How to make a PCB
A step by step guide to making you own PCB
Making PCBs can appear to be very difficult at first. Though they are very important for hardware related projects. In this tutorial, we will guide you through the steps of making your own PCB. This is derived from our own experience at the CambridgeAUV society in designing PCBs for our robotic submarine.
1. Designing the PCB
For designing PCBs, we would recommend a software package called Kicad. It’s free to use and has all the functionality needed to design simple PCBs. There is a useful guide provided on their website on how to use the software. Since this tutorial is on how to make a PCB, we will not go deep into the design process. However, a nice introduction to designing PCBs can be found on Sparkfun’s website: https://learn.sparkfun.com/tutorials/pcb-basics.
2. Manufacturing the PCB
The actual PCB is made through a complex process that involves various chemicals, so it ca n’t be done at home. Once the designs have been completed it is necessary to send the designs off to a manufacturer.
In order to make the boards for you, the manufacturer would need you to generate the Gerber and drill files. The Gerber files contain information about the copper traces and pads on your PCB, while the drill files tells them where to drill holes. Here is a nice tutorial on how to do it in Kicad.
We are very grateful to be sponsored by Cambridge Circuit Company Ltd (http://www.cambridge-circuit.co.uk/), who offered to manufacture our PCBs for us. They have a standard delivery time of 5 days but have the capacity to deliver in just 1 day if requested, while many other manufacturers require a turnaround time of around 2 weeks. We got our PCBs in just 3 days!
3. Buying the materials
The real fun/pain begins after you receive the PCB. You now need to buy and solder electric components onto your PCB.
The components you need to buy depends on your design, so we won’t cover that in this tutorial. However, there are a few things you need to solder the components on.
There are two types of components, they are through-hole and surface mount. Through-hole components have corresponding holes on the board, so you can just insert the component in and use a soldering iron to solder it on the other side.
Soldering surface-mount components is a lot trickier. These components only have copper pads on the boards, and they are usually tiny. This makes them almost impossibly to solder by hand. The way they are soldered is by applying solder paste to the pads using a stencil, placing the components on the paste, and heating the board in a reflow oven to melt the paste and connect the components. We will go through each of these items.
Solder paste is like solder but in paste form. It can be bought on Farnell. But different to normal solder, they must be kept in a fridge after they are opened.
A stencil is a thin piece of film with holes cut into it where the component pads are located. The mask can then be placed over the PCB and solder paste spread over the top. This ensures that solder is only applied to the surface mount pads. At CAUV, we make our stencils using a material called mylar. It can be bought on RS-online. We would recommend a thickness of 0.075mm as having a stencil thats too thick might cause the pads to short after reflowing.
And finally, a reflow oven is a special type of oven used for soldering. Please do not try to solder with a regular oven as the solder paste might contain harmful chemicals. These can be bought on RS-online but they are a little expensive. However, you might be able to borrow one from you school or some workshop.
4. Creating the Stencil
To make the stencil, we use a laser cutter to cut holes on a piece of mylar.
The following steps will be dependent on the exact laser cutter used but the following steps are what we found works best on the HPC Laser Ltd LS6090 Pro.
Once the designs have been imported into the laser cutter software, first select a section of the design where pads are close together and remove the rest of the design in order to test the laser cutter settings.
Select the design and choose the option ‘unite lines’ . This makes the cut smoother and less prone to error. Then select the engrave option rather than cut to allow the cutter to achieve finer precision. In the cutting options dialogue box choose: speed 550, power 35, scan gap 0.05, no blow and no bi-direction. Go ahead and focus the laser and start the laser cutting operation. Once it has finished check the cut holes and adjust the settings/focus as necessary to achieve the required precision.
Now the laser cutter is properly configured bring back the entire PCB design and make the final cut.
With the finished mylar sheet, use scissors to cut out the mask, making sure that the cut out area is larger than the PCB area to make the application of the solder paste easier.
5. Applying the solder paste
The first step is to secure the PCB and mylar sheet to the table. This can be achieved by using scrap pieces of metal to surround the PCB and then taping them down. Next, take the mask and place it on top of the PCB matching the holes to the pads underneath. Tape it down once it is in place.
Now that the mask is set up, it is time to apply the solder paste.
Apply 2 pea sized blobs of solder paste to a flat piece of metal and use this to scrape along the top of the mask, evenly spreading the paste across the top. Make sure that the mask does not lift up during this process as this can cause the solder paste to bridge (connect two pads together)
Remove the mask and check the quality of the paste application. Look for any bridges or pads that have too much/too little solder on. If there are any bridges, use a knife or thin wire to remove them. Once you are happy with the mask application, move on to applying the surface mount components themselves.
6. Placing the Surface Mount Components
Use a pair of tweezers to move the components onto their respective pads. Resistors, inductors and ceramic capacitors can be place anyway round while electrolytic capacitors, diodes and ICs will only work one way. For ICs there is usually a circle in one of the corners to aid positioning. If you find it hard to flip a small component, try dropping it until it lands the desired side up.
7. Reflow Soldering
This step is to heat up the solder paste such that it joins the surface mount components to the pads. This requires a carefully controlled temperature profile as to not damage the components through heat shock. The reflow soldering is done inside a specifically designed IC oven. If you were able to borrow an oven, it should already have the temperature profile set. Otherwise, you may have to search for a suitable temperature profile and set it manually.
8. Soldering Through-hole Components
The final step is to solder in the through-hole components with a soldering iron. If you are not familiar with using a soldering iron, here’s a good youtube video on how to do it. Just be careful not to get hurt with the hot soldering iron.
After soldering on the through-hole components, we are done! Take a look at the finished circuitboard.
If you have any questions after reading this tutorial, please leave a comment below or email email@example.com.
CAUV is proudly sponsored by Cambridge Circuit Company