Looking for issues that are present that does not cause failure? How far from the cliff is the part?

As part of the flow during reliability testing of devices, it is critical  to perform a failure inspection under magnification to ensure that  no devices have damage such as delaminations, voids, cracks  and material density changes. Performing failure inspection pre-stress  and post-stress will help identify issues that result in failure as  well as those that don’t so you can characterize how close to  failure your devices are.

• Die attach voiding and small delamination
• Minor cracking of the solder bumps
• Delamination of the metal layers in the substrate (like is shown on the via image)
• Voiding in the underfil or encapsulant
• Corrosion
• Change in the material appearance of the encapsulant, underfil, substrate
• Thickness of the intermetallic layers
• Just to name a few of the possible issues
• Or are your parts passing so well that some cost cutting materials consideration might be in order?