田口方法對薄形細間距球柵陣列封裝之最佳化設計

Optimal Design of Thin Fine-Pitch Ball Grid Array by Taguchi Method

本文先利用ANSYS有限元素分析軟體建立薄形細間距球柵陣列封裝的三維分析模式，接著建立相關的溫度循環負載條件及使用時的邊界條件，以計算出相關的應力和應變。同時根據最大的應力，找到並計算出一介面層厚度的關鍵破壞錫球在一個溫度循環負載下的平均黏塑性應變能密度。之後，再將所求得的平均黏塑性應變能密度，代入Darveaux 所提出的模式中，即可計算出薄形細間距球柵陣列封裝的疲勞壽命。本文接著進行封裝體的最佳化設計，其中所選定的因子有印刷電路板、基板、晶片、封膠的厚度及熱膨脹係數，在一次僅改變一個因子下進行分析，以了解各因子水準的變動對於封裝體疲勞壽命的影響。最後，再利用田口方法的直交表及變異分析後，找出最佳的參數組合，以期望封裝體的疲勞壽命達到最大化的目的。

In this paper, the finite element analysis software ANSYS is used tobuild the 3D analysis model for Thin Fine-pitch Ball Grid Array (TFBGA).Next, the relative temperature cyclic loading condition and the usageboundary condition are built. Thus, the relative stress and strain can bedetermined. Simultaneously, according to the maximum stress, theaverage viscoplastic strain energy of an interface thickness for the keyfracture solder ball under a temperature cycle is also found and calculated.Finally, substituting the calculated average viscoplastic strain energy intothe model proposed by Darveaux, the fatigue life of the TFBGA can beobtained.Next, the optimal design of the package is discussed. The selectedfactors include the printed circuit board, substrate, chip, mold compoundthickness and thermal expansion coefficient. Only one magnitude of thefactor changes during an analysis for understanding the influence the levelof the fatigue life of the package. Finally, by using the orthogonal arrayand analysis of variance of the Taguchi method, the optimal design of thecombination for the parameters is achieved. It is expected that the fatiguelife of the package can be maximized.