PCBs with a tan...

[LinuxMan]

Hi.

I've been thinking about making myself some PCBs the "pro" way. I
would like to make a photo sensitive transfer of the circuit.

Now, as I understand you have to put these under some UV light to
develop. As I wouldn't make that many PCBs there is no need to make
my own UV developer or even buy one especially for that purpose as they
are a bit costly. So I was thinking about alternatives....

Would it work if I'dd bring the boards and transparencies to the artifical
tanning solarium kinda place (yeah, I know ), pay 2$ for 15 mins, lay
my boards under the machine and let it "tan" for few minutes. Afterwards
I'dd put these in some kind of light-resistant box and develop them at
home. I persume the machines are pretty big over there so I would be
able to "tan" 20 to 50 circuits that way. And we are talking about nice and
even development here... Would this work? Is it OK to put these into
developing solution after some time has passed?

Thanks for the answers (and please no fooling around as I'm dead
serious).

Cheers
LM

[elberto]

i have no informed opinion here, except that this ingenious, if only in conception.

[LinuxMan]

Heh thanks....

Just thought of that while passing the beauty-salon that's on the same street I
live in.

I think one would certanly seem to save a lot if doing small amounts of PCBs
(those UV bulbs sure aren't cheap either you know).

Cheers
LM

[Paul Perry (Frostwave)]

I would think, if there is enough short wavelength UV to expose the board, then there is too much for your body. But only experiment can tell for sure. Keep us posted!

[LinuxMan]

Heh,

so what you are saying Paul is that I should ask the lady to set the thing
to "ultra brown" setting...

Well, I was thinking if the sun could make these boards to develop a
tanning machine should work way better (as it is the concentrated sun)...
Offcourse I have no knowledge in theory behind developing with UV (as
I've never done it).

So you are saying a short wavelength UV is important here. And I
persume these short wavelength UV rays are not good for your body?

Yah, I'll try the thing (as soon as I get a nice piece of PlexiGlass). Imagine
how will the woman that works these machines look at me when I'll
mention what I need.... Bet she never had THAT kind of a customer ...

Cheers
LM

[Hal]

HAHAHAHA Thats the best thing i've heard in a while!!!

if you're in high school, or have access to a high school, most high school chem labs (or at least mine) have little closets with UV lights in them that clean the safety goggles....

maybe you can tap into that somehow?  Im fine doing pnp, though :-D

[guitarhacknoise]

hello linux man,
I used to be a practicing lithographer, even hold an A.A.S. in this, for the most part, obsolete craft (mmm...computers...........thanx!).
Anyway....I hav'nt done any pcb's like these but I imagine the process to be approx. the same as exposing & developing printing plates or the old multi layered color profs.
even blue poly 2 stencil film for screen printing.
basically the U.V. light is important only or mostly for these reasons:
faster exposure time, sharp definition ( like lines and half-tones )
reduce the amount of dust having the chance to settle on the glass of vacuum frame there by blocking light (it takes alot to block the U.V.)
& even exposure of the material . also to limit the amount of light that can stray,
there are plenty more reasons but I think that's enough for now.

basically, with these types of light sensitive materials, you can expose them with a flourescent shop lamp, halogen lamp, I have even used the sun to expose the blue poly 2, on tour, makin' the ol' punk rock t-shirts.
basically it has to do with the amount of light, the distance away from the "film" and the exposure time. there are formula's that usually come with these types of materials, but that is fairly usless in this situation, unless of course you have a high quality light meter and a densitometer.

I guess the easiest way to figure it out, without the gadget-"tree" (high tech toolbox!)
is to do a graduated test exposure, like in photograpy, to figure out the best exposure times.
basically you make a film positive ( a xerox overhead sheet will do) of the pattern or traces, have your light of choice set up in a fixed position. I will pretend it is a flourescent shop fixture, about two feet above the surface with 4 , 4 foot tubes, the best is to use 2 warm white and 2 cool white tubes,
set up like : cw, ww, cw, ww. (every other)  it has to do with the color spectrum.......
place the film down (photo sensitive circuit board), place the film positive down, place a CLEAN & HEAVY piece of glass down, you will want to use some enamel to cover the edges of the glass to help with keeping the light from entering the sides of the pane, now you place a "mask" or dense or opaque cardboard over all of it except for a strip of about 1/6th of the material to be exposed, do the first exp. for 45 min. (guess). then move the mask over to uncover another 1/6th and exposure for another  45 min.  ( at this point you will have 1/3 of the material exposed, one section for 45 min and the first section for 90 min.) you keep this up till you have exposed the whole board, then you develop it.
pick the exposure time that gives the results closest to what you need and try it again to "fine tune"or just shoot for gold and guesstimate the time it'll need.
Like I said I've never done a pcb (photo) but I have worked with these type of exposures, with AND without the proper equipment. It should work.  of course the tanning bed thing will probably work but the exposure time will be harder to figure,
hell I used to be the only guy to get sunburned in the middle of the wisconsin winter
-matthias

[gez]

I've done PCBs using the fluorescent light in my kitchen.  It works and exposure time was no longer than it should have been.  However, as has been pointed out, distance makes a difference.  I had to tape the board to the surface of the light and it had to be narrow (anything wider than the light didn't get developed).

