Ron,
You are correct that the aspect ratio would be just a tad over 10:1. 
Many PWB shops advertise the ability to drill AND plate vias with aspect ratios well beyond this but it would be a good idea to give your fabricator a call to confirm that he can put enough Cu plating in the via barrel to meet your requirements. The ability to get Cu plating solution through the via becomes more challenging as the via size decreases. The same is true for hole fill. 
What IPC class is this being designed to?  This will dictate the signal catch pad size and whether or not you can have via breakout.  Of course larger catch pad diameters may limit your number of lines per channel, so there's always a compromise.
Good luck and good designing,

Ron Nowak
Electronic Packaging Applications
Lockheed Martin MST
1801 State Route 17C MD 0409
Owego, NY 13827-3998
phone: 607-751-2089
cell: 607-427-0870



 

-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Ron Olinyk
Sent: Thursday, February 18, 2016 6:56 PM
To: [log in to unmask]
Subject: EXTERNAL: [DC] Mechanical drill -6mil aspect ratio

Does anyone know what the typical aspect ratio would be for a 6mil
(0.152mm) drill in FR4 would be?
Can a 6mil drill be used as a full drill-thru on 0.062 thick circuit board? -which I think would be a 10:1 aspect ratio...

I've got a design with a 0.5mm uBGA (169 pin, full array) that i want to do fanout vias between pads.  I'm using a 8.7mil BGA pad and planning on a fanout via with a 12mil pad and 6mil drill.  I originally set this up as a blind via from top to inner1 layer, which works, but I am quickly running out of available via room around the BGA for connecting signals, power/gnd, ect.  I'm using an 8mil drill elsewhere on the board which I know is doable on a 0.062 board -just not sure if 6mil is doable -and with a 3mil annular ring!

Any advice greatly appreciated.
Thanks
Ron


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