Two-component mixture distributions for measuring area and compactness of intermetallic formation from the Au-Al wire bonding image

Abstract

The quality of the Au-Al wire bond is determined by the percentage intermetallic area (%IM) and compactness (Comp). Problems with visually estimating %IM provide strong motivation to fit mixture distributions to the brightness histogram of a wire bonding image. After some preprocessing it is shown that the two component mixture distribution may be fitted to the brightness histograms. The fitted mixture models are used to find optimal threshold points which in turn are used to define a binary image. Both %IM and Comp are estimated from this binary image. The results show that both %IM and Comp should be considered while accessing the quality of the Au-Al bond. Further, the use of 2-component mixture distributions provide an objective method for measuring both %IM and Comp.