An interfacial toughness between lead frame and epoxy molding compound in microelectronic packaging is measured. A sandwich type specimen used in the experiment is analyzed by FEM to obtain the individual stress intensity factors $K_I$ and $K_{II}$ with various load angles Φ$(=\tan^{-1}[P_x/P_y])$ and crack lengths α.
Here we employ the method proposed by Rice in order to define $K_I$ and $K_{II}$ unambiguously for the interfacial crack problem; namely, therefore, $K_I$ and $K_{II}$ are meant to the mode I and mode II stress intensity factors, respectively at the distance of $r = \widehat{r}$. In order to obtain separate values of $K_I$ and $K_{II}$ from the computed value of the J integral, we evaluate the mutual integral which has proposed by Chen and Shield for homogeneous material.
The critical load decreases as the crack length increases for the same load angle Φ, which is as expected, and it increases as the load angle Φ increases for the same crack length α, which leads to a higher interfacial toughness as Φ increases. Also the phase angle Ψ $(=\tan^{-1}[K_{II}/K_I])$ increases as Φ increases. Consequently, the interfacial toughness show a minimum approximately at Ψ=0. However the present experimental results for the interfacial toughness are less satisfactory due to the scattering of the data, which seems to require further study.
