[Zurück]

A. Bittner, H. Seidel, R. Kautenburger, A. Roosen, U. Schmid:
"Investigation on the Porosification Behaviour of Fired LTCC Substrates";
Vortrag: IMAPS/ACerS 5th International Conference and Exhibition on Ceramic Interconnect and Cermic Microsystems Technologies (CICMT), Denver, Colorado - USA; 21.04.2009 - 23.04.2009; in: "Proceedings of IMAPS/ACerS 2009", IMAPS, (2009), S. 238 - 244.

In this study, experimental results are presented giving a more detailed insight into the porosification process of fired low temperature co-fired ceramics LTCC substrates. In previous publications, a novel approach is described which allows to reduce locally the permittivity of LTCC substrates due to the generation of a tailored porosity in the glass-ceramic body utilizing the selective etching behavior of different glass phases. Furthermore, phosphoric acid, well known as etchant for aluminium and alumina-based thin films, also attacks the Al2O3 grains implemented in the glass matrix. But, to penetrate into the LTCC body up to about a depth of 40 μm, part of the glass-matrix needs to be dissolved. Besides glass and alumina being basic components in the green tape, crystalline anorthite is generated during liquid-phase sintering by partial crystallization of the glass matrix. Due to this process, a higher concentration of anorthite crystallizes from the amorphous glass phase
when the sintering temperature is increased, which is proved by TEM analyses. In these regions where anorthite has formed an enhanced diffusivity of Pb and Al is recorded utilizing EDX technique. The etching of anorthite in phosphoric acid is demonstrated by μ-XRD measurements. Furthermore, the etchant is chemically analyzed
before and after exposure to LTCC utilizing ICP-MS technique to get information of dissolved fractions. From all these investigations the etched fractions are identified as anorthite and glass enriched with Pb. Besides these basic chemical and morphological investigations these findings are proved when etching substrates fired at
different peak temperatures as higher firing temperatures caused deeper penetration depths at similar etching conditions.

Porosity, LTCC, glass ceramics substrates, sintering profile, wet etching, phosphoric acid.Porosity, LTCC, glass ceramics substrates, sintering profile, wet etching, phosphoric acid.