Open Access

ARTICLE

Rupture and Instability of Soft Films due to Moisture Vaporization in Microelectronic Devices

by Linsen Zhu¹, Jiang Zhou², Xuejun Fan²

1 Research Center of Mechanics and Mechatronic Equipment, Shandong University #180 W. Wenhua Road, Weihai, Shandong 264209, P.R. China. E-mail: zlinsen@sina.com
2 Department of Mechanical Engineering, Lamar University, Beaumont, Texas 77710, USA. E-mail: jenny.zhou@lamar.edt; xuejun.fan@lamar.edu

Computers, Materials & Continua 2014, 39(2), 113-134. https://doi.org/10.3970/cmc.2014.039.113

Abstract

In this paper, a damage mechanics-based continuum theory is developed for the coupled analysis of moisture vaporization, moisture absorption and desorption, heat conduction, and mechanical stress for a reflow process in microelectronic devices. The extremely compliant film has been used in wafer level lamination process. Such a soft film experiences cohesive rupture subjected to moisture absorption during reflow. The numerical simulation results have demonstrated that vapor pressure due to moisture vaporization is the dominant driving force for the failures. The correlation between the vapor pressure evolution and the film rupture observed from the experiments have been established through two case studies. The results are in excellent agreement with experimental observations. Further, to understand the mechanism of soft film rupture, the instability theory for rubbery material undergoing large deformation is introduced. Neo-Hookean, Mooney–Rivlin, and Ogden’s models are used to derive the analytical solutions. For any thickness of the spherical void with neo-Hookean materials, maximum vapor pressure is up to 2.5 times of shear modulus. The instability of the void with Mooney-Rivlin material depends on material property, coefficient of asymmetry, and thickness of the wall. In either case, it has been found that the hoop stress always increases monotonically even though the vapor pressure starts to fall below the cavitation pressure, and eventually this leads to the void to collapse. However, if the vapor pressure falls at a greater rate, the collapse may not occur.

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