Radio Frequency Identification (RFID, RBdio Frequency Identification) technology is a non-contact automatic identification technology, which automatically recognizes the target object and obtains relevant data through spatial coupling (alternating magnetic field or electromagnetic field) to achieve the purpose of target identification and data exchange , The recognition work does not require manual intervention.
The basic working principle of the RFID system can be illustrated in Figure 1: The signal to be sent by the reader is encoded and loaded on a carrier signal of a certain frequency and sent out by the antenna, and the electronic tag entering the working area of the reader receives this pulse signal , The relevant circuit in the chip in the tag demodulates, decodes, and decrypts this signal, and then judges the command request, password, authority, etc. If it is a read command, the control logic circuit reads the relevant information from the memory, encrypts, encodes, modulates and sends it to the reader through the antenna in the electronic tag. The reader demodulates, decodes, and decrypts the received signal. Send to the central processing system for relevant data processing; if it is a write command to modify the information, the internal charge pump caused by the control logic to increase the working voltage, provide to erase and write the content in the EEPQM for rewriting, if it is judged that the corresponding password and authority do not match , The error message is returned.
Application range of RFID system
The era of the international Internet of Things is coming. It is reported that RFID technology has been widely used in European and American markets. With the maturity of RFID technology in the Chinese market and the reduction of RFID tag prices, RFID electronic tags will replace traditional one-dimensional bar codes and two-dimensional codes. If the two-dimensional code is an extension of the one-dimensional code label, the birth of RFID is a revolution in the label industry. Its application areas are mainly in the following areas:
1. Logistics Management
Logistics is the largest market application space for RFID, which can greatly improve the efficiency of logistics links and provide technical support for achieving zero inventory. Global retail giants Wal-Mart and German Metro have tried their best to promote the application of RFID tags, and have realized the use of RFID technology in supermarkets to realize product identification, anti-theft, real-time inventory and product expiration control.
2. Food safety
Food safety is a major issue of people’s livelihood in a country. RFID technology can ensure food safety in an all-round way through the entire management record of the original planting or breeding process of food, and the forward and reverse traceability of food circulation links.
3. Commodity anti-counterfeiting
Commodity anti-counterfeiting can guarantee normal market order and consumer reputation, and has a huge market space. The use of RFID anti-counterfeiting technology and wireless communication network can realize the quality inspection of goods at any time and any place, and it is currently used in tobacco and alcohol. Pilot projects are carried out on medicines and other commodities.
4. Applications in other fields
RFID has a very wide range of applications, such as traffic management, military product management, security, animal breeding and pet management, library management and other fields, all have great application prospects.
RFID tag antenna preparation technology
The core issues affecting the promotion of RFID are chip technology and cost. As shown in Figure 2, the RFID electronic tag is mainly composed of a substrate, an antenna, and a chip. The antenna layer is the main functional layer, and its purpose is to transmit the maximum energy in and out of the tag chip. Compared with the traditional etching method and the winding method, the direct printing method of the tag antenna greatly saves the cost.
1. Traditional manufacturing process of tag antenna
①Process and prepare the tag antenna by etching
The antenna should be printed with a resist film before etching. The PET film sheet should be covered with metal (such as copper, aluminum, etc.) foil; then the printing method (screen printing, gravure printing, etc.) or photolithography method should be used. Anti-corrosion ink is printed on the double-sided antenna pattern area of the substrate to protect the circuit pattern from being etched away during etching: then etching is carried out, that is, the cured sheet of the printed ink pattern is immersed in the etching solution to dissolve the unprinted resist ink layer Area metal; then remove the anti-etching ink on the metal layer of the antenna pattern of the film sheet, so that the tag antenna is obtained. Alternatively, photolithography is used to pre-coat a photoresist film on the surface of the copper-clad substrate, and cover the exposure with a corresponding mask. After developing and etching, the residual resist film on the plate is removed to obtain a complete antenna pattern.
