How to make a printed circuit board (PCB) using the UV light LED method.

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.

PCB:
-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)

Chemicals:
-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)

Tools:
-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)
-Screwdriver
-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)
-Timer

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.

Comments

[f2a]

I made a UV light box out of a cigar box that turned out great.

[f2a]

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.

[agodinhost]

please, what's the dimensions of this box?

[JoeyJunior]

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.

[haze78]

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.

[conoral11]

What mcd rated LEDs are you using?

[haze78]

2000mcd, 395nm LEDs will suite you just fine

[JoeyJunior]

I am not sure on the mcd rating of the LEDs.  I bought the LEDs from a seller on ebay, he did not provide the mcd rating.  If you search for "UV LED" in ebay, I purchased the ones for sale by Asia Engineer.

[gulyman]

I have that exact C++ book. It's a pretty good one.

[JoeyJunior]

Haha nice, yup that's how I learned C++.

[haze78]

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).

[JoeyJunior]

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.

[ildefonso]

Hi!

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?

[JoeyJunior]

Yeah you could leave the photoresist on the tracks, no problem with that.

[Pyrotechnic-Robot]

Hello, i was wondering what solder paste you use?

[JoeyJunior]

I didn't use any solder paste. I just hand soldered everything at the end.

[Trickynekro]

You can also remove the photoresist with simple alcohol... ;-)

This can save some trying to find acetone....

[Cruwe]

 What is the pitch of the larger IC footprint?

[JoeyJunior]

It's .5 mm pitch.

[andreq]

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.

[Davad]

Hi andreq,

How are you doing your green solder mask?

[andreq]

There is no solder mask.

I've only removed the "positive" on the solder pad with a Q-tip imbibed in alcool.

The green part is the developed "positive" film.

[JoeyJunior]

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!

[andreq]

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"

[Skyriam]

Is this UV-Light method better for making PCB's? What's the difference to "normal" PCB making?  How is it better? Thanks!

[Davad]

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. 

[JoeyJunior]

Yup, it's better.  The differences are:

If you want to produce more than one PCB, this method allows you to make more than on PCB with the same transparency.  The other method (assuming the iron on method), you have to print out a new transparency every time. 

You will be able to accomplish thinner traces by using the UV light method.

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.  Plus I had fun making the lightbox :)

[Davad]

Also, MG chemicals now has negative dry film resist. All you need is a laminater
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  like you would in a dark room.

[Skyriam]

Ohh I see the light now...  thanks for answering!

[Skyriam]

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?  Thanks joey!!

[JoeyJunior]

Yup, you need a special copper clad that has the photoresist.  I bought these at Fry's Electronics:

http://www.mgchemicals.com/products/600.html

[sr1sws]

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

[microman171]

"at the risk of having a group of 4 go out if one failed" Gotta love LEDs! If one dies, it turns into a jumper. So you end up with 3 in series vs 4. I think you will need to design the circuit with this in mind - if you didn't, then your 3 LEDs may over current and die too. Then your really would lose a set of four. Reminds me of the time I spent with a multimeter and a 150 light chain at Christmas... Back before they put the little jumper resistors in them (the thin wire around the bottom).

[Pazzerz]

LEDs fail like a resistor fails. It either turns into a short or it blows wide open. I have yet to see one short.

[sr1sws]

Yeah... nothing's perfect. Another technique is to use an adjustable voltage regulator (lm317) as a constant current source. I did this in a set of puddle lamps I made for my 2000 Explorer. LEDs (white) were in sets of 3 or 4 (I don't recall which) and the sets wired in parallel. I'm sure there's some draw back here too, but it is another option ;-) Steve