Wetting and brazing of AlN by sputtered Al

The wettabilities of molten metals on ceramics are poor normally. In order to improve the wettability, all existing ceramic brazing methods introduce a compound transition layer that is formed by the reaction of active metal and ceramic. The transition layer between brazing seam and ceramic however creates negative effect on the properties of brazing joints. This paper reports our study of the wetting effect of sputtered Al particles on AlN, which enables the direct brazing of AlN using deposited Al-based films as fillers, thereby eliminating the need of a transition layer. The results show that under the bombardment of energetic sputtered Al particles, Al-N chemical bonding is formed at the interface between Al film and AlN, which typically requires temperatures above 850 ℃, much higher than the melting point of Al. The bonding remained intact even after the Al film has been melted, achieving the wetting effect on AlN. As a result, the direct brazing of AlN without the need of a transition layer becomes feasible. The shear strength of Al/AlN joint using this process reaches 104 MPa. The addition of 3.8 at.% Cu to film fillers increases the shear strength to 165 MPa. The fracture is generated in metallic brazing seam in both cases. When Cu content increases to 9.1 at.%, the segregation of Cu at the interface between the brazing seam and the ceramic reduces the shear strength of the joint to 95 MPa. With Al-20 at.% Ge, the brazing temperature can be lowered to 510 ℃, although the segregation of Ge at interface results in a low shear strength of 48 MPa. Instead of the traditional use of molten metals, utilization of the metallic vapor particles to bombard AlN achieves the wetting and the direct brazing of ceramics, with no negative effect of transition layers. This breakthrough method provides a brand new perspective to the technique of ceramic brazing.