Homebrew PCBs

Hello bjeff65,

18. May 2003, 21:01:39, you wrote:
(my comments mixed)


b> So I've decided to put it in the form of a question:

b> If you needed to put together a positive photoresist exposure setup
b> for small PCBs (no bigger than 4" x 6") and your only option are from
b> the typical home improvement store/department (think Home Depot,
b> Lowe's, Walmart, etc.)
b> what would you choose and why?

b> To assist in your answer I'll list some of the options that I've seen:

b> * Standard incandecents
   I do not recommend.

b> * Standard/Daylight flourescents.
   I do not recommend.
   
b> * Black light incandecents
b> * Black light flourescents
   These may work.
   
b> * Plant grow light incandecents/flourescents
   Never tried.
   
b> * Halogen 
b> * Floods of all types.
b> * Compact flourescents
b> * Germicidal flourescents (not really an option, but interested in
b> comments)
   Never use them if you are not wearing protective googles that absorb UV-C
   spectrum

   I can not remember at the moment for the good link discusing the spectral
   sensitivity of the photo resists, but all the informations that I've read
   are  stating  that the max. sensitivity is around 340 nm, or UV-A part of
   spectrum  (under  which  you can get some tan without the burns caused by
   UV-B). UV-C, from germicidal lamps, can cause the irrecoverable damage to
   your eyes, so stay as far as possible from them (unless you need to erase
   some UV-EPROMS).
   
   My typical setup is as follows:
   *  Two  fluorescent UV lamps (Philips) that are declared to have the peak
      radiation  value  around  340  nm, placed in the wooden box, cca 11 cm
      apart, with homebrew reflectors.
   *  Exposure  time (determined with the 21 step Stoufer wedge) from 20 cm
      distance: 5 min.
   *  I'm  always using presensitized (spelling?) boards that I'm obtaining
      in the local electronic shop.
   *  Developer: 7-10 gm/l Lye in pelets.
   *  Developing time cca. 2 min.
   *  Etchant: Fe3Cl solution
   *  Developing  tank:  homebrew one (similar to the Techno-Isel) vertical
      with  heater  and air bubbler (porous teflon tube, often used for fish
      tanks - made in Taiwan)
   *  Etching time cca. 10-15 minutes

   For typical design for exposing unit, best is to visit:
   www.thinktink.com  , but my exposing unit is without colimating grid, and
   I'm  able to produce the 8/8 boards if needed be. The Fluorescents can be
   easily  obtained from local Philips or Osram rep. All ypu have to ask are
   the fluo's for the solarium's.

   And  for  the  transparencies, I'm using services from one graphic design
   buro,  where  the owner is a friend of mine, and all my artworks are made
   on thye graphical film, directly from the PostScript files.





-- 
 Best Regards,
 Zoran
 mailto:zasto@...
 www.zas-elmed.co.yu