Tin Whiskers found in NASA Study of Toyota Unintended Acceleration Issue


Many people responded to my recent post, In Search of Tin Whisker Fails in Lead-Free Soldering.  A few pointed out that the recent NASA report on the Toyota Unintended Acceleration Issue  discussed numerous tin whiskers that were found, one implicated in a failure.  The tin whiskers were emanating from tin plating.

We don't know, however, if tin whisker mitigation techniques were used. In a mission critical application, such as this, it would appear unwise to use RoHS-compliant electronics, especially since they are not required for automobiles.  In other words, autos are exempt from RoHS.  Let me be very clear, from a tin whisker perspective, I am uncomfortable with RoHS-compliant tin plating in mission critical applications.  Much more work needs to be done before such tin plating should be used in mission critical applications.

In addition, in response to my post, a number of people pointed out the difficulty of proving a tin whisker fail and the reluctance of any manufacturer to admit that their products had them.

But my quest remains unfulfilled; the question remains:

"... who knows of any verified tin whisker fails when tin whisker mitigation techniques where used? Tin whisker mitigation techniques typically use 2% bismuth or antimony in the tin, assure that the tin has a matte finish and use a nickel strike plating between the copper and the tin to minimize copper diffusion into the tin."

Restated, here is my point.  Since RoHS, quite a few people take a position something like this:

With RoHS-compliant assembly, even the world of non-mission critical electronics is at considerable risk of numerous catastrophic failures, due to tin whiskers, that will cost $100s billions.

I still maintain, that with mitigation techniques, such as recommended by iNEMI, tin whisker control, for non-critical electronics, can be manageable.

As I pack up to leave my office today at Thayer Engineering School at Dartmouth, I am across the aisle from the chaps that provide our computers and IT support.  They buy millions of dollars of electronics a year.  In chatting with them they state two things:

1. They have noted no difference in electronics reliability since RoHS implementation

2. On the very rare occasion that they get an electronics failure, it is almost always a hard drive.

Bottom line: Except for hard drives, modern electronics are very reliable for their use life.

I expect my quest will uncover some tin whisker fails, even with mitigation, but the fails will most likely be isolated and not a significant threat to the industry at large.


Dr. Ron

The image is from Dr. Henning Leidecker of NASA, one of the world's leading tin whisker experts.