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September 2009

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Subject:
Re: Ground Pour Under BGA
From:
Kenneth Wood <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, Kenneth Wood <[log in to unmask]>
Date:
Wed, 16 Sep 2009 09:54:00 -0400
Content-Type:
text/plain
Parts/Attachments:
text/plain (109 lines) 
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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