Customer returns are defective parts that pass all functional and parametric tests, but fail in the field. To prevent customer returns, this paper analyzes wafer probe test data and tries to understand what it takes to screen them out during testing. Because these parts pass all tests, analyzing their signatures based on the original test perspective does not make sense. In this work, we search for a novel test perspective where the test signatures from parametric measurements can be used to separate the returned parts from the rest of population. Our study shows that in order to effectively screen customer returns during wafer test, a multivariate screening methodology is desired. This study is based on analyzing over 1000 parametric wafer probe tests and dies from seven lots, each lot containing one returned part. We demonstrate that analyzing customer returns from a multivariate test perspective leads to robust and conservative results.
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