Evaluation of the Strength of Interface for Multi-Layered Materials in Photonic Devices

Recent electronic device packaging, for instance, CSP has a bonded structure of IC chip and polymers, and delamination occurs frequently at the interface between IC and a resin. Furthermore, thermal stresses which are caused by a temperature variation in the bonding process of CSP and heat cycles for environment temperature will influence on the strength of interface. In the present paper, the delamination test for specimens with different thicknesses of an interlayer is carried out to investigate the strength of multi-layered joints, and the critical value for the intensity of singularity at delamination of interface is determined through a numerical analysis using a boundary element analysis. In experiment, a silicon wafer is joined with a silicon-on-sapphire (SOS) plate by a resin. The SOS is composed of silicon film and sapphire plate. The joining strength in silicon, resin and SOS joints with a rectangular bonding area is investigated. The bonded specimens are prepared under different cooling rate. Load is applied to the specimen so as to delaminate at the interfaces of silicon film and sapphire. Delamination occurs at the interface between silicon film and sapphire plate in the specimen. Nominal stress for delamination is about 2.23–3.59 MPa. From a comparison of the strength of joint for rapid and slow cooling conditions, it is found that the residual stress reduces the strength of joint. In the numerical analysis, the intensity of singularity at the corner of interface for a unit load is determined. The intensity of singularity at the corner of the interface is related to the intensities of singularity in the radial direction and on the angle from the side free surface. The critical intensity of singularity for delamination of the interface is obtained by multiplying the force at delamination. Then, the critical intensity of singularity is determined as 168 MPa•mm^0.18 regardless of the thickness of silicon film.