Journal Published Online: 28 February 2014
Volume 3, Issue 3

Role of Vapor Pressure on Popcorn Cracking in IC Packages



The strength and fracture toughness of polymer/silicon interfaces are sensitive to the porosity and moisture content of the interface as well as the yield strain of the polymer. Moisture degrades the strength of polymer/silicon interfaces. Rapidly expanding water vapor introduces high internal pressure within cavities thereby accelerating interface delamination by void growth and coalescence. The latter can cause a ten-fold decrease in the toughness of the interface. Vapor pressure acting on the delaminated surfaces contributes a mode I component to the crack driving force. This component increases as delamination progresses, changing the nature of the driving force from mode II to mode I dominant. The synergistic nature of intrinsic and extrinsic effects transforms an initially stable delamination under a rising R-curve to fast-running delamination exhibiting brittle-like cracking characteristics. The yield strains of polymers span a wide range. High yield strain lowers the macroscopic yield strength of porous polymers as well as decreases the toughness of polymer-silicon interfaces considerably. Vapor pressure and large yield strain effects on interface delamination are most pronounced at high mode mixities, thereby negating the beneficial effect of the latter on interface toughness. The approach adopted in this computational study is micromechanics-based wherein the cell model employs a Gurson constitutive relation augmented by vapor pressure as an internal variable.

Author Information

Wong, W.
Institute of High Performance Computing, Singapore
Guo, T.
Institute of High Performance Computing, Singapore
Cheng, L.
Department of Mechanical Engineering, Singapore
Pages: 22
Price: $25.00
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Stock #: MPC20130044
ISSN: 2165-3992
DOI: 10.1520/MPC20130044