Hi Ian - boy, that's a million dollar (or maybe a billion pound) question
that many of the JSTD-003 committee would love to have a definitive answer
on! The information/opinion that seems most agreed to within the JSTD-003
committee is that a printed wiring board that is keep in a 75 +/- 10F,
30-60% RH that has been produced in a well controlled, HASL process should
be solderable after 12 months of storage. The "well controlled HASL"
process refers to a consistent solder coating thickness across all features
of the printed circuit board. However, humid  conditions and/or elevated
temperature conditions have a definite impact on the printed wiring boards.
The level of impact will depend heavily on the process conditions (flux
type, process parameters, etc.) that the printed wiring board assembler
uses. The TechNet suggestion of bagging/sealing boards has been shown to
extend storage durations in some cases.  The JSTD-003 committee is
attempting to better address this issue with the use of "durability"
ratings - anyone with information on the subject should forward it to the
committee to help them in their efforts.


Dave Hillman
JSTD-003 committee chair
[log in to unmask]





[log in to unmask] on 04/21/98 12:10:00 PM

Please respond to [log in to unmask]; Please respond to
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To:   [log in to unmask]
cc:    (bcc: David D Hillman/CedarRapids/Collins/Rockwell)
Subject:  [TN] Storage conditions of pcb




Good Day!
Could anyone advise me on the specification to adopt ( temperature and
relative humidity ) for the optimium storage conditions for bare printed
circuit boards.
These boards are typically overmakes which we store until our Customers
can place their next order.
What length of time do you think the solderability of solder levelled
boards would remain excellent in these conditions.
Best regards
Ian Parker
Prestwick Circuits
Scotland
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