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