I have agree with Tom on the plain mercury vapor street lamps. they are
cheap, readily available and work great. I use 400W, no reflectors, 400 mm
distance and get 90 seconds exposure on dry film resist. I have heard from
several people about using quartz halogen lamps. Quartz halogen run hot and
put out significant UVA and even some UVC (if not shielded by normal glass),
the UV level depends on the operating temperature. Bulbs that run extra hot
and short lived are better, such as a photographic lamp. You could try
running one of those 12V 80W quartz halogen ceiling lights at say 15V.
Here is some info on dry-film photoresist spectral sensitivity,
http://www.circuitree.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2133,3647,00.htmlStandard 'soda' glass (windows) stops pretty much everything shorter than 350
nm. The sensitivity of dry film resists starts dropping off past this anyhow.
You won't loose much from the glass, Even a thick sheet, say 8 mm.
I tested the effect of glass by doing a 10 step exposure on a sample of dry
film. The effect of 4 mm glass sheet was virtually unmeasurable (passes
greater than 80% of light). probably somewhere around 90% - 95%.
Good work Steve on setting up this forum.
Adam.
Steve Greenfield wrote:
> 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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