# Influence of Quality of Mounting Process of RF Transistors on Their Thermal Parameters and Lifetime
## 6 Influence of Thermal Parameters on the Lifetime
The matrix shows how the indicators depend on each other. The degree of dependence is presented by the correlation coefficients on the scale from 0 to 1, which determines whether there are statistical relationships between the parameters under consideration or not. The correlations values exceeding 0.7 [53] indicate a significant influence of one quantity on another. It was checked whether the value of resistance \(R_{\rm th}\) depends on the area of the void. In none of the cases for both the TRA and TRB transistors the effect of the individual and total void sizes on the \(R_{\rm th}\) value approached the level of 0.7. The highest correlation value found was only 0.18, tested for the TRB transistor. This level of correlation is so low that it can be concluded that the \(R_{\rm th}\) value does not depend on the individual or total void value. Similarly to the determined value of \(R_{\rm th}\), the components influencing the value of thermal resistance resulting from the Formula (2), i.e., the value of the temperature emitted on its case, do not depend on the measured values of the void areas in the solder joint. Hence, when analyzing the obtained results, it was found out that there was no statistical influence of the total and individual void areas on the obtained values of thermal resistance of the tested transistors. Consequently, the size of the voids does not affect the lifetime of the tested transistors. Although no direct correlation was found between the size of the total or individual voids and thermal resistance \(R_{\rm th}\) and the junction temperature of transistor \(T_{\rm j}\), it was shown that transistors of the same type can significantly differ in thermal parameters (even by 25%). The discrepancy between the values of thermal resistance \(R_{\rm th}\) in the BLC10G22 LS-240 PVT and BLC9G22 LS-160 VT transistors is reflected in their lifetime, especially in the high-power range. From the curves shown in Figure 18, you can see how drastically the lifetime of these components decreases along with the power dissipated. For the tested modules with \(P_{\rm D}>15\) W, this lifetime decreases even several hundred times. The observed differences in \(R_{\rm th}\) values reach even 40% and may indicate the existing risk of damaging some components before the deadline provided by the manufacturer. To determine the absolute lifetime, additional aging tests, which were not part of the performed measurements and analyses, should be performed. \begin{table}
\begin{tabular}{c c c c} \hline
**Transistor Type** & **Index Used in the Analysis** & \(P_{\rm D}\) **[W]** & **Median \(R_{\rm th}\) [K/W]** \\ \hline BLC10G22 LS-240 PVT & TRA & \(\leq\)10 & 2.93 \\ BLC9G22 LS-160 VT & TRB & \(\leq\)10 & 2.99 \\ BLC10G22 LS-240 PVT & TRA & \(\geq\)20 & 2.46 \\ BLC9G22 LS-160 VT & TRB & \(\geq\)20 & 2.56 \\ \hline \end{tabular}
\end{table} 
Table 2: Values of the median thermal resistance \(R_{\rm th}\) for the tested TRA and TRB transistors with the dissipated power \(P_{\rm D}\leq 10\) W and \(P_{\rm D}\geq 20\) W.