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BGA Head-in-pillow Defects

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BGA Head-in-pillow Defects | 25 August, 2008

Dear All,

Recently, we found a strange defect called "Head-in-pillow" defect at CPU socket BGA. The strange thing here is that this problem only appear on that CPU socket BGA and not on the others BGA which were also mounted on the PCB. We suspect this could be BGA ball containminated. Some say reflow issue...Confuse..Any suggestion?

Thanks in advance, Sean


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BGA Head-in-pillow Defects | 25 August, 2008

We've gone through this a couple times. Once it was because the device was warping in reflow. We confirmed with shadow moire that the corners were lifting up. The supplier fixed some things in their molding process to reduce the warpage. Another time it was because our plant had the wrong paste apertures and were getting inconsistent paste deposits.

There's been some articles written in the trade literature and conference proceedings about modifying reflow profiles to reduce the problem too, but in our case modifying the profile never helped.

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BGA Head-in-pillow Defects | 26 August, 2008

If this board is waved soldered than you may want to look at the wave causing the BGA to reflow a 2nd time when it goes over the wave. The board bows down and the the joint liquidfies and then hardens before the board fully goes back to flat which could cause this problem. If this is your case then you may want to change to a different paste or somehting.

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BGA Head-in-pillow Defects | 27 August, 2008

Hi Sean,

It's an old problem with no definitive cure for now. However, there are a couple of things to look for.

First of all the location(s) of HoP. If it was due to the componetn warpage, then it would be most probably in the middle and it should be rather a large package. If that is the case, then it can be fixe with tweaking teh reflow profile.

If the location is random, then there is a good chance that the bottom of the BGA balls was contaminated (contamination on top of the printed solder paste is less likely). In that case a cafull SEM/EDS analysis can help.

I had dealt with a few cases of both.



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