Hi Ron,
I haven't worked with the 6mil drills much, but if it were me I'd get a call into your favorite fab house and see what they think. From the aspect ratio it seems doable, but I think you'd have a struggle with the annular ring and breakout.
I know that the smaller a drill gets, in conjuction with thicker material, you'd see more drill wander. This is a small bit, so the 3mil annular ring may not cut it, you could have breakout. You may be able to start with a smaller pad on the topside and have a bigger landing pad on the other side of the board, but again you'd have to field those options with the fab house.
Hope that helps.
-Jeffrey
Jeffrey A. Jenkins
Sr. PCB Staff Designer, CID+/CIT
L-3 Communications, Linkabit Division
-----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
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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