Sundar M. Kamath

Three-dimensional effects in thin film fracture mechanics

Abstract This paper presents the results of a three-dimensional finite element analysis of the mechanics of crack growth and decohesion in a highly compliant thin film bonded to a rigid substrate. Essential features of the model are a surface-breaking initial crack which has penetrated to the film-substrate interface, and a remote biaxial residual stress field in the film. Computational analyses show that, in the absence of decohesion, the stress intensity factor along the leading edge of the crack reaches a steady state value when the crack is about twice the film thickness. This steady state condition gives rise to a nearly parabolic crack front along the leading edge. The computed results also confirm the existence of high interface stresses that are the driving force for film decohesion. When decohesion is permitted, the stress intensity factor is observed to increase with debond opening angle. The equilibrium state between crack propagation and decohesion may be determined from the respective stress intensity factors and fracture toughness of the film and the interface.

High performance thin film single chip module

This paper describes development of high density single chip modules for flip chip (C4) area array interconnect such that the electrical, thermal, and reliability needs are met through an optimal tradeoff between system performance and module cost. Prototype test vehicles were designed and built using co-fired alumina as the base carrier for two levels of copper-polyimide thin films containing the bulk of signal wiring and a power/ground plane. Flip-chip die with high melt bumps were joined directly to copper pads on the thin film substrate. Reliability aspects of this interconnect product, such as, wettability and joinability characteristics of thin Cu films and integrity of thin film via interconnections as a function of pre- and post-thermal cycling have been studied. Also, module encapsulation aspects are briefly discussed. The results of electrical characterization of the thin film substrate prior to die attach, as well as simultaneous switching noise measurements with a functional test die are presented.

Multiple run-arrest phenomena in brittle fracture

ABSTRACT A special class of transient crack propagation problems arise from the interaction of stress waves with a rapidly moving crack. We study an extreme case in this class; namely, the repeated occurrence of sudden acceleration and intermittent crack arrests within a single test specimen. Using novel optical techniques, we have obtained real-time continuous measurements of the stress intensity factor and instantaneous crack-tip velocity during a series of run-arrest segments in brittle polymeric beams. Such observations provide new insights into the role of inertia effects in bending fracture.