Reliability testing provides an understanding of the fundamental failure mechanisms, compensation techniques for correction and prevention of long term drift, and finally provides statistical tools for lifetime prediction based on failure analysis. It is imperative that the successful micro and nano systems and products include all levels of packaging and reliability issues from the onset of the project. With the explosive growth in microfabrication techniques, designs, materials, devices, and the related infrastructure, the need to address MEMS packaging and reliability issues has become imperative.
While a variety of metallic, semiconducting, and dielectric materials are used as structural materials in MNT, silicon continues to maintain its dominant position in existing components. The introduction of novel materials has been slow primarily due to the perceived barriers to integrating micro and nanomachined components with CMOS electronics. However, future applications of MNT will invariably require higher performance structural materials than those that are currently available. Therefore, there is a critical need for materials development programs since the properties of the thin film and small-scale forms of materials used in MNT cannot be extrapolated from bulk forms of the materials. Fortunately, significant progress has been made in the measurement of the mechanical properties of structural film. Materials characterization techniques have been established for measuring elastic, plastic, and time-dependent properties, as well as the degradation, of these structural films.
Traditional approach in microsystems has been to primarily concentrate on the design and fabrication of the micromachined components and relegate the packaging and reliability issues to later stages of product development. However, the overall performance and reliability of microsystems depends as much on it’s packaging as on the micromachined part itself. The effects of the backend processing and the package on the micromachined part tend to degrade the performance and yield of microsystems especially when they have been omitted in the initial system design considerations. Thus the detrimental effects of uncompensated backend processes and packaging can make the micromachined part either immediately inoperable or can cause long term drift and reliability problems.
Reliability considerations are of immense importance in safety critical applications such as medical devices, accelerometers for airbag activation etc. where the cost of failure can be catastrophic. Constraints imposed by reliability requirements need to be incorporated either in the designs and performance of the micromachined part or the package such that the overall system is able to meet the desired performance requirements. The overall reliability of MNT can be divided into reliability associated with the micro and nano parts and electronics, and the reliability of package and packaging processes. Accurate prediction of microsystems reliability based on the application of accelerating factors is an important aspect of reliability testing. The eventual goal is to be able to accurately predict the failure of the microsystem (lifetime) based upon knowledge of the failure mechanism(s), operating conditions, design requirements, and accelerating factors. Such prediction is required for both the micromachined part as well as for the packaged devices.
