With the increasing power of semiconductor chips, the development trend of light weight and high integration is becoming more and more obvious, and the importance of heat dissipation has been becoming significant case, which undoubtedly puts forward more stringent requirements for packaging heat dissipation materials. As a new heat dissipation material with high thermal conductivity, ceramic has high thermal conductivity, insulation, heat resistance, mechanical strength and thermal expansion coefficient matching the chip, and has prominent advantages in the field of high-power electronic components packaging and heat dissipation. ceramic surface metallization is an important link for the practical application of Ceramic Substrates in the field of power electronic packaging, and the quality of the metallization layer will directly affect the reliability and service life of power electronic components.

1 Current status

1.1 Metallization Mechanism

The microstructure inside the ceramic is completely different from that of the metal, and it is difficult for the two to react, which makes it difficult for the metal to form effective wetting on the surface of the ceramic; at the same time, the metal is not easy to diffuse effectively on the surface of the ceramic, and the two are difficult to solid solution; The thermal expansion coefficient and thermal conductivity of the two materials are too different from those of ceramics, resulting in a large residual stress on the joint surface of the two materials during the metallization process. Therefore, when the ceramic surface is metallized, the transition layer at the interface between the two has become the focus of various manufacturers.

Currently, the main methods:

a. The active element has a strong bonding mechanism with the atoms of the ceramic and conductive layers, respectively.

b. Several types of vacancies in the transition layer and the interaction mechanism of electrons.

c. The migration mechanism of glass phase under capillary force, mainly the Mo/Mn method

d. Mechanism of metal atom dissolution, the currently embodied process, is coated with silver layer on the surface of Al2O3 ceramics by screen printing.

1.2 Organizational Structure

The current research mainly focuses on using different metallization methods to study the relationship between the microstructure of the transition layer and the physical properties of the metallization layer under the specified process parameters. Through research, it is found that the transition layer is usually composed of reaction layer, mesophase, eutectic structure and intermetallic compounds, etc. The morphology and distribution of these microstructures often determine the physical properties of the transition layer (adhesion force, wettability, dielectric electric constant, reliability, etc.)

1.3 Physical Properties

Reliable physical properties are a prerequisite for Metallized Ceramics to be thermally conductive in power electronic components. At present, the research on the physical properties of metallization layers mainly includes the following aspects:

1) tensile strength (bonding force or adhesion force of metal and Ceramic parts;

2) thermal stability, dielectric constant and surface resistance after metallization

3) Electrical properties of electronic devices (non-linear coefficient, varistor voltage, leakage current) and mechanical properties, etc.

1.4 New technology and method

With the increasing application of Ceramic Substrate, metallization technology has been further developed, and various new methods have emerged as the times require, such as hot dip aluminum plating, electroless plating, vibration plating and so on. In recent years, in view of the disadvantages of high operating temperature, complex process, long cycle, high cost, and large environmental pollution in traditional metallization processes, some new concepts of green metallization methods have emerged, such as using spray guns to emit metal particles and make metal The particles collide with the ceramic surface at high speed, thereby transferring kinetic energy to

The heat of formation provides the necessary energy for the combination of metal and ceramic, and finally realizes metallization on the surface of the ceramic, or by using ultrasonic-assisted shot peening equipment, a layer of Cu-Ni-W powder is pre-deposited on the surface of Al2O3, and then shot peening is performed. Finally, a Cu-Ni-W composite metallization layer with good bonding force is formed on the ceramic surface and so on.

2 Development Trend

The large-scale application of power electronic components has led to the advent of ceramics as a good heat-dissipating material metallization process. With the rapid development of electronic technology, researchers have also deepened their research on ceramic surface metallization. As mentioned above, the current research on Ceramic metallization mainly focuses on physical properties, microstructure, metallization mechanism, new technology and popularization and application.

At present, there are two main ways to realize the connection between ceramic and metal. One way is to connect the two in solid state, such as direct copper deposition, direct aluminum deposition, thick film method and so on. However, it turns out that there are not many metals that can be directly combined with a specific ceramic, and it is often necessary to introduce other elements at the interface between the two or to achieve bonding under extremely harsh conditions. Another way is to first form a metallized film on the ceramic surface as a transition layer to change the surface morphology and microstructure of the ceramic to prepare for the final metallization of the ceramic surface, such as physical vapor deposition, chemical vapor deposition Wait. The essence of the above method is to realize the combination of ceramic and metal by setting and controlling various process parameters and experimental conditions to increase the wettability of the metal to the ceramic surface. Although these two methods meet the practical application of power electronic components to a large extent, they also have shortcomings that cannot be ignored. The traditional metallization process often has high requirements on the operating temperature, and the process is complicated, sometimes even under the protection of vacuum or inert gas.

It can only be completed under the protection, which makes the metallization process more time-consuming and the cost increases greatly. And in the actual production process, a large amount of harmful substances will be produced, which is not conducive to environmental protection. In addition, these two methods will also form a large residual stress on the bonding surface of the metal and the ceramic, which is easy to cause interface cracking, and even form micro-cracks on the surface of the ceramic. Therefore, exploring and innovating new techniques and methods of ceramic metallization will be another important research direction of ceramic metallization.