Improvement and Practice of Metalized Ceramics for Electrical Components Process

Ceramic-metal bonding technology is a key process in the manufacture of electronic vacuum devices, with 95% alumina ceramic and its activated molybdenum-manganese metallization method being the most widely used. In actual production, the metallization process often faces problems such as low strength, uneven paste thickness, abnormal fracture modes, light transmission on the metallized surface, and oxidation, directly affecting product yield and reliability. Therefore, continuous optimization of the Metallized Ceramics for Electrical Components process to ensure product quality stability and consistency is of great significance for manufacturing high-reliability vacuum electronic devices.

The activated molybdenum-manganese method is essentially a liquid-phase sintering powder metallurgy process. Its metallization quality depends on the inherent characteristics of the Metallized Ceramic Housing for Power Semiconductors and the compatibility of the metallization process. Key factors affecting the microstructure and welding performance of the metallized layer include: metallization formulation, raw material particle size, activator ratio, metallized layer thickness and uniformity, sintering regime, and nickel layer quality. These factors collectively determine the bonding strength and hermeticity of High-Strength Metallized Ceramic Components.

Particle size and shape directly affect sintering density, sintering temperature, and microstructure. Using small and round particles helps achieve microstructure densification at lower temperatures. To ensure particle size and shape, the following measures are necessary: ​​select high-efficiency grinding equipment; determine the optimal loading and grinding time based on different materials; adjust the material-to-ball ratio and grinding ball mix ratio, using 10-35mm wear-resistant agate balls, mixed in a 5:3:2 ratio of large, medium, and small balls, with the material-to-ball ratio controlled at 1:(1.5-2.5); select a suitable dispersant to reduce agglomerates formed during the grinding process due to increased surface energy, thereby improving powder properties.

Sintering temperature is a decisive factor in the quality of Alumina Metallized Ceramics, directly affecting molybdenum particle sintering, component chemical reactions, and melt penetration. After determining the metallization formula and ceramic body, precise control of the sintering temperature is crucial.

First, the furnace temperature should be accurately measured, thermocouples calibrated regularly, and a precision temperature measuring ring should be used to improve the measurement accuracy to ±2°C. Phase diagram analysis should be performed based on the type and proportion of activator to preliminarily determine the metallization temperature regime.

For different precision metalized ceramics, optimization experiments should be conducted by changing the temperature gradient, maximum temperature, holding time, and furnace atmosphere in the sintering regime. Combined with tensile strength testing and metallographic observation, a suitable metallization sintering regime can be obtained.

Compared to the traditional molybdenum-manganese method, the activated molybdenum-manganese method can shorten sintering time and increase sintering rate. At the sintering temperature, liquid-phase-induced mass migration is faster than solid-phase diffusion, ultimately filling the pores within the sintered material and obtaining dense, high-performance sintered metallized aluminum ceramics for electrical components. Studies have shown that when the liquid phase content is below 30% (volume ratio), it is difficult to achieve densification solely through particle rearrangement.

Too low an activator ratio results in an incomplete metallization layer, with the molybdenum powder pores not being filled by the melt; too high a ratio may cause the melt to migrate to the surface, affecting the subsequent nickel plating quality. If a sintered nickel process is used, the activator ratio can be appropriately increased. By adjusting the activator ratio and conducting tensile tests and metallographic analysis, the optimal ratio can be determined for precision machining of different aluminum ceramic parts.

Using screen printing to apply the metallization paste allows for more precise control of the molybdenum-manganese layer thickness and significantly improved consistency. Key process control points include: the formulation of the printing adhesive, with a solute-to-solvent ratio and adhesive viscosity preferably between 2 and 6 Pa·s; the powder-to-adhesive ratio directly affects the printing effect and metallization strength, with the optimal ratio being (2-3):1; the selection of screen material and mesh size requires extensive testing; the hardness and abrasion resistance of the squeegee affect coating uniformity; temperature is sensitive to the printing adhesive viscosity, and room temperature must be controlled at 25±2°C to ensure stable coating thickness. X-ray fluorescence thickness gauges are used to detect the thickness of the Metalized Ceramic layer, ensuring the metallized coating thickness is 5-10 times that of the molybdenum particles.

Nitrogen plating is required on the molybdenum-manganese layer to enable welding to the metal parts. Traditional electroplating processes pose environmental problems, with wastewater discharge negatively impacting the environment. In recent years, with significant improvements in nickel powder purity and sintering performance, sintered nickel processes have matured. Sintered nickel layers prepared using high-quality nickel powder have a fine, dense, and bright surface, indistinguishable from electroplated nickel products in appearance, and exhibit uniform thickness.

The sintered nickel process completely avoids the pollution problems caused by electroplating wastewater and is comparable to electroplated nickel ceramic metallization in tensile strength and fracture mode. Microstructural observation shows that the optimized metallization formula and sintered nickel process are well-matched, exhibiting an ideal ceramic-bonded fracture mode at the sealed fracture surface. The metallization ceramic bond is tight, without delamination or porosity defects.

For different precision metalized ceramics, the optimal metallization formula and its corresponding batching methods, coating methods, sintering regimes, and suitable thicknesses and densities of the molybdenum-manganese and nickel layers are crucial for ensuring metallization quality. By optimizing process parameters through systematic experiments, the microstructure of the metallization layer can be effectively controlled, resulting in ceramic metallization with high sealing strength and good consistency, thus meeting the stringent requirements of high-reliability sealing for vacuum electronic devices.

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