Introduction: How to Make a Printed Circuit Board (PCB) Using the UV Light LED Method.

Picture of 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.

Picture of 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.

Step 2: Draw Your Circuit Schematic.

Picture of Draw Your Circuit Schematic.

One circuit schematic/layout program that is free is EAGLE. The program can be downloaded from http://www.cadsoftusa.com/

Once the schematic and layout are drawn, it is time to print the layout onto a transparency.

To print only the desired circuit, turn on only the Top Layer, Pads, Vias, and Dimension. This is done by selecting View -> Display/Hide Layers in the Layout editor and selecting the correct settings.

The Layout is now ready to be printed, make sure that the image is mirrored so that text shows up correctly after being transferred onto the PCB. We printed the circuit with our Brother HL-2070N (on highest quality) laser printer and MG Chemicals transparencies.

Note: We originally bought transparencies for inkjet printers and laser printers (one side was textured for use with inkjet printers, the other side was smooth for laser printers). We had read a PCB tutorial where the guy used the textured transparency paper without problem. From our experience, the textured side did NOT allow UV light to pass through. Only use transparency paper with smooth surfaces.)

Step 3: Expose the Presensitized Circuit Board to UV Light.

Picture of Expose the Presensitized Circuit Board to UV Light.

Place the printed transparency on the elevated plastic about 10 inches above the LEDs. The ink should be facing up towards the sky. While the room is somewhat dark, peel the white film off the presensitized circuit board to expose the photoresist. Place the PCB on top of the transparency, photoresist facing down towards the LEDs. Stack about 8-10 textbooks on top of the PCB to make sure the photoresist is tightly pressed against the ink of the transparency. No scotch tape is necessary to hold the PCB down to the transparency.

Turn the UV light box on. We found that exactly 1 minute exposure time worked well. You may have to experiment with different times depending on the height above the LEDs. Turn off after 1 minute.

The photoresist will look exactly the same after it has been exposed to UV light. We could not tell the difference between an exposed board and a non-exposed board.

Note: The first time you attempt to make a PCB, you will most likely fail (we failed literally about 40 times. Darn textured transparency paper!). We suggest buying a large PCB and cutting it into small squares with a Dremel (I also read a paper cutter works fine). This will save you a lot of money.

Step 4: Prepare the Developer Solution.

Picture of Prepare the Developer Solution.

Prepare the MG Chemical developer solution with 1 part developer, 10 parts tap water. I used 1/4 cup developer, 2 1/2 cups of tap water. Be sure to mix the solution with tap water thoroughly before placing the PCB in the solution, otherwise the photoresist will be eaten away in undesired spots.

Place the PCB in the mixed solution and shake it around face up. The parts where the photoresist was exposed to UV light will be washed away in about 5-10 seconds. Do not leave the board in the developer solution for too long, otherwise all the photoresist will be washed away. Place the PCB in cold water immediately to stop the reaction once the board is finished.

The developer solution can be re-used for multiple PCBs.

Note: The solution is dangerous to skin and eyes. We suggest wearing gloves and goggles.

Note: We tried all sorts of chemicals to eat away at the photoresist. We found that the MG Chemical brand developer worked the best. You could also try using Sodium Hydroxide (Lye from Ace Hardware) but you will have to experiment with what % to put in tap water. The percentage of Sodium Hydroxide to tap water is important because too strong of a solution will wash away your non-exposed UV photoresist.

Step 5: Etch the Copper Away.

Picture of Etch the Copper Away.

Prepare a solution of 1 part Muriatic Acid, 2 parts hydrogen peroxide. I used 8 oz. Muriatic acid, 16 oz. hydrogen peroxide. Be very careful with this acid, it's a lot stronger than the photoresist developer. I suggest using a fan over the bucket so you don't breathe in any of the fumes. Wear gloves and goggles.

Add the PCB to the solution and shake the bucket carefully. The solution will start to turn green as the copper is being etched away. As soon as all the copper is etched away, remove it from the bucket. The copper will take about 2 minutes to be etched away completely.

Wash the PCB off in a bucket or use a hose.

Step 6: Remove the Photoresist

Picture of Remove the Photoresist

Remove the photoresist with Acetone and a Q-tip. The photoresist will come off very easily with a Q-tip dipped in Acetone. Keep using new Q-tips until the Q-tips are white after you have swabbed the board.

Step 7: Populate Your PCB With Parts

Picture of Populate Your PCB With Parts

At this point, you have a PCB to populate with integrated circuits and parts. Enjoy your PCB and let me know if you have any questions.

Step 8: Mistakes

Picture of Mistakes

-Having the LEDs too close to the printed circuit board in the light box. The LEDs need to be sufficiently far enough for light to spread evenly throughout the circuit board. 10 inches away from the LEDs worked for us.

-Using textured transparency paper. The UV light did not pass through the transparency because of the texture. The solution is to use non-textured transparency paper. The photoresist will have little streaks of un-exposed UV. The MG Chemical brand transparencies worked well.

-Using sodium carbonate and sodium bicarbonate as a photoresist developer. Neither of these worked for us.

