Influence of accelerating ageing on LTCC and PCB substrates' dielectric properties in GHz area

This paper is focused on investigating stability of dielectric properties, dielectric constant and loss tangent, after exposing dielectric materials to accelerated ageing tests. Two types of Low Temperature Co-fire Ceramics (LTCC) substrates and four types of printed circuit boards (PCB) substrates were exposed to temperature loads. DuPont GreenTape 951 and DuPont GreenTape 9K7 represent LTCC substrates and Rogers 3003C, Rogers 4003, Rogers RT/duroid 5880 and Rogers RT/duroid 6010/LM represent PCB substrates. Thermal shock chamber and temperature humidity chambers provided two types of accelerating ageing test, temperature cycling and High Temperature Operation Life (HTOL) tests. Dielectric properties of these LTCC and PCB substrates were measured by combination of Vector Network Analyzer (VNA) and split cylinder resonator. This measuring method provided dielectric properties at two frequencies, which depend on concrete material, the first frequency is around 10 GHz and second about 12.5 GHz. Preliminary results show better stability of LTCC substrates after accelerating ageing test. It is caused by composition of these substrates which minimalizes moisture absorption, because moisture has major impact on degradation of dielectric properties.