Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

The inkjet/UV process is as follows:

You print the artwork on a transparent sheet of plastic (I called it
"paper" because it's that size and shape). Usually, this plastic has
a coating on it that makes the ink dry very fast so you can put a lot
down without it smearing. The result is a "mask" (also called "the
artwork" or "the print") which passes UV in some spots, and blocks it
in others. Whether you want to block where copper should remain
("positive") or where copper is removed ("negative") depends on the
PCB's coating - some harden with UV (negative) and some soften with UV
(positive).

Anyway, the next step is to put this mask on top of the coated PCB and
expose it to UV light. The light passes through the transparent parts
of the mask and reacts with the PCB's coating. The PCB is then put in
a chemical bath that removes some of the coating and leaves behind
your etch resist. This chemical bath is the "developer".

We use the word "film" inconsistently. The plastic sheet we print on
is often called "film" although it's just a transparent page. The
coating on the PCB is often called a "film", although often "UV film"
or "photofilm" (for liquid coatings, it's only a film after it's
applied, for laminated coatings, it's a roll of film you laminate on).

None of this has to do with regular photographic film, or regular bond
paper.


The Toner transfer process is different - you use a laser printer
instead of an inkjet, and it's the toner itself that becomes the etch
resist. You can't use an inkjet's print as etch resist because
there's no way to transfer it to the PCB (toner is plastic, it can be
melted and made sticky), but you can use plain paper as long as you
can get it off the toner later.


You ∗can∗ use a modified inkjet printer to print directly to a PCB,
but you have to remove the regular ink and replace it with liquid etch
resist.