A high-density interconnector (HDI) PCB is a circuit board with a higher wiring density per unit area compared to more conventional boards. They are constructed out of a number of layers of conducting materials that are separated by a dielectric material, which are glued together by adhesives and linked by microvias. By definition, these constitute any printed circuit board with an average of 120-160 pins per square inch.

HDI PCBs have finer spaces between lines, higher connection pad density, and more parts assembled onto a smaller surface. They rely on microvias in order to function. With many layers that must communicate with each other in order to properly function, the condensation of parts relies on extremely small parts delivering electrical signals from one layer to another. Microvias are a specialized type of via with a hole diameter of 150 microns or less that allow this kind of printed circuit board to function.