Steve,
You've had shorts under SMTs when the vias were "tented" with LPI?  I'm
concerned because we've got a board in prototype that has quite a few
under-SMT vias (32/16 size).  So far we've had no problems, but we've only
made about a dozen.  Looking at our bare boards, I see what you mean about
the soldermask drawing back from the hole on some vias, although others are
actually sealed.  But it seems there's enough soldermask to make it unlikely
for a solder bridge to be created.

Do you know what clearance you had between the vias and what size vias?
Were the shorts via-to-via, or via-to-pad?

> -----Original Message-----
> From: [EMAIL PROTECTED]
> Sent: Monday, March 18, 2002 8:53 AM
>
> In a message dated 3/18/2002 11:41:41 AM Eastern Standard Time,
> [EMAIL PROTECTED] writes:
> >
> > I am trying to determine if the Solder mask thickness that
> > I am specifying is thick enough.
> <snip>
> My experience has been that liquid
> photo-imageable soldermask does a really poor job of covering vias.
There's
> no liquid in the hole, and therefore surface tension seems to draw back
the
> soldermask from the edges of the hole. I've had problems with shorts when
> I've used vias under SMT parts. <snip>
> Steve Hendrix

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