Nemi Tin Whisker Test Method Standards

The need to better understand whisker growth has dramatically increased as component suppliers convert from tin-lead (SnPb) finishes to Pb-free finishes of Sn and low-alloy-content Sn-based finishes. Whiskers are spontaneous growth of metal filaments emanating from the finish surface. The issues with whiskers are they may grow long enough to cause short circuiting or break off and interfere with other devices in an application. Currently, there is not an industry-accepted test to assay the propensity of a plating finish to whisker and to estimate the risk of whisker growth for a given plating finish. The Whisker Test Method Standards Committee was formed under the sponsorship of the National Electronics Manufacturing Initiative (NEMI) to evaluate different environmental factors influencing whisker growth and to recommend test methods to assess whisker growth propensity of plating finishes. The Committee has completed two phases of testing. The initial Phase 1 evaluations, performed with lab-plated bright Sn samples, provided some insight on which environments would cause a plating finish to whisker but very few occurrences of whiskers were observed which made the results inconclusive. A Phase 2 evaluation was performed with production plated matte Sn from two integrated circuit (IC) suppliers. The results revealed that several environments were very effective in forming whiskers. Based on the results of both Phase 1 and 2 evaluations, NEMI is recommending three tests (two storage conditions and one temperature cycle condition) to evaluate the whisker growth propensity of plating finishes. The Committee is preparing a test method document to be presented to JEDEC, the Solid State Technology Association (once known as the Joint Electronic Device Engineering Council), for release.