Thanks for the report which provides some 'do not worry' information.
That said only the DPAK was a matte tin finish and therefore the
possibility of matte tin being a potential seed might need more
exploration (e.g. differing lead frame materials, differing lead form,
PIH, etc)
Also is it possible that the experimental method provided its own
mitigation process ( +40C for the thermal cycle and the once per week at
RT for observation) as commented upon in the report.
It would seem that if I have a customer who has a product that lives in
an environment equal to that used in the report then the customer is
probably OK for 33 months (plus elapsed time since the report was
written.)
I don't want to seem flippant but we, as an industry, do not seem to
have a good understanding of this phenomenon and what the mitigating and
accelerating processes are.
Given that it is a catastrophic fail once the allotrope has formed it
seems difficult to advise a customer who wants a 120 month life in a
cold environment as to what to do. 
Perhaps starting his life testing now would be a good
idea........................................

 


Rex


-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: 22 December 2008 15:21
To: [log in to unmask]
Subject: Re: [TN] Tin Pest

Hi Rex! Ah, it is good to be a material engineering these days as we
don't need to learn anything new, we just dig up old data sets! There
have been some good published work on tin pest in the last couple of
years. In fact, Dr. Chris Hunt of the NPL has done some of the newest
cutting edge work. I recommend you go to the NPL's website and download
his reports on tin pest. Rockwell Collins also has published some
investigation results which I'll send to you. The current industry
"thoughts" on tin pest is that leadfree electronics are at low risk of
the phenomena causing issues. 

Dave Hillman
Rockwell Collins
[log in to unmask]




Rex Waygood <[log in to unmask]> Sent by: TechNet
<[log in to unmask]>
12/22/2008 09:14 AM
Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to Rex Waygood
<[log in to unmask]>


To
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cc

Subject
[TN] Tin Pest






Can someone tell me why I should not worry?
I am told that tin pest has not occurred in electronic circuits where
lead free (high tin) alloys have been used for years.
I have seen the NPL video where tin pest propagates rapidly from a
seeded tin bar into lead free alloys that were anticipated to be immune.
When I buy components now it is likely they have a matt tin plating.
(Probably not the case historically)
Is that plating likely to be a seed for a lead free solder joint? 
I have customers where the end product goes to some very cold places,
they are not RoHS exempt, so what do I advise them? 


Rex Waygood
Technical Manager
 
PartnerTech Poole Ltd 
Benson Road
Poole
Dorset BH17 0RY
United Kingdom
 
Tel: +44 (0)1202 674333
Fax: +44 (0)1202 678028
DDI: +44 (0)1202 338222
Mob: +44 (0)7887 997403
 
[log in to unmask]
www.PartnerTech.co.uk

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