Novel transient liquid phase bonding method using In-coated Cu sheet for high-temperature die attach

Abstract

To meet the increasing demand for thermal stability in electronic packaging required for next-generation power modules, transient liquid phase (TLP) bonding of Cu/In system is concerned owing to its high remelting temperature and high strength. In this study, a novel TLP bonding method using In-coated Cu sheet was designed for high-temperature die attach. The microstructure and mechanical properties of joints bonded for different parameters were investigated. It was found that the In-coated Cu sheet could join electroless Ni/immersion Au (ENIG)-finished Cu disks strongly by forming two intermetallic compound (IMC) bondlines of δ-(Cu, In), Ni28In72, and AuIn2. With increasing bonding temperature and time, AuIn2 was consumed, while δ-(Cu, In) and Ni28In72 coarsened, reducing the defects in the bondline. Therefore, the shear strength of the bonded joint increased from 16.9 MPa to 38.0 MPa. However, the brittle characteristics and location of the fracture remained almost unchanged for the different bonding parameters.