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.