Hebei Messi Biology Co., Ltd. said that the heat dissipation of electronic devices has become increasingly important because the packaging density of these devices has continued to increase, resulting in a large amount of heat generated in a compact packaging space. Poor heat dissipation will greatly reduce the life and performance stability of electronic products. In order to improve heat dissipation, electrical insulating materials with high thermal conductivity are required. A common way to improve the heat dissipation capacity of electronic products is to use polymer-based composite materials containing thermal conductive fillers.
Generally, silica, alumina, aluminum nitride, boron nitride, etc. are widely used as insulating thermal conductive fillers. Silica is cost-effective, but its thermal conductivity is low, and its heat dissipation capacity cannot cope with the increase in heat generation. Alumina has higher thermal conductivity than silica, so it has better heat dissipation, but the disadvantage is high hardness and easy wear of manufacturing equipment. Nitride-based fillers such as aluminum nitride and boron nitride have excellent thermal conductivity, but they are expensive and have limited application range. The thermal conductivity of magnesium oxide is one order of magnitude higher than that of silicon dioxide, about twice that of aluminum oxide [45-60W/(m.K), and its hardness is lower than that of aluminum oxide (Mohs hardness of aluminum oxide is 9, and Mohs hardness of magnesium oxide is 6), which can reduce the wear of manufacturing equipment. Its price is lower than that of nitride series thermal conductive fillers, and it is regarded as an excellent candidate for “thermal conductive filler”.
The use of MgO filler with a volume fraction of 56% achieved a thermal conductivity of up to 3W/(m.K) for epoxy molding compound (EMC). The thermal conductivity of the EMC obtained by 56vol% filling is about twice that of the traditional silica-filled EMC with the same filler volume fraction, and has equivalent electrical insulation, thermal expansion and water absorption properties.
However, a fatal harm of magnesium oxide is that its hygroscopicity is higher than that of silicon dioxide and aluminum oxide. When it is hydrated with moisture in the atmosphere, the volume expansion will cause cracks in the composite material and a decrease in thermal conductivity. Therefore, it is necessary to improve the hydrolysis resistance of magnesium oxide to improve its practicality. In addition, when magnesium oxide is used as a thermally conductive filler, it is necessary to have high filling properties in the resin composition to obtain higher heat dissipation performance. Therefore, magnesium oxide with high fluidity and good compatibility with the matrix is also extremely important. The moisture resistance of magnesium oxide can be effectively improved through special surface treatment.
Hydrothermal reaction was carried out under CO2 pressure conditions to obtain a core-shell structure powder of magnesium oxide coated with magnesium carbonate (MgCO3) with excellent moisture resistance. Magnesium carbonate is a stable compound with low solubility in water. The core of the magnesium oxide particle should be completely covered by the shell of the magnesium carbonate reaction layer to avoid the reaction of magnesium oxide with water. However, the thermal conductivity of magnesium carbonate is 15W/(m·K), which is lower than MgO. The production conditions should be controlled to make the shell (magnesium carbonate) as thin as possible and dense enough to ensure that water does not pass through the shell.
Moisture-resistant magnesium oxide powder is manufactured in multiple steps. First, magnesium oxide powder is sintered. After that, a silicon dioxide film is formed on the magnesium oxide powder by spraying, chemical deposition or spray bonding to cover the surface of the magnesium oxide powder. Alternatively, by mixing fine powdered silica in magnesium oxide powder and sintering it, the surface of magnesium oxide powder is coated with a silica film. Due to such a scheme, there are problems that the manufacturing process is increased and equipment required for manufacturing is required.
Low hygroscopic magnesium oxide powder is manufactured using a simple method and applied to a thermosetting resin composition. The electrical insulating layer made using the resin composition has excellent moisture resistance, processability and thermal conductivity, and is suitable for use as an insulating layer of a circuit board such as a printed circuit board on which a heat-generating component is mounted. The inventor used magnesium oxide with a silica mass content of 1 to 6% as a raw material and sintered it at 1650°C to 1800°C (temperature near the melting point of silica).
Through this operation, the silica that seeps out on the surface of magnesium oxide powder will not be completely separated from the magnesium oxide powder, but will cover the surface of the magnesium oxide powder, forming a silica film on the surface of the magnesium oxide powder. No special process is required, and only the original sintering process of magnesium oxide powder is required, which can simplify the manufacturing process. The surface of the obtained magnesium oxide powder is coated with a silica film, which can improve the hygroscopicity of the magnesium oxide powder. If the silica content is less than 1% of the total mass, the molten silica cannot fully cover the surface of the magnesium oxide powder, and the improvement of reducing the hygroscopicity of the magnesium oxide powder cannot be completed. In addition, if it is more than 6% of the total mass, the thickness of the silica film covering the surface of the magnesium oxide powder becomes thicker, and the original thermal conductivity of magnesium oxide cannot be exerted, and the thermal conductivity of the resin molded product is reduced.
In order to increase the filling rate of the powder to the resin, it is necessary to make the shape of the powder close to spherical. The surface of the spherical coated magnesium oxide powder is coated with a composite oxide. The composite oxide coating the surface of the magnesium oxide powder preferably contains one or more elements selected from aluminum, iron, silicon and titanium and magnesium, such as forsterite (Mg2SiO4), spinel (Al2MgO4), magnesium ferrite (Fe2MgO4), magnesium titanate (MgTiO3), etc. The first purpose of the composite oxide coating is to improve the moisture resistance of the magnesium oxide powder, and the second purpose is to make the spheroidization treatment step of the magnesium oxide powder easy. By forming a composite oxide with a melting point lower than the flame temperature on the surface of the magnesium oxide powder, the surface of the magnesium oxide powder is made low-melting, making it easier to spheroidize.
The melting point of the composite oxide is preferably 2773K or less, and more preferably 2273K or less. In addition, the invention document mentions that the spherical magnesium oxide powder can be surface-treated with a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent as needed to further improve the filling property. Silane coupling agent: vinyl trichlorosilane, vinyl trialkoxysilane, glycidoxypropyl trialkoxysilane, methacryloxypropyl methyldialkoxysilane, etc. Titanate coupling agent: isopropyl triisostearoyl titanate, tetraoctyl bis (ditridecyl phosphate) titanate, bis (dioctyl pyrophosphate) oxyacetate titanate, etc.
A method for producing a phosphorus-coated magnesium oxide powder with good water resistance and a resin composition containing the powder. Magnesium oxide coated with composite oxides has good water resistance, but it is still easy to have incomplete coating areas. In order to fill the incomplete coating areas of the composite oxide on the surface of magnesium oxide powder to improve water resistance, a coating layer of a magnesium phosphate compound is further formed on the coating layer formed by the composite oxide, and magnesium oxide powder with better water resistance performance has been obtained.