I wonder what you would do when tackling this footprint suggestion.
It’s the land pattern example for Texas Instruments’ LM708x0 chip, a 29 pin VQFN.
In particular there is exposed copper that connects multiple pads, roughly polygon shaped but with some filleted corners.
I opted to draw a standard QFN pad pattern, and add a polygon to the F.Cu and F.Mask layers, like so (Mask and Cu layers are the same):
However I wasn’t able to capture the filleted corners. The “Shape Modification → Fillet Lines” command works nicely, but produces an outline rather than a filled shape. And the inner fillets in particular are hard to replicate with standard fill and line tools.
I think it probably doesn’t matter, but I wonder if I’ve missed an option here?
I did a short experiment in KiCad V8 with the footprint editor.
- Draw a graphical polygon.
- Right click, Shape Modification / Fillet Lines.
- Right click, Create from Selection / Create Polygon from Selection.
And this seems to work, although the fillets are not real arcs, but made up out of line segments.
But for the rest, I probably would not have bothered to do this, and at most draw chamfers in the polygon. There is no need to exactly follow the contours of the exposed metal. With small pads, there is a benefit with rounded corners (more accurate stencil manufacturing, and more reliable solder paste release). But for such big pads, these effects are much smaller.
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Oh wow, yep, step 3 does the trick (in v9)! Thanks.
Yes, it’s hard to imagine any starvation effect given the total area. And I’ve opted for more traditional rounded rects for the paste layer.
But the less departure from recommendations, the less nervous I feel. So this is good to know!
