I thought most people applied heat when vacuum drying - the greater the vacuum, the
lower the boiling piont of the water. Thus the water in the pores become highly
agitated and evaporates at a lower temperature, and with no oxidation of the
leads/pads, and slower intermetallic formation. The pores gradually become
evacuated, then the vacuum cabinet can be backfilled with dry nitrogen gas, filling
the pores with dry gas rather than moist air.

Hope that made sense. It can be overdoing it a bit though, depending on what level
of technology you are working on. Besides, someone was telling me the other day
that within the first two hours of being open to the environment, the board will
probably have more than half its old level of moisture back again. If you take a
batch out of bake in the early morning, and don't flow / reflow the last of them
until afternoon, moisture based problems may still occur. Therefore improved
moisture extraction should be coupled with improved procedures.

Hope this helps,

Regards,

Richard Tilbrook

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