Investigation of the intermetallic compounds growth in 10μm Cu/Sn and Cu/Ni/Sn microbumps under isothermal temperature aging

Due to diameter reduction of microbumps in higher integration packaging structures, the solder will be consumed quickly due to fast intermetallic compounds (IMCs) growth. Brittle IMCs can cause interconnection reliability problems. Limited by the height and volume in Ф10μm microbumps, a thin Ni barrier layer about 600 nm was introduced between Cu pillar and solder Sn to slow IMCs growth in this study. The microstructure evolution and IMCs growth behavior during 170 °C isothermal aging of both Cu/Sn and Cu/Ni/Sn microbumps were investigated. It has been found that thin Ni barrier layer can restrain IMCs growth rate. Cu/Sn and Cu/Ni/Sn systems diffusion coefficients were 4.44 × 10−17 m2/s and 1.33 × 10−17 m2/s. Thin Ni barrier blocked atomic diffusion and stabilized the high temperature Cu6Sn5 phase, avoiding stress induced by phase transformation. Reliability of microbumps was improved.