Managing Whiskers – Both Tin and Facial
A big topic in the last few years has been the occurrence of (and the damage caused by) the growth of tin whiskers in high-profile and high-reliability products. Elusive, often misunderstood, and difficult to prevent; tin whiskers have posed significant problems. In fact, even just two weeks ago TechEye.net was speculating that tin whiskers may be behind the massive Toyota recalls. Whether the whiskers are out to race cars, or are turning into conductive plasma arcs capable of carrying hundreds of amps, it is clear that they are a force to be reckoned with and have a flair for the dramatic.
I see a variety of similarities between Tin whiskers… and my own: Elusive, thin, short, and never helpful. And there is always the random single hair that frustrates you to no end.
Unfortunately, the costs associated with tin whiskers in the electronics, defense, health, and aerospace industries are astronomical compared to my need to shave once every two weeks. Failure of products due to tin whisker growth can undermine an entire mission, scrap a program, or take a life. I think about electronic pacemakers, our men and women traveling to space, or our servicemen and women flying at Mach speeds thousands of feet above the ground.
There has yet to be a definitive ruling made concerning the cause/prevention of whiskers, although pure tin components and plating seem to exhibit the highest likelihood of developing them. Best practices at this time are to use a tin/lead mix with no greater than 97% tin. However, RoHS regulations are throwing a wrench into this with its demands for lead-free products. Some RoHS frequently asked questions are answered here.
This issue received significant attention at the IPC Technology Interchange this last December. Also, the Center for Advanced Life Cycle Engineering at the University of Maryland (CALCE) and The Institute of Scientific and Industrial Research at Osaka University (ISIR) are putting on another International Symposium on Tin Whiskers this June. The call for papers is still out. Read more about this at PCB007. Proceedings from past Symposiums can be found here.
For a great overview of tin whiskers, be sure to check out the resources provided by NASA. The pictures in this article have all been sourced from NASA.
Have you dealt with tin whiskers in your products/designs? What types of damage have they caused? What are some of the things you have done to diminish the likelihood of them?