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I have been an avid electronics DIY guy for many years now, and I have spent a lot of that time struggling to learn how to make my own PCBs. I have tried every technique that I have come across on the internet, from iron-on print outs to dry photosensitive blue sheets. Sometimes I was successful in my efforts to make a passable PCB, but when it was time to reproduce those results, something would go wrong.

After a lot of attempts and frustration, I was determined to find a solution that didn't result in me sending my files off to a PCB fab house. I use a fab house after I have tested a design on a homemade PCB. I finally found a solution where I can reproduce aesthetically pleasing PCBs by using liquid negative photo-sensitive paint. In this Instructable, I will share with you a technique that I have developed to do this.

DISCLAIMER:

Hazardous chemicals are used in this tutorial and I am not responsible if you hurt yourself. Practice caution, follow common safety guidelines at all times, and use gloves and protective eyeware.

Step 1: Supplies

Gather the supplies needed.

1. Photosensitive paint

2. Small spatula

3. Mixing jar

4. Heat plate ( optional )

5. Silicon or plastic tongs

6. Protective gloves and eye-ware

7. Copper clad board

8. Scale ( optional )

9. Plastic container for etching

10. Aquarium pump with stone diffuser and hose

11. Inverted PCB artwork printed on a laser transparency

12. Paint brush

13. Jar to put the developing solution in

14. Clear plastic or glass plates and some clips

15. Chemicals:

Hydrochloric acid (aka Muratic Acid from hardware store in the pool section or also found as a concrete cleaner)

Hydrogen peroxide

Sodium hydroxide (drain cleaner)

Sodium carbonate (aka Washing soda found next to laundry supplies)

