We use encroached vias on the top side, and exposed vias on the bottom side
for ICT probes.
Our via-to-pad was set for the same clearance as other copper clearances on
this design, 7 mils
since the mask is 2mil oversize radius, it only leaves 3 mil mask, which is
less than the supplier requested 5.9 mil

I have been using the same rules for a long time, and 7mils isn't exactly
pushing it for copper clearance,
but I would be interested to know what others are using for via-to-via and
via-to-pad clearance
(if the vias are soldermask exposed)

thanks for replying,
Jack

On Tue, Feb 19, 2019 at 10:18 AM Decker, Scott Collins <
[log in to unmask]> wrote:

> Jack,
>   It wouldn't matter where or what the slivers are around, the board shop
> would be concerned it would float off and land in a bad place. Just for
> grins, can you let your Soldermask encroach on your vias like we do? On our
> vias, we let the mask come up on the pads and have a .006" over the
> finished drill size opening in the mask. This ensures we don't get mask in
> the holes, but you don't have to worry about slivers around the vias.  (If
> the vias are THAT close, you got other issues too. :-) ) Anyway, hope that
> helps.
> Later...
>
> Scott Decker | Senior Engineer, PCB Design Services CID+ | Electronic
> Systems Center
> COLLINS AEROSPACE
> 3445 S. 5th Street, Suite 170, Phoenix, AZ 85040 U.S.A.
> Tel: 602 308 5957  FAX: 602 243 2347
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>
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> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
> Sent: Tuesday, February 19, 2019 8:58 AM
> To: [log in to unmask]
> Subject: [External] [TN] soldermask silvers
>
> 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...
>