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Many substrates for microelectronic systems contain ceramic/glass layers and metal features (e.g. electrodes, vias, metal pads) built up in a complex 3D architecture. The combination of different materials with distinct thermo-elastic properties may yield significant (local) internal stresses, which are to be superimposed to external thermo-mechanical loads in service. Due to the various material junctions, interfaces, etc, failure of these multilayer systems can hardly be predicted. In this work, a strategy is proposed to quantify the effect of architecture and loading conditions on the mechanical reliability of ceramic-based substrates. Model ceramic structures containing important design features (e.g. inner electrode, via, top metallization) were fabricated and tested in different environments (i.e. humid or dry conditions) under uniaxial as well as biaxial bending. Significant difference in the characteristic strength between ∼260 MPa and ∼620 MPa were measured, associated with the particular architectural feature, type of loading, and/or environment.

For the fabrication of complex, micro-electromechanical systems (MEMS) devices based on low-temperature co-fired ceramic (LTCC), higher firing temperatures and longer times than those proposed by the LTCC producer are needed. These changes to the thermal budget may influence the material properties and consequently its functional properties. The effect of the firing conditions on the LTCC DuPont 951 and thus on the phase composition, that is, the alumina/anorthite ratio and porosity, on the mechanical properties is presented. The samples fired at low temperatures (800°C) had a high porosity (7%), which significantly contributed to the low elastic modulus (100 GPa) and the low mechanical strength of the LTCC (140 MPa). The samples fired at 850°C, which had only 1% of porosity, resulted in an elastic modulus of 122 GPa and a flexural strength of 224 MPa. A further increase in the temperature contributed to a slight decrease in the elastic modulus, while no significant difference in the flexural strength could be observed. The enhancement of the flexural strength with an increasing firing temperature was mainly related to a decrease in the porosity and to a lesser extent to the different ratio of the alumina/anorthite phases. The effect of firing time on the phase composition at selected temperatures (i.e., 100 h at 700 and 800°C) is also discussed.

Low temperature co-fired ceramics (LTCCs) are multilayered ceramic based components, which can be used as high precision electronic devices in highly loaded environments. In many applications, LTCC end components are exposed to mechanical stresses, which may yield different types of failure coming from different locations, thus decreasing the mechanical reliability of the device. The aim of this work is to assess the mechanical strength of LTCC parts and investigate the influence of the metal internal structure (supporting the maximum load) on the local fracture response. Strength of different positions (e.g. near vias, metal-pads, ceramic layers) has been measured under biaxial loading and compared with a reference bulk LTCC. The strength results were interpreted in the framework of Weibull theory. Fractographic analyses revealed a significant effect of the first metallisation layer below the tensile surface on the strength reliability of the structure, which should be considered to optimise LTCC designs.