Hi Ron,
A 6 mil drill in a 62 mil board is possible. What you'll find is your
available fabricators list will get a little smaller and the cost will get
higher. It will depend on the quantity you want to produce. If you're mass
producing these, then you may run into some issues. If you're making less
than 6,000 per year, you'll be ok finding fabricators.
Not only do the drills wander, but they break. This causes "fallout" in
production and the cost of scrap & tooling gets added to your order. You
may want to look at dual blind laser drilling: L1 to L2 and L1 to L3 (same
from the bottom) with no blind vias can open up connectivity and keep costs
down. Especially when L2 & Ln-1 are GND layers. Keeps other signal paths
clear using through vias and allows breakout on L3 & Ln-2. It will be a
cost trade-off negotiation.
I agree with Jeff, talk with your fabricators and find out what will work
best for them. Most likely they will want a 4-5 mil annular ring on the
through via. However, you can make a 12 mil pad on a 6 mil laser drill
(L1-L3) and a 10 mil pad on a 4 mil laser drill (L1-L2).
Also, there are noise canceling benefits to having GND only 2-3 mils from
the outer layers. This gives you more ammo for the "cost trade-off" of
laser drilling.
Good luck!
Cherie Litson, IPC-CID+/CMIT
Litson1 Consulting
PCB Design Solutions & Training
206-619-8844 [log in to unmask]
In a message dated 2/18/2016 3:58:43 P.M. Pacific Standard Time,
[log in to unmask] writes:
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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