Virginia TechXiao, KeweiNgo, Khai D. T.Lu, Guo-Quan2014-07-212014-07-212014-04-01Xiao, K.; Ngo, K. D. T.; Lu, G. Q., "A diffusion-viscous analysis and experimental verification of defect formation in sintered silver bond-line," J. Mater. Res., Vol. 29, No. 8, 2014, 1006-1017. DOI: 10.1557/jmr.2014.420884-2914http://hdl.handle.net/10919/49639The low-temperature joining technique (LTJT) by silver sintering is being implemented by major manufacturers of power electronic devices and modules for bonding power semiconductor chips. A common die-attach material used with LTJT is a silver paste consisting of silver powder (micrometer- or nanometer-sized particles) mixed in organic solvent and binder formulation. It is believed that the drying of the paste during the bonding process plays a critical role in determining the quality of the sintered bond-line. In this study, a model based on the diffusion of solvent molecules and viscous mechanics of the paste was introduced to determine the stress and strain states of the silver bond-line. A numerical simulation algorithm of the model was developed and coded in the C++ programming language. The numerical simulation allows determination of the time-dependent physical properties of the silver bond-line as the paste is being dried with a heating profile. The properties studied were solvent concentration, weight loss, shrinkage, stress, and strain. The stress is the cause of cracks in the bond-line and bond-line delamination. The simulated results were verified by experiments in which the formation of bond-line cracks and interface delamination was observed during the pressure-free drying of a die-attach nanosilver paste. The simulated results were consistent with our earlier experimental findings that the use of uniaxial pressure of a few mega-Pascals during the drying stage of a nanosilver paste was sufficient to produce high-quality sintered joints. The insight offered by this modeling study can be used to develop new paste formulations that enable pressure-free, low-temperature sintering of the die-attach material to significantly lower the cost of implementing the LTJT in manufacturing.application/pdfenIn CopyrightBondingKineticsSinteringShrinkageModelsPasteMaterials science, multidisciplinaryArticle - Refereedhttp://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9252135&fulltextType=RA&fileId=S0884291414000429https://doi.org/10.1557/jmr.2014.42