Step up your game with some PCB 101 at home.
So you’ve spent weeks designing some IoT gadget, the breadboard is packed with countless jumper wires and you carefully test that it works, hoping that you don’t knock loose any precarious connectors. Success! Now that you know your design works, you can put it to use, but wouldn’t it be nice to get rid of all those jumper wires and just have a single self-contained module on a circuit board?
The good news is that with a few ordinary household supplies (and ferric chloride) you can make your own custom pcb. Having a pcb to work with instead of a breadboard not only makes the design look cleaner, but it also makes troubleshooting far simpler than if you had to dig through a Medusa-like maze of wires to test a voltage. While kits can be purchased to accomplish the same task using UV transfer sheets and motorized agitators, these kits can cost a significant chunk of change-- often several hundred dollars at the cheapest.
When I was in college and needed to fabricate PCBs, I didn’t have that kind of money to spend, so I had to improvise. The following tutorial will demonstrate the process of fabricating your own PCBs using the toner transfer technique. This technique has been around for a long time, but there are a number of tips and tricks to this method that are key to making it a success.
Laser printer (MUST be a laser printer, inkjet will not work)
Magazines/ catalogs of any kind
Plastic tubs (two will be fine)
Small paintbrush or toothbrush
Copper clad boards
The two items NOT likely to be found in your house are ferric chloride and copper clad boards; ferric chloride and copper clad boards can usually be found together in places like Fry’s Electronics, or even your local Radioshack, but we've linked to online suppliers. The ferric chloride will go for about 16-20 dollars for a liter, but the good news is that you can reuse it over and over again (which is nice because this isn’t the kind of chemical you can just throw away).
Copper clad boards will usually be nearby and can be had for as little as a few dollars, though it is important to make sure you get the plain copper boards as opposed to the pre-exposed UV sensitive copper clad boards which are to fabricate boards using a different method.
The magazines or catalogs you are looking for are the kind with semi-shiny paper- this will make the transfer process much easier. Glossy paper or photo paper from an office supply store will also work very well, but magazines are free and gloss paper can be pricey for a package. The rest of the items needed are pretty self explanatory; you don’t have to use Kicad, there are many other programs that will accomplish the exact same thing, but Kicad is free and is pretty powerful as far as PCB software goes.
Safety note about ferric chloride: ferric chloride is a powerful acid that eats away at most metals, some more violently than others (watch out for aluminum!) but does not eat away at synthetics like plastic, ink, and nail polish. It isstrongly recommended you wear eye protection when working with this chemical and that you make sure to store it safely, as even the fumes can corrode metal. Take a look at the bottle:
If the symbols on the bottom of this bottle are not explanatory enough-if you like having skin, you will want to wear latex or nitrile gloves. In all likelihood you will not be getting any ferric chloride on your hands at all, but it is important to take precautions. If you do get some on your skin, wash immediately with soap and COLD water and you will be fine.
Step 1: Design Your Board
For this tutorial, I will be designing a simple breakout board for the RFM69HW 915MHz transceiver; the module itself uses 2mm pin spacing, which is finer pitch than a standard breadboard and makes prototyping more difficult. I will design a breakout board that uses standard spacing so I can attach a header strip and insert it into any standard breadboard. The method presented will work for both through-hole and surface-mount components, but for my purposes this board will be designed as surface mount. In this case the components are not small, but this process can be used on components as small as MSSOP, which is about as small can be done by hand.
This tutorial is mainly focused on the process of fabricating the boards, so I won’t go into a detailed how-to for Kicad, however there are a few things you will want to look out for. After you open the program you may begin to place components in the same fashion as a spice program, only in this case you are placing the footprints of the components; as you do this, make sure the selected layer is “F.Cu” as indicated by the right table in the picture below.
Everything in red will be printed on the front of the board, and everything in yellow (vias) will be on both sides, though in this case it is only the front that we care about. When you are finished with the design, it is time to export it to a PDF. Click the “plot” tool and set the output to PDF as shown. It is import to make sure you have the “mirrored” option selected, otherwise when you fabricate the board it will end up backwards.
