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A stacked assembly concept of substrate-chip-bump-chip-substrate has been developed for a bi-directional power switch based on the latest generation Infineon Technologies(R) 70 micrometer thin IGBTs and diodes, rated at 200A-600 V. Using solder joints as joining method, this paper mainly reports the thermo-mechanical simulation to optimize the design of such a stacked assembly with consideration of substrates and bump shapes for maximizing the thermal performance of the chips and minimizing stress and creep strain development in the solder joints.The simulated results reveal that the thickest AlN-based substrate offers the best thermal performance, while the thinnest Si3N4-based substrate leads to the lowest creep strain accumulation in the critical solder joints. The effect of the bump shapes on the thermal performance is negligible, while hollow cylinder bumps can reduce the creep strain accumulation in the critical solder joints when compared to the solid cylinder bumps. In addition, a preliminary experiment demonstrates that the stacked integration can achieve the electrical function of the bi-directional power switch. [ABSTRACT FROM PUBLISHER]

Ferroelectric and ferroelastic phases with very low domain wall energies have been shown to form miniaturized microdomain structures. A theory of an adaptive ferroelectric phase has been developed to predict the microdomain-averaged crystal lattice parameters of this structurally inhomogeneous state. The theory is an extension of conventional martensite theory, applied to ferroelectric systems with very low domain wall energies. The cases of ferroelectric microdomains of tetragonal (FEt) symmetry are considered. It is shown that a nano-scale coherent mixture of microdomains can be interpreted as an adaptive ferroelectric phase, whose microdomain-averaged crystal lattice is monoclinic. The crystal lattice parameters of this monoclinic phase are self-adjusting parameters, which minimize the transformation stress. Self-adjustment is achieved by application of the invariant plane strain (IPS) to the parent cubic lattice, and the value of the self-adjusted parameters constitutes a mixture of the lattice constants of the parent and product phases. Experimental investigations of Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) and Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) single crystals confirm many of the predictions of this theory. © 2003 American Institute of Physics [ABSTRACT FROM AUTHOR]