Tin whiskers in transistors other than the AF11x series.

[ukcol]

Originally Posted by mhennessy

That's an excellent couple of pictures, Colin - definitely whiskers there.

Thanks Mike; yes I am now belated convinced that the tin whisker problem is not confined to the AF11x series.

Originally Posted by Leon Crampin

It's entirely possible that due to the much lower circuit resistances in output stages, the available current levels in the c-e branch are such as to burn open any formative whiskers. This would explain why failures of AC128 and similar devices are seldom seen (or apparent).

This sounds entirely plausible Leon and would indeed explain the relatively low numbers of transistors in this group reported suffering from tin whiskers.

Any whisker forming would be likely to be zapped by the relatively high current available from the external circuit. This would also explain why the base to chassis path in my transistor did not clear, there being a relatively low current available from the base bias circuit.

[ukcol]

Those of you who may want to open one of these transistors and don't have access to a lathe may like to try the method that worked for me.

I used a variable speed drill and a Stanley knife. I put the transistor in the chuck about a quarter way up the case with the leads going in first. The drill was set to the first gear and the speed limit wheel on the trigger set to the lowest speed. The Stanley knife blade was pressed against the transistor case about a third of the way up the case. It takes a fair time to cut through but you will get there as the metal of the case is relatively soft.

[sentinel040]

I have seen "tin whiskers" growing from the outside of ACxxx devices, I currently have a Pye Bantam which shows this phenomenon.

Regards

Ian

[ms660]

If the whiskers are pure metallic tin you should be able to bend them a bit.

I've seen whiskers on cadmium plated stuff, never checked to see if they were metallic though.

Lawrence.

[Goldieoldie]

Hi All
Thought you might like this pic of these whiskers
They are from a Hacker Mayflower 11 tuner slug
Cheers Pete

[G6Tanuki]

Re. post #44: there is a photo somewhere on the NASA website showing 'whiskers' grown on the inside of a UHF tuned-cavity filter from a receiver, where there had only ever been RF and no DC.

I can't remember what they said the plating was.

[NASA-ish Sidethought: if whiskers were to grow on a component in zero-gravity, what form would they take?]

[ukcol]

Originally Posted by ukcol

Thanks Mike.....................

I've just spotted this error, sorry Mark.