Optimal design of thin fine-pitch ball grid array by Taguchi method

In this paper, the finite element analysis software ANSYS is used to build the 3D analysis model for Thin Fine-pitch Ball Grid Array (TFBGA). Next, the relative temperature cyclic loading condition and the usage boundary condition are built. Thus, the relative stress and strain can be determined. Simultaneously, according to the maximum stress, the average viscoplastic strain energy of an interface thickness for the key fracture solder ball under a temperature cycle is also found and calculated. Finally, substituting the calculated average viscoplastic strain energy into the model proposed by Darveaux, the fatigue life of the TFBGA can be obtained. Next, the optimal design of the package is discussed. The selected factors include the printed circuit board, substrate, chip, mold compound thickness and thermal expansion coefficient. Only one magnitude of the factor changes during an analysis for understanding the influence the level of the fatigue life of the package. Finally, by using the orthogonal array and analysis of variance of the Taguchi method, the optimal design of the combination for the parameters is achieved. It is expected that the fatigue life of the package can be maximized.