Clewer,Brian wrote:
> 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.

Try more like two minutes exposure, and don't develop it for as long.
Your developer may also be too strong. Don't heat the developer either
(though it does help to heat the etchant a little, especially if you
don't have a bubble etch bath).

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