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Combined experimental-numerical fatigue and interface fracture testing methodologies and loading stages

Combined experimental-numerical methodologies for failure analysis applicable in the field of microsystems and new electronic packaging solutions have been developed. The results are related to the in-situ determination of critical thermo-mechanical failure processes for electronic materials under thermal fatigue loadings. Additionally, a methodology related to materials interface fracture has been developed.

Strength criterions based on elastic materials descriptions are commonly used in industry. In contrast, descriptions of materials non-linearity and related failure criteria as well as failure criteria based on fracture mechanics, required for a new quality of predictive capabilities, are proposed.

The phenomenon of material fatigue was shown to be particularly important for several dominant failure modes induced by cyclic temperature changes. However, no standard testing methodology is available for thermal fatigue investigations. To fill the gap a combined experimental-theoretical procedure is proposed by the IZM, called the "Thermal Lap Shear Test". In collaboration with a subcontractor a laboratory prototype of a loading stage was developed for deformation of material compounds subjected to cyclic thermally induced shear loading. The test specimen is a single- or double lap shear specimen made from one material containing an arbitrary shaped joint. The joint can be made forming a layer, a cluster of bumps, or a similar array, and can contain cracks or interface cracks. It allows also investigations of fatigue crack initiation and propagation. The temperature loading can be applied in a thermal cycle equipment, i.e. an air-to-air thermal shock oven. Microscopic in-situ observation of the damage progress is one part of the methodology. The damage progress can also be monitored by electrical resistance measurement performed in parallel. The localized loadings in the joint have to be calculated by the finite element method. The experiment can be accompanied by quantitative deformation analysis by the microDAC Method®. This deformation measurement allows for checking of the constitutive material assumptions used in the FE-analyses.

Both improved constitutive descriptions and damage properties of the joint material can result from the procedure.

A second failure mode addressed was the interface delamination of electronic polymers on ceramic substrate. An interface fracture mechanics approach was developed to determine advanced failure measures. The theoretical framework was accompanied with an interface adhesion testing methodology. The test setup requires in-situ deformation measurement facilities and is combined with the microDAC Method®.

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