For sure, this is not the first time you hear the term Printed Circuit Board (PCB). This is because PCBs are the fundamental building blocks of electronic devices, hence, the gradual growth of the PCB industry. In fact, this industry is very lucrative such that analysts project it to be worth US$75 billion by 2026.
In itself, PCB design is a crucial stage in the engineering product design cycle. Here, engineers use layout software to bring the electronic circuits to the physical world. In simple terms, PCBs are flat laminated composites that permanently support and electrically connect the components using conductive tracks and other features.
In this tutorial, we will continue the discussion on EDA/ECAD software tools. The previous article talked about Schematic Design, but today we will talk about PCB Design. We will focus on the best practices for designing PCB layouts and discuss some of the terminologies we use in the PCB world.
Best Practices for Designing PCB Layouts
After successfully designing the schematic, you will want to design a PCB layout for your project. This is a crucial step, and engineers spend a lot of time optimizing and producing a visually appealing product. Although aesthetics are not the main requirement, steps such as PCB optimization, among others, produce a simple yet effective board while having a professional look.
Below are some of the most common practices engineers use.
Power Planes to Manage the Distribution of Power Lines and Signal Traces
Without a doubt, power planes and power traces are a fundamental part of any PCB. So to avoid “burning” your PCB and ensure reliability, you need to have an idea of how much current will flow in your circuit. Having this information will help you to size up your PCB power traces properly.
As a rule of thumb, wider traces have a higher current carrying capacity than narrow traces. Another common practice these days, especially for single layer or simple double layer PCBs, is to create a Ground plane.
Pour a layer of copper on all areas that are not used and connect them to the Ground. By doing this, you’ll get better signal integrity and create a higher current carrying capacity for the ground return path.
Group Related Points Together
A circuit typically has many modules that have to work together to achieve the goal.
For example, in a simple micro-controller sensor project, you may have a power supply circuit, sensor signal processing circuit, display circuit, and communications module. It is usually a good habit to place the components according to their functional groups on the PCB. By doing so, you keep the track length short, direct and have better control of their return path.
Furthermore, this gives you a clear picture of any components or modules that may dissipate heat or introduce noise. Therefore, the noisy signals are away from sensitive components, and you would like to place other components a bit further.
Design Rule Check
You may consider running a Design Rule Check (DRC) if you want to verify whether your PCB meets the specifications set out by the geometric constraints. Typical examples of design rule checking include physical checks of trace width, pitch, and spacing among components or vias. You may also use DRC to identify conflicts in your design.
Component Placement and Orientation
Component placement on a PCB is key. This affects everything from functionality, cost of production to field performance in terms of signal integrity and EMI.
As a general guideline, you may want to keep the traces short between components. Aligning similar components in the same direction is also a good practice. This will help you route your board effectively.
Lastly, to increase the ease of access, it is usually a good practice to place the board-to-wire connections near the PCB edge. Power supply connections and other input/output connections are convenient when they are at the board’s edge.
Take an Arduino Uno board, for example. Just imagine what would happen if the power jack or the USB port were in the middle of the board.
Resistive components dissipate heat when an electric current flows through them. Potential heat sources may include copper traces and vias. But if you include linear devices such as voltage regulators in your circuit, you will have to think about the best practices for removing excess heat from the PCB.
During PCB design, you may use some software tools to conduct a thermal analysis of your PCB. If the PCB is already in the field, you can use an infrared camera to measure and characterize the heat signature of your PCB. This will help you to identify components or sections that emit more heat than the rest.
Consider replacing linear voltage regulators with switching voltage regulators. You may also use heat sinks and cooling fans. However, this makes the overall package heavier and bulky, requiring more space. This can work if you are designing rugged products, but you will have to think of other options when the project requirements are not flexible. Here are some thermal management practices you may adopt:
- Thermal via arrays
- Thick copper traces
What are Traces
The purpose of a PCB is to hold components in place and electrically connect them using conductive traces, just like a regular breadboard or a Veroboard. Therefore, a trace is a conducting track that electrically connects components on the PCB. Traces can be made of any conducting material, but the most popular is copper.
How to Route Traces to Minimize EMF Noise/Interference
Electromagnetic noise or interference is an electrical phenomenon that causes concern to sensitive industries, such as airlines. In fact, electromagnetic noise from passengers’ devices has been reported responsible for unusual incidences during flight. But how do we create electromagnetic noises on the PCB?
Well, in the Electricity and Magnetism course, recall that a moving charge produces a magnetic field. Also, a changing magnetic field can produce an electric field. Now, if you look at your PCB, there are conducting traces everywhere, and through these traces, electric currents of different magnitudes are flowing in different directions. If the board is poorly designed, this may give rise to the creation and transmission of electromagnetic energy. This unwanted electromagnetic energy is called electromagnetic interference and this can be harmful to sensitive circuits.
