Reliability Assessment of Electronic Packaging with Hybrid Approach of Experimental and Computational Mechanics

As electronic devices and components get smaller and faster in its speed, the package of the microelectronics rapidly changed to high density configuration of short pitch distance and small interconnection size and chip stacking. Consequently direct measurement of strain on electronic package become very difficult yet the reliability assessment of microelectronics packages become critical issue. Some optical methods are successfully adapted to measure the deformation, but there are many restrictions such as limited resolution of the experimental methods, unable to use in complex geometry. Moreover stress could not be obtained through optical method, because various materials in packages obstruct the converting optical-measured strain to stress. To assess the reliability of complex electronic packages, computational mechanics can provide the useful information that experimental mechanics can not provide. So the finite element analysis can be a powerful tool to assess the reliability of the advanced electronics packages. The accuracy of the results by computational mechanics, however, strongly depends on the material properties and the boundary condition. This paper shows the procedure of reliability assessment for electronic packages, the hybrid approach of experimental and computational mechanics. First step is to create the reliability evaluation test suitable for the packages. Next step is to perform the simulation of stress/strain or deformation distribution using finite elements analysis. Finally, results of the test and the simulation are compared and correlated to get a damage parameter. In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. Two compositions of solder are tested in all test conditions, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). A three-dimensional finite element analysis model was constructed. Computational analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. A constitutive model which includes both creep and plasticity was employed. From FEA results, the portion of the creep and plastic deformation are compared between the cyclic bending and thermal cycling tests. Lastly, the life prediction models are proposed.