Theoretical and Experimental Study on the Thermally Induced Packaging Effect in COB Structures

As a packaging technique, COB (chip-on-board) structure provides a simple solution for high-density packaging by directly bonding a device chip to a second-level substrate with epoxy resin adhesive. However, CTE (coefficients of thermal expansion) mismatch of different materials in COB lead to coupling deformations and strains of the multilayer structure and greatly affect the reliability and performance of the devices. In this paper, a theoretical model is proposed for thermal deformation and strain distribution of the chip surface in COB packaging structures. In addition, a novel optical measurement approach named digital speckle correlation (DSCM) is applied to study the actual deformations in COB structures. The test data are compared with the calculated out-of-plane displacements of both the theoretical model and FEM simulations. And the effect of substrate type is also investigated