Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of Lid Assembly
Lid Glue.jpg
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

Picture of 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

Picture of 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

Picture of Prepare the Veroboard
Veroboard Track.jpg
Veroboard Track + Holes.jpg
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

Picture of Negative and Positive Rail Links
Negative Rail Link.jpg
Links Bent and Insulated.jpg
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)

Picture of Soldering the Resistors (surface mount style)
Resistors Done.jpg
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

Picture of 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

Picture of 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

Picture of 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

Picture of Position LEDs
LED Iron.jpg
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

Picture of Finish the Row
LED Clipped.jpg
Now solder the other leg of each of the LEDs in this row and clip all the legs to length.

Step 16: Solder Links

Picture of 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

Picture of 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

Picture of 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

Picture of Make the Second Panel
Both LED panels.jpg
Now repeat the last 10 steps for the second panel, and fit standoffs to the six holes on each board.

Step 20: Control Panel

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of 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.
1-40 of 137Next »

*NB Make sure you get the less the right way round. They will still work backwards but burn out and smoke in 60secs!!! ouch!!

This is a great project. The instructions are pretty good. However I found that 2 leds on each 3 led blocks failed to power up. Seems like it needed more soldering than directed. It's perfect to get started making a more refined UV lightbox. Bravo!

shortw6 months ago

Why use so many resistors?

In step 7, you have 4 sections of led's on the board/print.

You could have 1 resistor per section, instead of 7 resistors.

And if I am right that resistor need to be 10.71 ohms.

So instead using 28 resistors, you would be using 4 resistors


MátéG shortw3 months ago

Yes, if the LEDs were perfectly identical, that would work. (Also, you could merge the 4 section resistors into one 2.7R resistor for the whole thing.) The thing is, they're not perfectly identical, and LEDs do not behave like a resistor would. Check out the voltage-current graph on any LED datasheet. They have a "voltage drop", most of the time the voltage across their terminals is this much, regardless of how much current flows across them. If you connect more voltage, they'll attempt to conduct infinite current, which results in the Magic Smoke(TM) leaving the LED (burning out). If you connect less, they will not conduct any current. This voltage drop for these LEDs is approximately 3.4V, but it varies a little, even within the same batch.

The good thing is, we can use current limiting resistors to set the current of one or more LEDs connected in a row. Their cumulative voltage drop is approximately 10.2V, the rest of the 12V is across the resistor, so the whole row gets approximately 25mA. If the cumulative voltage drop happens to be 0.1V less or more, the resulting current doesn't change significantly, the brightness stays the same.

The problem comes if you use a common resistor for two or more rows of LEDs. If one of the rows has a lower voltage drop than the others (and since they're inequal, there will always be a row with the lowest drop), the voltage across the whole circuit will be equal to the drop of that row. Then that row will conduct all the current that was meant for all the rows, because the others don't conduct anything at all. Burnination! When the row with the lowest drop burned out, comes the next and so forth. Of course, in reality, this doesn't happen this dramatically, because the LEDs don't keep their voltage drops perfectly (look at a datasheet again), but the brightness of the different rows will be vastly different. Some won't even light up, some will be so bright they will cure your PCB on the opposite side too, and that's not what we want.

jswitzer15 months ago

I don't know if this has been posted before but, I found this site that seems to have everything a decent prices. http://www.flexfireleds.com/shop-by-project/uv-led-lights/

jscoppetta1 year ago

Can i use the plexiglass instead of normal glass ? Or the result will be worse ?

Plexiglass will filter out the UV light.

JacobZ16 months ago

Can you recommend a seller on ebay? Seems all I can find are sellers who can't provide me with a datasheet and it would be nice to have the information handy so I know exactly what I'm buying.

