## 1 Introduction
[28], the results of experimental studies on the aging of high-power white LEDs are presented, with the most significant emphasis on tests of the optical components of the tested LED chips, i.e., lenses and phosphors. An apparent decrease in the optical power emitted by the tested chips was observed in all three tested LED chips. At the same time, the thermal properties and angles of maximum light intensity did not change after the aging process. [PERSON] et al. [29] brought an overview of APC (Active Power Cycling) tests of SiC (silicon carbide) half-bridge modules. This description covers all aspects of accelerated aging tests, from the preparation of the APC test to the post-failure analysis of SiC half-bridge modules, ending with identifying their reliability model. Moreover, the tested SiC modules were subjected to special 14-week tests after the aging process to determine the further degradation of electrical parameters. In the paper of [PERSON] et al. [30], different aging models of white power LEDs were analyzed, which improved their multi-domain model with a component describing the influence of lifetime on selected parameters of the tested devices. The authors of the cited paper take an approach based on the LM-80-08 testing method [31], supplemented with additional specific thermal measurements of white power LEDs. The power semiconductor devices operate not only in ideal environmental conditions but also in elevated temperatures and relative humidity, often reaching 100%. The results of aging tests of white power LEDs and RGB power LEDs in such unfavorable environmental conditions were presented in the work of [PERSON] et al. [32]. It was found that the influence of the humidity (85%) is much more considerable than expected, and the power LEDs show very different behaviors in terms of their operating parameters, such as forward voltage, electrical power, emitted optical power, energy conversion efficiency, thermal resistance, total luminous flux, and CCT. The material from which the luminophore is made extensively impacts aging processes activated by environmental conditions. It can be seen that RGB power LEDs show a more negligible dependence on the degradation of optical parameters than white power LEDs, whose luminophore contains large amounts of luminophore used to convert blue light into white light with different correlated color temperature (CCT). Large amounts of phosphorus in the luminophore cause more significant absorption of water molecules from the atmosphere. It was also proven that water molecules penetrating the lower luminophore layers in white power LEDs with a high CCT (Cold White) lead to the degradation of the lower phosphor layers and cause the degradation of thermal interfaces under the LED chip, which leads to the deterioration of thermal and optical parameters of the tested power LEDs. The aging test results of white LEDs with a power dissipation of 1 W, excited with direct current, and a half-wave rectified sinusoidal waveform were presented by [PERSON] et al. [33]. The aging tests lasted 6500 h at a temperature of 85 \({}^{\circ}\)C. It was reported that supplying power LEDs with direct current has a negligible effect on their lifetime (exceeding 50,000 h), while supplying with a half-wave rectified sine current drastically reduces their lifetime--to about 7000 h--and damages the luminophore manifesting by blue light emission. Currently, in soldering alloys, TiO\({}_{2}\) is used the most frequently as a reinforcement material [34; 35]. The enhanced metallurgical properties (toughness, ductility, and yield strength) of soldering alloys can be obtained as a result of grain refinement [34]. On the other hand, the reinforcement addition could change many important properties of solder joints. For example, it can cause surface instability [36], the grain boundary/interfacial characteristics and the variation in the physical properties [36; 37]. For the classical SAC alloy, the solder joints contain a \(\beta\)-Sn matrix and Intermetallic Compounds (IMCs).