Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Dan Pickard <dlpwebmail@...> wrote:
>
> Has anyone ever tried using silk screen printing emulsion as a cheap
photo resist for PCB fabrication? I have an order in with my neighbor
for some from his shop. I'm going to give it a try,  just want some
input from anyone with experiance with emulsion. 
>   Dan
> 
>  
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One way to coat the bare copper board is to use a blank silkscreen.
Tape off an area slightly smaller than the size of the board and use a
squeege to flood coat the copper panel with the screen emulsion. This
method will print an even coating of emulsion. Let it dry and expose
it with a UV lamp. Keep in mind most screen printing emulsions are
negative acting. Any areas exposed to the UV lamp will remain after
development. This would probably work good if the adhesion to copper
is sufficient. Diazo type screen emulsions can be stripped after use
with chlorine bleach. Diazo screen emulsions also have a short shelf
life (about 30 to 45 days) once the two parts are mixed.

Coating boards with a bare screen is one way to apply photoimageable
soldermask. I used to apply Taiyo photoimage soldermask this way by
using a 110 mesh polyester screen. Finer screen meshes will result in
a thinner coating on the board. This coating method works but the only
question is how well it will adhere to bare copper.

Several years ago I tested a sample of screenable photo resist. It was
made by a company in Germany but I can't remember their name. This
screened photo resist worked great but was expensive. The main
application for this product was for imaging inner layers for
multilayer boards. If I can find the information on this product and
company I'll post it later. This type of product would be excellent
for making print and etch boards.

Tom