Hi Chris,
I guess one question to ask is why you decided to go negative resist instead of positive resist? I have been using positive resist with pre-coated boards for several years and only once had a failure. That one failure was due either to too short an exposure or too weak a developer. I increased the concentration of potassium hydroxide in my developer, and got a decent, but not great board. I hang out on this list just in case someone has a discovery that works better. The only problem with pre-coated boards, besides cost, is the limited choice in copper thickness and board thickness that is available.
My printer is an HP970Cse inkjet. It's now getting old, but works well, and I have not had any problem with UV leakage where I don't want it. I use maximum resolution and either regular or heavy on the ink flow, which is determined at the time of use by simply printing at each density and seeing which one looks better on the transparency. It does not waste any of the pre-coated boards.
One detail that may be important: I use a "premium" OHP transparency film made by Pictorico. The film is available at my local PC store. It has an extremely fine ceramic coating to aid retention of the ink. One can barely tell the coated (print) side from the non-coated side. The print side is slightly duller in reflected light. There are probably other films out there that work just as well, and I have not done any side-by-side comparisons -- just reporting what works for me. As for the image density, I can say it is fairly dense. There are no clear pinholes, but one can see some light through the black areas. The ink tends to form a darker ridge (maybe just an artifact of refraction) right at the interface between clear and black areas, which may help to give the sharp edges one gets with the process.
John
----- Original Message -----
From: lcdpublishing
To: Homebrew_PCBs@yahoogroups.com
Sent: Sunday, May 20, 2007 8:31 AM
Subject: [Homebrew_PCBs] Photo-resist etching questions....
Hi guys,
I have almost given up on direct ink-jet resist and on "plotting"
with Staedtler pens using the CNC machine, and I am about to abandon
toner transfer. Only problem with toner transfer is the "scaling"
issues either through the printer or from the paper not being stable
which causes problem with CNC drilling.
Anyway, I ordered up some negative type resist chemical, the
developer, a lamp, and an exposure frame. I am not expecting this
to go "perfectly" either, but am hoping to have a bit less
frustration in other areas.
I am thinking the best accuracy I can get when printing is to use an
ink jet printer (I have Epson R220 and Epson CX6600). I have a PDF
editor program that allows me to edit trace colors and back ground
colors so that I can make negatives so that shouldn't be a problem.
The first "problem" I suspect I will run into is getting enough
density on the transparency to make sure the "black" areas are dense
enough to block out the UV exposure lamp where needed. Has anyone
run into this issue and how do you deal with it?
Any other pointers would be greatly appreciated as well as this is
my first time for "photo-processing".
Thanks
Chris
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