In this issue, we show you how to etch a PCB at home using the toner transfer method and ferric chloride etchant.
If you have been following our 'How to design a PCB using EAGLE' series in Issue 34 and Issue 35, you would have designed a square wave generator circuit board that you could send off to a circuit board manufacturer. This tutorial uses the same square wave generator circuit board design that we will etch at home instead.
You can certainly use your own circuit board design for this tutorial or download the square wave generator design from our website if you prefer.
Being able to etch your own circuit board at home is a great skill to have. This can save you from having to make your complex circuit on a perfboard, or having to wait for weeks to get a board from a local or international circuit board manufacturer.
Many techniques exist for etching a Printed Circuit (PCB) board at home. There are different ways to apply your design to the copper board, and different etchants to choose from, all with their own pros and cons.
For this tutorial, we are using the Press-n-Peel film that you can get from your local electronics store, including Jaycar (Part no. HG9980) or Altronics (Part no. H0770, pictured).
Note: This toner transfer method will require the use of a photocopier or laser printer to get your design onto the film, as inkjet printers cannot be used.
We will use ferric chloride etchant, available from Altronics (Part no. H0800). This is supplied in a 500ml bottle, premixed for easy use.
In our next issue, we will teach you how to use positive resist coated PCBs and use ammonium persulphate as our etchant.
SAFETY
Ferric chloride, whilst one of the safer etching chemicals, is still a very caustic chemical capable of producing severe burns and is hazardous to animal life. Thus, before we get started, it is imperative that you take a moment to consider the safety aspects of this process. You will be dealing with high heat and very caustic chemicals. As such, we implore you to follow at the very minimum the basic safety precautions outlined here:
- You need to have a clean work area, and free of any flammable materials.
- Read the label on the etching chemical’s container
- Read the material safety datasheet (MSDS) for the chemical you are using!
- Remove any trip hazards in the area where you are using the Ferric Chloride. This includes making sure children and pets are not in the room at the time.
- You MUST wear basic PPE including long sleeves, nitrile gloves, and eye protection.
- Work in a well-ventilated area.
- Cover all work surfaces in a disposable drop sheet, newspaper at a minimum.
- Do not dispose of this material into the garbage or drains. It MUST be stored in a clearly marked bottle and disposed of at a chemical disposal/recycling facility.
- Ferric Chloride will permanently stain nearly any surface (even glass) it comes into contact with, and will start corroding any ferrous metal on contact. You must take practical steps to ensure that the liquid does not make contact with any surfaces you don’t want to be damaged.
The process also uses other chemicals that makers are likely more familiar with such as Isopropyl alcohol and Acetone. If you are not familiar with the safety precautions for these chemicals you will also need to consult the MSDS from them and follow the directions.
TONER TRANSFER METHOD
The first step in the etching process is transferring your PCB CAD model onto the copper-clad PCB. Our favourite method is to print the design onto some glossy paper using a toner/laser printer.
Note: This method will not work with an inkjet printer. Toner is essentially a very fine plastic powder that is melted and deposited onto paper. This process takes this plastic and by reheating it while in contact with the copper clad PCB causes it to transfer from the glossy paper onto the copper.
Whilst this can be done with any glossy paper, we like to use the Press-n-Peel PCB film that you can find at most electronics stores. The film is specially formulated and safer for your domestic iron due to having a high temperature tolerance.
To print the PCB design, you need to use the layer settings to turn off the layers that are not needed. For our example (using EAGLE), all we need is the Bottom layer and Pads.
Press CTRL + P to print (Command + P on a Mac). This will bring up the print dialog box. Make sure your printer and paper settings are set correctly, the scale factor is set to 1, and the Solid and Black options are both selected (ticked).
To save paper, you can have the board print in the corner rather than the default centre. This allows you to print more designs on one sheet.
Make sure you print on the matte side of the Press-n-Peel paper, so you need to know which way to put it in your printer. There is usually a small icon on the printer tray to show you which side gets printed on. Another trick to work out which side prints on your printer is to write on a piece of A4 paper and feed it through the printer.
ETCHING PROCESS
Once you have familiarised yourself with the Material Safety Data Sheet (MSDS) for Ferric Chloride, identified potential hazards, and implemented practical control measures, you can get started with the etching process.
The first step is to get the necessary equipment ready, including:
- Kettle
- Paper towel
- Nitrile gloves
- Eye protection
- Sandpaper / scourer pad
- Dishwashing detergent
- Ferric Chloride
- Isopropyl alcohol
- Acetone
- Iron
- Sticky tape
- Sheet of A4 paper
- Felt tipped permanent marker
- Containers and bowls
- Plastic drop sheet or large garbage bag
- Lanolin or Vaseline (for hands and forearms followed by gloves)
- Plastic tongs or cheap tweezers (to pick up the PCB)
You will need a container of Ferric Chloride and a container of cool water. These must be something you are either happy to keep for the sole purpose of etching PCBs or something you’re happy to discard. If you intend to keep the container, it is imperative that you clearly mark the container as not suitable for use with foodstuffs. This should prevent someone from using the container at a later date to store food.
