Reduction of dielectric constant of LTCC

with use of controlled porosity

Beata SynkiewiczPBS Research Project - ActiSkan

To examine the effect of controlled porosity on LTCC parameters, two experimental glass-ceramic powders were performed.

First composition based on glass type E with low content of alkali substrates (mainly SiO2, Al2O3, CaO, B2O3) and on Al2O3 ceramics.

Second composition was created basing on first one but doped in a weight ratio of 1:1 with starch powder (for porosity obtainment during co-firing process).

Glass ceramic powders were a basis for slurries, which in the next step were tape casted to get LTCC green tapes.

METHODOLOGY

During co-firing (in 900 °C), starch component was burnt out with other organic ingredients, leaving empty spaces in the structure. The sintered samples were of good quality, without deformations and delamination.

EFFECT OF CO-FIRING

The porosity is shown on SEM images of materialcross-section

1. Cross-section of LTCC multilayer structure made of glass-ceramic tape

with porosity caused by graphite (SEM images)

2. The structures after co-firing

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For examination of electric permittivity, in the final step, silver electrodes were manually printed at both sides of experimental samples. The parallel capacitance was measured at frequency of 1 KHz -2 MHz (in room temperature) using RLC Quad Tech device. In the next step, dielectric constant was calculated.

RESULTS

The percentage decrease of dielectric constant after applying a 50% admixture of starch powder in the internal layers of the LTCC, was about 56%.

Application of non-porous glass-ceramic covers resulted in greater mechanical strength of the structure and its smooth surface, allowing printing with conductive paste at both sides of the sample

CONCLUSIONS