Homebrew PCBs

In "Re: [Homebrew_PCBs] Re: Developing dry film photoresist", Kerry
Koppert wrote about trouble with the track resist not being solid enough
after development:

> Ah right on. Careful examination of the negative show mottling in the
> black (I'm using artist's tracing paper in a Kyocera FX720 laser but
> I've also tried over-head projector transparency film). The mottling
> corresponds to the unexposed(?) resist left behind. I guess my next
> question is how do you get really black black on transparent film
> using a laser?

I have had good, high-contrast, results with a laser film from Canada:

  http://screenprinting.asc365.com/index.asp?ID=TT1029

I got about 7:1 contrast - so the clear parts let through 7 times as
much as the black parts.  This is an average reading in visible light,
but the toner is plain black, so I guess it should be the same for the
350 to 380nm UVA light to which Riston MM540 negative acting photoresist
is sensitive.

  http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/31293?var=0&l=1

http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/datasheets/mm500series.pdf


There is a little unevenness (what an odd looking word!) in the black,
depending on the laser printer and exactly how the toner roller puts
toner on the drum.  So the contrast ratio in the lightest parts of the
toner would probably be 5:1 or 4:1 at worst.

I am using Brother laser printers. 600DPI is fine.  I have some 1200 x
1200 DPI Brother printers and they are marginally better.  With 1200 x
1200 I could get 0.005 inch tracks with 0.005 inch
spacings (127 micron).  That was pushing the limits, but the results
were really solid at 0.010 inch (254 micron) which is as small a track
as I would probably want on a PCB.

I wrote more about this in August last year:

  http://tech.groups.yahoo.com/group/Homebrew_PCBs/message/30467?var=0&l=1

Thid laser film is also available from Australia:

  http://myworld.ebay.com.au/printingsupplies2009/

I haven't tried the blackening agent at the Canadian site.  I see no
need for it with my current setup, which involves a reasonably
collimated light source - a 400W 230V halogen lamp.  The Riston I am
using has high contrast.  Ideally I would use a 10 watt UV LED light,
which would not heat up the PCB and phototool to the degree which the
400W lamp does.

  - Robin