As a PCB designer, there are various steps that you can use to minimize EMF noise/interference. One example is how you route your traces. Poorly routed traces can act as an antenna. So to avoid this phenomenon, you may consider:
- Keeping the traces short to avoid picking electromagnetic radiation
- Avoiding sharp right-angle bends
- Keeping high speed signals separate from low speed signals
- Keep return paths short
- Route differential traces as close as possible
Daisy Chain vs Star Configuration Layouts
There is more to PCB component placement than just placing them around. If you recall from the Computer Networks course, there are various ways to connect the network nodes. Each of them has its own set of unique advantages and disadvantages.
Today we are not talking about computer networks, but we are borrowing some important networking topologies. We are talking about the star topology and the daisy chain topology.
In a star topology, multiple components or sections are directly connected to a central power supply unit. The advantage is that if one component or section fails, other components of the PCB will remain functional. This highly reduces fault-finding time.
On the other hand, a daisy chain topology is one component or section attached to the next in a chain until the circuit is returned to the ground. This reduces the traces and saves space on the PCB, but if one component fails, other components might also fail.
What are Single-Layer PCBs
If you want to design a PCB, one of the first choices that you will make is the number of layers to use for your PCB. Of course, there are a lot of factors that may affect this decision. Examples include the complexity of your circuit, manufacturing costs, pin density, signal layers, operating frequency, and PCB turnaround time, among others. For most hobby projects, single or double layers are easy to work with from a layout perspective. But what really is a single-layer PCB?
The easiest way to understand this concept is to take an unused PCB. If it has one dielectric layer, solder mask (single or both sides), and only one copper layer, it is a single-layer PCB. This means that there is only one side where you can electrically connect your components. Single-layer PCBs are cost-effective, easy to understand, and convenient for manufacturing.
Double-Layer and Triple Layer PCB
As design complexity increases, the efficiency of single-layer PCBs decreases. This calls for more PCB layer configurations that can handle such demands. That is when we talk of double-layer, triple-layer, or multi-layer PCBs.
Simply put, double-layer PCBs have two conductor patterns on the PCB, and three-layer PCBs have three-conductor patterns. Multi-layer PCBs pack more conducting patterns inside the PCBs. Very complex PCBs have up to 100 layers.
What is a Via
When you are working on a multi-layer PCB, you may want to create links between the various layers of your PCB. You may use a via to achieve that.
In Latin, via means a path or way. In the context of PCBs, vias create an electrical connection between layers in the PCB. Basically, a via is simply a conductive hole that has copper pads on each layer. The three main types of vias are through-hole via, blind via, and buried via.
What is a Ground Layer
A ground layer on the PCB is usually a large layer of copper connected to the PCB’s ground point. PCB designers usually prefer to pour the ground layer because it reduces the ground traces on the PCB since every electrical component requires a ground connection.
What are Component Footprints
By definition, a footprint is an impression that is left by an object on the surface. In PCBs, a component footprint is a pattern for an electronic component that will eventually be soldered there. A lot of components are common, so their footprints are easy to find. But in some circumstances, however, you may need to create your own footprint for the component.
Most EDA/ECAD tools enable you to create your own footprints, and it is not difficult as well. You only need the dimensions from the component datasheet.
How to Find the Footprint for a Component
You can find the component footprints from a lot of online sources. Developers and engineers worldwide have contributed to developing layouts, footprints, and libraries for many components. Accessing these resources will save you a lot of time, so it’s not really necessary to “re-invent the wheel” when someone has developed and provided the same solution for free. Here are some examples where you can find such resources.
What is a Silkscreen Layer
The silkscreen layer is the top layer of the PCB, and this is where you find text-based or human-readable information on the PCB. You can also put part outlines, warning symbols, component reference designators, component identifiers, part numbers, test points, and logos.
How to Get Your PCB Manufactured
Now that your PCB is ready and you need to bring your ideas to reality, the last step is to send your PCB for manufacturing.
There are a lot of PCB manufacturing houses that promise high-quality production and quick turnaround times. You can choose any provider you want, but for this tutorial, I will show you how to use the services provided by EasyEDA.
EasyEDA is an EDA/ECAD tool that provides all the necessary tools for online PCB design and manufacturing. They offer a web-based solution from PCB design right through to manufacture. I assume that you have already completed the PCB design in EasyEDA. For demonstration purposes, I used an example from the EasyEDA library.
On the EasyEDA page, click on the Fabrication button on the menu, bringing a drop-down menu. Then click on PCB Order. This will take you to another page where you can select your choices for the PCB. Once you are satisfied, click on Place Order, and that’s it.
Yes, you can place an order for your PCB from EasyEDA in just a few clicks!
What are Gerber Files
In simple terms, Gerber files are software files given to the PCB manufacturing house for production. They contain every information about the PCB that you have designed.
Although showing you how to design a PCB was beyond the scope of this article, I hope this tutorial has given you a gentle introduction to the world of PCBs. In the next tutorials, I will delve deeper into the world of PCBs and show you how to design a PCB for a custom circuit.