Homebrew PCBs

> I've never used pre-coated positive photoresist boards so I cannot 
> comment. Does anyone know how this resists is applied, since I don't 
> think dry film positive resists exist. All the positive resists I've 
> come across are in liquid solvent.
> 
> I've use the old spray on Electrolube PRP photoresist , and all I can 
> say is its a pita to use compared to negative dry film. Even when you do 
> manage to get a uniform, contaminate free, well adhering coating, the 
> stuff is lot less forgiving in the developer and exposure time compared 
> to negative dry film.
> 
> Professional PCB manufactures exclusively use negative dry film 
> photoresist. It must be economical overall, weather that's because it is 
> easier to process with simple equipment or lower bulk material cost.
>

I use the M G Chemicals 600 series boards normally the 630 8" x 12" this is positive resist.  I have had good results in using them.  One of my boards is pictured on the home page of this group.  Sorry I do not know off hand cost compared to doing neg. dry film.  I have been thinking about trying out the Neg. Dry Film resist.  M G Chemicals is now offering the Dry Film resist in small quantity, 5 ft x 12". Mouser carries it but does not seem to keep a lot of it in stock and list a 2 week lead time for it.  

I do not recommend trying to use the DIY positive resist liquid.  It can and does work but it is a real pain to use, I used it back some 17 years ago.

www.mouser.com is the best source that I have found for the M G Chemicals products.

Ben