Evaluation of Mechanical Strength of Miniaturized Functional Substrates and Components in Different Environments.

Functional components such as multilayer, lowtemperature cofired ceramics are examples of the combination of a ceramic-based substrate with internal electrodes as well as surface features (e.g., metallization, contacting pads, and cylindrical vias) employed to provide the component with a given functionality. Another example is that of functionalized silicon chips to be embedded into polymer circuit boards to enhance integration and save costs. The functionality of the system can be influenced by the mechanical reliability of the different components. Due to miniaturization and design complexity, no standard methods for mechanical testing can be applied for the characterization of these brittle components. In this work, an experimental approach is presented that enables the determination of the strength distribution in functional components (e.g., rectangular plates as small as 2 ? 2 ? 0.12 mm³) in different environments at different temperatures. The method is based on localized biaxial testing using a ball-on-three-balls fixture. The high accuracy of the test allows quantification of the effect of surface quality, surface features, and/or metallization (e.g., contact pads or cylindrical vias) on the component strength distribution. Experimental findings show that the strength distribution of ceramic components can be affected by environmental degradation, whereby subcritical crack growth phenomena can be enhanced in environments with high relative humidity. In addition, metallization at the surface subjected to tensile stresses can even raise the strength of the component, acting as a protective layer against environmental degradation, whereas cylindrical vias can become weak points in the design. It is shown that functionalized layers such as those used in silicon chips can have a significant effect on the strength parameters, thus influencing the lifetime of the device. [ABSTRACT FROM AUTHOR]