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Soldermask Clearance On Planes Causes Increased Pad Size

aemeehan

We always have in our designs situations where one pin of a row of SMD discretes (mostly 0201's) is tied to a solid plane of copper with no thermals. Over the years, our fab houses flag this and have requested to adjust the mask opening on the plane connection to make it smaller so that it doesn't become a larger 'pad' than the other side of the discrete. We've had this done this successfully over the years. The question has arisen whether we could make this adjustment ourselves within Allegro so that the fab house doesn't have to do it. I can't think of a quick and easy way to do this. How does everyone else accomplish this? Thanks for any insight you can offer.

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  • CadAce2K

    Thermally relieve the discretes, so that the GND pads actually show. (e.g. tie the pads to GND with a large copper trace, essentially 'pouring' them as you've done historically) That way the fab shop sees a pad on each side of the discrete and opens the soldermask equally on both sides. Your problem should go away, with little changes to your process. Thermally relieving the GND pad should not affect any performance.

  • UlfK
    in reply to CadAce2K

    ...Except when doing RF layout where thermals add a small parasitic to the C or L. For LF work its OK, but for RF/uWave it may not be a good idea.

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  • UlfK
    in reply to CadAce2K

    ...Except when doing RF layout where thermals add a small parasitic to the C or L. For LF work its OK, but for RF/uWave it may not be a good idea.

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