Local Modification of Fired LTCC Substrates for High Frequency Applications

Abstract

In this study, a novel process is presented to generate a defined and homogeneous degree of porosification in fired LTCC (low temperature co-fired ceramics) substrates. For this purpose, a phosphoric-based acid is used which represents a standard wet chemical etchant in MEMS and microelectronic industry. This surface-near process is very attractive for the realization of selected areas on conventional LTCC substrates having modified dielectric properties, especially for high frequency applications. From morphological investigations, this portion of the glass matrix enveloping the Al 2 O 3 particles is very important to enable the penetration of the acid into the LTCC body. Increasing the time of the etch attack at a given bath temperature, pores are preferentially formed due to a selective removal of the Al 2 O 3 particles compared to the residual glass matrix. High frequency measurements of the permittivity using ring oscillators showed a significant reduction compared to the original bulk value.