pcb-rnd knowledge pool

Abstract: When exporting a designw ith assy or fab text outside of the drawing area, those objects are not showing up in the output. This pool node explains the reason behind this and how the outline concept evolved over the decades. It also describes how to place text or other objects (e.g. comments) around the board without violating the drawing area rule.

1. Background

In the old days, in the 90s, PCBs were rectangular. When you etch your board in the kitchen and cut it using a hand saw, you don't want to go fancy on the board shape... So pcb had this idea of "board width" and "board height", very much assuming your board is rectangular.

Then in the 2000s the whole user base started to move away from this and do more boards at professional fabs; then in the 2010s, especially with the cheap chinese fabs (offers like $5 for 5 boards) almost nobody cuts their board with a hand saw anymore. So in the 2000s, before my time, pcb introduced the "outline layer".

Unfortunately pcb developers were not very good in planning ahead, so the whole outline feature was a mess. It was really a copper layer with the name "outline" and the code checked the name of the layer to override normal copper behavior and do different things for outline. Even worse, they didn't really rename or remove the "board width" and "board height" property so we inherited two, fundamentally incompatible concepts...

2. The way you should do it in pcb-rnd

In pcb-rnd I've started to clean this mess up, but because of user's muscle memory and file format compatibility it's not something I can fix in short term, but we are doing a long, 10..20 years transition...

The idea is that I reframed the "board width/height" concept into "drawing area width/height", indicating that it's typically not the actual board dimensions, only some virtual size of a canvas you draw on. Plus we have a much better layer support since 2016, so pcb-rnd really understads what's an outline layer and it's not guessing from a copper layer's name.

For legacy designs, if you do not have anything on your outline layer, we still say "drawing area" == "your rectangular board's contour". But I do not recommend this for new design.

For new design please always choose a drawing area larger than your board and use the outline layer to draw your board's contour. Can be a simple recatangle of 4 very thin lines. Properly using the grid (e.g. set to 1mm) it should be easy to get the corners connected and get the exact board dimensions you want.

Then you can place your assy text, fab text and whatever else around the board: outside of the outline contour you drew, but inside the drawing area.