RFID printed antenna technology and application value
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RFID (Radio Frequency Identification) radio frequency identification technology has become the focus of attention of all countries. The basic components of the system include RFID electronic tags, RFID readers and antennas. Among them, the antenna is a device that receives or radiates the radio frequency signal power of the transceiver in the form of electromagnetic waves. In the RFID system, the antenna is divided into a tag antenna and a reader antenna. The goal of the tag antenna is to transmit the maximum energy into and out of the tag chip: when transmitting, the high-frequency current is converted into electromagnetic waves; when receiving, the electromagnetic wave is converted into a high-frequency current.
RFID antennas have a variety of manufacturing processes. This article will summarize and analyze the production technology of RFID antennas, focusing on the latest production methods of RFID antennas, RFID printed antennas and related technologies, and look forward to its prospects.
Three RFID antenna fabrication technologies
RFID antenna manufacturing technology mainly includes etching method, coil winding method and printed antenna. Among them, the RFID conductive ink printed antenna is a new technology developed in recent years.
The above RFID tag antenna manufacturing methods are respectively applicable to RFID electronic tag products of different frequencies. The low-frequency RFID electronic tag antenna is basically made by winding. The high-frequency RFID electronic tag antenna can be realized by the above three methods, but the etched antenna is mainly used, and the material is generally aluminum or copper, and the UHF RFID electronic tag antenna is It is mainly based on printed antennas.
The etching method is also called a subtractive fabrication technique. The production process is as follows (taking a copper antenna as an example): firstly laminating a flat copper foil on a plastic film; then coating the copper foil with a photosensitive paste, drying it and passing a positive film (pattern with a desired shape) It is irradiated; it is placed in a chemical developing solution, at which time the illuminated portion of the photoresist is washed away to expose copper; finally, it is placed in an etching bath, and all copper not covered by the photoresist is etched away to obtain a desired shape. Copper coil.
Because of its high precision, the etched printed antenna can match the interrogation signal of the reader, and the impedance of the antenna and the RF performance applied to the object are good, but its only drawback is that the cost is too high.
When the RFID tag is manufactured by the coil winding method, the label coil is wound and fixed on a winding tool, and the number of turns of the antenna coil is required (typically 50-l500 匝). This method is used for RFID tags with a frequency range of 125-134 KHz, which has the disadvantages of high cost and slow production speed.
The printed antenna directly prints conductive lines on the insulating substrate (film) with conductive ink to form an antenna and a circuit, which is also called an additive manufacturing technique. The main printing methods have been extended from screen printing to offset printing, flexographic printing, gravure printing, etc. The more mature production processes are screen printing and gravure printing. Advances in printing technology and its further application in the manufacture of RFID antennas have reduced the cost of producing RFID tags, thereby facilitating the use of RFID tags.
The printed antenna itself has the following unique features compared to etched antennas and wound antennas:
First, the printed antenna manufacturing can more accurately adjust the electrical performance parameters to optimize the card performance.
The main technical parameters of RFID tags are: resonant frequency, Q value and impedance. In order to achieve optimal performance, all RFID tag manufacturing techniques can be obtained by changing the antenna number, antenna size and wire diameter. The printed antenna technology can also be precisely adjusted to a desired target value by locally changing the width of the line, changing the thickness of the wafer layer, and the like.
Second, the printed antenna manufacturing can arbitrarily change the shape of the coil to meet the user's surface processing requirements.
In response to the versatile use of RFID cards and the increasing variety of personalization requirements, printed antennas can be easily changed to any shape, such as surface surfaces of different curvatures and angles, to meet customer requirements without any reduction. Use performance.
Third, the printed antenna can use a variety of different card base materials.
Printed antennas can be used with different card materials according to user requirements. In addition to PVC (polyvinyl chloride), PET-G (copolyester), PET (polyester), ABS (acrylonitrile-butadiene-benzene) can also be used. Ethylene copolymer), PC (polycarbonate) and paper-based materials. If winding technology is used, it is difficult to produce RFID tags that are adapted to harsh environmental conditions using materials such as PCs.
Fourth, printed antenna manufacturing is suitable for wafer modules provided by various manufacturers.
With the widespread use of RFID tags, more and more IC chip manufacturers have joined the team that produces RFID chip modules. Due to the lack of uniform standards, the electrical performance parameters are different, and the flexibility of the printed antenna structure can be matched with different wafers and modules in different package formats to achieve the best performance. [next]
RFID conductive ink and printed antenna technology
RFID printed antennas have stronger characteristics than traditional antennas, mainly depending on the characteristics of conductive inks and their perfect combination with printing technology.
Conductive inks consist of fine conductive particles or other special materials (such as conductive polymers, etc.) printed on flexible or rigid substrates to make printed circuits that act as wires, antennas, and resistors. The conductive ink determines the impedance of the RFID printed antenna to a large extent as an important parameter of the performance of the RFID antenna.
Depending on the manufacturing process, conductive inks can be classified into indirect conductive inks and direct conductive inks.
The conductive ink includes a carbon paste ink, a copper paste ink, a silver paste ink, and a gold paste ink according to a composition of a conductive factor contained in the conductive ink. Because of the lower resistivity of silver paste inks, it is the best choice for RFID tags. In addition, since copper is very fast in oxidation, it is not suitable for printing on RFID antennas.
