Study of the thermomechanical coupling effect in COB packaging structures

As a packaging technique, COB (Chip on Board) structure is usually used in IC and MEMS. However, the thermomechanical coupling effect because of CTE mismatch of different materials in COB will greatly affect the reliability and performance of the devices. A theoretical model for thermal deformation distribution of the chip surface in COB packaging structure is proposed. And a novel optical measurement approach named digital speckle correlation method (DSCM) was applied to study the actual deformations in COB structure under certain temperature excursions. The test data are compared with the calculated out-plane displacements of both the theoretical model and FEM simulations. And we also compared the effect of substrate type. The theoretical model was verified by the result of FEM simulations and experimental testing. And the value of the model to the package-device co-design is also discussed.