Ben,
The short answer is yes!
The longer version is that there are numerous issues when you exceed
the Tg of the coating material for extended periods.
Among them;
1. contamination penetrating the coating
2. carbonizing/changes to the chemical/electrical properties (turning
brown)
3. de-lamination weakening of the surface bonding
4. evaporation/flowing of the coating material (to thick/thin or
going where it is not wanted)
In short you have exceeded the design limitations of the coating
material and may be forced to "re-qualify" the product after this
procedure.
David A. Douthit
Manager
LoCan LLC
--------------------------------
On Nov 19, 2007, at 3:52 AM, Gumpert, Ben wrote:
> Yes, that is the process I would use as well.
> I have a BGA on a 63/37 HASL Polyimide board.
> But I am not concerned about the board and what moisture it has
> absorbed, the BGA is my main concern (MSD Level 4). It is expensive
> enough that I don't want to throw it away, so I feel the need to
> bake it
> prior to rework.
>
> But when I bake the board, the conformal coating turns brown - is
> this a
> problem?
>
> Ben
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Rodney Miller
> Sent: Thursday, November 15, 2007 4:00 PM
> To: [log in to unmask]
> Subject: [TN] Conformal coating Rework
>
> Per Ben Gumperts email.
>
>
>
> I'm not sure the logic on baking a Conformal coated PCB? If the
> coating
> is working or you have residually absorbed moisture, you are
> creating a
> problem by baking a CC'ed PCBA in my opinion. The barrier of
> conformal
> coating Ureathane or otherwise should be easy to remove and locally
> repair with localized Reflow system. If you are totally reflowing the
> PCBA, that is even larger problem on rework.
>
>
>
> I would remove the part, with hot air.
>
>
>
> Remove Conformal coating with appropriate solvent from the area of
> repair.
>
>
>
> Rework/re-solder components
>
>
>
> Reapply Components with localized Reflow and/or HotAir system.
>
>
>
> There will be some aesthetic issues, but with proper solvents and
> cleaning, you should not have issue with moisture in the PCBA more
> than
> any other issue.
>
>
>
> Is this RoHS or 63/37 solder?
>
>
>
> How long have they been in Ambient conditions?
>
>
>
> What is the laminate?
>
>
>
> What is the plating?
>
>
>
> What technology is the components that are to be reworked?
>
>
>
> Just my couple of CNY..
>
>
>
> Rodney
>
>
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