[PEDA] First BGA design with blind-buried vias.

[Richard Sumner]

Brian,

As I said, my board is old technology, except for the bga. I used 6 
layers, top, bottom and one internal wiring, one ground (not split) 
and 2 power planes, split to handle my 7 different power sources 
(fpga took 3 by itself!). And only ordinary thru vias, 10 mil 
finished, not tented. 30 ga ww wire fits in a 10 mil hole (not every 
board us perfect on the first rev), and the vias make nice test 
points. I did bring several unused fpga pins out to vias, to use as 
test points to probe inside the fpga (you have to compile what you 
want it to show, but the change, compile, reload and test cycle can 
be as short as 10 minutes).

Richard


At 05:50 PM 6/21/2006, you wrote:
>Richard, you basically hit the strategy I was working toward.
>
>I guess my question would bettee be how to configure the signal layer pairs
>in 99se & any other size/optimal settings regrading blind/buried vias.
>
>____________
>Brian G.
>
>
>
>----- Original Message -----
>From: "Richard Sumner" <rls at rsumner.com>
>To: "Protel EDA Discussion List" <PEDA at techservinc.com>
>Sent: Wednesday, June 21, 2006 5:08 PM
>Subject: Re: [PEDA] First BGA design with blind-buried vias.
>
>
> > Brian,
> >
> > I'm currently debugging a 6 layer board with a 676 pin bga. I
> > actually needed only 316 of the i/o pins, and I simply avoided the
> > deep rows of the bga. With only 1 trace between bga pads, I can get
> > the first two rows (counting from the outside in) on the top layer,
> > and using thru vias I can get the next two rows (equivalent, you have
> > to avoid blocking the planes with adjacent clearance around the vias)
> > on the bottom (or any other layer). This is a low volume product, not
> > very (parts) cost sensitive, so I can justify the larger package
> > (It's actually a trade off with a more expensive board). It was my
> > first board with ad2004, and I did make use of the fpga pin swapping
> > (much easier than with 99se, but still not simple)
> >
> > Richard
> >
> >
> > At 04:14 PM 6/21/2006, you wrote:
> >>Ok, I'm still using P99SE.
> >>
> >>     I need to upgrade an existing project with the main IC being a 240
> >> QFP,
> >>going to an Altera 484 pin, 1mm fineline BGA, however, there are some
> >>parts
> >>under the chip.
> >>
> >>     My PCB is only 6 layers.  I've never done blind/buried vias before in
> >>protel.  How should I configure protel to handle the blind-buried vias
> >>under
> >>the BGA pads.  Am I attempting something that shouldn't be done?  Can some
> >>BGA pads just be pads with no holes at all without upsetting the mounting?
> >>Is there any good reason to switch to microvias?
> >>
> >>
> >>____________
> >>Brian G.
> >>
> >>
> >>
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