Jerry

IMHO, the secret is to ensure that the voltage gradients never exceed a
certain value, depending on working conditions. Solder masking MAY allow
you to increase the gradient a little (say, by 2 maximum) PROVIDED you
can be sure that the bare PCB is clean before the mask is applied and
that the mask is fully cured. As you can never be 100 % sure of this
(unless you make the boards yourself) my approach would be to use bare
boards, ensure as near-perfect cleanliness as possible and then to use a
darn good conformal coating that you can cure yourself under scientific
conditions. This way, your pads are coated, as well. I am not an amateur
of generalised solder masking AND conformal coating because it costs
more and the adhesion of a coating on a mask may be less than on a bare
board, depending on the materials used (some solder masks are decidedly
poor in this respect). Another approach is to reserve an inner layer for
the hi-V circuitry, so that it comes to the surface only on the pads
where the components are mounted, normally with adequate spacing. In
this case, the quality of the solder mask will be less important.

Brian

Jerry Mosur wrote:
>
> Hi,
>
> I am looking for solder mask material that would reduce voltage creepage
> across the surface of the PCB. We are routinely designing boards with few kV
> across component's pads. The only solution is to route the board between
> pads and as we reach higher levels, route and pot the whole assembly.
> Any info, leads would be appreciated.
>
> Regards,
>
> Jerry Mosur
> Spellman High Voltage
>
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--
Brian Ellis
Protonique SA
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