RFID (Radio Frequency Identification) radio frequency identification technology has become the focus of attention in various countries. The basic components of its system include RFID electronic tags, RFID readers and antennas. Among them, the antenna is a device that receives or radiates the RF signal power of the radio transceiver in the form of electromagnetic waves. In RFID systems, antennas are divided into tag antennas and reader antennas. The goal of the tag antenna is to transmit maximum energy into and out of the tag chip: when transmitting, convert high-frequency current into electromagnetic waves; when receiving, convert electromagnetic waves into high-frequency current.
There are many manufacturing processes for RFID antennas. 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 manufacturing technologies
RFID antenna manufacturing technology mainly includes etching method, coil winding method and printed antenna. Among them, 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, and the high-frequency RFID electronic tag antenna can be realized by the above three methods, but the etching antenna is mainly used, and the material is generally aluminum or copper, and the UHF RFID electronic tag antenna is Mainly printed antennas.
The etching method is also called a subtractive manufacturing technique. The production process is as follows (take copper antenna as an example): first, a flat copper foil is laminated on a plastic film; then photosensitive adhesive is coated on the copper foil, and after drying, it passes a positive film (pattern with the desired shape) It is irradiated; placed in a chemical developer, at this time the light-sensitive part of the photoresist is washed away, exposing copper; and finally placed in an etching bath, all the copper that is not covered by the photoresist is etched away to obtain the desired shape Copper coil.
Because of its high accuracy, the etched printed antenna can be matched with the interrogation signal of the reader. At the same time, the impedance of the antenna and the RF performance applied to the article are very good, but its only disadvantage is its high cost.
When the RFID tag is manufactured by the coil winding method, the tag coil is wound on a winding tool and fixed. At this time, the number of turns of the antenna coil is required to be large (typically 50-1500 turns). This method is used for RFID tags in the frequency range of 125-134 KHz, which has the disadvantages of high cost and slow production speed.
The printed antenna directly prints the conductive circuit on the insulating substrate (film) with conductive ink to form the antenna and the circuit, also known as the additive manufacturing technology. The main printing method has been expanded from only screen printing to offset printing, flexographic printing, gravure printing and other production methods. The more mature production process is screen printing and gravure printing technology. The advancement of printing technology and its further application to the production of RFID antennas have reduced the production cost of RFID tags, thereby promoting the application of RFID electronic tags.
Compared with the etched antenna and the wound antenna, the printed antenna itself has the following unique features:
1. The manufacture of printed antennas can adjust the electrical performance parameters more accurately and optimize the performance of the card.
The main technical parameters of RFID tags are: resonance frequency, Q value and impedance. In order to achieve optimal performance, all RFID tag manufacturing technologies can be obtained by changing the number of antenna turns, antenna size and wire diameter. Printed antenna technology can also be precisely adjusted to the desired target value by locally changing the line width and the thickness of the wafer layer.
Second, the manufacture of printed antennas can change the shape of the coil arbitrarily to suit the user's surface processing requirements.
For the multi-purpose use of RFID cards and the increasing requirements for various personalizations, the printed antenna can be easily changed to any shape, such as the surface of objects with different curvatures and angles, to meet customer requirements without reducing any Use performance.
3. The printed antenna can use various card base materials.
Printed antennas can use different card materials according to user requirements. In addition to PVC (polyvinyl chloride), PET-G (copolyester), PET (polyester), and 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 adapt 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 wafer manufacturers have joined the production team of RFID wafer modules. Due to the lack of a unified standard, the electrical performance parameters are also different, and the flexibility of the printed antenna structure can be matched with a variety of different chips and modules with different packaging forms to achieve the best performance. [next]
RFID conductive ink and printed antenna technology
The reason why RFID printed antennas are stronger than traditional antennas mainly depends on the characteristics of conductive ink and its perfect combination with printing technology.
Conductive ink is composed of fine conductive particles or other special materials (such as conductive polymers, etc.), printed on flexible or hard substrates can be made into a printed circuit, play the role of wire, antenna and resistance. The conductive ink determines the impedance of the RFID printed antenna to a large extent, which is an important parameter related to the performance of the RFID antenna.
Currently, Flint, Parelec, DuPont, ABC Nanotechnology, South Korea Baoyin, Beijing Rio Tinto Technology, and Wuhan Sanlai Technology Development Co., Ltd. have respectively developed various RFID Conductive ink for printed antennas.
