Ken,
With all the BGA pads and possible vias I don't see how a top side can
have a better mesh of copper paths than an internal layer. I would think a
poor copper mesh plane would be a generator of large GND return loops. Aka
antennas.
As for a GND plane being a few mils closer to the BGA and this reducing
EMI, that sounds like hog wash. Consider that conductor lengths from a ball
to chip is probably about 1/2 inch at times. How is adding 10 mils going to
affect anything?
I am open to Hog Wash ideas but they need to be well defined.
Thanks,
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Kenneth Wood
Sent: Wednesday, September 16, 2009 9:54 AM
To: [log in to unmask]
Subject: Re: [TN] Ground Pour Under BGA
It is an technique used in HDI designs that utilize micro vias.
Top layer is GND and layer 2 can be a power layer. It also helps with EMI.
Ken
Saturn PCB Design, Inc.
www.saturnpcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Robert Kondner
Sent: Wednesday, September 16, 2009 8:42 AM
To: [log in to unmask]
Subject: Re: [TN] Ground Pour Under BGA
Hi,
What would be the goal of placing atop side GND plane under the BGA?
Low Z Gnd return? Electrostatic shield?
Having a plane under the BGA vs another layer is not going to make a
difference in plane Z.
Sounds like a good chance of creating shorts if the solder mask chips or is
damaged during rework.
Bob Kondner
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Guy Ramsey
Sent: Wednesday, September 16, 2009 7:43 AM
To: [log in to unmask]
Subject: Re: [TN] Ground Pour Under BGA
IPC 7095, BGA Technology by Lau.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Toby Carrier
Sent: Tuesday, September 15, 2009 8:45 PM
To: [log in to unmask]
Subject: [TN] Ground Pour Under BGA
Hello all,
Is it a good idea to create a top layer ground flood under a BGA package? I
am
guessing that the fanout will not allow much area for the ground pour, am I
correct in thinking so? Does anyone have any good reference info on this
topic?
Also, if you don't have a ground pour under the BGA, how will that affect
the
impedance control of the traces going to the BGA ball?
Thanks for the help,
Toby
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