The heat dissipation of electronic devices is becoming more and more important, because the packaging density of these devices continues 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.
To improve heat dissipation, electrically insulating materials with high thermal conductivity are required, and a common approach to improve the heat dissipation capability of electronics is to use polymer-based composites containing thermally conductive fillers.
Generally, silica, alumina, aluminum nitride, boron nitride, etc. are widely used as insulating and thermally 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 silicon dioxide, so it has better heat dissipation, but its disadvantages are high hardness and easy manufacturing equipment. wear and tear.
Nitride-based fillers such as aluminum nitride and boron nitride have excellent thermal conductivity, but are expensive and have limited applications. The thermal conductivity of magnesium oxide is an order of magnitude higher than that of silicon dioxide, about twice that of aluminum oxide [45-60W/(m.K), the reference value is from Konoshima], and the hardness is lower than that of aluminum oxide (alumina Mohs hardness 9, magnesium oxide Mohs hardness Its hardness is 6), which can reduce the wear and tear on manufacturing equipment, and its price is lower than that of nitride series thermal conductive fillers, so it is regarded as an excellent candidate for “thermal conductive fillers”.
In reference 1, the researchers used MgO filler with a volume fraction of 56% to achieve a thermal conductivity of epoxy molding compound (EMC) as high as 3W/(m.K). The thermal conductivity of EMC obtained by filling 56vol% is about Twice the EMC of conventional silica filling with the same filler volume fraction, and has equivalent electrical insulation, thermal expansion, and water absorption properties.
However, a fatal injury of magnesium oxide is that its hygroscopicity is higher than that of silica and alumina. When it hydrates with moisture in the atmosphere, volume expansion will cause cracks in composite materials and a decrease in thermal conductivity. Therefore, The hydrolysis resistance of magnesia needs to be improved to enhance its utility. In addition, when magnesia is used as a thermally conductive filler, it needs to have high filling in the resin composition to obtain higher heat dissipation performance, so magnesia with high fluidity and good compatibility with the matrix is also extremely important. Through special surface treatment, the moisture resistance of magnesium oxide can be effectively improved.
In reference 2, the researchers carried out hydrothermal reaction under CO2 pressurized conditions, and obtained magnesium carbonate (MgCO3)-coated magnesium oxide core-shell structure powder with excellent moisture resistance. Magnesium carbonate is a stable compound with low solubility in water. The core of magnesium oxide particles should be completely covered by the shell of the magnesium carbonate reaction layer to avoid the reaction of magnesium oxide with water, but the thermal conductivity of magnesium carbonate is 15W/(m K ), lower than MgO, the production conditions should be controlled so that the shell (magnesium carbonate) is as thin as possible and dense enough to ensure that water does not pass through the shell. The detailed process can refer to reference 2.
The moisture-resistant magnesia powder described in Japanese Patent Application Laid-Open No. 6H83648 is produced in multiple steps. First, the magnesia powder is fired. After that, a silicon dioxide film is formed on the magnesium oxide powder by sputtering, chemical deposition or spray bonding to cover the surface of the magnesium oxide powder. Alternatively, the surface of the magnesium oxide powder is covered with a silicon dioxide film by mixing fine powdered silica with the magnesium oxide powder and firing the powder. Since it is such an aspect, there exists a problem that the manufacturing process increases and the facility for manufacturing is required.
In the patent document CN102485804A, a simple method is used to manufacture magnesium oxide powder with low hygroscopicity, and it is applied to a thermosetting resin composition. The electrical insulating layer produced using the resin composition has excellent moisture resistance, processability, and good thermal conductivity, and is suitable as an insulating layer of circuit boards such as printed circuit boards on which heat-generating components are mounted. The inventors used magnesia with a silica mass content of 1 to 6% as a raw material, and fired it at 1650°C to 1800°C (a temperature near the melting point of silica). By this operation, the silica oozing out on the surface of the magnesium oxide powder does not completely separate from the magnesium oxide powder, but covers the surface of the magnesium oxide powder, forming a silicon dioxide film on the surface of the magnesium oxide powder. No special process is required, only the sintering process of the original magnesia powder is required, the production process can be simplified, and the surface of the obtained magnesia powder is covered with a silicon dioxide film, which can improve the hygroscopicity of the magnesia powder. According to the patent document CN102485804A, if the silicon dioxide content is less than 1% of the total mass, the molten silicon dioxide 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, since the thickness of the silicon dioxide film covering the surface of the magnesia powder becomes thicker, the original thermal conductivity of magnesia cannot be exhibited, and the thermal conductivity of the resin molded product decreases.
In order to improve the filling rate of the powder to the resin, the shape of the powder needs to be close to spherical. In the patent document CN1839182A, it is mentioned that the surface of the spherical coated magnesium oxide powder is coated with a composite oxide, and the composite oxide coated on the surface of the magnesium oxide powder is It 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) and so on. 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 facilitate the step of spheroidizing the magnesium oxide powder. By forming a complex oxide having a melting point lower than the flame temperature on the surface of the magnesia powder, the surface of the magnesia powder has a lower melting point and spheroidization is facilitated. The melting point of the composite oxide is preferably 2773K or lower, more preferably 2273K or lower. In addition, it is mentioned in the invention document that the surface of spherical magnesium oxide powder can be treated with silane-based coupling agent, titanate-based coupling agent, and aluminate-based coupling agent to further improve the filling property. Silane-based coupling agent: vinyltrichlorosilane, vinyltrialkoxysilane, glycidoxypropyltrialkoxysilane, methacryloxypropylmethyldialkoxysilane, etc. Titanate coupling agent: isopropyl triisostearyl titanate, tetraoctyl bis (ditridecyl phosphate) titanate, bis (dioctyl pyrophosphate) oxyacetic acid Ester titanate, etc.
CN1930084A provides a method for producing phosphorus-coated magnesium oxide powder with good water resistance and a resin composition containing the powder. Magnesium oxide coated with composite oxide has good water resistance, but there are still areas where the coating is not complete. This invention is to fill the area where the coating of the multiple oxides on the surface of the magnesium oxide powder is not complete to improve the water resistance. On the coating layer formed by the composite oxide, a coating layer of a magnesium phosphate compound is further formed to obtain water resistance. Magnesium oxide powder with better performance.