Now it's time to route the prototype MultiSpork board... and it's kind of a bear, with over five hundred air wires. Even as complex as the board is, it shouldn't be too troublesome to route it with four layers. 

At this point, I've added top and bottom digital and analog ground pours. This took the air wire count down to about four hundred. Since this board has four different power rails (+10V, -10V, +5V, +3V3) and two ground rails (digital and analog) this is just the beginning. I'll add a couple of internal pours to distribute the ground and the other power rails as needed, especially to the series protection diodes.

Once the various pours are in place, the next thing to route is the fastest & most path sensitive signals. In the case of this board, that's the 2.4 GHz signal path, the clock crystals for the MCU and the WiFi chip, and the USB signal lines. One thing that really helps with keeping everything organized is to make all of the traces on each layer more or less parallel. In the case of this board, the bottom layer runs crosswise, the top layer lengthwise, and the two inner layers alternating

Next up is the somewhat slower but widely distributed SPI bus. That bus goes to every major chip on the board as well as the SD Card slot, so it goes everywhere. It's also a fast SPI bus, in order to ship data back and forth from the MPU to the MAX11300 at the speed required. 

With all the fast stuff laid down, next step is to get the analog and the regulators laid out. None of that is particularly hard, since those groups of components are laid out to make this bit easy. Once those are in, hook up the power rails. 

The last bit is all the low-speed logic connections and ancillary trouble required to make the whole business work. Simple, right?