Homebrew PCBs

I would be more inclined to drill just two holes on opposite
sides of a double-sided board before exposure/etching so 
that alinement would be a lot easier.

Best,
Charlie

On Sun, 5 Jul 2015 17:13:52 +1200 "James bitsyboffin@...
[Homebrew_PCBs]" <Homebrew_PCBs@yahoogroups.com> writes:
  

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:
http://item.taobao.com/item.htm?spm=a1z10.5-c.w4002-1192550948.12.TIEXsq&
id=35870048695

http://item.taobao.com/item.htm?spm=a230r.1.14.4.VdTsRT&id=21105435798&ns
=1&abbucket=3#detail



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.