A Printed Circuit Board or PCB is one component that is present in almost all the electronic equipment we use in our daily life. It forms the foundation of any circuit. A PCB is where all the electrical/electronic components are held together and interconnected without any wires. The connections on the PCB, is not only permanent but also fairly neat and easily understood.
If you are keen on building an electronic circuit, you need to be really familiar with the basics of PCB design.
In this article, I will break down some of the commonly used PCB terminologies, the PCB design process, and some of the popular PCB design software.
But first, let me explain what is a PCB really!
What is a Printed Circuit Board (PCB)?
Have you ever opened up an old, worn-out electronic equipment like tv remote or mobile phone? If yes, then you must have seen a green sheet(sometimes red, blue) with lots of silver threads and components. This sheet is nothing but a PCB.
At first, understanding the circuit may seem like an uphill task. However, once you get familiar with its design, these complications may instigate your inner electronics nerd.
PCB forms the foundation of various complex circuits and is one of the main reasons that you get slimmer TVs, Mobile phones, and laptops. They are manufactured with either one, two, or multi-layer depending upon the complexity of the circuit.
You can imagine PCB to be like a trifle made with layers of different materials- all laminated together to form a single PCB sheet.
If we take a typical two-layer PCB, it will have a composition like this:
Here the Substrate refers to the non-conductive dielectric part, I mentioned above.
The popular choice for the substrate is FR4 glass, owing to its stability with variance in temperature. It is also easy to sandwich between layers of copper strands(the conductive sheets). For complex circuits, where only minimal losses can be allowed, the PTFE substrate is used.
In the pictorial depiction above, two copper sheets cover the substrate and is referred to as a double layer PCB. For simple circuits like that used in musical toys, thisPCB will be enough to suffice the purpose. An increase in the number of layers ensures more wiring areas for high-end circuits, such as that of your smartwatch or smartphone.
The copper strand is masked by a layer called a solder mask to prevent accidental contact with any conducting leads. This layer gives the board its green (In some cases red) color. The numbering, lettering, and other markings (usually in white) which you see on the PCB surface is done through a silkscreening process.
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As we dive into the design process of PCB, let me get you familiar with a couple of commonly used words from the PCB glossary.
- Soldermask – The green/red/blue (non-conducting) layer that you see on top of any PCB. It shields the entire PCB from a possible short circuit. It also makes the entire soldering process a tad easy.
- Silkscreen – The white markings on the PCB which depicts the letters, component symbols, manufacturer’s logo, and other important symbolic information regarding the circuit connection.
- Pads – Small surface of copper on the board, which are used to make the electric connection between the components and the copper tracks using solder.
- Layers – Each surface that is bound together to form PCB. The outermost layer is where the mounting/soldering of components happens. The inner layers are used for connecting the components internally.
- Footprint – All the information available of pads and the circuit online are saved in the PCB design software as footprints.
- Jumper – A saver in the time when the circuit demands are so that the copper tracks overlap each other. It helps to connect two different points on the PCB.
- Via or thru-hole via – The current gets a path through the PCB outer layers (top and bottom). You can spot them on the PCB board by the colored pads (usually yellow)
- Blind Via – They connect between the outer layer(either top or bottom) and its immediate layer and not just the outer layers. If your PCB allows light through it, it has blind vias
- Buried Via – Same like blind via. It connects the inner layers in the case of multi-layer PCB.
- Copper Traces – Coloured conductive tracks that connect the components, vias, pads.
- Annular Ring – The copper ring that encircles the plated hole.
- Design rule check (DRC) – Software-based check to find any glitches in the circuit design.
- Gerber file – File generated during the software design of the circuit. It contains important information like where to make holes, copper traces, names of the components etc.
Now that you are familiar with the basic definition and design of PCB, the next thing you need to know is the types of PCB available. Basic knowledge of it will help you choose the right type for your circuit.
Once you start designing the circuit, the different types of PCB might overwhelm you.
I have put out a simple list below; a breakdown of types according to different aspects.
First we classify the PCB type according to the way the components are connected to the PCB.
Classification based on the mounting technology used
In a typical PCB, the components are connected on its surface using two technologies, based on which it can be classified as:
As the name suggests, in this PCB type, the components are connected to the lead wires which go through the holes of PCB. This method can be easily implemented in a single layer PCB. However, as the layers increase, the difficulty to implement it also increases.
Due to this reason, this technology is now seldom used and is on the verge of being an obsolete one.
Surface Mount PCB
One of the newer technologies, here the need to drill holes to connect the leads to SMD components is eliminated. The components are directly mounted on to the PCB. This is easy to implement irrespective of the number of layers a PCB has.
Classification based on the number of layers
Single Layer PCB
True to its name, this type has only one layer of a conductive material such as a copper sheet. The conductive sheet is then protected by a solder mask followed by the silkscreen to mark all the components.
