Homebrew PCBs

>> Leon wrote:
>> I've just made another PCB with a footprint
>> for a Hirose 50 way DF12 connector with 0.5
>> mm lead spacing, it turned out very well.
>> The DF12 pads are 0.38x1.00 mm.

> Stuart wrote:
> <snip>
> I'd like to be able to make double-sided
> boards with 8/8 traces and spaces but this
> seems problematic.

8/8 thou should be doable with photo as long
as you use pre-coated boards and have a good
light source and photo tool.

Most people say vellum works better than
transperancies.   Laser-star and jet-star
some people talk of are special vellum that
is meant to be "specialy formulated for laser
and ink jet printers respectivly.

I just use common garden variety cheap
vellum.

If you want to do the occasional 8/8 part of
a board then any laser printer or inkjet will
do.  If you want to reliably get a WHOLE PCB
that is choccas full of 8/8 stuff then a
photo tool with good density is a must.

If you want to get down to 6/6 or 4/4 then
you HAVE to go to a local print shop and ask
them to do a photo tool for you on their
typesetting machine.

> I'd be interested to hear
> from anyone who's done this! My two biggest
> problems are contamination of the board while
> handling it between stages of the process,
> and alignment between the two layers. I need
> aligment errors of less than 1mm, and I'm not 
> sure that this is achievable in a DIY set-up.
> At the moment I drill guide holes before
> exposure and use PCB pins to tack each side of 
> artwork in place, in turn, before taping the
> artwork to the board and placing it in my UV
> box.

Everyone has thier own trick for lining up DS
boards.

Mine is to get an L shaped peice of FR4 with
double sided tape on it.  I then use a clear
sheet of perspex of similar thickness in
place of the final pre-coated PCB.  Line this
up ontop of a light box by eye.  Then slip in
the real PCB to do the exposure.

You should be able to get things lined up
almost an order of magnitude better than 1mm
just by eye on your first attempt :D