Acetone

<p>Nice work. Very professional looking.</p><p>I have a suggestion. Printers use a small rubber roller, called a <a href="https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcQArEocBIu5-Qb0plSF2xdHK37LWFBwG45yLYu2rvcocbdAS5Notg" rel="nofollow">brayer</a>, to create a thin uniform layer of ink on a platen. The same technique may be suitable here. A small blob of paint at the center of the board and randomly roll across it with the brayer until a uniform film is produced. That would avoid the need to thin the paint (one less messy and smelly step) and would give a very uniform thickness. The uniformity of the film would make it easier to get uniform contact with the negative.</p><p>Let me know if you try it, and if it works out.</p>
<p>good idea</p>
<p>Excellent idea! I had been thinking about using a simple paint roller too, but I think a brayer would be a lot easier to clean. I have to get one now, thanks!</p>
<p>The use of a brayer is a good idea, when you might think of using is a hand roller on a flat surface like a thick plate of glass to uniformly spread the photosensitive paint. The glass and roller can both be easily cleaned. Another idea is using a photosensitive spray. </p>
<p>I used a similar product in the 70's. It was a Kodak red coloured positive resist. We had a dipping system to make sure the coating was of a consistent thickness. It used a small motor gearbox to lower and then raise the PCB in to and then out of a tank filled with resist liquid. </p><p>The tank was about 300hx300wx25d and was filled with the resist. We made a lid that fitted snugly when it was not in use to prevent evaporation and keep it sealed from UV light. </p><p>The motor was designed so when you pressed the start button the PCB was lowered into the resist. Once it reached the bottom it began to raise the PCB. The motor had a speed control to adjust its operating speed, so you could control the speed that it entered and more importantly the speed that it was raised from the resist. By controlling the speed it was raised out of the liquid resist you were able to control the thickness of the resist. At a slower speed the resist coating was thinner, because the resist had more time to drain off the surface of the PCB. Raising the PCB more quickly would give less time for the resist to slide off the surface of the PCB and so the resist would be thicker.</p><p>It gave very consistent results when adjusted correctly. After coating the PCB it was baked in an oven at 80 deg C, for 10 min. The oven was actually an incubator used for chemical cultures and incubating eggs. If you didn't have an oven you could leave the coated PCB overnight in a box or cupboard for the resist to dry (maybe your resist is similar).</p><p>The downside is that both sides of the PCB were coated, so more resist was used and the PCB had to be made slightly larger, to enable 2 holes to be drilled along one edge so it could be attached by a couple of hooks to to the motor system.</p><p>Before we designed the dipping tanks we simply used a soft brush to coat the PCB as evenly as possible before putting it in the oven. after doing this for a<br>while you got pretty good at it.</p><p>Nowadays I use Kinsten pre coated positive resist PCB, which gives the most consistent results you could wish for..</p>
Can you add instructions about how to green mask this board that woud complet this instructable <br>Thank you in advance
<p>Does the stripping solution have to be heated/boiling, or does the heat just speed up the process? And what material does the frying pan need to be (stainless steel, cast iron, teflon coated, etc)?</p>
The sodium hydroxide solution has to be boiling hot to help strip the cured paint off. You should do it in a stainless steel pan or pot, and be VERY CAREFUL! Use gloves and work slowly. Don't breath the fumes and have good ventilation. The paint should strip off in a few mins while the pcb is simmering.
<p>You said that when exposing the circuit on the transparency to the copper board, you had the toner side facing down, against the board. Did you mirror the image as well as invert it? It seems like the orientation would be wrong otherwise.</p><p>Otherwise, awesome work. It looks really nice!</p>
Yes the pcb traces are inverted in EAGLE. Thank you for the kind words!
<p>How long can you store the Photo resist?</p><p>What is the concentration of the H2O ? Here (Germany) an Islamist was busted because his wife bought 3 1ltr bottles of 10% H2O2, which was not illegal btw. But over 10% you must show your ID and will be registered.</p><p>The concentration of the hydrochloric Acid is also missing.</p>
<p>I dont know how long you can store the photo resist. The H202 is 3%, and the acid is 31%. You can see it on the labels in the pics.</p>
<p>Use a hair dryer to dry the paint</p>
<p>Hi @jscanlan. hows the result using the hair dryer to dry the paint? it is works good?</p>
<p>Guys please help me... I don't know what I am doing wrong... I use regular paint thinner to make photoresist easier to apply, after I use hot plate to make it dry. everything is great until I start to expose and develop. Nothing happening at all, resist not changing colour doesn't matter how long I exposing. sodium carbonate not working at all. Before I tried to work with dry negative film, and results was great, but now I want to do metal etching so I am use liquid photo resist. please help me to fing my mistake. </p>
<p>How do you discard the etching solution?</p>
I don't discard it, I reuse it. After a few uses the solution will turn a dark green color or even brown. If you simply leave the the solution bubbling with air, it will turn back to a lime green color and be ready to use again. If you don't plan on using it again you can neutralize it by diluting baking soda ( sodium bicarbonate ) in water and then adding it to the etching solution. You will need a lot of baking soda solution to deactivate the acid. You know its done when the solution can not etch anymore. Take the remains of all solutions in this tutorial to your local hazardous waste disposal facility. Do not pour it down the drain!
<p>@synthdood, have you personally reactivated that kind of solution with air? If so how long did it take to reactivate?</p>
<p>I used to use ferric cloride from radio shack at 7.99/bottle. Now I use the cupric cloride solution. I have been using the same solution for 3 years with little maintenance. I bubble air through it till it is bright green when I drip it on a white paper. I use a battery hydrometer to keep the specific gravity at 1.3, and I check the acid concentration by titration, which is very easy after you try it. The whole solution maintenance takes less time than the time it takes to heat it up before an etch. I keep it in a (VERY clearly marked) bleach bottle between uses. Check out </p><p><a href="http://home.exetel.com.au/adam.seychell/PCB/etching_CuCl/index.html" rel="nofollow">http://home.exetel.com.au/adam.seychell/PCB/etching_CuCl/index.html</a></p><p>it is a very detailed article on the cupric cloride etchant and how to maintain it. At some point, I guess the copper will saturate the solution, but I have etched over a hundred boards and I haven't got there yet. At that point, I guess I will take a portion of what I have to the hazwaste facility and thin the rest to use more.</p>
