Enhancing mechanical reliability of silver sinter joints through deformability-contrasted graded structures

• Fracture path tailored by bilayer structuring with graded deformability. • Pre-sintering temperature controls dislocation density and Ag layer bondability. • Graded microstructures mitigate interfacial fracture via stress redistribution. • Nanoindentation evidences elastic modulus gradients enabling stress relaxation. • Graded deformability design applicable to diverse dissimilar material joints. Ensuring the mechanical reliability of Ag sinter-bonded joints remains a critical challenge in power device packaging. In this study, the mechanical reliability of Ag sinter-bonded joints was investigated, with an emphasis on bilayer structuring that introduces deformability gradients to suppress interfacial fractures. As a basis for this design, the influence of the pre-sintering temperature on the microstructure and bonding behavior was first examined. Low-temperature pre-sintering retained fine grains with a high dislocation density, providing a driving force for densification, whereas high-temperature pre-sintering promoted porous structures with a reduced dislocation density and lowered bondability. Electron backscatter diffraction and X-ray diffraction analyses consistently demonstrated that dislocation density evolution correlates with the stored strain energy, which governs sintering and grain growth. Based on this understanding, bilayered Ag structures were fabricated via two-step pre-sintering: a porous lower layer to accommodate plastic relaxation and a dense upper layer to ensure interfacial bonding. This design markedly improved the shear strength, accompanied by a fracture deflection from the interface to the Ag layer. Nanoindentation further confirmed the elastic modulus heterogeneity, indicating stress relaxation as a strengthening mechanism. These findings establish deformability-contrasted structuring as a strategy for enhancing the reliability of sintered Ag joints in advanced electronic packaging.