Effect of surface silanol density of silica fillers on the performance of packaging materials

Silica filler is a key material for the advanced electronic packaging, due to the low coefficient of thermal expansion (CTE) and the high stability, and has been widely used in the underfill, epoxy molding compound, ajinomoto build-up film, and other packaging materials. With the addition of silica filler, the packaging materials are expected to have low CTE, high modulus, low humidity absorption [1] and the high strength [2]. Despite the size, surface modification and the gradation as reported, the surface silanol density of the silica filler also has great impact on the performance of packaging materials. On one hand, the hydrophilic and polar silanol groups makes the packaging materials have low resistance for the humidity, and occupy the large dielectric loss. On the other hand, the surface silanol density determines the fully grafting ratio of silane coupling agent, and has significant impact on the surface energy of the filler, which are critical for the dispersibility of fillers in the resin matrix. Therefore, it is of great importance to study the effect of silanol content on the performance of packaging materials.In this paper, the acid-base titration method is used to test the surface silanol density of silica fillers by an automatic potentiometric titrator. The packaging materials performance, e.g., humidity absorption, dielectric loss, viscosity, CTE, et al., are fully characterized. The results show that under the optimum surface silanol density, the highest performance of the packaging materials can be achieved, which are promising for designing the high-performance packaging materials.