Qualification of the Assembly Process of Flip-Chip BGA Packages ...

Texas Tech University, Nivetha Shivan, May 2012
Figure 6.1: CSAM Image Showing White Area in Underfill Region
Figure 6.2: SEM Image Showing Bump and Underfill Delamination
It is evident from the SEM image that the bump has been delaminated from the die and
the underfill has separated from the die as well. This is a serious concern as it could cause
electrical continuity failures in the functional device.
� A white halo around the bumps
When there is a vertical separation between the underfill material and the solder bumps, a
white area around the bump is seen in the CSAM image. This is a very common feature
seen in the CSAM images of the Flip Chip BGAs, hence is most cases these are not
considered as defects. These voids around the bumps are created due to filler particles
migrating around the bump. The Si particles in the UF material are of varied sizes. The
larger ones stick around the bump while the smaller particles creep into the tight space
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