Microstructural investigations of aluminum and copper wire bonds

Abstract

Ultrasonic wire bonding is a widely used technology to interconnect chips in the packaging industry. It is known that the bond quality depends on the microstructure prevalant in the bond. Similarly, the materials used as well as the bonding parameters depend also on the microstructure. However, the actual used materials such as aluminum and gold are either characterized by poor conductivity or high costs. Due to the outstanding properties of copper, it is a promising candidate for wire bonds. Nevertheless, a thorough investigation on the interrelationship between the material combinations, the processing parameters and the resulting microstructure for copper and aluminum wire bonds need to be conducted. Facing these unresolved issues, samples of aluminum and copper wires were extracted during various states of the bonding procedure. The samples were analyzed to gather information about microstructural influences on the bonding parameters. As a result a conclusion can be drawn regarding the ultrasonic wire bond strength/load subject to the bonding parameters. Furthermore, the different deformation behaviour of copper and aluminum will be depicted by employing the following analytical methods: hardness tests, light microscopy, and scanning electron microscopy.