I have been in email correspondence with a collector (Chris Walter) about the whiskers that develop in AF117 etc transistors. He initially contacted me offering a couple of photos showing these in an OC170 transistor he had opened up. His photos are attached and the main text of his accompanying email is here
Quote:
Attached I send you two pictures from an OC170, which I found inside a Philips L3X09T from 1960.
It is very hard to take these pictures, since only a few of the many whiskers (I guess there are about 100 visible with naked eye) reflect the light at any given moment. The whole inside is covered with these whiskers whose lenghts (~2 mm long) and direction (around 90 degree to surface) do not vary very much. In sunshine and in artificial light I observed rainbow colouring of the hairs, which means their diameter must be in the order of the wavelength of visible light, that is 0.4 to 0.7 micrometer, which is about 1/200 th of a human hair. If I find time I will do some more observations, for example if the whiskers also grow into the grease.
No, I did not reassemble the transistor, since I broke two of the legs when opening it (I had to sacrifice another nice radio, to get an AF125 for replacement). But there is another reason: The transistor was intermittendly working before unsoldering it. I then applied the charged capacitor trick, not with 50 microF at 50 Volt, but with 200 microF and 15 Volt. I tied the three active legs together before. It turned out I had killed the base-emitter diode by doing the trick, this is when I decided to open it.
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A while later he sent me a further email containing this website link
http://nepp.nasa.gov/whisker/index.html. We are assuming that the transistor cases are made of tin or are tin plated internally.
Reading this website, in particular the Basic Info/FAQ section, shows that "tin whiskers" are a MUCH bigger problem than the irritating failure of transistors in a few old radios. It has caused an emergency recall of a batch of pacemakers, failure of sattelite control systems etc. It seems that the move to lead-free soldering etc could cause further problems as more tin is used in electronic assemblies.