Printed circuit board:
A printed circuit board (PCB) is a physical base or platform on which electronic components can be welded. Copper traces connect these components to each other and enable the PCB to function the way it is designed.

The printed circuit board is the core of the electronic device, it can be any shape and size, depending on the application of the electronic device. The most common substrate/substrate material for PCB is FR-4. FR-4-based PCBs are commonly found in many electronic devices, and their manufacture is common. Compared with multilayer PCBs, single-sided and double-sided PCBs are easier to manufacture.

FR-4 PCB is made of glass fiber and epoxy resin combined with laminated copper cladding. Some of the prime examples of complex multilayer (up to 12 layer) PCBs are computer graphics cards, motherboards, microprocessor boards, FPGAs, CPLDs, hard drives, RF LNA, satellite communications antenna feeds, switching mode power supplies, Android phones, and more. There are also many examples where simple single-layer and double-layer PCBs are used, such as CRT televisions, analog oscilloscopes, hand-held calculators, computer mice, FM radio circuits.

Application of PCB:
1. Medical equipment:
Today's advances in medical science are entirely due to the rapid growth of the electronics industry. Most medical devices such as pH meters, heartbeat sensors, temperature measurements, ECG/EEG machines, MRI machines, X-rays, CT scans, blood pressure machines, glucose level measuring devices, incubators, microbiological devices and many other devices are separately based on electronic PCBs. These PCB's are usually compact and have a small shape factor. Density means that smaller SMT components are placed in smaller PCB sizes. These medical devices are made smaller, portable, light and easy to operate.

2. Industrial equipment.
PCBs are also widely used in manufacturing, factories, and imminent factories. These industries have high-power mechanical equipment driven by circuits that operate at high power and require high current. To do this, a thick layer of copper is pressed on top of the PCB, which is different from the sophisticated electronic PCBs, where the current of these high-power PCBs is as high as 100 amperes. This is especially important in arc welding, large servo motor drivers, lead-acid battery chargers, military industry, clothing cotton looms, and other applications.

3. Lighting.
When it comes to lighting, the world is moving towards energy-efficient solutions. These halogen bulbs are rarely found now, but now we see LED lights around and high intensity LEDs. These small LEDs provide high brightness light and are mounted on PCB based on aluminum substrate. Aluminum has the property of absorbing heat and dissipating it in the air. Therefore, due to the high power, these aluminum PCBs are commonly used in LED lamp circuits for medium and high power LED circuits.

4. The automotive and aerospace industries.
Another application for PCBs is the automotive and aerospace industries. A common factor here is the reverb generated by the movement of an aircraft or a car. Therefore, in order to meet these high force vibrations, the PCB becomes flexible. So a PCB called a Flex PCB is used. Flexible PCBs can withstand high vibrations and are light weight, which can reduce the total weight of the spacecraft. These flexible PCBs can also be adjusted in a narrow space, which is another big advantage. These flexible PCBs serve as connectors, interfaces, and can be assembled in compact Spaces such as behind panels, under dashboards, etc. A combination of rigid and flexible PCB is also used.
PCB type:

Printed circuit boards (PCBs) fall into 8 major categories. They are

Single sided PCB:
The components of the single-sided PCB are mounted on one side only, with the other side used for copper wire. A thin copper foil layer is applied to one side of the RF-4 substrate and then a solder mask is applied to provide insulation. Finally, screen printing is used to provide the marking information of C1, R1 and other components on the PCB. These single-layer PCBs are easy to design and manufacture on a large scale, are in high demand, and are cheap to buy. Very commonly used in household products such as juicers/blenders, charging fans, calculators, small battery chargers, toys, TV remote controls, etc.

