Flow Analysis for Underfill of Flip-Chip Packages
Flip-Chip is an interconnection technique of advanced electronic device. The advantages of Flip-Chip are high I/O counts, short electronic signal path and small size. Most of electronic device of Flip-Chip are packaged by underfill that the encapsulant was driven by capillary force into the space between the chip and substrate. Underfill technique can protect the electrical device and prevent the device from destroying because of external force. Underfill has many defects including the fill time is too long, the situation of short shot and air trap are caused easily, the yield of product of Flip-Chip is not highest and the products are universal. Therefore, there are many factors being studied in this paper to sum up the influence of underfill of Flip-Chip process cause by model parameters.
The theory of underfill of Flip-Chip was studied in the first part of the paper. The fill time equation was corrected and calculated by dynamic surface tension. Therefore, the Runge-Kutta method was used in program to compare the characteristics of fill time equation and corrective equation. The experiment was established in second part to measure the fill time of underfill flow. The influences of gap height, bump pitch and bump pattern were discussed, at the same time, the CAE software was used to simulate the fluid flow. Compare the experimental results with analytical results and sum up the factors which affect the flow front of underfill to find the method which can control the flow front, reduce the chance of short shot and air trap; therefore, enhance the reliable of underfill process of Flip-Chip.
摘要
覆晶（Flip-Chip）接合技術為先進電子訊號連接技術中的一種，具有高I/O數、電子訊號路徑短以及尺寸小等優點，而採用覆晶接合之電子元件大部分均以底部充填技術進行封裝；底部充填是一種以毛細作用為驅動力在晶片與基板之間的間隙充填底膠的封裝技術，可以確保晶片不受到外力的影響而損及封裝體，但此技術具有充填時間長、容易產生短射與包風等缺點，使得覆晶封裝製程良率不高，間接影響覆晶封裝產品的普及率，因此本文將依各種可能之參數模型對覆晶封裝底部充填製程的影響，以供業界參考。
本論文第一部份針對覆晶底部充填相關理論進行研究，並對充填時間方程式依動態表面張力進行部份修正與推導，再應用數值分析中的Runge-Kutta 法撰寫程式，比較原始充填時間方程式與修正後充填時間方程式之間的差異性與優缺點；第二部份則建立實驗模組進行底部充填流動實驗量測，探討間隙高度、凸塊間距與凸塊配置等模型參數對底部充填流動的影響， 同時進行CAE(Computer-Aided-Engineering)模流分析模擬其流動情況；在完成實驗與分析模擬之後，進行實驗與模擬結果比較，歸納出影響底部充填波前形狀的因素，並尋求控制底部充填流動波前形狀的方法，降低短射與包風的發生，提高覆晶底部充填製程的可靠度。
關鍵字：覆晶、底部充填、毛細作用、Runge-Kutta 法、模流分析
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