Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Here are some additional ideas for UV exposure systems. The UV system
I use is a Colight DMVL-930 which has two lamps operating at 1500
watts. The lamps are standard 1000 watt mercury vapor. These lamps are
mounted vertically with one on top and the other on the bottom. During
the exposure cycle a capacitor is switched in to over drive each lamp
to 1500 watts.

Sheet aluminum with a mirror finish is in place on four sides forming
a rectangular enclosure for each bulb. The aluminum is angled at 45
degrees to the bulb to reflect the light to the exposure surface.

The exposure frame is 1/4" thick window glass held in a frame that has
a hinged top. The top section of this frame uses a 10 mil mylar sheet.
There is a rubber gasket around the edge and a vacuum line is attached
to one corner. This is the standard exposure frame for double sided
systems. Sandwich your board between top and bottom artwork films,
place it on the glass close the mylar top and pull a vacuum. The mylar
will conform to the board and hold everything in tight contact for a
perfect exposure.

After the vacuum is pulled this entire frame rolls into the machine
and is centered between the top and bottom lamps and reflectors. It
triggers the timer and when the preset time has elapsed the frame is
released and it rolls out of the machine.

It's really a simple system and a home made system like it could be
constructed from easily obtained materials. The easiest way would be
to mount a mercury vapor lamp assembly in a box about 18" to 24" tall.
At the bottom of this box and at the front edge cut a slot tall enough
and wide enough to slide in a contact frame for exposure. The lamp has
to warm up for a few minutes and then runs continuously with the
exposure time determined by how long the contact frame is slid into
this light box. It's just that simple. No automation is needed unless
you want a fancy system. A kitchen timer could be used to time the
exposure cycle.

Mercury vapor bulbs use quartz glass and emit ozone but this is not a
problem since the quartz tube is enclosed in a second glass bulb.
Regular window glass works fine in a system like this. I have never
had a problem when using regular window glass (untinted) in eposure
systems.

A friend of mine bought a used mercury vapor lamp assembly with
reflector for $20.00 and made his exposure unit from that. I laminate
his boards with dry film photoresist and he gets the same results as
my commercial exposure unit which is 17 seconds with a 1000 watt bulb.
We use DuPont 1.5 mil dry film and can easily do 5 mil lines and
spaces with almost zero defects when using photoplotted films.

Smaller wattage lamp and reflector assemblies are available such as
the 400 watt types. These would also work but the exposure time would
be slightly longer.

Another type of lamp to consider is the quartz bulb 500 watt portable
lamps. These bulbs will expose dry film photoresist but it will take
about a minute at a 12" distance. With this lamp there would be no
sliding exposure frame needed as the lamp could be switched on and off
while the mercury vapor type can not.

Maybe these ideas will help some of you planning to set up a UV system.

Tom