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Zeitschriftenartikel:

A. Hajian, T. Konegger, T. Bielecki, B. Mieller, S. Schwarz, Ch. Zellner, U. Schmid:
"Wet chemical porosification with phosphate buffer solutions for permittivity reduction of LTCC substrates";
Journal of Alloys and Compounds, 863 (2021), 158059; S. 1 - 13.



Kurzfassung englisch:
The wireless high-frequency technology requires a robust, cost-effective, and highly integrated substrate
technology offering the capability for areas of tailored permittivity. The wet-chemical porosification of low
temperature co-fired ceramics (LTCC) substrates offers such an approach by locally embedding air.
Porosification of LTCC in both extremely acidic and alkaline media has been investigated in previous works.
However, for improving the available knowledge on the porosification of LTCC with H3PO4 as a standard and
a widely used etching solution, the impact of solution concentration was systematically investigated and a
substantial improvement in the etching performance was achieved. Moreover, in the present study, for the
first time, the intermediate pH values, and the impact of pH as a key parameter on the etching process have
been investigated. For this purpose, the applicability of phosphate buffer solution (PBS) as a prospective
novel etchant mixture for the porosification of a commercially available LTCC tape (Ceramtape GC) was
explored. Valuable information about surface morphology, crystalline composition, and the pore structure
of the etched LTCCs was gathered employing scanning electron microscopy, transmission electron micro-
scopy, X-ray diffraction analysis, and mercury porosimetry measurements. Based on these findings, the
performance of PBS-based etchant systems towards the generation of porous LTCCs combining high depths
of porosification with acceptable surface characteristics for subsequent metallization is demonstrated.
Based on the obtained results, by application of a 0.2 mol L−1 solution of PBS, the effective relative per-
mittivity of test samples with a thickness of approximately 600 µm and a porosification depth of 186 µm
from each side, could be reduced up to 10% of its initial "as fired" value. Also, based on the measurement
results and by measuring the depth of porosification, the permittivity of the etched layer was estimated to
show a reduction of up to 22% compared to the initial "as fired" value.


"Offizielle" elektronische Version der Publikation (entsprechend ihrem Digital Object Identifier - DOI)
http://dx.doi.org/10.1016/j.jallcom.2020.158059


Erstellt aus der Publikationsdatenbank der Technischen Universität Wien.