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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]

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.