Homebrew_PCBs

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.

I read yesterday about someone modifying his laser so the paper always fed in the same position. As far as my inkjet goes I have no idea what the system is that senses the paper edges, how accurate that sensing is, and how accurate the paper positioning is once it is sensed.

Taking this one step further, has anyone made a cnc plotter style printer with an inkjet. This way the paper could just be fixed in position and could be printed on several times (easier said than done I bet).

On 06 Nov 2013 00:34:37 -0800, you 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.
>
> I read yesterday about someone modifying his laser so the paper always fed in the same position. As far as my inkjet goes I have no idea what the system is that senses the paper edges, how accurate that sensing is, and how accurate the paper positioning is once it is sensed.
>
> Taking this one step further, has anyone made a cnc plotter style printer with an inkjet. This way the paper could just be fixed in position and could be printed on several times (easier said than done I bet).

A bit of ancient history on HP "grit wheel" pen plotters.

There was an article in the HP Journal about paper positioning. IIRC they
stated that the drive wheels pinched the paper quite firmly and impressed
the grit wheel pattern into the paper on the first couple of passes.
Note that the plotters ran the paper back and forth several times before
plotting began. The paper then had a strong tendency to run in the
pattern impressed in the paper for the duration of the job. Once the
paper was ejected all bets were off; there was no hope of regaining the
previous alignment. Far as I know there is nothing like this in
laser printers. They are designed to put toner in approximately the
right place in a single pass. By approximately I mean close enough that the
customer won't notice any shifts from sheet to sheet. In general, they
were never designed as high precision devices; just "good enough" for consumers.


Keith Bowers WB4LSJ- Thomasville, NC

> 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.

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.

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.