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
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.