This is a BSE SEM image of a glass rectifier diode that was chemically decapsulated to remove the glass case.
This is the diode die, which showed two separate breakdown sites that likely occurred simultaneously.
The die fractures are due to thermal shock due to the thermal effect rapid quenching by the surrounding die material immediately after the event.
This type of breakdown is likely due to a fast voltage transient.
BGA warpage can cause a condition called “pad cratering”.
This condition occurs when the assembly cools down below the solidus temperature after reflow soldering and the solder joint is put under tensile loading that exceeds the cohesive strength of the PWB laminate.
The condition often leads to open circuit failures that affect assembly yields.
BGA solder joint microsections are useful for evaluating microstructure, interfacial intermetallic layer thickness, voids, and other conditions. The example below shows a nominal BGA solder joint on 0.8 mm pitch.
In addition, the geometry of the solder joint can provide useful data such as deviation from the nominal condition and the magnitude of residual warpage.
For the above example, i.e. nominal BGA solder joint geometry, the parameters of the solder joint geometry are …
Nominal SJ Height (mm) = 0.25
PWB Pad Dia. (mm) = 0.50
BGA Pad Dia. (mm) = 0.40
h2 (mm) = 0.10
h3 (mm) = 0.15
r1 (mm) = 0.30
Solder Vol. (mm^3) = 0.0661
In summary, there is much to be learned from BGA solder joint microsections.