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80 PCB007 MAGAZINE I APRIL 2024 In the world of PCB design, miniaturization can be achieved by using low dielectric con- stant (Dk) materials. Low Dk materials can allow for a reduction in thickness while main- taining a given trace width, leading to lower transmission loss and higher density circuitry: In this equation, Z 0 is the characteristic impedance, ε r is the dielectric constant, w is the trace width, and h is the distance from the trace to the ground plane. When the characteristic impedance of a transmission line matches the impedance of connected devices (source and load), there is minimal reflection of the signal, and energy is efficiently transferred. Utilizing a material with the appropriate dielectric con- stant to achieve impedance matching is imper- ative to ensure signal integrity and proper cir- cuit operation. But from a materials science perspective, what is the dielectric constant? Why do some classes of materials inherently have lower or higher dielectric constants? Scientifically, the dielectric constant of a material represents its ability to store electri- cal energy when exposed to an applied electric field. It also represents how well a material's dipoles (i.e., internal charge distribution) align with that applied field. Just like how a magnet has a north and south pole, all materials have an internal charge distribution, contingent upon the atoms that make up that material and The Dielectric Constant of PCB Materials Material Insight by Preeya Kuray, Ph.D.