[Dehoyos, Ramon]   My previous company sent coupons to be tested for
humidity and the lab sent us a chart. At 135 C the humidity chart was flat
in two hours. At 90 C it took about 6 hours to remove 90 percent of the
board's humidity. We bake the boards for 4 hours at 105 C.  They are good
for three days, unless they are sealed in a bag with a desiccant bag ( do
not need to be vacuumed ) or stored in a dry environment. A room may be
conditioned to have low humidity and a 40 deg temperature where carts with
boards not fully populated can be walked in and stored. ( i.e. one side of a
SMT board was done and due to a reason the second side can not be done right
away).
                Regards,
                Ramon




>  >
> > Fellow Techheads,
> >
> > I am continually being challenged about the amount of time &
> > temperature required to safely remove moisture from
> > multilayered FR4 bare boards so they can be safely populated
> > and reflowed.  And, the time/temperature required to remove
> > moisture from a populated board when a BGA needs to be
> > replaced using a hot air rework station such as an AIR-VAC
> > DRS24.  I realize that baking out boards at an elevated
> > temperature will degrade solderability with time as well as
> > age components so ideally boards should not be baked out any
> > longer than necessary.
> >
> > Everyone seems to have a slightly different idea of the time
> > vs. temperature required which generally ranges from 4 to 24
> > hours at temperatures as low as
> > 85 to 125 C.    85C definitely seems to low to me.  IPC/JDEC
> > J-STD-033A list
> > bakeout times for components depending on thickness which
> > seems excessive
> > for a circuit board.   I have not found any IPC guidelines for circuit
> > boards.
> >
> > Anyone like to comment on what has worked for them?   Is
> > there an industry
> > standard out there?   thanks in advanced for the feedback.
> >
> > joe
> >
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