Mechanical properties of intermetallic compounds in solder joints

Intermetallic compounds (IMCs) that grow on the interface between the solder alloy and its bonding pads play a crucial role in the reliability of solder joints. It has been identified that the cracking around the IMC layer is the primary failure mode in lead-free solder joints. Therefore the mechanical behavior of the IMC has attracted great attentions. In this paper, mechanical properties of two kinds of intermetallics, Cu₆Sn₅ and Cu₃Sn, which are two major species of IMCs in lead-free solder with Cu pad metallization, are collected and discussed. The measurements on Young´s modulus and hardness of Cu₆Sn₅ and Cu₃Sn show a great diversity among different researchers´ work. Although the strength of IMC exhibits diversity, some common trends emerge. Tensile and shear strength if the IMC decrease with the increasing of the thickness of interfacial intermetallic layer.