Re: [PEDA] put via under the BGA pad

[Jeff Condit]

The safest practice is to not put vias in pads.  If you have to do it, there 
are three problems that arise: thermal deprivation, solder thieving and 
blowouts.  The first is minimized by using the smallest practical vias 
having the smallest acceptable thermals to planes and pours, coupled with an 
assembly reflow process thermal contour which preheats and soaks the board 
sufficiently long prior to the reflow peak.  Unconnected pads on internal 
layers are best retained to help stabilize the via barrel.  The last two can 
be solved by plugging these particular vias with conductive silver epoxy, 
sanding flush, and then plating over with copper such that a flat pad 
results without a visible hole and which meets co-planarity requirements.

Jeff Condit
.
----- Original Message ----- 
From: "é" <[EMAIL PROTECTED]>
To: "Protel EDA Discussion List" <[EMAIL PROTECTED]>
Sent: Thursday, October 28, 2004 7:07 PM
Subject: [PEDA] put via under the BGA pad


Hello everyone,
Your replies are really helpful to me. Thank you very much.
1)I want to put via under the BGA pad.  But I do not know if there is any 
problem when to install the BGA chip.

2)Another question, may be a fool question. When I do auto route for a 
6-layered board, no track is routed in MidLayer1 and MidLayer2. Could you 
please tell me what setup must be done.

Thank you very much.
Xiangchen

____________________________________________________________
You are subscribed to the PEDA discussion forum
To Post messages:
mailto:[EMAIL PROTECTED]
Unsubscribe and Other Options:
http://techservinc.com/mailman/listinfo/peda_techservinc.com
Browse or Search Old Archives (2001-2004):
http://www.mail-archive.com/[EMAIL PROTECTED]
Browse or Search Current Archives (2004-Current):
http://www.mail-archive.com/[EMAIL PROTECTED]



____________________________________________________________
You are subscribed to the PEDA discussion forum
To Post messages:
mailto:[EMAIL PROTECTED]
Unsubscribe and Other Options:
http://techservinc.com/mailman/listinfo/peda_techservinc.com
Browse or Search Old Archives (2001-2004):
http://www.mail-archive.com/[EMAIL PROTECTED]
Browse or Search Current Archives (2004-Current):
http://www.mail-archive.com/[EMAIL PROTECTED]