## 4 Results and Analysis
### Thermal Mechanical Cycling Tests  
The initial testing involves one cycle from 30 min at the lowest temperature of \(-33\)\({}^{\circ}\)C to 30 min at the highest temperature, \(63\)\({}^{\circ}\)C, with a maximum transfer rate of 1 min between the two extremes. The event component of this test involves three 24 h cycles, 30-43 \({}^{\circ}\)C while the circuit is operational, and three 4 h tests at \(-21\)\({}^{\circ}\)C, again, while the board is operational. Finally, the test is repeated for three 24 h cycles, 30-63 \({}^{\circ}\)C, and three 4 h cycles, \(-33\)\({}^{\circ}\)C, to replicate non-operational storage stresses. All tests were carried out under ambient air conditions.  
The results of the thermal mechanical cycling show that a number of components failed (indicated in red in Table 3) or are at risk of failing (yellow). Examining the failures shows the large box capacitors, toroidal inductor, and connectors failed. More surprisingly, perhaps, transistors Q1, Q2, and Q001 also failed. Q1 and Q2 are supported against the heatsink and hence the failure may be due to the movement of the heatsink causing solder fatigue. By comparison, the box capacitors, toroidal inductor, and various test sockets/plugs are large objects made of plastic and metal having a high thermal expansion factor. Figure 7a-d shows where the highest strain in the components was induced.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline Part Type & **Material** & **Max. Temp.** & **Max. Disp.** & **Max. Strain** & **Score** \\ \hline Transistors (02 in no.) & Overmold-headed & 63 \({}^{\circ}\)C & 1.2 mm & \(72.2\times 10^{-4}\) & 0.0 \\ \hline Transistors & & & & \(34\times 10^{-4}\) & 0.0 \\ (02 in no.) & Epoxy encapsulant & 63 \({}^{\circ}\)C & 1.2 mm & \(43.3\times 10^{-4}\) & 0.0 \\  & & & & \(18.8\times 10^{-4}\) & \\  & & & & \(2.5\times 10^{-4}\) & 0.0 \\  & & & & \(2.8\times 10^{-4}\) & \\ \hline Plug Con. & & & & \(2.0\times 10^{-3}\) & \\ (07 in no.) & Polyester & 63 \({}^{\circ}\)C & 1.2 mm & \(21.1\times 10^{-3}\) & 0.0 \\  & & & & \(23.3\times 10^{-3}\) & \\ \hline Plug Con. & & & & \(3.0\times 10^{-4}\) & 0.0 \\ (02 in no.) & Aluminum & 63 \({}^{\circ}\)C & 1.2 mm & \(3.2\times 10^{-4}\) & 0.0 \\  & & & & \(2.1\times 10^{-3}\) & \\  & & & & \(2.4\times 10^{-4}\) & 0.0 \\  & & & & \(2.6\times 10^{-4}\) & \\ \hline Capacators & & & & \(81\times 10^{-4}\) & \\ (02 in no.) & & & & \(85\times 10^{-4}\) & 0.0 \\ \hline Inductor & Aluminum & 63 \({}^{\circ}\)C & 1.2 mm & \(5.6\times 10^{-4}\) & 0.0 \\ Transformer & Ferrite & 63 \({}^{\circ}\)C & 1.2 mm & \(2.9\times 10^{-4}\) & 0.0 \\ \hline Resistor & Alumina & 63 \({}^{\circ}\)C & 1.2 mm & \(4.6\times 10^{-4}\) & 3.1 \\ Capacitor & Alumina & 63 \({}^{\circ}\)C & 1.2 mm & \(3.8\times 10^{-4}\) & 6.0 \\ Schottky Diode & Overmold-headed & 63 \({}^{\circ}\)C & 1.2 mm & \(4.1\times 10^{-4}\) & 6.8 \\ Schottky Diode & Overmold-headed & 63 \({}^{\circ}\)C & 1.2 mm & \(3.4\times 10^{-4}\) & 9.0 \\ \hline \hline \end{tabular} (red—failed, and yellow—risk of failing).  
\end{table}
Table 3: The state of PCB components subjected to thermal mechanical stress.  
Figure 7: Thermal mechanical cycle impact on the PCB. (**a**) Different levels of displacement. (**b**) Strain on various components. (**c**) Stress at 63 \({}^{\circ}\)C. (**d**) The impact of temperature at 63 \({}^{\circ}\)C.