Strength assessment for direct-sintered Al2O3-to-Cu joints based on damage modeling

Abstract

Abstract Metal-to-ceramics direct sintering was carried out with Al2O3 and Cu / 3 μm Ni / 1 μm Au substrates. The bonding paste consisted of micron-sized Ag2O particles and a reducing solvent that provokes Ag2O-to-Ag reduction during processing accompanied by the formation of Ag nano particles. Five different sets of process parameters resulted in different joint microstructure and strength. The experimental data was used to calibrate an elasto-visco-plastic finite element model of the sintered assembly which yielded a quantitative damage function and criterion to predict the strength of direct-sintered joints. The developed ductile damage formulation introduced a parameter ξ, i.e. the product of equivalent creep strain and stress triaxiality, that controls the tolerable plastic strain at fracture. An extended numerical parameter study subsequently revealed the complex interaction between the joint strength and microstructural joint features. Thinner joints were found to provide a slightly higher strength while the amount of sinter material and costs is significantly reduced. Moreover, it is recommended to aim at a higher level of densification at the edges and corners of sintered joints since these areas apparently contribute more to the overall mechanical strength. The developed concept is capable of tailoring the microstructure of direct-sintered joints according to the requirements or vice versa.