PCBs are non-conductive boards that hold electronic components and allow electricity to flow through circuitry etched onto their surfaces, and they have been used since the 1940s in devices like radios, computers, and appliances; PCBs can be single sided, double sided, or multilayered and come in rigid, flexible, or rigid-flex styles to suit different applications; They connect components like resistors, capacitors, and ICs through pads and traces on one or more metal layers.