You can easily identify a single layer PCB, as it will have markings and traces only on one side.
It is used in relatively simple circuits like digital camera circuits, toy circuits, radio and stereo sets etc.
Double Layer PCB
Double-layer PCB has two layers of conductive material.
A non-conductive material such as a fiber or glass is sandwiched between two sheets of copper. This is one of the popular types of PCB for medium to complex circuitry. It is so because it allows close routes tracing unlike a single-sided PCB.
Multi-layer PCB refers to PCB with more than 2 layers of conductive material. It can be viewed as batches of double-layer PCB where the 2 conductive foils are glued and laminated with a dielectric sheet placed in between them.
The manufacturing process is quite tedious. As the number of layers increases, the thickness of copper sheets is kept in check, so that the overall circuit board does not look bulky.
As more and more layers are incorporated in a PCB, it results in a powerful high-density assembly. This is the reason behind the high capacity and speed of multi-layer PCB.
Here the electrical connection between the layers is achieved through “vias”. Since the layers are more, multiplayer PCB are highly reliable and durable for high-end applications like smartphones, GPS circuit, etc.
Type of PCB based on their flexibility
Next, PCBs can be grouped into three categories depending upon their flexibility. It solely depends on the substrate used.
Here the substrate or the dielectric used is quite rigid and abstains the PCB from any kind of twisting and turning. One of the commonly used substrates for Rigid PCB is the FR4(with stiffener).
As the name suggests, once this PCB is manufactured it cannot be folded to fit any shape. It has good strength and life and is therefore preferred for computer motherboard.
Flexible PCB or Flex PCB as it is commonly referred is one that can be bent easily. It saves space and also is lighter in weight when compared to a rigid PCB. Here the non-conducting part is made of materials like polyamide, PEEK (Polyether ether ketone) or transparent conductive polyester film. Since these are easy to fabricate, it is available as single, double and multi-layer PCB
Its application includes: LCD Fabrication, Flex solar panels, smartwatches
This PCB type has a combination of both rigid and flexible layers. Since flexible PCB lacks strength, combining it with rigid layers gives the PCB the flexibility and rigidity in its structure. These can be fabricated as single layer, double layer and multi-layer PCBs.
Owing to its space and weight optimal design it is an ideal choice for medical electronics circuit like a pacemaker, and can be used circuits related to aerospace, phones, etc.
PCB Design Process
The first step to designing PCB is to draw a schematic on a PCB design software. There is numerous software available. Some of which I have listed out in the next section of this article.
Use the component library and prepare a circuit diagram on your computer screen. Here you can change the circuit layout to fit into the PCB board in the most optimal way.
Next, once the circuit diagram is done, you are ready to generate it on a plastic sheet. The Gerber file is sent to be printed as a mask or a negative image on the plastic sheet.
This helps you to pick up the right substrate sheet that would best fit the purpose of your circuit. You can choose from unbreakable glass, fiber sheets etc. The next task is to create vias by drilling through the PCB. This can be done manually or using a computer numerical control (CNC) machine.
Once you sort this out, you can print the circuit using a laser printer on the copper sheets.
Now you’ve reached halfway through the process. Next once the circuit is on the copper paper, prepare to take it to the next step of etching and striping. The board goes through the rigorous chemical wash to remove the unwired copper traces. At the end of the process, you will get a PCB with a distinct copper outline.
The PCB is now ready to undergo the testing process. Nowadays you have an automatic testing kit like ATG test kit, to ensure that the PCB would work and serve its purpose well.
PCB Designing Software
In this last section, I have listed out 5 popular PCB design software you can try. We have published a big list of pcb design and layout tools – where you can learn about all the popular software’s out there.
KiCad is free software and a Cross-Platform, Open Source Electronics Design Automation Suite. It comes with a 3D schematic view and a PCB Editor which can produce PCB layouts for up to 32 copper sheets.
Pioneer in 3D visualization of PCB directly from the PCB editor, Altium also offers features like FPGA, schematic capture, and release data management. It can be used to develop a schematic of medium to complex circuits.
One of the most popular schematic platforms is the Autodesk eagle, formerly known as CadSOFT Eagle boosts of several useful features. Some of them include schematic editor, PCB layout editor for designing PCBs, component placement, and PCB routing. It is compatible with most of Operating system like linux, windows, and Mac.
Upverter, is one of the web-based collaborative Electronic design automation(EDA) platform, owing to its open-source hardware design format. It boasts of features like 3D view, easy export to hardware, PCB editor , schematic capture to name a few.
Osmond PCB is purely tailored for Macintosh users and provides a high resolution of 10 Nanometers, to give a high precision output. It gives you flexible features like supporting both metric and imperial unit system, provides tools to modify traces, re-structure the circuit at any point, unlimited board sizes and many more.
With this, we come to the end of the article, Hope it was able to give you a brief idea about a PCB and its design process.
Thank you for reading.