I use a similar arangement with two tubes, but they are about 8 inches from
the board, and exposure time is about 5-6 minutes.

The concentration of the sodium hydroxide is also quite important...
I have found that about 5 grams in half a litre of water is about right.
You'll just have to experiment a bit to see what suites your equipment.

Cheers
Anders



At 10:52 1998-05-11 PDT, you wrote:
>Hi all,
>
>I made a UV exposure unit for producing PCB's at the weekend.  It
>consists of 2   8watt tubes inside an old PC case.  I have a photo
>sensitive PCB held behind a glass plate about 1 and a half to two inches
>above the tubes.  The tubes are brand new and are replacements for the
>normal unit you can buy in the shops.
>
>My question is 'how long would be a reasonable time for exposure' ,
>because I tried this out last night with an exposure time of one minute
>and when I was developing it in sodium hydroxide, it appeared to work at
>first but it then took all the photo sensitive layer off.
>
>Any help is appreciated,
>
>Thanks,
>Brian.
>
>