On round soldered pads, I've had the mask come loose between two pads, and
then solder got under it and bridged the pads. I haven't had any issues
with thin mask webs between unsoldered pads. Someone with more experience
in the actual soldermask printing process may be able to illuminate this
further- I'm not sure whether there are equipment limitations that may
cause issues.

That said, I do typically avoid thin webs between unsoldered pads in my
designs, sometimes by partly covering the via pad with the soldermask
(creating something that looks a bit like a mask defined pad).

Tom

On Tue, Feb 19, 2019 at 10:57 AM Jack Olson <[log in to unmask]> wrote:

> In my experience, what a PCB fabricator would consider a sliver would be
> the strip of soldermask material between RECTANGULAR pads being less than a
> minimum width.
> We got a "DFM report" for a board where minimum distance between ROUND vias
> is being reported as slivers.Has anyone ever heard of problems with minimum
> mask material between round, unsoldered vias?
> I can't imagine any real-world problems that could cause, but I have an
> open mind...
>