Effects of
Viscoplasticity on Perimeter Stress Distributions and Reliability in
Multilayered, Ductile/Brittle Electronic Packages
M.C. Shaw and J. He*
Physics Department, California Lutheran University,
60 W. Olsen Rd., #3750, Thousand Oaks, California, 91360, USA
*Intel Corporation, 2111 NE 25th Street, Hillsboro, Oregon
97124, USA
Abstract:
The results from a recent series of
detailed experimental and theoretical analyses will be reviewed that have
revealed, with unprecedented resolution, the in-situ spatial and temporal
distribution of thermo-mechanical residual stress develops within an elastic
layer joined to an elastic substrate with an elastic or viscoplastic layer.
Specifically, experiments have been conducted with silicon bonded to a variety
of substrates utilizing four solder/braze materials, and the distributions of
stress within the silicon have been measured utilizing piezospectroscopy with 1
micron and 20 MPa resolution. Special emphasis is devoted to examining the
stress fields in the vicinity of the free surfaces and edges. These results are
analyzed within the context of simple, micromechanics models and found to yield
excellent agreement with the theoretical predictions. Furthermore, the effects
of creep relaxation on the redistribution of stress will be demonstrated
through direct experimental observations, and the effects of the layered
morphology on the creep rate within the adhesive will be described. Finally,
the effects of thermal cycling on the distribution of stress, fatigue crack
initiation and growth will be presented and analyzed. In conclusion, the
implications of these results on the design and reliability of multilayered
systems will be summarized.