Failure Probability Evaluation Due to Tin Whiskers Caused Leads Bridging on Compressive Contact Connectors

Abstract

This paper presents a failure probability assessment of compressive contact connectors due to tin whiskers caused leads bridging. Based on scanning electron microscope measurements, we establish probability distributions of four involved variables: whisker length, orientation, origin location, and counts. A failure probability model is developed and used to calculate the failure probability in terms of two types of failure definition: 1) national electronics manufacturing initiative (NEMI) acceptance criteria, and 2) leads bridging caused by tin whiskers. Results indicate that, in terms of the NEMI criteria, there is more than a 50% chance that the connectors would fail to meet the maximum allowable whisker length for class 2 products at six-month ambient storage, while the probability goes up to 74% for class 2, or 62% for class 3 at one year. However, the failure probability for tin whisker caused leads bridging is fairly low, only 0.0002% for six-month storage, 0.0074% for one-year storage, and even 0.0515 % for five-year storage. Therefore, although the connectors may fail to meet NEMI acceptance criteria for maximum allowable whisker length, the whiskers do not pose significant field risk to cause leads bridging at ambient storage.