Great build by the way. I was initially going to use an old scanner, but I think I like this project better, plus it keeps me away from mains power and I like that. I'm still not that comfortable working with mains. This project makes me want to build my own design, but I like yours quite a bit. It's definitely got my mind reeling right now.

ddzahn7 months ago

What is that attached to your iron? Is that a hot air rework or something like that?

dudes8 months ago
you could also add a PWM controller for dimming.
johnip49 months ago
I just finished soldering up one board. I did spoil one board. It is a good idea to lay out one row of resistors and LEDs to make sure it fits on your strip board. Mine have a wide trace down each side which had be accounted for. I cut the traces with a small burr in my dremel. I placed the resistors on the copper side but fed the leads thru the holes, soldered at the end of each resistor and then cut the leads flush on the other side. I put my power rails on the component side. There is just enough room with the layout that is provided. In my case when looking from the copper side it would be best to move everything up and to the left at least one row.

Now on to building the box.
I3L4ck5h33p9 months ago

Which sellers on that auction site are you guys getting your LEDs from? I've been reading the reviews for alot of sellers and they mostly turn up negative reviews. I've been coming back to this particular listing (link below). Has anyone done any business with this individual?


PeterH2 made it!10 months ago

I built one of these (1 sided) and it works brilliantly. I compared it with a commercial UV PCB exposure unit and I find the results are much more reliable with this one.

The only problem is that I got a bit of falloff of light at the edges on a large board so I I rebuilt the board using a single sided PCB which was a bit larger and fitted right to the edges of my existing box. It was much easier to solder up and works great. This one has 117 LEDs

I attach a PDF of the track layout in case anyone is interested

dalpets1 year ago

Decided to go thro' hole with the resistors instead of a facsimile of smd. I had no problem with solder track shorts with this method, mainly because I used a 2mm BEVEL tip with .015" (.381mm) 62/36/2 silver solder

dalpets1 year ago

I've come to the conclusion, despite the foregoing, that the only way to make sure that each led is flat is to put something flat directly below the led being soldered. Even so you need to check there is no slack.

Sometimes it might not quite work out that way so it's a good idea to solder only one leg & check for slack. If there is, just apply more heat to that leg. I don't like doing this as there is the risk of lifting the copper track, which has happened to me, so I'm very wary (leary) now on that score. A lifted copper track can cause big problems & if you are near completion of the board it is a real bummer to have to correct with bridges.

Hope this helps.

dalpets1 year ago

Just remembered-I found the the recommended spot tool not nearly sharp enough & very very laborious work when you consider the number of spots you have to do. Save your money on this excuse for a cutter.

On the other hand rolling a new drill bit back & forth between the thumb & forefinger was surprisingly quick & effective. No comparison really.

I originally used a Proxxon hobby drill press with a Dremel drill using an adaptor & a burring drill bit (the Dremel drill press is well known not to be an accurate design). This method is quick but requires a degree of control, and its OK if your doing them all at once, but the real downside is that the resulting dust from strip/Vero board, albeit not huge, is apparently very toxic to the respitory system. If doing it this way make sure it is done in the open air.

Hope this helps.

dalpets1 year ago

A few more tips.

Before doing any soldering I found it obligatory planning to do a dummy placement of leds on the top horizontal row & the left vertical column to make sure that the design is workable for the board size, also making sure that there is room at the bottom of the board for the two power rails. I then marked component placements with texta around the side of the board. When you start soldering use your continuity meter for every solder joint to ensure there are no short circuits between adjoining rails. Its easy to slip up otherwise.

Don't be tempted to follow the instructable blindly, particularly the pics. Make sure you understand how the first of all the blocks works. If necessary do a practice circuit of 2 vertical blocks (of 3 leds each) on scrap board to make sure you have continuity working between blocks.

The author says it tricky to get the leds to sit flat with only two hands. Yes it is, but that can be overcome by using the following simple method. Place temporary unsoldered leds in the 3 corners, ie., other than the corner where you are soldering the first led. Bend their leads over flat to the board. That's a reasonable start. Then place the board on an even flat surface with the temporary leds facing down, whereupon they act as stabilizing legs. There will still be some small slack between the board & leds but if you place a reasonably heavy weight on the top of the board ( I used a cheap steel sticky tape dispenser) the slack will be taken up completely & voila the leds then sit perfectly flat.

