AN 672: Transceiver Link Design Guidelines for High-Gbps Data Rate Transmission

ID 683624
Date 1/29/2020

1.1.1. Loss Tangent and Dissipation Factor

Loss tangent (tan(δ)) (also referred to as dissipation factor (Df) by many PCB manufacturers) is a measure of signal attenuation as the signal propagates down the transmission line. This attenuation is the result of electromagnetic wave absorption in the dielectric material and is commonly known as dielectric loss. As frequency increases, the dielectric loss also increases proportionally. Common material choices for high-speed signal layers include Nelco 4000-13EPSI, Rogers 4350B, and Panasonic Megtron 6. For very high-Gbps transceiver designs, Intel has successfully used Panasonic’s Megtron 6 material as the laminates for the core and prepreg layers surrounding the high-speed routing layers.

Figure 2.  Comparison of Material Loss Tangent

Comparison of Material Loss Tangent

Note: Given the choice, select the material with the lower loss tangent to reduce signal attenuation from dielectric losses.