Phase evolution and nanomechanical properties of intermetallic compounds in solid-liquid interdiffusion bonding

Indium is one of the commonly used solders for Solid-liquid interdiffusion bonding (SLID) bonding, which is also known as transient liquid phase bonding (TLPB) and widely used in the manufacturing of electronic joints for high temperature applications via low temperature processes. Since the joints by the SLID bonding usually consist of intermetallic compounds entirely, this study investigated the phase evolution and mechanical properties of the In-based intermetallic compounds obtained from the reactions between In and substrate metals of Cu, Ag and Au during isothermal heating at 180 °C. In addition to hardness (H) and elastic modulus (E), yield strength (Y) and work hardening exponent (n) are also estimated and investigated using nanoindentation technique. Experimental results show that the main reaction products was Cu₁₁In₉ for the In/Cu samples, Ag₉In₄ for In/Ag and AuIn₂ for the In/Au samples. Hardness and Young´s modulus of Cu₁₁In₉ are greater than those of Ag₉In₄ and in turn greater than AuIn₂. Among the IMCs investigated, AuIn₂ exhibits a stronger dependence of strain rate on mechanical properties (strain rate sensitivity) than the others. The nanoindentation responses and indent morphology indicate that AuIn₂ exhibits a greater ability for plastic deformation. Worthy of notice is that strain induced precipitation of AgIn₃ occurs at the indents of Ag₉In_4.