Not quite true.
Any bake will drive out some moisture, but the combination of time and
temperature and the surrounding relative humidity is what determines the
amount of removal.
But you also need to know that baking is going to have some negative
impact on the solderability. You also need to know what effect it may
have on the components, if they are present. Many components are not
able to withstand a sustained bake process.
Baking can also affect the flex performance, depending on what type it
is. Not all flex is polyimide, and baking will negatively affect both
PEN and polyester.

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Steve Kelly
Sent: Tuesday, April 29, 2008 1:53 PM
To: [log in to unmask]
Subject: Re: [TN] Baking Flex boards

Hi Bill,
Most flex materials will withstand 125C continuous so you should have no
issues. What is the point of this? If it is to drive out moisture before
assembly all you are doing is warming the water. Regards Steve Kelly

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bill Dworak
Sent: April-29-08 2:46 PM
To: [log in to unmask]
Subject: [TN] Baking Flex boards

I would appreciate some input on a subject that I was just hit with
today. I am being asked if my customer baked flex boards for 10 hours at
150F would there be any chance of long term reliability issue? The board
is what I would call standard issue stack up for a flex board nothing
wild polyimide material with a  FR4 Stiffener 4 layers, no fine traces
.004/.004. HAL
(leaded) surface finish.
 I had an issue several months ago with some rigid boards that where
being baked for long periods of time but that was on the assembly side
of issues not durability. 
Any particular issues that might come from the baking?  Any input is
welcome. 


           Bill Dworak

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