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Hop is my guess. Warpage...
Joyce Koo
Researcher
Materials Interconnect Lab
Office: (519) 888-7465 79945
BlackBerry: (226) 220-4760
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of David D. Hillman
Sent: Tuesday, November 26, 2013 11:11 AM
To: [log in to unmask]
Subject: Re: [TN] Separation between the BGA sodler ball and pad on the PCB
Hi Andy - if you can send the pictures to Steve Gregory, he can post them
so we can all view them. What you describe sounds like Head on Pillow or
possibly Brittle Nickel Fracture but having the pictures will assist in
making an accurate assessment. One action you can take that will be very
informative is to run shadow moire on the BGA to measure how much warp
happens during the reflow process. Excessive package warp could be the
root cause of your issue.
Dave Hillman
Rockwell Collins
[log in to unmask]
From: Andrzej Zielinski <[log in to unmask]>
To: <[log in to unmask]>
Date: 11/26/2013 09:34 AM
Subject: [TN] Separation between the BGA sodler ball and pad on the
PCB
Sent by: TechNet <[log in to unmask]>
Dear Colleagues ..
I am facing an issue with the BGA part where in three locations we found
separation between the BGA solder balls and pads on the PCB (ENIG finish).
This condition was discovered during the cross-section that we have
requested from our local lab.
I can share few pictures I have taken from our report (can't attach the
whole document as this report is confidential to our business).
Basically this BGA is the plastic ACTEL package 896 pins, SAC305 finish,
soldered with leaded process using 62Sn/36Pb/2Ag solder paste. Temperature
was slightly elevated to accommodate SAC305 solder finish from the BGA
package.
The separation condition we have observed was only found in location A1,
A16 & T16 which are the corners of the BGA package. As well all 3
separations occurred after the reflow process was completed because there
is an evidence of completed inter-metallic fusion.
In location A16 & T16 you can see the copper is protruding of the pad but
I have been told this is not an issue and cause of the separation.
I was considering package or PCB warpage as the cause of this separation
or something related to cooling the board after reflow.
I asked our lab to measure the height of the solder balls across row A & T
and they all deem to be ok.
I have asked to check for the phosphorus content as the pad level to see
if this is related to black-pad symptom and the phosphorus was measured as
10.3%.
So far the board assembly house is adamant their reflow profile is
correct.
PCB manufacturer is confident with their PCB and pointing to the assembly
house.
There is a thought about poor sample preparation where the separation
issue would be caused by the lab (during cross-section).
We are attempting to perform another cross-section on different board but
here I am not really sure if this is the right way to go (extra cost).
Because I have never seen such a defect, I am not sure what should be the
next step to take.
Any advice guys ?
Andy
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