[clug] PCB manufacturing

[Darren Freeman]

Alastair,

On Wed, 2003-11-19 at 08:46, Alastair D'Silva wrote:
> I don't supppose anybody on the list has access to PCB manufacturing
> facilities and would be willing to run off a prototype open-hardware
> board I've designed?

I have a friend from Adelaide, in Canberra for tonight, who works in the
industry. Plus there's various companies that do this.

> Its a multi-output board for the Xbox (including VGA) that should work
> both with XBox Linux and the retail machine as it can feed the VGA
> signal directly from the machine (in the case that you're using Xbox
> Linux) or by decoding the HDTV signal.
> 
> I would have just done it at home, except its a dual layer design
> requiring plated through holes, which is beyond my ability to do.

Don't despair - plated through holes are not strictly necessary. I've
done double-layer boards with regular photoresist and transparencies.
You simply design the board so that the interconnects are via component
legs that you can access from both sides, like resistors and
through-hole ICs. Worst case is you make "vias" by adding a regular size
pad on both sides and a bit of tinned copper wire offcut through the
middle. It's tricky as you solder and cut one side, then very quickly
solder the other so it doesn't fall through. But worth not having to get
help.

Last resort - talk to the electronics unit at the Research School of
Physical Sciences and Engineering, ANU, they have the UV exposing
machine that vacuum sucks the transparency against the board and
exposes. Does a fantastic job on double-sided although they may tell you
otherwise. Make sure your printer doesn't slightly warp the image or
both sides might not line up in places. Don't forget corner marks on the
transparency as you need both sides to line up on the board. Minimum
recommended track size is about 30 mil but smaller features work too,
just don't rely on them as reworking may be needed. Also fill in any
unwanted space with ground planes on both sides, even if you don't
really want them. Less etchant required (by far), more likely to get it
for free.

Plus they are really helpful. I don't know how far they will go for
someone outside ANU, but when I was across campus working on an
unrelated project, they did all they could and it made a huge
difference. Someone who is clearly keen will probably get the whole job
done for the cost of materials. Don't forget a cake when the job's done
- traditionally that's what happens and it really makes an impression.

Darren