The inelastic deformation properties of sintered metal nanoparticle joints are complicated by the inherent nanocrystalline and nanoporous structures as well as by dislocation networks formed in sintering or under cyclic loading. Creep rates of sintered nanocopper structures were found to be dominated by the diffusion of individual atoms or vacancies, while dislocation motion remained negligible up to stresses far above those of practical interest. Rapid sintering of one material led to unstable structures the creep of which could be strongly reduced by subsequent annealing or aging. Longer sintering of another material led to more stable structures, but creep rates could still be strongly enhanced by subsequent work hardening in mild cycling.

Fused or sintered Cu nanoparticle structures are potential alternatives to solder for ultra-fine pitch flip chip assembly and to sintered Ag for heat sink attach in high temperature microelectronics. Meaningful testing and interpretation of test results in terms of what to expect under realistic use conditions do, however, require a mechanistic picture of degradation and damage mechanisms. As far as fatigue goes, such a picture is starting to emerge. The porosity of sintered nano-particle structures significantly affects their behavior in cycling. The very different sensitivities to parameters, compared to solder, means new protocols will be required for the assessment of reliability. The present study focused on fatigue in both isothermal and thermal cycling. During the latter, all damage occurs at the low temperature extreme, so life is particularly sensitive to the minimum temperature and any dwell there. Variations in the maximum temperature up to 125 °C did not affect, but a maximum temperature of 200 °C led to much faster damage. Depending on particle size and sintering conditions deformation and damage properties may also degrade rapidly over time. Our picture allows for recommendations as to more relevant test protocols for vibration, thermal cycling, and combinations of these, including effects of aging, as well as for generalization of test results and comparisons in terms of anticipated behavior under realistic long-term use conditions. Also, the fatigue life seems to vary with the ultimate strength, meaning that simple strength testing becomes a convenient reference in materials and process optimization.

No abstract

No abstract

In the presented work, electrical traces were directly printed on 2 mil thick polyimide flexible substrate by a dispenser system using two different silver pastes, SW 1400 paste from Asahi Co. and 125-13 HV paste from Creative Materials Co. The dispenser printing parameters were optimized to achieve the finest possible line width and the printing quality of both materials was investigated. The electrical behavior of the dispensed traces was investigated by monitoring the change in the electrical resistance of the test samples during fatigue cycling at different strains, strain percentage of 1.50%, 2.0%, and 2.5% for different number of cycles up to 1000 cycles. The life time of the dispensed traces versus the applied strain was modeled using Coffin-Manson relation setting 20% change in the initial resistance as the failure criteria. Based on the change in the trace resistance during testing, we concluded that the dispensed SW 1400 silver paste traces were less robust than the dispensed 125-13 HV traces. The finer microstructure, smaller particle size, and shorter inter particles distances of the 125-13 HV silver paste enhanced its durability when subject to fatigue cycling. Moreover, 125-13 HV paste presented better and more uniform printed traces.

No abstract

No abstract