## Results
### Inspection of Adhesive Interfaces  
The investigations on adhesive interfaces were performed on a commercial inverter module with five half bridges depicted in Figure 9a. The thermomechanical set-up was identical to that described previously in Figure 1a. Two identical unpackaged silicon MOSFETs soldered to a DBC represented one half bridge, and each half bridge was realized on an individual DBC. Ribbon and wire bonds were used to connect the top contacts of the MOSFET dies to the DBC, and the DBCs themselves were attached with nonconductive thermal adhesive to an aluminum body used as the case and heat sink. For our investigations, the inverter modules were in a semi-fabricated state, where, amongst other things, the control unit and gate drives were missing and the connections between the half bridges and to the outer connectors were not yet present. Thus, the half bridges were isolated from each other, which allowed an individual electrical measurement required for TTA. The semi-fabricated state was reached by removing the modules at a certain point from the production line. Overall, five modules with 50 MOSFETs were inspected. Differences in the thermal adhesive layer were evoked by manipulations within the adhesive process and, thus, the MOSFETs were divided into seven groups. Group M1 was used as a reference and was assembled without manipulation. For groups M2 and M3, the thermal adhesive was partially removed under the DBC before curing. For M2, the removal was performed below the high-side MOSFETs (HS-M) of the half bridges, and, for M3, adhesive was removed from one half of the DBC area, whereby the separation was carried out to affect the HS-M and low-side MOSFET (LS-M) in the same way. For groups M4 to M7, a tilting of the DBC was provoked by an approximately 300 \(\upmu\)m thick wedge between the DBC and aluminum body to impede homogenate spreading of the adhesive by squeezing. These groups were separated by the direction of the tilt. M4 and M5 were tilted around the short edge of the DBC with M4 tilted toward the HS-M (no lift-off for HS-M but for the opposite side) and M5 tilted away from the HS-M (lift-off for HS-M but not for the opposite side). M6 and M7 were tilted around the long edge of the DBC with M6 tilted to the left (lift-off on the right side) and M7 tilted to the right (lift-off on the left side). All manipulations are schematically described in Figure 9b. The results from the NDTs are summarized in Figure 10 with X-ray images, SAM images, \(Z_{th}(t)\) curves, and normalized logarithmic derivative for one generic HS-M of groups M1 to M5. The X-ray and SAM images include markings of the area without adhesive or the tilting direction, and the \(Z_{th}(t)\) curves are normalized to the reference module M1. Additionally, the averaged termination values of \(Z_{th}(t)\) over all HS-Ms and LS-Ms in one group are listed in Table 1 normalized to the reference M1. SAM images were recorded with a 30 MHz transducer required to penetrate the DBC to reach the adhesive layer, but limiting the resolution and TTA performed with the same equipment from Section 4.2 with the settings P\({}_{\text{Heat}}\) = 15 W, P\({}_{\text{Sense}}\) = 0.1 W, and t\({}_{\text{Heat}}\) = t\({}_{\text{Sense}}\) = 3 s. \begin{table}
\begin{tabular}{c l c c c} \hline \hline
**Gr.** & **Description of Manipulation** & **Sample Count** & \
\begin{tabular}{c} **High-Side** \\ **MOSFET** \\ \end{tabular} &
\begin{tabular}{c} **Low-Side** \\ **MOSFET** \\ \end{tabular} \\ \hline
**M1** & Reference & 10 & 1.00 & 1.00 \\ \hline
**M2** & Adhesive remove under HS-M & 10 & 2.11 & 1.09 \\ \hline
**M3** & Adhesive half removed & 10 & 1.08 & 1.18 \\ \hline
**M4** & Tilt around short edge toward HS-M & 6 & 1.03 & 1.36 \\ \hline
**M5** & Tilt around short edge from HS-M & 6 & 2.61 & 1.24 \\ \hline
**M6** & Tilt around long edge to the left side & 4 & 1.25 & 1.57 \\ \hline
**M7** & Tilt around long edge to the right side & 4 & 1.35 & 1.4 \\ \hline \hline \end{tabular}
\end{table}