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BGA pads lifting from PCB

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EWC

#59172

BGA pads lifting from PCB | 1 July, 2009

can anyone suggest possible causes or further analysis for the lifted pads in attached picture. thanks.

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kpm

#59188

BGA pads lifting from PCB | 2 July, 2009

On first glance it looks like those particular pads were not attached to any traces. If I had to guess I would say that your rework profile got hot enough to melt away the glue holding the pads to the board and they came away with your part when you lifted it off the pads due to surface tension with the solder. This can be a problem sometimes because those pads are not attached to any other copper they heat up more quickly. I would recommend attaching a thermocouple to one of the pads that lifted and a pad more internal to the BGA and tweaking your profile.

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EWC

#59189

BGA pads lifting from PCB | 2 July, 2009

thanks kpm. agree the cause of those pads lifting. all of them were no connects so they cannot be the cause of the electrical failure. when the bga was removed, all the solder balls on the pcb turned into conical shape due to the separation, except for two balls (which appear to have flat tops) in one corner of the board. the corresponding two pins on the bga package also showed flat irregular solder. that seems to indicate that those two pins did not have a good solder joint. could that have been due to head-in-pillow defects at assembly, or broken joint after assembly? the board came back from the field after exhibiting intermittent failures.

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kpm

#59214

BGA pads lifting from PCB | 7 July, 2009

I agree with your assessment of the two pins with irregular solder. The head-in-pillow or broken joint are both probable events for your defect. At this point in the process it will probably be difficult to pinpoint the exact cause. If it was a broken joint though I would think it would have reflowed when you removed the BGA and look much the same as the other joints when you removed your part. I would think that intermittent failures also point to defects of this type. Given that the component would still be connected by touching the pad. So end guess, possible contamination on those pads, BGA or PCB.

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EWC

#59220

BGA pads lifting from PCB | 7 July, 2009

kpm, you are probably right. under magnification those two pads show some exposed copper which means that they were contaminated or had insufficient solder paste before reflow.

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