封裝效應於SOI電容式三軸微機電加速度計之探討

Research on Packaging Effects of Three-axis SOI MEMS Accelerometer

楊宏德(Yang, Hung Te)

指導教授 ： 江國寧

國立清華大學/工學院/動力機械工程學系/碩士(2015年)

摘要

近幾十年來手持裝置與微機電系統元件快速的發展，在微小化、低成本、低功耗和高精度的要求上，封裝後之微機電元件的可靠性已被提出了許多挑戰，如封裝效應產生之殘餘應力和翹曲行為等。因感測元件在製造後之共振頻率與各組織結構的勁度等性質具有不確定性，將導致其輸出性能產生不穩定性，故本研究將探討感測元件受殘餘應力影響下，其共振頻率之變化趨勢。接著將對於SOI電容式三軸微機電加速度計封裝於閘型陣列封裝之結構，進行塑封材料之固化降溫製程模擬，探討因材料間之熱膨脹係數的不同產生之封裝效應，使得感測元件因殘餘應力而產生輸出偏移之現象及其影響度。
於本研究中，利用平行板電容公式及振盪頻率原理提出一個修正電容偏差之模型，此修正模型可透過量測電容式加速度計之變化共振頻率，即可將偏移之電容差值補償至標準電容差值。由結果顯示，加速度計受到較大殘餘應力結構影響時，其引起的電容偏移量較大，加速度計之靈敏度亦明顯下降。本研究利用修正電容偏差模型，將產生偏差之電容偏移量補償至標準電容偏差量，且成功地將偏移量補償至標準量。另外，為了研究電容式加速度計之封裝溫度效應，將建立三維閘型陣列封裝模型，並嵌入電容式加速度計，並模擬環境溫度由0至300⁰C。結果發現，受溫度效應影響而產生之偏移量比受殘餘應力效應影響而產生之偏移量來得小，因此加速度計之殘餘應力效應是影響靈敏度偏移的關鍵因素之一。

關鍵字

封裝效應 ； 微機電系統 ； 加速度計 ； 共振頻率 ； 殘餘應力 ； 模態分析 ； 製程模擬 ； 有限單元應用及模擬

並列摘要

In the recent years, the rapid development of handheld devices which have become smaller, cheaper, and more functionalities. However, the MEMS accelerometer after packaging has presented many challenges such as residual stress and warpage. After the sensor device processing, there were many process uncertainties may cause changes in the resonance frequency and stiffness. These uncertainties can cause the performance of MEMS sensor unstable. Furthermore, the MEMS accelerometer sensor will be embedded in the LGA packaging and simulate the shrinkage of molding compound after molding. More details of packaging effect in device will be discussed in this research.
In this research, the resonance frequency of the three-axis SOI accelerometer is successfully simulated by modal analysis, and also presents a simple compensation model for trimming the offset of capacitance differentiation using the measured resonance frequency. From the result, the accelerometer structural under high residual stress can cause the offset of capacitance differentiation. Furthermore, the sensitivities of the accelerometer are dropped significantly. By using the compensation model, the capacitance differentiation offset and the sensitivity are successfully trimmed. In addition, in order to investigate the packaging temperature effect on accelerometer structural (0-300⁰C), the LGA packaging 3D model was established. The results found that the sensitivity offsets of temperature effects are smaller than the offsets of residual stress effects, the residual stress effects will be a key factor affecting the sensitivity offsets.

並列關鍵字

Package effect ； SOI MEMS ； Accelerometer ； Resonant frequency ； Residual stress ； Modal analysis ； Process modeling ； FEM Applications and simulation

參考文獻

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