An investigation on nanoscale bondability between Cu-Al intermetallic compound

Abstract

The aim of present research is to investigate the interfacial nanoscale bondability between copper and Aluminum intermetallic compound (IMC) for copper wire and aluminum pad. In addition, the growth mechanism of IMC layer is carefully examined. Preliminary results demonstrated that IMC cracks from the edge of bonding interface and spreads into the center area. This is the cause of open fail. The IMC between Cu and Al was initially generated in the form of CuAl2, and gradually increased the content of Cu and turned into CuAl when the working temperature was increased. The final stage of IMC growth is Cu9Al4 and the aluminum pad will be vanished as the result of Cu diffusivity. Bondability on nanoscale IMC of CuAl2, CuAl and Cu9Al4 are also cautiously investigated by using a special self-designed pull test fixture. Nanoscale atomic modulus and rupture strength are validated by using molecular dynamics (MD) simulations. Atomic-level tensile stress and tensile strain are predicted to examine the bonding strength of two IMCs along the bonding interface. Temperature and tensile speed are two major factors on determining the bonding strength. Material in high temperature has greater kinetic energy and has better formability. Higher pulling speed in tensile test would results in material easier fracture. Interfacial fracture is different in different tensile speed as well as the working temperature. A series of experimental works and MD simulations are conducted in this research.