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Metallized alumina ceramics are commonly used in many applications, for example in power electronics components placed under extreme load, electrical drive engineering and electrical engineering as well as in electronic components for computer technology.
CeramTec ceramic-metal joining technology makes high vacuum-tight ceramic-to-metal joints possible (≤10-8 mbar x l/s) with extremely high bond strengths of more than 200 N/mm² (measured using ASTM test specimens). Even more important than mechanical strength in typical applications are good heat transfer properties, minimum electric resistance and vacuum tightness. The metallic layers make the component suitable for integration by means of both hard and soft soldering.
A common product that uses this technology is a surge arrester, which requires ultra-high vacuum-tight ceramic-to-metal joints. A surge arrester is a component that limits dangerous surges in power lines and devices like those caused by lightning strikes near telephone or power lines.
The excess voltage is released by the triggered ignition of a gas discharge. Depending on the current and voltage, this results in a glow, spark or arc discharge. Spark gaps for ignition sets work according to the same principle. These are used in the ignition of gas-discharge lamps such as xenon lights in automobiles.
CeramTec offers a comprehensive program of standard products with a variety of ceramic ring inner diameters for housings for power semiconductors such as diodes, thyristors and GTO thyristors in electrical drive engineering and electrical engineering. The corresponding connections and fittings, caps and gate pipes can be varied and combined in any number of ways
High-percentage, high-purity alumina ceramics (Al2O3) are used as a ceramic base material and are offered under the Rubalit® brand name: e.g. as Rubalit® A1894 with an Al2O3 percentage of 94%. CeramTec can also use a number of other ceramic base materials on request.
The alumina ceramic Rubalit® A1894 is characterized by its outstanding properties with regard to thermal conductivity (18 W/mK), electrical insulation capacity (>1014 Ωm at 20°C), electrical dielectric strength (25 kV/mm) and corrosion resistance. CeramTec developed a thermally adjusted metalization system especially for this ceramic material.
Common metalizations consist of a primary layer of tungsten or molybdenum. They have a minimum layer thickness of 6 µm and are deposited in a screen printing process with subsequent sintering. Other deposition methods are possible as well, depending on the geometry of the component, such as pad printing or coating.
A defined percentage of glassy material ensures the high bond strength of this base metalization on ceramic. A thin layer of nickel (typically 0.5–5 µm thick) is electrically or chemically (electroless) deposited on the tungsten layer to achieve the required wettability of the solder on the metalization.
A gold flash layer (approx. 0.1 µm) can also be deposited on the nickel layer for corrosion protection. Another possibility is to cover the electrolytic nickel layer with a bondable gold plating. An additional layer of tin is applied when soft solder is used.
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