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Saichuang's latest AIN ceramic surface metallization method

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AlN ceramics have excellent thermal conductivity, high temperature insulation, low dielectric constant, and thermal expansion coefficient similar to Si. They are widely used in aerospace and other intelligent power systems as substrate materials. The ideal material for semiconductor substrates and electronic device packaging has received extensive attention at home and abroad. AlN is used as a substrate material in microelectronic system packaging, and metallization on its surface is necessary. As a leader in the domestic ceramics industry, Slyton recently introduced the AIN ceramic laser surface metallization method. The following is a brief introduction to the AlN ceramic surface metallization technology.

First, AlN ceramic surface metallization technology

At present, AlN ceramic metallization methods mainly include thin film method, thick film method, direct copper plating method, electroless plating method and Selitong laser copper coating method.

1, film method

The thin film method combines a film material and an AlN ceramic surface by a vacuum deposition method such as vacuum evaporation, ion plating, or sputtering. In the metallization process of the AlN ceramic surface, the thermal expansion coefficient of the metal film layer and the ceramic substrate should be as uniform as possible to improve the adhesion of the metal film layer. AlN ceramic film metallization mainly relies on solid-state displacement reaction to connect the metal layer and the ceramic substrate. For active metals such as Ti and Zr, the Gibbs free energy is negative, and the reaction is easy to realize. At present, the most studied is the Ti slurry system. The Ti layer is generally several tens of nanometers. For the multilayer film, a metal such as Ag, Pt, Ni, Cu or the like is deposited on the Ti layer and then heat-treated.

The advantages of the film method are: uniform metal layer and high bonding strength. The disadvantage is that equipment investment is large, production is difficult, and it is difficult to form an industrial scale.

2, direct copper method

The direct copper plating method is carried out on the AlN substrate by a chemical bonding reaction between the Cu-O eutectic liquid phase and Al2O3. Before preparing the AlN-DBC substrate, the surface of the AlN ceramic must be heat treated to form a thin layer of Al2O3 on the surface, and then the copper foil is attached to the substrate to form a Cu-O eutectic solution at about 1065 ° C, which is thinner than Al 2 O 3 . A bonding reaction occurs in the layer to bond AlN and Cu together. In the process of direct copper plating, the temperature, atmosphere and time of pre-oxidation of copper foil and AlN ceramic substrate should be strictly controlled to oxidize copper to form Cu2O, react with Al2O3 in the boundary zone, and improve the bonding strength of AlN and Cu.

The advantages of direct copper plating are: low bonding temperature (1065~1075°C), good thermal conductivity, high adhesion strength, excellent mechanical properties, easy etching, high insulation and thermal cycling capability, and broad application prospects. The disadvantage is that the oxide layer formed by surface heat treatment of the AlN ceramic reduces the thermal conductivity of the AlN substrate.

3, thick film method

Thick film metallization technology generally uses a paste or ink color containing glass frit, and forms a metal layer for sealing, a conductor (circuit wiring), a resistor, etc. by screen printing on a ceramic substrate, and forms a brazing metal layer and a circuit by sintering. And lead contacts, etc. The conductor paste plays a vital role in the AlN ceramic thick film metallization process. The thick film paste is generally composed of a metal powder having a particle size of 1-5 μm. At present, the researchers used Cu-Ag alloy doped Ti as the metallization system, and dibutyl phosphate (DBP) as the organic carrier, and the surface of AlN ceramics was metallized by screen printing.

The advantages of the thick film method are: simple process, suitable for automation and multi-variety small batch production, and good electrical conductivity. The disadvantage is that the bonding strength is not high enough, especially the high temperature bonding strength is low, and the temperature is greatly affected.

4, electroless plating

The electroless plating method refers to reducing the metal ions in the solution to the surface of the catalytically active object by using a reducing agent without forming an external current to form a metal plating layer. The metallization mechanism of electroless plating is mainly mechanical interlocking. The bonding strength depends largely on the roughness of the surface of the substrate. Within a certain range, the roughness of the surface of the substrate is larger, and the bonding strength is higher. The Ni-P alloy is electrolessly plated on the surface of the AlN ceramic. The AlN substrate is first ultrasonically cleaned to remove surface impurities, placed in a NaOH solution for etching, and then placed in a plating solution containing a nickel salt for electroless plating.

The advantages of electroless plating are: simple equipment, low cost, no need for secondary high temperature treatment, and easy mass production. The disadvantage is that the bonding strength between the surface of the AlN ceramic and the metal layer is not high.

5, Slyton laser copper coating method

Slyton laser copper-clad method is a new ceramic metallization method developed by the United Nations Optoelectronics Laboratory. It uses high-energy laser to decompose ceramic and metal surfaces, and then combines them in an ionic state. The bonding strength can reach an unprecedented 45Mpa, stability. Extremely high and greatly increased production efficiency, a milestone for the entire ceramic industry.

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