Hi Brad,
For assembly purposes 105C for 24 hours is more than adequate to drive moisture out.
Polymeres do not like to sit at high T's like this—remember they consist of highly cross-linked molecules. This cross-linking brakes down with time and temperature, some of it mostly reversible like glass-transition, however, mechanical, thermal, dielectric properties will all change. This may not be significant for most applications but for other (high speed) it may well be.
You do not know what polymeres are inside any of these components—some may have quite low Tg's, some may only be partially cured and continue curing, there certainly will be differential thermal expansion which could cause stresses high enough for plastic deformation/cracking.
So, on a whole, this is not a good idea, and on top of which, totally unnecessary.
Werner
-----Original Message-----
From: Brad Saunders <[log in to unmask]>
To: Werner Engelmaier <[log in to unmask]>
Sent: Thu, Aug 5, 2010 9:48 pm
Subject: Re: [TN] Baking CCA's for hours
Get that moisture out of components, including bare board, during the assembly process. Underlying question is what effects can industrial rated components have in this process (industrial temp rating at 105 degree C), verses good ole 150 degree C parts (those rare birds).
Thanks for a great question.
----- Original Message -----
From: Werner Engelmaier
To: [log in to unmask] ; [log in to unmask]
Sent: Thursday, August 05, 2010 8:54 PM
Subject: Re: [TN] Baking CCA's for hours
Hi Brad,
WHY???
Werner
-----Original Message-----
From: Brad Saunders <[log in to unmask]>
To: [log in to unmask]
Sent: Thu, Aug 5, 2010 7:07 pm
Subject: [TN] Baking CCA's for hours
Howdy folks,
I have an application where Circuit Card Assemblies are baked at 125 degree
Celsius for 48 continuous hours (2 days), this is repeated a few times. No vibe
or operating, etc just on a shelf, any thoughts?
Thanks Brad
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