The delamination problem in plastic ball grid array electronic package was investigated analytically and experimentally. The ANSYS code was used in the analysis to find the deformation and the stress distribution in electronic package due to the thermal mismatch between different materials at reflow temperature with saturated moisture pressure at the delaminated region. The stress intensity factor and the strain energy release rate at the tip of interfacial delamination were calculated using the fracture mechanics approach. The results show that the delaminaton occurs at the corner of the die pad and at the middle region of the die attach/die pad interface. The delaminaton grew from the middle region of the die attach/die pad interface, along the epoxy molding compoend/die pad interface, the epoxy molding compound/substrate interface to the exterior surface. Possible growth directions of the interfacial delamination in plastic ball grid array electronic package were identified and observed in the experimental results. In addition, the reflow temperature affected the stress distribution and the strain energy release rate at the tip of interfacial delaminaton.