Hello all - Table 6-1 Electrical Conductor Spacing in IPC-2221 is an excellent reference for spacing/voltage design requirements.  My question is are these requirements the same regardless of axis?  In other words, are the requirements the same whether you are looking at two traces on the SAME layer as they are if the traces were on DIFFERENT layers (z-axis vs xy-axis)  If they do apply to the z-axis (different layers) wouldn't the different breakdown voltage characteristics of the dielectric materials come into play?  Thanks in advance.