黏著劑結合之接頭應力分析及其在取晶過程之應用

Abstract

本文主要探討一黏著劑(adhesive)接合二個黏著物(adherends)在銷-銷(pin-pin)之邊界條件(boundary conditions)下受到集中力(concentrated force)作用，在此條件下導出其統御方程式(governing equations)為複雜之偶合方程式(coupled equations)，其解析解(analytic solutions)利用符號運算(symbolic manipulation)求得，並使用奇異值分解法(singular value decomposition, SVD)求得符合邊界條件之數值解。 文中討論黏著層(adhesive layer)的剝離應力(peel stress)及剪應力(shear stress)受到黏著物及黏著劑之材料性質、幾何形狀(厚度、長度)、接合長度、力作用點等的影響。在無因次化參數(non-dimensional parameter) 的值為 =1, 及參數 d = 0的情形下，對於上層黏著物(upper adherend)能夠從下層黏著物(lower adherend)完全分離，必須滿足下面的條件，下層黏著物的厚度大於10倍的黏著層之厚度且小於1/3上層黏著物之厚度，並且黏著層厚度相對的薄( mm)，接合時，其長度相對的短，也就是說厚長比(thickness to length ratio)大於0.08 ( )。 接著將上述黏著接頭之分析(analysis of adhesive joint)方法結合C++語言的基因演算法(genetic algorithm)運用於取晶過程之探討。當0.1mm厚的晶片受到4.8N的集中力，取晶良率(success rate)很低，且晶片不是破裂就是無法從藍膜(blue tape)分離。但當0.34mm厚的晶片受到3.5N的集中力，取晶良率很高，且晶片幾乎没有破裂且可以完全成功的從藍膜分離。對這二實驗中，其取晶良率差異很大。本文利用基因演算法結合黏著接頭之分析方法去找尋黏著劑之材料性質。對0.1mm厚晶片的例子中，當黏著劑的厚度為0.01mm時，完全尋找不到材料性質符合之黏著劑。另外本文希望以不同的黏著劑的厚度來改善晶片厚度為0.01mm的取晶良率，但是結果也完全找尋不到材料性質及厚度符合之黏著劑，但是對晶片厚度為0.34mm的例子，當黏著劑的厚度為0.01mm時，就可以找尋到黏著劑的彈性係數(Young’s modulus)為 pa，而且本文希望以一般黏著劑取代實驗所使用的輻射黏著劑(radiation-cured adhesives)或稱為紫外線黏著劑(ultra-violet adhesive)時，也可找到黏著劑的彈性係數及厚度分別為 pa 及 0.027mm。這些理論分析的結果一致於實驗的結果。 為了改善先前例子，對晶片的厚度為0.1mm易於破裂或無法從藍膜分離，藍膜的彈性係數必須再予增加。只要藍膜的彈性係數大於1/10倍的晶片之彈性係數，皆可找得到黏著劑的彈性係數及厚度值，且其畸變能應力(von Mises’s stresses)皆大於130Mpa，超過一般黏著劑的臨界應力(40-80Mpa) [51]，因此可預知當厚度0.1mm的晶片在取晶時，改變藍膜的材料性質，就能夠提高從藍膜成功分離之機會。

In this study, a concentrated force is applied to both adherends bonded by an adhesive under the pin-pin boundary conditions. First a mathematical model is derived with governing equations and boundary conditions. These complicated, and analytically problematic, coupled equations are solved numerically using symbolic manipulation and singular value decomposition (SVD). Also discussed are the effects of major factors, including the relative thickness of, material properties of adherends and adhesive, joint length, and the action point of the concentrated force on the peel and shear stresses in the adhesive layer. As non-dimensional parameters =1 and the parameter d = 0, this study identifies the conditions under which the upper adherend without breakage can be fully separated from the lower adherend. Particularly, it is found that the thickness of the lower adherend should be greater than ten times that of the adhesive layer but less than one-third that of the upper adherend, the adhesive layer should be relatively thin ( mm), and the adhesive joint should be relatively short (thickness to length ratio ). Subsequently, the aforementioned analysis of adhesive joint is associated with the C++ program of genetic algorithm and is applied to investigate IC chip pick-up process. As the thickness of IC chips subjected to the concentrated force 4.8 N is 0.1 mm, IC chips are easy to fail in the IC chip pick-up process while as the thickness of IC chips subjected to the concentrated force 3.5 N is 0.34 mm, IC chips are fully separated from blue tape without breakage. The two experiments have a great difference in the success rate of the IC pick-up process. The experimental results are discussed by genetic algorithm searching associated with analysis of adhesive joint. The former case is as the thickness of the adhesive layer is 0.01mm, the solution to Young’s modulus of the adhesive layer is not found. Additionally, it is expected that the success rate of the IC pick-up process can be raised by changing the adhesive’s thickness. However, the searching result does not also find any solution to material properties and thickness of adhesive. The latter case is as the thickness of the adhesive layer is 0.01mm, Young’s modulus of the adhesive layer is searched and the value of Young’s modulus obtained is pa. In addition, it is expected that in the IC pick-up process, radiation-cured adhesives (ultra-violet adhesives) can be replaced by general adhesives. The searching result can also obtain Young’s modulus of and the thickness of the adhesive layer which are respectively pa and 0.027mm. These results are in accordance with those of the experiments. In order to reduce the easy failure of the former case regarding IC chip’s thickness 0.1 mm, the Young’s modulus of blue tape has to be increased. The conclusions are that only if the Young’s modulus of blue tape is greater than one-tenth that of IC chips, genetic algorithm can obtain the searching results of adhesive’s Young’s modulus and adhesive’s thickness. Thereby, only if the mechanical properties of blue tape are changed, the probability of IC chips which can be fully separated from blue tape is expected to be able to increase because the von Mises’s stresses of the searching results are greater than 130Mpa exceeding the critical value (40-80Mpa) [51] of general adhesive.