## 3 Results and Discussion  
### Thermal Characteristics of Packages Under Voltage Stress  
In this work, temperature variations by heat generation due to voltage stress were investigated in both air and immersion cooling environments. The maximum temperature was measured for 30 min as described in the section above. In the immersion cooling environment, thermally accelerated degradation seemed to minimize because of the higher cooling performance of immersion cooling than air, and no sudden temperature changes were observed [Figure 3c]. However, a relatively rapid initial increase in package temperature was observed. At 2.5 V, the temperature initially increased by 1.1 \({}^{\circ}\)C, then began to decrease after 7 min. At 2.8 V, the temperature initially increased by 2.9 \({}^{\circ}\)C, followed by an additional rise of 0.1 \({}^{\circ}\)C at 10 min and 0.5 \({}^{\circ}\)C at 30 min, based on the 5 min measurement  
Figure 3: **(a)** Experimental setup with an infrared camera for temperature measurement. **(b)** Temperature variation over time in an immersion environment measured using a contact-based thermometer under different voltage conditions. **(c)** Infrared thermal images captured by an IR camera, showing the heat generation and temperature distribution changes over time under different voltage conditions. interval. At 3.0 V, the temperature initially increased by 4.9 \({}^{\circ}\)C, with further increases of 0.2 \({}^{\circ}\)C at 10 min and 0.8 \({}^{\circ}\)C at 30 min. At 3.1 V, the temperature initially increased by 5.4 \({}^{\circ}\)C, then rose by 0.3 \({}^{\circ}\)C at 10 min and 2.2 \({}^{\circ}\)C at 30 min [Figure 3b]. As described above, the immersion cooling ensured that the package temperature increase remained below \(\sim\)10 \({}^{\circ}\)C, even at voltages 2.5 times higher than the regular operating voltage. In the air environment, natural cooling was observed; however, when the package experienced relatively high voltages, heat accumulation accelerated, leading to a rapid increase in the package's maximum temperature compared with the initial state [Figure 3c]. At 2.5 V, the temperature increased by 8.6 \({}^{\circ}\)C at 5 min but gradually decreased as time passed because of air cooling, preventing further thermal acceleration. At 2.8 V, the initial temperature rise was 21.2 \({}^{\circ}\)C, which was higher than that at 2.5 V. However, temperature variation was not accelerated because of the natural cooling effect. At 3.0 V, the increase in initial temperature was 40.4 \({}^{\circ}\)C, leading to additional temperature rises of 1.8 \({}^{\circ}\)C at 10 min and 9.6 \({}^{\circ}\)C at 30 min. At 3.1 V, thermal degradation progressed rapidly as soon as the voltage was applied. The temperature increased by 75.2 \({}^{\circ}\)C at 5 min, followed by additional rises of 33.5 \({}^{\circ}\)C at 10 min and 50.2 \({}^{\circ}\)C at 30 min. At relatively low voltage stress (2.5 V, 2.8 V) in both air and immersion cooling environments, thermal accelerations were not critical because of lower heat generation. However, as the stress voltage exceeded 3.0 V and 3.1 V, a nonlinear increase in maximum temperature was observed because the generated heat effectively dissipated. At 25 \({}^{\circ}\)C, air has a thermal conductivity of 0.026 W/m\(\cdot\)K [18], while FC-3283 exhibits a higher value of about 0.066 W/m\(\cdot\)K [19], which is approximately 2.5 times greater than that of air. The improved cooling performance in immersion environments can be attributed not only to the higher thermal conductivity of the liquid coolant but to the generally higher heat transfer coefficient at the solid-liquid interface, which enhances heat dissipation efficiency compared with solid-air systems. This difference explains why thermal accelerations were minimized in the immersion cooling environment, confirming that this advanced cooling method provides greater thermal stability than air cooling even under elevated voltage conditions.