Chris,

As you say that you are awaiting new Dip coating equipment, I thought I
should offer this belated caution.

Dip coating with moisture sensitive materials such as these, will probably
cause frequent changes of partially cured coating material even if you have
an inert gas blanket over the coating material.

I have experience where assemblies, thought to be dry after an 8 hour bake,
were still wet enough to influence the coating material Dow 2577 over 2
weeks at high volume production. Throwing away 10 gallons of coating every 2
weeks can be a hurtful experience - it gets you right in the pocket!

You may need to consider vacuum drying to minimise this risk if your PCA's
have entrapment areas such as transformers or coils.

Regards, Graham Naisbitt
__________________________________________________________________________

[log in to unmask]

Concoat Ltd
Alasan House, Albany Park
Camberley GU15 2PL UK                        http://www.concoat.co.uk

-----Original Message-----
From: Chris_Smith <[log in to unmask]>
To: [log in to unmask] <[log in to unmask]>
Date: 17 February 1998 14:28
Subject: [TN] Conformal coating cure for Dow Corning 2577 and 3-1765


     All,
       We are currently using a Dow Corning 3-1765 silicone coating in a
     PVA machine.  The problem lies in a execrated cure time for this
     material.  I am seeking information on a profile that will work with
     the curing process.  I have been told that without adding humidity to
     the process you can't go over 65ºC or you boil out the moisture it
     needs to fully cure.  However, I was also told that 150ºC for ten
     minutes w/out humidity is the proper cure.  I have a Vitronics IR
     reflow oven that I've been trying to get to cure this coating.  I know
     its not the best situation, but it was meant to be crutch until we
     could obtain new equipment.  This new equipment, a dip tank is
     intended to run Dow Corning 2577 and I also need cure profiles for it.
     If anyone has cure information on either the 3-1765 or the 2577 I
     would greatly appreciate it.

     Thanks
     Chris Smith   M.E.

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