多層陶瓷電容之機械性質與可靠度增強之分析檢測

Abstract

隨著電子裝置朝向輕薄短小發展的趨勢，多層陶瓷電容因為其擁有小尺寸高電容量的緣故，逐漸變成一不可或缺的電子元件。因此，多層陶瓷電容的機械強度、使用壽命以及可靠度便是一個考量的重點。因為多層陶瓷電容尺寸的關係，傳統試驗機械強度的方法無法直接使用在其上，現今測試多層陶瓷電容的機械強度使用的方法，是將電容焊接至電路板上，對電路板進行彎曲測試。在彎曲試驗後，測其電容值，當電容值下降超過一定量或是裂紋產生將電容完全破壞，則判定此電容的機械強度不通過測試，反之則代表電容擁有一定機械強度而通過測試。 本研究利用聲波發射裝置，並配合望遠顯微鏡對焊在電路板上進行彎曲試驗的多層陶瓷電容進行即時的觀察，以檢測電容在彎曲試驗下的機械強度，並配合有限元素分析，模擬電容在彎曲試驗下的應力場分布以及應力集中的情形。此外，奈米壓痕試驗也將被使用來測定多層陶瓷電容在奈米尺度下的機械性質，並配合有限元素法來進行電腦模擬分析。同時，本研究也採用了一種不同於傳統焊接電容於電路板上的方法，研究當某些參數改變時，對於轉移在彎曲試驗下電容內部最大應力的位置，以及導致的電容裂縫產生位置以及破壞的情形的影響，提供一些不論是電容設計或是減輕應力集中、改變裂縫生成位置以及生長方向的一些想法及指導方針。經由以上的研究，我們希望不只能夠測定並了解多層陶瓷電容破壞的位置及原因，並且透過這些研究，在提高多層陶瓷電容的機械強度以及可靠度上，提供一些材料選擇或是設計上的一些原則及想法。

The multilayer ceramic capacitor (MLCC) is becoming one of the indispensable electronic components. Therefore, its mechanical strength, lifetime and reliability are of great concern. The characterization of the mechanical properties of MLCCs, direct loading by conventional facilities is not suitable because of its small size. To date, the standard method used to determine MLCC’s mechanical properties is board flex test; i.e., mounting the capacitor onto a printed circuit board (PCB) and applying bending to the entire system. Failure is defined as cracking or capacitance loss of the MLCC when the mounted PCB is subjected to a specified deflection, and the measurements are usually performed after the test. In this thesis, acoustic emission was used to detect cracking of MLCCs during the board flex test. To confirm cracking-induced acoustic emission, telemicroscope was used to perform the in-situ observation of cracking. Finite element analyses were also performed to analyze the stress field resulting from the test to compare with the observed cracking path. In addition, nanoindentation was used to explore the mechanical properties of the constituents of MLCCs in the nanoscale. Meanwhile, an alternative soldering method was used to mount the MLCC onto the PCB and fracture pattern was observed and compared to that from the normal soldered MLCC. The shift of the location of crack and stress concentration provides design guidelines on improving the MLCC’s lifetime and mechanical strength. Our work not only allows identification and understanding of the fracture origin, but also provides guidelines in the material design.