In article <92d95e01-02d7-41cb-b8fe-cc6251132d3bn@googlegroups.com>, gnuarm.deletethisbit@gmail.com says...> > What parts of pre-1970 equipment developed tin whiskers? Was it non-electrical components? > > >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.
Old Ge transistors and Whiskers
Started by ●November 28, 2021
Reply by ●November 29, 20212021-11-29
Reply by ●November 29, 20212021-11-29
On 11/29/2021 7:47 AM, Chris Jones wrote:> On 29/11/2021 22:42, Rick C wrote: >> On Monday, November 29, 2021 at 1:16:24 AM UTC-4, palli...@gmail.com >> wrote: >>> On Monday, November 29, 2021 at 12:35:21 PM UTC+11, Chris M. White >>> wrote: >>>> 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? >>>> >>> **See: >>> >>> https://nepp.nasa.gov/whisker/anecdote/af114-transistor/index.html >>> >>> ** Seems it's related to age, not usage. >> >> 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? >> > > 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. >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 by ●November 29, 20212021-11-29
On Monday, November 29, 2021 at 4:56:33 AM UTC-8, gnuarm.del...@gmail.com wrote:> On Monday, November 29, 2021 at 8:47:25 AM UTC-4, Chris Jones wrote:> > 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. > 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?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 by ●November 30, 20212021-11-30
On 29/11/2021 23:56, Rick C wrote:> On Monday, November 29, 2021 at 8:47:25 AM UTC-4, Chris Jones wrote: >> On 29/11/2021 22:42, Rick C wrote: >>> On Monday, November 29, 2021 at 1:16:24 AM UTC-4, palli...@gmail.com wrote: >>>> On Monday, November 29, 2021 at 12:35:21 PM UTC+11, Chris M. White wrote: >>>>> 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? >>>>> >>>> **See: >>>> >>>> https://nepp.nasa.gov/whisker/anecdote/af114-transistor/index.html >>>> >>>> ** Seems it's related to age, not usage. >>> >>> 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? >>> >> 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. > > 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? >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.
