A reliable thermosonic wire bond of GaAs-devices analysed by infrared-microscopy

Due to the delicate sensitiveness of GaAs devices, ultrasonic energy is generally regarded as a critical reliability parameter for wire bonding. Therefore wire bonding is usually performed using thermocompression. The subject of this work is a description of bond parameters for thermosonic wire bonding using 25 μm Au-wire and a gold plated pad-metallization. The range of optimal bond parameters which lead to reliable and reproducible contacts is described. By the use of this parameter range cratering in ball-wedge as well as wedge-wedge thermosonic bonding can be avoided. The adhesion of the bond-interface is investigated with destructive analysis methods such as pull and shear-tests. Additionally infrared-microscopy is used to investigate cratering and pre-damaging of GaAs. Pre-damaging can lead to sudden failures in the metallization/chip interface. Because pre-damaging can not be detected electrically, infrared microscopy is very helpful to define parameters for reliable bonds. Due to the more sensitive infrared analysis method, infrared microscopy leads to a small but well defined range of optimal bondparameters. In accelerated aging tests the contacts show a good reliability. The results of infrared analysis are compared with SEM investigations of the etched devices