Study on the evolution of interfacial (Cu,Ni)6Sn5 and shear property of (111)Cu/Sn/Ni micro joints under isothermal and TG-bonding

Single-crystal Cu can be potentially applied as pad or micro bump in bonding technology for advanced packaging. A novel bonding method with an extra temperature gradient (TG, TG-bonding) was carried out to bonding single-crystal (111)Cu and poly-crystal Ni substrates with Sn as interlayer. The morphology and orientation evolution, elemental distribution and growth kinetics of interfacial (Cu,Ni)₆Sn₅ intermetallic compound (IMC) in (111)Cu/Sn/Ni micro joints during isothermal and TG-bonding were investigated. Regular roof-type (Cu,Ni)₆Sn₅ grains along three intersectant directions with an angle of 60° formed at the initial Sn/(111)Cu interface and maintained the roof-type morphology with $\left(11\bar{2}0\right)$ preferred orientation throughout the isothermal bonding. For TG-bonding, TG-induced atomic thermomigration (TM) and Cu–Ni cross-interaction co-played a critical role in the morphology, grain feature and growth kinetics of the interfacial IMCs. Moreover, rapid growth of (Cu,Ni)₆Sn₅ phase was achieved by TG-bonding with (111)Cu as hot end to fabricate full IMC joints which had higher shear strength than the cases of isothermal and TG-bonding with (111)Cu as cold end. The proposed method would provide a further insight for developing bonding technology for advanced packaging.