Graphite and metal vacuum brazing

Graphite has excellent properties such as low specific gravity, low thermal expansion, high thermal and electrical conductivity, easy processing, and resistance to high temperature, corrosion, wear, thermal shock, fatigue, etc., making it indispensable in metallurgy, electronics, automobiles, nuclear power, aerospace and other fields. Material. In recent years, graphite has been increasingly used in heat dissipation fields such as 3C products, high-power multi-chip components, and CT machine X-ray tubes. With the continuous advancement of weapons technology, military electronic products are gradually developing towards high power and high integration. The subsequent increase in temperature and the increase in thermal stress between packaging materials and chips seriously affect the performance and reliability of the devices. sex and service life. The heat dissipation problem has been
It has become a bottleneck restricting the development and application of high-power devices. Therefore, choosing thermally conductive graphite sheets with higher heat dissipation capacity and lower density as the heat sink material, and connecting it with the structural material aluminum alloy, is an ideal solution to solve the heat dissipation problem of high-power electronic device packaging.

The application of graphite inevitably involves its connection with alloy materials such as aluminum, copper, steel, tungsten and molybdenum. However, the huge differences in the physical and mechanical properties (melting point, thermal expansion coefficient, elastic modulus, etc.) and metallurgical properties (bonding type, microstructure, etc.) of graphite and metal lead to difficulties in metallurgical connection. In particular, the residual stress at the welding interface will directly lead to The connection interface and even the graphite body are cracked, which restricts the integrated forming of high heat flux heat dissipation structures. At present, the main methods for connecting graphite and metal include bonding, mechanical embedding, vacuum brazing, vacuum diffusion welding, etc.” The most researched and widely used welding methods are undoubtedly vacuum brazing and diffusion welding.

Among them, vacuum brazing has the advantages of low heating temperature, small impact on the structure and properties of the base metal, small welding deformation, and the ability to achieve mass production. It is the preferred method for joining graphite to aluminum, copper, tungsten, molybdenum, titanium, and iron alloys. Commonly used and effective connection methods use solder including Ag-Cu-Ti, AI-CuSn-Ag-Cu-Ti, Ni-Cr-P-Cu, Ti-Zr-Cu-Ni, etc. In addition, diffusion welding with an intermediate layer and even discharge plasma welding have also been used to a certain extent. Through the construction of a metal intermediate layer, the interface thermal resistance can be reduced; the transition between its connection performance with the metal can also be achieved through welding surface modification treatment.

Although carbon materials with various structures have different properties, their atomic bonding methods are mostly covalent bonds, which is very different from metallic materials with a large number of free electrons. This makes the metallurgical compatibility of carbon materials and metal materials poor, resulting in many difficulties in vacuum brazing of carbon materials and metals. In recent years, many studies have shown that by adding active elements to the brazing filler metal, the carbon material and the active elements react at the solid-liquid interface during the vacuum brazing process to form continuous interfacial reaction products (carbide), achieving a higher It has the effect of well wetting the graphite surface, thereby achieving the metallurgical connection between carbon materials and metals.