I hope this helps for those of us that are challenged with circuit design.

dalpets1 year ago

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.

dalpets1 year ago

Got it to work at last. This is very, very detailed work. Easy to make mistakes along the way. Needs some serious time, effort, continuity testing & unlapsing concentration to get it to work first time. Don't do it when you're tired. Screw up with the spot cutter too many times & you'll need to toss the board.

Saves heap on buying a commercial unit, but hey you need to be a masochist to do it.

Great project mate, followed as best I could but am having problems getting all of the LEDs to light up despite checking the circuit and replacing components. I am using .5w 75r with 3.2-3.8 V, 75ma peak, 20ma forward LEDs. And a 12v 7.5a power supply to test. Could it be a problem with this combination? Any advice appreciated!
Bertz1 year ago

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.

jmatharu1 year ago
hey! very useful post!
I was wondering instead making a new circuit board can we use the LED light strip?
I am a graphic student and want to use it to expose my screen printing screens will it work on them?
Many thanks.
dillonxti1 year ago
Parts express has UV led kits of 100 for $9.99
jbromley2 years ago
This is a very nice instructible. It is the most complete UV box I've seen. I do have one question. Is there a reason you put the jumpers and resistors on the copper side of the board and not on the component side? Was it just an aesthetic decision? Or will the UV cause component degradation of some type?
agodinhost4 years ago
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.
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
Isnt 200mcd WAAAY too little?
jeddar3 years ago
I have a question, would the output from this UV box be enough for it to be used as a sterilizer box? I do my own beer/wine brewing and I'd love to be able to fit a rig I could use to sterilize equipment in between batches..
Sterilization also takes place at 365nm, however, to get the type of power needed would require a much more robust, i.e. $$$, set of LEDs that can output some real power. You'd also have to do some extensive testing to make sure sterilization is taking place, the research articles I've seen were using 15 to 30 minutes exposures to achieve complete sterilization of bacteria.

I think using a non-toxic spray method would be a lot quicker and cheaper in the end.
CODIY jeddar3 years ago
No, the wavelength for sterilization is much shorter than this type of LED can emit (<300 nm where these are likely closer to 400 nm). UV LEDs for sterilization are expensive and difficult to find in small batches.
MFXPYRO2 years ago
I built a double sided UV exposure box with vacuum pulldown around 10 years ago using tubes and it is still going strong without replacing the tubes. Also my box will do boards up to A3 size, How many LED's and what would they cost for an A3 sized double sided unit? Yes they're more energy efficient but no one is going to have a unit running for more than a few minutes at a time so cost is negligible. You've made a nice looking unit but I just can't see any real benefit of LED's over tubes both in cost and construction time. TBH. Hopefully I'll post an indestructible of my unit soon but as I built it so long ago I'll need to dismantle it for photos.
Aquafuz2 years ago
I'm a bit lazy to research this so I guess I'll just ask,
Which will give better and faster results; total watts, total mcd or both?
lsilva142 years ago
I managed to finish this project, but with some mods of my own :p

Instead of painting the wood white, I covered it with metallic duck tape which gives me extra brightness.

I also tested some pcb that usually take 120s in a retail exposure box with UV lamps and they took the same 120s in my box with the LED.

Thanks for the idea and the design, it is excellent!
So i found some LEDs but they peak at 400-405nm, everything else checks out. Will they still work?
Jake3132 years ago
Awesome project! Are those Metal Film Resisters?
Jakob28032 years ago
Looks very nice, I might copy your project and make a scaled-down version! ;)
rlorenzo3 years ago
can i just use a normal LED.....?
no because a normal coloured LED does not operate at the right frequency to be used for this purpose due to the wavelengths being different this diagram i found on google images shows the uses of the wavelength. :)
rlorenzo3 years ago
can i just use normal LED's ??? this parts are hard to find here back in Pilippines.

UV LED is available at e-gizmo (taft ave, along DLSU). 3.50 PHP a piece.
1-40 of 137Next »