②The process of preparing tag antenna by winding method
Currently. The manufacturing process of copper wire wound RFID tag antenna is usually carried out by using an automatic winding machine, that is, directly wound on the base carrier film and coated with insulating paint, and use low melting point baking varnish copper wire as the base material of the RFID tag antenna , And finally use adhesive to mechanically fix the wire and the substrate. Its technological process is shown as in Fig. 4. This method has high reliability, but the cost is too high for RF19 electronic tags.
2. Tag antenna printing process
Based on the disadvantages of the traditional tag antenna preparation method that it pollutes the environment and the cost is relatively high, and the process is complex, the production time of the finished product is long, and it will be replaced by a new process. Directly printing RFID tag antennas by printing is an environmentally friendly, energy-saving, and low-cost manufacturing process. Existing feasible printing methods for printing RFID tag antennas include screen printing and inkjet printing.
①Preparation of antenna by screen printing method
Screen printing is a process of direct printing using a stencil, that is, printing directly on paper or plastic film rolls with conductive ink. The general process flow is:
The screen printing of the label antenna is to sweep the conductive ink from the other side of the screen with a squeegee across the screen, and the ink penetrates the mesh gap of the antenna pattern on the screen, and sticks to the printed On the substrate. When printing RFID tag antennas, the antenna coils of RFID tags with different operating frequencies will correspond to different numbers of turns, the thickness of the coil and the distance between each turn (such as HF band using 13.56MHz chips, usually it requires a coil The number of turns is 6, the thickness is about 20um: UHF band uses 868MHz and 950MHz chips, the thickness of the coil section is about 4um), so the thickness of the printed ink layer, the width of each line and the outline of the dried figure are strict Tolerance range (such as the error of two overlapping overprints must be within 0.1mm).
The thickness of the ink layer of screen printing can reach up to 100um, which is several times that of flexo, offset and gravure printing, which is very advantageous for printing label antennas with conductive ink. In the actual printed circuit production, the thickness of the ink layer is generally required to be 8-12um, and the drying can be done by means of UV, IR and hot air.
② Preparation of antenna by inkjet printing method
Screen printing saves costs to a certain extent, but its ink uses about 70% of high-silver conductive silver paste to obtain antennas between 15-20um. It is a thick film printing method with high cost and some problems during the printing process. Solvent discharge, ink layer flexibility is poor. The inkjet printer is used to prepare the conductive circuit. It only needs to spray the conductive ink on the substrate by the nozzle of the inkjet printer according to the pattern designed by the computer system to form the conductive circuit. As a non-traditional printing method, inkjet printing has attracted wide attention in antenna production due to its short production cycle, no pollution, and low cost. Many well-known universities and research institutes at home and abroad have been committed to the research of inkjet conductive ink for a long time, and have made remarkable achievements. The research team led by Professor Li Luhai of Beijing Institute of Graphic Communication has successfully developed an inkjet conductive ink with a conductive film thickness of about 1um and a resistance of about 1Ω: Kovio of the United States launched an FFD prepared by inkjet printing nano-silicon ink in 2008 , Became the first commercial success case of inkjet printing ink; Suncheon University in South Korea developed a fully printed 1-bit radio frequency label based on carbon nanotube ink in 2009.
The use of inkjet printing for the production of RFID labels can be divided into three methods: ①Use inkjet printing to spray anti-corrosion ink, solder mask ink and character ink onto the copper clad board, and obtain the finished product after curing; ②Use ink The conductive ink of nano metal particles directly sprays the circuit pattern on the polyester film base, and forms the circuit after low-temperature firing and curing: ③The capacitors and resistors in the RFID label are manufactured by using ink with corresponding characteristics and inkjet printing. And other electronic devices. Compared with traditional printing methods. The use of inkjet printing can achieve faster production speeds and reduce printing costs. More importantly, it can increase its wiring density, thereby improving the quality of finished products.