Homebrew PCBs

scratch_6057 wrote:
> 
> 
> Could those of you who are using Dry Film Photoresist
> please give any recommendations as to what you are
> using, results, and sources for small quanity supplies in
> the states?
> 
> I have a Xerox 9" Laminator that I have successfully
> Passed 0.060 board thru, so that's not a problem.
> Markings on the temperature controller go up to
> 125C / 257F.
> 
> I am aware of "Think N Tinker" and "Micro-Mark"
> in addition I have found quite a few suppliers of
> Dry Film Photoresist for "Intaglio" (SP?) print plate
> making.
> 
> It looks as if what I've found so far is "Negative Acting"
> and if I'm thinking correctly then a transparency for that
> would require a LOT of ink / toner?
> Any "Positive Acting" resist films available?
> 
> Looking to laminate my own FR4 board and probably do some
> etching of Brass / Copper sheet.
> 
> Thanks

The problem I found with dry film is getting your hands on the stuff 
without buying 25 life times supply of it. Well thats my experience in 
Australia. Anyway, if you have some then this is what I do.

For small PCB that are under 100x100mm you can quite easily use the 
'cold wet lamination' method. You scrub, clean copper as normal until no 
water beading. Wet the surface with cold water (< 30\ufffdC) and place 
horizontal on bench. Next to it you cut film to size, and peal away the 
protective polyethylene cover (not the polyester side covering). 
Carefully hold it by your finger tips at one edge, and slowly lay down 
the film over the copper, starting from one corner. The cold water will 
not allow the film to adhere for the first 30 seconds or so and gives 
you time to correctly position the film. Once the film is in position, 
you now press out the water layer with a smooth rubber rolling pin or 
cloth. This takes some practice because wrinkles are a problem. Once the 
film is tightly lay down wrinkle free over the board you now finalize 
the lamination by heat. You can either wave a hot air gun (<150\ufffdC air) 
or dip in some hot water. The board should be about 60\ufffdC or so. This 
causes the small amounts of the photoresist to dissolve with remaining 
water film and fully bonds to the copper. Dry off water, cool and its 
ready to expose.

notes:

Larger boards become increasingly difficult to remove wrinkles.