I hate to be cynical here, but with the topic of tin whiskers it comes
naturally.
In my opinion, the JEDEC testing standard has been given far
more credibility than it deserves. There is no known permanent
mitigation of tin whiskers. It is not a matter of IF, but WHEN
tin whiskers grow from a pure tin surface. Using the testing
standard generates a false sense of security.
In my opinion, when it comes to tin whiskers, your level of concern
(and your mitigation efforts) should mirror the consequence of
failure coupled with the expected service life of your assembly.
David Pinsky has created a tin whisker risk algorithm that helps
to put things in perspective. You can download his paper at
https://www.reliabilityanalysislab.com/tl_dp_0403_TinWhiskerRiskMitigation.a
sp
He is presenting an update to this algorithm at the December
IPC/JEDEC Lead Free conference in Boston.
Wishing whisker-free holidays to us all -
Sheri Elliott Harris
-----Original Message-----
From: Genny Gibbard [mailto:[log in to unmask]]
Sent: Wednesday, November 23, 2005 10:56 AM
To: [log in to unmask]
Subject: Re: [LF] Tin Whisker testing on assemblies
That may be so, but there is a Jedec document standard for doing whisker
testing. It was revised and re-released in May of this year. That
document is what the whisker testing is based on.
It uses the most common triggers that they believe cause whiskers.
Temperature cycling and humidity.
Our products are built to Class 2. They need to be reliable - they are
not throwaway electronics (is there such a thing anymore, with WEEE?),
but probably the most stress they'll see from their environment may be
the shipping air travel, and probably some ongoing vibration fan noise
during use. There are also screws and washers or other metalwork
sometimes in contact with the PCB, when mounting a heatsink, or chassis
frame to the assembly.
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Phil Nutting
Sent: 23-Nov-05 9:16 AM
To: [log in to unmask]
Subject: Re: [LF] Tin Whisker testing on assemblies
Genny,
I find this interesting because from my readings both here on the LF
List serve and in the various trade magazines most organizations are
unclear what the exact cause is or how they can best generate
"controlled failures" on command. Tin Whiskers are real, but being able
to generate them at will seems allusive.
Am I off base here?
Phil
-----Original Message-----
From: Leadfree [mailto:[log in to unmask]] On Behalf Of Genny Gibbard
Sent: Wednesday, November 23, 2005 9:57 AM
To: [log in to unmask]
Subject: [LF] Tin Whisker testing on assemblies
The components we've been sourcing all say that they've been thru tin
whisker testing.
Is there any value or reason to doing additional testing at the finished
assembly level that uses those components, as well?
Are lots of companies doing this?
Just for information purposes, I investigated the cost of tin whisker
testing on one assembly, and I was told we should test three samples,
the test would take 18wks +, and cost $14-17K.
They recommended we test components or coupons, instead. Since the
components have already been tested by the manufacturers, the only
reason I can see for doing that is if we didn't trust the manufacturer,
or wanted independent validation.
Are there conditions on an assembly, though, that might not exist at the
component level that make it important to retest?
This is a huge investment. Just trying to figure out whether it is
worth it.
Genny
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