A PCB, or Printed Circuit Board, is one of the most important parts of the keyboard. It contains all of the important electrical circuitry, including the MCU, the USB port, and many other parts. The functionality of the keyboard wholly depends on the PCB: for example, without diodes on a PCB, the keyboard will not support N-key rollover. (The ability to press multiple keys at once) The color of the PCB can vary, but black and white are the most common colors. The materials used in a PCB can affect the typing feel and sound; in some cases, the PCB is exposed and affects the aesthetics of the keyboard.

PCBs are based on schematics. Most keyboards will use a matrix of rows and columns to make up for the lack of pins on the microcontroller. This allows for the creation of bigger keyboards than possible without matrixes. Without a matrix, a 104-key keyboard would require 105 in/out pins; however, by using an 11x10 matrix, the number of io pins required can be reduced to 21.