A 6 mil drill in a 12 mil pad will not meet the design requirements in IPC-2221, paragraph 9.1.1.  Even using the Level C fabrication allowance, the minimum pad would be .0179 plus the tolerance of the drill diameter.

-- 
Louis Mathis 
Member of the Technical Staff
Cobham Microelectronic Solutions
T : +1 858-505-3151

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-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of Ron Olinyk
Sent: Thursday, February 18, 2016 3:56 PM
To: [log in to unmask]
Subject: [DC] Mechanical drill -6mil aspect ratio

** Please note that the Sender of this email is from outside the Cobham NA IT Hub **

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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