Double PCB:
Double-sided PCB is applied to the copper layer PCB on both sides of the board. Drill holes in which THT elements with leads are installed. These holes connect one part to the other via copper rails. Component leads pass through the hole, the excess leads are cut by a cutter, and the leads are welded to the hole. This is all done manually. You can also have SMT components and THT components with 2 layers of PCB. No holes are required for the SMT components, but the pads are made on the PCB and the SMT components are fixed to the PCB by reflow soldering. SMT components take up very little space on the PCB, so they can use more free space on the board to achieve more functions. Double-sided PCB is used for power supply, amplifier, DC motor driver, instrument circuit, etc.

Multilayer PCB:
Multilayer PCB is made of multi-layer 2-layer PCB, sandwiched between dielectric insulation layers to ensure that the board and components are not damaged by overheating. Multilayer PCBs are available in a variety of shapes and layers, ranging from 4-layer to 12-layer PCBs. The more layers, the more complex the circuit, the more complex the PCB layout design.
Multilayer PCBs usually have separate grounding layers, power layers, high-speed signal layers, signal integrity considerations, and thermal management. Common applications are military requirements, aerospace and aerospace electronics, satellite communications, navigation electronics, GPS tracking, radar, digital signal processing, and image processing.

Rigid PCB:
All PCB types discussed above belong to the rigid PCB category. Rigid PCBs have solid substrates such as FR-4, Rogers, phenolic and epoxy resins. These boards do not bend and twist, but can stay in shape for many years up to 10 or 20 years. This is why many electronic devices have a long life because of the rigidity, robustness and rigidity of a rigid PCB. PCBs for computers and laptops are rigid, and many home TVs, LCD and LED TVs are made of rigid PCBs. All of the above single-sided, double-sided, and multilayer PCB applications also apply to rigid PCBs.

A flexible PCB or flexible PCB is not rigid, but it is flexible and can be bent easily. They have elasticity, high heat resistance and excellent electrical properties. The substrate material for Flex PCB depends on performance and cost. Common substrate materials for Flex PCB are polyamide (PI) film, polyester (PET) film, PEN and PTFE.
The manufacturing cost of Flex PCB is not just rigid PCB. They can be folded or wrapped around corners. They take up less space than their rigid counterparts. They are light in weight but have very low tear strength.

The combination of rigid and flexible PCBs is important in many space - and weight-constrained applications. For example, in a camera, the circuits are complex, but the combination of rigid and flexible PCBs will reduce the number of parts and reduce the PCB size. The wiring of two PCBs can also be combined on a single PCB. Common applications are digital cameras, mobile phones, cars, laptops, and devices with moving parts

High speed PCB:
High speed or high frequency PCBs are PCBs used for applications involving signal communication at frequencies higher than 1GHz. In this case, signal integrity issues come into play. Material of HF PCB substrate should be carefully selected to meet design requirements.
Commonly used materials are polyphenylene (PPO) and polytetrafluoroethylene. It has stable dielectric constant and small dielectric loss. They absorb less water but cost more.
Many other dielectric materials have variable dielectric constants that cause impedance changes, resulting in distortion of harmonic and digital signals and loss of signal integrity

Aluminum based PCBS substrate material has the characteristics of effective heat dissipation. Because of the low thermal resistance, aluminum based PCB cooling is more efficient than its copper-based counterpart. It radiates heat in the air and in the hot junction area of the PCB.

Many LED lamp circuits, high brightness LEDs are made from aluminum backed PCB.

Aluminum is an abundant metal and is cheap to mine, so PCB costs are low. Aluminium is recyclable and non-toxic, making it environmentally friendly. Aluminum is rugged and durable, thus reducing damage during manufacturing, transportation and assembly
All of these features make aluminum based PCBs beneficial for high-current applications such as motor controllers, heavy-duty battery chargers and high-brightness LED lights.

Conclusion:
In recent years, PCBs have evolved from simple single-layer versions suitable for more complex systems, such as high-frequency Teflon PCBs.
PCB now pervades almost every area of modern technology and evolving science. Microbiology, microelectronics, nanoscience and technology, aerospace industry, military, avionics, robotics, artificial intelligence and other fields are all based on various forms of printed circuit board (PCB) building blocks.