This example is a SMT connector where the solder joint appeared suspect.
Below is a BSE SEM image of a microsection through the suspect solder joint and its neighbors. Note the coplanarity issues for these connector leads.
This appeared to be a creep rupture failure of the solder joint where the lead that failed was under stress that caused creep (time dependent plastic deformation) of the solder joint. The vertical displacement of the lead after the solder joint fractured is the key feature that suggests this was a creep rupture failure.
Check out SEM Lab, Inc. to learn more.