<p>Yes, it takes a long time. I let it bubble for a day or two.</p>
<p>I use sodium hydroxide (available for sale as a drain opener at the hardware store) to raise the PH until the copper precipitates out of the solution. This releases a lot of energy, so be careful not to let the solution boil. Now the solution (from my understanding) should be safe to pour down the drain.</p>
<p>Yes that works but don't pour the precipitated copper down the drain. If you have the resources you could melt it down into a copper nugget! The other part of the solution will be salty water.</p>
<p>Good point Synthdood, I should have been more clear. You can filter out the copper precipitate and then pour the solution out. What you do with the copper depends on how much you have, but at least you won't be using it to inadvertently poison fish!</p>
<p>I tried to work with this paint, but is not drying... is over 3 days but still wet...</p>
You have to apply a thin layer of paint, and you have to use heat to dry it. It does take a long time to dry.
<p>how long should I wait for it? can I bake it in the oven? how hot is should be?</p>
<p>Oh, I see now. The last pictures were from a different board with blue copper</p>
<p>Everything make sense, and this may sound dumb, but did you coat both sides of the board when applying the photo-paint? It looks great with the components on the blue side, so I was wondering at what point of the process did the other side become blue as well. Thanks, Bryan</p>
<p>I have blue flourescent that looks like a UV or black light, but it's blue. it came with my PC long ago.<br><br>can I use this instead of UV lights or common Daylight bulbs?<br>does it work like UV lights on PhotoPCBs? or Daylight bulbs are better?<br>i know nothing about light wavelenghts </p>
<p>Blue light Tube*</p>
<p>I have a suggestion as I work in an industry that uses identical equipment as board manufacturers and we use a Fe3Cl2 (ferric chloride) acid to etch designs into metals as this chemical milling technique will give you a uniform engraving/milling depth</p>
<p>I have used ferric chloride and it works fine, but its main problem is that it is not reusable. I have made only one acid peroxide solution and I have been reusing it for months now. If I was using ferric chloride I would have over a gallon of spent solution that I would have to dispose of properly.</p>
Yeah I guess at home it could be a little dicier to use these types of acids but all you have to do is keep the metal content low, I believe our ORP should be around 580, and the SG 1.38-1.42. We use a hydrochloric acid and something else to treat it, I forget off the top of my head but still should have my paperwork from some of the PCMI workshops/conferences I have been to all over the world. PCMI is PhotoChemical Machining Institute which is the Community for large mass production board manufacturers material suppliers. PCMI.org has some source materials also I believe. Would you like me to send you some info on the regeneration of the Fe3Cl3 back to Fe3Cl2 in pdf or some other form?<br>Regards,<br>Keith W.
Hi. I am currently doing a thesis about printing and etching pcbs. Id like to know what chemical is best for developing and etching? And it's reusability and disposal. Thank you
<p>The solutions I am using in this tutorial will work according to your needs.</p>
<p>Yea sure send it over.</p>
I also meant to mention that waste water treatment plants in the US use ferric chloride and its waste (we ship over 1,000 galons of our waste a month to one town in Michigan) so you can ask your local waste water plant manager if he will use it. PS - The town pays us $700 on top of paying for sucking, hauling, and pumping of waste we used to have to treat internally or pay to have hauled and treated.<br>-Keith
Hi. Does this work with a photoseneitive pcb? We are making an automated printing and etching machine for pcbs for our thesis and we arencurrently looking for the hest etchant for photosensitive pcbs. Thank you
You don't need the blue paint with photosensitive PCB's, but for etching you can follow the steps in my tutorial. The best etching solution that I have used so far is hydrochloric acid and hydrogen peroxide.
<p>I used a foam brush on applying the paint to the board and it worked very well. It was a very even and smooth painted surface. Afterward I got a roller at my local art store and that worked even better.</p>
<p>I tried this method and I think I missed one step. I used a common CFL bulb to expose the board to light. I think I need to use a UV bulb. I know the instructions call out a UV bulb but it looks like a white light bulb in the picture? Can a white light bulb be used instead? Thanks.</p>
I used a florescent light bulb. If you use a regular light bulb let us know if it works.
<p>Is there an alternative to using lye to remove resist? Can it be done with acetone or something like a nail polish remover? I know it works for positive resist. Not sure about negative.</p>
I have tried acetone and it did not work. The paint becomes very hard to remove after it has been hardened. You need an industrial strength oxidizer.
<p>I have a suggestion. I don't use heavy acids to etch board. I use salt, hydrogen peroxide and white vinegar. These are very benign chemicals not dangerous. I found tutorial here .. http://quinndunki.com/blondihacks/?p=835 I tried it and it worked fantastically.</p>
<p>I have a suggestion to make the hole drilling easier when the holes are on 10th inch centers, as they are on your board. Get a piece of unclad perf board with 10 holes to the inch. Mark with marker which holes are to be drilled (when it is aligned over your board). Clamp together, and use perf board to guide drill.</p>
<p>Very well done, bookmarked immediately. Just out of curiosity, what fab shops do you recommend? I've considered several, but have always become frustrated with the process before pulling the trigger.</p>
<p>I have been happy with OHSPark and Seeedstudio. The quality and price is very similar between the two. Which is cheaper depends on the quantity and size of your boards. I think that OHSPark boards are made in the U.S. as well. </p>
<p>Yes OHSPark is in Oregon. They make nice looking purple boards. We should support them as the are is USA!</p>
<p>Thank you! I use Elecrow, and have had excellent results with them. They have the best prices too. 5 boards for around $30. If you choose their basic shipping it will take a month for you to receive it so you might want to pay for expedited shipping if that's important to you.</p><p>http://www.elecrow.com/services-c-73.html</p>

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