--- 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