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

----- Original Message -----
From: "Radra" <infositeus@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Thursday, February 23, 2006 5:22 PM
Subject: [Homebrew_PCBs] Re: Photolithography - resolution


> 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?

I get better results with an inkjet printer (8 mil tracks without any
problems) than when I used to use a laser printer. The latter was rather
old, though, and only 600 dpi resolution. Best results are obtained with
photoplots, of course.

Leon