Tin Whiskers Are Real and Complex

Norm - W7CK

I came across this article being referenced in another forum.  I just thought it was pretty interesting and thought I'd post it here for anyone interested.  I realize it's not exactly Flex related but certainly electronics related.  There were a couple other manufacture's rigs that had failed and folks were suspecting it was possibly due to tin wiskers shorting out one of the circuit boards.

Abstract: "Tin whiskers" is not an imaginative, fanciful term for some
aspect of electronics manufacturing. Tin whiskers are real. They are
microscopic conductive fibers emanating from pure tin surfaces, and they
pose a serious problem to electronics of all types. These whiskers can form electrical paths, which affect the operation of the subject device. This article discusses the problems caused by the removal of lead from electronics and describes some techniques to mitigate tin whiskers.

The full article can be found at https://www.maximintegrated.com/en/app-notes/index.mvp/id/5250

In another article found at http://nepp.nasa.gov/Whisker/background/ they suggest avoiding pure tin plated components if possible.  The military does not allow pure tin in the manufacturing of their electronics and the medical field received an extension to continue to use lead based solder for medical related electronics.

Anyone know if flex avoids pure tin processing?

Norm

David Decoons, wo2x

I remember the VCOs in the Motorola 900 MHz MSF repeaters and the Motorola 800 MHz Mostar mobiles would develop whiskers and the VCO would go out of lock.

Dave wo2x

Tim - W4TME

Most consumer gear does not last long enough in service to have the problem. Vibration, shock, fans, turbulent air flow tend to destroy or prevent whiskers before they create problems.

NASA suspects this was the cause of failures in a few deep space probes.  Ten years or so of zero vibration, and no moving air around the components because they are in the vacuum of space..

The only documented cases of modern electronics failures involve long duration service, 10 or 15 years, of no vibration and no moving air.  Some suspected deep space failures, some documented
failures of oil-field telemetry gear in Australia that were in closed cabinets without fans for over ten years.

Once NASA went looking for it, lots of things were found. Dramatic photos of tin plated variable capacitor spare parts from WW-II that were in warehouse storage for 40 or 50 years are full of whiskers.  But if you turn the capacitors a few times, particularly with some Voltage across it, and it works again.

Yes, NASA is concerned about ultra high reliability in deep space probes and satellites as they should be.

And yes, the military is concerned about putting stuff on the shelf in "The Warehouse" for 30 years and having it still work.

I think our radios, as typically used, hauled out to field day once or twice a year, and moved around some when the XYL dusts the ham shack, with our cooling fans running, particularly if they kick to high every now and then, are not going to see it as a practical problem.

RoHS requires us to use no-lead solder if we are going to sell in any CE country.  We have not seen any problems with our products since we converted to RoHS 10 years ago.  Europe believes the benefits outweigh the risks. Other than the space and military agencies, the rest of the electronics industries, including China are going RoHS.

DrTeeth

An XYL allowed in the shack to clean? Shudder!