**2. Methods of soldering ceramic materials**

The biggest issue in the fabrication of joints of ceramic and non-metallic materials with metals consists in the fact that the commercial solders generally do not wet the ceramic materials. Poor wettability of ceramics is caused by the non-metallic character of bond, which is mostly ionic or covalent, in contrary to metallic materials with different structure of energy levels of electrons.

The following methods are mostly used to ensure the wettability:


All the mentioned technologies are applicable for soldering the ceramics/metal combinations. Regarding the versatility of technology, its ease end economic efficiency, there is increasing tendency to apply the soldering with an active solder. Soldering of metallized ceramics requires several additional operations, when compared to the application of active solders [2].

### **2.1. Soldering of metallized ceramics**

Metallizing of ceramics eliminates the issues connected with its wettability. Regarding the selection of metallizing, it is necessary to know at what working temperature the soldered part will be servicing. Then, either solder and/or brazing alloy will be used. The desirable metallic layer may be obtained:

• By burning-in of metallic solution either of heat-resistant metals such as Mo, Mn, W or precious metals such as Ag, Au, Pt and so on.

Recent Advances in Solderability of Ceramic and Metallic Materials with Application of Active... http://dx.doi.org/10.5772/intechopen.69552 65

whether ceramic material is wetted with the metallic solder. Wetting the ceramics with a

Several ways may be used for ensuring the wettability of a ceramic material. For example, the

However, more modern methods seem to be the application of solders which are alloyed with some active metal such as Ti, In, Si, Al, Mg and/or lanthanides, which exert a strong chemical

The first group comprises the active solders based on Sn or Sn-Ag, which may contain from 1.5 to 4 wt.% Ti. Another group of solders, which may wet the ceramic material, consists of solders alloyed with a small amount of lanthanides, for example, La, Ce and so on. The content of lanthanides usually varies from 0.5 to 2 wt.%. The last group are the solders containing indium in the amount from 20 to 100 wt.%. However, solving the mentioned issue still involves the requirement to ensure a joint that should resist the effects of residual stresses formed owing to different coefficients of thermal expansivity of metal and ceramics, which usually exerts much lower expansivity. This condition is most essential from the viewpoint of

The biggest issue in the fabrication of joints of ceramic and non-metallic materials with metals consists in the fact that the commercial solders generally do not wet the ceramic materials. Poor wettability of ceramics is caused by the non-metallic character of bond, which is mostly ionic or covalent, in contrary to metallic materials with different structure of energy levels of electrons.

• Metallizing of ceramics (e.g. metallic deposit of Mo-Mn paste, physical vapour deposition

• Application of an active brazing alloy and/or solder alloyed with active elements (Ti, Zr, Hf). All the mentioned technologies are applicable for soldering the ceramics/metal combinations. Regarding the versatility of technology, its ease end economic efficiency, there is increasing tendency to apply the soldering with an active solder. Soldering of metallized ceramics requires several additional operations, when compared to the application of active solders [2].

Metallizing of ceramics eliminates the issues connected with its wettability. Regarding the selection of metallizing, it is necessary to know at what working temperature the soldered part will be servicing. Then, either solder and/or brazing alloy will be used. The desirable

• By burning-in of metallic solution either of heat-resistant metals such as Mo, Mn, W or pre-

metallic solder is an essential precondition for soldered joint formation.

deposition of solderable coating on ceramic material is often employed.

ensuring the reliability of ceramics/metal joints [1].

**2. Methods of soldering ceramic materials**

The following methods are mostly used to ensure the wettability:

(PVD) and chemical vapour deposition (CVD) processes).

**2.1. Soldering of metallized ceramics**

cious metals such as Ag, Au, Pt and so on.

metallic layer may be obtained:

affinity to oxygen.

64 Recent Progress in Soldering Materials

**Figure 1.** Schematic representation of vacuum brazing of metal and ceramics, metallized (with Ag72Cu brazing alloy) in comparison with non-metallized substrate (brazing with active Ag72CuTi brazing alloy) [3].

• By physical and chemical deposition, with a thin coatings, for example, of Au, Ag and Ni are created.

The classical method of metallizing Al2 O3 ceramics is shown in **Figure 1**. A powder deposit (70% Mo, 17.5% Mn, 3.5% titanium hydride, 9% kaolin) is applied onto ceramics surface, followed by sintering at 1200–1400°C/10 min in humid hydrogen. If a silver brazing alloy (e.g. Ag72Cu) is used for brazing, then the sintered surface must be coated with nickel, to allow the brazing operation in vacuum. Optimum thickness of metallizing is 0.02 mm. Deviations from this value may affect the strength of soldered/brazed joint. The paste is deposited on the soldered surface by a brush and on/or by silk-screen printing. The layers formed by this process ensure at certain conditions a good reliability, however, paid by high power demands and necessity of costly equipment and extensive safety precautions at their preparation [4].

Chemical reactions between the Al<sup>2</sup> O3 substrate and molybdenum-manganese suspension allow joint formation. In case of this method, the reactions take place in the following manner:

• At sintering the metallic suspension with Mn in humid hydrogen, the manganese oxide is formed by the reaction [5]:

$$\text{Mn} + \text{H}\_2\text{O} \rightarrow \text{MnO} + \text{H}\_2\tag{1}$$

• The formed oxide then react with Al2 O3 , forming thus the manganese-aluminium spinel as the product of reaction [5]:

$$\text{MnO} + \text{Al}\_2\text{O}\_3 \rightarrow \text{MnAl}\_2\text{O}\_4\tag{2}$$
