D. Farley and A. Dasgupta
University of Maryland
College Park, MD 20742
Philips Electronics Singapore, Centre for Industrial Technology (CFT)
620A Lorong 1, Toa Payoh, Singapore 319762
This study aims to establish a methodology for determining the residual contact stress developed during fabrication of nonconductive adhesive (NCA) bonded flip-chip-on-flex (FCOF) microelectronics systems. The method is demonstrated for a selected non-conductive adhesive. Fabrication of an NCA bonded FCOF system requires a compressive force large enough to compensate for the inherent coplanarity differences in chip bump heights. This paper investigates a method for determining the residual contact stress in the flip-chip bump and flexible substrate pad interconnects. This is done via a global-local methodology using finite element simulation, with results to be compared with forthcoming experimental data. The magnitude of the residual compressive contact forces is key to the performance and durability of the interconnects under life cycle loads, as it serves as an initial condition" for the degradation of interconnect stress.
Key findings include: The accuracy of the simulation is very sensitive to the accuracy of the gold and flex constitutive models used; the inclusion of viscoelastic properties for the epoxy has a dramatic effect on simulations; and better stress development comes from a higher concentration of short bumps than tall bumps.
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