Insertion Loss Reduction Using Rounded Corners to Mitigate Surface Roughness Effect in PCB Transmission Lines

Signal integrity (SI) can be interpreted as a measure of the distortion of the incident pulse, which is attributed to various contributors, e.g., inter-symbol interference (ISI), crosstalk, jitter, etc. The channel insertion loss is generally the most critical concern in SI designs, since it determines the working bandwidth of a high-speed channel, and the bandlimited channels are known as the root cause of ISI. At the tens of Gigabit rates in use today, PCB transmission lines may have appreciable losses, which can be divided into frequency-dependent dielectric loss and conductor loss, and noticeable amount of losses can be generated at high-frequencies due to the skin effect and copper rough surfaces. In order to reduce the additional conductor loss due to the surface roughness, the employment of low-profile copper foils is a common practice in high-speed digital design. However, this existing method is not cost-effective. In this paper, insertion loss reduction using rounded corners are proposed and verified using both 2D and 3D full-wave simulations for the first time. Rounded corners can mitigate the increased insertion loss due to copper surface roughness in PCB transmission lines, and can be applied in high-speed interconnect designs to increase eye margins. The impact of applying rounded corners on far-end crosstalk is also discussed.