Hardware Projects » M.2 (NGFF) WWAN modem USB breakout board

normally, the inner two layers are supply planes and shouldn't be interrupted. The main reason for this is that they serve as return path for the signal traces on outer layers.

However, we now have four signals basically cutting the entire plane into half for almost the entire length of the board. We can actually see it quite nicely in the PDF preview from Eurocircuits:

This is problematic, particularly if any of the affected signals are fast or have steep edges.

• try to keep Layer3 traces short and bring them to the bottom layer as soon as possible
• add stitching caps between GND and VCC layers to enable return current to switch between bottom (GND) and L3 (VCC) when the bottom signal trace crosses the L3 signal trace