Methods for Increasing Dimensional Stability of Buried Cavities in LTCC Substrates

Buried cavities in low temperature co-fired ceramic (LTCC) substrates, whether completely blind or fabricated with ports, are often utilized in industry in areas such as microelectronics packaging, microfluidic sensor fabrication, and microwave resonant chamber creation. These applications often have stringent requirements for cavity volume, parallelism, and wall planarity that are critical for the performance of a given device. While there has been significant research and reporting on the fabrication and functionality of these structures, there is a lack of available literature regarding methods used to mitigate deformation of these structures during the fabrication process while providing for precise dimensional control of the final structure. Although essential processes in the fabrication of LTCC structures, the lamination and sintering steps both pose challenges to creating uniform and precise buried cavities in LTCC substrates: deformation due to high pressure on unsupported green tape during lamination, as well as volume loss and deformation during the sintering process. This paper will report on methods, technologies, and processes used to mitigate deformation and allow for precise and repeatable dimensional control of buried cavities in LTCC substrates. Specifically, fugitive materials and rigid cavity inserts will be used in conjunction with the manipulation of lamination pressures and sintering profiles to understand and control the forces resulting in the deformation of these buried cavity structures. The results of these technologies and processes will be examined through cross sectioning and optical inspection as well as through optical profilometry.