Peter,

I would guess that the coating is not fully cured. We know that this can
take up to and beyond 72 hours.

When a UV curable coating is uncured and un-reacted it can be highly
conductive. There are usually many ionic species present in such coatings.

I am curious - why are you using this type of coating?
How are you managing to apply the coating so thin?

In view of your test method, could it be that there is something else under
the surface of the coating - as David Douthit stated, there may be many
other issues lurking....

Your problem with the via's will most likely be due to the UV light not
penetrating into this area.

The problem with the resistors/capacitors - is this under them or over them?
If its under them - then it is as per the via's. If it is over them, you've
got me stumped. (Olde English cricketing term).

If you are likely to be in Minneapolis next week, we could review over a
beer!
--
Regards Graham Naisbitt

[log in to unmask]

Cell: 079 6858 2121
Office: +44 (0)1252 813706

Concoat Limited - Engineering Reliability in Electronics

Web: www.concoat.co.uk  and  www.concoatsystems.com


> Hi Everyone,
>
> Having trouble with conformal coating.  Currently using a UV cure silicone
> based spray on a PCB with gold plating.
>
> The problem we are experiencing is after the conformal coating is applied
> and curred (0.002" thick), using simple probes with very little pressure on
> the probes, we obtain conductivity between certain traces.  In other words,
> the conformal coating is not preventing electrical conduction between points.
>
> Specificially, we are having difficulty coating vias and SMT
> resistor/capacitors.
>
> We tried increasing the thickness of the conformal coating sprayed, but no
> luck.
>
> Does anyone have any ideas?
>
> Thanks,
>
> Pete
>
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