含玻纖效應之傳輸線電性分析及設計

Analysis of Fiber Weave Effects on Transmission Lines and Mitigation Design

王謹熏(Chin-Hsun Wang)

指導教授 ： 吳瑞北

國立臺灣大學/電機資訊學院/電信工程學研究所/碩士(2022年)

https://doi.org/10.6342/NTU202203615

摘要

隨著科技提升，終端及伺服器產品速率不斷提高，設計規格日趨嚴格。現今，印刷電路板常見的基板及預浸材料皆由玻璃纖維和樹脂交織而成，此非均勻性材料所造成的玻璃纖維編織效應將導致嚴重的信號完整性問題。本論文介紹了玻纖效應對傳輸線特性的影響，提出了層等效介電常數ε_r^'的層等效模型，用於快速計算受玻纖效應影響的傳輸線有效介電常數ε_eff、特性阻抗Z_0及差值和相關的時序偏移。 根據該模型，不需借助三維電磁求解軟體，利用蒙特卡羅方法快速分析層等效介電常數與傾斜傳輸線之間的關係，研究減輕玻纖效應的適當傾斜角，當傳輸線長一英吋，傾斜角度達5度或以上即可大幅減輕玻纖效應;並推導出最佳拉鍊式佈線設計，不僅減少因旋轉增加的佈線面積，且每段轉折線前後兩端旋轉偏移為玻纖間距的正整數倍或是玻璃纖維間隔的3倍以上，亦大幅降低玻纖效應造成的時間延遲差異。

關鍵字

印刷電路板 ； 玻纖效應 ； 層等效模型 ； 特徵阻抗 ； 時間偏移 ； 差模-共模轉換 ； 蒙地卡羅方法

並列摘要

Nowadays, glass fiber and resin are very common dielectric substrate in PCB. With the increasing data rates, fiber weave effect will cause severe signal integrity issue. This paper introduces the influence on transmission line characteristics due to fiber weave effect, and proposes a layer equivalent model with layer equivalent dielectric constant ε_r^' for fast calculation of effective dielectric constant ε_eff、characteristic impedance Z_0 and the associated timing skew. According to this model, Monte Carlo method is used to quickly analyze the relationship between layer equivalent dielectric constant and slant transmission line without resorting to three-dimensional electromagnetic simulation. The appropriate slant angle to mitigate fiber weave effect is investigated and the optimum zig-zag routing design is derived. Assuming a transmission line of length 1 inch, if the slant angle is greater than 5 degrees, the influence of delay difference caused by fiber weave effect can be greatly eliminated. When the zig-zag routing method is adopted, once the rotation offset is a positive integer multiple of glass fiber pitch or greater than 3 times of glass fiber pitch, it not only reduces the space caused by wiring rotation, but also dramatically eliminates the delay difference caused by fiber weave effect.

並列關鍵字

Printed circuit boards ； fiber weave effect ； layer equivalent model ； characteristic impedance ； timing skew ； differential to common mode conversion ； Monte Carlo method

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