## 4 Results of the Measurements and Analyses
### Discussion  
Summarizing this part of the analyses and the results presented in Figures 7-9, it can be concluded that the position of the transistors on the PCB laminate is important and affects their thermal parameters. Depending on whether the tested components lie closer to the center of the PCB module or are mounted on the edge of the PCB, the tested thermal resistance R\({}_{\text{th}}\) may change several times with similar actuation. Thus, the temperature on the case of the extreme device was at least 10% higher than on the others, with very similar control conditions (the range of power changes for the same type of the transistor TR_B was only 2.5%).  
The conducted analyses made it possible to claim that, taking into account all the dependences between the individual parameters presented in the paper, the most important factors influencing the behavior of the transistor are: the type of the transistor, the cooling system (position on the PCB) and selected control parameters. Changes in the power value  
Figure 9: Two variances test in the Minitab for R\({}_{\text{thaverage}}\) and the transistor TR_B in the positions 2 and 4 in PCB modules.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Transistor Position**} & **Measurement** & \multirow{2}{*}{**Mean**} & **Standard Deviation** & **SE Mean** \\  & **Samples N** & & **(StDev)** & **SE Mean** \\ \hline TR\_B2 & 5 & 2.193 & 0.212 & 0.095 \\ \hline TR-B4 & 4 & 2.547 & 0.0543 & 0.027 \\ \hline \hline \end{tabular}
\end{table}
Table 3: T-test results of two groups of R\({}_{\text{thaverage}}\) values determined for two transistor positions TR_B2 and TR_B4.  
by 10 W, i.e., from the value of 10 W to 20 W (twice), cause a change in the case temperature of about 45 \({}^{\circ}\)C (from 47 \({}^{\circ}\)C to 90 \({}^{\circ}\)C). The Rth values were compared with the determined void values and no correlation was found between these parameters. This is inconsistent with the common opinion that an increase in the surface area of the void deteriorates the efficiency of heat removal from the devices.  
It was also noticed that the temperature value on the component case is influenced by the location of these devices on the PCB. The transistor in the extreme position reached the highest temperature values. It is predicted that the cause may be a smaller mass surface, which means that for this component, the heat could be dissipated least efficiently. From the results of the analyses of one of the T-test hypotheses, a clear variation was found, determined as the average value of the thermal resistances measured in the cross-section of the transistor, described as Rthaverage. The value of this thermal resistance for the extreme position of the TRB-4 device was several times lower than those of the other transistors located in the positions 1-3.  
Returning to the HoQ shown in Figure 3, the result of which was the importance rating of the main 10 parameters and the selection of six with the highest score value for the analysis, it can be noted that, among them, the \"position of the tested components on the PCB\" was not initially taken into account. This parameter was only classified as item 7. The location of the components did not seem to be such a significant factor influencing the changes in the temperature distribution on the case of these components and thermal resistance Rth, compared with the others. However, following the DMAIC methodology described in Section 2 and the in-depth study of the influence of some parameters on others, it was possible to verify the initial assumptions. As demonstrated by the results of the statistical analyses, depending on whether the tested components lie closer to the center of the PCB or are mounted on the edge of the laminate, the tested thermal resistance Rth may change several times with similar values of the dissipated power.