--- In
Homebrew_PCBs@yahoogroups.com, James Bishop <bishopaj@...> wrote:
>
> I found that an old overhead projector worked. It needs to have a mercury
> lamp (they are the more 'modern' version, with whiter light, mine is 3M
> brand). About 1 minute exposed my boards pretty well.
>
> I used it because it has a convenient flat glass surface, and the light
> seems to be evenly distributed, and it exposes quickly. I'm not totally sure
> about the 'collimation' or angle of the light, but it seemed to work fine
> for my purposes and i used it for a 0.5mm pitch chip.
>
> If I was going to build an exposure box, I would consider re-purposing on
> old overhead projector, or even a broken digital projector - I think those
> have mercury lamps.
>
Those are UHP mercury, or occasionally metal halide lamps. The lamps themselves are expensive, most are over $100 for a replacement bulb. It would work fine, but you can get bug zapper fluorescent tubes pretty inexpensively and they will work off the ballast and starter from one of those $10 under cabinet lights. If you want to use a mercury lamp, just buy a cheap yard light if you can still find the mercury ones. The manufacture of mercury ballasts was banned in the US but they are still plentiful. You'll want a clear lamp too, the coated ones put out much less UV. Bug zapper fluorescent tube is the best choice though IMO, you can get them at any hardware store or on ebay. Sometimes they're also called unfiltered blacklights, the suffix will be /BL as opposed to /BLB of the traditional dark purple blacklight tubes.