I do not think that you never seen a PCB ! PCBs are every where , it is a small board inside any electronics products whether it is 80's radio or modern computer , it is the brain of every electronics . So PCB (printed circuit board ) more commonly printed wiring board is the compact board that reduces the wiring of any electronic
. That means It is a board that has lines and pads that connect various points together. In the picture above, there are traces that electrically connect the various connectors and components to each other. A PCB allows signals and power to be routed between physical devices. Solder is the metal that makes the electrical connections between the surface of the PCB and the electronic components. Being metal, solder also serves as a strong mechanical adhesive.
There are different types of Printed Circuit Board , single layer and multilayer . In single layer PCB only one sides are connection traces and other side consists of different components , But if there are many components required in a single board then we need multilayer pcb . it means we need to slice up board like a burger , and connection between them are made via machines , multi-layer board cannot be made in our home . Other kind of PCBs are flexible PCB , transparent PCB etc etc ,
The base material, or substrate, is usually fiberglass. Historically, the most common designator for this fiberglass is “FR4”. This solid core gives the PCB its rigidity and thickness. There are also flexible PCBs built on flexible high-temperature plastic (Kapton or the equivalent).