UV LED Exposure Box

Intro: UV LED Exposure Box

How to build an Ultra Violet Exposure box using LED's.

Your last Veroboard project!

A UV exposure box is an extremely useful piece of kit. It can be used to make proper PCB's. It can also be used to make other things such as intricate photo etched parts (a subject for another instructable). The trouble is they can be a little pricey for the hobby enthusiast especially if you want the double side type.
This instructable outlines the construction of a double sided UV exposure box using the recent generation of high brightness UV LEDs.

Why use LEDs?
LEDs are far more energy efficient than either incandescent or fluorescent lamps offering between 5-10 times more efficiency making them cheaper to run and kinder to the environment. They also (unlike fluorescent tubes) do not contain mercury. LEDs have a far greater life span than the other types of lamp measured in decades rather than months. The frequencies being emitted are also in a tighter band making UV LEDs safer than the traditional UV tubes. There's also just something cool about LEDs, I can't put my finger on it, but ever since I was a kid I've found them to be one of the more fascinating electronic components.

Is there a disadvantage to using LEDs?
Not really, however the UV exposure box I have detailed here is a little less powerful than the commercially available ones. This means that your exposure times will be around 2 ~ 3 minutes as opposed to 30 ~ 40 seconds, but come on, do you really need your PCB's to be produced that quickly? Anyway sometimes having a slightly slower exposure time can be an advantage allowing you a little more control.

This UV Exposure box will consist of 2 UV panels; each having 84 LEDs a total of 168 LEDs. Each panel will draw about 700mA at 12v. This makes each panel 8.4watts a total of 16.8 watts for the whole thing.

STEP 1: Materials

The most critical parts of this project are the UV LEDs, you are looking for 5mm Ultra Violet LED 2000mcd 395nm, 3.4V 20~25mA.
I bought two 100psc packs from eBay.
If you find something better then ensure that they are;
- At least 2000mcd in brightness
- Have a peak wavelength of less than 400nm.
- A viewing angle of at least 20 degrees.

You will also need 2x 160mm x 100mm pieces of Veroboard and 56x 75R resistors.
Another important choice is the PSU. I used a plug in, 12 volt 24 watt switch mode power supply. Switch mode power supply's are far more energy efficient than most other types and are also very stable.

All the other parts and materials are easy to find. Some I bought, some I salvaged. This is where you own judgement and taste comes in. In the end it's up to you how closely you follow my design. I've included all the CAD drawings and schematics as metafiles so they're easier to read when you print them out.

STEP 2: Box Parts

First cut out all of the parts as shown in the drawings. I used some salvaged 6mm MDF. Then cut out the holes in the glass lid, the apron and the recesses on the side inserts. And route the recess for the glass using a router cut the surface recess on the underside of the glass lid.

STEP 3: Box Sides

Now glue together the 4 outer sides of the main box using the base as a guide (make sure you don't glue the base though). Then glue the inner sides in place so that when fitted, the apron is flush with the edge and the base is slightly recessed.

STEP 4: Lid Assembly

Glue together the lid just as you did the main box but the lid can be assembled all in one go.

STEP 5: Fit, Fill, Sand and Drill

Fit the lid, hinges, catches and glue the apron and support in place. This step will require a lot of test and adjustment to get things just right. Pay particular attention to the glass lid. I've slotted the holes for the glass lid hinges to make for easy adjustment. I've also chosen some hinges that only open to 95 degrees and some toggle catches.

STEP 6: Holes

Drill holes for the PSU connector, and for a cable to go from the box to the lid. Make one final check that everything fits, drill pilot holes for the base screws. Then remove all the hinges etc. give everything one last going over with filler and sand paper and then paint all the wooden parts. I recommend using white for the inside to help reflect and diffuse the UV light but the outside can be whatever colour you like.

STEP 7: UV LED Panels

I've mounted everything except the LEDs on the copper side of the board to keep the LED side uncluttered.

STEP 8: Prepare the Veroboard

First cut the tracks with a spot face cutter as per the track diagram and drill the 6 holes (3.2mm). Buzz the tracks with a multimeter at each stage to check for short circuits and bad connections.

STEP 9: Negative and Positive Rail Links

Next solder on the links putting some insulating tube between the solder joints. Put kinks in the wire where it contacts the board.

STEP 10: Soldering the Resistors (surface Mount Style)

Put dogleg bends in the resistors wires. Then solder in position testing each one with an Ohmmeter to check for shorts.
Take care not to melt the paint on the resistors and cause a short!