From the perspective of future development, RFID printed antenna technology will become the mainstream RFID antenna fabrication technology, which stems from the following advantages of using conductive ink for antenna printing:
Low cost
The cost reduction depends mainly on the two aspects of the conductive ink material and the screen printing process. In terms of the cost of the material itself, the ink is cheaper than stamping or etching metal coils, especially in the case of rising prices of copper and silver, it is an ideal alternative to fabricating RFID antennas using conductive ink printing; In terms of material consumption, etching consumes a large amount of metal, and conductive ink printed antenna circuits are fast, material-saving, low-cost, and highly efficient.
One of the reasons why the screen printing process can reduce costs is that the investment in the introduction of printing equipment is much cheaper than the introduction of copper etching equipment. In addition, since there is no need to add additional investment due to environmental requirements during the printing process, the maintenance cost of production and equipment is lower than that of the copper etching method, thereby reducing the cost per unit of the label.
Good electrical conductivity
After the conductive ink is dried, since the distance between the conductive particles becomes small, the free electrons move in the direction of the applied electric field to form a current, and thus the RFID printed antenna has good electrical conductivity.
Easy to operate
Printing technology, as an additive manufacturing technique, is an easy-to-control, one-step process that is inherently a subtractive fabrication technique (such as etching).
No pollution
Photosensitive adhesives and other chemical agents that must be used in the copper etching process have a strong erosive effect, and the generated wastes and effluents cause greater pollution to the environment. Printing with a conductive ink directly on the substrate eliminates the need for chemical reagents and therefore has the advantage of no contamination.
Flexible substrate selection
Conductive inks can be printed on almost all substrates, including polyester, polyimide, ABS engineering plastics, PVC (polyvinyl chloride), polyethylene, polypropylene, polycarbonate, (coating) paperboard. Copper etching technology can only use substrates with high corrosion resistance, such as polyester, which are generally more expensive than the substrates selected for printing.
Printed conductive ink antennas are also capable of withstanding higher external mechanical stresses. In addition, RFID tag printed antennas made with conductive inks have better flexibility and higher reliability.
When printing RFID antennas with conductive inks, the following aspects of operation require special attention to achieve the best printing results.
Operating environment: The choice of printing environment has a direct impact on the printing effect. The dust and foreign matter in the printing area should be minimized. The environmental requirements are at least 100000 level clean room.
Pre-treatment: To ensure that the printed surface is clean and free of pollution, grease and oxide, etc., the shorter the residence time after the printing surface treatment, the better, to prevent oxidation or pollution.
Dilution: After adjusting the viscosity of the ink, add a small amount of thinner to improve the printing effect of automatic printing. Stir well for 10 minutes before use.
Pre-baking: Temperature and time can be adjusted according to the specific production process.
Storage: The temperature is stored at 20-25 degrees, protected from light and heat.
It can be seen that the use of conductive ink to make RFID printed antennas has high requirements on the process. For the conductive ink itself, it should have the characteristics of strong adhesion, low resistivity, low curing temperature and stable electrical conductivity to meet the functional requirements of the RFID antenna. [next]
RFID printing antenna application value
RFID technology has been used in logistics, retail, military, urban management, library management, food safety traceability and other fields. Especially in the retail field, RFID electronic tags have been added to merchandise packaging by numerous retailers due to their advanced technology and convenient management to track the flow of goods in real time. Major international retailers such as Wal-Mart and Metro have asked their suppliers to attach RFID tags to the products they offer.
Therefore, RFID and related technologies need to be continuously improved to meet the application needs of different industries and different fields. The use of conductive inks and advanced RFID antenna printing technology can optimize the application value of RFID electronic tags and further promote the application of RFID. Therefore, the application value of RFID antenna printing technology is mainly concentrated in the following two aspects:
First, reduce label costs and promote RFID applications across industries.
The high cost of labels has always plagued the RFID industry and users. The cost of RFID tags is the largest in all aspects of RFID. Therefore, in the process of promoting the application of RFID electronic tags, how to reduce the cost of the tags and improve the performance is a top priority.
For general merchandise, the use of RFID tags can lead to increased product costs and hinder the further application of RFID technology. But conductive ink technology can make RFID applications out of the cost bottleneck. The use of conductive inks for printing RFID tag antennas can greatly reduce the manufacturing cost of HF and UHF antennas, thereby reducing the overall cost of RFID tags.
Conductive ink RFID printed antenna has been used in RFID electronic tag tickets used in China's bus ride system. Anti-counterfeiting of products in medicine and other fields is also an area in which RFID electronic tags can be used. The reduction in the price of the label allows it to be applied to the anti-counterfeiting system of high value-added products such as medicines and alcohol.
Second, promote the development of the printing industry.
In addition to conductive inks, the production of RFID antennas requires advanced printing techniques. This undoubtedly broadens the direction and road of development for the printing industry, so that it is no longer confined to traditional paper printing, but has an intersection with the automatic identification industry and the semiconductor industry, which can promote the common progress of various industries.
In addition, in order to cooperate with the development of RFID electronic label technology and conductive ink RFID printed antenna, the printing industry will continue to develop more advanced printing technology, thus promoting the rapid development of the printing industry itself.
With the development of conductive inks and printing technology, RFID printed antenna technology will be popularized and used on a large scale, and the cost of RFID tags will be further reduced, thereby promoting the application of RFID technology in more fields.