Automatic process control of wire bonding

For the real-time recording of essential bond parameters: bond-force; ultrasonic amplitude; bonding time; during the bonding process, sensors are applied to the bond arm. The methods (measuring procedures) and necessary hardware and software for the monitoring of the measured values have been developed. Strain gauges are fixed to the bond arm and provide a signal proportional to the applied bond-force. A piezo-ceramic sensor is attached to the horn of the bond arm to measure the amplitude of the ultrasound. The bond-time is deducible from the duration of the ultrasonic signal. The electrical signals are recorded and interpreted in real-time using a PC compatible PCD3T (Siemens) computer. The sensorised bond arm can be used advantageously with either nail-head or wedge-wedge bond machines, with both thick and thin wire bonds. Results are discussed for 25 μm Al-wire bonds on different surfaces. To show correlation for ultrasound and bond-sticking, frequency-distributions are presented. To check bond quality, extensive shear tests and pull tests were performed. Results show that shear tests are more sensitive to bond quality than pull tests. The data from automatic process control can be used to substitute SPC (Statistical Process Control) and minimise destructive tests. Bond quality can be monitored by observing the 2nd harmonic of the ultrasonic signal. Bond parameters drifting towards bad bond quality can be avoided