Novel pore-sealing of ordered, porous silica, SBA-15 for low-k underfill materials

Underfill materials, consisting of organic resin and inorganic filler, have been widely employed in flip-chip technology for preventing the failure of solder joints during packaging process. In order to meet the requirements of high frequency device applications, low-dielectric-constant underfill is highly desired to alleviate the power consumption issue. However, it is disadvantageous to introduce low-k into organic resin because of its high cost and low volume fraction. Alternative approach is to use highly porous silica filler with appropriate pore sealing prior to mixing with epoxy. In this paper, a siloxane compound, polymerized vinyl-trimethoxysilane (poly-VSQ), was synthesized and applied to an ordered, porous silica structure, SBA-15 to study its effectiveness in pore sealing and interaction with SBA-15 matrix for low-k underfill applications. We have developed a convenient pore sealing treatment using poly-VSQ to achieve a 10.9% reduction (from 3.2 to 2.85) in dielectric constant of underfill material with 15% filler content by fully retaining the high porosity (61%) of SBA15. Moreover, excellent mechanical strength could be maintained as 3.0 GPa without any interfacial delamination.