[Back]

A. Hajian, M. Brehl, T. Koch, Ch. Zellner, S. Schwarz, T. Konegger, D. de Ligny, U. Schmid:
"Wet-chemical porosification of LTCC substrates: Dissolution mechanism and mechanical properties";
Microporous and Mesoporous Materials, 288 (2019), 1 - 10.

Low temperature co-fired ceramics (LTCC) technology has been successfully used in microelectronics, automotive, and telecommunication applications. However,
their generally high permittivity is unfavorable for micromachined devices operated at high frequencies. To overcome this drawback, we have established a wetchemical
etching process as an effective approach which can be applied to LTCC substrates in their as-fired state and allows for a local permittivity reduction in
regions of interest. Understanding the etching mechanism is essential for the selection of appropriate etching conditions to control the degree of porosification.
Therefore, in the present work, we report on an effective approach to achieve a tailored porosification of LTCC substrates. Different characterization techniques such
as scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction analysis, and Raman Spectroscopy were used for investigation
of the morphology and chemical composition of the substrates and thereby studying the etching mechanism. Furthermore, using dynamic-mechanical
analysis at temperatures up to 550 °C, the stiffness behavior of the LTCC substrates after wet-chemical etching was investigated, and promising results for the
applicability of such modified modules were obtained, even when operated at elevated temperatures up to 550 °C. Finally, a practical correlation between the
mechanical properties and the relative porosification depth is presented, which is independent of etching conditions and the substrate thickness, and is valuable for
optimization of the suitable depth of porosification for securing the desired mechanical properties.

http://dx.doi.org/10.1016/j.micromeso.2019.109593