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Author Topic: Ciruit board etching problem, my tale of woe  (Read 1353 times)
KE6WNH
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« on: August 01, 2009, 08:01:23 AM »

OK, so I bought a roll of that MG Chemicals photosensitive resist film, along with the exposure lamp and a bottle of developer. I have hardly any darkroom experience, but I *did* hardwire a wall lantern onto my garage wall and put a red bulb in it for the purpose. Well, I had no problem whatsoever exposing & developing the film... however, the problem lies with the film itself. The emulsion layer comes sandwiched between 2 layers of thin clear plastic---just try to find a corner and peel the stuff off under a red bulb!---and it has to be pressed onto the copper circuit board before exposure.

Try as I might, I could not get that emulsion to stick to every little blivet of that copper, because there were always specks that caused bubbles. Worse, the emulsion which DID stick to the board tended to pucker and work loose during developing and rinsing. I tried it twice, and neither time yielded a usable PC board. Never got to the ferric chloride stage.

Conclusion: film-type photo resist is junk, don't buy it. Fortunately, Ocean State Electronics of Rhode Island sells a spray-on liquid photo resist emulsion on page 54 of their catalog, and it looks much more economical. $20 buys you a roll of film that comes out to 720 square inches (1 ft x 5 ft), but $10 buys you a spray bottle of emulsion which is said to cover 1700 square inches of board... so go figure. The only thing OSE doesn't sell is a lightproof box for drying the sprayed boards, but big deal, you can always make one. I made mine out of black acrylic plastic which I glued together with chloroform, then used black felt for the vent holes.
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N3OX
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« Reply #1 on: August 01, 2009, 08:51:14 AM »

I found that the "toner transfer" method with a laser printer worked pretty well for me on my first try.

http://tinyurl.com/la22f3
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KE6WNH
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Posts: 126




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« Reply #2 on: August 01, 2009, 09:22:50 AM »

You mean pre-sensitized boards? TTBOMK PC board stock won't fit in a laser printer.
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W5FYI
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« Reply #3 on: August 01, 2009, 09:43:01 AM »

N3OX is talking about printing the etch pattern onto paper in a regular laser printer, in reverse, then placing the paper ink side against the bare copper of the pcb and using a hot iron to press the ink onto the copper. Everything can be done in daylight.

The right type of paper insures success. While regular bond copy paper will work for many projects, others swear by dextrin-coated papers, used x-ray film, specialty plastic sheets, and even Sunday supplement magazine pages.

One paper that seems to work well is Pulsar paper. See www.pulsarprofx.com/PCBfx/main_site/pages/products/transfer_paper/transfer_paper.html.

Also check out the sponge method of etching pcb. www.instructables.com/id/Sponge-Ferric-Chloride-Method-Etch-Circuit-Bo/.

GL
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KB1LKR
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« Reply #4 on: August 01, 2009, 01:21:48 PM »

If your photo-resist is only blue & UV sensitive (likely) not orthochromatic (sensitized into the to green and yellow too, but not as far as red), a standard yellow filtered safe-light, e.g. Kodak/Wratten "OC" will be much easier to see by than a red safe-light. A Kodak "OA" (yellow-green) may even be okay.  

Laser print toner thermal transfer method is hard to beat for ease these days though.
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KE6WNH
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« Reply #5 on: August 01, 2009, 04:23:28 PM »

I'll wait until the spray and developer arrive, and if I can't get those to work then I'll look into buying the darkroom-less dextrin paper system.

Another idea: KE6VRK once dealt with an art studio which had a gicle' reproduction machine, essentially a large, expensive plotter which uses cartridges of oil or acrylic paints instead of ink or toner. Too bad someone hasn't invented a smaller, similar device for under $100... I'd just plug it into my Mac's USB and switch it on, and it would plot out any B&W jpg design I wanted, in acid-resist ink made from alcohol and rosin. Just an idea.
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W5FYI
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« Reply #6 on: August 01, 2009, 06:58:04 PM »

"Too bad someone hasn't invented a smaller, similar device for under $100... " Some years ago QST printed an article where a ham used an HP 7475A pen plotter to do that. He modified the standard pen holders to hold Stabil permanent ink pens and drew the design right onto the copper pcb. I think he said his plotter was modified to work through an IBM PC, so it might be worth the time to look through the archives. At one time these surplus plotters were available in the $20 price range (I think). Maybe someone else remembers them.

