Why are advanced ceramics metallized?

Advanced ceramics, often referred to as inorganic non-metallic materials, can be seen to be defined directly on the opposite side of metal. Since each of them has entirely different outstanding advantages because of the different internal microstructures of ceramics and metals, so in many practical applications, it is necessary to combine ceramics and metals together to show their respective advantages, thus giving birth to a very important Technology - Ceramic metallization.

Ceramic metallization is to apply a layer of metal film on the surface of the technical ceramics, so that the ceramic surface offers the characteristics of metal. Then, the metal film can be firmly bonded with the ceramic insulator after high temperature sintering in a vacuum furnace, afterwards, the welding of engineering ceramics between metals can be realized. At present, the main metal films include Mo/Mn, Ag, Copper and Tin, Au. The more advanced application is to form electrical circuits on the Ceramic Substrate, which can not only be welded, but also can be used as conductor to transmit current.

What is ceramic metallization principle? The mechanism of this process utilizes what various substances in the advance ceramics and metallization layer undergo different chemical reactions and diffusion migrations in different sintering stages, such as oxides and non-metal oxides. As the temperature increases, the liquid phase is formed when all substances react to form intermediate compounds that reach a common melting point. The liquid glass phase has a certain viscosity and at the same time produces plastic flow. After that, the particles are rearranged by capillary action, and atoms or molecules are diffused and migrated driven by the surface energy. The pores gradually shrink and disappear with the grains growing, thereby realizing the densification of the metallization layer.

Nowadays, the main preparation methods of ceramic metallization mainly include Mo-Mn method, activated Mo-Mn method, active metal brazing method, direct copper cladding method (DBC), and magnetron sputtering method.

The basic process flow of ceramic metallization is as follows:

1. Matrix pretreatment: The sintered ceramics were ground to optical smoothness with diamond abrasive paste to ensure that the surface roughness was ≤1.6µm. The ceramic bases were placed in acetone and alcohol, and ultrasonically cleaned at room temperature for 20 minutes.

2. Metallization paste preparation. The raw materials are weighed according to the metallization formula, and the metallization slurry with a certain viscosity is made after ball milling for a certain period of time.

3. Coating, drying. Apply the paste on the ceramic insulator or ceramic substrate by screen printing technology. The paste thickness should be appropriate. If the paste is too thin, the solder will easily flow into the metallization layer. If it is too thick, it is not conducive to the migration of components.

4. Heat treatment. The dried substrate is sintered in a reducing atmosphere to form a metallized layer.

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