A Weak Solder-to-Intermetallic Interface Can Fracture After Reflow

What the evidence preview establishes

The joints fractured primarily between bulk solder and the tin-nickel intermetallic layer at the board surface. Evidence supported a combination of post-reflow mechanical or thermal stress and an unusually weak interface, with inadequate reflow and pre-plating nickel contamination remaining plausible contributors.

Why this case matters

Interfacial solder fractures can require both a weak metallurgical boundary and a later stress event. Evaluate reflow adequacy, finish preparation, depaneling, and board flexure together rather than assigning the failure to a single visible feature.