DC Relay Metallized Welded Ceramic Housing: Core Technology of Hermetic Relay Packaging

The DC Relay Metallized Welded Ceramic Housing serves as the critical insulating and hermetic-sealing component for high-voltage DC relays. It uses ceramic metallization and ceramic-metal brazing to create a fully sealed arc-extinguishing cavity, isolating internal contact systems from moisture, dust, and the external environment. This solution addresses the bottlenecks of plastic housings under high voltage and high-temperature cycling, and is widely adopted in energy storage, EV battery disconnects, and DC power distribution systems.

Ceramics and metals have vastly different physical properties. Ceramic is an inorganic non-metallic material with outstanding insulation and thermal stability, while metal delivers excellent electrical conductivity and ductility. To combine their strengths for Al2O3 Alumina Ceramic Vacuum Relay Casing, ceramic metallization becomes the indispensable pre-treatment step. The process deposits a firmly bonded metal thin film on ceramic surfaces, making the ceramic weldable for subsequent brazing assembly with metal rings or end caps. The quality of metallization directly determines the air tightness and long-term reliability of the finished relay housing.

Joining ceramic and metal for Alumina Metallized Ceramic for Electrical Relays brings several inherent material challenges.

• Mismatched coefficient of thermal expansion. Ceramics feature low thermal expansion while metals expand much more under heat, which easily triggers cracks at sealing joints. Engineers must carefully manage thermal stress via matched intermediate metal layers.
• Low thermal conductivity and poor thermal shock resistance of ceramics. During brazing, temperature gradients around the weld zone must be minimized, with controlled cooling rates after joining.
• Most ceramics are non-conductive, ruling out conventional electric welding methods. Ceramic metallization or active metal brazing is required to create a reliable bonding interface.
• Stable electronic coordination inside ceramic molecules creates high barriers for direct ceramic-metal bonding. Surface modification is mandatory before welding.
• Ceramics are covalent crystalline materials with limited plastic deformation. Brittle fracture frequently occurs at joints. Intermediate buffer layers and indirect diffusion welding are commonly applied to lower joining temperature.
• Specialized sealing structures are required for relay housings, categorized as flat seal, sleeve seal, pin seal and butt seal. Sleeve sealing delivers the best performance, with strict manufacturing requirements for all joint types.

The metallization mechanism is a complex combination of physical diffusion and chemical reactions, including plastic flow and particle rearrangement. Oxide components inside the metallization paste react and diffuse in different sintering stages. As temperature rises, raw materials form intermediate compounds and turn into a liquid glass phase at the eutectic temperature. The viscous glass phase generates plastic flow; particles rearrange under capillary force. Driven by surface energy, atoms diffuse and grains grow, pores shrink and disappear, finally forming a dense metallized layer for the High Precision Alumina Ceramic Components.

1. Substrate pre-processing. Polishing sintered ceramic blanks to optical smoothness with diamond abrasive paste, controlling surface roughness ≤1.6μm. Ultrasonic cleaning in acetone and alcohol at room temperature for 20 minutes.
2. Metallization slurry preparation. Weigh raw materials according to the formulation, then ball mill to prepare slurry with targeted viscosity.
3. Coating and drying. Screen-print metallization slurry evenly on ceramic substrates. Slurry thickness needs precise control: too thin allows brazing filler to penetrate the metallized layer, while excessive thickness hinders elemental migration. The coated parts are dried inside an oven.
4. Heat treatment. Sinter dried workpieces under a reducing atmosphere to form the bonded metallized layer.

Mo-Mn Method

Mo-Mn metallization uses refractory molybdenum powder mixed with manganese powder, coated on Al₂O₃ ceramic and sintered to form a metal layer. The traditional Mo-Mn process requires high sintering temperatures and consumes more energy; without activators, the sealing strength remains relatively low.

Activated Mo-Mn Method

Activated Mo-Mn is optimized from the classic Mo-Mn route. Modifications include adding activators or replacing metal powder with molybdenum/manganese oxides or salts, aiming to reduce sintering temperature. Although the process is complicated and costly, it creates strong bonding and improves wetting performance. It remains the most mature and widely adopted metallization solution for hermetic relay packaging.

Active Metal Brazing

Active metal brazing is widely used for ceramic-metal sealing. Compared with Mo-Mn technology, it was developed roughly 10 years later. The whole ceramic-metal joint can be completed within one heating cycle. The braze alloy contains active elements such as Ti, Zr, Hf, and Ta. These active elements react with alumina ceramics and form metallic reaction layers at the interface. This process is simpler and cost-effective for mass production. Its limitation lies in limited braze material selection, making it more suitable for large parts or low-volume batches instead of continuous high-speed production.

Direct Bonded Copper (DBC)

DBC bonds copper foil directly onto ceramic substrates, mainly Al₂O₃ and AlN. Developed alongside COB chip packaging, DBC introduces oxygen between copper and ceramic. At 1065~1083°C, a Cu- O eutectic liquid forms and reacts with the ceramic and copper foil, generating CuAlO₂ or Cu(AlO₂)₂ phases to achieve solid bonding.

Magnetron Sputtering

Magnetron sputtering is a physical vapor deposition technique that deposits multi-layer metallic films on ceramic substrates. It provides strong adhesion, low contamination, and controlled grain structure for high-quality thin metal coatings. The resulting metallized film is ultra-thin and maintains tight dimensional tolerance. However, it cannot be applied to heat-sensitive ceramics like piezoelectric ceramics or single-crystal materials.

1. Metallization formulation. Formulation design lays the foundation for qualified metallization layers.
2. Sintering temperature and holding time. Metallization sintering is classified into ultra-high temperature (>1600°C), high temperature (1450~1600°C), medium temperature (1300~1450°C), and low temperature (<1300°C). Insufficient temperature stops glass phase diffusion; overheating weakens bonding strength and causes metallization layer peeling and seal failure.
3. Microstructure of the metallization layer. Metallization microstructure determines final sealing performance. A high-quality metallized coating is dense with strong adhesion. A clear layered structure without continuous brittle intermetallic compounds reduces crack propagation and braze penetration risk.

Other influencing factors include powder particle size and gradation. Fine powder tends to agglomerate and ruin coating uniformity. Overly coarse powder increases sintering temperature and degrades quality. Coating technique and coating thickness also exert significant impact on metallization outcomes.

Metallized Alumina Relay Ceramics depends on mature ceramic metallization and brazing technology to achieve reliable hermetic packaging. Material stress matching, metallization formulation, and sintering parameters are the core variables determining insulation, helium leak rate, and service life for high-voltage DC relays. As energy storage and electric vehicle markets expand, precise ceramic-to-metal sealing technology continues to evolve to meet higher voltage, miniaturization, and long-lifetime requirements for power relay components.

Reach out to our engineering team now for prototype validation and bulk quotation of DC Relay Metallized Welded Ceramic Housing, backed by our in-house ceramic metallization and hermetic welding production lines.