I don't think you'd have a problem using a tanning bed but it's not a very practical solution if this means visiting a salon.  You'd need to do tests to see how long boards need exposing and this means pen and paper, tub of developer (would they be happy about potentially hazardous substances being sloshed around in their workplace?) and running water to wash off the developer.  If you use a different bed the next time you go, it might need different exposure times.  You'd need eye protection too, plus amber solaire and a pair of swimming trunks (not unless you want the 'all over' look)....er, I've lost the plot.

Ah, yes.  It's not that hard to build one (and I know all about this having never built one!) and there are websites detailing how to do this.  You might be able to pick up a cheap unit on Ebay or somewhere.

If you're only making small boards it might be worth experimenting with fluorescent lights if you have one in your kitchen/bathroom.  I did this and eventually I just went the whole hog and bought an exposure unit.

[guitarhacknoise]

cool gez!,
what were the exp. times you came up with? and how good was the definition?
yeah, the closer to the light the narrower the effective exp. area and the further, the wider the exp. area . did you use anything to hold the positive tight to the surface of the board? if not how bad was the definition? how detailed of a layout could be done?
this is very interesting to me cuz, well, besides the past experience, I have stayed away from trying this due to cost of trial and error? (i'm not that good with electronics, even with a pcb! LOL!)
-matthias
oh, linux man, I thought of this latter,
You could also go to print shop that has, preferably a vacuum frame for exposing metal printing plates and get them to do it, or kinda like hal suggested except go to the graphic communications area and talk to the teach and see if you can use the "flip-top" to expose it
a little hint: school shop classes are ALWAYS strapped for cash = supplies, so you could go to the office store and pick up a gift of paper! I bet a case (10 reams) of 20 lb. white 8 1/2" x 11" will at least buy you SOME lab time! ( on the down-low of course!)
-matthias

[gez]

The definition is as good as when using an exposure box.  The only problem is getting the transparency to be perfectly flat on the board (not a problem with exposure boxes) and the width you can make a board is a little limited .  If the transparency isn't totally flat the traces can be eaten away slightly (or added to if it casts as shadow).  In practise it hardly makes a dent to the finished board, but it's something to be aware of.

When using the fluorescent light I cut the board slightly longer than I needed to so that I could (masking) tape the transparency to the surface of the board without it 'buckling'.  It also makes strapping to the light easier.  Once etched the board can be cut down to its proper size.  

I use inkjet transparencies.  Don't reverse them, you place it on the board inkside down then cover with a sheet of tracing paper (makes the image more opaque) then strap it to your strip-light.  Any board wider than about 1.75 inches and you might have a problem with it not developing.  A lot will depend on your light fitting/wattage of light etc.

Exposure time will depend upon the board you use. The info you need will often be on your supplier's website, or on a data sheet you recieve with the board, or even on a sticker stuck to the surface of the board.

You might need slightly longer than the figures quoted, but we're only talking about 30 seconds or so.  The stuff I use takes/took about 2.5 minutes to expose and about 30 seconds to develop...and a few days to etch (well, it seems like that!)  

[gez]

PS you might have to experiment with different types of tracing paper or number of layers.

It might seem daunting doing all this but it's pretty easy when you get the hang of it.  Initially I cut a board up into little samples (I anticipated problems) but I got it spot on with the second sample.

[LinuxMan]

Thanks for all the replies.

I liked the part about the swimming trunks... Let's do PCBs naked, shall we?

Yes, I know practice makes perfect. I'm thinking of making me some
samples (small boards), put them all in and then put them out at about
15sec interval one at a time. I'dd mark every PCB for time it has spent in
there and then develop at home.

As I said I wouldn't do anything chemical-involved over there. I would buy
the PCBs that have photo sensitive stuff allready on them. My question is,
is it possible that I take these developed PCBs out of the machine after
they are finished and just put them in a box that lets no light in? I would
then run them through the water and develop them at home. Or is there a
time limit to develop these PCBs once they were UVed?