STEP 11: Soldering the LEDs

Solder all the LEDs in place, note their polarity. The diagram shows which side the flats should be. This step can be tricky, as all the LED bases need to be flat against the board to ensure an even spread of light. Resist the temptation to insert them all and then solder. The best method I found follows in the next few steps.

STEP 12: Insert LEDs

Do one row at a time. Insert all the LEDs in the row checking you've got them the right way round.

STEP 13: Solder 1st Leg

Then place a block of foam rubber (or something similar) on top and flip over. Then solder just one of the legs of each LED.

STEP 14: Position LEDs

Now hold the board in your hand supporting an LED with your finger. Reheat the solder, as the solder melts the LED will become free and you can wiggle it with your finger till you feel it is flat against the board. Hold for a few seconds as the solder cools. Repeat this step for each LED in the row.

STEP 15: Finish the Row

Now solder the other leg of each of the LEDs in this row and clip all the legs to length.

STEP 16: Solder Links

You need to create a bridge at the end of each series of three LEDs to ground. Use a small piece of wire or an offcut of the resistor wires.

STEP 17: Test That Block

After you've completed every 3rd row you can test that block by applying up to 12volts to the board. I recommend using a bench PSU and turning the voltage up slowly. Be careful not to go over 12 volts and watch your eyes, don't stare directly into the LEDs!

STEP 18: Test That Panel

Finally add the red and black flying leads to the positive and negative rails.
Do a final test with your bench PSU. If any of the LEDs are duds then replace them (you should have 32 spares). And remember, check the polarity!

STEP 19: Make the Second Panel

Now repeat the last 10 steps for the second panel, and fit standoffs to the six holes on each board.

STEP 20: Control Panel

Make a control panel out of 1 ~ 1.5mm sheet steel and cut a hole to fit your power switch.

STEP 21: Fitting the Glass

First cut the glass to size. Then stick the upper glass into the recess on the glass lid using silicone sealant.

STEP 22: Glass and Foam

Cut some thick foam rubber (about 1 inch thick) to the same profile as the shelf. Make the cuts in the foam by compressing it with two rulers side by side and then run a craft knife between them. Then Place the foam on top of the shelf and the lower glass on top of the foam and then run a fabric strap around the ends of the glass, adjust the length of the straps so the glass sits flush with the top of the box and fix the straps to the shelf.

STEP 23: Assembly and Wiring

Fit the lid, its hinges, the toggle catches and the LED panels. Run a wire between the lid and box and either fit connectors or solder it directly to the LED Panel. You may also want to cover the wires in PVC tubing. Attach the control panel with short screws, and fit the power switch. Then fit the power connector and the power switch and wire it all up as per the schematic.

STEP 24: Final Assembly

Fit the shelf, foam and glass assembly and the glass lid and its hinges and check that everything still opens and closes smoothly.

STEP 25: Testing

You may want to check everything is OK by hooking up a bench PSU and turning the voltage up slowly. You may also want to check the voltage of you PSU. When you're confident everything is OK plug it in and switch it on.
Safety note! Do not stare directly into the UV LEDs. UV light is harmful to your eyes. It's also a good idea to get hold of some laser goggles, these should block all the light below 532nm. To get an idea of the amount of time you should expose your PCBs for you can do an exposure test. Coat a piece of scrap metal with Photo resist on one-side and mark minutes on the other. Then with a piece of card mask of the metal expose for 1 minute then move the card to the next, mark expose for another minute and keep going until you reach the end. Remember start at the 10-minute mark and work down.

STEP 26: Go Make Some PCB

And you're done. Go and experiment with the photo resist and get a feel for how it responds to the UV light and the chemicals you're going to use with it.
A great first project might be a timing device for your UV Exposure Box. I've deliberately left plenty of room on the control panel for this and in fact it will be the subject of my next Instructable.

Comments

[NeeilG]

Greetings,
I am from University of Central Florida. For my Senior Design Project research paper, I wanted to ask for your permission to use your image of the Box with LED and bottle in it that you have posted here.
Hope it is alright from your side to use this image for our paper. Proper citation will be given to it.Thank you!

