Preparetion and properties of SiO2 filled underfills with controllable chemical groups on the surface of filler

Abstract

With the miniaturization of electronic packages, the flip-chip gap has become smaller, and the SiO2 with very small particle size has been used as filler for underfill. The volume fraction of interfacial phase increases with the decrease of the size of SiO2. The control of the chemical groups on the silica surface has an important influence on the overall properties of underfill, for instance, processing fluidity, rheological behavior, thermomechanical properties, coefficient of thermal expansion (CTE), storage modulus, loss modulus, curing time, curing temperature, adhesive strength, etc. Here, we control the groups on the surface of SiO2 by changing the reaction conditions of two kinds of silane coupling agents. One of the modification methods is to use an acid as a catalyst in an aqueous alcohol solution to hydrolyze and graft the silane coupling agent onto the surface of silica. Another method is to directly modify the silica by using a silane coupling agent as a solution. Compared with in the presence of water, the silane coupling agent-modified silica reduces the hydroxyl groups on the silica surface more obviously under anhydrous conditions, which is better for the viscosity reduction and viscosity stability increase of underfill.