Homebrew PCBs

Don't stop! It is good to have you here.

So can you tell us, is my memory faulty or does it only require
near UV to expose PCB photoresist? 

I used to use a plant grow light incandescent floodlight bulb,
150W. I don't recall the exposure times but they weren't terribly
long or terribly short. IE, somewhere between 30 seconds and 5
minutes is the closest I can remember, with the bulb about 1 foot
away and the film/PCB held under glass. The film was mylar with a
variety of things on it, drafting tape, those rub-on pads from
Radio Shack, paint, copier toner, and anything else opaque.

What about those inexpensive 150W quartz halogen shoplights? Or are
they built to block too much of the UV?

An idea I had long ago but never tried out- use a bare xenon
flashtube, calibrate by number of flashes. Use one of the larger
tubes rather than the tiny ones in modern cameras. Easy to power it
with AC and to set up a programmable counter circuit to flash it. A
PIC or even just a 555 timer that enables flashing.

It is my understanding (could be wrong) that a fair amount of UV
(low UV, anyway) gets through the tube and that the plastic cover
on the flash serves two purposes, color balance and UV block.

Someone said standard window glass blocks some UV. What types of
glass block less UV? What percentage is blocked? Is it just a
matter of using a thinner sheet of glass to hold the artwork to the
PCB?

Steve Greenfield

--- twb8899 <twb8899@...> wrote:
> I'm new here but find this list very interesting. A good UV
> lighting 
> system is the plain old mercury vapor lamps. 
-snip lots of good stuff-
> I do enjoy the hobby side of this technology and would be willing
> to 
> help out with ideas and maybe some equipment projects that could
> be 
> posted on this list. If there is any interest let me know. Sorry 
> about the long post... sometimes I get going and don't know when
> to 
> stop!!! Hope I can help out.
> 
> Tom 


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