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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]

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]

Ag sinter-joining technology has become one of the leading candidates to replace conventional high-Pb soldering technology for wide bandgap (WBG) power modules. In many cases of die-attach applications, Ni/Au plating is an inevitable choice for both die-back faces and substrates. In this study, a preheating treatment of the Ni/Au plating was utilized to increase the bond strength of the Ag sinter-joined structure of Cu-to-Cu to the electroless Ni/Au plating. Our research determined that the microstructure of the Ni/Au plating can be modified by performing an optimized preheating treatment. The thickness of the Ni underlayer was fixed at 5 μm, and the Au was plated with two different thicknesses of 0.1 μm and 0.3 μm. Ni/Au plated Cu substrates and Cu chips were preheated at various temperatures from 150°C to 350°C and then bonded with hybrid Ag particles at a low temperature of 250°C with a pressureless sintering process. Without the preheating treatment, average shear strength was 14.2 MPa (as plated Au), however, after a 1 h preheating treatment at 250°C, the interface microstructure change resulted in a 26.3 MPa shear strength, an increase of about 85%. The same improvement effect was also confirmed for the Au plating layer with a thickness of 0.3 μm. Energy dispersive x-ray spectrometry (EDS) and x-ray diffraction (XRD) analysis indicated that the preheating treatment influences the grain structure of the Au plating layer and removes defects, resulting in an increase of bond strength for the Au plated joint structure. [ABSTRACT FROM AUTHOR]

This study reports a novel high-temperature and high-current wire interconnection by printing Ag sinter paste for WBG semiconductor power devices. The Ag sinter paste wire interconnection (APW) was successfully fabricated connecting two Cu electrodes coated by Ag. Both the high-temperature reliability and the high-current reliability of the APW were evaluated by aging test at 250 °C for 1000 h and by electro-migration (EM) test at 2.2 × 104 A/cm2 for 2000 h. In the aging, a resistivity of about 4.1 × 10−6 Ω cm was achieved, which further decreased to 3.4 × 10−6 Ω cm after aging for 1000 h. This reduction can be attributed to further sintering of the sintered Ag network. The initial shear strength was 17 MPa, which, while high enough, was maintained even after an aging test of 1000 h. In the EM test, the resistance of APW was not changed significantly up to 1000 h and then only slightly increased at 2000 h. This only slight change in resistance demonstrates greater stability than that of conventional wire interconnection material such as Al and Cu under high temperature and high current density. The influence of EM on the interface between APW and a Cu substrate was observed by scanning electron microscopy with EDX. The change of resistance of the APW was induced by the formation of Cu oxide at a cathode side, which leads to a crack extension along the interface between APW and a Cu substrate. Thus, the results obtained in the present work show the APW as a promising new alternative to wire bonding technology for WBG power electronic devices. [ABSTRACT FROM AUTHOR]

Low-stress design of bonding technology with a sandwich structure of sintered Ag and tungsten (W) thin film was developed for SiC power die-attached modules. The die-attached bonding layer was designed as sintered Ag/W/sintered Ag structure. Experiment results show that the initial bonding strength was larger than 65 MPa for this die-attached structure and larger than 35 MPa with a thermal shock test from − 50 to 250 °C for 1000 cycles. These results are largely better than that almost all sintering Ag technology reported in previous studies. Furthermore, the sandwich structure also compared with the sintered Ag structure which just using sintered Ag paste as bonding layer. The thickness of Ag paste is set as 100, 200 and 500 µm in the sintered Ag structure. The results show that the initial bonding strength of sintered Ag structure was about 60-70% of the value of W sandwich structure and about one-third of that after 1000 cycles. X-ray and SEM observation revealed that sandwich structure significantly decreased the size of crack extension in the sintered Ag layer during the thermal shock test. Finite element analysis reveal that the shear stress at the pore location of sandwich structure decreased to almost half values of the sintered Ag structure with the thickness of sintered Ag of 500 µm, and decreased almost 20% compared with the thickness of sintered Ag of 100 µm. The bonding technology with the W sandwich structure should be an attractive for low stress design in SiC power die-attached modules, which significantly increased its function for long-term high temperature applications. [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]