Also, remember window soda glass shuts off anything below 270nm so that
includes _all_ UVB. I haven't done side by side comparisons between the
various HID MV lamps, but I do know that standard phosphorised MV "white
dulux" works pretty well for photoresist. Might be better to get a clear
MV or the more expensive Philips 125W MV blacklight. Clear MV bulbs may
be available in the electrical section at supermarkets in the USA, but
here in Australia, clear bulbs are rare as hens teeth. I was forced to
buy a bulb with the phosphor coated.
As now everyone seems to be aware that photoresist are primarily
sensitivity to UVA, then buying specialized UV MV lamps will only waste
your money.
See figure 1 in,
http://www2.dupont.com/Imaging_Materials/en_US/assets/downloads/tech_bulletins/tb0169.pdfMy setup parameters are:
Lamp: 400W "dulux white" MV HID bulb,
Distance to PCB = 300mm
Materials in light: 3mm windows glass + 0.2mm inkjet Epson transparency film
Photoresist: "dry film" negative
Exposure time: 80 to 120 seconds
I would recommend 250W MV, as more suitable size for hobby work.
william.kroyer@... wrote:
> So basically UVB is useless for photoresist and it's UVA output that's key? Wouldn't
> a full spectrum plant bulb work fairly well then? If I recall most put out a fair amount of UVA
> and fairly cost effective.
>
> Andrew wrote:
>
>
>
> Yes the mecury vapour lamps work fine for
> PCB resist. Most expensive comercial
> machines use them I think.
>
> They also (as others have pointed out) need
> to be run for a while to be up to temprature.
>
> This means you either need to have some kind
> of shutter to expose the PCB or as someone
> else said (can't remeber who or when) you can
> pre-heat them at a lower voltage and then up
> the power for the exposure.
>
> The light from them is also more like a point
> source. This has good and bad points.
>
> I good point is that you can more easily
> collimate the rays. Bad point (as Leon-H
> pointed out) you need to have the bulb at a
> long distance from the PCB.
>
> Fish tank STERILISING tubes are NOT suitable.
> They are shorter wave length UV that is both
> useless for the photoresist and dangerous.
>
> AFAIK The arc lamps with covers removed also
> produce dangerous UV rays as well as the
> usefull (for PCBs) rays.
>
> All up - I think that black light tubes are
> probably the most convenient and easiest to
> setup and use option.
>
> They don't produce appreciable amounts of
> dangerous UV. Several of them in parallel
> will put out plenty of UV. They are easy
> to get. I think the biggest problem with
> them is they don't seem to age gracefully
> (at least im my experience they didn't)
>
> If you can't get or have surplus arc lamps
> then they should be great for PCBs though.
>
>
>
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> Be sure to visit the group home and check for new Links, Files, and Photos:
> http://groups.yahoo.com/group/Homebrew_PCBs
>
> If Files or Photos are running short of space, post them here:
> http://groups.yahoo.com/group/Homebrew_PCBs_Archives/
> Yahoo! Groups Links
>
>
>
>
>
>
>
>
>
>