###### Abstract
The last topic is the increase in drain-source resistance, as a consequence of trapping phenomena during the transition between off and on states [27; 28; 29; 30]. A parametric analysis of the impact of parameters, such as off voltage and time, frequency, current, and temperature, based on the available literature, is presented in [31]. High-frequency operation would reduce the passive components requirements; however, the interaction between parasitic inductances and capacitances, and dv/dt and di/dt, can produce more losses [32], switching oscillations [33; 34], and false turn on [35]. Related to this issue, there exists a more general topic regarding the power losses, in terms of both models and experimental methodologies [36; 37; 38; 39]. Moreover, the hysteretic losses related to the output capacitance must also be taken into account, especially in soft-switching applications (i.e., where there is not a hard intersection between the drain-source voltage and drain current at the transient stage) [40]. From the back-end side [41], integrated packaging solutions for WBG-based devices are gaining attention [42; 43; 44], because they can furtherly reduce the occupied area and, as a consequence, the power density. Nevertheless, the package integrity must be assured, also from a structural point of view [45]. In this paper, a system in package (SiP) GaN-based power device is considered [22]. In general, monolithic integration solutions usually comprise half- or full-bridge topologies, the driver, the protection, and the control logic [46]. GaN-based power switches are usually surface-mounted devices (SMDs), i.e., they are directly soldered on the printed circuit board (PCB). Regarding the cooling, traditionally, the SMDs have been bottom-side cooled. There exist, in this case, several solutions to cool the device in the application, among them: PCB thermal vias, copper pads beneath the device, heatsink (if present) attached to the PCB bottom. Nowadays, double side cooled power SMDs are spreading. They have the exposed pad on the top of the package. In such a way, this solution is more advantageous because the heatsink can be directly attached to the top of the package, thus ensuring a more pronounced heat exchange. Then, also another heatsink would be present on the bottom side of the PCB. Regardless of the cooling systems used on the package and at the applications level, the heat removal from the GaN power device is critical, either for the die and for copper traces dissipation inside the package [24; 47; 48; 49]. Numerical simulations are today commonly used in industry frameworks, also in order to validate various design proposals, without spending time and cost on releasing many prototypes. These techniques are nowadays also widespread for power electronics [50; 51]. However, to the best of our knowledge, an integrated simulation approach, using finite element model (FEM)-based software packages, starting from electromagnetic output to calculate the temperature of interconnects, has not been proposed for power devices. The aim of the study is to calculate the copper traces temperature, induced by package electromagnetic self-heating by means of an integrated simulation. This approach is made by electromagnetic and thermal FEM. The electromagnetic FEM calculates the spatial distribution of power losses due to a dynamic current input at 500 kHz. The power losses geometrical output map is indeed exported in the post-process of electromagnetic FEM and imported in the pre-process of thermal FEM. The copper traces temperature is finally calculated considering the imported power losses' map as simulation input. This can be possible if an integration among the two physical environments is accomplished. The test vehicle considered in the paper is a GaN-based 2 SPAK SiP, from STMicroelectronics.