Optimized Design of Through-Hole Via in High-Speed Printed Circuit Board

In the printed circuit board (PCB) of high-speed optical transceiver module, the signal transmission speed is limited by many effects. In a multilayer PCB, a through-hole via is usually used to connect the signal path between the upper-layer and lower-layer. The impedance of signal path in PCB significantly influences on the signal performance. While the impedance of through-hole via mismatches with the impedance of signal path, the transmission bandwidth of the PCB can be limited. In this paper, the optimized design of impedance of through-hole via in high-speed PCB will be investigated for increasing the transmission speed in PCB. First, the Rogers 4350B high-speed PCB is used and the vertical K-type connectors are used to connect measure equipment and PCB. The vertical K-type connectors are connected with signal traces by through-hole vias. The impedance mismatch occurs at the through-hole via, so the design of the anti-pad is optimized. The anti-pad size is varied to compensate the impedance mismatch. The impedance of the through-hole via is increased from 44-Omega 51-Omega. We have optimized the design of the anti-pad for the vertical K-type connectors connecting with signal traces. Next, the Rogers 3003 high-speed PCB is used, its transmission loss is lower and its transmission speed is higher than the Rogers 4350B PCB. The S-parameters of 5-cm signal traces in Rogers 3003 and 4350B PCBs are measured through a network analyzer. According to the S21 insertion loss, the 3-dB bandwidth is 21.3-GHz in Rogers 3003 PCB and the bandwidth is 9.58-GHz in Rogers 4350B PCB. The higher transmission speed in Rogers 3003 PCB can be verified. The design of the through-hole via between the upper-layer and lower-layer is also optimized. Using the Rogers 3003 PCB, the distance between the through-hole via and nearby ground vias and the size of anti-pad are varied to improve the impedance mismatch of signal path. The impedance of the through-hole via is increased from 47.6-Omega to 52.5-Omega, and the transmission bandwidth is improved and increased from 18.3-GHz to 24.5-GHz. The eye diagram of through-hole via transmission in Rogers 3003 PCB is also measured, and the clearer eye diagram can be obtained. We have optimized the characteristic impedances of the throughhole vias between the vertical K-type connector and signal trace, and between the upper-layer and lower-layer. The transmission bandwidths of the through-hole vias can be improved. The optimized deign can be applied in PCB of high-speed optical transceiver module.