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[Display omitted] • Fatigue characteristics of high-purity Cu films from RT to 200 °C were investigated. • TMF characteristics of high-purity Cu were systematically and numerically revealed. • The change in the grain of Cu at high temperatures leads to a reduced fatigue life. • Ʃ3 fraction decreases and the LAGB fraction increases as the temperature increases. • Fatigue life is significantly changed even below the recrystallization temperature. This study conducts stress-controlled cyclic tension-tension tests from room temperature (RT) to 200 °C, at 50 °C intervals, on high-purity Cu films to comprehensively understand the temperature-dependent fatigue life and the related microstructural and fracture characteristics. As evidenced by the electron backscattering diffraction analysis, the Ʃ3 boundary fraction decreases and the low-angle grain boundary fraction increases as the temperature increases. The significant change in the grain structure at high temperatures leads to a reduced fatigue life. The fatigue striations are closely spaced at RT and the fracture surface develops into the typical fatigue striation and the void zones. [ABSTRACT FROM AUTHOR]

This study systematically investigates the effect of oxygen on the microstructural evolution as well as the macro/micromechanical characterization of Ag sinter paste during the aging process at 250 °C for 1000 h. The sintered Ag joint is separated into two groups and, respectively, kept in air and vacuum (10−4 Pa) atmospheres. The microstructure of sintered Ag paste become clearly coarsened after aging at 250 °C in air for 100 h, while it remains almost the same as in the initial state in vacuum, even after aging for 1000 h. The different microstructural evolutions are investigated in detail by transmission electron microscopy, which reveals that coarsening are involved in the Ag-O reaction and form a large number of Ag nanoparticles around sintered Ag particles, as well as enhance coalescence. Furthermore, the macro/micromechanical properties of sintered Ag paste, after aging in air and vacuum atmospheres, are evaluated by a die shear test and a nano-indenter system with a spherical diamond tip. Shear strength and fracture mode were systematically analyzed. The micromechanical properties of sintered Ag paste, including Young's modulus and hardness, depend on its microstructure and are largely influenced by its porosity, which decreases from initiation to 250 h and recovers after aging for 500 h in air. However, there is almost no change during the aging process in the vacuum atmosphere. The results of this study contribute to a better understanding of the microstructural evolution and the mechanical properties of sintered Ag joints, including the change in bonding quality and Young's modulus during aging for actual power modules, which are packaged by a resin. Image 1 • Oxygen effect on the microstructural evolution and mechanical properties of Ag sinter paste were investigated. • Microstructure of Ag sinter paste become coarsening in air aging but almost not any change in vacuum aging. • Coarsening behaviors maybe mainly caused by Ag-O reaction but not the self-diffusion kinetics of Ag atoms. • In-suit formation of Ag nanoparticles played a crucial role in the coarsening behaviors of Ag sinter paste. • Micromechanical properties of Ag sinter paste depend on its microstructure and influence by aging atmosphere. [ABSTRACT FROM AUTHOR]

Abstract Solid-state porous Ag was utilized to achieve interface bonding under low temperature and low-pressure for large area, high-reliability designs for high performance die-attach power modules in high temperature applications. In this process, solid-state porous Ag was first fabricated by sintering Ag particles onto both a Cu substrate and an Si die with different bonding areas. After polishing the surface of the solid-state porous Ag, the Ag-Ag interface was bonded together under low pressure (0.4 MPa) and low temperature (250 °C and 300 °C). The bonding strength was greater than 30 MPa for a 15 mm x 15 mm bonding area at a bonding temperature of 300 °C. The electrical resistivity of the solid-state porous Ag was about 7 µΩ cm, or half that of Pb-free alloy solder materials. The bonding mechanism of the Ag-Ag interface was analyzed by a transmission electron microscope. It was observed that Ag hillocks and nanoparticles had been generated and bridged the Ag-Ag interface. This resulted in a large interface connection ratio and a high bonding strength. In addition, it was observed that the shear strength of the solid-state porous Ag with a thick bonding layer decreased thermomechanical stress in the die-attached power module and thus improved structural reliability. This bonding process featuring solid-state porous Ag presents an attractive technology for the fabrication of large area bonding and high-reliability die-attached module structures for high temperature applications. [ABSTRACT FROM AUTHOR]

A bonding technology is introduced by using surface polished porous Ag in die-attachment structure. Bonding strength did not change much as the chip size varied from 3 × 3 mm 2 to 15 × 15 mm 2 . This confirms that the technology was not influenced by the chip size, and thus can be used in large area bonding. Bonding mechanism based on stress-induced migration was discussed with the three dimensional finite element analyses. Transmission electron microscopy (TEM) observation further confirmed that single crystal hillocks and Ag particles formed at the bonding interface, bridging the interface together. [ABSTRACT FROM AUTHOR]

This study investigated the power cycling performance on a transfer-molded power module with Cu clip bonding for the next-generation green automotive applications. A 700 V/900A class 2-in-1 half bridge power module was designed and fabricated by using Cu clip bonding and transfer-molding technologies. The switching was precisely controlled so that t on was 0.5 s and t off was 4.5 s by a constant current mode. The condition of the power cycling tests (PCTs) was ∆ T = 125 °C with the maximum repetition of 97,000 cycles. The performance and life of the power module was evaluated based on AQG-324, and thermal resistance of the junction (R th-ja) was monitored during PCTs. The major failure in this investigation was increase in the thermal resistance (R th). Microstructural integrity of the interconnections were characterized in detail by scanning acoustic tomography (SAT) and interfacial microstructure analysis using a scanning electron microscopy (SEM). The degradation mechanism of the interfacial material was numerically revealed through finite element method (FEM) simulations. • Power cycling performance of transfer-molded power module with Cu clip bonding was investigated. • Reliability test of A 700V/900A class 2-in-1 half bridge power module was conducted with T jmax = 175 °C and T c = 50 °C. • Increase in thermal resistance induced by IMC growth and crack propagation of the chip was main cause of module failure. [ABSTRACT FROM AUTHOR]