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November 2007

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Subject:
From:
Ian Hanna <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Ian Hanna <[log in to unmask]>
Date:
Wed, 14 Nov 2007 12:25:22 -0500
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For driving out moisture, is there something magical about the boiling point?  Ian

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stadem, Richard D.
Sent: Wednesday, November 14, 2007 8:25 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coating Breakdown

Ben,
You do not need to bake at 125C. You simply need to get the board above 100C, perhaps for a little longer time.
I have yet to see an assembly that did not lose 80% of its saturated moisture content when baked at 105C for 12 hours. If you get below 20% moisture content, you should not have any trouble. 

-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Gumpert, Ben
Sent: Wednesday, November 14, 2007 6:01 AM
To: [log in to unmask]
Subject: [TN] Conformal Coating Breakdown

Anyone have some information on what happens to conformal coatings as you heat them up, what temperature do they start to deteriorate? (Specifically acrylics and urethanes)

What I'm really getting at is that I have some boards that need hot air rework, but they have been coated. There are moisture sensitive components on the board, so I would like to bake the boards prior to rework. I would prefer to make the bake as short as possible, but that puts the temperature (125°C) at the top of the temperature range for these coating materials. (In fact, some boards that I have baked have gotten a brown tint to the coating).

Will I do any damage to the conformal coating by baking at this temperature? If not, what temperature would cause damage?

Thanks,
Ben Gumpert

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