Bonding of Aluminum Nitride to Copper for Reducing Thermal Stress

Abstract

The crack susceptibility and properties of AlN to copper joints brazed with the Ag-27 mass%Cu-2%Ti filler metal and the Sn-38 mass%Pb solder were investigated. The heat conduction analysis suggested that the thermal conductivities of AIN-copper joints using the Ag-Cu-Ti insert metal added to tungsten interlayer and using the Sn-Pb solder with a thickness of less than 0.5 mm exceeded that of the AIN substrate (180 W/m- K). Thermal stress distribution in the AlN-copper joints was numerically calculated by a finite element method. The calculated maximum principal stress in A reduced by the use of a soft insert layer and/or a low expansivity interlayer. The crackings of brazed joints could be prevented when the tungsten interlayer thickness exceeded 0.8 mm in the brazed joint, and when the Sn-Pb solder was employed during the bonding operation. The tensile strength of the AlN-copper joints brazed at 1078 K for 120 s added to the 1.0 mm thick tungsten interlayer reached about 50 MPa, and that of the metallized AIN-copper soldered joints was about 20 MPa. The superior reliability for thermal cycling and heat conduction could be obtained for the AlN-W- copper joints using the Ag-Cu-Ti filler metal and titanium-copper multilayer-metallized AIN-copper joints using Sn-Pb solder