Optimized design of through-hole via in high-speed printed circuit board

Abstract

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-Ω to 51-Ω. 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-Ω to 52.5-Ω, 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 through-hole 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.