Hi Andy, dye and pry test ,after which cross-section, will eliminate the lab handling process. As mentioned by other,...warpage...temperature different will be the key suspect of the problem
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Phil Bavaro
Sent: Wednesday, 27 November 2013 4:51 AM
To: [log in to unmask]
Subject: Re: [TN] Separation between the BGA sodler ball and pad on the PCB
Andy,
I think we need more data.....is this a one off defect or is this happening on all of the PWAs in the lot?
Do all of the BGA balls have the same shape and heights on all four sides?
Can you share the reflow profile temps for the solderballs under this device? I've had an EMS not actually measure the temp at the balls yet claim they were doing it correctly.
Take same lot part and heat it up using your rework equipment and look for what Dave is referring to (if you don't have access to the SM).
The copper protruding out of the pad is intriguing.....doesn't sound right if everything actually melted correctly.
The location of the fracture is very important because it sounds like your reflow did not achieve the results you were after but we need a picture to confirm.
Phil
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Joyce Koo
Sent: Tuesday, November 26, 2013 8:13 AM
To: [log in to unmask]
Subject: Re: [TN] Separation between the BGA sodler ball and pad on the PCB
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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