Paper towel and lots of it. As we said earlier, Ferric Chloride will stain nearly any surface it comes into contact with and even skin.
Note: Lanolin or even Vaseline should be applied to hands and forearms followed by gloves. Plastic Tomgs or cheap tweezers should be used for picking up the PCB. Paper towel can be placed on the work surface to help reduce the staining in the event of drips or spills, however, it’s also needed to clean the PCB and your hands.
An iron or, in our case, a modified laminator. You need a way to transfer the toner from the glossy paper to the PCB substrate. For this, you can simply use an iron set to about 110°C – 170°C.
Isopropyl Alcohol and Acetone are both needed for the process. The alcohol is used to clean the PCB surface allowing the toner to transfer as best as possible, and the Acetone is used to remove the toner from the etched PCB, preparing it for soldering.
Ferric Chloride works much quicker when the solution is warm. We like to fill a large bowl with warm water at about 50°C and place the Ferric Chloride bowl into it. This allows the Ferric Chloride to heat up and it also adds another level of protection from spills.
To ensure the best possible transfer, the PCB needs to be clean and free from oxidation. You could use a very fine sandpaper, a powder like Ajax, soaped fine steel wool or 3M green scourers, but avoid using heavy grit sandpaper or metal scourers. We wet the blank PCB and add a small drop of dishwashing detergent to the surface. This helps remove any oils from the surface (Copper clad board often ships with a fine machine oil coating to reduce oxidation in transit). We then use the scourer or sandpaper to thoroughly clean the surface until it is shiny.
Being careful not to touch the now clean copper side of the PCB, you want to secure the Press-n-Peel sheet with the printed / matte side facing the copper of the PCB using a small piece of sticky tape. This will ensure that the design does not move during the transfer process.
Pay very careful attention to the placement of the design on the PCB to ensure that all of the desired detail will be transferred correctly. Once you’re happy with the placement you can then fold a sheet of A4 paper in half and place the PCB with attached transfer sheet inside the sheet of paper. This paper will protect your iron or, in our case, modified laminator if the plastic tape or sheet melts.
TRANSFERRING THE TONER
To transfer the toner, we need to heat the PCB and Toner up to between 110°C – 170°C. This allows the toner to reach its glass transition point and thus, melt sufficiently to stick to the PCB. This can easily be done using a clothes iron. In our case, we have an A4 laminator that has been modified to heat to 160°C.
The idea here is to keep the toner in the glass transition temperature range and have sufficient pressure on the PCB printout sandwich to allow for the transfer to happen. The temperatures, pressure, and time are essentially dependent on the toner your printer is using.
Some printers may use toner that reaches this glass transition temperature at the lower range while others may need a much higher temperature. Too low of a temperature and the toner will not transfer correctly and too hot a temperature and the toner becomes very low viscosity and smudges on the copper, producing poor results.
The best practice is to find the ideal temperature for your printer / toner configuration. Start by setting your iron to the lower / synthetic setting. With the PCB and transfer inside the A4 sheet and placed on a hard and heatproof surface, apply the iron to the PCB / A4 sandwich.
Keep firm pressure on the PCB without any movement for about one minute, then gently move the iron around on the A4 paper for another minute or two.
Remove the iron and wait a few minutes for the PCB to cool enough for you to safely touch the surface. Once cool, carefully peel the Press-n-Peel paper away from the PCB and inspect the transfer.
In the images shown here, the image transfer has failed. You can see large areas where the image simply did not stick to the PCB and other areas where the toner was patchy. This can be caused by either an improperly cleaned PCB or insufficient heat / pressure.
Check the design has transferred completely to the PCB and that all of the traces are clear and complete. If the transfer has significant issues, it’s possible that the iron was not hot enough or the board was not cleaned sufficiently. In this case, use Acetone to clean the toner from the PCB and repeat the process with another printout increasing the temperature a little.
A successful transfer will look similar to this image. The traces are well detailed with fairly sharp edges, with no breaks or smudges.
The transfer wasn’t perfect though, as we can see here there are a few areas where the transfer missed or was not great. This can be caused by a little dust on the PCB between the PCB and the transfer or some oils remaining on the PCB. In either case, these can be rectified by using a Etch Resist Pen or Staedtler permanent marker to touch up the area. This marker will cover the copper and prevent the etchant from eating into that specific area.
Note: Also look for any excess toner, perhaps in fine areas, and use a model makers scalpel to scratch away unwanted toner, or even to cut a track perhaps to add a fuse or resistor, etc.
