Grinding: The finishing process of the machined surface by the relative movement of the grinding tool and the workpiece under a certain pressure using abrasive particles coated or pressed on the grinding tool. Grinding can be used to process various metal and non-metal materials, and the processed surface shapes include planes, inner and outer cylindrical surfaces 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 uses mechanical, chemical or electrochemical effects to reduce the surface roughness of the workpiece to obtain a bright and flat 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 particle size used is coarser than that used for polishing, that is, the particle size is larger.
02
Ultra-precision polishing technology
Ultra-precision polishing is the soul of the modern electronics 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 several millimeters square can form ultra-large-scale integrated circuits composed of tens of thousands to millions of transistors through this "global flattening". For example, the computer invented by humans has changed from tens of tons to hundreds of grams today, which would not be possible without ultra-precision polishing.
Taking chip manufacturing as an example, polishing is the last link of the entire process, and its purpose is to improve the tiny defects left by the previous process of chip processing to obtain the best parallelism. Today's optoelectronic information industry has increasingly precise requirements for the parallelism of materials such as sapphire and single crystal silicon as optoelectronic substrate materials, which have reached the nanometer level. This means that the polishing process has also entered the ultra-precision level of the nanometer level.
How important is the ultra-precision polishing process in the modern manufacturing industry? Its application fields can directly illustrate the problem, including integrated circuit manufacturing, medical equipment, automotive accessories, digital accessories, precision molds, and aerospace.
Only a few countries such as the United States and Japan have mastered the top polishing process
The core component of the polishing machine is the "grinding disc". Ultra-precision polishing has almost stringent material composition and technical requirements for the grinding disc in the polishing machine. This steel disc made of special materials must not only meet the nano-level precision of automated operation, but also have an accurate thermal expansion coefficient.
When the polishing machine is in high-speed operation, if the thermal expansion causes thermal deformation of the grinding disc, the flatness and parallelism of the substrate cannot be guaranteed. And this thermal deformation error that cannot be allowed to occur is not a few millimeters or microns, but a few nanometers.
At present, the top polishing processes in the United States, Japan and other countries can already meet the precision polishing requirements of 60-inch substrate raw materials (super-large size). Based on this, they control the core technology of ultra-precision polishing technology and firmly grasp the initiative in the global market. In fact, mastering this technology means controlling 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 almost only conduct self-research at present.
What level is China's ultra-precision polishing technology at?
In fact, China is not without achievements in the field of ultra-precision polishing.
In 2011, the "Cerium Oxide Microsphere Particle Size Standard Material and Its Preparation Technology" developed by Dr. Wang Qi's team at the National Center for Nanoscience and Technology of the Chinese Academy of Sciences won the first prize of the China Petroleum and Chemical Industry Federation for Technological Invention, and the relevant nano-scale particle size standard material obtained the National Measuring Instrument License and the National First-Class Standard Material Certificate. The ultra-precision polishing production test results of the new cerium dioxide material surpassed the traditional foreign materials in one fell swoop, filling the gap in this field.
But Dr. Wang Qi said: "This does not mean that we have reached the top of this field. For the overall process, there is only polishing liquid but no ultra-precision polishing machine. At most, we are just selling materials."
In 2019, Professor Yuan Julong's research team at Zhejiang University of Technology founded the semi-fixed abrasive chemical mechanical processing technology. The series of polishing machines developed have been mass-produced in Yuhuan CNC Machine Tool Co., Ltd. More than 1,000 units have been mass-produced. They have been identified by Apple as the world's only precision polishing equipment for iPhone4 and iPad3 glass panels and aluminum alloy back panels. More than 1,700 polishing machines are used for mass production of Apple's iPhone and iPad glass flat panels
This is the charm of mechanical processing. In order to pursue market share and profits, you have to do everything you can to catch up with others, and the technology leaders will always improve and improve, and make them more precise. Constantly competing and catching up has promoted the great development of human technology.
