High Performance Boron Nitride/Bismaleimide Composites

Studying high performance resins for the rapidly developed electronic information industry has become a hot issue. To meet the demands of the new generation of electronic information industry, these materials must have outstanding integrated performance including good processing characteristics, high mechanical properties, outstanding heat resistance, high thermal conductivity, favorable electric insulation and low thermal expansion. Obviously, the traditional resins, for example, epoxy resin, phenolic resin, polystyrene ether, polytetrafluoroethylene etc., cannot cut the above mustards. Bismaleimide (BMI) resin is the representative of present high performance thermosetting resins, which has outstanding integrated performance, especially high thermal and mechanical properties, good processing characteristics and dielectric properties, so it is regarded as the most promising high performance resin matrix in microelectronic field. However, present BMI resins exist some defects including relatively low thermal conductivity, high coefficient of thermal expansion and dielectric loss, so developing new high performance BMI resins is of great interesting.The aim of this thesis is developing new high performance materials with high thermal conductivity, low coefficient of thermal expansion and dielectric loss while maintaining the high heat resistance and good processing characteristics of original BMI resin. In this thesis, novel high performance hexagonal boron nitride (hBN)/BMI composites were designed and fabricated, and the main factors that affect the structure and the properties of the composites were discussed. Results show that with the increase of the content of hBN, the thermal conductivity increases linearly, while the coefficient of thermal expansion decreases linearly; in addition, dielectric loss gradually decreases and becomes more stable over the whole frequency from10-109Hz. In the case of the composite with35wt%hBN, its thermal conductivity, coefficient of thermal expansion in glassy state, and dielectric loss are about3.3,0.63and0.5times of the corresponding value of BMI resin, respectively. As is known to all, the interface between inorganic and organic phase plays a key role in the comprehensive properties of the composite. The surface of hBN has a very small amount of amine, second-amine and hydroxyl, but the activity of these functional groups is low, so the good dispersion of hBN in polymer is hard to achieve, and the interface adhesion between hBN and the resin matrix is not quite good, consequently, the advantage of hBN can not fully express in the composites. Therefore, the surface treatment of hBN becomes the key point in the preparation and application of high performance hBN/polymer composites. In this thesis, the weak sec-amine and hydroxyl are changed into active amine through the chemical bonds, and the grafting rate is about17.6wt%. This modified method not only increases the amount of functional group, but also enhances the functional activity, which provides a very good compatibility condition for hBN to get good dispersion in the resin matrix.The experimental results show that in the case of the composite with15wt%organized hBN, its storage modulus, dielectric loss, thermal conductivity and coefficient of thermal expansion are about1.2,0.56,1.11and0.92times of the corresponding values of pristine hBN/bismaleimide composite, respectively; moreover, the glass transition temperature of the former is15℃higher than that of the latter.