A defect modeling approach is developed which allows the determination of the true failure rate with a minimal sample size. A model was developed using the proposed approach to estimate the failure rate of an aluminium/1% silicon wire ultrasonically bonded to aluminum and to gold pads. For this reliability model the variable was wire-bond width. Dependent upon the width of the bond, the failure mode can be either a wire-bond lift or a heel break. The purpose of the model was to determine the true wire-bond failure rate and to understand the bond width limits by defining the failure potential curve. To determine the process capability of the manufacturing line, a sampling plan was put in place to collect data from different bonders, different shifts, and different operators over a span of two weeks. The data were compiled and fitted to a statistical model. The probability of failure is the mathematical summation of the failure potential curve along with the probability of occurrence data. Factors that could influence the results of this analysis are discussed.
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