Homebrew PCBs

Hello Stefan,

18. May 2003, 21:20:47, you wrote:

ST> it is nice to see this here.
ST> i have also seen this effect of stronger exposure in the center.
ST> i have used a setup with distance about the same as pcb with.
ST> i used a nitraphot 200W photo exposure lamp.

ST> i think this gets only visible if you have the exposure time on the too short edge.
ST> i never again have seen this error (but i increased distance, made smaller pcb, and had to increase 
ST> exposure time).

ST> the nitraphot is also no good lamp for exposure.

ST> but there is a reason for using a point light source:
ST> if you use some fluorescent tubes you have a wide area of light emitting surface.
ST> if you look at one point at the film/pcb you can see different lightbeams fall on it, from different 
ST> angles. if your film does not perfectly lie down on the pcb it will make a "washed out" edge there. this 
ST> would make the tracks smaller. each pcb has some sort of uneven surface. i think this also depends on 
ST> your overall setup how strong this effect is (and on pcb quality).

ST> a friend of mine uses because of this effect a setup with a daylight halogene bulb.
ST> this bulb is relatively cheap (75eur) and works directly from mains.
ST> but you would need a fan with this, it gets very hot.

    For  EUR 75.00 you can make more than one exposure unit that I described
    in reply on one other post in this thread.

    2 (two) UV-A fluorescent lamps made by Philips:               EUR  5.00
    2 (two) pairs of lamp holders with integrated starter holder: EUR  1.50
    2 (two) 20W fluo ballasts:                                    EUR  5.00
    Some wires for interconnecting, some MDF for box, mains cable,
    homebrew countown timer with PIC microcontroller:             EUR 30.00
                                                                  =========
                                                          TOTAL:  EUR 41.50

    Don't  hold  me for all the prices that I've mentioned because I can not
    dig  through  all  my sent messages where (on this forum) I gave all the
    prices for the stuff that I've bought.

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