Low Temperature Bonding of Alumina/Alumina and Alumina/Copper in Air Using Sn3.5Ag4Ti(Ce,Ga) Filler

Abstract

Sn3.5Ag4Ti(Ce,Ga) active filler was used for joining alumina with alumina and alumina with copper at 250°C in air. The joining process was done without flux and without the need for pre-metallization of alumina or a protective atmosphere. After mechanical activation of the bonding surfaces of alumina and copper, the filler showed good wetting on both alumina and copper and led to a strong bond between alumina and copper. Through tensile testing, a bonding strength of 23.7 MPa was found in the alumina/copper joint region. The shear strengths for alumina/alumina, copper/copper and alumina/copper joints were 13.5, 14.3, and 10.2 MPa, respectively. The affinity of cerium for oxygen protects titanium from oxidation, giving rise to the reaction of titanium with alumina at such a low temperature. Electron probe microanalyzer (EPMA) elemental mapping revealed that titanium segregates effectively at the alumina/solder interfaces. After aging tests at 200°C and 150°C, a double layer of Cu3Sn and Cu6Sn5 intermetallic compound was formed at the solder/copper interfaces. With an increase of aging periods, the amount of brittle compound in the joints increased and resulted in decreases in the shear strengths of the alumina/copper joints.