Yes, on future designs I can just set a 10mil rule instead of 7mil on the
bottom layer,
but I wanted to make sure I understood what the issues were.
thanks, Richard

On Tue, Feb 19, 2019 at 11:27 AM Stadem, Richard D <[log in to unmask]>
wrote:

> Is it possible to leave more mask width around some vias, but not others?
> Or is that only controlled by a general rule in the design software?
>
> But I still don’t see how a thin sliver of mask between two unsoldered
> vias is an issue, other than for breaking off/FOD.
>
> I know you’re not feeling any shame, Jack! LOL.
>
>
>
> *From:* Jack Olson [mailto:[log in to unmask]]
> *Sent:* Tuesday, February 19, 2019 11:16 AM
> *To:* Stadem, Richard D
> *Cc:* TechNet E-Mail Forum
> *Subject:* Re: [TN] soldermask silvers
>
>
>
> We don't rely on the mask for insulation, we rely on a 7 mil clearance
> copper-to-copper, but that leaves a smaller mask width between them.
>
> For dog bones we do similar, but pad-to-via is the same potential, and
> those vias are encroached with mask anyway.
>
> not feeling any shame, but thanks for writing back.
>
> (This report also flags "copper slivers" which I've never heard of, but to
> them it is the thin copper plane that floods between vias!)
>
>
>
> On Tue, Feb 19, 2019 at 10:45 AM Stadem, Richard D <
> [log in to unmask]> wrote:
>
> For soldered BGA dog-bone pads, that is a major issue, common within the
> industry. If the soldermask strip between the via and the BGA pad is too
> small, there is not enough adhesion and the molten solder runs right under
> the soldermask strip down into the via hole. Too thin of a strip of
> soldermask allows solder thieving from the solder ball. But for unsoldered
> vias not connected to a soldered pad on the opposite side, I cannot imagine
> what issues there would be. Soldermask is not considered an electrical
> insulator, so if a designer was depending on a thin sliver of mask to
> provide insulation between two vias of different potential, shame on them.
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of Jack Olson
> Sent: Tuesday, February 19, 2019 9:58 AM
> To: [log in to unmask]
> Subject: [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...
>
>