DIY PhotoResist?

I would guess PCB is made by gluing foil with the PCB board stuff when it's molded. You could try electroforming on top of blank board, but don't expect nice results, and certainly don't expect a good bond. If you have a vacuum chamber you could deposit copper vapor before electroplating, but somehow I doubt that's any cheaper.

I don't know what photoresist consists of, but I'm sure it's a bitch to cook up at home.

Tim

-- Deep Fryer: A very philosophical monk. Website @

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Huhhhh... I've posted this so times.... 'Try out dry film photoresist..'.. :P mmmm...maybe I should start selling the stuff on here.. :)

You could try out toxic potassium dichromate + a protein. (So I've heard.) But I don't think it's popular.

D from BC

-- but if you offered dry film for sale in modest quantities, you very well could find some takers. Supposedly Injectorall will coat boards for you, too.

I used to coat my own boards with Shipley AZ-111, but that was when I needed enough for other things to buy it by the quart, and a couple quarts wasn't all that expensive. I believe it's now close to $1000 a quart and is sold in 6 quart lots, minimum--though I may be mistaken. But given the time it takes to lay out a board and the cost of the parts to put on it, even paying one of the fast-turn proto shops to make a board for you isn't all that bad. And if you do etch your own, paying something like 30 cents per square inch for top-quality pre- coated double sided board material seems cheap.

$1000.00/qrt !!! Damn might be more expensive than ink jet ink.

For small boards, I use precoated Injectorall boards from Digikey. For larger boards, I wet laminate the dry film onto cheapo surplus boards.

Using keyword 'photoresist' on ebay returns no relevant results. Time to set up shop :) Or figure out why no one else has... :P

D from BC

norland 60 or norlan 61 UV optical cured cement is 16$ a bottle for a ounce or two. start there. They probably have something hackable on their web site.

Steve

These guys have KPR-3 for only $478 US a quart.

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

The classic glop was KPR, Kodak PhotoResist. I still have some around. You'd spin or spray it on some copperclad, bake dry, and expose through a negative. There was a developer which was mostly xylene. It polymerized where UV hit it, making those regions insoluble to the developer.

I think KPR and/or its developer were mildly toxic, so I don't know if they're still on the market. I've seen references to KPR3, maybe the newer generation. Google

It was easy to do clean 8 mil lines/spades with KPR and decent emulsion-down film.

John

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KPR?? Yeccchhhhh!

Sorry, but I'd a lot rather pay the price for some good resist. That could be a personal bias, but I gave up on KPR within, um, microseconds of trying the Azoplate resist. It ended up being a good choice also from the standpoint of what I was doing; the processing took fewer steps with the AZ111 than it would have with KPR. But the world of photoresists has moved on, rather a long ways I suppose, since the days of KPR and AZ111. These days, perhaps Rohm and Haas Photoposit SN66??

Cheers, Tom

Photoresist is cheap as hell to make: egg white for the base and potassium dichromate for photosensitivity. After exposure, use the universal solvent (water) as the developer.

Correct, not "popular" but useable.

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So what's the difference between the various KPRs?

Best regards, Spehro Pefhany

--
"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I studied the chemistry of photoresists with a view to making a homebrew or a cheap'n safe version for the homebrew market. The evolution of photoresists is way to complex to cover in a single post. But their is a book called oddly enough "Photoresists" by Williams which IIRC was published about 1970. Photoresists have moved on a lot from there, as the IC industry has required better and better lithography for IC manufacture. Now the gotcha's wet resist needs to be of a consistent thickness to get consistent exposure times. This is a real PITA for home use. One solution to this is a record player used as the spin on table. The best solution are dry negative resists which are used by the PCB manufacturers. Applying them with a machine made for the process, or wetting the circuit board and then floating a precut out sheet of resist you can do at home. Then the film is rolled onto the board, so that no bubbles get to form. Exposure with an inkjet negative and etching will get you a very nicely made board. If you want very high resolution lines a homebuilt spray etcher is the way to go. There is a Yahoo group devoted to Homebrew.

There are allsorts of tips and techniques in that group

Best of luck

Andrew

Yes, KPR, I used it for many years with good results (Xylene was the 'cheap' developer instead of the real ($$$) stuff. It was very important to get a thin coat, I used to swab it on, as thin as possible, then spin it on a much-modified turntable

Actually, I still have much of the quart bottle I paid (IIRC) $16 for in about 1973. I last used some a year ago, and it still works perfectly!

I'll bet it's not as cheap as surplus PCB stock, I have acquired good stocks that way. Also check out a local PCB house, if nearby, they will generally give you offcuts free, I still operate from a donated boxful from about 10 years ago.