Failure paths of the Cu-based leadframe/EMC joints

Copper-based leadframe sheets were oxidized in a black-oxide forming solution and molded with epoxy molding compound (EMC) to measure the fracture toughness of leadframe/EMC interface using sandwiched double-cantilever beam (SDCB) specimens and sandwiched Brazil-nut (SBN) specimens. Results showed that the pebble-like Cu2O precipitates on the leadframe had almost no adhesion to the EMC, while the opposite was true for the acicular CuO precipitates. Under the mixed-mode loading condition, the fracture toughness increased parabolically with mode mixity. For phase angle (ψ)<−34°, the interface crack kinked into the EMC. Failure path study based on XRD, AFM, SEM, EDS and AES analyses revealed that the failure path varied significantly with the surface condition of leadframe prior to molding and the phase angle.