An interfacial fracture toughness between lead frame and epoxy used in microelectronic packaging is measured. In this experiment, a sandwich type specimen is used, where a part of the side of the specimen is displacement-controlled to obtain the wide range of phase angle (= $\tan^{-1}[K_{II}/K_I]$). The specimen is analyzed by FEM to obtain the individual stress intensity factors $K_I$ and $K_{II}$, phase angle ψ, and J integral. We employ the method proposed by Rice in order to define $K_I$ and $K_{II}$ unambiguously for the interfacial crack problem and we evaluate the mutual integral proposed by Chen and Shield for homogeneous material in order to obtain separate values of $K_I$ and $K_{II}$ from the computed value of the J integral.
The interfacial fracture toughness increases as the absolute value of phase angle ψ increases. That is, the resistance to crack growth increases as the ratio of shear stress to normal stress at the crack tip increases. This result is consistent with other interfacial fracture toughness experiment.