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Thermo-mechanical simulation of sintered Ag die attach
Keywords: Sintered Ag, failure mechanisms, finite element modeling
Diverse electronic packages operate under exceptionally harsh environments, which require extended lifetimes, presenting a significant challenge for the microelectronics community. Operating temperatures above 200°C together with high pressures, vibrations and potentially corrosive environments implies that some technical issues regarding the development of electronic systems that will operate at such high temperature remain. Technology based on sintering has been recently emerging for power modules, capable of withstanding up to 300°C. Sintered Ag is one potential candidate for die attachment for extreme environments. The application of sintered Ag has proven already to significantly increase the lifetime of interconnects when compared to solder joints. Both characterization of the failure mechanisms as well as prediction of product life in such environments is critical to the long term reliability of these devices. The present work aims to develop an understanding of how and why attach materials for Si dies degrade/fail under harsh environments by investigating sintered Ag material. New failure mechanisms will become dominant in the sintered Ag technology. Modeling helps understanding how a particular system behaves if conditions are altered. Thus, a 2D axis symmetric die attach model, commonly used to represent microelectronic package assemblies, was generated using Ansys Workbench. The FE-model provided a good understanding of the effect of single parameter variation of different leadframe materials (K64, K14, and FeNi42), chip height, sintered Ag and metallization thicknesses. The FE-model provided a rapid assessment of delamination, cracking and other defects and their location within the package. The effect of the sintered Ag thickness on the plastic strain was only slight. Furthermore, on the chip side, the local thermal mismatch between the Si die and the sintered Ag was the most important loading factor. Also, thicker chips generated higher stresses. Further analysis of simulation and experiment of sintered Ag interconnects will give more insight on dominating failure mechanisms, and help reduce failure risks.
M.F. Sousa, Materials Scientist/Researcher
Fraunhofer IZM, Berlin, Germany
Berlin, Berlin

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