About the cost of it all. I look at it this way. If I'dd make myself (or buy) a
unit to transfer via UV and develop these things at home it would cost me
(in best case scenario) about 50$+. And that sure would be on a cheap
side. If I bring these to the shop I could do 25 of these circuits with ease
per session and it would only cost me 2$. If I would make 25 PCBs per
month that's 2$ a month. That means I'dd be happy developing at the
solarium for full 2 years before the unit would finnaly seem like a well
worth expense. Offcourse I don't make 25 PCBs per month so to make or
buy the unit is certanly out of the question. It's all about economy.

Cheers
LM

[Mike Burgundy]

a tanning machine should work - I use one at home to expose my boards. Be aware it's FAST (at least it is in my case). I use 5-10 seconds with transparancies, 30-40 for regular paper (which works just fine) and that's with a sheet of glass on top to keep everything nice and flat...
The weird thing is that a pro special purpose UV lamp in a local darkroom needs 5-10 minutes. One would think this would be even faster...
One problem with these large tanning booths is that they are designed for a person to lie down on and you really want a nice horizontal flat surface to put everything on. Also, they usually don't turn off when you want them, only after 15 minutes. You'd have to devise a way of securely keeping the transparencies on while you take the boards out and stash them in a light-proof box.
Let us know how it turns out (and don't forget to wear those little glasses)
By the way - an old broken scanner you should be able to find for free. All you need to buy are two UV lamps - there's your box!

[LinuxMan]

Oh great,

So I should decrease my 15 sec testing interval to 5 sec.

Will do that... Maybe I'll get a discount if I'm out of the booth in 1 minute...

Cheers
LM

[gez]

My question is, is it possible that I take these developed PCBs out of the machine after
they are finished and just put them in a box that lets no light in? I would
then run them through the water and develop them at home. Or is there a
time limit to develop these PCBs once they were UVed?

Once developed the boards can survive quite a long time exposed to natural light before any deterioration of the image occurs.  Obviously the less time the better, but it would take (I think) about 24 hours of daylight to have any effect on your artwork.

The problem is that your boards will still have developer on them unless washed after exposure and, I gather, this will bugger things up slightly.  The developer I use is by seno and has a longer safty margin (you can leave a board in the developer for a long time without it going wrong) so if you can get hold of something similar it might help.  Either that or take a flask of water in with you.

OK, it's not cheap buying a box, but do you really want to look like an old leathered scrotum painted with creosote?!  

[LinuxMan]

Heheh...

Nice point there. Picture says more than a 1000 words eh?

Anyhow I could wash the thing off at their bathroom (I suppose that wouldn't
be a problem) or at my house (as I'm less than 5 minutes from the place).
We'll see how things will go. I plan to do it in the next week or so.

Cheers
LM

[David]

Gez:

Will this photo process work with a halogen lamp?  I have one down in my shop that's the perfect size to expose a board.  I checked the web and couldn't find enough data to conclude whether enough UV was emitted by a halogen bulb or not.

[Ansil]

Hi.

I've been thinking about making myself some PCBs the "pro" way. I
would like to make a photo sensitive transfer of the circuit.

Now, as I understand you have to put these under some UV light to
develop. As I wouldn't make that many PCBs there is no need to make
my own UV developer or even buy one especially for that purpose as they
are a bit costly. So I was thinking about alternatives....

Would it work if I'dd bring the boards and transparencies to the artifical
tanning solarium kinda place (yeah, I know ), pay 2$ for 15 mins, lay
my boards under the machine and let it "tan" for few minutes. Afterwards
I'dd put these in some kind of light-resistant box and develop them at
home. I persume the machines are pretty big over there so I would be
able to "tan" 20 to 50 circuits that way. And we are talking about nice and
even development here... Would this work? Is it OK to put these into
developing solution after some time has passed?

Thanks for the answers (and please no fooling around as I'm dead
serious).

Cheers
LM

i have a uv lamp in a box i got it from cleaning out a warehouse space. you can have it for the shipping price. i have no earthly use for this thing.

[LinuxMan]

Erm...

Sure Ansil thanks. I've sent you an email.

Cheers
LM

[guitarhacknoise]

The stuff I use takes/took about 2.5 minutes to expose and about 30 seconds to develop...and a few days to etch (well, it seems like that!)  [/quote]
wow! I way over estimated the exposure time! the metal plates i was doing at home for the old multi-lith took a hell of a lot more time than this! of course I had the light a further distance away to get a larger exposure area.
also gez wrote:PS you might have to experiment with different types of tracing paper or number of layers.
I think that the tracing paper might cause more diffusion of the light, but it might be the only way to help keep the density of the image unless you feel like tracing the positive with an opaque pen. try a heavy piece of glass to hold the image tight to the board.
-matthias