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Tin whisker observation on PS3 BRIR diode

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LAN_403

Conundrum

Sat May 08 2010, 12:06AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi all.
Was doing some experiments with "failed" PS3 KES400A blocks and noticed a strange effect.
On at least one, both blue and red diodes had failed which is unusual.
Measured pins between red and blue diodes, and noticed a 22 ohm "short" (?!?!)
so at this point figuring the diode was toast, applied 1.5V coin cell between red and blue anodes (i'd first installed 47K and 1K resistors to guard against ESD)
Lo and behold short go byebye.

Tested both diodes, not only do they work fine but if anything seem better than most i have tried.
Red 100%, blue threshold within specs. at 28mA.

has anyone else ever seen this effect? i am not sure but the short could have been inside the can itself as i'd noticed it before removing the drive chip or applying resistors.
unlikely to be external due to the distance between pins.

EDIT:- If I find another one with a clear short, I'll put it under a microscope and "blow out" said short while videoing the results to show its presence clearly.

regards, -A

#include "laser_experts_spitting_feathers.h"

GeordieBoy

Sat May 08 2010, 08:33AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

I had an optical wheel mouse fail due to tin whisker formation. The scroll-wheel stopped working shortly after I bought it, and it used to sporadically scroll up or down sometimes when I was reading a document or browsing the web.

One day I opened up the mouse and took a look inside. There was a dual-photodiode thing that looked through the spokes of the plastic scroll wheel. Both diodes measured s/c with a multimeter and on closer inspection with a microscope I could clearly see little metal whiskers sprouting from scratches on the lead-frame and bridging the leads.

Whisker formation really is a strange thing, but something I predict we might see a lot more of with the banning of lead from solder!

-Richie,

IntraWinding

Sat May 08 2010, 09:06AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

I read somewhere that lead was originally added to the solder formulae to prevent tin whiskers. I guess they need to find something else to add.

Conundrum

Sat May 08 2010, 09:18AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

well it could explain the 2012 thing..

i heard a rumour that the recent well blowout could have been caused by a tin whisker in the control circuitry, causing an overpressure and subsequent explosion.

<ducking into flame-proof bunker>

Bjørn

Sat May 08 2010, 11:29AM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

A thin layer of plastic coating is enough make sure the whiskers do no harm. There is no doubt countless other things that can be done.

Proud Mary

Sat May 08 2010, 02:26PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

There was a forum thread about these whiskers a few years ago

Weird phenomenon called metal whiskers

Conundrum

Sat May 08 2010, 09:09PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

BjÃ¸rn wrote ...

A thin layer of plastic coating is enough make sure the whiskers do no harm. There is no doubt countless other things that can be done.

Plastic coatings can help but eventually the whiskers will grow through them.
Short of complete encapsulation that is.

in fact the sulphur content of some solder fluxes can encourage whisker growth...

Bjørn

Sat May 08 2010, 09:43PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Have a look here, conformal coatings can stop whiskers on worst case materials, so on normal materials it will be completely efficient:

radiotech

Mon May 10 2010, 06:56AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

There was a paper done by Bell Laboratories on metalurgy of whisker growth problems in the days prior to ess when their latest switching was #5 crossbar needing thousands of relay contacts to make to complte a phone call. In the days of radio servicing we used a noise tester amplifier input that used about 100 volts to find these damned problems.

Steve Conner

Mon May 10 2010, 09:02AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Metal whiskers aren't a lead-free thing. You see hobbyists who are into vintage radio restoration complain that the old germanium transistors fail because of whiskers growing inside the can and eventually shorting something.

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