Messi Biology says that in semiconductor packaging, as an encapsulation material used to encapsulate semiconductor components around them, the cured resin compositions obtained by mixing and kneading electrically insulating thermosetting resins such as epoxy resins and fillers such as magnesium oxide powders and silicon dioxide powders are widely used. In semiconductor packages, as semiconductor components become highly integrated, operate at high speeds, and consume high amounts of power, the amount of heat generated increases. In order to quickly release the heat generated inside the semiconductor package to the outside, it is desirable to improve the thermal conductivity of the packaging material. As a method for improving the thermal conductivity of the package material, it is known to use magnesium oxide powder having high thermal conductivity as a filler, and to fill the package material with magnesium oxide powder in a high concentration so that a plurality of particles in the magnesium oxide particles are in contact with each other. By this method, heat is conducted between the magnesium oxide particles that are in contact with each other, and the overall thermal conductivity of the encapsulation material is thereby improved.
Magnesium oxide powder is a material with high thermal conductivity and excellent heat resistance and electrical insulation. Therefore, magnesium oxide powder is widely used as a filler in resin compositions such as thermally conductive resin compositions and electrically insulating resin compositions. As such magnesium oxide powder used as a filler for resin compositions, it is known that the shape of primary particles is rectangular magnesium oxide powder and spherical magnesium oxide powder.
As the magnesium oxide powder used as a filler for the resin composition, it is known that the primary particles have the shape of rectangular magnesium oxide powder and spherical magnesium oxide powder. According to the research, if the magnesium oxide powder having a rectangular shape of primary particles is added to a resin at a high concentration and kneaded, the particles of magnesium oxide collide with each other during kneading, and as a result, the corners of the particles are partially missing or the particles are broken, and the resin intrudes into the interstices between the particles and the particles, and it is difficult to obtain the solidified resin composition in which a plurality of particles are in direct contact with each other. On the other hand, in the case of a magnesium oxide powder having a spherical shape of primary particles, it is difficult to produce defects or rupture of primary particles even if a high concentration is added to the resin and pinched, but the thermal conductivity of the particles is low due to the small contact area of the particles with each other.
Therefore, it is an object of the present invention to provide a magnesium oxide powder which can be filled into a resin at a high concentration, and in which the particles are contacted with each other with a large contact area when filled into the resin, and in which the thermal conductivity between the particles can be improved. It is also an object of the present invention to: provide resin compositions and semiconductor packages having high thermal conductivity. The magnesium oxide powder of the present invention can be advantageously used as a filler for a resin composition in which electrical insulation and high thermal conductivity are desired, and said magnesium oxide powder has a BET-converted particle size in the range of 0.5 to 20 μm, and contains polygonal magnesium oxide particles having a chamfered shape in at least one of the vertices and/or edges of a rectangular body in an amount of more than 30% on an individual basis.