The application is very tight with many close keep out areas. That is why 
we are using a precision coating machine with a UV cure. The boards area 
cured seconds after that are coated so the coating does not spread out 
onto keep out areas.  This is new equipment and the manufacturer has 
resolved the bubble problem but we now have to determine what to do with 
the product that is already coated. 



Joel Alexander
Quality Assurance Manager
TT APSCO, INC. 

----- Forwarded by Joel Alexander/perry/apscoinc on 04/24/2007 10:05 AM 
-----

"Bloomquist, Ken" <[log in to unmask]> 
Sent by: TechNet <[log in to unmask]>
04/24/2007 09:24 AM

Please respond to
TechNet E-Mail Forum <[log in to unmask]>; Please respond to
"Bloomquist, Ken" <[log in to unmask]>


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Subject
Re: [TN] Conformal  Coating Voids






Joel,

We use a moisture cure urethane and if we get the coating on too thick
and the humidity is high we get foam like bubbles. I believe the coating
skins over too fast trapping all the volatiles underneath. We resolved
this by doing a 40% first coat and then a 60% second coat to get the
required thickness. We only allow about 20 - 30 minutes between coats.
And like Ramon said, don't put them in an oven too soon after coating if
you oven dry your boards.

KennyB

-----Original Message-----
From: BADRI [mailto:[log in to unmask]] 
Sent: Tuesday, April 24, 2007 6:15 AM
To: [log in to unmask]
Subject: Re: [TN] Conformal Coating Voids


> 
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Joel Alexander
> Sent: den 23 april 2007 21:47
> To: [log in to unmask]
> Subject: [TN] Conformal Coating Voids
> 
> We are using Urethane coating on an assembly that uses  63/37 solder. 
> We are using organic water soluble flux. We are Ionic testing after 
> wash and we are well within IPC cleanliness specifications. We 
> installed a selective coating machine and in our initial run of 
> product we had some small bubbles that look like foam. Our customer 
> does not like it but our stand is that it meets IPC-A-610 and
> J-STD-001 requirements since there in no obvious voids between 
> conductors. They were worried about corrosion if a bubble was against 
> a lead. The bubbles are fully encapsulated. Does anyone think this is
a valid concern?
> 
> 
> 
> Joel Alexander
> Quality Assurance Manager
> TT APSCO, INC. 
> 
>

ForwardSourceID:NT000B42FA 

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