Thermal Stress Analysis in a SLIM/SHOCC Package
by
R. Panneer Selvam and Y. Peng
HiDEC, University of Arkansas
Coauthors: Len Schaper (HiDEC)

A complex electronic package with 5 layers called SLIM/SHOCC (Single Level Integrated Module /Seamless High Off-Chip Connectivity) is considered for thermal stress analysis using finite element methods. The objective is to choose optimum ma terials in the 2nd and 3rd layer from the top so that the package survives due to thermal stresses. In the analysis, the materials in the top layer (Silicon), 4th layer which is a BGA without undrfill (Eutectic 63/27 Pb-SN) and the 5th layer which is cal led printed wiring board (FR4) are considered to be same in all the analysis. Different materials are considered in the 2nd layer (BGA with underfill) and the 3rd layer which is called interposer for survival of the package. A three-dimensional finite ele ment model, UASTRESS (Peng et. al., 1998) is used to analyze stress for this package. This package is subjected to a temperature cool-down procedure of 150 °C range. Linear elastic analysis is done to investigate the reliability of the package. Different metals and composite materials are considered as interposer to find the optimum package with respect to thermal management. Among the materials used for the interposer, 85NT is the optimum one. In addition to the interposer optimazition, the effect of underfill materials on the maximum stress is also considered. The computed stress for different combinations of packages will be reported in the full paper.

The computer modeling issues will be discussed in the full paper. Analysis will be done using the inelastic and creep properties of the materials if necessary. The finite element model uses eight-node brick elements and the equations are solved by the pre conditioned conjugate gradient method.

Acknowledgement
The study ahs been supported by ARPA grant no: MDA 972-96-1-0008 through HiDEC, University of Arkansas

Reference
Peng, Y., Selvam, R. P., Schmidt, W. F., Gordon, M. H., Lohrmann, K. V., and Reynolds, R. R., Nonlinear finite element modeling of brazing a die to a diamond substrate, in the 31st International Symposium on Microelectronics, San Diego, Oct.31 to Nov. 4, 1998

Date received: April 15, 1999

Copyright © 1999 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cacr-68.