Optimum rotation angle for mitigating differential skew induced by glass cloth in PCBs

In high speed signal transmissions, glass cloth of the dielectric in printed circuit boards can cause a differential skew. It has been reported that the differential skew is mitigated when the angle between the differential transmission lines and the thread of the glass cloth is around 10°. However, the angle dependence between 10° and 45° and the optimum angle have not yet been investigated. This study focuses on the angle between the trace of the differential transmission lines and the thread of the glass cloth to investigate the angle dependence of the differential skew. We conducted a preliminary evaluation by analytical estimation of the phase delay difference in the differential transmission lines using our simple glass-cloth model. In a full-wave simulation, it was confirmed that the optimum angle between the threads of the glass cloth and the traces of the differential transmission lines is around 40°.