保角屏蔽封裝中近場遮蔽效應之量測與等效電路模型

Abstract

本論文主要針對系統級封裝的保角屏蔽技術評估近場屏蔽效果。透過利用磁場探針進行近場屏蔽效果之量測，並根據傳輸線理論及網路分析，提出一簡易評估屏蔽效果之傳輸線模型。此外，為驗證本文提出之預測方法，利用ANSYS HFSS模擬軟體的分層阻抗邊界條件之設定並將模擬資料作後處理，得以精準迅速地模擬複雜的薄膜屏蔽材料。本論文將詳盡討論使用保角屏蔽技術待測物的設計理念、等效傳輸線模型、及其模擬與量測結果。 本文將介紹如何設計一簡單系統級封裝模組，探討兩種走線於近場的輻射效益，並在線路末端串聯一匹配電阻以達到寬頻的量測設計。接著，分別探討單層及多層保角屏蔽之效果。在單層屏蔽方面，實作不同厚度的鍍銅及鍍鎳於待測物上；多層屏蔽方面，藉由相互堆疊的銅鎳材料探討不同厚度及層數間的遮蔽效果。本文提出之預測方法可快速評估單層及多層保角屏蔽的效益，跟模擬及量測相較下，從10兆赫茲到1千兆赫茲皆有很好的一致性。值得注意的是，由實驗結果發現，利用濺鍍技術鍍上薄膜於待測物上，將會使磁性材料失去原有磁性特性，因此需要修正其相對導磁率於模擬及傳輸線模型，亦顯示出對於磁性材料的鍍膜製程仍有改進空間。 最後，根據本文提出之傳輸線預測方法，設計一銅及鎳鐵合金材料交互堆疊之六層結構，理論上可於10兆赫茲達到35分貝的屏蔽效果，其總厚度僅12微米。此遮蔽效果相當於使用鍍單層50微米銅於待測物。

In this thesis, a near-field shielding effectiveness (SE) is investigated to deal with the shielding performance of conformal shielding on system-in-package (SiP). By using a magnetic probe, the measurement of near-field SE is accomplished. Based on transmission-line theory and network analysis, a simple SE estimation using the transmission-line-based (TLB) model is proposed. Furthermore, to verify the proposed model, a simulation method called “layered impedance boundary” is set using ANSYS HFSS with post processing to accurately and readily solve the SE of complicated thin shielded SiP. The design procedure of conformally shielded SiP is demonstrated in detail, whereas the equivalent model, simulation, and measurement are proposed. First of all, a simple SiP module is designed and two layout patterns are investigated to evaluate the near-field SE. To achieve a broadband testing, 50-Ω resistor is terminated at the end. Next, single- and multi-layered shielding structures are investigated separately. For single-layered shielding structures, different thicknesses of Cu and Ni are measured. On the other hand, multi-layered shielding structures are presented with Cu and Ni for different thicknesses and sequence arrangement. The proposed model could quickly evaluate the SE in single- and multi-layered shielding structures; moreover, it has a good consistency with simulation and measurement from 0.01 to 1 GHz. It is worth noting that the magnetic materials are sputtered as thin films on the DUT; however, it would lose its magnetic characteristics according to the experiment results. Consequently, the relative permeability of magnetic materials should be modified in the simulation and modeling. It implies that the manufacturing processes still require an improvement for coating magnetic materials. Finally, by using the TLB modeling, 5-layered shielding structure composed of the staggered Cu and NiFe with a total thickness of 12 μm can achieve 35-dB SE at 10 MHz theoretically. For a single-layered design, 50-μm copper is required to get such a high SE.