**2.1 SnTi2 solder**

*Lead Free Solders*

joint and its technological parameters (e.g. the joint width) as well [26]. The work cycle of soldering with application of mechanical activation by ultrasound is roughly 10

Acting upon the active solder by ultrasound may be performed in several ways. The technology depends on the size and geometry of the joint, soldering temperature, type of parent metal, number of produced pieces and other parameters. The most used technique of laboratory activation of melts by ultrasound comprises the method, where the solder is molten on the surface of a joined unit by an external heat source, and the ultrasonic power is supplied through the solder from a sonotrode point on the part surface. This method makes it possible to solder selectively the localised surfaces on large parts or to cover the entire surfaces of parts. This principle is shown in **Figure 7** [24].

times shorter than in the case of high-temperature activation (**Figure 6**).

*Work cycle of soldering with application of mechanical activation.*

*Principal scheme of an equipment for ultrasonic soldering.*

**32**

**Figure 7.**

*Manual soldering with ultrasound assistance.*

**Figure 6.**

**Figure 5.**

**Figure 8** shows the microstructure of SnTi2 solder. This solder was manufactured by free casting in a vacuum. The solder exerts heterogeneous composition. The matrix consists of 100% Sn. The round, dark and oblong grey phases are the intermetallic compounds of the Ti-Sn system. The zones of solder containing 35.2% Ti and 64.8% Sn consist of Ti6Sn5 phase. Composition of SnTi2 solder in the selected spots is shown in **Table 2**. Diffraction analysis performed on a sample of SnTi2 (**Figure 9**) solder has revealed the presence of the following phases: Ti6Sn5, Ti3Sn, Sn3Ti5 and Sn5Ti6. Solder microstructure consists of a tin matrix (100% Sn) with non-uniformly distributed phases of the Ti-Sn system. The coarse dark-grey phases in **Figure 8** represent the Ti6Sn5 phase; the smaller bright-grey phases with Sn designation contain 3.6% Ti and 96.4% Sn.
