Controlled Dielectric ExampleConfusion abounds regarding the topics of controlled dielectric and controlled impedance in the printed circuit board industry. We’ll try to clarify the subject.

What is the difference between Controlled Dielectric and Controlled Impedance regarding PCB fabrication?
The purpose of controlling dielectric or impedance is essentially the same, to achieve a target impedance on one or more signal lines on a printed circuit board.  For example, your design has a USB signal pair that must have an impedance of 90 ohms (±10%) to function properly. To make sure this will happen, there are many factors that need to be considered and calculated such as 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, as well as a few other factors.  more…