Dear Leon, You are definitively using the wrong type of tubes. Short wavelength UV, used for erasing EPROM's is not suitable for photosensitive PCB's. Use for photosensitive PCB's tubes with the (Philips) color 05, with long wavelength UV glass plates are no problem. With a distance of 2 cm of the tubes to the PCB exposure time is 1-2 minutes, dependant of the transparency of the masks. expose as long as possible, dependant of the density of he print of the mask. I use calque drawing paper printed with a Deskjet 870 printer, and expose 90 seconds for optimum result. Never use the concentration of the developer to shorten exposure time. Bad PCB's will be the result. Developing time must be about three minutes, a 1% sodium hydroxide solution, always fresh made will work in most cases. Look at http://www.thinktink.com for excellent information. Leo van Loon sbb.simpeltronics@tip.nl -----Oorspronkelijk bericht----- Van: Leon Heller Aan: PICLIST@MITVMA.MIT.EDU Datum: dinsdag 12 mei 1998 7:00 Onderwerp: Re: PCB Exposure Time. >In message <35573B63@tarkus>, "Clewer,Brian" > writes >>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. > >You need to experiment - there are lots of variables, such as the >distance of the PCB from the tubes, the strength of the developer, >temperature, etc. I use perspex rather than glass in my UV exposure unit >(a modified cardboard box), and use a 6 min. exposure for a >transparency, and 7 min. for a print on tracing paper. Sodium >metasilicate has a lot more latitude than NaOH, when developing the >resist. I heat the developed PCB in the oven on a low setting to harden >the resist, prior to etching. I often use spray-on resist - if I cock >things up I just strip off the resist and try again. > >Leon >-- >Leon Heller: leon@lfheller.demon.co.uk http://www.lfheller.demon.co.uk >Amateur Radio Callsign G1HSM Tel: +44 (0) 118 947 1424 >See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850 >DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system. > >