# Influence of Quality of Mounting Process of RF Transistors on Their Thermal Parameters and Lifetime
## 5 Results of Measurements
The measurements, the result of which are shown in Figure 12, were performed with the power dissipation equal to about 6.74 W, and in Figure 13 with the power of \(\rm P_{D}\) = 21 W. The temperature \(\rm T_{C}\) of the measured area was determined as the average value obtained from the measurements with the IR camera. In Figure 12, the case and reference temperature difference is \(\rm\Delta T\) = 20 \({}^{\circ}\)C. Under such conditions, \(\rm R_{thc-a}\) = 2.97 K/W. For the BLC9G22 LS-160 VT transistor, the lowest \(\rm R_{th}\) value is 1.86 K/W at power \(\rm P_{D}\) = 7.1 W (for the TR2_B transistor in the PCB3 module), while the highest \(\rm R_{th}\) = 3.65 K/W was recorded for the TR4_B transistor in the PCB4 module. The  
Figure 12: Thermogram and the case temperature distribution measured for the BLC10G22 LS-240 PVT transistor with the dissipated power \(\rm P_{D}\) = 6.74 W.  
Figure 13: Thermogram and the case temperature distribution for the BLC10G22 LS-240 PVT transistor with the dissipated power \(\rm P_{D}\) = 21 W.  
difference between the highest and the lowest value of \(\rm R_{th}\) is \(\rm\Delta R_{th}\) = 1.79 K/W, which is 32% of the mean value of \(\rm R_{th}\) = 2.76 K/W. For the BLC10G22 LS-240 PVT transistor measurements, the lowest \(\rm R_{th}\) value measured was 2.03 K/W with power \(\rm P_{D}\) = 21.67 W for the TR3_A in the PCB2. The highest value of \(\rm R_{th}\) was 2.69 K/W for the TR3_A transistor of the PCB4 module at power \(\rm P_{D}\) = 21.51 W. The changes in the \(\rm R_{th}\) value were therefore \(\rm\Delta R_{th}\) = 0.66 K/W. This represents a 14% change in the \(\rm R_{th}\) value compared with the average value of 2.36 K/W. The distribution of the obtained results of the measurements of thermal resistance \(\rm R_{thc\_a}\) for all the tested transistors for both power values is shown in Figure 14.  
For the described operating conditions (\(\rm T_{a}\) = 29.5 \({}^{\circ}\)C and the dissipated power \(\rm P_{D}\) = 22.5 W) when measuring \(\rm R_{th}\) for the BLC9G22 LS-160 VT transistor, the lowest value was noted for the TR2_B transistor in the PCB2 module. It is \(\rm R_{th}\) = 1.98 K/W. The highest value of \(\rm R_{th}\) = 2.9 K/W was determined for the TR2_B transistor in the PCB4 module. In relation to these values, the maximum difference \(\rm R_{th}\) in the measured transistors was as high as \(\rm\Delta R_{th}\) = 0.92 K/W. This is as much as 19% of the deviation from the average value of the measurements of 2.44 K/W. It should be noted that the maximum deviation \(\rm R_{th}\) was obtained during the measurements for the TR2_B transistors in the tested modules. Figure 14: Comparison of the measured \(\rm R_{th}\) values of the tested transistors with the considered power values, BLC10G22 LS-240 PVT (**a**) and BLC9G22 LS-160 VT (**b**). The noticeable differences between the values of thermal resistance of each transistor may be caused by the following factors:  
* Varying the size of voids in the soldering area;
* An influence of the distance between the tested transistors and the PCB edge or the differences in the distribution of copper on the PCB in the vicinity of the tested transistors;
* Differentiation in the quality of the transistors manufacture resulting in differentiation of their thermal properties. One can see in Figure 14a that for the BLC10G22 LS-240 PVT transistor, a change in the power dissipated caused an average decrease in the R\({}_{\rm th}\) value by 0.5 K/W. For the transistor BLC9G22 LS-160 VT (Figure 14b), the changes in R\({}_{\rm th}\) at different power values were different depending on the tested module and the position of the component on the PCB. It is worth noticing that the R\({}_{\rm thc\_a}\) values measured by the indirect electrical method were 4 and 1.5 K/W for free and forced cooling, respectively.