Graham,

I have seen numerous examples of dust and dirt that had "sunk into" Acrylic coatings on PCBs
in the field. The coatings were a coagulated mess. These boards were subjected to internal
forced air cooling with no filtering. Operational and ambient air temperatures would reach
about 50 degrees C.

I do agree that the ESS tests being done in this case are likely causing more damage than
they are worth.

David A. Douthit
Manager
LoCan LLC



Graham Naisbitt wrote:

> Dear Wee Mei
>
> As implied by David Douthits message, the coating has become "soft". This
> may have allowed certain particulates to "adhere" to the surface - they are
> not likely to "sink-in"!
>
> These coatings are "thermo-plastic" materials, so this condition is not
> surprising but, the coating is NOT becoming liquid.
>
> If this issue cause you some reliability issues - the assembly is failing in
> test or real conditions because of this condition - then you might like to
> try another variant, details of which I will give you off-TechNet. It is
> simply another acrylic material that has a different thermal withstand that
> permits it to be less "sticky" under high temp conditions.
>
> If you are NOT getting failures in test or service, is there a problem?
>
> Regards, Graham Naisbitt
>
> [log in to unmask]
> www.concoat.co.uk <http://www.concoat.co.uk>
>
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>
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> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]]On Behalf Of fullname
> Sent: Tuesday, September 25, 2001 08:34
> To: [log in to unmask]
> Subject: [TN] Dirt on Coated Board (UC)
>
> Some assembled boards were coated with Humiseal 1B31. After the ESS
> tests at 110 degree C, dirts were found on the board and component
> surfaces on both sides. I have checked the data specification on 1B31
> and found that under cured enivronemnt, the coating should withstand -65
> to +125 degree C.
>
> Can someone advice me what could be the cause of this problems?
> Your assistance is greatly appreciated.
>
> Regards - Wee Mei
>
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