I have constructed an UV light box using the innards of a commercially available finger nail drying unit consisting of 4* 9w tubes. (should be more than enough). I have had very poor results in exposing both pre coated and DIY board. My question is –
Is 10mm thick polycarbonate too thick to transmit sufficient UV or should I be using Acrylic sheet or glass?
Electronic – Clear material for UV Box
pcb-fabrication
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Best Answer
Polycarbonate is almost perfectly opaque to UV, so it's no wonder your setup isn't working. You can get special UV Transparent (UVT) plexiglass, which will gain you energy in the 300 - 400 nm (long-wave). http://www.plasticgenius.com/2011/05/infrared-and-ultraviolet-transmission.html
You really need to find a data sheet for your resist, and see what wavelengths are required.
I would recommend that you don't use a plate for support of your board. Rather, make an adjustable framework which will just contact the board corners, and support the board that way.
And I agree that I'm not being helpful, but I can't resist (get it?) pointing out that sapphire will work excellently for your application. http://www.valleydesign.com/sapppic.htm