One-pot synthesis of silica nanospheres with bimodal size distribution for application in underfill composite

As the bump diameter and pitch of flip chip packages getting smaller, the application of nanosilica in underfill has been an inevitable trend. However, reducing filler particle size will cause server issues, such as serious particle agglomeration in the polymer matrix and significant increase of viscosity, which will lower the flowability and deteriorate other properties of underfill. In order to address this problem and take full advantages of the positive effects of the nanosilica on the underfill properties, a new kind of silica nanospheres with bimodal size distribution has been synthesized through a sol-gel process and was applied into underfill composite. With this kind of silica as reinforcement fillers, the dispersibility of the nanosilica particles in the polymer matrix was greatly improved, the viscosity was dramatically decreased and the glass transition temperature was increased especially at high filler loading in comparison with the corresponding single-sized nanosilica filled underfill composite.