C. A. Walker, F. Uribe, S. L. Monroe, J. J. Stephens, R. S. Goeke, V. C. Hodges, Sandia National Laboratories, Albuquerque, NM
Experiments were run in which various compositions of low temperature co-fired ceramic (LTCC) sections were brazed to Kovar™ (Fe-29Ni-17Co) metal sections in inert gas atmospheres using silver-based braze filler metals at temperatures up to 755C in an attempt to identify optimum processing conditions. The tensile buttons fabricated were similar to standard ASTM-F19 samples except that the metal and non-metal positions were reversed. Therefore, in the brazed assemblies the LTCC was brazed between two metal tensile button halves. Brazed in this unique manner, the tensile buttons assemblies more accurately represented the actual component. Thin-film metallization schemes were varied, along with thermal processing parameters. The brazed assemblies were subsequently helium leak checked and tested for tensile strength at room temperature. Results of trials with varying filler metals, thermal profiles parameters will be discussed and compared to results obtained using alumina ceramics.
Summary: Hermetic samples (helium leak rates < 1.0E-09 atm-cc/sec) were made with all three types of LTCC used in the study. The average strengths for the three types of LTCC varied from 3300 psi to 8000psi compared to 12300 psi achieved using high-temperature (alumina) ceramic with the same filler metal. In general, thin-films with platinum outer layers outperformed thin-films with outer layers of gold or palladium in both hermeticity testing and tensile strength.
