Graphical based characterisation and modelling of material gradients in porosified LTCC

Abstract

The chemical composition of low temperature cofired ceramics (LTCC) allows to locally embed air into sintered substrates by a selective wetchemical etch process. Therefore, LTCC substrate with areas of low permittivity can be created without material combination. The presentedgraphical method of material component contrast images enables the evaluation of their most important material properties which are theircomponent distribution, their porosification gradient and their residual bearing surface. The graphical method, including focused ion beam andscanning electron microscopy analyses, is applied to different commercially available LTCC types having two porosification states each. Derivedmathematical models, which are suitable for finite element method implementation, allow the characterisation of the effective permittivity reductionwhile keeping a maximum residual surface area for, e.g., metallisation purposes. The shape of the optimum material distribution function featuresan 'air pocket' of small width and a depth being dependent on the application specific operating frequency.

The chemical composition of low temperature cofired ceramics (LTCC) allows to locally embed air into sintered substrates by a selective wetchemical etch process. Therefore, LTCC substrate with areas of low permittivity can be created without material combination. The presentedgraphical method of material component contrast images enables the evaluation of their most important material properties which are theircomponent distribution, their porosification gradient and their residual bearing surface. The graphical method, including focused ion beam andscanning electron microscopy analyses, is applied to different commercially available LTCC types having two porosification states each. Derivedmathematical models, which are suitable for finite element method implementation, allow the characterisation of the effective permittivity reductionwhile keeping a maximum residual surface area for, e.g., metallisation purposes. The shape of the optimum material distribution function featuresan 'air pocket' of small width and a depth being dependent on the application specific operating frequency.