15 Thermal Solution

Figure 15-1 shows the complete solution with the cold plate attached. The solution uses liquid cooling with a maximum coolant temperature of 65°C. All hot components access the cold plate from the back side of the printed wiring board (PWB).

Figure 15-2 shows a cross-section of this solution illustrating how the GaN FETs interface to the PWB and cold plate. Using a thermal interface material (TIM) will facilitate heat transfer from all hot spots.

Figure 15-2 also shows the placement of the TIM relative to the cold plate and GaN FETs. The FETs themselves have a θ_{Junction-Case} of 0.15°C/W. The TIM has a thermal impedance of 1.2 to 1.25°C/W. Overall, θ_{Junction-ColdPlate} is 1.35 to 1.5°C/W.

Figure 15-3 shows the bottom side of the PWB, while Figure 15-4 shows the top side of the cold plate. By comparing these images, you can see how the cold-plate features provide access to the thermally significant components highlighted in Figure 15-3.

Figure 15-5 is a thermal scan of the top side of the board. Given that the significantly hot components are located on the bottom side, there is very little of interest to see here.