Issue link: https://iconnect007.uberflip.com/i/1285883
SEPTEMBER 2020 I DESIGN007 MAGAZINE 21 a nearly star-shaped arrange- ment of traces on top. With respect to the bottom, IC3 lies above a bundle of tracks surrounded by a flooded rest. Nevertheless, the cooling is not very good. The calculated thermo- graphs of the top and bottom are shown in Figure 2. The shape of the isotherms is very irregular, and the yellow and green sections end abruptly. The heat spreading does not manage to distribute the heat over a larger surface. The reason can be seen illus- tratively if the temperatures are superimposed on the layout in the area around the component (Figure 3), the heat spreading ends where the gaps between the traces form an FR-4 barrier for the heat flow. This is not only true for the top layer, but also for the bottom. The overall result is then the superposition of the two structures (Figure 4). 2. RS-ChipKit Max32 This board is a standard example of a DesignSpark PCB [5] installation. The four- layer board ChipKit Max32 by Digilent is a prototyping platform that demonstrates the power of the Microchip PIC32 microcontroller. The board is the same size as the Arduino board. On top and bottom, around the central micro controller PIC32MX795F512L (=IC2), the tracks are orthogonally aligned like a woven pattern. Both inner layers are thoroughly floo- ded (Figure 5). Because of the two massive inner layers, the shape of the calculated thermographs closely approximates that of circular isotherms from the theory of heat spread. The board is the same size as the Arduino, and even though the Figure 3: Calculated thermographs of the Arduino board for the top (above) and bottom (below). R th,C-A would be about 39 K/W. Figure 5: Diligent evaluation board ChipKit Max32. The top layer in pink, first inner layer blue, and second inner layer in brown. Figure 4: TRM calculated temperature field for the Arduino model with superimposed top-layer artwork. The parallel running traces can obstruct (left) or improve (above) the heat flow.