Acceptable Average Gold Can Hide Severe Local Embrittlement

What the evidence preview establishes

The joints failed because Au-Sn intermetallic platelets segregated at interfaces and void surfaces, creating local gold concentrations above the embrittlement threshold. The platelets also may have obstructed volatile escape during reflow and contributed to severe voiding.

Why this case matters

Bulk gold calculations can miss interface segregation. Examine fracture surfaces and void walls, quantify local Au-Sn phases, and evaluate reflow-controlled platelet morphology before concluding that nominal gold dilution prevents embrittlement.