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Just letting you all know how I went. Fantastic success. I have some transparent inkjet sticky label sheets which I printed on so together with the backing they are fairly thick. Yet a used two prints stacked on top of each other to ensure good opacity. I know stacking like this can decrease the trace edge "sharpness" but I aligned them very accuarately and for what I'm doing at present the traces came out very good.
My Kinsten PCB says expose for 60-90 secs (proper exposure lamps) but I did a longer 2 minutes.
Developed with Sodium Metasilicate and at a risk of over developing did a little longer even when all the photo resist appeared to have gone (I had etching problems last time most likely caused by some microscopic thickness of photo resist remaining).
Made up Ammonium Persulphate solution (heated) from several year old crystal stock which has all bound together and needed chopping up. Board etched perfectly in about 5 minutes and no etching on the areas where photoresist remained.
I'm putting this success down to having a much more opaque photo positive film, and using transparency instead of tracing paper. This allowed me to give plenty UV exposure while still protecting the areas that didn't want developing (I may be wrong, just my calculated guesses).
The attempt previous to this one was double stacked laser prints on tracing paper, and not very good success. I'm pretty sure some UV got through the "black" because I did get some spotting etching where it shouldn't be.
What is exciting about this is that despite the good results there is still room for much improvement. With some proper high density opaque screen printing ink, I should be able to use one single sheet of transparency, which will increase the edge sharpness of traces. Then there's also a vacuum system to pull the transparency hard onto the board at every point.
So just another word of thanks to everyone that's gave their help since I joined this forum. Just a few weeks ago I had never made a PCB and now I can make a fairly good one.
Cheers,
Keith.
---In Homebrew_PCBs@yahoogroups.com, <beefyzee@...> wrote:Thanks very much guys.
Cunningfellow, the more I Google and read, the more I hear of people having issues with the lack of opacity from laser printers, and that's why industry used inkjets.
This weekend I'll be doing my first tests with my inkjet made positive transparenies on Kinsten PCB.
I ran some basic paper through my inkjet twice and the alignment was actually very good, at least good enough for the big fat tracks I always try to use as a beginner to this. The hairline width border around the board showed no signs of crossing, but looking close up the edges of the print were not as defined. Might be better on quality transparency and photo print settings.
---In homebrew_pcbs@yahoogroups.com, <andrewm1973@...> wrote:> Keith wrote:> Has anyone ever simply refed an already printed photo> positive transparency to print a second and even a third> time, in order to double/triple the density of the ink, thus> increasing opaqueness.
> <SNIP>
For a laser printer it is only the large black areas that have opacity problems and need over printing.
Don't double print thin traces.
Shrink ground/power planes by a little bit more than your average misalignment.
Only print the ground/power planes on the 2nd/3rd run
Expect an occasional wildly different feed position to ruin a print.
Inkjets (for me at least) don't have an opacity problem.