Studies on three-dimensional moulding, bonding and assembling of low-temperature-cofired ceramics for MEMS and MST applications

This paper broadly illustrates the preparation of three-dimensional shapes in low-temperature-cofired ceramics (LTCC). Test structures are fabricated by moulding single-layer green tapes into cylindrical form of different dimensions in order to investigate the penetration of cracks and the limiting value at which they appear. The factors responsible for the propagation of cracks have been analysed. Another important aspect which has been exemplified is the bonding of processed LTCC modules to metal parts with a dissimilar coefficient of thermal expansion. This is important from the point of view of attachment of LTCC-based micro-electromechanical systems (MEMS) or micro-system technology (MST) devices to a functional mechanical element. A methodology has been discussed for a smooth transition in the coefficient of thermal expansion of ceramic and metallic part in order to minimise stresses and avoid micro-cracks in the interconnections. An assembly of different post-fired modules by a fastening mechanism of individual modules for realizing a complex system are also described. Based on the above studies, a preliminary design to fabricate, shape, bond and post-process the LTCC substrate for the realization of a complex system together with the crucial processing issues is presented. Efforts have been made to implement this design and process steps on a real-time ball-bearing to prove the suitability of LTCC material for MEMS, MST and other complex systems.