-Too much sodium hydroxide when used as a photoresist developer. All of the photoresist (including the non-exposed UV) was washed away in a few seconds. We suggest measuring the amount of sodium hydroxide and finding a mixture that works. If you don't want to spend the time doing that, use the MG Chemical photoresist developer.

-Adding sodium hydroxide while the PCB is already in the photoresist developer solution. This will instantly remove undesired parts of your photoresist. We suggest stirring the solution first, then dipping the PCB in the solution. If you need to add more sodium hydroxide, take the board out, add sodium hydroxide, stir the solution, then put the board in when the solution is mixed up well.

-Using "party" blacklights. We originally used three 4W party blacklights in an old scanner. The blacklights did work but not as well as the LEDs.

-Using a 500W halogen bulb. This bulb was too intense. It was difficult to find the correct exposure time.

-Using full size PCB's for testing. Don't waste your money using full size PCB's when testing, expecting the first board to work. Use a Dremel or paper cutter to cut a large PCB to save money.

Comments

purpulhaze (author)2012-09-28

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.

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.

JohnathanW15 (author)purpulhaze2017-06-11

pst...miter or tabel saw with 10inch 80 tooth $25 buck blade from harbor freight. my 5400rpm compound miter blasts through 1/4 in plexi w/o a chip... only issue i have is ryobi cm saw doesnt get or stay square very well so for my current project i took the blae to a friends house cause he had a compadible dewalt table saw. saw was like 3xxx rpms and still very little a few chips to none at all

haze78 (author)2010-11-25

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 (author)haze782011-03-08

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.

apburner (author)JoeyJunior2015-07-14

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.

haze78 (author)apburner2015-07-15

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...

JohnathanW15 (author)haze782017-06-11

uh in practice it would seem connecting a bunch in series and multiplying nominal FV is done all the time. esp if hooked to a cc/cv dc-dc converter. Pull the light strip off a dead lcd once (make sure its not old ccfl style )

mitchells365 (author)apburner2016-01-15

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.

throbscottle made it! (author)2016-08-30

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)

I used cheap prototype board off eBay, but the 198 LED's don't quite fit, so there are a couple in odd places!

I have mostly made a box 11" 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!

Thanks for a great instructable :)

rajkumar181 (author)2016-07-26

i want to buy hole setup . how i can get it.

puvanv (author)2016-01-26

1. which chemical should i have to use for photoresistive coating

2. I am using CFL(28 w) lamp to transfer my circuit through ohp sheets, please guide me the wattage required for cfl

kunstlich (author)2015-05-15

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.

agr00m (author)2015-02-27

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?

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 :)

agr00m (author)agr00m2015-03-13

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?

adryanroman (author)2015-01-10

Hy, can I use just acid muriatic for etch ?!

Azeunkn0wn (author)adryanroman2015-02-02

hmmm... i don't think so.

jedike (author)2014-09-26

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 ?

Its like they don't want to light up completely ?

I got them on ebay like you did from the same guy actually.

Any suggestions what went wrong ?

I use also 12 Volt and same resistors as in your example.

I tried with other normal leds in this configuration and they do work, only the UV leds don't seem to work normally.

Triakdiak (author)jedike2014-11-29

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.

baecker03 (author)2014-04-05

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.

conoral11 (author)2010-05-09

What mcd rated LEDs are you using?

VadimS (author)conoral112013-01-26

mcd is a reading of the brightest spot of the LED, not the total output, so it's useless.
Just look for some 20ma LEDs.

haze78 (author)conoral112011-04-11

2000mcd, 395nm LEDs will suite you just fine

JoeyJunior (author)conoral112010-05-16

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.

VadimS (author)2013-01-26

Looks good, definitely on my to do list.
Glass doesn't block UV in the 400nm range so it's the best bet.
Some plastic does but most should be alright sins 400nm is borderline and is actually in the visible spectrum.

cc67 (author)2012-03-03

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

f2a (author)2010-08-12

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

f2a (author)f2a2010-08-24

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 (author)f2a2011-05-27

please, what's the dimensions of this box?

JoeyJunior (author)f2a2010-08-24

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 (author)JoeyJunior2011-04-11

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.

gulyman (author)2010-11-28

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

JoeyJunior (author)gulyman2011-03-08

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

ildefonso (author)2010-11-17

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 (author)ildefonso2011-03-08

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

Pyrotechnic-Robot (author)2011-01-07

Hello, i was wondering what solder paste you use?

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

Trickynekro (author)2010-12-12

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

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

Cruwe (author)2010-03-12

 What is the pitch of the larger IC footprint?

JoeyJunior (author)Cruwe2010-03-16

It's .5 mm pitch.

Skyriam (author)2009-11-08

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

JoeyJunior (author)Skyriam2009-11-23

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 (author)JoeyJunior2009-12-28

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 (author)JoeyJunior2009-11-24

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

Davad (author)Skyriam2009-12-28

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. 

andreq (author)2009-07-06

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 (author)andreq2009-12-28

Hi andreq,

How are you doing your green solder mask?

andreq (author)Davad2009-12-28

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 (author)andreq2009-07-06

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 (author)andreq2009-07-06

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 (author)2009-12-09

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!!

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