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.