Critical parameter selection for thermal cycle of FBGA fatigue life

This paper will focus on the fast assessment methodology of FBGA fatigue life through simulation and physics of failure (PoF) analysis under thermal cycle. The structure of fine pitch ball grid array (FBGA) that has been investigated, and been modeled by ANSYS to compare with experimental data. There are two temperature cycling will be used, one is used to verify FEA model, and the other one is used to do failure analysis. The aim of this paper is fist discussing the ability of finite element analysis (FEA) in executing the virtual thermal cycling reliability analyzing the reliability of solder joints fatigue life in local modeling. FBGA packages can warp due to local and global mismatch of the coefficients of thermal expansion and the asymmetric package geometry. Temperature cycling condition including dwell time and ramp rate is an important factor that will affect the solder joins reliability. This paper will identify the critical parameters that influence by using a Design of Experiments (DoE) approach using simulation results from ANSYS. Two types of analyses include the physics-based analysis and the statistical-based analysis. The paper presents the physics-based analysis, three steps, uses by DoE tool. The first step we have to select the parameters, such as PCB thickness, PCB Young's modulus, PCB coefficient of temperature expansion (CTE), solder joints height, die thickness, mold compound thickness, and so on. The second step is to find important factors. And the final step is going to DoE, in this paper used response surface methodology (RSM). The use of DOE and ANOVA to identify the critical parameters and a response surface to generate a functional form will be discussed. In this study, we will concentrate on the approach of deformation information to the critical stress. The critical stress is then fed into a fatigue damage model, which outputs life, or cycles to failure. Throughout the work, DoE and ANOVA techniques will be used to determine the key parameters and help in the development of a fast assessment model of FBGA fatigue life through simulation and physics of failure (PoF) analysis under thermal cycle.