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How to Make Paste and Mask Shapes Different Sizes

erix

Hello,

I'm trying to make a custom component for a very small LED. The manufacturer's documentation suggests specific geometry for solder pad, solder mask, and solder paste. I can create the custom pad easy enough but I'm not able to make the other layers different sizes. From this dialog box it seems one could adjust the geometry for each of the three tabs (Top Layer, Top Paste, and Top Solder) but in reality, changing the Size and Shape on one tab changes them on all tabs. Is there a way to do this in CS?

image

  • Use the solder and paste mask expansion settings.  Use negative values to make the expansions smaller so the paste mask is smaller than the pad and make the solder mask expansion positive to open up the solder mask.  Or make the solder mask negative to encroach the pad (or via) as needed.  I don't recall if you see this directly in the display or only after generating the fabrication files.  I'm pretty sure you see the solder mask expansion in the 3D view.

     

    Actually tested this and you can see the changes on the PCB.  I edited a footprint on a board rather than in the library.  The solder mask (green) is now absurdly large and paste mask (gray) is smaller than the pad (red)

    imageimage

  • in reply to tarribred61

    Thanks for the quick reply Thomas!

     

    I like your method but for this LED I need to offset the paste to one side of the pads. I wound up making (2) pads that represents the paste size with zero expansion. I then added a new pad on the solder mask layer to represent the larger mask and covers both pads. Lastly I added two pads on the top layer that represent the actual solder pads on the board. I think it'll work, will verify with the gerbers later today.

  • in reply to erix

    Ahh, for your case it is not a simple expansion then.  A simpler way to do what you want is to draw shapes on the layers you want.  For example, if you want to make a special paste mask such as for a windowed stencil pattern for an enhanced thermal pad, then set the paste mask expansion to a large negative value to close it up on the pad.  Then, in the part library draw shapes on the paste mask layer for the openings you want on the stencil.  This is also a way to do gang relief on the solder mask layer for a part.