Study of Thickening Soldermask Coated Microstrip Lines on High-Speed PCBs for Crosstalk Reduction in DDR5

摘要

Far-end crosstalk (FEXT) is one major factor impacting performance of DDR signals on printed circuit board (PCB) external layers (microstrip routing). Bigger spacing can help reduce FEXT. However, as there are lots of DDR signals, in most cases, there is little room to increase spacing. In this paper, we develop a simple and efficient DDR5 crosstalk reduction approach by using thickening soldermask coated microstrip lines (TSCMLs). The type of soldermask is regular low-loss material, which is mainly used for resistance welding transform. The simulated results show the achieved FEXT can maintain under -36.0 dB from dc to 16 GHz, and 23 dB reduction in FEXT is achieved at 3.2GHz in comparison with the initial microstrip lines. The measured results show that the peak FEXT voltage can be decreased by 83% of that without thickening soldermask. The experimental results are in agreement with the simulation and both validate the proposed design.