Hi Constantino,
I'll reply to this not from a standards perspective, but from a mechanical engineering perspective. It looks like there is excessive bending stress in the product. The sharp transition from the pad to the trace acts as a "stress riser" that concentrates stress at the corner and initiates the crack. It is also possible that the ductility of the copper is low to start with. 
The revised pad design will help, but it is a mitigation and does not address the root cause of failure. Look at both the material properties of the copper involved, the mounting of the PWA in the product, and the flexural response of the PWA to the stresses expected in transportation.

Regards,

Fritz Byle

-----Original Message-----
From: IPC-600-6012 [mailto:[log in to unmask]] On Behalf Of Constantino Gonzalez
Sent: Monday, December 22, 2008 21:04
To: [log in to unmask]
Subject: [IPC-600-6012] Pad to trace interface on BGAs.
Importance: High

Hello, I have a customer with a problem described below, Could you PLEASE HELP ME?
The problem is that several boards are being returned to the plant after failing in the field.
 
After Failure Analysis the engineers have found that the reason for the failure is that one of the traces of the PCB connected to a BGA pad is becoming cracked (Micro crack at BGA Pad AJ29 in the corner of the BGA) as showed in picture below:
 
image001.gif   image002.gif
 
They have concluded that Copper qty at PCB layer is not enough to support the normal Mechanical Stress in the unit chassis during the Transportation resulting in the trace and pad crack.
Based on Jedec JESD22B113 standard, they are suggesting that the customer change design on the traces connected to BGA pads as shown below: Does the
IPC7351 suggest anything related to this...
 
image003.gif
 
I have not heard before about this type of junction from traces to pads, and being honest I did not know the Jedec STD mentioned.
 
Have any of you ever heard about this special union from traces to BGA pads to avoid stress or any other recommendation to reinforce trace to pad joints?
Could you please enlight me with your thoughts or opinions about this issue?
 
Regards.
 
Constantino J. González, ACME, INC. - GALUSAMEX REPAIR Co.
President / Consultant Engineer - Official IPC MASTER INSTRUCTOR - IPC-A-610 Committee Chairman USA 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] 

  
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