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Photo PCB chems

Hi, a few quick questions please.

  1. Positive photoresist aerosol is exceedingly hard to find. It looks like lots of places carried it in the past, but now nobody does. Are there any sources left? Liquid would also work but please, no
55-gallon drums. :)

  1. Positive developer is commonly dilute solution of sodium hydroxide. Will equal parts potassium hydroxide also work?

  2. During exposure, it is said that faster exposure time yields better resolution. Is this necessarily true?

Thanks.

Reply to
Mark Jones
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Electrolube makes it, but it doesn't work very well since they changed the formula. Seno makes a liquid resist in a wipe-on applicator. That works quite well.

Probably, but NaOH is easier to get hold of.

Can't see why.

Leon

Reply to
Leon Heller

I read in sci.electronics.design that Leon Heller wrote (in ) about 'Photo PCB chems', on Sat, 18 Dec 2004:

Vibration.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

Surely the effect of vibration would be minimal, even if there was any present. There will be virtually no relative movement between the artwork and the PCB material, especially if a foam rubber pressure pad or vacuum is used to keep the two in contact.

Leon

Reply to
Leon Heller

I read in sci.electronics.design that Leon Heller wrote (in ) about 'Photo PCB chems', on Sat, 18 Dec 2004:

If there is any vibration, it will find a way of making the print fuzzy. Murphy's Law.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

Don't waste your time with it. Use precoated board.

Use silicate based developer - MUCH less fussy about concentration and temp and almost impossible to over-develop.

Not really.

see

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for more info on making good quality homebrew PCBs

Reply to
Mike Harrison

Thanks for the replies. Being the typical "frugal engineer type" I figured rolling my own would save some bucks and give more freedom for the oddball one-off fab. But since sprays are crap and the only bottle of Seno I could find was 70 euros (and on the other side of the pond), presensitized boards are looking better and better.

Hmm, interesting. Why isn't this developer more popular? It seems perfect.

I found one source of sodium silicate solution on ebay, one pint for $13 at

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or even better, one gallon for $11 at
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I have a pound of potassium hydroxide. I'm rusty with chemistry, will that work in place of sodium hydroxide in the silicate developer mix? Or should I ask on sci.chemistry.

That's a good page indeed, thanks.

Reply to
Mark Jones

I read in sci.electronics.design that Mark Jones wrote (in ) about 'Photo PCB chems', on Sun, 19 Dec 2004:

Yes, it will work. You need more of it, because potassium has heavier atoms. Think 39/23. But you might see if you could sell it on Ebay. I think it's quite a lot more costly than sodium hydroxide, which is an industrial product.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk
Reply to
John Woodgate

Do you have a full recipe for sodium silicate based developer? I'm curious about the chemistry involved. Anyway, you should be able to use the potassium hydroxide, just use 56/40 = 1.4 times as much by weight to get the same hydroxide concentration.

-- Regards, Carl Ijames carl.ijames at verizon.net

Reply to
Carl Ijames

Yes the notes and formula for the developer can be found at the website which Mike gave:

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It looks like 560g of potassium hydroxide would work, although I suppose a little experimenting is in order. (Thanks for refreshing my memory.) eBay is a surprisingly great place to find chemicals. Once I bought 2 pounds of KOH crystals for soap-making... $20! Some places charge an arm and a leg for chemicals, it pays to shop around and consider other sources. :)

-M

Reply to
Mark Jones

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