In this paper, we present a combined experimental and computational study of the thermomechanical reliability of multilayer ceramic capacitors (MLCC’s). We focus on residual stresses introduced into the components during the cooling down step of the sintering process. The technique of microindentation turned out to be a useful method to measure the stresses locally. The computations were done with three-dimensional finite element simulations. We find that the cooling step introduces compressive in-plane stresses in the ceramic layers. There is reasonably good overall agreement between the residual stresses obtained from the indentation experiments and the numerical simulations. Some discrepancies do exist, though, for measurements on cross-sectioned MLCC’s. Possible reasons for the differences are discussed.
Two different specific surface area of starting BaCO3, 10 and 30 m2/g, are used to prepare solid‐state BaTiO3 powder. Pure tetragonal BaTiO3 was obtained at a lower calcination temperature with smaller BaCO3, and the kinetic calculations of activation energy also agree with it. A clear, thin, and nano‐sized cubic BaTiO3 clusters on TiO2 particles were also observed. A narrower particle size distribution of BaTiO3 powder (350 nm) was obtained from 30 m2/g of starting BaCO3 at 1000°C. After sintering with reducing atmosphere, the ceramics with potential of X8R or X7R specifications and a clear core–shell microstructure were obtained in this study.
The Y5V-1206 base-metal electrode (BME) multilayer ceramic capacitor (MLCC) chips have been characterised for crystalline phases using X-ray diffractometry (XRD), and microstructure using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The microstructure features found in the Ni electrode and the BaTiO 3 dielectric layer are discussed in terms of the tensile backstresses induced upon firing due to constrained sintering heterogeneously. The chemical compositions containing BaO-excess and additives CaO and ZrO 2 , determined for BaTiO 3 grains by energydispersive spectroscopy (EDS) equipped in the TEM are also reported. However, no rare-earth oxides were found in the grains. The representative microstructure of BaTiO 3 grains containing dislocations is the "solid-solution" type distinctive from the "core-shell" of the X7R compositions. The fact that no ferroelectric domains were detected suggests that the BaTiO 3 grains are pseudo-cubic with the c/a ratio ≈ 1.0.
Composite powders, prepared by coating coarse ZrO, particles with fine A1,0, powder using a chemical precipitation technique, were compacted and sintered freely at a constant heating rate of 4"C/min to -1600°C. Composites containing up to -30 vol% inclusions were sintered to nearly full density under the same conditions used for the unreinforced matrix. Furthermore, the sintering kinetics were not influenced significantly by the inclusion volume fraction. The sinterability of the composites formed from the coated powders was significantly better than that for similar composites formed from mechanically mixed powders. The present data provide a further demonstration that the use of coated powders may have widespread applicability for the fabrication, by free sintering, of dense ceramic particulate composites.
Composite powders were synthesized by coating coarse Z r 0 2 inclusion particles with a cladding of tine-grained, crystalline ZnO powder using a chemical precipitation technique. Three different inclusion sizes (1,3, and 14 p m ) were used by selecting the size of the starting ZrOz powder, and the volume fraction of the inclusions was controlled by the amount of ZnO precipitated. The powders were compacted by uniaxial pressing in a die and then sintered at a constant heating rate of 4"C/min to 1500°C. The sintering kinetics were almost independent of the inclusion volume fraction, and of the inclusion size, for inclusion contents up to =40 ~0 1 % . Furthermore, composites containing up to =40 vol% inclusions were sintered to almost full density under the same conditions used For the unreinforced matrix, This is considerably better than the densities obtained for conventionally mixed powders, where a modest inclusion content (<=lo ~0 1 % ) has been observed to cause a severe reduction in the sintered density of the composite matrix. The kinetic data and microstructural observations are a further indication that the main factors which oppose the free sintering of ceramic particulate composites are processing-related; these factors are (i) inclusion-inclusion interactions which constrain the matrix and (ii) the packing of the matrix phase in regions immediately surrounding the inclusions.
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