VN7004SLH 4-layer board design example on datasheet

[jsmith]

On p23 Fig 35 of https://www.st.com/resource/en/datasheet/vn7004slh.pdf, Are the big copper areas on the 4-layer PCB around the IC GND or VCC?  The figure seems to be GND, but how can GND help dissipate the heat from the ICs if the thermal vias are connected to VCC?  Just to confirm.  Thanks. 

[jsmith]

This is the figure 

 

[TDK]

The Mid1 layer is GND, the others are VCC. This can be seen by looking at the top-right of each plane and seeing which via they're connected to.

(Even though 3/4 of them are) the layers do not need to be electrically connected in order to help dissipate heat. Simply being copper instead of bare board helps. Heat travels easily over a 0.010" distance from the trace to the adjacent plane. Directly connected is better of course, but not by as much as you may think.