My DIY UV developing box. Pretty pictures!

[darron]

i'm soooo tired of this PNP nonsense. It's a much neater upgrade to when I was originally drawing the circuits. I decided that I will try photo developing as it seems more professional, and the results will be more constant with less trial and error (I hope!). I find that now I am even starting to prefer drawing the circuits again. I'm sure PNP is great if you have a perfect system, but I've been through about 10 packets and often need to transfer something about 4 times to get a perfect (or touchup-able) mask. Also, my luck is pretty poor with etching enclosures. It's also a pain that you have to really think about what you want to print as you can't just print on a little square of the PNP sheet next time you want a single circuit.

Enough of my rant...

Here's my UV box:

The top, or 'lamp'. It's a matrix of 41x 5mm UV LEDs at a spacing of 4cm, and two power terminals:




The copper side of the circuit board. I actually didn't etch this, I just ran an engraving tool from my dremel style tool roughly around the board. It's all just one long groove. To get the placement of the LEDs right, I first printed it all on paper and stuck it to the board and drilled. Then I engraved.




It is houses in a pretty, metalic/3D purple box. This also shows the power supply:




All the lights illuminated, but house lights on and camera flash:




A shot in the dark:






Some things that I had to consider:
1. The current draw is significantly higher than a stomp box. They are all run off a 2A power supply which heats up quite a bit after a while. With 41 LEDs, this allows for 48.78mA of current draw per LED. Consider that some LEDs even use 50mA.

2. Getting the required voltage. These LEDs were rated at 3.7V. The power supply I could find in my junk box is 3.3V. Good enough for me
If you were going to use a limiting resistor, remember that a 1/4W metal/carbon film will NOT do the trick! Calculate the wattage...

3. Quality of light. These LEDs have a viewing angle of 30 degrees. As you can see by looking at the last photo, they overlap nicely. Also, when you point a single LED at a fixed spot the light doesn't have rings and inconstancies. This results in a smooth consistent light at the top of the box. Some quick maths told me that at the hight they are projecting, and they viewing angle, and the distance at which I spaced them, I would have no problems with areas not getting equal light.

4. Safety. This is REALLY bright. Perhaps a lot of overkill. The camera does not show it. It hurts your eyes being in the same ROOM as this box even if you are not looking at it. That's NOT healthy! I've done very little testing, and will not use this box again until I have my UV protective glasses (not at home). You don't want to develop eye damage, or even cancer!

5. I took a look at the LED datasheet to check out the wavelength. I didn't want an LED that was just UV 'coloured'. UV is out of the human visible range, which is why it can be terribly harmful without us even seeing it. The bit that we can see is from what is just within out range. I looked up in Wikipedia to make sure that the wavelength was correct.

All it needs now is some glass or perspex on top. I might buy a cheap photo frame from an Asian junk store or something. All up it cost me about AU$130.00



Any further information I should consider would be much appreciated. I'd also love some feedback. (:

Darron

[markm]

Nice work. 
I think I would have learned how to use PNP rather than go this far but hey, to each his own. 

[Andre]

I used a home made UV light box with 2 30 cm UV FL tubes for years , but since one of the tubes broke  I now use my wife's sunbed for this purpose (and some occasional
tanning too  ) with good results.

André

[darron]

Nice work. 
I think I would have learned how to use PNP rather than go this far but hey, to each his own. 

markm... if i could PNP as good as you then I probably wouldn't be bothering! ha
I've played with as many variables as I could, but I think PNP and I just are not friends. Plus, it's fun to build stuff.

[markm]

Nice work. 
I think I would have learned how to use PNP rather than go this far but hey, to each his own. 

markm... if i could PNP as good as you then I probably wouldn't be bothering! ha
I've played with as many variables as I could, but I think PNP and I just are not friends. Plus, it's fun to build stuff.

Understood.
It seems one of those things that either works for you or doesn't.
Nice job though....I haven't seen anything you've built that hasn't looked well done and thought out! 

[(doug harrison)]

I have yet to try PNP, although I do have sheets that I've run off on a photocopier. I like the photopositive method. Master artwork is a transparency. I tape the it to the emulsion side of the board along the sides (so it doesn't mask the circuit traces), then expose for 1-2 minutes in direct sunlight. If it's a large board, I might use a picture frame with styorfoam padding in the back to keep the board in good contact with the glass. Then I develop until the image comes through, rinse in running water, and etch.  A couple of things you might find useful:

1) Developer temperature makes a difference. The warmer, the faster. I usually keep my developer in a clear plastic container with a fli-top lid (the kind you can buy at a grocery store for $1). The developer keeps, and if I need to warm it up, I put it in a warm water bath in a sink or larger tray.

2) If the developer concentrate says 10 parts water to 1 part developer, it may really need about 10:3 (or more). Maybe the concentrate I'm getting is less-than-fresh. (I order DATAK brand from Jameco.)

3) Ferric chloride.  I keep it in a clear, lidded plastic container. It's good for several 4 X 6 boards. Again, higher temperature yields faster etching action.

The good thing about photopositive boards, as you say, is that you can expose and develop only small pieces of board in order to test exposing and developing times.

[darron]

I have yet to try PNP, although I do have sheets that I've run off on a photocopier. I like the photopositive method. Master artwork is a transparency. I tape the it to the emulsion side of the board along the sides (so it doesn't mask the circuit traces), then expose for 1-2 minutes in direct sunlight. If it's a large board, I might use a picture frame with styorfoam padding in the back to keep the board in good contact with the glass. Then I develop until the image comes through, rinse in running water, and etch.  A couple of things you might find useful:

1) Developer temperature makes a difference. The warmer, the faster. I usually keep my developer in a clear plastic container with a fli-top lid (the kind you can buy at a grocery store for $1). The developer keeps, and if I need to warm it up, I put it in a warm water bath in a sink or larger tray.

2) If the developer concentrate says 10 parts water to 1 part developer, it may really need about 10:3 (or more). Maybe the concentrate I'm getting is less-than-fresh. (I order DATAK brand from Jameco.)

3) Ferric chloride.  I keep it in a clear, lidded plastic container. It's good for several 4 X 6 boards. Again, higher temperature yields faster etching action.

The good thing about photopositive boards, as you say, is that you can expose and develop only small pieces of board in order to test exposing and developing times.

thanks dough. my experience with it photoresist is somewhat limited, but i really liked what i tried. my first attempt i got the printing inverted, and most of it only developed in one corner where i experimented with holding a UV lamp for a bit longer. the developing solution that i used must have been super duper as it took effect really fast. it said to mix one part solution to one part water, which i roughly guessed. i'm most interested in etching images onto enclosures. i didn't like that there were so many variables with pnp, such as temperature, duration, pressure, moving the iron. also, when you are having most of the image transfered on pnp (like etching an enclosures, not like etching a pcb where it's practically inverted) the pnp seemed to buckle in the heat and bubble.

another advantage that i'm hoping for is that with photo resist i will be able to get almost perfect registration easilly, this will give me more confidence in putting borders on the enclosures and etching in the drilling holes. i'm thinking of drilling a small hole for the pots also to wedge that little chunk of metal in that i normally snap off, to stop the pots from spinning. it's never happened, but it's a fear.

can't wait for my resist spray to arrive from RS components. all the parts for this project came from Jaycar by the way. the board is 18cm x 18cm chopped from a 30cm x 30cm fiberglass/copper clad board.

[mdh]

Very cool.  I don't mean to thread hijack, but can anyone name a supplier for positive photoresist in the US?  I'd like to try it for enclosure etching, but so far all of the suppliers I can find are in the UK and Europe.