Hi Bryan,

Long ago we ran into this problem with Humiseal 1B31, especially when the
coating was applied thicker than 'normal' (we were running 4-5 mils, or
.004-.005 inch).  The problem was not so much thickness, but the smooth
solder resist surface.  There was no problem coating non-resist cards,
because of the toothy surface remaining after copper removal.  Nor did the
problem show itself on solder resist boards that were hot air leveled, as
that process tends to drive microcracks in the resist.   Anyway, the way we
finally resolved the issue and kept our jobs was to require all soldermasked
PWBs to go through a plasma exposure as a final fabrication step at the
board shop.  This sorta bites into the organic resist surface, and offers a
rougher terrain for coating attach.

Ralph Vaughan

> ----------
> From:         Bryan Kerr[SMTP:[log in to unmask]]
> Reply To:     TechNet E-Mail Forum.;Bryan Kerr
> Sent:         Wednesday, July 07, 1999 4:39 PM
> To:   [log in to unmask]
> Subject:      [TN] Conformal Coating
>
> Hi all,
> Any experiences with Humiseal 1B73. I'm finding it tends to pull away
> easily from a solder resist surface, particularly on boards with
> heatsinks, along the edge of the heatsink profile. Thermal cycling makes
> it much worse. Any similar problems out there ?
>
> Bryan
>