Abstract
In general, power semiconductors are highly sensitive to thermal stress, and thus are required to be highly reliable. Some typical failure modes of the power semiconductors are caused by thermal stress. One example of such mode is cracks in joints. There arises a need for an effective method for non-destructive and quantitative evaluation of cracks, to identify possible deterioration of semiconductors over time and to reduce man-hours required for the evaluation. Conventionally, crack evaluations are based on changes in electric resistance and in temperature of semiconductor components. However, the accuracy of such evaluation is insufficient, which is a great concern. This research focuses on changes in transient thermal resistance caused by cracks. Especially, discussion is made on the correlation between the changes in transient thermal resistance and the crack propagation rate. Consequently, the research reveals a close correlation between these two elements. The research also shows that the discussed approach allows measurement of cracks, including those in the early phase of semiconductor deterioration, with high accuracy.
