Whiskers - have you seen them? - Page 1
Forum section: electronics / general

author: jahonen
author_rank: Super Contributor
timestamp: July 03, 2010, 02:33:01 pm
content: This might me pretty old stuff for someone but I think it is anyway quite interesting phenomenon worth of mentioning of very pure metals, like tin or zinc. When I first read about whiskers, I out of interest grabbed some random D-connectors for closer inspection under the microscope at work, and there it was - very thin filaments of tin sticking out from the tin plating. Not one, but several ones. No question about it.NASAhas quite nice site about this, with large collection of pictures.Problematic aspect about this is that whiskers make short circuits when the whisker grows long enough. This growth may take some time, like years. Although thin, they can still withstand enough current to cause problems (see the relays destroyed by whisker initiated arc flash!). NASA site says that even nuclear reactor was shut down due to whisker short circuit, kinda scary. I believe RoHS has make situation worse since lead was banned. Lead essentially prevents the whisker growth.Regards,Janne

author: saturation
author_rank: Super Contributor
timestamp: July 03, 2010, 03:06:43 pm
content: Yes, have heard of it but have not seen it. Makes for an interesting justification for prophylactically replacing a device in service after some years to avoid failure during service.http://en.wikipedia.org/wiki/Whisker_%28metallurgy%29

author: Zero999
author_rank: Super Contributor
timestamp: July 03, 2010, 03:54:12 pm
content: Applications such as military, aerospace, nuclear and some medical devices are exempt from RoHS so it's not a problem in safety critical applications.

author: tecman
author_rank: Frequent Contributor
timestamp: July 03, 2010, 04:01:08 pm
content: Recently had a board with whisker shorts. Very fine, had to be seen under a scope.Went to the PCB manufacturer for test and eval.Paul

author: djsb
author_rank: Super Contributor
timestamp: July 03, 2010, 04:02:06 pm
content: I was hoping to repair an old FM stereo generator at work that had been stored away since the 1960's. Had to abandon the idea after I found out it used germanium transistors and that internal whiskers where a common form of fault on such old equipment. Lost interest after that.David.

author: jahonen
author_rank: Super Contributor
timestamp: July 03, 2010, 05:31:31 pm
content: Quote from: Hero999 on July 03, 2010, 03:54:12 pmI think that there are plenty of safety critical industrial stuff which must comply to the RoHS. And if you looked the NASA site, there are a numerous whisker-related failures in satellites and nuclear power plants, and those were even before the whole RoHS was even invented.Another problem is that there might not even be whisker-free plated version of a component available, which makes it even more difficult even if you don't need to care about RoHS.Regards,Janne

author: saturation
author_rank: Super Contributor
timestamp: July 03, 2010, 05:34:57 pm
content: Are whiskers relatively easy to remove? Are they fine enough to be brushed off?

author: NiHaoMike
author_rank: Super Contributor
timestamp: July 03, 2010, 08:18:58 pm
content: The bad part about RoHS, apart from forcing lead-free too early, is failing to regulate what really matters. For example, they should phase out NiCd batteries in favor of superior NiMH batteries. And at some point in the future, phase out small lead acid batteries in favor of LiFePO4 batteries.Then again, engineers don't understand politicians and politicians don't understand engineers.

author: tecman
author_rank: Frequent Contributor
timestamp: July 04, 2010, 06:07:44 pm
content: Quote from: saturation on July 03, 2010, 05:34:57 pmWhiskers are actually dendrites. They are generally attached on one end, but a firm brushing will remove them.If they have started to form, brushing will only delay the return.paul

author: jahonen
author_rank: Super Contributor
timestamp: July 04, 2010, 06:20:34 pm
content: Quote from: tecman on July 04, 2010, 06:07:44 pmThey are not dendrites. Whiskers grow from the base, whereas dendrites grow from end.And yes, you can brush them off. They are very fine and can be easily removed mechanically. I think that there must have been dozen failures of TV-tuner boxes when tin-plated casings have developed whiskers inside and those naturally short out internal components. Fault was mysteriously fixed by opening the tuner box, which caused the whiskers to detach. Actual fault remained a mystery for service technician. I'm currently on vacation but when I get back to work, I'll try to take some whisker photos of the D-connectors I mentioned.A quote fromNASA Whisker site FAQ:QuoteRegards,Janne