Evaluation of Strength in Joints of Silicon and Sapphire Coating Silicon

Abstract

Recent electronic device packaging, for instance, Chip size package (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 bonding areas and geometries is carried out to investigate the strength of multi-layered joints. In particular, a silicon wafer is joined with a silicon-on-sapphire (SOS) plate by a resin. The SOS is composed of silicon film, SiO2 film and sapphire plate. The thicknesses of silicon film, SiO2 film and sapphire plate are 0.45μm, 0.2μm, 600μm, respectively. The joining strength in silicon, resin and SOS joints with triangular and rectangular bonding area is investigated. The triangular and rectangular shape bonding areas are 3mm2 and 12mm2, respectively. The bonded specimens are prepared under different cooling rate. Load is applied to the specimen so as to delaminate at the interfaces of SiO2 film and sapphire. From the delamination test, it is found that residual thermal stress and the geometry of bonding area affect the strength of interface. In the case of the triangular area specimen, delamination occurs at the interface between SiO2 film and sapphire plate in the silicon-resin-SOS specimen. The nominal stress for delamination is about 1.99MPa. In the case of rectangular bonding area specimen, delamination occurs at the interface between SiO2 film and sapphire plate in the silicon-resin-SOS specimen. Nominal stress for delamination is about 2.23MPa. 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.