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In the article, acoustic emission (AE) was applied to monitor the wear-out failure in discrete SiC Schottky barrier diodes devices with a Ag sinter die attach to successfully monitor the real-time progress of failure of Al ribbons for the first time. After eliminating background AE noise including the power on–off switch and the ambient noise via a noise filtering process, AE signals were successfully collected for the SiC devices during a power cycling test. Furthermore, AE monitoring was compared to the traditional failure monitoring method using forward voltage. Physics-of-failure analysis was performed, and fatigue cracks, and lift-off in Al ribbons were confirmed as the dominant failure modes for the discrete devices. Specifically, AE counts that correspond to one of the time-domain parameters of AE signals increased with power cycling, thereby corresponding to the observed fatigue cracks in Al ribbons leading to lift-off failure. Additionally, the AE count rate was highly correlated with the crack growth rate. Based on the relationship between an AE count rate and fatigue crack growth rate, the results indicate that AE monitoring can be used to understand the fatigue propagation in Al ribbons (i.e., failure mechanism) and also as an early warning before catastrophic lift-off fracture for power electronic devices. [ABSTRACT FROM AUTHOR]

[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]

The thermal cycling life of direct bonded aluminum (DBA) and active metal brazing (AMB) substrates with two types of plating—Ni electroplating and Ni–P electroless plating—was evaluated by thermal shock tests between −50 and 250 °C. AMB substrates with Al2O3 and AlN fractured only after 10 cycles, but with Si3N4 ceramic, they retained good thermal stability even beyond 1000 cycles, regardless of the metallization type. The Ni layer on the surviving AMB substrates with Si3N4 was not damaged, while a crack occurred in the Ni–P layer. For DBA substrates, fracture did not occur up to 1000 cycles for all kind of ceramics. On the other hand, the Ni–P layer was roughened and cracked according to the severe deformation of the aluminum layer, while the Ni layer was not damaged after thermal shock tests. In addition, the deformation mechanism of an Al plate on a ceramic substrate was investigated both by microstructural observation and finite element method (FEM) simulation, which confirmed that grain boundary sliding was a key factor in the severe deformation of the Al layer that resulted in the cracking of the Ni–P layer. The fracture suppression in the Ni layer on DBA/AMB substrates can be attributed to its ductility and higher strength compared with those of Ni–P plating. [ABSTRACT FROM AUTHOR]

Ag sinter joint is gaining greater attention for use with wide-bandgap die attach modules in high-temperature applications. In this study, we have investigated both the necking growth of Ag grain and the mechanical properties of sintered Ag with different Ag particle shapes in a low-temperature, pressure-less sintering process in air and N2. The necking growth ratio of Ag grains plays an important role in the mechanical properties of sintered Ag. Large necking growth corresponds to stronger tensile fracture strength of sintered Ag paste and stronger die shear strength. Self-generated Ag nanoparticles (AgNPs) with of a size less than 10 nm were observed under an air atmosphere, an atmosphere that produces larger necking growth than does that of N2. In addition, self-generated AgNPs were observed in sintered Ag flake particles specimens. Ag flake particles also lead to larger necking growth than that of sintered Ag spherical particle specimens. Self-generated AgNPs accumulated together due to their high surface energy, thus improving the necking growth of Ag grain and leading to a stronger fracture strength. In addition, it was revealed that both the oxygen element and the grain residual strain of initial Ag particles play important roles in the AgNPs self-generation during the sintering process. This study enhances our understanding of the sintering mechanism of Ag particles and the relationship between grain necking growth and its mechanical properties. [ABSTRACT FROM AUTHOR]

This paper examines a unique mechanism in Ag micrometer flake sintering which reveals that self-produced Ag nanoparticles, created by the heating of the sintering process, contribute to larger necking and lead to enhanced bonding strength. Ag nanoparticle production, followed by rapid crystal growth, realizes faster mass transfer than spherical Ag submicrometer particles governed by conventional atomic-scale thermal diffusion at the particle surface. Thus, the Ag flakes provide thicker necking, resulting in higher shear strength of the bond layer. The natural properties of the initial particles have obvious differences: Only the flakes have a certain microstrain due to the higher dislocation density of the crystalline structure. The release of microstrain in the flake particles during heating leads to the production of Ag nanoparticles, which is a significant driving force in the sintering process. [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]