Homebrew PCBs

Hi Emil,

I found I did not need to improve the contrast ratio of the phototools I
made with a laser printer.  I am using Riston MM540 from the Czech
Republic, via eBay:

  http://www.tech-place.com/pyralux/23-photosensitive-film.html
  http://myworld.ebay.com/gaminn/

I used a ~1mm photodiode with light from an incandescent lamp to test
how much light passed through the black areas of the phototools I
created by laser printing on this "A4 transparency film":

  http://screenprinting.asc365.com/index.asp?ID=PD007003

I am using a Brother HL-5250DN, running at 1200 x 1200 DPI.

The black areas passed about 1/7th the light of the clear areas.  There
is some variation in the darkness of the black areas, due to
irregularities in the drum, the toner cart and how the toner arranges
itself on the film.  600 x 600 mode looks the same and is just as good
for most PCB designs.  I get a more even pattern of darkness with the
HL-4040CN colour printer operating in monochrome mode.

The lighter parts of the image are the limiting factor for exposing
photoresist.  Without a smaller photodiode, I can't tell exactly what
the light level is there.  (I could scan it with a transparency scanner
to find out for sure.)  I guess I have a 5:1 contrast ratio between the
clear parts of the image and the lightest parts of the black part.

I find this is plenty of contrast for the Riston.  I am using a 500W
240v quartz halogen lamp to expose the Riston.  Most of the exposure
occurs in the violet and near ultraviolet ranges.  As far as I know, the
toner is just as opaque there as it is for visible light.

  - Robin   http://www.firstpr.com.au/pcb-diy/