Abstract: Based on the Saint Venant's principle, the finite element model of flip chip packaging was established by combing the global model and sub model. The stress and strain of the micro copper pillar bumps were analyzed to study the failure mechanism of the micro copper pillar bumps by high density flip chip packaging and to analyze the crack growth behavior of the key micro copper pillar bump. The results show that the micro copper pillar bump with the maximum distance from the center of the chip has the biggest deformation and the highest stress, which is the key micro copper pillar bump of the flip chip packaging. The accumulative plastic strain energy density are mainly distributed on the substrate side of the key micro copper pillar bump, and the maximum accumulative plastic strain energy density is outside of the micro copper pillar bump, and gradually decreases towards the inside, which shows that the crack initiation appears on the outside of the micro copper pillar bump at substrate side, and expands from the outside to the inside of the solder throughout the whole micro copper pillar bump, eventually lead to the failure. The results are consistent with the simulation results.