As a filler, silicon micropowder is used in copper clad laminates, which can not only reduce costs, but also improve some properties of copper clad laminates (such as thermal expansion coefficient, bending strength, dimensional stability, etc.), and is a real functional filler. Therefore, the market The FR-4 copper clad laminate with the largest output mainly uses silicon micropowder as a filler.
1. Several kinds of silicon powder commonly used in copper clad laminates
At present, silicon micropowder for CCL is mainly divided into the following categories:
(1) Crystalline silicon powder
That is, selected high-quality quartz ore, quartz powder processed by ore washing, crushing, magnetic separation, ultra-fine crushing, grading and other processes. After the use of crystalline silicon micropowder, the stiffness, thermal stability and water absorption of the copper clad laminate have been greatly improved. With the rapid development of the copper clad laminate market, the output and quality of the crystalline silicon micropowder have been greatly improved.
(2) Fused silica micropowder
That is, the selected quartz raw materials with high-quality crystal structure, through acid leaching, water washing, air drying, high temperature melting, crushing, manual sorting, magnetic separation, ultra-fine crushing, grading and other processes to refine silicon powder.
Compared with crystalline silicon micro, it has lower density (2.2g/cm3), lower dielectric constant, lower thermal expansion coefficient (0.5×10-6/K), this kind of powder is mainly used in high frequency Used as filler in copper clad laminates.
Today, with the continuous development of high-frequency technology, from the traditional frequency below 1GHZ to 2G, 3G, 5G and even higher frequencies, the dielectric constant Dk and loss factor Df of the copper clad laminate have become particularly important indicators for applications in the high-frequency field. The high Dk of the CCL will slow down the signal during the transmission process, and the high Df will cause the loss of the signal during the transmission process. Therefore, how to reduce the Dk and Df of the CCL has become a hot issue in the CCL industry.
At present, the commonly used methods for reducing Dk and Df are: selecting resin with low Dk and Df and selecting glass fiber with low Dk and Df. Reducing the Dk and Df of glass fiber is mainly achieved by changing the chemical composition of glass fiber, that is, changing the melting formula of glass, which requires close cooperation of upstream manufacturers. Because such resins are generally more expensive and less processable. Therefore, under non-special circumstances, CCL manufacturers are more willing to modify the epoxy resin and add fillers to reduce the Dk and Df values of the board. Fused silicon powder is a good choice as a filler.
(3) Composite silicon micropowder
Composite silica powder is also called low hardness silica powder. The silicon micropowder is made of several inorganic minerals, which are melted into an amorphous glass body with a precise proportion, and processed by crushing, magnetic separation, ultra-fine crushing, and grading.
The Mohs hardness of this powder is about 5.5, and the composition of silica is greatly reduced. The change of chemical composition can effectively reduce the hardness of silicon powder, reduce the wear of the drill bit during the drilling process, and reduce the drilling process. Dust pollution.
(4) Spherical silica powder
It refers to the silica micropowder that the individual particles are spherical, and the irregularly shaped quartz powder particles are instantly melted at high temperature to spheroidize under the action of surface tension, and then processed by cooling, grading, mixing and other processes. This kind of powder has good fluidity, high filling rate in resin, low internal stress, stable size and low thermal expansion coefficient after it is made into a plate.
The technology of spherical silicon micropowder has been very mature in Japan. At present, there are several domestic manufacturers that can mass-produce spherical powder for epoxy molding compound. Due to the high price of spherical powder, it has not been used on a large scale in the CCL industry at present, and a small amount is used in IC carrier boards, HDI boards and other fields. It is believed that with the development of high-end CCL, the application of spherical powder will increase day by day.
(5) Active silicon powder
That is, the silicon micropowder is modified by adding an appropriate amount of coupling agent to the silicon micropowder and modifying it at an appropriate temperature. This kind of powder has very low viscosity in the resin, and has strong bonding performance with the resin. The resulting sheet has good peel strength, excellent high temperature resistance, and can also improve drilling performance.
However, at present, the resin systems used by CCL manufacturers are not the same. It is difficult for silicon micropowder manufacturers to make the same product suitable for all users’ resin systems, and CCL manufacturers prefer to add modifiers due to their usage habits, so the active It will take time to promote the use of silicon micropowder in the copper clad laminate industry.
2. The development trend of silicon micropowder in copper clad laminates
(1) Promising ultrafine crystalline silica powder
The average particle size of ultra-fine silicon powder currently used in CCL is 2-3 microns. With the development of ultra-thin substrate materials, fillers with smaller particle size and better heat dissipation will be required. In the future, copper clad laminates will use ultra-fine fillers with an average particle size of about 0.5-1 microns. Crystalline silicon powder will be widely used because of its good thermal conductivity. Considering the dispersion of fillers in resin and ensuring the smoothness of the gluing process Development, crystalline silica micropowder is likely to be used in conjunction with spherical powder. Although there are many fillers with better thermal conductivity than crystalline silica powder, such as alumina spherical powder, they are very expensive and difficult to be used by copper clad laminate manufacturers on a large scale in the future.
(2) Rapidly developing fused silica micropowder market
With the development of various advanced communication technologies, a variety of high-frequency equipment has been widely used, and its market has grown at a rate of 15-20% every year, which will certainly drive the rapid development of the molten silicon powder market to a certain extent.
(3) Stable composite silicon micropowder market
At present, most domestic CCL manufacturers have begun to use composite silicon micropowder instead of crystalline silicon powder, and gradually increase the proportion of use. The market of composite silicon powder will reach saturation in the next two years. While increasing production, silicon micropowder manufacturers are also constantly optimizing product indicators. In order to further reduce drill bit wear, it is necessary to develop fillers with lower hardness.
(4) Optimistic high-end spherical powder market
PCB substrate materials are rapidly developing in the direction of thinning, especially the thinning of substrate materials for HDI multilayer boards is more prominent. Many portable electronic products require more layers and thinner PCBs as they continue to push them to be “thin, light, small” and multi-functional. With the development of electronic products in the direction of miniaturization and integration, the proportion of HDI boards will increase significantly in the future. At the same time, domestic IC carrier board projects are also being carried out in many places across the country. In a good market environment, it is even more required that domestic silicon micropowder manufacturers can launch high-end spherical silicon powder products with high purity, high fluidity, low expansion coefficient and good particle size distribution. Therefore, the application prospect of spherical silicon powder in the copper clad laminate industry is very worth looking forward to. .