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

The purpose of my original post was to query the group regarding
resolution limitations of the photolithography process. My attempts
to fabricate a useable 1 mil (0.001 inch) track have proved
unsuccessful leading me to ask "why"? So far I have received two
comments (thank you): one related to collimation of the UV source and
the other related to etching considerations.

Let me provide a little more information regarding my goals and
processes. My intent is to devise a simple "at-home" process which
will produce PCBs with finer resolution and without the pin holes
associated with the toner-transfer process. I am an RF engineer and
need to produce good looking prototypes.

I created a test pattern which I used to assist me in the development
of the process. The pattern consists of 100, 50, 10, 5 , and 1 mil
parallel lines and a grid made of 1 mil lines. My UV light source is
a Blak-Ray B-100A long-wave source made by UVP. This source produces
an intense spot beam. I position my artwork about 2 feet from the
lamp and expose the dry-film PCB for 1 minute. Trial runs were made
using exposure times between 10 seconds and 6 minutes; 1 minute
proved to be satisfactory.

My test runs demonstrated I could reliably produce 5 mil lines but
not the 1 mil lines. Microscopic examination of the 1 mil line
artwork revealed that the two parallel edges of the line tended to
not have a clearly defined area between them. Thus when I used this
artwork to expose the PCB, the resulting pattern on the PCB was not
well defined prior to etching. It is then natural to wonder if my
transparency artwork can be improved "at home" and, if so, will I be
then able to fabricate a higher resolution product.

Lastly, my goal is not to actually fabricate 1 mil lines as I don't
need them. Instead my goal is to learn what can be reasonably
accomplished "at home" and apply that knowledge to fabricate the best
looking PCBs possible. So, setting aside etching considerations for
the moment, my original question still stands, does anyone have
suggestions regarding how I can improve the processes employed prior
to etching?

Lyman