Electronic – Is it possible to create a double layer PCB by gluing together two single layer PCBs

After you make sure power/ground aren't shorted, make sure that any silk screen or pin 1 markings for polarized components are correct - you don't want to go soldering that kind of stuff in backwards. After that it's really kind of random.

I was involved in bringing up a number of multi-layer boards over the years (not my designs) and we had pretty much any kind of screw-up you could make - traces that didn't go where they should, traces that simply weren't there, pads that weren't connected to their traces, etc, etc. I once even saw an issue where a broken trace was caused by the guys who built up the board gripping it wrong with pliers to break off a break-away section.

We were doing high layer-count designs, so we also had a lot of internal layer foolishness that you aren't going to see on a 2 or 4 layer board (registration can be...interesting when you've got 10 or more layers).

Once you get past the power/ground thing, you're probably not going to have too much trouble. Just take your time, test each bit of functionality one by one, and you should be good to go. If you're feeling paranoid, you could try building up the board one bit at a time (first put on and test the power, then the CPU and it's communications.

If you're feeling REALLY paranoid, you can sit down with the schematic and a meter and buzz-out the entire board. But unless the board is really small, that's gonna take a while.

You definitely want to get the main board working before you start on the secondary boards.

Good luck!

Assuming you're only using USB-low-speed or full-speed, you should be fine.

Generally, layout considerations only really have to be taken if you're going long distances (many inches), or using USB-2.0. Even then, USB is surprisingly tolerant.

• USB 1.1 or USB2.0 low/full speed

  • You really don't need to worry. There are (possibly apocraphyal) stories of people running USB2.0 low-speed of 50' of CAT-5 wire. As long as you keep your wire-runs a few inches or less, I wouldn't worry.
  • The fastest edge you will need to worry about in low/full speed applications is 12 Mhz. As such, you're not really approaching the point where making sure your traces/wiring is properly transmission-lined/impedance-controlled is that important, at least as long as your overall uncontrolled-impedance sections are less then, say ~6".
  • As I said, most USB controllers are impressively tolerant of USB devices that are widely out-of-spec. If this is something for production, I would spend the effort to do it properly (there is one guy out there who has a motherboard that throws a hissy-fit if anything connected to it deviates from the spec by a tiny amount), but if it's just a test-board, I'd say just lay it out neatly, and don't worry about it.

• USB2.0 High-speed.

  • Here layout becomes more important. USB2.0 High-Speed has a maximum edge rate of 480 Mhz. As such, even short traces start to approach the wavelength of the data, and as such proper impedance-control becomes important.
  • Assuming you EDA package has proper impedance-controlled routing options, just set your differential-pair impedance to be ~90Ω, and you should be fine. Be careful to make sure you have a contiguous ground-plane, though

• USB3.0

  • So you hate yourself?