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Failure mechanism of interfacial thermal stress of MCM

Interfacial thermal stress between bonded dissimilar components is the major cause of Multi-Chip Module (MCM) thermal failure; the crack and poor contact and so on are the main failure modes for this problem. With the power density increasing, this problem will become more severe and prominent. In this paper, the interfacial thermal failure mechanism of MCM is investigated in depth by finite element method (FEM) and theoretical analysis. Firstly, the coupling relationships and failure of MCM are analyzed; secondly, finite element simulation is given to analyze the thermal stress distribution and find out the maximum stress; thereafter, base on the simulation results, complex stress function method is adopt to calculate the stress singularity and oscillation indexes, and then the interfacial stress expression is derived; finally, the imaginary crack is introduced and crack extension criterion is selected to evaluate the interfacial strength, and failure mechanism of interfacial thermal stress is analyzed. The analysis results show that the singular and oscillating interfacial stress not only can induce crack, but also may lead to the crack overlapping, namely, poor contact phenomenon.