I saw such a report a long time ago: scientists from Germany, Japan and other countries spent 5 years and spent nearly 10 million yuan to create a ball made of high-purity silicon-28 material. This 1kg pure silicon ball requires Ultra-precision machining, grinding and polishing, precision measurement (sphericity, roughness and quality), it can be said to be the roundest ball in the world.
Let’s introduce the ultra-precision polishing process.
01 The difference between grinding and polishing
Grinding: Using abrasive particles coated or pressed on the grinding tool, the surface is finished by the relative movement of the grinding tool and the workpiece under a certain pressure. Grinding can be used to process various metal and non-metal materials. The processed surface shapes include plane, inner and outer cylindrical and conical surfaces, convex and concave spherical surfaces, threads, tooth surfaces and other profiles. The processing accuracy can reach IT5~IT1, and the surface roughness can reach Ra0.63~0.01μm.
Polishing: A processing method that reduces the surface roughness of the workpiece by mechanical, chemical or electrochemical action to obtain a bright and smooth surface.
The main difference between the two is that the surface finish achieved by polishing is higher than that of grinding, and chemical or electrochemical methods can be used, while grinding basically only uses mechanical methods, and the abrasive grain size used is coarser than that used for polishing. That is, the particle size is large.
02 Ultra-precision polishing technology
Ultra-precision polishing is the soul of modern electronic industry
The mission of ultra-precision polishing technology in the modern electronics industry is not only to flatten different materials, but also to flatten multi-layer materials, so that silicon wafers of a few millimeters square can form tens of thousands to VLSI composed of millions of transistors. For example, the computer invented by humans has changed from tens of tons to hundreds of grams today, which cannot be realized without ultra-precision polishing.
Taking wafer manufacturing as an example, polishing is the last step of the whole process, the purpose is to improve the tiny defects left by the previous process of wafer processing to obtain the best parallelism. Today’s optoelectronic information industry level requires more and more precise parallelism requirements for optoelectronic substrate materials such as sapphire and single crystal silicon, which have reached the nanometer level. This means that the polishing process has also entered the ultra-precision level of nanometers.
How important the ultra-precision polishing process is in modern manufacturing, its application fields can directly explain the problem, including integrated circuit manufacturing, medical equipment, auto parts, digital accessories, precision molds and aerospace.
The top polishing technology is only mastered by a few countries such as the United States and Japan
The core device of the polishing machine is the “grinding disc”. Ultra-precision polishing has almost strict requirements on the material composition and technical requirements of the grinding disc in the polishing machine. This kind of steel disc synthesized from special materials must not only meet the nano-level precision of automatic operation, but also have an accurate thermal expansion coefficient.
When the polishing machine is running at high speed, if thermal expansion causes thermal deformation of the grinding disc, the flatness and parallelism of the substrate cannot be guaranteed. And this kind of thermal deformation error that cannot be allowed to occur is not a few millimeters or a few microns, but a few nanometers.
At present, top international polishing processes such as the United States and Japan can already meet the precision polishing requirements of 60-inch substrate raw materials (which are super-sized). Based on this, they have mastered the core technology of ultra-precision polishing processes and firmly grasped the initiative in the global market. . In fact, mastering this technology also controls the development of the electronics manufacturing industry to a large extent.
Faced with such a strict technical blockade, in the field of ultra-precision polishing, my country can only conduct self-research at present.
What is the level of China’s ultra-precision polishing technology?
In fact, in the field of ultra-precision polishing, China is not without achievements.
In 2011, the “Cerium Oxide Microsphere Particle Size Standard Material and Its Preparation Technology” developed by the team of Dr. Wang Qi from the National Center for Nanoscale Sciences of the Chinese Academy of Sciences won the first prize of the China Petroleum and Chemical Industry Federation’s Technology Invention Award, and related nanoscale particle size standard materials Obtained the national measuring instrument license and the national first-class standard substance certificate. The ultra-precision polishing production test effect of the new cerium oxide material has surpassed the foreign traditional materials in one fell swoop, filling the gap in this field.
But Dr. Wang Qi said: “This does not mean that we have climbed to the top of this field. For the overall process, there is only polishing liquid but no ultra-precision polishing machine. At most, we are only selling materials.”
In 2019, the research team of Professor Yuan Julong of Zhejiang University of Technology created the semi-fixed abrasive chemical mechanical processing technology. The series of polishing machines developed have been mass-produced by Yuhuan CNC Machine Tool Co., Ltd., and have been identified as iPhone4 and iPad3 glass by Apple. The world’s only precision polishing equipment for panel and aluminum alloy backplane polishing, more than 1,700 polishing machines are used for mass production of Apple’s iPhone and iPad glass plates.
The charm of mechanical processing lies in this. In order to pursue market share and profit, you have to try your best to catch up with others, and the technology leader will always improve and improve, to be more refined, to constantly compete and catch up, and to promote the great development of human technology.
Post time: Mar-08-2023
