Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "Mike Putnam" wrote:

> Hans,
> I looked at the picture of your UV exposure setup. I just wanted to
comment
> that I would never use the round bulb. Use the florescent tubes and your
> results will be better. I have found that the round bulb tends to
give more
> exposure in the center than at the outer edges. Even more apparent with
> larger boards.  This is the reason all exposure units sold on the
market use
> the florescent tube. You can compensate somewhat by having the bulb
not so
> close, but this just increases your exposure time. The other bad
thing about
> the round bulb is the heat. This will actually get in the way of your
> process, depending upon what type of photo etch you are using. I am
trying
> to recall if it was a problem caused to the developer or if it was a
> consistency problem in the exposure. Nevertheless, I found it to be a
> problem several years back. If you modify your design to use the
florescent
> bulbs, you will notice a marked difference in detail as well as less
> exposure time needed.
> -Mike

Mike,

This seems like a great place to jump in. I'm very carefully trying to
get into the
homebrew photofab business and exposure is what I'm currently
researching. The problem with it is that there are so many options.
It's become clear to me that almost any strong light will do the job.
But I'm having a problem determining what is the best options in terms
of cost, efficiency, and availability. And oddly enough after
reading/skimming most of the nearly 2000 posts in this group there
doesn't seem to be a clear cut definitive answer. 

So I've decided to put it in the form of a question:

If you needed to put together a positive photoresist exposure setup
for small PCBs (no bigger than 4" x 6") and your only option are from
the typical home improvement store/department (think Home Depot,
Lowe's, Walmart, etc.)
what would you choose and why?

To assist in your answer I'll list some of the options that I've seen:

* Standard incandecents
* Standard/Daylight flourescents.
* Black light incandecents
* Black light flourescents
* Plant grow light incandecents/flourescents
* Halogen 
* Floods of all types.
* Compact flourescents
* Germicidal flourescents (not really an option, but interested in
comments)

I know I'm probably overthinking the problem. But frankly no light
bulb manufacturer gives any real indication of what wavelength and
what power their bulbs emit. So there's an overwhelming number of choices.

Now that being said I'd like to offer up for comment my ideal setup,
which Mike has already given partial comment on above. In an ideal
world I'd like to have 5 50W black light incandecents organized in a X
pattern using standard incandecent sockets. It would be the winner in
the cost and availablity criteria because I can set it up for about
$10 in Home Depot/WalMart parts. However in all of my reading I
haven't yet gotten clarity of how well it'll actually expose. And
frankly I'm fearful of screwing up and buying the wrong setup.

BTW for starting out I purchased the MG Chemicals Photofab kit:

http://www.mgchemicals.com/products/416k.html

Which has everything to get started short of transparancies and you
guessed it
exposure lights. BTW their instructions here:

http://www.mgchemicals.com/techsupport/photo_inst.html

suggest using 18" flourescents. But I'd be interested in something
better and/or
cheaper if possible.

Comments?

BAJ