Delamination between lead frame and epoxy in electronic packaging of surface mounting type is analyzed in terms of the J integral in fracture mechanics. The effects of chip/epoxy thickness ratio, and the material properties (elastic moduli, thermal expansion coefficient, etc) on the delamination are investigated taking into account the temperature dependence of the material properties, thus, a more realistic result is obtained.
The J integral as well as the stress intensity factor is reduced as the chip/epoxy thickness ratio increases when the initial crack exists in the interface of the lead frame and epoxy. As the crack length increases the J integral (accordingly, the stress intensity factor) increases, which suggests that the crack propagates if it starts growing. Also it is found that the initiation of the crack is more likely to take place at the early stage of thermal conduction when the temperature loading is applied.
