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The drilled holes will never line up properly, it’s a fundamental property of universe.
When gluing use a bright light underneath so you can see both sets of tracks, and use something like the mounting hole outlines to align them.
Tony
From: Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com]
Sent: Sunday, 5 July 2015 3:14 PM
To: Homebrew PCBs
Subject: [Homebrew_PCBs] Gluing 2 single sided boards to make a double sided board.
Double sided boards as we all know can be a bit of a pain, the biggest problem is getting that precise alignment between sides correct so that when you drill in the center of your pad on one side, it comes out in the center of the pad on the other (and not, as is not uncommon, breaking out, and probably messing up the trace, or a trace nearby...). Especially if your only able to expose/imprint artwork one side at a time.
Even more frustrating when one side comes out perfect in part of the process (eg, developing) and the other side is too flawed to be useful, meaning you get to start from scratch again.
So, the thought randomly occurred to me today, if you could prepare, expose, etch, drill the two sides of a double sided board completely separately, and join them up at the end of the process, it would make getting precise alignment of those sides almost a non-issue, assuming you can drill even roughly vertically and hit the center of the holes it's just a matter of lining up the holes you drilled on each side. And also means that the success or failure of each side is independent of the other.
Of course, it does double the drilling, but that's the easy bit really.
This is also of course more or less how multi layer PCBs are made by fabricators, a stackup of already prepared pcb layers and resin impregnated sheets.
Single sided laminate at 0.8mm thick (and you can get down to 0.5mm) is available out of China for cheap.
Eg:
Has anybody done this... am I reinventing a triangular wheel here, is it doomed to failure? Suggestions on suitable adhesive... maybe just spray on contact adhesive might work, it's a pretty big flat contact area.