Advanced Sintering Technology Group of Advanced Manufacturing Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), an independent administrative institution, has developed an innovative sintering technique for thick film ceramics and ceramic laminates, in collaboration with Sinto V-Cerax, Ltd., a subsidiary specialized for ceramics business under the Sintokogio, Ltd

This technique is characterized by controllable orientation and percentage of shrinkage through the application of high gravitational field at the time of heating, effectively suppressing film cracks and peel-offs, and delamination caused by differential contraction between substrate and ceramics. The newly developed technology is expected to contribute to upgrading performance and improving durability of ceramic devices, such as ceramic sensors, piezoelectric devices, and solid fuel cells.

The present study has been carried out as a part of “Strategic Development Program for Rational Energy Utilization Technologies” entrusted by the New Energy and Industrial Technology Development Organization (NEDO), an independent administrative agency, based on funds from the Ministry of Economy, Trade and Industry (METI).

The R&D work yielded fruits through the utilization of the “Sintering Equipment Using Centrifugal Force” announced by the CRI-AIST on February 2, 2004.

Nowadays, more than 80 % of fine ceramics industry products are being used for electronic materials. Particularly, inspired by rapid spread of miniature cellular phones and down-sizing of electronic equipment, and in response to demands for miniaturization and integration of important components such as capacitors, piezoelectric devices, semiconductor devices and circuit boards, it has been urgently requested to establish sintering technology for thin and thick ceramic films on substrate, ceramic-metal laminates and small-sized ceramic components. Moreover, since the performance and service life of devices are seriously affected by technologies for film deposition on substrate and bonding to base materials, new sintering techniques will constitute a key technology.

In the conventional ceramic sintering technology, powder materials are applied to a substrate in a specified pattern and heated to sinter powder particles together to form a ceramic film. The adhesion of powder particles makes the film shrink usually by 10 to 20 %. However, as the degree of deformation of substrate is much smaller than that of ceramic film, tensile stress occurs within the film to prevent powder particles from adhering together. The tensile stress is maximal at the interface, causing onset and growth of cracks, peeling of film and decrease in adhesive strength of interface.

In order to eliminate these troubles, it is necessary to control the orientation of sintering shrinkage of powder particles and the sintering behavior of particles in the vicinity of substrate interface. The centrifugal sintering process applying high gravitational field to powder particles makes it possible to reduce shrinkage in the in-plane direction, that is, direction parallel to interface, while allowing large shrinkage in the thickness direction, i.e., direction perpendicular to interface. The new sintering technique successfully solved the trouble related to differential shrinkage.

Powder specimen is loaded within a rotor, and the rotor is spun at a very high speed to apply high gravitational field to powder particles. The centrifugal force acts vertically to the substrate to compress particles, and grows to maximum at the interface. The specimen is heated under the gravitational field to sinter powder particles. At present, it is possible to apply a gravitational field of acceleration 780 km/s² (equivalent to 80,000 G, G: gravitational acceleration) at 1200 ^oC. The gravitational field makes powder particles contract in the thickness direction, while keeping the shrinkage in the in-plane direction to within a few percents. This effect works in exaggerated manner in the vicinity of interface allowing suppression of crack onset (Fig. 1). Besides, it has been verified that the technology is effective for sintering ceramic laminate and suppressing defects within the ceramics such as coarse pores and cracks.

Fig.1 Suppression of crack onset in the process of thick film formation. Figures represent the magnitude of gravitational field, at temperatures 850oC.