View Single Post
Old 23rd Sep 2005, 9:30 pm   #11
Paul Stenning
Administrator
 
Paul Stenning's Avatar
 
Join Date: Dec 2002
Location: Cardiff
Posts: 9,059
Default Re: Whiskers in germanium transistors etc

I have just replied to their email as below:

Quote:
Dear Jay, Henning and team,

Thank you for your kind offer to analyse a sample to determine what type of whiskers we are experiencing. I have a number of these transistors that have never been used and have identified a few experiencing this problem. Could you please let me have a mailing address to send them to?

Because the whisker growth is internal I would assume the transistors will have to be opened somehow to examine the whiskers and analyse the internal surface of the case. I believe the case is soldered together but do not know whether the heat of desoldering would affect what we are trying to see.

In any event I can send you three or four to examine, and I do not need them to be returned. Therefore if you need to cut them open or otherwise damage them during examination, this is of no concern.

It would be interesting to know whether the growth also occurs in the area where the 'goo' (a type of grease?) is, or whether it is just in the areas containing air. Information from someone who has dismantled a couple of these implies that it is only in the areas of air. However it is likely that removing the grease would also remove the whiskers, so this may well be spurious.

We would also be interested in having an anecdote published on your website, however I think we should wait until after the analysis to see if this is appropriate, and to have more information to include.

Many thanks for your interest, and I hope you are able to gain a little useful information for your own research from this too.

Best regards,
Paul.
I have found four NOS AF114 transistors (from a batch of around 30) which have short circuits of a few tens of ohms between the case and either the collector or emitter, which I will send them. The rest of the batch are currently OK but of course it is only a matter of time.

Quote:
Originally Posted by paulsherwin
I imagine an accident caused by tin whiskers would be very difficult to explain subsequently.
From this page http://nepp.nasa.gov/whisker/failures/index.htm and external pages it links to it is clear that a number of organisations have already had to explain why tin whiskers have caused the loss of satellites, nuclear reactor shutdowns, an emergency recall of a batch of pacemakers and recurring server faults in a data centre. As an example the loss of several Hughes satellites worth around $250 million each was exlained (in the media) along these lines:

Quote:
Although the Solidaridad I failure is still being investigated, an earlier HS 601 processor defect could be the problem. The previous failure resulted from electrical shorts caused by internal tin-plated relay latching switches that act as on/off switches within the Spacecraft Control Processor. Hughes found that under certain conditions, a tiny, crystalline structure, less than the width of a hair, can grow and bridge a relay terminal to its case, causing an electrical short. Hughes is now using nickel-plated switches and improved processes, which appear to have corrected the processor defect on newer satellites. Engineers are currently studying data received from Solidaridad I to determine if the failure occurred in a similar fashion to previously recorded incidents.
__________________

Paul Stenning
Forum Admin/Owner and BVWS Webmaster
Paul Stenning is online now