All,

I have a PCB of thickness 60mils(0.060"/1.53mm) and has a smallest through hole via is 4 mil(0.004"/0.1mm). These are NOT  Via in pad.
The aspect ratio here is 15.

Fab vendors asking for via fill here. Does these 4 mil via need to be filled?  I have boards done without fill for a 8mils drill on a 120mil thick board (Aspect ratio is 15 here). 

Appreciate to help to understand what parameter or factors determine the filling here.

Thanks,
Nagaraj.