I gather that you're using the CNC table to move a board under a UV source, much like a Gerber plotter. Years ago this was called 'direct imaging.' The object was to eliminate photo tools (artwork). I spent a lot of time working with UV lasers and other techniques. They worked, but they were too slow for commercial applications. We had to expose an 18" x 24" board in 30 seconds. Fortunately you don't suffer from that requirement. In the last few years laser diodes that emit at 370 to 375 nm have become available. Great columination, but low power.
You'll need a bright UV source that radiates around 365 nm. There are UV sources intended to be mounted in forced air heating systems to kill microbes, spores, etc. that would be fine for this application. They are continuous duty lamps, but they need LOTS of cooling air. The easiest way to get columniation is to move the lamp further away. You might consider putting a parabolic reflector behind the lamp to increase the intensity. I'd just use a piece of PVC or aluminum pipe, about 18" long, painted black inside. Put your pinhole at one end, and the lamp housing at the other. Make sure you have good light traps to prevent stray UV light from escaping. This is going to be a long exposure and stray light will expose photoresist. You might consider a light shield at the end of the pipe to shield the board. Set the pinhole as close to the board as you possibly can - a couple thousandths of an inch max if you want to do really fine lines.
I'd also consider using a larger pinhole. You're probably going to have to give the photo resist a 10 second exposure. With a .025mm pinhole that will mean a head speed of .0025 mm per second. For a typical small board with 50% of the area exposed you might be looking at 2500 sq mm to expose. You may want to check the math, but I come out with an exposure time a bit longer than a year. If you go with a .125 mm pinhole you get down to 50 hours - still long, but at least reasonable.
----- Original Message -----
From: Cristian C
To: Homebrew_PCBs@yahoogroups.com
Sent: Monday, May 02, 2005 12:49 AM
Subject: [Homebrew_PCBs] collimator help
Anyone knows where to order an UV Collimator?
I'm working to replace the mill on a CNC Milling Machine with a .0254mm UV beam, on presensitivized PCB.
Cristian
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