Tin Whiskers all over the Place

Question:

We have received a large shipment of tin plated parts from one of our venders in Asia. Upon inspection of the parts, we observed fine hair-like growths on almost all of the surfaces. What are these, and, more importantly, how can they be prevented? J. R.

Answer:

Welcome to the world of tin whiskers! This phenomenon of tin whiskers was first reported in the 1940s. Typically, the whiskers will grow from the surface and, once they are long enough, can cause shorting out of electronic components. The classic way of preventing this is to incorporate some lead in the tin plate. Hence, much of the electroplating of tin, particularly in the electronics area, uses tin/lead alloys. The deposit typically contains 1- 3% lead.

In the last 10 – 15 years great effort has been made to remove lead from all things including tin electroplates. Much effort has been expended in trying to find solutions to this problem. Obviously the whisker problem is particularly critical in today’s world of tightly packed electronic components.

If you want to learn more about the tin whisker problem, go to your computer and type in “tin whiskers” in your search engine. I did just that and came back with many hits.

There are a few suggestions that can help you reduce whisker formation:

• Use tin alloy deposits instead of pure tin. Tin/nickel alloys are one such example.
• Reflow the tin coating after deposition. Reflowed deposits tend not to form whiskers.
• Avoid very thin tin deposits (less than five microns).
• Avoid bright tin deposits if possible.
• Avoid mechanical stress of your parts during assembly operations. Stress seems to increase the chance of whisker growth.