pcb-rnd knowledge pool


Drawing the board outline

outline by Tibor 'Igor2' Palinkas on 2020-11-20

Tags: howto, outline, contour, board, shape, cutout

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Abstract: How to draw the outline of shaped boards. How to draw internal cutouts.

  Anything that is related to board shape, is done by drawing on a boundary layer group. If you use the the default board template in pcb-rnd, there will be layer called 'outline'.

1. Make sure your board dimensions, which is really your drawing areas dimensions, is larger than your final board - it's in preferences, 3rd tab (Size & DRC)

2. Draw your board outline with very thin lines and arcs on the outline layer. If your board is a rectangle, draw a rectangle using 4 lines.

TIP: choose some reasonable grid: 25 mil, 100 mil, or 1mm. A typical novice error is using grid too fine, like 1mil or 0.1mm, trying to manually hit line endpoints with the mouse - but with that fine grid, endpoint object snap won't help much and you will end up with lines not perfectly connected. And that will cause problems later. So use a coarse grid and rely on object snap jumping into line endpoints. If you are in doubt, switch on the wire frame drawing mode (key sequence: {m d w}, that is, pressing m, then release, then press d, release, press w, release) and zoom in.

Make sure you draw with thin lines/arcs! I assume you will send the board to a fab to make it. You will use gerber. Gerber is a real broken file format on many levels. There's no well specified outline/rout/cut layer convention in it. So the outline layer will look like a copper layer, and they will try to figure what shape you meant. You don't know what tool size they will use, so you can't use the same diameter line/arc on your design. So at the end, there's always the question: is your board's final size defined by the centerline of your outline drawing, by the inner edge or by the outer edge. If are drawing this with 1 mil thin line, it doesn't really make a difference, so do that.

3. Once you are done with the outer contour of your board, any large unplated cutout should be drawn the same way. If you have a circular cutout, place an arc, which is 1/4 circle initially. Then zoom in much, make sure your mouse cursor (the pointer, not only the crosshair!) is over the arc, right click, edit properties. This will open the property editor on that arc. Click on the row p/arc/angle/delta, on the right modify it to 360, click apply, close the property editor -> now your arc is a full circle.