Joe,

I don't know of any IPC specs for baking out boards. All boards differ from
one another in terms of size, thickness and composition, so it's difficult
to specify in general terms. I have always used 1 hour at 90 degrees C for
FR4 boards that are about 10 or 12 layers - up to 2 hours for thicker
boards with more layers and as short as 1/2 an hour for thin boards.

You maybe need to do a little testing on times and temps versus weight loss
if you want to be precise for your own boards, but our standard bake-out
times have worked for us.

Peter



"Macko, Joe @ IEC" <Joe.Macko 11/01/2003 03:19 AM
Sent by: TechNet <[log in to unmask]>

Please respond to "TechNet E-Mail Forum."; Please respond to "Macko, Joe @
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              cc:  (bcc: DUNCAN Peter/Asst Prin Engr/ST Aero/ST Group)
              Subject: [TN] board bakeout recommendations








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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