Printed circuit boards (PCBs) are a vital component of modern electronic hardware. Serving as the backbone of the electronic industry, PCBs are the foundation for almost all electronic devices and machines. From smartphones and computers to medical devices and industrial robots, PCBs provide the necessary connections for components to work together in an integrated system. This comprehensive guide provides an overview of PCBs and their components, advantages, and uses. It also offers an in-depth look at the design and fabrication of PCBs, as well as their current and future applications. Whether you are a student, hobbyist, or professional engineer, this guide is an essential resource for anyone interested in learning more about printed circuit boards.
What is a Printed Circuit Board (PCB)?
A printed circuit board (PCB) is a flat piece of material that is etched with conductive pathways and components (resistors, capacitors, etc.). This conductive network allows electricity to travel to various points on the PCB where components are connected. Printed circuit boards have been the backbone of electronic hardware since the 1940s. Today, they are used in almost all electronic devices and machines. From smartphones and computers to medical devices and industrial robots, PCBs provide the necessary connections for components to work together in an integrated system. The word “printed” in printed circuit boards refers to the fact that the design on the board is created by etching away parts of the copper on the board. Electricity flows through these copper traces, which are the pathways on the board, and connected components.
The Anatomy of a PCB
Printed circuit boards (PCBs) contain many layers that are laminated together to form a single printed circuit board. The two most common types are single-sided and double-sided PCBs.
- Top Layer - A top layer is the first layer of the PCB where components are connected. It is also referred to as the component side, or the “top side.”
- Silkscreen Layer - A silkscreen layer is an optional layer that contains markings and labels for the top and other layers of the PCB.
- Soldermask Layer - A soldermask layer is an insulating layer, typically composed of a clear material (such as polyamide), that protects the copper traces from oxidation and corrosion by solder.
- Ground Layer - A ground layer is an insulating layer that provides a path for current travelling through the PCB to reach the ground of the circuit.
- Middle Layer - A middle layer is an insulating layer that separates the top, bottom, and silkscreen layers.
- Bottom Layer - A bottom layer is the second layer of the PCB and is typically copper-coated.
Benefits of PCBs
- High Reliability: Printed circuit boards are highly reliable, thanks to their low failure rate and high repeatability. They are also easier to maintain than other types of boards. Printed circuit boards can be repaired or replaced. They can also be reused in the same or different products.
- Low Cost: PCBs are the cheapest type of electronics boards. This is primarily due to their high volume production and the low cost of materials used to make them.
- High Flexibility: PCBs are highly flexible, enabling designers to create many products like wearable electronics, modular robotics, and even soft boards.
- Efficient Design: By designing printed circuit boards, engineers can efficiently use components. This is especially true for complex circuits and products that would otherwise require a large space.
Types of PCBs
- Rigid Printed Circuit Boards: Rigid printed circuit boards (RPCBs) are the most common type of printed circuit boards. They are completely rigid and are often used in industrial and commercial applications.
- Semi-Rigid Printed Circuit Boards: Semi-rigid printed circuit boards (SRPCBs) are similar to rigid printed circuit boards. They are rigid in some parts, but flexible in other areas. Such boards are used in PCB applications that require a combination of rigid and flexible properties.
- Flexible Printed Circuit Boards: Flexible printed circuit boards (FPCB) are printed circuit boards that are completely flexible. They are used in applications that require flexibility. Such boards are mostly used in wearable electronics, such as fitness trackers and smartwatches.
- Soft Printed Circuit Boards: Soft printed circuit boards (SPCB) are printed circuit boards with a flexible, bendable, and soft substrate. They are used in applications that require a soft surface, such as wearable devices and electronics that are integrated into fabric.
Designing a PCB
The first step in designing a printed circuit board (PCB) is to identify the components for the circuit, including the number and size of parts needed for the PCB. From there, engineers need to draw a schematic diagram (schematic) of the PCB and identify the electrical connections between components.
- Identify Components: First, engineers need to identify the components for the circuit. For each component, they need to know the type, size, connections, and any special considerations. The types of components include resistors, capacitors, inductors, transformers, and other electronic and electromechanical components.
- Draw a Schematic: Then, engineers draw a schematic diagram of the PCB. The schematic diagram is a wiring diagram that shows the circuit connections between components. It includes a list of components, their schematic symbols, and electrical connections between components. For example, a schematic diagram for a simple LED circuit is shown in the figure below.
- Identify Electrical Connections: Finally, engineers identify electrical connections between components in the schematic diagram. This lets them determine the type of printed circuit board needed for the PCB. There are two types of PCBs – single-sided PCBs and double-sided PCBs.
Fabrication of PCBs
The next step in PCB fabrication is creating circuit boards by etching traces onto a copper-coated board. There are two ways to etch PCBs – manual and automated. Manual PCB fabrication is done with a chemical etchant. Automated PCB fabrication uses an electron beam or a laser to etch PCBs.
- Manual PCB Fabrication: Manual PCB fabrication uses a chemical etchant to etch the copper traces on a PCB. The process starts with a stencil (or photoresist) applied to the top side of the PCB. Next, an etching solution is poured into a tray and the PCB is placed on top of the tray. Then, the tray is placed in a chemical bath, which removes copper from areas not covered by the stencil.
- Automated PCB Fabrication: Automated PCB fabrication machines use either an electron beam or a laser to etch PCBs. Electron beam machines use high-voltage electron beams to remove copper from areas not covered by the stencil. Laser machines use high-power lasers to remove copper from areas not covered by the stencil.
Testing and Troubleshooting PCBs
After manufacturing PCBs, engineers test the electrical connections between components. The testing process includes electrical measurements to verify that components are connected as expected. When there are electrical issues with the PCB, engineers troubleshoot the problems to identify the source of the issue. There are various ways to troubleshoot PCBs.
- Electrical Measurements: The testing process begins with electrical measurements to verify that components are connected as expected. To do this, engineers use an electrical multimeter to measure voltage, resistance, and other parameters of components.
- SMT rework: When there are issues with the electrical connections between components, engineers use SMT rework to fix the issues. SMT rework is used to unsolder components that are connected incorrectly or in the wrong places.
- Visual Inspection: When the problems are not related to the electrical connections, engineers use visual inspection to troubleshoot PCBs. Visual inspection involves visually inspecting the PCB and its components for defects, defects in the soldermask, and other issues.
Current and Future Applications of PCBs
Although printed circuit boards have been around for more than 75 years, they are still used in modern electronic systems. This is because PCBs have many advantages over other types of boards, making them the most popular choice among engineers.
- High Reliability: PCBs are highly reliable, thanks to their low failure rate and high repeatability. They are also easier to maintain than other types of boards. Printed circuit boards can be repaired or replaced. They can also be reused in the same or different products.
- Low Cost: PCBs are the cheapest type of electronics boards. This is primarily due to their high volume production.
PCBs are an integral part of today’s electronics industry. They provide an efficient, reliable, and cost-effective means of connecting components, and are used in a wide variety of products. PCBs are also highly customizable, allowing designers to create unique and innovative products. As technology continues to advance, the demand for PCBs will only continue to grow.