Densification kinetics and anisotropic microstructure evolution in LTCC films constrained by rigid substrate

LTCC films with thickness of 130 μm were cast on the alumina substrate and the free and constrained sintering behavior was measured by utilizing an optical dilatometer. It was found that constrained films started to densify at a low temperature of 720 °C. The apparent activation energies for free and constrained films were calculated through densification data obtained in the constant-heating-rate experiment. Of particular notice, with increasing density, the activation energy for constrained films decreased from 690 kJ/mol to 359 kJ/mol, whereas a relatively fixed value of 530±30 kJ/mol was yielded for the freely sintered ones. The final density for constrained films was lower than that of the free ones, which could be attributed to the constraint from the substrate. Moreover, anisotropic microstructure was evolved in the constrained film with the increase of density and elongated pores were more prone to align parallel to the substrate.