CREEP-BEHAVIOR OF A FLIP-CHIP PACKAGE BY BOTH FEM MODELING AND REAL-TIME MOIRE INTERFEROMETRY

In this paper, the creep behavior of a flip-chip package under a therm al load was investigated by using nonlinear finite element technique c oupled with high density laser moire interferometry. The real-time moi re interferometry technique was used to monitor and measure the time-d ependent deformation of flip-chip packages during the rest, while the finite element method was adapted to analyze the variation of stresses at edges and corners of interfaces with time by considering the visco elastic properties of the underfill and the viscoplastic behavior of t he solder balls. The results show that the creep behavior of the under fill and the solder balls does not have significant effect on the warp age of the flip-chip under the considered thermal load due to their co nstrained small volume. The variation of the time-dependent deformatio n in the flip-chip package caused by the creep behavior of the underfi ll and the solder balls is in the submicro scale. The maximum steady-s tate U-displacement is only reduced by up to 6.7 percent compared with the maximum initial state U-displacement. Likewise, the maximum stead y-state V-displacement is merely reduced by up to 10 percent compared with the maximum initial state V-displacement. The creep behavior slig htly weakens the warpage situation of the flip-chip package. However, the modeling results show that the localized stresses at corners and e dges of interfaces greatly decrease due to the consideration of viscoe lastic properties of the underfill and the viscoplastic properties of the solder balls, and, thereby, effectively preventing interfaces from cracking, in addition, the predicted deformation values of the flip-c hip package obtained from the finite element analysis were compared wi th the test data obtained from the laser moire interferometry techniqu e. It is shown that the deformation values of the flip-chip package pr edicted from the finite element analysis are in a fair agreement with those obtained from the test.