Tests spot tin whisker problems

The US-based International Electronics Manufacturing Initiative has released two documents intended to help component suppliers reduce the risk of tin whiskers in lead-free products.

First is JEDEC standard JESD22A121, “Test Method for Measuring Whisker Growth in Tin and Tin Alloy Surface Finishes,” and the second is an updated “Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products” from the iNEMI Tin Whisker User Group.

Tin whiskers have presented a problem to the components industry, as pure tin will grow tiny whiskers under stress. The whiskers can break off, causing shorts and malfunctions in electronic parts.

In the past, lead has been added to tin to mitigate this problem. With the industry move to lead-free components, engineers have warned about tin whisker problems. The tests released by iNEMI are designed to help component manufacturers determine if their products are safe from the tin whisker phenomenon.

The JEDEC tin whisker growth test method details a suite of tests that provide an industry-standard method of measuring and comparing whisker propensity for different plating or finish chemistries and processes. JESD22A121 also offers a consistent inspection protocol for tin whisker examination and a standard reporting format.

The test method was initially developed by an iNEMI group. Then it was expanded and modified with additional industry input as it went through the JEDEC development process. JEDEC is a developer of standards for the solid state industry.

The iNEMI group that published “Recommendations on Lead-Free Finishes for Components in High Reliability Products” is made up of 11 large manufacturers of high-reliability electronic assemblies that annually purchase billions of dollars of components.

Their publication is intended to help manufacturers minimise the risk of failure from tin whiskers. The newly released revision reflects the uniform test requirements set out by JEDEC. The recommendations have been organized to provide easy-to-follow guidance on the various lead-free finish options.

Both sets of the user group recommendations are available from iNEMI.