||Warpage Simulation of Fan-Out Wafer Level Chip Scale Package
||Department of Mechanical Engineering
Wafer level packaging
Mold Filling Analysis
半導體封裝技術中一個重要的發展方向為晶圓級封裝（wafer level packaging﹔WLP）。晶圓級封裝具有覆晶之形態，採用薄膜重分佈（thin-film redistribution）技術佈線，接著利用凸塊或錫球與印刷電路板直接相連。和一般打線之球柵陣列（wirebond BGA）封裝相比，晶圓級封裝具有較佳之電性、較低的電力消耗、及較小之元件尺寸等優點。
隨著半導體元件輕薄短小的趨勢，在封裝製程中所產生的翹曲（warpage）問題也日益受到重視。以往研究中，大部分均認為造成IC構裝元件翹曲的主要原因為構成材料之熱膨脹係數不同所造成的不均勻體積收縮，卻因此忽略了環氧樹脂（EMC）本身固化收縮的材料特性，因而造成利用電腦模擬分析時，容易低估成品翹曲量。本文將同時考量環氧樹脂之固化效應與溫度效應所造成的體積收縮，以建立一套分析封裝體翹曲的分析方法。在研究中用來描述環氧樹脂行為的關係式為P-V-T-C關係式，也就是將環氧樹脂因固化效應所造成的體積收縮行為表示成壓力（pressure）、體積（volume）、溫度（temperature）、熟化率（degree of cure）相關之方程式。而溫度效應所造成的環氧樹脂體積收縮量則考慮是由於構成封裝體的材料之熱膨脹係數不同所造成。
Wafer level packaging is an important development trend for IC package design. The fan-out wafer level package discussed here has the flip chip form which uses thin-film redistribute then uses solder bump to connect the package to the printed wiring board directly. Liquid compound was used for the encapsulation process. Comparing with wire-bond BGA, the fan-out wafer level package has better electric properties, lower power consumption, and smaller package size.
Warpage problem plays an important role in IC encapsulation processes. Previous researchers had focused on warpage analyses with temperature changes between constituent materials and neglected the cure shrinkage effects. However, more and more studies indicate that prediction of warpage according to CTE (Coefficient of Thermal Expansion) was not able to accurately predict the amount of warpage in IC packaging. This paper used mold filling simulation and predicted the amount of warpage considering both thermal and cure induced shrinkage. The liquid compound properties were obtained by various techniques: cure kinetics by differential scanning calorimeter (DSC), cure induced shrinkage by P-V-T-C testing machine. These experimental data were used to formulate the P-V-T-C equation.
The P-V-T-C equation was successfully implemented and verified that warpage was governed by both thermal shrinkage and cure shrinkage. The amount of warpage after molding could be accurately predicted with this methodology. The simulation results showed that cure shrinkage of liquid compound was the dominant factor for package warpage after encapsulation. Even after post mold cure, the amount of warpage was still significant.
第一章 緒 論 1
1-1 晶圓級封裝製程簡介 2
1-2 收縮與翹曲現象 9
1-3 研究目的 11
1-4 文獻回顧 13
1-5 本文架構 20
第二章 理論分析 21
2-1 模流充填理論 22
2-2 黏度本質方程式 26
2-3 量測熟化反應速率之方式 29
2-4 固化反應動力方程式 32
2-5 P-V-T-C關係式 34
2-6 應力應變統馭方程式 41
2-6-1 固化收縮理論模式 41
2-6-2 應力應變關係式 42
第三章 翹曲分析 53
3-1 建立有限元素模型 54
3-2 模流分析 64
3-3 翹曲分析流程 69
3-3-1 基本假設 69
3-4 樣品量測驗證 79
第四章 結論與展望 82
4-1 結論 82
4-2 展望 84
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