Microstructure Characterization of LTCC Glass-Ceramic Composites with Various Degree of the Introduced Porosity

Low temperature co-fired ceramics (LTCC) materials are commonly used in many areas of microelectronics.Special application includes microwave devices packaging because of the possibility of dielectric constant controlling and the simplicity of the three-dimensional structure obtainment by multilayer lamination.The LTCC composites based on Al2O3 or cordierite ceramics with SiO2-Al2O3-B2O3-type glass co-fired with graphite addition are promising low dielectric constant materials.The presence of the introduced inner porosity, as well as not uniform microstructure of a glass-ceramic composite have a strong impact on its mechanical and electrical properties.The composite microstructure can be modified by graphite powder addition at the stage of preparation of slurries for tape casting.The graphite powder addition at the level of 25-50 wt% leads to the advantageous significant decrease of the dielectric constant although causes also detrimental lowering of mechanical strength of the composite, especially in the case of irregular pores distribution.This work was aimed at characterization of the microstructure, pore distribution and elemental composition for a series of the multilayer laminates containing dense external and porous internal layers with various degree of porosity formed as a result of burnout of graphite.The scanning electron microscopy study showed that both the degree of porosity irregularity and pores distribution and size depend on graphite content in the slurry.Mapping of the composition using energy dispersive spectroscopy method at the cross-section of the composite specimens allowed to observe distribution of the particular elements in the different regions of the multilayer composites.