What is PCB(printed circuit board)?

A printed circuit board (PCB) is a structure for assembling electronic components and their connections

 into a unified circuit that allows electrical current to pass between components. 

The PCB baseboard is typically made of a rigid nonconductive material, 

although it can also be built on a flexible base or on a base made up of both rigid and flexible materials.

 Electronic components such as diodes, inductors and transistors attach to the circuit board, 

and traces (electrical conduits) connect components.

Printed circuit boards support electronic devices of all types and sizes. For example, many consumer products contain PCBs,

 including laptops, tablets, smartphones and smartwatches, as well as appliances, entertainment systems and IoT devices. 

PCBs also drive communication and navigation systems and are found in industrial and medical equipment, automobiles, aircraft and sea vessels.

Multi-Layer PCBs Features: 

Composed of three or more layers of conductive material, separated by insulation

Rigid PCBs Features: 

Made of a solid substrate that maintains shape and rigidity

Flexible PCBs Features: 

Built on a flexible substrate, enabling bending and folding

Rigid-Flex PCBs Features: 

Combines rigid and flexible layers for versatile designs

A PCB can be single-layer, double-layer or multilayer. Single-layer PCBs are typically used for simple electronic devices such as home appliances, 

while multilayer PCBs tend to be built for more complex hardware, such as computer graphics cards and motherboards. 

Double-layer PCBs allow for greater density than single-layer PCBs and are used for electronic devices such as automotive dashboards or LED lighting, for example.

A PCB's layer count is commonly based on its number of conductive layers. However, a PCB also includes other types of layers, 

which are laminated together in alternating patterns of conductive and insulating material. Today's PCBs always contain the following four types of layers:

Substrate. This is the base, or core, layer. It is typically a rigid insulating material such as FR-4, a fiberglass/epoxy composite. 

In some cases, the substrate is a flexible material, usually plastic, which can fold or bend to accommodate space requirements.

 Flexible substrates can also withstand higher temperatures and other harsh conditions. Some PCBs use a combination of both rigid and flexible substrate materials.

Conductive. This layer is usually made from a thin sheet of copper. On a single-sided (or single-layer) PCB, there is one conductive layer laminated to the substrate.

 On a double-sided (or double layer) PCB, there are two conductive layers, one on each side of the substrate. A multilayer PCB alternates between the substrate and conductive layers.

Solder mask. The conductive layer is covered with a solder mask, a nonconductive material that gives PCBs their green color, although other colors can be used. 

The solder mask acts as an insulator for the underlying traces that are etched in the conductive material. The solder mask is also applied to the bottom of a single-sided PCB.

Silkscreen. This layer is simply the labeling that is applied to the PCB after all the other layers have been added. The labeling can include numbers, letters, 

symbols or other information that indicates the various functions of each connection point. The labeling is usually white, but other colors can be used.

A PCB is made up of a mix of these four types of layers. The mix and its organization varies depending on the PCB's purpose. 

A single-layer PCB includes one of each of these four layers. A double-layer PCB includes one substrate, but two of each of the other types of layers. 

A multilayer PCB will contain a mix of conductive and nonconductive layers, although the exact organization can vary. In some cases, a multilayer PCB might also use prepreg as a layer. 

Prepreg is a dielectric material that's sandwiched between two core layers or between core and conductor layers.

Many of today's PCBs adhere to a high-density interconnect (HDI) design, which incorporates a higher wiring density than traditional PCBs.

 HDI circuit boards require less space and can accommodate more components. The design also makes it possible to create more compact PCBs, 

which weigh less and require fewer materials. The HDI design is well-suited for use cases where space is an important factor, such as smartphones, 

home appliances or medical implants.