Your Expert for Innovative Ceramic-to-Metal Integrated Systems:
Ceramic soldering
The main problem of joining metal to ceramic by means of soldering is the different thermal expansion coefficients (CTE) of the materials. The greater this difference and the higher the soldering temperature, the greater are the "frozen" voltages in the ceramic-metal composite at room temperature. Therefore, it is attempted to use metal alloys such as Ni42 or Kovar, as they have a CTE similar to aluminum oxide at room temperature. In addition, an attempt is made to adapt the shape and material thickness of the metal parts in such a way that composite stresses are reduced by plastic deformation. Alumina Systems distinguishes between three types of soldering as a connection technique.
Passive Al2O3 brazing of ceramic and metal
The most widely used method for brazing of ceramic and metal is passive Al2O3 brazing with an AgCu28 eutectic solder having a melting point of 779 ° C. Prerequisite here is always a metallization of the ceramic. Depending on the requirements and material pairing, various other solders are used. The solder is mostly used as wire and foil partly also as paste. An advantage of passive soldering of ceramics is the good wetting and flow behavior of the solder on the nickel-plated metallization layer. Alumina Systems manufactures more than 90% of the vacuum-tight ceramic-metal systems. It forms between the metallization and metal part of a Lotkehle, which represents an optimal voltage transition. Thus, these compounds have very high strengths (at least Mpa). Soldering is performed mostly under forming gas (90% nitrogen (N2) and 5% hydrogen (H2)) for protection against oxidation. At e.g. Stainless steel composite components, this is not enough. Therefore it is soldered here in a vacuum.
Active soldering in metal-ceramic solder composite
The main advantage of this method is the use of mostly titanium-containing active solders, which enable a direct connection between the solder and the components without metallization of the ceramic. A disadvantage is the poor wetting behavior of the ceramic. This can cause problems when creating vacuum-tight connections.
Brazed technical ceramic joint by means of glass solder
Alumina Systems often uses glass solders for the vacuum-tight bonding of ceramics with ceramics. The ceramic does not have to be metallised for this purpose. Since the material connection using glass without metals such as Ni manages, such compounds can also be used in the field of magnetic fields.
Formation of a soldered ceramic-metal compound
The micrograph shows that a thin, soft and flexible copper membrane (OF-Cu: oxygen-free copper) was soldered between the solid copper part and the ceramic. This minimizes the composite stresses in the ceramic-metal system by deformation.
