Plating chemistry vendors are now coming out with two-step acid coppers which should be able to completely electroplate solid copper into these high aspect ratio through vias.  Think of it as copper electroplate for micro-via fill on steroids.


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-------- Original message --------From: Nagaraj Shanmugam <[log in to unmask]> Date: 4/24/17  3:13 AM  (GMT-05:00) To: [log in to unmask] Subject: [TN] Via fill - what parameters drive via filling? 
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.