[tjackson2112]

Mounting all the LEDs nice and flat against the protoboard can be a challenge. You can insert all of them and bend the leads so that they don't fall out and then turn the board over and press the LEDs against compressible foam to try to keep them all consistently flat against the prototyping board, if you want. But that's a bit clumsy and problematic. The technique I like is to insert three in series leaving the leads straight, push the leads gently side to side so as to keep them from falling out while turning the board upside down and upon a hard flat surface. Then solder all three leads on one side, not caring if they are perfectly flat yet. After that it is easy to hold the board with one hand while pushing one LED with a finger and with the other hand remelt that LED's solder joint, while pushing the LED flat with the finger. It may take a little practice to get a feel for it. Repeat for all three LEDs. Now that the three LEDs in series are firmly in place, place the board back down on the hard surface and solder the other lead of each LED (being careful not to remelt any of the already soldered joints). Then to be sure you haven't shorted anything, check for NO continuity at the power input. If all looks good, then you can check that the three LEDs light properly and then move on to the next set of 3. As you continue and grow more confident, you can do a whole row of sets of 3 and THEN check for NO continuity and proper operation. Remember that if you're using a 12VDC wall wart that isn't regulated, you may see a considerably higher voltage than 12V (and probably will) until the total load is close to the wall wart's rated current. So checking the operation of only a relative few LEDs may burn them out. So, either buy a regulated wall wart, or include a discrete 12V regulator, or risk a difficult to find short if you insist on soldering all LEDs before checking for NO continuity. If you have perfect continuity at the power terminals (not good), you might burn out your regulator and/or wall wart. And you might find it a real headache to identify any short without building the circuit a little at a time. That's particularly true if you follow djhamer's recommendation to mount everything but the LEDs from the copper side, which can be a headache too, if not done carefully and also a little bit at a time, since shorts on long intricate ground and power lines can be ANYWHERE electrically and VERY difficult to isolate. Cheers.

[tjackson2112]

Can anyone suggest a minimum thickness of glass that will not distort under compression so as to provide an even pressure upon the photoresist film or presensitized board being exposed?

[Bertz]

I just completed my own UV exposure box. I used 96 UV LEDs in a 12 x 8 matrix (good for 4" x 6" boards). LEDs were approx. 3" from exposure window. The LEDs were 1200 mcd with 160 degree viewing angle. Exposure time was 2 minutes.

[tjackson2112]

Be sure you have three LEDs in series with each 75 ohm resistor, each series set going from 12V to gnd and that each LED is oriented properly (forward biased). You might just have some duds among the good ones. Also, check each LEDs forward voltage drop. If it turns out to be too high (more than about 3.4V), three in series might drop more than the available 12V. They should leave whatever voltage is left across the resistor (about 1.8V). And from that voltage you can apply ohms law to determine the current through each LED (or just measure that directly with an ohmeter), which should be around 20-25mA.

[agodinhost]

Hi, please, were did you bought your leds? I did looked in ebay but I can't say for sure that those leds there really have 20º view angle. All leds that I found there are kinda suspicious, chinese cheap fake stuff, even tough they say they are 20º I can't trust. I'm in Brazil and at here ebay is the more easy way to get electronics by a decent price but not in this case.

[quillby]

I found these in Germany. They are more expensive, but because of the angle of 120° they are more suitable for illuminating flat surfaces. This is exactly what we need. http://www.ebay.nl/itm/50-UV-Leds-4-8mm-120-200mcd-Led-STRAWHEAD-schwarzlicht-ultraviolett-/370543226494?pt=LH_DefaultDomain_77&hash=item564618ee7e#ht_1926wt_1139

[mhenriksen1]

Isnt 200mcd WAAAY too little?

[tjackson2112]

Actually, the term 'mcd' doesn't even apply to light emitters whose predominant wavelength is outside the visible range. It's a term appropriate for visible light emitters and human perception. I'm still looking for an equivalent wattage (electrical or emissive) that is more appropriate for UV LEDs. But some of the emission band spills out into the visible spectrum (hence the blue color of the LEDs in this instructable, which obviously isn't UV per se). mcd is a unit of 'luminous intensity' - a measure of the amount of light falling on a given area, as opposed to 'luminous flux' (in lumens) - a measure of total light output, so mcd also incorporates beam angle. Trying to get precise about things gets a bit hairy. I'm still looking for a really good treatment of the subject.

[dalpets]

Not immediately obvious what the diagonal spot cuts are for? They are necessary to electrically isolate each vertical bank of 3 leds.

