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Most electronic devices including medical equipment, phones and household appliances rely on printed circuit boards to function. Known as PCBs, the electronic boards are made from a combination of silkscreen, copper circuitry, solder mask and substrate.
While this is the standard construction of a PCB, the actual design can differ considerably between the individual boards: some have only one layer of copper circuitry, while advanced examples can contain more than 50 layers.
What are the main types of PCB?
The main types of PCB designs include single sided, double sided and multi-layer printed circuit boards. Each is suited to different applications.
A single sided PCB has a single layer of conducting material on one side of the board. Different electronic components are incorporated onto the other side. This type of PCB consists of respective layers of substrate, a conductive metal, a protective solder mask and a silkscreen. The simplest and most cost-effective type of PCB, applications include vending machines, stereo equipment and printers.
A double sided PCB, also called a two-layer board, has more complex circuits and designs. Copper can be mounted on both sides of the PCB and the components can be connected by through-hole technology or surface-mount technology. The same layers used in a single sided PCB are also used for a double sided PCB, but they are applied to both sides of the board, rather than just one. They are used in more advanced electronic systems including car dashboards and lighting.
Several layers of base material make up the multi-layer PCB, which normally features a minimum of three conductive layers. Multiple double sided conductive layers are used to construct the PCB, based on a “sandwich” model. Separated by the corresponding number of sheets of insulating material, these are all laminated and bonded together.
Multi-layer PCBs are used to manufacture medical equipment, computers and GPS trackers. For complex devices and circuits, they are preferred over double sided PCBs, as they enable more detailed circuits to be created with a smaller footprint.
What are the components of PCBs?
Printed circuit boards are assembled from numerous electrical components and other materials.
Common components include resistors to transmit the electrical current that produces the voltage and dissipates the electric power as heat. The capacitors hold the electrical charge in the board, releasing it wherever more power is needed anywhere in the circuit.
Similar to capacitors, the inductors store energy and also block signals such as interference from other electronic devices from impacting the PCB.
The transistor controls the electronic signals on the PCB. The bipolar transistor is the most widely used, although there are several versions available. Transformers increase or decrease the voltage to transfer electrical energy from one circuit to another.
Diodes enable the electrical current to flow in one direction only, preventing it from damaging the device and the board by flowing in the wrong direction. The most commonly used is the light-emitting diode, known as the LED.
Sensors can recognise changes in the environment and will generate the relevant electrical current to correspond to the change. The signal is circulated to the other components.
What are the four common PCB layers?
Every PCB has the same four essential foundations. First, a substrate layer provides rigidity for the board. Usually made of fibreglass because it’s a durable material, it can also be made using epoxies.
The copper layer, manufactured from a fine layer of copper foil, is heat-laminated to the board. A single sided PCB has only one layer on one side. A double-sided board mounts conductive copper and components on both sides. A PCB built to handle a high level of power needs a thicker copper layer relative to the amount of power the board has to withstand.
A solder mask layer on top of the copper gives most PCBs their green hue. The solder mask is an insulating material that ensures the copper isn’t touching any other elements.
Finally, the silkscreen layer adds numbers, letters and symbols to the PCB so it’s easier for the user to understand the functions of the different LEDs and pins.
Rigid PCB vs Flexible PCB
There are two different types of printed circuit boards, rigid and flexible PCBs. Each is suitable for different applications.
The rigid PCB is inflexible and solid, as its name suggests. Made from several different layers joined together using heat and an adhesive; rigid PCBs come in single sided, double sided and multi-layered variations, depending on the application. Cost-effective and hardwearing, they can be produced in large quantities and are commonly used in industries and products where the components must be durable and remain fixed.
Flexible PCBs are also called “flex PCBs” or “flex circuits”. Designed to fit a specific product or device that requires a lightweight, thin board, they can work effectively in contoured shapes or small spaces. The flexible boards don’t use fibreglass as the substrate layer, as it’s too rigid a material. Instead, flexible PCBs use plastics. This type of PCB takes up less space than the rigid design and can withstand extremes of temperature. It is compatible with many different connectors and components.
There is also a rigid-flex hybrid PCB, combining elements of both types of board. It can be continually flexed, or even folded. Designed in 3D, this allows for the board to be flexed or twisted into a specific shape.
It’s also possible to manufacture a custom PCB suited to an individual project. This is becoming an increasingly popular solution for complex designs, or to balance a budget effectively.