Since the issues in our example were only on the ground plane and not on any crucial traces, we simply ignored them and etched the PCB.
ETCHING AWAY THE COPPER
The next step is to remove the copper from the exposed areas of the PCB. This can be done with different chemicals, such as Ferric Chloride and Ammonium Persulphate. In either of these cases, warming the chemical can help speed up the etching process. Each has a best temperature for best etching speed, and most economic use.
Our preferred method to warm the etchant is to use a bain-marie type setup using a large tray to hold the hot water and the smaller tray to hold the etchant. This method evenly distributes the heat, without getting water into the etchant.
In our demonstration, we will use Ferric Chloride, which is used undiluted and has a recommended temperature between 20-50°C according to the instructions.
Note: Ammonium Persulphate is an alternative to Ferric Chloride. It is a cleaner chemical to handle compared to Ferric Chloride, however, it isn’t as effective. This white powder needs to be mixed with water (1:5 ratio) and heated to around 60-70°C. (Review the container’s label and read the MSDS for proper instructions and safety precautions before using).
With your protective gear on, put enough etchant liquid into the smaller tray so the PCB is fully immersed. Gently place this smaller tray into the larger tray and fill the larger tray with hot (not boiling) water. Ideally, we want the Ferric Chloride to reach around 50°C.
Be very careful here, as we don’t want the tray of Ferric Chloride floating in the water and nor do we want water getting into the Ferric Chloride.
You can now carefully place the PCB into the Ferric Chloride solution. With the PCB in the solution, we gently rock the tray of Ferric Chloride to keep the solution moving. Leaving it sitting stationary will not only significantly slow down the process but it can also cause the copper to be etched from the outer edges in which can potentially cause under-keying on the outer tracks. This is when the copper at the bottom of the trace starts to be corroded. It’s best when fresh etchant is moving over the board.
The length of time it will take to etch the PCB is dependent on many factors. The temperature, solution strength, copper thickness, agitation applied, and the age / number of times the Ferric Chloride has been used. Our board took about an hour to etch.
Note: You can refresh Ferric Chloride by adding some Hydrochloric Acid (HCL) -within limits, of course. Ferric Chloride dissolves the copper from the PCB and as such, it becomes less effective the more use it has seen. In our case, the etchant was nearly at the end of its lifecycle and the process took quite a while. With brand new etchant and at the higher temperature a board such as this can etch in as little as 5 minutes.
To tell if the board has been fully etched you can remove it from the Ferric Chloride solution and give it a rinse in some warm water.
As you can see in our example here, the etching is not uniform. The pink areas are more dissolved than the darker gold areas. Ideally, you should see the copper change from a gold colour to pink, so in our case, the etching is in process but clearly needs longer in the solution.
When the copper has been fully etched away your board should look like this.
Note: This PCB still has the toner / Press-n-Peel film covering the PCB. This film has gone pink during the etching process.
Note: If you’re not going to use the PCB straight away, we recommend leaving the toner / Press-n-Peel film on the surface of the PCB. This will prevent the PCB surface from becoming oxidized, which makes it difficult to solder to.
If you’re going to use the PCB straight away, use some Acetone to clean the toner and Press-n-Peel film off the PCB. You could also protect the circuit board with circuit board lacquer if you have that available.
Now all that is left is to drill the holes and populate the PCB.
DRILLING THE HOLES
It’s now time to drill the holes. Ideally, this will be done in a drill press with a very fine drill bit (about 1mm). Using a drill press will ensure that the drill is 90° perpendicular to the PCB, which will create clean holes, and more importantly, reduce the chances of damaging your drill bits.
If you don’t have a drill press then a rotary tool such as a Dremel is ideal, but in a pinch, any drill can be used. You just need to make sure you keep the PCB as perpendicular to the drill bit as possible.
We find it isn’t necessary to centre-punch the holes as the etching process creates a divot in the PCB where the copper was removed. Generally, this prevents the drill bit from (walking) on the surface of the PCB.
POPULATE THE PCB
With the holes drilled you can populate the PCB with your electronic components and solder them in, just as you would another PCB. However, you will note that this PCB does not have any silkscreen to identify item placement, and nor does it have soldermask to ensure that only the solderpads are exposed.
To help identify what parts go where we print out the Tplace, Tnames and Tvalues layers on a sheet of A4 and keep this handy when building our home etched PCBs.
The lack of soldermask is a little more difficult to overcome. We recommend a soldering iron with a fine chisel tip and very thin solder of 0.7mm or ideally less. This will help to reduce the chances of creating undesired short circuits when soldering.
If you’re still having problems, consider increasing the clearances in the design rule options we set earlier.
You should now have a completed circuit board. Congratulations! Now all that is required is to apply power to your circuit and use it in your future electronics projects.