Sn₅ ranges from 3.07 to 8.42 µm after aging process The diffusion coefficient (D) is 1.80 × 10⁻³ µm² h⁻¹ and growth rate (dH/dt) is 4.08 × 10⁻⁷ µm s⁻¹ of the Cu₆Sn₅ when the Ni content come to 0.15 wt%. The (Cu,Ni)₆Sn₅ phase formed in the IMCs layer when Ni was added to the solder, and it can effectively hinder the diffusion of Cu atoms and depressed the growth rate of Cu₆Sn₅.