Amorphous solder foil

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As amorphous soldering foils , eutectic alloys of transition metals such as nickel , iron , copper etc. are produced, which contain large amounts of the semimetals / metalloids silicon and boron and / or phosphorus .

Due to the high proportion of said semimetals, these alloys are too hard and brittle to be produced in the form of foils using conventional production methods such as hot and cold rolling. Sufficient plastic and elastic properties can only be found if these alloys are produced without a crystal structure , i.e. amorphous. The content of metalloids in eutectic concentrations is very beneficial for the formation of the amorphous structure.

In conventional, crystalline metal alloys, the atoms are arranged strictly regularly. The atoms of amorphous materials, on the other hand, are completely disordered, similar to in a liquid or melt. Since this also applies to glass, amorphous metals are also referred to as metallic glass . The Greek term amorphous means misshapen or shapeless.

Manufacturing

The production of amorphous metals requires a corresponding production technology due to the cooling rates required for this - the rapid solidification technique ( melt spinning ). The liquid metal melt is pressed onto a cooling roller rotating at 100 km / h. When it hits the roller, the melt cools down by approx. 1000 ° C in one millisecond. This corresponds to a cooling rate of one million degrees per second. In this way, a very uniform, thin amorphous film with thicknesses between 0.02 and 0.05 mm and film widths between 0.5 mm and 125 mm is created.

Application forms

Amorphous soldering foils are only offered in the form of thin metal foils or molded parts made from them. These molded parts can be made as cut-to-length film strips, punched or photochemically produced molded parts for special applications. The foils / parts are then placed between the components to be joined and soldered in the soldering furnace under a protective gas atmosphere or in a vacuum. With ready-made soldering foils, waste is avoided and material is saved. Solder foils or molded parts are very well suited to be implemented in automatic assembly processes. The foil thickness, which can be finely varied, makes it possible to set the required amount of solder exactly to the specific application. By using foils or molded parts made of foil that are specially designed for the application, waste is avoided and the production speed is increased, which increases the profitability of the soldering process.

properties

Amorphous soldering foils have a particularly uniform composition even after crystallization . Due to this property, the atoms of the alloying elements involved only have to cover very short diffusion paths when the solder foil melts in order to form a completely molten phase. As a result, amorphous soldering foils have the most uniform melting and flow behavior of all soldering materials. They therefore differ greatly in their soldering properties from similar soldering materials in powder or paste form. The quality of the soldered connections made with amorphous foils is very constant and of the highest level. Compared to conventional nickel solders, which are mainly applied in paste form, amorphous soldering foils are characterized by a metal content of 100%. Drying and outgassing processes, as are necessary with these solder pastes, can be completely dispensed with when using amorphous solder foils. The absence of organic components and the particularly low content of gaseous impurities ( oxygen , nitrogen ) brought about by the special manufacturing process are particularly advantageous for vacuum soldering. There are no deposits of organic residues on the soldered seam, components or on the soldering furnace.

literature

  • Thomas Hartmann, Dieter Nuetzel: New Amorphous Brazing Foils For Exhaust Gas Applications . In: Anatol Rabinkin (Ed.): Brazing and soldering. Proceedings of the 4th International Brazing an Soldering Conference, April 26-29, 2009, Hilton Walt Disney World Resort, Orlando, Florida, USA . AWS et al., Miami FL 2009, ISBN 978-0-87171-751-1 , pp. 110–117 ( PDF; 385.30 kB ).
  • Thomas Hartmann, Dieter Nuetzel: Nickel-Chromium-Based Amorphous Brazing Foils for Continuous Furnace Brazing of Stainless Steel . In: Hard and high temperature soldering and diffusion welding. Löt 2010. Lectures and posters at the 9th international colloquium in Aachen from June 15 to 17, 2010 = Brazing, high temperature brazing and diffusion bonding (=  DVS reports ). tape 263 . DVS Media, Düsseldorf 2010, ISBN 978-3-87155-589-3 , p. 42–47 ( PDF; 159 kB ).