Joe,

In a past life we baked out polyimide boards (6 layers if I remember right)
@ 85 C for 4 hours.

Hope this helps,

Mike

~ ~ ~
Mike Di Giacomo
Process Development Engineer
microHelix Inc

-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Macko, Joe @ IEC
Sent: Friday, January 10, 2003 11:20 AM
To: [log in to unmask]
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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