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Old 20th April 2006, 05:21 PM   #11
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Fairly certain the folks at technics.com will ship to you.
"Ferric chlorite" from crystals? If so, dissolving in the correct amount of water is important for strength. You can control the etch activity with temperature. Some agitation of the etch solution over the board is required to carry away the etched copper from the board.
The ole guy who showed me called this process "payin' yur dues".
Keep on tryin'. Once you get it, the knowledge lasts a lifetime.
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Old 21st April 2006, 04:48 PM   #12
rephil is offline rephil  Europe
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Hi safetyman,

the pic has been drawn using a CAD program (Proteus from Labcenter in UK). The pic has been printed on a transparency suitable to my HP deskjet 5652 (here I use Tartan 707 transparencies). It is printed twice on the same transparency in order to get black 'more black than black'

You should draw such a pic in order to adjust your process.

I cut a board and get a few 10cmX3.5cm small boards from it. Then I do a sandwich with one of the small boards and proceed with the exposure to UV.

Then I proceed as you do with chemicals. I use ammonium (or sodium or potassium) persulfate instead of ferric chloride because it is not colored. This allows me to get simple visual control of the etching process.

2nd part follows.

Regards

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Old 21st April 2006, 05:13 PM   #13
rephil is offline rephil  Europe
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Default 2nd part

Hi safetyman,

I use a small 6X magnifier lens in order to inspect the PCB. If not OK, I do some change in the process and create a new etched small board as before. This until needed.

In order to get info do a google search on : etching pcbs. A lot is available IMO.

A must : download the catalog from www.megauk.co.uk. They are friendly and will cut a big board into smaller one on request. Their DM9001 shear works very fine. A good buy. Don't try to use shears aimed at paper cutting : they can't do it with PCBs.

Take a look at www.electricstuff.co.uk (How to make really good homebrew PCBs) and at www.ladyada.net/resources/inhouseetch.html.

I hope this helps you. Have fun.

Best regards

rephil
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Old 22nd April 2006, 10:37 AM   #14
gerhard is offline gerhard  Germany
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Hi,
I think that the exposure time is about right.

WRT the thin horizontal line: this looks like there was too much distance between the film and the resist. The toner should have direct contact to the photo resist.

I usually make such a sandwich: glass plate - bottom film printed normally - double sided board - top layer film printed mirrored - glass plate. Then I execute some pressure between the glass plates by applying lots of duct tape. 6 mil traces are no problem. (HP Laserjet 6 MP, Avery/Zweckform 3491 "laser film for print master production", Bungard presensitized boards)

The glass attenuates the UV light somewhat; you may need the double or even triple exposure time depending on thickness and material. Make a test board whith a strip of film that you move away inch by inch every 30 seconds.

When making double sided boards, I first mount the bottom film on the bottom glass. Then I surround the location of the board proper with old FR4 material on two or 3 sides. On this I mount the top film. It is easy to align top and bottom in the tru light so that the holes meet and the film stays completely flat. This all takes a lot of adhesive tape.

Then I insert the presensitized board into the poach. Got to be careful here not to scratch the toner. Finally, I add the top glass plate and press the stack together.


The voids in the traces of your board seem to have very sharp edges, so they probably do not result from over-exposure. I speculate that your developper has been prepared just before the development process and still contained NaOH pieces.


... and when preparing developper: First the water, then the NaOH. Play it save.


regards, Gerhard
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Old 22nd April 2006, 06:52 PM   #15
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ace, there's so much truth in your wise words and onwards I plod.

rephil, I got what your drift. I'll definitely look at calibrating once I have the chance.

gerhard, the exposure process was done in a machine that sucks the air out of the compartment thus a vacuum b4 the developing process. Don't think the contact is a problem but will check.

Thanks again guys. Out of town now but when I get back, I'll be trying the next round.

And I'll report back.

Thanks for all the suggestions.
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Old 24th April 2006, 11:25 PM   #16
mfratus is offline mfratus  United States
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Looks to me like you had something splashed on the coated board before exposing it. If these were pre-sensitized boards, they may not have been in good shape. I know of no way to clean them beforehand, but that isn't to say there is no way... just haven't looked into it. The fine lines could be scratches or hair on the mylar pattern or on the board.
I usually look at my boards, then touch up with an indelible marker, a really fine one. I thicken up thin traces and draw circles around pads. Your first board you showed up looked like the right exposure. The etching is critical, though. If etched too long or too strongly, it can eat under the resist.
I've made quite a few using sensitized boards and UV light, but lots of bad ones, too. About 50% yield.
It takes practice, and good materials, clean solutions, known temperatures.

Mike.
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Old 28th April 2006, 01:20 PM   #17
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Default PCB ETCHING

Am Going in the same direction with making PCB 'S .When making the transparency for use with positive resist boards which part of the board is exposed to the UV light, the trace portion or the waste portion??? I did this years ago with the old Kepro stuff and I cant remember which part of the transparency was black!!
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Old 28th April 2006, 02:31 PM   #18
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Default PCB

I had the exact same problem! I swapped to the press 'n' peel option which works very well. You need to make sure the iron is not too hot and don't press hard and this produces some great results?
After all, you can touch up your design with permanant markers.
Good luck,
wotsascott.
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Old 30th April 2006, 06:37 PM   #19
Magura is offline Magura  Denmark
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It is is kinda strange to me that you have problems with photo PCB's. I have made hundreds of photo PCB's, and the only trouble I've ever encountered were related to exposure time. When starting out with a new type of board, I usually make a quick test by exposing a couple of small pieces 60 to 120 seconds, develop them and see what went well. Besides that all you need to do is to make sure your development solution is right and pay attention when developing/etching, which is fairly easily done by visual check.

Magura
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Old 16th May 2006, 08:00 AM   #20
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press 'n' peel is really the way to go. very precise and a cinch to fix up with a permanent marker, as someone said previously. here are some boards done with pnp, see for yourself

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