Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, Paul Atkinson <pma32904@...> wrote:
>
> I've used some of the Kepro pcb materials in the past. I still have
one of their hobbyist kits, but I expect it's exceeded it's shelf
life. I wouldn't mind having some more of their presensitized PCB
stock if it's available and reasonable.
> 
> Concerning the dry film processing, you mentioned stripping the
material after etching. Isn't dry film also used for "solder mask" ,
in which case it remains on the PCB?
> 
> I'd expect that the etching of copper is completed, rinsed, then
dry-film for solder mask is laminated on, then some type of light
(UV?) exposure is performed through artwork for the solder mask, then
the exposed portions of the mask are washed off. Perhaps this last
"wash off" is actually called stripping?
> 
> I'd like to learn how to do solder mask and silk screens via dry
film at home. Especially if it can be done little to no chemical solvents.
> 
> Paul
> 


Paul,

Soldermask material is screen printed on the board after all the
etching and drilling is done. Curing of the soldermask coating is by 
heat or UV light depending on what masking material is used. In my
shop we use UV soldermask and screen printing inks. 

Most boards made today use photo imaged soldermask. The board is
coated with solder masking liquid, cured, UV exposed and the final
image is developed out in a spray tank. It's similar to processing dry
film etch resist. Primary etching resist would not hold up as a
soldermask because it gets brittle with age (like all of us... lol ).
It can't take the soldering temperatures either and would begin to
melt or delaminate.

Tom