Thermal deformations of CSP assembly during temperature cycling and power cycling

In this paper, thermal deformations of CSP assemblies during temperature cycling and power cycling were investigated using high sensitivity moire interferometry and finite element analysis. To observe the thermal deformations during thermal cycling, a moire test was performed for isothermal loading conditions from 125°C to 25°C. In the case of power cycling, the actual operating conditions were simulated by using a thermal chip in the package, and the real-time moire interferometry technique was used to measure the steady-state thermal deformation. The results show that the assembly bends in the opposite direction in power cycling as compared to its bending during temperature cycling. In addition, test results obtained from the moire interferometry technique were compared with predicted values obtained from finite element analysis. It is shown that the deformation values predicted from finite element analysis have good agreement with those obtained from the test. The FEM results show that the shear deformations of solder joints are almost same, but the normal deformations are fundamentally different between temperature cycling and power cycling