Tin Whiskers

Question:

My company has given me an assignment that requires a report on the current state of tin whisker research. Can you supply any information or suggest information sources? W. J.

Answer:

Tin whiskers are a major issue in the world of high reliability electronic components. For those readers who are not familiar with this phenomenon of tin whiskers, a tin whisker is a thin, whisker-like growth that "grows" from tin plated surfaces. They are electrically conductive and have been observed to grow as much as 2–3 mm in length. These whiskers can cause short circuits by bridging circuit elements. The classic method used to minimize this problem is to add a small amount of lead to the tin deposit. However, this approach will no longer be viable after July 1, 2006 due to new regulations promulgated by the European Union.

Lead-free finishes are now required. Another complication has been the lack of standards for testing. The International Electronics Manufacturing Initiative, iNEMI, www.inemi.org, has formed a tin whisker user group. This group has published a number of reports that are available at their web site. Their latest report, Recommendations on Lead-Free Finishes for Components Used in High-Reliability Products, Version 3, May 2005 gives an excellent overview of the tin whisker problem and how to reduce the likelihood of tin whisker formation.

Some of the many alternatives that are mentioned are:

 

• Non-tin plating – Nickel/palladium/gold or nickel/palladium
• Nickel barrier layer between the copper substrate and tin layer
• Silver layer between the copper substrate and tin layer
• Hot dip tin in a molten tin bath

 

Another document at the iNEMI site, Test Method for Evaluating Tin-Whisker Growth on Plated Surfaces, addresses the issues of testing.

A Google search will lead you to many additional references regarding tin whiskers.