PCB exposure box
 

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??
--
Dick
GM0MNL Fra' Auld Reekie

On Fri, 28 Nov 2003 16:30:48 +0000, Dick
wrote:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??

Basically, you are right, it is relatively simple.

Some standard glass will not pass certain bands of UV. Test first (put
a sliver of the glass partially over some sensitized material for a
standard exposure time and note any difference.)

You may not need the glass if the mask adheres well to the substrate.

You want enough spacing to get reasonably even coverage, but too much
will increase exposure time. Consistency is more important, so you can
develop a standard timing for the unit.

Consider mounting the lights to face down, as a safety precaution.
Also, you might add a microswitch and relay to prevent your box from
lighting up with the cover open. This would be a lot worse for your
eyes than a photocopier.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

On Fri, 28 Nov 2003 16:30:48 +0000, Dick
wrote:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??

Basically, you are right, it is relatively simple.

Some standard glass will not pass certain bands of UV. Test first (put
a sliver of the glass partially over some sensitized material for a
standard exposure time and note any difference.)

You may not need the glass if the mask adheres well to the substrate.

You want enough spacing to get reasonably even coverage, but too much
will increase exposure time. Consistency is more important, so you can
develop a standard timing for the unit.

Consider mounting the lights to face down, as a safety precaution.
Also, you might add a microswitch and relay to prevent your box from
lighting up with the cover open. This would be a lot worse for your
eyes than a photocopier.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

Glass could stop UV? Depends on the ingredients. Some are OK, others are
not.

Some plexiglass does not transmit UV either. Some types are formulated for
outdoor use and have a built in UV filter. Check with a piece of white
cotton if it fluorescenses (cheapo UV indicator)

Wim

Glass could stop UV? Depends on the ingredients. Some are OK, others are
not.

Some plexiglass does not transmit UV either. Some types are formulated for
outdoor use and have a built in UV filter. Check with a piece of white
cotton if it fluorescenses (cheapo UV indicator)

Wim

Dick wrote:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??

I made my own from three pieces of MDF, some wood strips and a sheet of
glass. It's got the tubes etc. in the MDF base and two upright pieces of
MDF with two strips of wood acting as a shelf for the glass, about 9"
above the tubes, to give a bit of collimation. Glass is quite
transparent to the long-wave UV used for PCBs. I just put a book on top
of the board to press it down when exposing. I keep meaning to make a
proper lid with a foam pressure pad, but can't really see the point as I
don't use it much. It's some distance away, so I'm not bothered about
getting sunburnt. 8-)

Leon

Dick wrote:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??

I made my own from three pieces of MDF, some wood strips and a sheet of
glass. It's got the tubes etc. in the MDF base and two upright pieces of
MDF with two strips of wood acting as a shelf for the glass, about 9"
above the tubes, to give a bit of collimation. Glass is quite
transparent to the long-wave UV used for PCBs. I just put a book on top
of the board to press it down when exposing. I keep meaning to make a
proper lid with a foam pressure pad, but can't really see the point as I
don't use it much. It's some distance away, so I'm not bothered about
getting sunburnt. 8-)

Leon

Thanks for all suggestions, think I've enough info to get the project
finished.
--
Dick
GM0MNL Fra' Auld Reekie

Thanks for all suggestions, think I've enough info to get the project
finished.
--
Dick
GM0MNL Fra' Auld Reekie

in article , Dick at
wrote on 11/28/03 11:30 AM:

Has anyone home brewed a UV exposure box for making PC boards ?
I've got a couple of 8w UV tubes & a 0-30min timer and looking at
pictures of commercial designs I think all I have to do is:

1. Mount the tubes & timer in a light proof box.
2. Fix a sheet of glass 1-2" above them to act as a flat mount for the
photo sensitised PC board & photo master.
3. Fix a mask to the glass, blanking off all but a working area directly
above the UV tubes.
4. Make a lid for the box & fit a foam pad inside it that'll press the
PC board and master firmly down onto the sheet of glass thus stopping
those sneaky photons from getting round the corners of the PC master.

Is it as simple as this or am I missing something blindingly
obvious ?? Is 1-2" a suitable spacing between the tubes & glass plate &
will normal, thin, glass sheet be suitable ??


I use regular 2-3 mm window glass, I place the pcb board with the artwork on
my washing machine (nice flat white surface, good in low light), cover it
with the glass and place the light, a 12 cm long unit, on two wooden blocks
about 6 cm above the PCB board.
Hit the switch, leave the room and come back when the time is up.
For large boards I have to shift the lamp every few minutes for an even
exposure.

I have done quite a few exposures this way and would recommend this
primitive appraoch before I set out to build anything. Experience will then
guide you how to do your "final" exposure box.
Besides, my approach is dirt cheap and dissappears completely when I am
done, nothing much to store.

regards Uwe