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. Sent from my Verizon, Samsung Galaxy smartphone -------- 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.