Tino,  

Intel has done a fair amount of work to quantify pad cratering.  Here is a rather poor picture I lifted from one of their presentations showing the epoxy resin fracture under the BGA pad.  You can see that if the epoxy is cracked, there is nothing to support the copper trace, and that will fracture with thermal cycle.  I will see if I can find the full Intel article.  Denny. 

-----Original Message-----
From: Constantino Gonzalez <[log in to unmask]>
To: [log in to unmask]
Sent: Mon, 22 Dec 2008 10:04 pm
Subject: [IPC-600-6012] Pad to trace interface on BGAs.



Hello, I have a customer with a problem described below, Could you PLEASE
ELP ME?
he problem is that several boards are being returned to the plant after
ailing in the field.

fter Failure Analysis the engineers have found that the reason for the
ailure is that one of the traces of the PCB connected to a BGA pad is
ecoming cracked (Micro crack at BGA Pad AJ29 in the corner of the BGA) as
howed in picture below:

mage001.gif   image002.gif

hey have concluded that Copper qty at PCB layer is not enough to support
he normal Mechanical Stress in the unit chassis during the Transportation
esulting in the trace and pad crack.
ased on Jedec JESD22B113 standard, they are suggesting that the customer
hange design on the traces connected to BGA pads as shown below: Does the
PC7351 suggest anything related to this…

mage003.gif

 have not heard before about this type of junction from traces to pads
, and
eing honest I did not know the Jedec STD mentioned.

ave any of you ever heard about this special union from traces to BGA pads
o avoid stress or any other recommendation to reinforce trace to pad
oints?
ould you please enlight me with your thoughts or opinions about this issue?

egards.

onstantino J. González, ACME, INC. - GALUSAMEX REPAIR Co.
resident / Consultant Engineer - Official IPC MASTER INSTRUCTOR - IPC-A-610
ommittee Chairman
SA Cell Phone: 605-381-5963 - Mexico Cell Phone: 55-2709 - 6392 -
mailto:[log in to unmask]> [log in to unmask] or  <mailto:[log in to unmask]>
[log in to unmask] 
 
oes your Company need Rework, Repair or Inspection of Electronic Assemblies
ervices. 
o you have too much Rework, Scrap or Rejects from your Customer…..Call us,
e can help!
ALUSAMEX REPAIR Co.
  



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