Saw elsewhere a tip recommending cutting the leads before soldering to avoid mechanical strain on the solder joint and the potential for later breakdown of the joint. Seems a worthwhile precaution, although too long with soldering iron heat may destroy leds with such shorter leads.

Probably wise to test each LED before soldering because if you have to wrestle with removing a dud LED, depending on technique, you could destroy the copper strip, which too easily lifts with excessive heat on a standard board, & if you don't have room to bridge the broken continuity you've wasted a hell of a lot of time & energy building the array.

I found it preferable to install a vertical column of 3 led sets, rather than horizontal banks in order to make sure from the outset that the there are no errors in the design. I found it easy thereafter to duplicate succeeding columns use the first as a guiding template.

[tjackson2112]

Or just a droplet of superglue to keep the LEDs in place prior to soldering.

[LaurentM50]

Hello, very nice work. I am planning to build my own uv light box and so far I have a simple question: Where did you get the 90 degrees locked hinges and what is the name of such hinges? Thanks.

[Arthur Mullard]

Great instructable thank you. Can this be used to create cyanotypes?

[PierreV16]

Who can we give a helping hand?
Am not yet so strong in these matters but already have different issues.
What I also know is that a series of scaling is going from + to-, so 3leds and resistance I see consecutive
Resistance led led led
+ -+ -+ -+ to -
According to that I see the leds start right counted on line 4 column 4 and the other leg to column 5, following led line 4 column 9 and 10 etc
2nd row start to line 9 in the same columns
3rd row sart on line 14 in the same columns
What I don't see is how they are in it, the right side of the led the anode and the left the cathode?
Who can we give a helping hand?
Am not yet so strong in these matters but already have different issues.
What I also know is that a series of scaling is going from + to-, so 3leds and resistance I see consecutive
Resistance led led led
+ -+ -+ -+ to -
According to that I see the leds start right counted on line 4 column 4 and the other leg to column 5, following led line 4 column 9 and 10 etc
2nd row start to line 9 in the same columns
3rd row sart on line 14 in the same columns
What I don't see is how they are in it, the right side of the led the anode and the left the cathode?
Who can we give a helping hand?
Am not yet so strong in these matters but already have different issues.
What I also know is that a series of scaling is going from + to-, so 3leds and resistance I see consecutive
Resistance led led led
+ -+ -+ -+ to -
According to that I see the leds start right counted on line 4 column 4 and the other leg to column 5, following led line 4 column 9 and 10 etc
2nd row start to line 9 in the same columns
3rd row sart on line 14 in the same columns
What I don't see is how they are in it, the right side of the led the anode and the left the cathode?
Who can we give a helping hand?
Am not yet so strong in these matters but already have different issues.
What I also know is that a series of scaling is going from + to-, so 3leds and resistance I see consecutive
Resistance led led led
+ -+ -+ -+ to -
According to that I see the leds start right counted on line 4 column 4 and the other leg to column 5, following led line 4 column 9 and 10 etc
2nd row start to line 9 in the same columns
3rd row sart on line 14 in the same columns
What I don't see is how they are in it, the right side of the led the anode and the left the cathode?

[PierreV16]

I dont no way, is marked 4 times

[PierreV16]

I think I have found.
Start on the left side on height of the left pin of the resistance.
Start the 1st row the LEDs with the + (anode)
2nd row start with the-(cathode) 3rd row start with the + (anode)
That would make it so.

[andreq]

Great instructable! Here is my first ever PCB using this method. I was previously making them by hand. I'll never go back to sharpies! I've built a simple UV light box using an average size plastic shoe box and 35UV led (30degree view angle). I've made some calculation, but in the end I've just placed the led 1 inch apart as it seemed to light more uniformly. This is my "test pattern" From left to right, 30 seconds to 5 minutes exposure time. The Second picture is a close-up of the best result, 3:30 minutes I'm using 3 layer of ink jet transparencies. 1 print is black, one is photo green and the third is black. I've read somewhere that photo green should have some UV repellent in it. Anyway, the result where perfect! p.s. See full size images for better comparison

[djhamer]

Nice one! It looks like you got some really good results. I like the tip about the green layer. I usually use the laser printer at work but I want to experiment with using my home ink jet. Isn't 3 layers a little overkill though?

[andreq]

Here is my first "real" PCB. It's a simple PSU for an audio amp I'm currently building. I really like the result I get from my ghetto plastic shoe box :). I should post picture of the box itself.

[SebastianS29]

I like the layout of your PCB, bridge in the middle! epic