Investigation of viscoelastic effect of molding compound on the warpage and stresses of a power plastic package

In this paper, the creep deformation behaviour of a plastic power package u nder a thermal load condition was investigated by using a non-linear finite element technique coupled with a high-density laser moire interferometry. The real-time moire interferometry technique was used to monitor and measur e the time-dependent deformation of the plastic power package during the te st, while the finite element method was adapted to analyse the variation of stresses at the edges of all interfaces with time due to the viscoelastic properties of the molding compound. The results show that there does exist the obvious time-dependent deformation in the plastic power package under t he thermal load due to the creep behaviour of the molding compound. The max imum steady state U-displacement is reduced by up to 21% compared with the maximum initial one. Likewise, the maximum steady state V-displacement is a lso reduced by up to 20% compared with the maximum initial state V-displace ment. The creep deformation in the molding compound weakens the warpage sit uation of the plastic power package. In particular, such deformation greatl y relieves part of the stresses at the edges of all interfaces and thereby effectively prevents interfaces from cracking. In addition, the predicted d eformations of the plastic power package obtained from the finite element a nalysis were compared with the test data obtained from the laser moire inte rferometry technique, It is shown that the deformations of the plastic powe r package predicted from the finite element analysis are in a fair agreemen t with those obtained from the test when the viscoelastic behaviour of the molding compound was considered.