Invented in the early 20th century, printed circuit boards (PCBs) have become an integral part of electronic devices. Using circuits, diodes, substrates, and other electrical components, these boards are responsible for sending and receiving electronic signals in devices ranging from smartphones to vehicles to a wide variety of industrial applications.
But, despite their prevalence in almost every industry, many people do not know how PCBs work.
For this reason, we’ve created a detailed guide explaining how printed circuit boards function. With a comprehensive understanding of printed circuit board components, their function, and the many types of PCB options on the market, you can optimize your design for better cost, performance, and manufacturability.
How Do Circuits Work?
Among all PCB components, circuits are perhaps the most important. A circuit is a complete path that electrons can flow through from start to finish. In order for the current to flow, there must be a closed loop with no breaks or gaps in the circuit.
When it comes to printed circuit boards, the vast majority of circuits are etchings on the board’s surface that have been coated in a thin layer of metal. These conducting pathways can be made from different metals, including copper, aluminum, and silver.
The width, thickness, and shape of the metal lines all play a role in the circuit’s resistance. The amount of current that can flow through a circuit is also determined by its voltage.
The two laws of charge transfer, also known as Kirchhoff’s laws, govern how electrons flow through a circuit. The first law, also known as the current law, states that the total current flowing into a node (the point where two or more circuits intersect) must equal the total current flowing out of that node.
The second law, known as the voltage law, states that the sum of voltages around any closed loop must be equal to zero. Together, these laws help ensure that the current flowing through a circuit is constant and that there are no sudden voltage changes that could damage sensitive electronic components.
By applying these laws to PCB design, engineers can create circuits optimized for their specific applications and free from electrical issues such as shorts and open circuits.
Components of a PCB
With circuits acting as the PCB’s backbone, other components are needed to provide the necessary support. Without the following components, a PCB would not be able to function as intended.
Resistors
Resistors are an integral part of any circuit — they are responsible for limiting and controlling the flow of current by using heat as the primary method to dissipate energy. By adjusting the amount of resistance in a circuit, resistors can control the current flowing through a PCB without affecting the voltage.
Transistors
Electronic signals are often too weak to be used on their own, which is where transistors come in. A transistor is a semiconductor device that amplifies or switches an electronic signal. Amplification or switching is necessary when the signal needs to be sent over a long distance or when it needs to control a high-power device.
Capacitors
Capacitors store electrical energy in an electrostatic field and are able to discharge this energy very quickly. This makes them ideal for use in circuits where a sudden burst of power is needed, such as in audio applications.
Inductors
Inductors are used in circuits to store energy in a magnetic field. They are often used in conjunction with capacitors to create what is known as an LC (inductance-capacitance) circuit. This type of circuit is used in radiofrequency applications where it is necessary to tune the inductance and capacitance to create a specific frequency.
Transformers
Energy transfer between circuits is moderated by transformers. A transformer is an electromagnetic device that uses inductance to transfer energy between two or more circuits. The primary benefit of using a transformer is that it allows for the isolation of circuits, which protects sensitive components from damage.
Diodes
Diodes are semiconductor devices that allow current to flow in one direction only. This unidirectional flow of current is what makes diodes ideal for use in rectifier circuits. Rectifier circuits are used to convert alternating current (AC) into direct current (DC), which is necessary for many electronic applications. A familiar type of diode is a light-emitting diode (LED), which is often used as an indicator light.
Common Types of Printed Circuit Boards
The question, “How does a printed circuit board work?” offers many different answers depending on the type of PCB being discussed. The following are some of the most common types of PCBs and their applications.
Single Layer PCB
Also known as single-sided PCBs, these are the most basic type of PCB. The term refers to printing conductive paths and applying other components on one side of the board only. Highly versatile and inexpensive, single-layer PCBs are a good choice for applications where only a few components are needed.
Double Layer PCB
As the name suggests, double-layer PCBs are printed on both sides of the board. This type of PCB offers increased connectivity and is often used in applications where space is limited. Utilizing through-hole and surface-mount technology, they can be used with a wide range of components for more flexibility.
Multi-Layer PCB
Multi-layer PCBs are composed of two double-sided PCBs bonded together with an insulating layer between them. The number of layers can vary from three to twelve, with eight being the most common. This makes them ideal for use in applications where a high degree of connectivity is needed, such as in computer networks.
High-Density Interconnect PCB
High-density interconnect (HDI) PCBs are multi-layer PCBs that use laser-drilled microvias, advanced laminate materials, fine lines and tolerances, and conductive layers to increase the density of connections. HDI PCBs are used in applications where miniaturization is crucial, such as complex routing chips, medical devices, and cell phones. They offer increased connectivity and reduced size and weight compared to traditional multi-layer PCBs.
PCBs Are Used Everywhere
At the end of the day, how a PCB works is best explained through its applications. From single-layer to multi-layer, HDI, and more, there is a PCB design that can fit any need in applications such as:
- Medical devices
- LEDs
- Consumer electronics
- Industrial equipment
- Automotive and aerospace
- Safety and security
- Telecommunication
And with advances in technology, the capabilities of PCBs are only continuing to grow. To learn more about the process behind manufacturing printed circuit boards or to get more information on the best PCB designs, check out the manufacturing equipment used in PCB assembly.