Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Brian" <blue_eagle74@...> wrote:
>
> Never thought of this. Cool idea. You said to use thin foil.

I've been doing something similar, but using brass shim stock.  I
started with 5 mil but that was getting too much solder paste on the
fine-pitch stuff, and also I was having some sideways etching problems.
I changed to .003" shim stock, and have had great results so far.  I
clean the shim stock with fine sandpaper on both sides to remove oil
or plastic preservative coatings.  I laminate both sides of the shim
with DuPont Riston etch resist dry film.  I then expose with aligned
mirror-image films and etch like a circuit board in a Kepro spray
etcher.  This has a heater that brings the etchant temperature to 35 -
40 C.  I have had a little problem in that the board holder in the
etcher is designed to hold rigid things like PC boards, and the .003"
shim stock is too flexible, so I will have to provide a frame next
time I do it.  But, the results have been quite good.  I have done
down to 0.5mm pitch chips.  I had some breakdown of the "bars" between
adjacent apertures with the .005" shim, but it is working great on the
.003" material.

Jon