The influence of contact angle, wettability, and reactivity on the development of indirect-bonded metallizations for aluminum nitride

The use of aluminum nitride (AIN) as a substrate and packaging material for microcircuit applications is of present interest due to its many advantageous physical properties. A limitation to the widespread use of AIN is the lack of an adequate metallization system. In this paper, the indirect-bonded metallization of AIN will be reviewed-in particular, thick-film metallization, where the intermediate material is often a glass, and brazing, where the intermediate material is an active metal. Requirements which must be considered in producing successful metallizations include wetting of the substrate and the metal by the intermediate phase, and the reactivity between the intermediate phase and the substrate. In the case of thick-film metallization, these reactions can often be deleterious to the properties of the metal layer. In brazing, reaction between the active metal and the substrate is essential for achieving wetting of the ceramic surface by the molten braze and, thus, for producing high-strength joints. The reactions which occur in many of the systems considered can be predicted by examination of thermodynamic data.