I’ve had a lot of fun etching away PCB’s lately. As some of you may know, I took on a little hobby building guitar pedals, outboard analogue gear and other gizmos of the sort (oscillators, pocket synths etc.)
Most people like to play around with breadboards and some sort of perfboards. I never got the hang of breadboarding. I always spent more time trying to debug the breadboard than testing components in the circuit.
Etching your own PCBs – now THIS is a whole different game.
You will feel like a bit of a Picasso designing the thing. Load up your favourite software (I’ve been using Eagle, the guys at CadSoft - now AutoDesk - been kind enough to provide a freeware version for non-commercial uses, such as mine). There are plenty of tutorials out there, and the guys at diystompboxes.com are extremely helpful (in fact, download the gm-library for Eagle, it will make your life extremely easy!). There are other alternatives, namely Target3001! seems to be the new favourite in many DIY forums
The rest of the article will show you how to etch some PCB using the ferrochloride method. There are other methods, but found this the most fun, easy and cost effective. This is not an in depth tutorial but more a record of how it can be done, with tricks and tips that I found useful.
There are many, many factors to consider when designing a PCB – crosstalk, ground loops, capacitance between the paths, etc – but this is not the scope of this post.
When you have your layout done and ready to print you should, at this point, print the schematic, the layout (PCB with the silk screen of component number and value) and the PCB traces.
This process is complex and involve use of very aggressive chemicals, as well as power tools.
You also need to contact your council on information on how to proceed to get rid of FeCL and it's derivates, as they are highly corrosive and acidic
You will then need:
- A laser printer (for some reason, Brother printers don’t like PNP as explain on the PNP blue website);
- A document ready to print the layout view of your PCB;
- PNP Blue (available at Farnell, Rapid Electronics, etc.);
- Scotch tape (thin), scissors;
- copper clad board that suits your requirements (dimension of the board and thickness of copper in case you require large amounts of current to pass through it);
- hacksaw with carbide blades (without carbide blades it will be very hard to cut through the copper clad boards, as they are made of fiberglass);
- Clamps, gloves, goggles and other security equipment;
- Some sort of working station (I have a B&D workmate 301 and it’s more than enough for my requirements. It cost me about £25 on B&Q);
- Iron and Ironing board, preferably an iron that is clean but you don’t intend to use it again;
- FeCl solution (found at Maplins, rapidonline, Farnell, rs, etc.);
- Polypropylene Etching Tray (again, available at Maplins, rapidonline, Farnell, rs, etc.). I cannot stress how important a dedicated chemical tray is for this. Without one, proceed at your own risk;
I first print the PCB layout on an empty A4 paper. Before printing, I draw a little arrow on the corner so I know the direction of the paper when I feed it again to the printer. Once you have your board printed, this will give you an idea of the size, so you know what size of PnP Blue paper and copper clad to cut.
Tape the PNP to the layout you just printed. Use the previous printed area to make sure you are lining the PNP properly. Make sure the grainy side is facing up (shiny side against the paper. Put the A4 back on the printer for a second time. We are now printing on the dull side of the PnP paper, ready to initiate the transfer process.
Meanwhile, clean the copper clad with a soft sponge that won’t leave residues or will scratch the board to much using IPA. It needs to be sparkling clean with no grease or dirt!
Check the board again thoroughly for cleanliness. if it’s not shiny and immaculately clean, the next steps will not work!
Carefully align the printed PnP with the freshly cut copper clad bit (this time, dull side against the copper, shiny side facing up). Ready your iron and apply heat to the board.
You’ll have to do a bit of trial and error to find the correct temperature and for how long you will need to apply pressure. On my iron, I have it set to 3 (slightly more than medium heat) and run it for 5minutes, alternating between applying no pressure and sweeping through different parts of the PCB.
The worst case scenario here problem is that the P’n’P might melt, turning into a very solid goo. In which case, that goo will be very hard to remove from your iron.
Let the board cool down completely BEFORE removing the P’n’P paper. I suggest you place the PCB under cold water and then – when the board is cold – peel one corner off carefully to ensure the toner has thoroughly transferred to the copper clad. If not, more heat may be needed.
Carefully check the traces against the printouts from Eagle. The PCB’s shown here are for the Marshall Bluesbreaker and a JFET project based on the dual rectifier red channel preamplifier section.
If at this stage, you notice a pad missing, you can fill it in with a sharpie pen. In fact, you can draw entire traces on the copper clad with a sharpie pen and it will work. Let it dry properly before proceeding.
You need to make sure your “tray” can withstand the heath and the chemical reaction. Rapidonline sells these polypropylene chemical trays. Mind you, this reaction will be using corrosive elements AND will be releasing a lot of heat. If you don’t have a dedicated tray for these types of chemical procedures, DO NOT ATTEMPT TO DO THIS.
Disposing the “leftovers” of this experiment is not easy, but I’ve recently found a liquid that turns the spent etchant into a goo that can be safely disposed in the bin. These are available at your local Maplins. If you don’t get some of this stuff, make sure you have some sort of container that can carry the spent etchant to a skip or a chemical disposal facility (remember – no metals, because this stuff eats through it. Your container cannot have a metal cap).
I need to reinforce this: These are rough guidelines and a very basic documentation of the process to do etching. If you are attempting to do this at home, I suggest you do some further reading on the procedure and proceed at your own risk.
I cannot be responsible for any damage or injury that might occur. If you are unsure about laboratory procedures and safety with chemicals I would NOT attempt the following.
Make sure you have gloves and are performing the etching in a well ventilated area!!!!
Fill the tray with etchant, and place one of those really warm lights above it. I use a hair drier. The solution needs to be warm to work properly. The colder the etchant is, the longer it will take to properly etch away the copper. The issue is it will start eating away the covered areas as well. You want the process to be moderately fast so al the copper is removed without eating away the traces protected by the P’n’P. The process should take up to 20min and you should stir/rock the tray gently. Be careful not to spill the etchant everywhere. This stuff is mean!!!! (PCB’s being etched: Dr. Boogie and MXR Dist+).
The PCB’s will change colour slightly and all the copper NOT covered by ink will be eaten away. The result should be an almost transparent PCB and the ink mask. Compare it once again to the printout of the layout. If it’s not ready yet, then it needs more time in the solution.
When you are happy, grab a kitchen scourer, and remove the ink from the PCB:
Check for continuity:
And lastly, drill the pads. You will need carbide drill and a vertical drill post. As with the hack saw, if you are not using carbide drills you will have a very hard time drilling through the fibre glass.
Some people are using Dremels – not really the same thing (they wobble too much and that means you will break the very VERY thin carbide drill bit).
Use protective goggles. You will be amazed of how easily the carbide blades break.
As you can see from the picture, I simply use my drill and my elbow as a vertical guide. This is extremely time consuming and tiring and I break the carbide bits very often. Get a vertical drill post if you can!
And that's it! Now start populating your PCBs and enjoy your new audio toys!