具繞折式彈簧之電容式微機電麥克風可靠度研究

Reliability Analysis of CMOS-MEMS Capacitive Microphone with Serpentine Spring

倪培榮(Pei-Rong Ni)

指導教授 ： 葉孟考

國立清華大學/工學院/動力機械工程學系/碩士(2018年)

摘要

進行微機電元件開發時，微機電元件結構與整體封裝型式的可靠度分析是相當重要的一環。本研究以有限單元模型對CMOS-MEMS具繞折式彈簧電容式微機電麥克風進行可靠度分析，模擬微機電麥克風在運作時受到聲壓、振動、衝擊等外力負載時之應力與變形，並以振動與掉落實驗驗證模擬結果。
為分析具繞折式彈簧結構微機電麥克風之可靠度，本文首先探討單一麥克風元件結構，分析麥克風結構在運作時受到外界負載聲壓、振動、衝擊與兩電極板間靜電力，多種負載耦合下之變形與受力之靜、動態行為。文中也以靜電力關係式簡化靜電與結構的複雜負載耦合問題。結果可知當振膜受到靜電力、聲壓與衝擊負載後，振膜最大主應力比只受到衝擊負載提升1.89倍;而以多晶矽(Polysilicon)作為微機電麥克風振膜之材料可減低最大主應力23.1%，減低最大位移61.6%；也發現考慮製程誤差時，麥克風可能發生吸附現象無法運作。另外進行模態分析時，發現整體模型之共振頻率遠小於麥克風元件結構之頻率，顯示整體模型更容易發生共振現象。從微機電麥克風陣列模型受衝擊負載之結果可知，當麥克風受衝擊負載時，在彈簧轉角處、彈簧與固定端連接處轉角、彈簧與振膜連接處及矽基板中央皆為應力集中和結構脆弱處且與掉落實驗麥克風破裂位置相似。最後在封裝可靠度分析上以板級模型進行分析，結果顯示板級模型受衝擊負載時黏膠層應力值已超出其鍵結強度，可能因黏膠層脫層或破裂而發生失效；也發現使用剛性較低之黏膠可有效降低應力。本文中對微機電麥克風結構與整體封裝型式的可靠度分析結果，可給予設計者參考。

關鍵字

有限單元分析 ； CMOS-MEMS微機電麥克風 ； 掉落實驗 ； 板級掉落試驗 ； 可靠度分析 ； 麥克風陣列

並列摘要

The reliability analysis of MEMS (Micro Electro Mechanical System) components is an important issue when developing the novel MEMS sensor. In this study, finite element models are used to analyze the reliability of CMOS-MEMS capacitive microphone with serpentine spring under sound pressure, vibration, shock and electrostatic force. The simulation results were verified by vibration and drop test experiments.
The deformation and stress distribution of single MEMS microphone diaphragm under multiple loads, including sound pressure, vibration, shock and electrostatic force were analyzed to obtain the static and transient behavior of MEMS microphone. The equilibrium equation of multiple loads was used to simplify the loading coupling problem. The results show that the maximum 1st principal stress of MEMS microphone under sound pressure, shock loading and electrostatic force is 1.89 times higher than that of MEMS microphone under shock loading only. Replacing the diaphragm material of MEMS microphone from silicon dioxide to polysilicon can reduce 23.1 % of maximum stress and 61.6% of maximum displacement of MEMS microphone. The pull-in effect of MEMS microphone may occur due to possible imperfection in manufacturing process. Additionally, the fundamental frequency of MEMS microphone packaging model with printed circuit board is much smaller than that of single MEMS microphone and is more likely to resonate. The stress concentration regions are found at the corner of spring, the connection of spring and fixed end, the connection of spring and diaphragm and the center of silicon substrate in the MEMS microphone array and are consistent with those found from drop test experiment. Finally, the reliability of MEMS microphone packaging was evaluated by board level drop test simulation. The results show that the maximum von Mises stress of adhesive layer under shock loading exceeds the adhesive bond strength and the adhesive may fail possibly. And using an adhesive with a smaller stiffness can effectively reduce its stress. The results presented in this study can give valuable suggestions for the MEMS capacitive microphone designers.

並列關鍵字

Finite element analysis ； CMOS-MEMS microphone ； Drop test experiment ； Board Level Drop Test ； Reliability Analysis ； Microphone array

參考文獻

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