NEMI Team Recommends Three Test Conditions for Evaluating Tin Whisker Growth

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Herndon, Va. — The National Electronics Manufacturing Initiative's (NEMI's) Tin Whisker Accelerated Test Project presented its recommendations for tin whisker testing at the SMTA International conference in Chicago.

The NEMI project team submitted a test method document to JEDEC that recommends two storage conditions and one temperature cycling condition to evaluate the propensity of tin-based plating finishes to grow whiskers.

Currently, there are no widely accepted test conditions for determining the predilection of a specific plating finish or plating process to grow tin whiskers. NEMI's Tin Whisker Accelerated Test Project was organized in 2001 to try to identify and/or develop such test methods. The team — which has involved more than 40 organizations — began with a benchmark study to collect all existing methods for growing whiskers. They then evaluated those test methods reported to successfully grow whiskers on some, but not all, tin-plated samples.

The NEMI project tested eight-lead small outline integrated circuit (SOICs) packages with varying thicknesses and different tin-based finishes. These samples were subjected to different environment combinations. Based on the results of the tests conducted, the NEMI group has recommended three test conditions:

• temperature cycling (-55°C to 85°C, approximately 3 cycles/hour)
• temperature humidity tests at 60°C/93 percent RH.
• ambient storage (air-conditioned facility)

All three tests are required, and each test must be performed independently.

In addition to the test specification submitted to JEDEC, NEMI is collaborating with two industry groups to develop a test protocol to submit to the International Electrotechnical Commission (IEC). The three groups are working to establish unified whisker test methods worldwide, including pass/fail criteria and fields of application.

The Tin Whisker Accelerated Test Project also has proposed this definition of a tin whisker: A spontaneous columnar or cylindrical filament, which rarely branches, of monocrystalline tin emanating from the surface of a plating finish.

The National Electronics Manufacturing Initiative's mission is to facilitate leadership of the North American electronics manufacturing supply chain. For more information, visit www.nemi.org.