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In my opinion, the solder will not run into the via as long as there is a reliable soldermask web between them. Is that right?

As I know, PCB manufacturers change gerbers all the time to make the boards more manufacturable on their end. If the soldermask web in the gerber is too small, PCB house will reduce the soldermask clearance(enough soldermask annular ring) in order to make a reliable web. That is why I am concerned about the via pad to toeprint spacing cuz PCB house is not allowed to modify the pad/trace, but the solder mask.

My question: What's the min space between exposed via pad to exposed component pad during reflow?

Thanks!

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    \$\begingroup\$ If your board house is screwing with your design without your permission, you need a new board house. Unless you're violating their design rules, in which case, you deserve it. \$\endgroup\$ – Matt Young Oct 20 '16 at 2:09
  • \$\begingroup\$ As I know, PCB manufacturers change gerbers all the time to make the boards more manufacturable on their end. If the soldermask web in the gerber is too small, PCB house will reduce the soldermask clearance(enough soldermask annular ring) in order to make a reliable web. That is why I am concerned about the via pad to toeprint spacing cuz PCB house is not allowed to modify the pad/trace, but the solder mask. \$\endgroup\$ – fatjay Oct 20 '16 at 6:06
  • \$\begingroup\$ Any reason not to just tent the Via on the top side? \$\endgroup\$ – Dan Mills Nov 23 '16 at 16:03
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In my opinion, the solder will not run into the via as long as there is a reliable soldermask web between them. Is that right?

Yes, that is generally correct. The fab will however have requirements on minimal distance in order for you to get the solder mask in between.

My question: What's the min space between exposed via pad to exposed component pad during reflow?

This is hard to answer and depends on the amount of solder you are applying, the chemical composition in solder, the laminate used, amount of flux used, heat applied etc. As mentioned already it also depends if you have solder mask between the copper. Most fabs would probably have difficulties with solder mask if distance is less than 4-5 mil so I would say that this is a good limit to have in mind. I guess the minimal space could be even lower without problems but why push your luck ?

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