Shelf-life time periods are typically reference or guidelines...not set in
stone. I told this story some time back about finding some boards in an
empty desk drawer that were over 6 years old...just for grins I soldered one
and it flowed well. These were boards that had an initial good coating of
solder and were stored in a good environment (some would question the empty
drawer as a good environment; however, the office where this desk was at was
controlled to a certain extent). On HASL we recommend no longer than 1 year
before being "reevaluated" for solderability.

Some may say thinner coatings will degrade over time...I say that would have
to be an extremely thin layer of solder to degrade, or 'fuse' with the
copper and that it would most likely cause solder issues at any time,
anyway, not just 6 months to a year or more later.

If the boards have a good coating (aside from tarnish or surface
contaminates) I would simply recoat (if they can be sent back through the
HASL process) them with solder, or even reflow them. Whatever method though
do a solderability test to ensure good flow.

There's magic in IPC??? Where did I miss that?

Franklin

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