Methodology for identifying wire bond process quality variation using ultrasonic current frequency spectrum

Life time prediction of power electronic modules is becoming increasingly important in order to reduce unscheduled maintenance and unexpected failures. Recent developments in life time estimation of standard power electronic modules determine the nominal life time degradation under operating conditions and/or under harsh environments. However, it is important to obtain life time degradation information considering underling process variation originating from the manufacturing line. In this work, a methodology for obtaining a non-destructive assessment of bonding quality is investigated. This is done with the view of capturing information about bonding quality prior to service exposure, and hence determining the effect of the observed variation in bond quality on reliability. Analysis of the frequency spectra of signals obtained from the ultrasonic generator of a wire bond machine reveals it is a process sensitive parameter. The analyzed results show a good correlation between the frequency and amplitude values of the generator output signals and bond quality. 3D x-ray scans of bonds provide further non-destructive evaluation and validate the observed link between the observed generator output signals and bond quality.