Andy
It depends.  Are you trying to remove the coating from the entire board
(global stripping) or just trying to remove it from the BGA area only?
Second, have been trying to use urethane conformal coating as an underfill
material, i.e. flooding the underside of the BGA?

The problem with most urethane coating strippers is that in order to be
strong enough to eat the urethane, it is usually aggressive enough to
attack plastic, solder mask, part markings, etc.  If you have a large part
of the space between BGA and board surface filled with coating, then you
have a significant challenge because the coating acts as both sealant and
adhesive.

I have found the material UResolv 411 to work pretty well.  You might try a
technique I find useful here.  Get a piece of square metal tubing, with
about a 1/16" or 1/8" wall, slightly larger than the BGA you want to
rework.  Bond it down to the surface using Dow Corning 3145 (an RTV
silicone), forming a good seal to the surface.  Let it sit for one hour.
This lets the silicone setup but not fully cured.  Fill the reservoir with
the stripping solution and allow it to sit for several hours.  Empty the
stripping agent out, rinse repeatedly with hot DI water, peel off  the
metal shell.  Use a suitable brush to work on any visible material present.
Rinse several times again.  Allow to dry, usually with baking.  Usually the
BGA then comes up with a hot gas rework station.  Repeat the process to get
the remaining urethane coating off.  Works equally well on silicone
coatings.  How well this works depends on how much coating you force under
the BGA.

Doug Pauls




             "Joseph H. Smith"
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             12/13/2005 08:47          [TN] Help with removing UR
             AM                        Conformal  Coating


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Has anyone had experience or success with removing conformal coating for
PWA that has been coated with UR coating especially using a chemical means.
I am particularly interested with how you handled coating around or under
BGA's.

Any help would be grateful.


Thanks.

Andrew Kettlewell
Process Engineer
Sypris Electronics
Tampa, FL
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