Homebrew PCBs

Alberto Colorado wrote: 
> I always wanted to know the formula of "fotorresist" or something
> similar to make PCBs. 


Curiosity can be a great thing but in this case practical results are
only for chemists, or people with number of equivalent readings as a
chemistry degree. (and access to a wide range of chemicals)

One short/light introduction to various types of photoresists can be
read on (page 4 and forward)
http://www.htp.ch/lib/pdf/Liquid%20resist%20for%20PCM.pdf

Your example don't seem to be from any known/working photoresist. But if
it would work will be a positive acting one. Negative acting
photoresists are preferred. Dry film is the most used type and not
liquid photoimaginable resists (LPI). 
Riston from Dupont and Dynachem's Laminar were the first dry films on
the market. The biggest supplier actually is Eternal Chemical Company
(Taiwan) who bought Shipley Company dryfilm business.
Start points for your curiosity:
US3469982 PROCESS FOR MAKING PHOTORESISTS (first dupont dryfilm patent)
US4295948 Photocurable adhesive from acrylic acid, acrylamide,
dimethylaminoethyl methacrylate, benzophenone and methyl ethyl ketone
(some other dry film example)
http://atlas.cc.itu.edu.tr/~yusuf/PDF/288.pdf (see how related chemistry
looks) 
http://books.google.pt/books?id=A-TC5tGGBz8C&pg=PA151 (dry film history
or something like it, and lots of related examples in previous chapters)

If you wish to coat your own boards with positive acting resist the
easiest to buy is Diazo naphto quinone (DNQ) type, is the thing you can
get for serigraph screens locally or from eBay, its priced at about
30eur for base, sensitizer and remover here. But don't know if anyone
tried it on pcb. This Brazilians uses a similar thing:
http://www.inape.org.br/circuito.html
http://eletronicaoob.blogspot.com/2010/02/tutorial-criando-pcb-facil-e-com-alta.html ( se Portugu�s n�o for um problema para ti ).

But just buy the thing. There is so much in the evolution history of dry
film. Going from 50% benzophenone and MMA solvent working dryfilm to <5%
benzophenone and very specific acrylates semi-aqueous working dry film
of todays. And LPI aqueous resists are a really evolute product. I am
sure you won't be able to mix anything similar.


Saludos
Sim�o