There's also plans for a do-it-yourself desk milling machine on www.instructables.com. It seems that something like it could be used to grind the copper off a copper board, or modified to hold a Stabil or Sharpie pen to draw traces directly on the copper.
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AB9LZ
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« Reply #7 on: August 02, 2009, 04:18:29 AM »

The toner transfer method is great, I've done over two dozen boards that way. Clay coated papers works best, the whacker pages torn from a qst are perfect : )

Most of my new projects have been with surface mount stuff, I've found that a mototool with an engraving burr and a steel straightedge are much better than etching, allowing for each section of the circuit to be put down and tested before moving onto the next.

73 m/4
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KC9PMG
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« Reply #8 on: August 02, 2009, 08:17:31 PM »

gicle' = Inkjet printer nowadays, usually a high end large format with pigmented inks. I wonder if that would work. Some of the larger models can take fairly thick materials in sheets. It would almost be too easy.

If the ink works as etching, you could probably pick up an older used Epson large format for a few hundred. Older models without the extra shades of color and newer inks (not needed for this use) are generally unwanted paper weights in the photo business now. Of course, getting a 6'wide 300 pound printer home would also be a problem.
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K3AN
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« Reply #9 on: August 06, 2009, 07:37:28 PM »

Express PCB (www.expresspcb.com) is a WHOLE lot easier. Their layout software is free and you can quickly get double-sided boards with plated-through holes for a pretty reasonable price.

http://www.eham.net/articles/16958
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KE6WNH
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Posts: 126




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« Reply #10 on: August 23, 2009, 11:55:59 AM »

Well, screw this... I tried 3 different methods, and none of 'em worked. Anyone know a good place on L.A.'s west side where I can job out the artwork cheap?
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VK2TIL
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« Reply #11 on: August 23, 2009, 11:19:25 PM »

I was once in love with PCBs but no longer.

I have used the toner-transfer method mentioned by 'OX with success; there are some good tips here;

http://www.users.on.net/~endsodds/pcb.htm

Although I am not the person in the QST article (that I have never seen) mentioned by'FYI (I wrote an article for the now-extinct VK magazine Radio & Communications), I developed a "plotter" method.  I used a HP7475 and a (larger) HP7550; I used Stadtler 313 O/H transparency pens.  

Plotting was direct to the copper stock.  Here's a picture;



This was a narrow/wide/bypass audio filter for a DC receiver I think; I have done much more complex boards.

Design was in EasyTrax which plots via EasyPlot.

I have never used photo-sensitive stock so I can't comment.

I found my work becoming more & more "experimental" and PCBs are too restrictive; I now use "ugly" for RF circuits and "Manhattan" for such things as audio and power supplies.

I use "cut & peel" for SMD boards eg microstrip; I have a MiniMill and I use an engraving cutter to produce SMD boards eg return loss bridges or "adaptors" for SMD ICs.

These are simple circuits; where design, test & modification is required I use "ugly" or "Manhattan".

I am in the middle of moving house; the two "spare" plotters went in the dumpster yesterday and the one shown in the above photo will probably follow in a few days!!

I can do something in "ugly" or "Manhattan" in a fraction of the time it takes to design, plot and etch a PCB.
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W0BTU
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« Reply #12 on: August 30, 2009, 10:56:23 PM »

"OK, so I bought a roll of that MG Chemicals photosensitive resist film,..."

I didn\'t know they had film that you could apply to plain copper boards. Have you tried their boards with photo resist already applied?

We\'ve had great success with MG Chemicals\' pre-sensitized boards. The kind that already has the photo resist already applied, and you peel off the white plastic just before you expose it under the fluorescent lamps.

And we\'ve only used plain incandescent lamps, not the red safelight. You just have to be careful not to expose it too long.

For us and our equipment (iron, photocopier), the MG Chemicals stuff words far better than the Toner Transfer system for very fine traces.

73 Mike
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KE6WNH
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Posts: 126




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« Reply #13 on: August 31, 2009, 04:12:37 PM »

Thanks but no thanks. I found an outfit in Long Beach where I can job them out and let someone else deal with the hassles of transfers.
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