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F. Steinhäußer, K. Hradil, S. Schwarz, W. Artner, M. Stöger-Pollach, A. Steiger-Thirsfeld, A. Bittner, U. Schmid:
"Wet chemical porosification of LTCC in phosphoric acid: Anorthite forming tapes";
Journal of the European Ceramic Society, 35 (2015), 4181 - 4188.

The wet chemical porosification of low temperature co-fired ceramics (LTCC) applying ortho-phosphoric acid enables the implementation of areas with low permittivity directly into the as-fired substrate surface. Currently, the corresponding chemical reaction is only investigated for the widely used anorthite forming tape DuPont 951. In this paper the research is extended to cover celsian forming tapes with different ceramic particles. As the investigations show, the residual glass after porosification together with the grains should provide stable phases or components and ensure a bearing surface for further metallization. In the LTCC investigated here, the necessary selective etching to the containing celsian phase is given. However, the locality of the pores suffers from the presence of willemite, which is a second predominantly dissolved phase. The high amount of modifier oxides and the agglomeration of the dispersed corundum grains further weaken the stability of the LTCC substantially with respect to this treatment.

LTCC; Porosification; Wet chemical etching; High frequency applications; Anorthite

http://dx.doi.org/10.1016/j.jeurceramsoc.2015.06.032

http://www.sciencedirect.com/science/article/pii/S0955221915300455