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I'm new here but find this list very interesting. A good UV lighting
system is the plain old mercury vapor lamps. These are commonly used
for dusk-to-dawn lighting. The bulbs are available in several
wattages such as 175, 400 and 1000 watts. One of these bulbs and a
reflector makes a great UV exposure system. Visit any large warehouse
and check out the lighting system since these are very commonly used
in larger buildings.

I have a commercial exposure system that uses this type of bulb. It
is a Colight Model DMVL-930 with 1000 watt bulbs on the top and
bottom. The exposure time when using 1.5 mil dry film photoresist is
17 seconds. If there is any interest in this I can photograph the
"guts" of this machine next time I clean the reflectors and post the
photographs in the photo section of this list.

It really would not be hard to make this exposure unit. Polished
aluminum sheeting or aluminmum foil could be used to make the
reflector system. I have helped several of my ham buddys set this
type of unit up and they have all been amazed at how fast this can
expose the photo resist. You can also make silk screens with this
setup.

I made my first hobby circuit board in 1966 and owned a commercial
printed circuit business for 23 years. We closed that plant last year
due to foreign competition and rising costs. I did keep the best
"small" equipment for my own home shop. This still allows me to make
boards for the instruments I make as well as my ham radio projects.

We gave away the plating operation because it was really a drag
putting up with the evironmental issues etc. I kept one smaller
photoplotter, several semi-automatic drilling machines, silk
screening equipment and all of the tooling and setup stuff. The big
Excellon CNC drilling and routing equipment was all sold off.

I started my company on the kitchen table in the late 1970's and it
looks like I've gone full circle but this time ended up in the
basement! It's much more fun this way I might add. We made boards up
to ten layers back then but it was just way to much work and the
headaches just kept getting worse. Too much work, too many hours, too
little pay and no more fun !!

I do enjoy the hobby side of this technology and would be willing to
help out with ideas and maybe some equipment projects that could be
posted on this list. If there is any interest let me know. Sorry
about the long post... sometimes I get going and don't know when to
stop!!! Hope I can help out.

Tom

Don't stop! It is good to have you here.

So can you tell us, is my memory faulty or does it only require
near UV to expose PCB photoresist?

I used to use a plant grow light incandescent floodlight bulb,
150W. I don't recall the exposure times but they weren't terribly
long or terribly short. IE, somewhere between 30 seconds and 5
minutes is the closest I can remember, with the bulb about 1 foot
away and the film/PCB held under glass. The film was mylar with a
variety of things on it, drafting tape, those rub-on pads from
Radio Shack, paint, copier toner, and anything else opaque.

What about those inexpensive 150W quartz halogen shoplights? Or are
they built to block too much of the UV?

An idea I had long ago but never tried out- use a bare xenon
flashtube, calibrate by number of flashes. Use one of the larger
tubes rather than the tiny ones in modern cameras. Easy to power it
with AC and to set up a programmable counter circuit to flash it. A
PIC or even just a 555 timer that enables flashing.

It is my understanding (could be wrong) that a fair amount of UV
(low UV, anyway) gets through the tube and that the plastic cover
on the flash serves two purposes, color balance and UV block.

Someone said standard window glass blocks some UV. What types of
glass block less UV? What percentage is blocked? Is it just a
matter of using a thinner sheet of glass to hold the artwork to the
PCB?

Steve Greenfield

--- twb8899 <twb8899@...> wrote:

I'm new here but find this list very interesting. A good UV
lighting
system is the plain old mercury vapor lamps.

-snip lots of good stuff-

I do enjoy the hobby side of this technology and would be willing
to
help out with ideas and maybe some equipment projects that could
be
posted on this list. If there is any interest let me know. Sorry
about the long post... sometimes I get going and don't know when
to
stop!!! Hope I can help out.

Tom

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I have agree with Tom on the plain mercury vapor street lamps. they are
cheap, readily available and work great. I use 400W, no reflectors, 400 mm
distance and get 90 seconds exposure on dry film resist. I have heard from
several people about using quartz halogen lamps. Quartz halogen run hot and
put out significant UVA and even some UVC (if not shielded by normal glass),
the UV level depends on the operating temperature. Bulbs that run extra hot
and short lived are better, such as a photographic lamp. You could try
running one of those 12V 80W quartz halogen ceiling lights at say 15V.

Here is some info on dry-film photoresist spectral sensitivity,

,2133,3647,00.html



Standard 'soda' glass (windows) stops pretty much everything shorter than 350
nm. The sensitivity of dry film resists starts dropping off past this anyhow.
You won't loose much from the glass, Even a thick sheet, say 8 mm.
I tested the effect of glass by doing a 10 step exposure on a sample of dry
film. The effect of 4 mm glass sheet was virtually unmeasurable (passes
greater than 80% of light). probably somewhere around 90% - 95%.


Good work Steve on setting up this forum.

Adam.


Steve Greenfield wrote: