This instructable shows how to create well done PCB's using Ultraviolet light. It took us about 40 boards before we perfected our PCB, so we will share what worked and what didn't work. All the supplies can be bought from Fry's Electronics, Ace Hardware, Goodwill, Radio Shack, and Ebay . Our PCB tested the Atmel 208 pin PQFP Integrated Circuit (it may not look like it from the poor image quality but there were no shorts between all 208 pins! ).

The materials needed are as follows.

-Transparencies (MG chemicals brand http://www.mgchemicals.com/products/416t.html )
-UV Presensitized Copper Clad Boards (MG chemicals brand http://www.mgchemicals.com/products/600.html )
-Laser printer (Brother HL-2070N)
-200 UV LEDs (Bought from Ebay - Asia Engineer, seller giorgio11185. 5mm size, 3.4~3.8 forward voltage, forward current 20 mA, wavelength (nm) 395-400-405, view angle about 25 degrees.)
-200 470 ohm resistors (included with Asia Engineer LEDs bought on ebay. I used 12V for each LED).
-4 Breadboards for LEDs (http://www.radioshack.com/product/index.jsp?productId=2102843 )
-PCB Standoffs (http://www.radioshack.com/product/index.jsp?productId=2102848 )
-Chest/box to house LEDs (Bought at Goodwill. 20 inch length x 12 inch width x 11 inch height)
-Picture frame transparent plastic (Bought at Goodwill)

-Muriatic Acid (http://www.acehardwaresuperstore.com/transchem-muratic-acid-for-use-in-etching-concrete-p-5243.html )
-Hydrogen Peroxide (http://www.walgreens.com/store/product.jsp?CATID=302248&navAction=jump&navCount=0&nug=VPD&skuid=sku1375525&id=prod1375535 )
-Photoresist Developer (MG chemicals brand http://www.mgchemicals.com/products/418.html )
-Baking Soda (local grocery store. Use if any acid is spilled on your skin)
-Acetone (Ace Hardware)

-Soldering Iron (any soldering iron will do, I used http://www.amazon.com/Weller-WESD51-Digital-Soldering-Station/dp/B000ARU9PO/ref=sr_1_1?ie=UTF8&s=hi&qid=1246827601&sr=1-1 )
-Solder (We originally bought Lead free solder. This type of solder did not work. Instead we used Sn63/Pb37, 2.2% Flux, 23 gauge MG Chemical brand)
-26 and 16 gauge wire
-Wire stripper
-Gloves (bought at Ace Hardware)
-Goggles (bought at Ace Hardware)
-Power Supply (wall wart or benchtop power supply will do. Make sure your power supply can handle the current the LEDs consume. As you can see from my photo, my voltage was 11.9V and 3.47 Amps were consumed).
-Q-Tips (local grocery store)
-Buckets for chemicals (Ace Hardware)

Step 1: Build Your UV LED Light Box.

We purchased our chest at Goodwill for $6. We suggest finding a box that is about 1 foot in height.

Elevated transparent plastic/glass is used to hold the transparency paper and presensitized copper clad about 10 inches above the LEDs. The transparent plastic was taken off a picture frame purchased at Goodwill. Keep in mind that some plastics/glass do not allow UV light to pass. Some experimenting is needed to find one that works well.

The picture below shows how Monnie arranged the LEDs on the breadboards purchased at RadioShack. We spaced the LEDs out by 6 holes from all sides.

Banana jacks were inserted in the backside of our box to be powered by a benchtop power supply.
<p>I changed the power supply arrangement so it runs directly off the mains (at the moment an isolation transformer whilst I test things). I discovered that the mains voltage can change by as much as +10% and -6% in the UK, so I found this voltage limiting circuit to keep the DC down to 300V. The 3 4k7 resistors drop 84V each, and the 3 LM317's provide 18mA per series chain of 66 LED's. (see pdf)</p><p>I used cheap prototype board off eBay, but the 198 LED's don't quite fit, so there are a couple in odd places!</p><p>I have mostly made a box 11&quot; deep with the board this is mounted on forming the base. It's not a very good box - I need to find one like yours!</p><p>Thanks for a great instructable :)</p>
<p>i want to buy hole setup . how i can get it.</p>
<p>1. which chemical should i have to use for photoresistive coating</p><p>2. I am using CFL(28 w) lamp to transfer my circuit through ohp sheets, please guide me the wattage required for cfl</p>
Thanks for the project. Just one advice; LED powering system you're using is rather inefficient, only 29% percent efficiency, you're using 41W to power up 12W worth of LED's. You might consider some circuitry to drive LED's more efficiently, or maybe chain 2 LED's in series at least, this way you could increase efficiency to about 63%. Other more efficient solutions require more complicated and expensive circuitry (like max LED drivers, or constant current circuitry).
Yup, you're right. The reason I didn't put a couple LEDs in series was because the LEDs came with 470 ohm resistors and I didn't want to buy more resistors. Something like a 5V buck DC/DC converter would be pretty cool to add in the box (something like an LTC3835), maybe I'll make a PCB for one.
<p>LED's run just fine on 3 volts without a resister. So you could wire then as 4 in series and then just hook them up to a 12v supply. Then there would be no resisters to waste power as heat.</p>
<p>Nope, very bad idea!!! The internal resistance of an L.E.D. is very low which is why it needs a resistor. Semiconductors behave differently than passive circuit components. without at least one resistor the L.E.D.'s will have a very short lifespan. Just because the voltage drop of a single LED can be 3 volts(Not always), doesn't mean you can just hook up 4 L.E.D.'s in series and expect everything to be alright. An L.E.D. usually can only be driven with about 20 milliamps of current, and without a carefully chosen resistor, the LED's will receive much more than their rated current; which of course can burn them out.</p>
No my friend. LEDs do NOT run fine just on 3v without resistor. You do need to limit current, and this is a MUST! Secondly, not all leds run on 3v, that is usualy correct for white LEDs, however red LEDs take something like 1.6v, so it is not a true statement for every LED. Thirdly, you cannot just connect bunch of LEDs in series and multiply nominal voltage with number of LEDs, due to voltage balancing issues. What you need is constant current source or a resistor to limit current, otherwise your LEDs are not going to glow for a long time...
<p>What was the power rating of your LED's? I've just bought some on eBay but they don't seem very bright. I appreciate that they're UV though so the 'brightness' I see might not be relevant to the brightness that it's actually emitting though.</p>
<p>Thanks for the writeup! Question about the developer solution. About how many uses did you get from 2-3/4 C mixture you made? Is it like etching solution where it loses potency after several uses?</p><p>FYI - I know your UV board is already built, but for those that have not it would probably be better to run 3 LEDs in series with a 30-90 ohm resistor (depending on actual LED voltage). It would save a lot of power loss and heat dissipation, not to mention less soldering :)</p>
<p>One more question. Do you need to take any precautions when transporting the UV exposed PCB to the developer solution? Should the PCB be put immediately back in a light-protected sleeve, or did you just immediately move it from the UV box to the solution?</p>
Hy, can I use just acid muriatic for etch ?!
<p>hmmm... i don't think so.</p>
<p>Hi, I tried this but the problem is that my UV leds don't give the nice glow like I se on this picture. It is more like just a small red point in the middle of each led ?</p><p>Its like they don't want to light up completely ?</p><p>I got them on ebay like you did from the same guy actually.</p><p>Any suggestions what went wrong ?</p><p>I use also 12 Volt and same resistors as in your example.</p><p>I tried with other normal leds in this configuration and they do work, only the UV leds don't seem to work normally.</p>
<p>Hi.I have bought this UV leds from the same seller on ebay and they are ok. I think that maybe seller has sent you wrong LED diodes. They also sell infrared LED diodes and human eye can not see that light , maybe you can see only small red dot in the middle of LED diode. You can make one test , point your camera on this LED , and you will se light which this diode is producing on your camera if that is the case then you have wrong diode.</p>
<p>you can buy uv smd leds on ebay fairly cheap (guessing 10-20 bucks) just use a collimating lens to create parallel light waves. you would of course want to keep it a distance away.</p>
What mcd rated LEDs are you using?<br />
mcd is a reading of the brightest spot of the LED, not the total output, so it's useless. <br>Just look for some 20ma LEDs.
2000mcd, 395nm LEDs will suite you just fine
I am not sure on the mcd rating of the LEDs.&nbsp; I&nbsp;bought the LEDs from a seller on ebay, he did not provide the mcd rating.&nbsp; If you search for &quot;UV&nbsp;LED&quot; in ebay, I purchased the ones for sale by Asia Engineer.<br />
Looks good, definitely on my to do list. <br>Glass doesn't block UV in the 400nm range so it's the best bet. <br>Some plastic does but most should be alright sins 400nm is borderline and is actually in the visible spectrum.
My boards are not far from the leds and they' ve came out ok. Though I am using straw hat leds and I also have a diffused piece of plexi over the top of them. What are you using to cut your boards? I can't get a clean straight edge to save my life. <br> <br>I also used the acetone a few times but have switched to using a solution of water and 3-5% lye drain cleaner. I just let my boards sit in the solution for a few seconds and they come out shinny and resist free.
Is there anyway of doing this method... but instead of using laser printer, use inkjet? I just do have an inexpensive deskjat printer... tnx in advance
I made a UV light box out of a cigar box that turned out great.
Unfortuantely I haven't tried it out yet. But I used flat top leds with around a 120 degree angle. So you can put the leds really close and make a much smaller box.
please, what's the dimensions of this box?
Looks awesome! Did you have any troubles with the LEDs being too close to the PCB? You can see a picture of a failed PCB on my last page where the PCB was too close and you can see the holes of the LEDs on the photoresist.
You can solve LED distance problem by puting 2 sheets of tracing paper over LEDs. Paper sheets should be separated 5mm minimum. Two layers of tracing paper will blur UV light, without inerfering with its intensity. That's the way I did it, works good, and I use 20 degree LEDs on 4cm distance.
I have that exact C++ book. It's a pretty good one.
Haha nice, yup that's how I learned C++.
Hi!<br><br>Just one question: why not remove the photoresist from the pads and leave the rest of the tracks covered with the photoresist? I think the photoresist could help protect the copper. What do you think?<br><br>
Yeah you could leave the photoresist on the tracks, no problem with that.
Hello, i was wondering what solder paste you use?
I didn't use any solder paste. I just hand soldered everything at the end.
You can also remove the photoresist with simple alcohol... ;-)<br><br>This can save some trying to find acetone....
&nbsp;What is the pitch of the larger IC footprint?
It's .5 mm pitch.<br />
Is this UV-Light method better for making PCB's? What's the difference to &quot;normal&quot; PCB making? &nbsp;How is it better? Thanks!
Yup, it's better.&nbsp; The differences are:<br /> <br /> If you want to produce more than one PCB, this method allows you to make more than on PCB with the same transparency.&nbsp; The other method (assuming the iron on method), you have to print out a new transparency every time.&nbsp; <br /> <br /> You will be able to accomplish thinner traces by using the UV light method.<br /> <br /> The main reason I chose this method was because I tried the iron on method and could not get the ink to stick to the PCB.&nbsp; Plus I&nbsp;had fun making the lightbox&nbsp;:)<br />
Also, MG chemicals now has negative dry film resist. All you need is a laminater<br /> to put the film on a copper clad board. The resist is exposed with a daylight fluorescent lamp One can do single or double sided boards. The only draw back is you have to work under a yellow or red light&nbsp; like you would in a dark room.<br />
Ohh I see the light now...&nbsp; thanks for answering!
Way better boards from this method. I thought using LEDs to build an exposure box would be kind of expensive so I went out and bought a fluorescent black light for $15 to do the exposure. An 8 minute exposure time worked great. Plus you can reuse your artwork.&nbsp; <br />
Hi, I' using the same method to make my own PCB. I didn't have to waste 40 pcb to get good result :) I first did a test pattern ( 5mil to 50 mil lines on a small 1"x6" pcb) to find the best exposure time. You can see it in my gallery. I've attached my third PCB. It's a small i2c digital volume control for an Amp I'm currently building. The only issue I have is that my design is wrong. I grounded a pin that shouldn't be grounded. Anyway it was easy to repair with a small cut and 2 jumper wire. The second picture show a little "too much copper" under the "OUT" wire pad. The text is 3 or 4 mill I think. I'm using Staple Ink jet transparency paper (somewhat textured) and print at 600DPI. Stacking 2 or 3 layers is the key, you will get a perfectly dark (no light pass trough) pattern. Also, do not click "Print in Black only" (or gray scale) in your printer setting, the mix of color ink in the black ink seem to works better at blocking light than black ink only... I use the same mg chemical board with 3:30min exposure time.
Hi andreq,<br /> <br /> How are you doing your green solder mask?<br />
There is no solder mask.<br /> <br /> I've only removed the &quot;positive&quot; on the solder pad with a Q-tip imbibed in alcool.<br /> <br /> The green part is the developed &quot;positive&quot; film.<br />
That's a good idea using 2 or 3 layers so UV light is not allowed through the transparency. I'll have to try that and see what happens. Nice boards!
Furthermore, my first and second PCB where cleaned of all the positive uv resistant material, but I found that only rubbing the solder pad give a nicer "professional" finish and also protect the non soldered traces. As I don't tin my board, I think it's a good idea. That's why this board is part "green" and part "copper"
Sorry to bother you again =s.... stupid question: How do you make pcb's out of uv light? Do you need a special copper clad that has a photoresist material? &nbsp;Thanks joey!!
Yup, you need a special copper clad that has the photoresist.&nbsp; I&nbsp;bought these at Fry's Electronics:<br /> <br /> http://www.mgchemicals.com/products/600.html<br />
Nice job! A somewhat pissy observation, but you could have wired the LEDs as 4 in a series and done away with the resistors. This would have saved some power - at the risk of having a group of 4 go out if one failed. Steve

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