Thanks all for the insight!
I think it makes the most sense now to use laser drilling on this
design. I was trying to avoid that to save cost, but it looks like it
might be more costly overall using a thru-drill (breakout, drill
breakage, ect).
Thanks Cherie for the L1-L3 suggestion -I think this will free up area
on the L2 layer for more routing -despite some added cost.
My only quandary now is whether to place power fanout on L2 (signal
layer) or split up the L3 (Gnd layer) with power copper. This design is
not super high speed (CPU, which is the only 0.5mm BGA, only runs at
24MHz)....Any advice?
Thanks
Ron
On 19/02/2016 2:49 AM, [log in to unmask] wrote:
> 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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