BGAs are susceptible to damage from thermal-mechanical warpage stresses as well as mechanical bending stress.
The damage tends to be subtle and isn’t visible at low magnifications such as the image above of a microsectioned device.
At higher magnification a fracture became apparent in the upper layers of the die.
In the image above, the die attachment appears to have failed and there is a void in the molding compound due to a processing flaw at molding.
The bottom of the die separated from the molding compound and a fracture radiates away through the molding compound.
However, the PWB laminate under the BGA pads also showed fractures suggesting that the assembled PCBA was bent out of plane. It doesn’t take a great deal of bending to induce this type of damage, so the problem may not be apparent at the moment it is caused.
Check out SEM Lab, Inc. to learn more.