Step 2: Print your board
Now that the plot is exported, you can print the design. Tear off a page from the magazine and insert it into the manual feed tray of the laser printer. It doesn’t matter that there is already something printed on the page; the toner getting onto the page is all we care about. Make sure that the printed design does not have any blotches or smears; if your design comes out smudged like the picture below, insert another page and try again.
With your design printed, it is almost time to transfer it to the copper, but first we need prepare the board. When you take it out of the package it may have a patina on it; buff this off with steel wool or a scotch-brite pad. You want the board to be very shiny so that the toner will adhere. After cleaning the board, use a fine piece of sandpaper to lightly rough up the surface. This is not required, but the roughed up surface can help the toner adhere even better.
Step 3: Transfer the design
Now take your printed design and place it toner-side down on the copper. Turn on your iron and wait for it to heat up, placing it on its highest heat setting and lowest steam setting if available. When the iron is hot, place it on the paper and copper board, but don’t move the iron around yet. Give it about 30 seconds and you can begin moving the iron around. Continue ironing for about 2 minutes; this will have melted the toner and caused it to adhere to the copper board. Now you have to get the paper removed (this is a very delicate step, patience will be rewarded): take the board/paper and drop it in a tub of cold water.
The water will penetrate the paper, making it weak and allowing you to very carefully peel/rub away the paper, leaving a clean copper board with a black toner imprint. If you have toner peeling off at this point, it means that you did not get the board hot enough and will need to try again, leving the iron on for longer. Alternatively, a friend of mine who owns an electronics parts store in town came up with a novel idea for making the transfer if you have access to a laminator machine: place the magazine paper and the copper board into the laminator and let it pull the two through together. Run them through a couple times and you will end up will a very good transfer after soaking the board.
Step 4: Etch the copper
This is where the fun starts: go outside or into another well-ventilated area and pour the ferric chloride into a plastic tub. The hotter the ferric chloride is, the faster the reaction will go, so if it is a hot day, leave the bottle out in the sun before you start making the board and by the time you get to this step it will have gotten hot. To make handling the board easier and safer, I usually drill a hole and insert a wire to use as a handle, but this is not required. Before you drop the board into the acid, take note of its orientation; if you have a double sided board and are not using the back, place the board in with the back side facing down. Whichever side faces down will be eaten away faster and you want to make sure you have no copper left on the back. After dropping the board in, gently brush the circuit side of the board; this will help the copper etch more quickly and evenly.
The process will take quite some time: you most likely won’t even see any copper start disappearing for about 8 minutes. Gradually the acid will have eaten away at the copper from the outside-in, and you can begin to see progress. If your board is large, it will take longer, but normally by around 20 minutes, the board will have etched all the way to the center and you have to remove the board and drop it in a tube of water and soap, neutralizing the acid. Here you can see my blue tub of water and soap ready to receive the etched board:
After cleaning the board, you should end up with a clean board with only the black toner on the protected copper as shown below.
Use the steel wool again to scrape away the toner, exposing the copper traces.
After trimming any excess parts of the board, you should be left with a fresh PCB ready to be soldered. Double check all the traces to make sure that none have been broken in the process. If you are making a through-hole PCB, use a very small drill bit to drill out your vias. Congratulations, you’re ready to solder parts to your board!
This method will help you print PCBs on a budget, or if you need them in a hurry; however an engineering student would also do well to know that these days there are a few places around online that are willing to make PCBs in as few as a 5 unit order.
OSHPark and Tinyos Shop are based in China and will fabricate PCBs for you for as little as 20 dollars depending on the size of your board. They are a great resource if you want to make many boards, or want a silkscreen printed. You will still need to design your board on Kicad, but you can send the files to either of these two companies and within two weeks you should receive the boards, ready to solder. The disadvantage to this is that if you made a mistake in your design, you have five bad boards and you have to wait another two weeks to get new ones. With this in mind it is a good idea to print a prototype board using the above method; if it works as expected, you can order the PCBs with peace of mind.