[PCB_FORUM] HDI L1-L2 trace routing

Hi,
I am doing my first HDI Micro-Via design with a .5mm pitch BGA.
I am planning to use a 4mil laser drill L1-L2 in a 10 or 12mil pad.
L1 to L2 dielectric will be roughly 3.5mil thick 1080 pre-preg.
The question I have is there a concern from a reliability standpoint routing traces on L1 that may cross L2. 
Voltage breakdown, voids, etc...
Is it a standard design practice to avoid any traces crossing on such a thin dielectric? 

Thanks in advance,
Mark



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