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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