Controlled Dielectric vs. Controlled Impedance

What is the difference between controlled dielectric and controlled impedance regarding printed circuit board (PCB) fabrication? The purpose of controlling dielectric or impedance is essentially the same—the goal is to achieve a target impedance on one or more signal lines on a printed circuit board. To make sure this will happen, there are many factors that need to be considered and calculated. This includes trace width, spacing between copper features on the same layer, distance between copper features on other layers, the Dk (dielectric constant) of the laminate used to manufacture the board, and a few other factors. Managing the impedance of certain traces on printed circuit boards is a critical part of the creation process. To have a properly functioning device, impedance aids in reducing the signal reflections and distortions in high-speed designs or achieving maximum power transfer to a load.

Controlled impedance means the matching of substrate material properties with trace dimensions and locations in an effort to create a specific electrical impedance for a signal moving along a trace. It is implied that the printed circuit board is manufactured so that the impedance of traces is within a certain percentage of a specified value.

Controlled dielectric refers to the specified thickness of the insulating layers between a signal and power or ground planes. This approach takes the guesswork out of designing a printed circuit board by specifying that the dielectric constant of the PCB substrate is within a certain percentage of a specific value.

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