**4. Conclusions**

The aim of this chapter was to study the soldering of metallic and ceramic materials by the lead-free active solders based on Sn and Bi. Possibility of soldering ceramic materials is in considerable measure limited by the poor wettability of ceramic substrates with commercial solders at classical soldering technologies and owing to different thermal expansivity of soldered materials. Solderability study includes the application and subsequent study of soldering technology with ultrasound assistance applicable for ceramic materials and design of solder which allows to fabricate qualitatively acceptable soldered joint. From amongst the numerous methods used at present for joining ceramic materials, the technology of soldering with active solders was selected. This technology allows to wet both the metallic and also non-metallic materials as glass, ceramics, silicon, composites, etc. The power ultrasound was selected for mechanical activation of solders. Wetting of hard-to-wet materials is achieved just by ultrasound application, since it generates the cavitation in the liquid solder which disrupts the surface oxides, changes the surface energy of ceramic materials and supports the diffusion processes in the interface. The solders and soldered joints were subjected to a wide scope of analyses and experiments. The microstructure of solders was assessed in an initial state. The phase composition of solders was identified by the diffraction analysis.

Also static shear test was ranked to the tests of technological solderability of soldered joints. A series of combined soldered joints of Cu/Al2O3, fabricated with SnTi2, SnAg3.5Ti4(Ce,Ga) and BiIn25Sn18 solders was assessed by the performed experiments. The interfaces of soldered joint were analysed by the optical and scanning microscopy and by the SEM technique with EDX microanalysis. By the gradual selection, based on the desired properties, the soldering alloy type SnAg3.5Ti4(Ce,Ga) was finally identified as the most perspective solder. This solder exerts a narrow melting interval from 221.4 to 224.6°C. The attained tensile strength was 53 MPa, whereas the shear strength varies within the range from 29 to 45 MPa. Regarding the mechanism of bond formation, it was revealed that the joint between the SnAg3.5Ti4(Ce,Ga) solder and substrate is created by the formation of a continuous reaction layer of Ti with the surface layers of Al2O3 ceramics.
