Solder mask opening for vias for hole only

Issue #104 resolved
Guan Yang
created an issue

(We've discussed this before. This is a clearer explanation of the issue.)

This is an array of thermal vias under the exposed pad of a QFN. They are 0.35mm drills, with width/height of 0.7mm. For one of them, I have checked the “stop” flag.

This causes an opening on the bottom for the entire 0.7mm diameter. In my experience, this is not standard: I want a hole in the solder mask so air can escape during reflow, but I don't want more than a negligible amount of exposed copper to avoid the risk of shorts, corrosion and other accidents.

Why don't I simply set width/height to 0.35mm? Because then DRC complains.

I see two solutions:

1) DRC option to ignore “annular ring” (or consider it simply an additional distance) for vias entirely enclosed by the same net (whether a pad or a polygon), or consider it an additional required spacing.

2) Have solder mask apertures for vias only apply to the drill. (I think this should be the default anyway.)

Comments (6)

  1. Razen repo owner

    Ok, so does it not make sense to have the stop mask be defined in terms of a dimension property. This lets you create all varieties of vias:

    • fully tented: stop = 0
    • thermal: stop = drill-diameter
    • as they are now: stop = via-diameter

    then default the stop diameter to the drill?

  2. Guan Yang reporter

    It makes sense. More than I need myself right now. Most of the time I am fine with fully tented, and I only worry when it's a thermal under an exposed pad.

  3. Razen repo owner

    Added via stoptop and stopbot dimension properties in v0.8.2 Route tool now has a "Via Mask" option to toggle between tented (default), hole, or open vias

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