UV light box - energy saver bulbs

[manie]

I have finally built a light box. It has five 11W energy saver "warm white" fluoro bulbs.
The bulbs are right alongside each other (almost touching one another) and covers
a 250mm area length wise. Distance to the board will be about 100mm from the bulbs.
I will expose pre-sensitised board through 90gsm tracing paper.

Here is the inevitable question: approximately how long for the exposure ?

I have read somewhere over exposure is better as development is key, any comments ?

I have done a number of boards using a 120W incandescent bulb (black light but bulb) before
where the exposure was at +- 200mm for +- 12 minutes, through transparency sheet.
Now the UV light source has changed.

Comments and ideas welcome. I will post a photo as soon as I have one........

 

[JimPerry]

Get an opaque sheet and move it along a test board a cm or so each minute (exposing more and more test pattern) then you can see from the final exposure what has worked best and time it was exposed

 

[geoff07]

It depends on the board you use, and the form of the transparency (hence the test suggested above). In my case I have four Blacklight 350 tubes in a lightbox, and use 6 mins on rev-ed board using transparencies, and 9 mins when using plain paper laser print/olive oil

 

[Dippy]

Hi Manie.
I would have thought it would be quicker to chop up and expose some 1" squares of board than waiting for a complete guess

I'll serve the first ball in the ping-pong.
1. Do you have sheet of glass?
2. If so, how thick?
3. Do all CFLs leak the same amount of UV?
4. What make of board?
5. What make of etchant? (Please don't say it's the cheapest stuff off Ebay )


When I built my home-made box I used proper UV tubes and used a strip of Board and masked it and moved the mask along.
This gave me exposures of 1 to 10 minutes in 30 second increments.

Comments.
I found that using OHP transparent film resulted in half the exposure time compared to 80 (eighty) gsm tracing paper.
I also found that tracing paper shrunk slightly if laser printed - messing some pitch/spaces.
A proper UV box with transparent film with Fotoboard will take about 1 or 2 minutes.
Yours might take 10 minutes. Spend an hour hour experimenting. It's so much easier as you have quite a few variables.
Good luck.

(Oh, the others beat me to it. )

 

[manie]

Just the answer I did not want......................................... but alas................................. I will test with a board but have decided to stay with transparency film..................... at least I know that it works. I have read ((somewhere !! )) that OVER exposure is better, sounds about right as the developer will REMOVE the exposed parts of the board. Your views appreciated.

Edit: Dippy, no, I don't have glass to penetrate with light. Board is a German made one which I have interchanged with RevEd board in the past without problems. CFL's are same make and brand and wattage so presume leakage to be the same. Etchant is Hydrochloric Acid and H2O2...........

 

[Pongo]

I often see used letter/A4 size flat bed scanners for sale very cheaply ($10 or so). I was thinking it would be a nice project to mount an array of UV LED's on the scanning bar and hook up a picaxe to drive the stepper motor...