微感測器受熱循環負載之有限單元應力分析

Finite Element Stress Analysis of Micro Sensors under Thermal Cycling

鄭至宏(Cheng, Chih Hung)

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(2015年)

摘要

近年來科技產品逐漸往追求多功能性的目標發展，電子產品由起初較大型超級電腦進展為桌上型、筆記型電腦，近年來更進一步精巧如平板電腦、智慧型手機等手持式裝置，此類裝置內部具有多種不同微型化的智慧感測元件，同時具有高精度與高價格之特點。當電子產品同時追求輕薄短小與高性能時，元件的高密集性將造成熱量的累積，雖然目前在散熱系統上擁有相當多研究與應對，但長期運作下，內部產生升溫情形依然存在，隨溫度變化後，因熱膨脹係數(Coefficient of Thermal Expansion)不匹配而產生應力集中現象。
本研究主要使用有限單元分析進行元件熱應力分析，以加速度計(Accelerometer)為例並結合FR-4印刷電路板(Print Circuit Board)為研究對象，分別研究加速度計受熱負載與熱循環兩種負荷，使用JEDEC規範進行熱循環(Thermal Cycling)分析，探討溫度變化時，感測器內部受熱後應力的變化情形，進一步分析較早破壞處之塑性行為。本研究使用有限元單分析軟體ANSYS，針對JESD22-A104-D規範下的熱循環條件進行模擬，探討不同循環次數之模擬結果，而後改變部分參數，利用電腦模擬多種條件下的溫度循環分析，提供設計上的參考，避免應力對結構產生的破壞，進行更完整的評估。結果顯示本研究之微加速感測器藉由以上分析，在經過多次熱循環後，MEMS結構連接晶片之彈簧結構有較大應力產生，將使結構發生破壞，本研究可對微感測器開發提供相關設計之參考。

關鍵字

微感測器 ； 加速計 ； 有限單元分析 ； 熱應力分析

並列摘要

In recent years, the electronic products are developed towards light, smaller and multifunctional, such as desktop and laptop computers, as well as the handheld tablet and smart phones. The handheld devices composed of various miniaturized, sophisticated and expensive smart sensors with high-density electronic components, which would cause heat accumulation after operating for a long time. As the temperature changes, the stress concentration would occur due to the mismatch of coefficient of thermal expansion (CTE) between different components.
In this paper, the finite element code ANSYS was used to analyze a micro-sensor, an accelerometer, on FR-4 printed circuit board (PCB) under thermal load and thermal cycling according to JEDEC standards. The results show that after thermal cycling, the spring structure connecting to accelerometer had greater stress which would cause failure. The thickness of the bottom layer in the spring connecting the accelerometer and material constants, such as Young’s modulus, the yield stress and the tangent modulus, were varied to study their effects on the failure behavior of the micro-sensor. These results could be used to evaluate the thermal stresses of different micro sensors under similar conditions in the future.

並列關鍵字

Micro Sensors ； Accelerometer ； Finite Element Analysis ； Thermal Stress Analysis

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