Robust LTCC/PZT sensor-actuator-module for aluminium die casting
The present paper reports on a new module design based on LTCC-PZT laminates. The assembly of modules is achieved by packaging of ceramic PZT plates between LTCC green layers and subsequent sintering of the evolving multilayer. The challenge exists in avoiding tension cracks at shrinking of LTCC layers on the already sintered piezoceramic during the firing process. Thermal characteristics of several LTCC green ceramic products were investigated, systematically, to obtain crack free ceramic modules. The advantages of a module with full integrated PZT ceramic tiles are the mechanical stabilisation of the piezoceramic, the electrical insulation and the shielding of external environmental influences. More general, our approach combines LTCC microsystems technology and piezo technology and allows for a tremendous improve of functional integration, e.g. sensing, actuation, buried electronic circuits, and strain-stress transformation. After preparation, the ceramic modules were introduced in the manufacturing chain of aluminium die casting. Thus aluminium components with integrated sensor-actuator modules could be prepared by die casting for the first time (in cooperation with the University of Erlangen-Nuremberg). The piezoelectric modules survived this manufacturing step without deterioration and fortify the concept of adaptive metal structures in automotive and machine building industry. The functions of the moulded LTCC/PZT modules are estimated by electro-mechanical characterisation methods (e.g. measuring and determination of dielectric coefficient, loss angle tan delta, remanent polarisation and deflection).