Failure of Electronic systems because of Tin Whiskers

[SuperFreak]

With the introduction of ROHS to control the use of hazardous materials in electronic equipment it was decided that lead-tin solder would be replaced with tin solder (2006). Lead in solder for electronics represents about 1% or less of man made lead in the environment; the primary source of lead is in batteries which if I am not mistaken is not regulated by ROHs. This sounds great on face value but there is a problem with Tin solder; it forms microscopic "whiskers" that can short out electronic systems. This has led to failure in Satellites and at least one nuclear power plant. In fact it is most likely that the computer you are reading this post on (as is mine) is built with lead free solder.

see http://www.tinwhisker.us/

http://nepp.nasa.gov/whisker/photos/index.html

I haveonly glanced at this as it is a bit too technical for me
http://www.electroiq.com/articles/ap/print/volume-13/issue-1/features/global-trends-in-lead-free-soldering.html

it should be noted that while lead in solder may not pose much harm to the environment it can do to the person doing the soldering
http://www.sentryair.com/solder%20fume.htm

[Paqman]

Sure, one of a million failure modes for an electronic circuit. It's a manageable engineering issue.

Switching back to lead-based solders isn't going to happen. Lead-free solders are still developing, metallurgy is far from a perfect science and there are new alloys being developed all the time.

You're right about car batteries being the main source of scrap lead, but they're now restricted by the WEEE legislation (in Europe at least). You can't just dump any kind of battery into landfill these days.

[SuperFreak]

I am not trying to spread FUD only remarking on an issue that may become quite serious as electronic components age. This may be a nuisance in consumer goods but in Infrastructure and Industry may pose serious problems. I think lead is allowed to be used in medical and aeronautic/space applications now

[Old_Grey_Wolf]

I don't know what you are trying to say with this post.

Tin Whiskers have been know about for 5 or 6 years. Most manufacturers have learned to deal with it.

By the way, satellites don't tend to use lead based solder. Satellite components are often spot welded, braised, or use silver soldering. For example, search this site for "silver" (http://en.wikipedia.org/wiki/Solder). These techniques allow them to withstand higher temperature variations and vibration.

[SuperFreak]

True as I posted before Space (nor medical)applications do not use tin only based solder anymore after the failure of of numerous satellites where tin only solder was used (http://nepp.nasa.gov/whisker/failures/
However from what I have read there is so far no reliable way to prevent tin whiskers and other metals including gold and silver have similar problems. The regulation by ROHs to eliminate lead-tin solder was premature.
Also if I am not mistaken tin whiskers have been known for over 50 years and that is why lead was used in solder for several decades with few if any problems with tin whiskers

[Old_Grey_Wolf]

Can you point me to data about Tin Whiskers that is not older than 5 or 6 years?

Thank you.

[SuperFreak]

]http://nepp.nasa.gov/whisker/background/

This link does not show the reason science was interested in the phenomenon of tin whiskers in the 1940s (see first paragraph of article) but I believe that early faults in the telephone systems where tin only solder was used was the initial electronic sytem where it occurred and the system failure occurred.

see also this thread http://www.sigcon.com/Pubs/news/10_01.htm which goes into some of the reasons lead free solder is not really environmentally sound practice


Fortunately, military products get a special exemption from RoHS. They can use as much lead as they want. The exemption was granted on the basis that the E.U. commission understands quite clearly that no suitably reliable substitute for lead-based solders has yet been found.

and also

Already happened? Yes. 17 April, 2005 — Millstone Nuclear Generating Station — A single tin whisker created a bridge (short circuit) between a diode and the output trace on a circuit card, causing a partial reactor shutdown. P. Daddona, "Reactor Shutdown: Dominion Learns Big Lesson from a Tiny Tin Whisker", The Day (New London, CT), July 4, 2005

[Paqman]

True as I posted before Space (nor medical)applications do not use tin only based solder anymore

I'd be surprised if they ever did. Lead-free solders aren't pure tin, they're alloys.

The only solder I ever used soldering aircraft components was standard lead-tin or silver solder.

[SuperFreak]

My mistake I have put tin only solder in my posts where I should have put lead free
Silver solder is also known to produce whiskers

[juancarlospaco]

Programmed obsolescence

[mips]

Not a big fan of lead free solder, with age things fail especially where heat is involved. One example being GPUs

[Paqman]

Not a big fan of lead free solder, with age things fail especially where heat is involved. One example being GPUs

That's a problem even with lead solder. The mechanical qualities of the joint make more of a difference to reliability than the metals involved (although that is obviously a factor).

That's why high reliability soldering techniques were developed by NASA and the US military, they were getting a lot of failures in the early days.

[SuperFreak]

Tin whisker growth is not a new problem. The Bell System has documented the growth of tin, cadmium, and zinc whiskers and subsequent short circuit failures, on electroplated hardware in telephone switching equipment as early as 1946 (1). After extensive study, Bell Laboratories recommended alloying the tin with lead, and the result has been essentially whisker free electronic assemblies, using tin-lead alloy plating on component leads and circuit boards and using tin-lead solder attachment in assembly, for the last 60 years.

Because of the recent global environmental emphasis in eliminating lead (Pb) from electronics, a firm metallurgical understanding of tin (Sn) whisker growth and methodologies to predict or mitigate growth are needed. Such mitigation techniques are not conclusively known, making the situation of electrical failure risk due to tin whiskers, particularly in high reliability systems unacceptable.

http://www.aciusa.org/leadfree/leadfree_verdi-11-5-04.htm