Get Used To Tin Whiskers

By Ed Sperling -- Electronic News, 5/5/2006

Tin whiskers can be reduced, but it's doubtful they will ever be eliminated once lead is completely removed from solder.
 
The International Electronics Manufacturing Initiative (iNEMI) -- a collection of electronics manufacturers that produce high-reliability products -- has developed a list or recommendations for testing and mitigation. But the group says the body of information is still not perfect for long-life products, and whiskers will still form under certain conditions.
 
"This document took us more than three years to do," said Joe Smetana, who chairs iNEMI's tin whiskers user group. "We started even before there was a user group and rolled in five companies. We spent a tremendous amount of time. But the conclusion is there is no way to take test data and no way to definitively say a coating won't whisker."
 
With the European Union's Restriction of Hazardous Substances (RoHS) legislation scheduled to take effect on July 1, and other countries such as Korea, China and parts of the United States scheduled to follow suit in coming months, lead-free solder has become a requirement for many industries. The problem, however, is that a suitable replacement has not be found so far. While whiskers probably won't be a problem in consumer electronics, where product life is short, over time they can grow and short-circuit devices.
 
The document is intended to reduce the threat of whiskers, but eliminating it is currently impossible. It deals with mitigation practices, testing and process control. Smetana noted that even though coatings can be tested, that doesn't take into account things like corrosion.
 
"The problem is that all with the things we can do to mitigate whiskers, there will still be whiskers at certain temperatures," he said. "Corrosion breaks down coatings. If you get compressive stress on a finish, there is not a finish out there that will prevent it."
 
In addition to iNEMI's document, JEDEC released a standard called "Environmental Acceptance Requirements for Tin Whisker Susceptibility of Tin and Tin Alloy Surface Finishes." Both documents are intended to deal with the whiskering problem.
 
For further information, visit JEDEC www.jedec.org and iNEMI www.inemi.org/cms/projects/ese/tin_whisker_activities.html online.