多層印刷電路板走線之電磁輻射快速預測方法

Abstract

本論文主要內容是針對多層結構的印刷電路板所造成的電磁干擾問題做分析與探討。主要可以分成兩個部分。 第一個部分為板邊輻射的部分，由於許多訊號層所產生的接地彈跳雜訊，使得電磁波在板內來回傳播反射，並在邊緣產生等效的磁流，進而產生遠場輻射。本論文除了利用空腔振盪器模型結合市售模擬軟體SIwave來預測板邊輻射外，也提出了利用接地連通柱在板邊加一圈的方法來抑制板邊輻射並給予最佳化設計。 第二個部份是表面輻射，首先利用電磁理論的方法推導出單一微帶線之遠場輻射方程式，並利用SIwave取得端電壓和端座標，即可得到最後整個空間的電磁輻射效應。再結合天線陣列因子的概念可以得到一般印刷電路板走線的遠場總輻射估計，另外此方法的時間也較市售模擬軟體SIwave與HFSS來得快速。此外，也適用於一般常見的差模訊號線與共模訊號線。 最後，整合表面輻射和板邊輻射，並利用全波模擬軟體和GHz橫向電磁波傳輸室量測來驗證其分析之準確性及接地連通柱設計。

This thesis focuses on the problems of Electromagnetic Interference（EMI）of multilayer Printed Circuit Board ( PCB ), and it can be separated into two parts. First part is edge radiation which is mostly contributed to the ground bounce noise of PCB arising from current flowing through vias or the signal trace crossing slot lines. The electromagnetic waves reflecting back and forth from edges of the substrate generate a standing wave, which creates effective magnetic currents causing serious EMI issues. Here, the cavity resonator model is used to predict the edge radiation. This thesis also proposed using stitching vias around the PCB to suppress the edge radiation, thereby leading to the optimal design of shorting vias is given. Second part is surface radiation. Based on electromagnetic theory, a closed-form formula for far field radiation by a straight microstrip transmission line section is derived. The far field information can be obtained by combining SIwave, which gives the node voltage and location information of routing. The total radiation prediction of general PCB routing can also be obtained by applying the concept of array factor in antenna theory. The simulation time of this method is faster than HFSS and SIwave and furthermore, this method can be applied in common differential and common-mode signals. Finally, this thesis integrates the surface and edge radiation. Full-wave simulation and GTEM Cell measurement are used to validate the accuracy of the proposed analysis and shorting via design.