Old Ge transistors and Whiskers

Hi,

Anyone know if NOS (old, but never used) germanium transistors are prone to forming whiskers to the same extent as used ones? I'm not sure if it's a phenomenon which arises from the electrical potential applied during the service life of the device or not. Anyone know?

Chris.

Reply to
Chris M. White
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I don't know for sure, but I've never heard that metallic whiskers were grown by electrical potential. I believe it is just a metallurgical matter.

Reply to
Rick C

I aagree. Some old GE comercial radios would do that in the tuned cavities and there is no power in them.

Reply to
Ralph Mowery

**See:

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** Seems it's related to age, not usage.

...... Phil

Reply to
Phil Allison

My understanding is these whiskers are very fragile requiring only a tiny current to remove them. It is mentioned on one of the NASA pages how measuring the short with a standard ohm meter is enough to clear the short. It seems the short would be cleared by the currents flowing in most circuits the devices would be used in. No?

Reply to
Rick C

No. Murphy's law and all that. Often the circuit dows not supply enough current to clear the short, and in other cases, a lot of current is available and the whisker starts an arc that vapourises big important parts of the equipment.

I've seen quite a few whiskers, but so far always on very old (pre-1970) equipment. I've not yet seen any on RoHS compliant stuff. I wonder if it is just that the whiskers grow slowly, or if they used worse kinds of plating a long time ago.

Reply to
Chris Jones

I didn't know tin whiskers had impacted the nuclear power industry. Seems, as is not uncommon, they didn't think events that affect other industries would impact them. The effect of tin whiskers was first documented in 1951 and satellites were lost due to tin whiskers as early as 1998. Medical implants were recalled in 1984 for tin whisker defects. Methods of mitigating tin whiskers were developed in 1974. Yet, it was allowed to impact the nuclear power industry directly right up to 2005. Right up until they had a reactor scram at Millstone, CT the nuclear industry believed they were immune from the effect or more accurately kept their head in the sand while other industries were hit by the issue.

No wonder the nuclear industry is not much trusted.

Reply to
Rick C

Mostly they used tin-lead solder in the good old days which is not subject to tin whiskers. RoHS compliant, lead free solder is exactly the material that grows tin whiskers. Seems pure tin coatings have also been used though. The can around a pacemaker was the cause of a recall when the can maker messed up and shipped a batch that was tin plated. The company using the cans did not test the coating.

What parts of pre-1970 equipment developed tin whiskers? Was it non-electrical components?

Reply to
Rick C

Certain products were more affected than others. IIRC the AF117 found in large numbers of early transistor radios was particularly prone to growing whiskers. A typical remedy involves tying EBC together and then zapping a HV cap between them and the screen. Use enough voltage and you can pretty much vaporise the whiskers. They will grow back again in time, but this method usually 'fixes' the problem for several years. --

"In one word, you reproach us with intending to do away with your property. Precisely so; that is just what we intend."

- The Communist Manifesto, Marx & Engels.

Reply to
Cursitor Doom

I've seen them on post year 2000 equipment that wasn't RoHS. They're real odd and far too small to play with. Even true needle point meter probes are too big.

Reply to
Cydrome Leader

Some if it was the tin or tin plated shielding between parts. The GE MASTR transceivers did that in the antenna circuits before they went to a different material.

Reply to
Ralph Mowery

I got my hands on a number of NOS ~60 y/o germanium transistors a number of years back from a a ham's estate, they were all junk with shorts between various leads.

Reply to
bitrex

It happens in formed steel parts (maybe even Invar as used in frit-seal DIP packages) when the steel gets a tin-plate finish. Food-grade tin plate, presumably, was the rule back half a century ago, and tin is notorious for having unstable crystal structure (look for 'tin pest' on YouTube). Tin/lead and tin/silver/copper are relatively whisker-free, but it's only tin/lead that has a long field trial history,

Early steel deep-drawn transistor cans are a prime tin whisker demo site.

Reply to
whit3rd

I've had transistor cans from the 1960s, and a relay from a WWII radio that had lots of whiskers on its housing, and I think some other parts that I have forgotten. All electronic components, but usually parts of the component that don't have any electronic function.

Reply to
Chris Jones

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