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August 2005

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From:
Joyce Koo <[log in to unmask]>
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Date:
Wed, 10 Aug 2005 14:28:47 -0400
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Neil,
Depend upon what kind of oxide on the surface of the HASL board, for Pb/Sn
finishing.  If you form the lead rich oxide, it actually grow thicker and
causes solderability problem after storage.  I agree with you that normally
the tin rich oxide at the HASL surface is very stable (shinning oxide) and
normally do not grow much after its formation.  However, the lead-rich oxide
(dull looking) normally is not that stable... grow relatively fast after the
initiation(I am sure someone in their early life did PhD on it... Not
me...).

my 1.64 cents...
                             jk

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Atkinson, Neil
Sent: Wednesday, August 10, 2005 12:37 PM
To: [log in to unmask]
Subject: Re: [TN] PCB Storage


Any oxidation will take place very quickly and has little effect on the
long term solderability which for HASL boards is dependant on SnPb
thickness and storage temperature. Intermettalic growth rate increases
exponentially with temperature - I love the freezer idea!

Check out this link at the National Physics Laboratory here in the UK.
http://www.npl.co.uk/ei/presentations/storage.pdf

They found some interesting results where plastic bags appeared to have
a detrimental effect on the solderability of various PCB finishes.

Neil

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