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Design for Solder Joint Fatigue Life of BGA Package Subject to Mechanical Environment
Keywords: Fatigue Life, Mechanical Environment, Physics of Failure
There has been a dramatic proliferation of research concerned with thermal stress in electronic package for the last three decades. Moreover, knowing the mechanical bending during printed circuit board (PCB) assembly has become important in the reliability assessment of modern electronic systems. The primary research demonstrates that the assessment approach can be applied successfully to the design model of a ball grid array (BGA) package with a more complete and accurate assessment model for solder joint fatigue life under mechanical bending. Previous research has focused mostly on the thermal analysis in electronic packages; however, most modern portable electronic products used in mobile devices, personal digital assistants, and aircraft have to endure extreme environments that involve not only thermal but also mechanical bending conditions. Initially, mechanical bending tests were conducted to demonstrate the reliability of the electronic packaging during the manufacturing and shipping process. Currently, the microelectronic packaging faces mechanical bending when everyone uses his or her Smartphones. The mechanical bending occurs when the user touches the screen on the Smartphone. Therefore, interest in the mechanical bending of BGA packaging has increased with the uptake in mobile device use. Few research works have been undertaken in this field to investigate the mechanical bending in packaging. Various mechanical bending tests have been used to estimate the reliability of the solder joints using experimental testing and the finite element method (FEM) [1–6]. Researchers have presented an analytical solution for the stress in the solder joints of the PCB assembly subjected to mechanical bending [7–10]. In this research, the analytical solution and finite element analysis (FEA) are both presented to investigate the solder joint fatigue life. The analytical solution is presented for a PCB assembly subjected to mechanical bending by taking the axial stress, shear stress, and moment of the solder joints with discontinuity function into account. A FEM is proposed to analyze the solder joint fatigue life and to investigate the reliability of solder joints in BGA packaging subjected to mechanical bending. In this paper, the purpose of this study was to investigate the effect of the solder joint fatigue life subjected to cyclic mechanical bending. In view of the preceding research proposal, three major sets of research points were addressed in this study: 1) The analytical theory for the stresses in the solder joint between the component, including the molding compound, the chip, and the BT substrate, and the PCB with a discontinuity function when the PCB assembly is subjected to mechanical bending have been developed; 2) A FEA with plasticity and creep constitutive equations was conducted that calculated the solder joint fatigue life subjected cyclic mechanical bending; and 3) experimental testing, analytical theory, and FEM were conducted to determine the solder joint fatigue life and to validate each one individually. Thus, the study may lead to a better understanding of the failure of solder joint based on the Physics of Failure model.
Jia-Shen Lan, Master's student
National Sun Yat-sen University
Kaohsiung, Taiwan

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