Because nearly all of my printed circuit boards are for one-off homebrew projects, I tend to not obsess over getting the last air wire down on the copper. Instead, I route those pesky all-the-way-across-the-board stragglers on Layer 15 with big fat vias on each end, then solder a jumper wire across the board.
In effect, my Layer 15 is outside the board.
The screen shot shows a chunk of a board with some Layer 15 wires. I make ’em fat and use swooping semicircular arcs on the ends: they’re easily visible.
I don’t worry about actually routing the traces; they’re just straight lines and arcs. This generates all manner of overlaps with the rest of the components & wiring, but after I go down through the DRC list and approve ’em all one time, that’s the end of that hassle.
Two key advantages:
- All the remaining air wires are genuine unrouted connections
- I can print out Layer 15 separately to get a hand wiring map
I make the vias fairly large (here, 100 mils) and a unique shape (octagonal) so that I know each one should get a wire.
I usually wind up doing the power connections the same way; those vias are square. Conversely, ground vias stitching the top & bottom planes together are round; they get a short Z-wire through the board.
This probably won’t work if you’re having the boards built by an actual PCB vendor, as they’ll try to make a three-layer board or kick the board out on layout rule violations… but, on the other hand, if you can afford a four-layer board, then most likely you won’t have any trouble routing the wires.