Development of Nickel Wire Bonding for High-Temperature Packaging of SiC Devices

This paper describes a detailed investigation of an ultrasonic nickel wire bonding technique for silicon carbide (SiC) devices, and its comparison with a thermosonic wire bonding process, for high-temperature applications. The study focuses on bonding 25-mum-diameter Ni wires to 750-nm-thick Ni pads deposited on 3C-SiC substrates. First, the Ni wire bonding recipe is optimized for maximum bond strength using a response surface methodology (RSM) statistical approach. Maximum pull strengths as high as 13.1 gram force (gf) are achieved, far surpassing the military specifications for conventional Au (3.0 gf) and Al (2.5 gf) wire bonds. Scanning electron microscopy (SEM) and electron dispersive spectroscopy (EDS) are used to characterize crack defects on the heel of the bonded wires and verify the absence of cratering. Pull strength and electrical performance of the Ni wire bonds are studied up to 550degC. The utility of Ni wire bonding to Ni pads for wire bonding prior to chemical release of SiC micromechanical devices in KOH and HF is demonstrated. Demonstration of use of Ni wire bonding with Ni pads in a SiC-based chemical sensor and a poly-SiC lateral resonant device is provided, up to 280degC operation for the former and 950degC the latter. Such devices are for example of interest in combustion-related sensor instrumentation.