According to different manufacturing processes, conductive ink can be divided into indirect conductive ink and direct conductive ink.
According to the composition of conductive factor contained in conductive ink, conductive ink includes carbon paste ink, copper paste ink, silver paste ink and gold paste ink. Because silver paste ink has lower resistivity, it is the best choice for RFID tags. In addition, copper oxidation rate is very fast, so it is not suitable for RFID antenna printing.
From the perspective of future development, RFID printed antenna technology will become the mainstream RFID antenna manufacturing technology, which stems from the following advantages of using conductive inks for antenna printing:
low cost
The cost reduction mainly depends on the two aspects of conductive ink material and screen printing process. In terms of the cost of the material itself, the price of ink is lower than that of stamped or etched metal coils. Especially when the prices of copper and silver increase, it is an ideal alternative method to use conductive ink printing to make RFID antenna In terms of material consumption, etching consumes a lot of metal, and the conductive ink printed antenna circuit has high speed, material saving, low cost and high efficiency.
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, because there is no need to add additional investment due to environmental protection requirements during the printing process, the maintenance cost of production and equipment is also lower than the copper etching method, which also reduces the unit cost of the label.
Good conductivity
After the conductive ink is dried, because the distance between the conductive particles becomes smaller, free electrons move in the direction of the applied electric field to form a current, so the RFID printed antenna has good conductivity.
Easy to operate
As an additive manufacturing technology, printing technology is an easy-to-control, one-step process compared to subtractive manufacturing technologies (such as etching).
No pollution
The photosensitive adhesives and other chemical reagents that must be used in the copper etching process have a strong erosive effect, and the generated waste materials and emissions cause greater pollution to the environment. The conductive ink is used to print directly on the substrate without the use of chemical reagents, so it has the advantage of no pollution.
Flexible substrate selection
Conductive ink can be printed on almost all printing materials, including polyester, polyimide, ABS engineering plastics, PVC (polyvinyl chloride), polyethylene, polypropylene, polycarbonate, (coating) cardboard, etc. 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.
The printed conductive ink antenna can also withstand higher external mechanical pressure. In addition, RFID tag printed antennas made with conductive ink have better flexibility and higher reliability.
When using conductive inks to print RFID antennas, the following aspects of the operation need to pay 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 body pollution in the printing area should be reduced as much as possible. The environmental requirements are at least a clean room above 100,000.
Pre-treatment: to ensure that the printed surface is clean and free of pollution, grease and oxides, etc., the shorter the residence time after the printed surface treatment, the better, to prevent oxidation or pollution.
Dilution: After adjusting the viscosity of the ink, adding a small amount of thinner can improve the printing effect of automatic printing. Stir thoroughly for 10 minutes before use.
Pre-drying: temperature and time can be adjusted according to specific production process.
Storage: The temperature is stored at 20-25 degrees, protected from light and heat.
This shows that the use of conductive inks to make RFID printed antennas has high requirements for the process. For the conductive ink itself, it should have strong adhesion, low resistivity, low curing temperature, stable conductive performance and other characteristics to meet the functional requirements of the RFID antenna. [next]
RFID printed 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 product packaging by many retailers due to advanced technology and convenient management to track the flow of goods in real time. International retailers such as Wal-Mart and Metro have all asked their suppliers to put RFID tags on the products they provide.
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 the cost of labels and promote the application of RFID in various industries.
The high cost of tags has always been a problem that plagues the RFID industry and users. The cost of RFID tags accounts for the largest proportion in all aspects of RFID. Therefore, in the process of popularization and application of RFID electronic tags, how to reduce the cost of the tags and improve the performance is a top priority.
For general commodities, the use of RFID tags will increase the cost of products and hinder the further application of RFID technology. But conductive ink technology can make RFID applications out of the cost bottleneck. The printing of RFID tag antennas using conductive ink can greatly reduce the production cost of HF and UHF antennas, thereby reducing the overall cost of RFID tags.
Conductive ink RFID printed antennas have 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 where RFID electronic tags can show their talents. The reduction in the price of the label makes it possible to apply it to anti-counterfeiting systems for high-value-added products such as medicine and alcohol.
Second, promote the development of the printing industry.
In addition to conductive inks, the production of RFID antennas also requires advanced printing technology. This undoubtedly broadens the development direction and path of the printing industry, making it no longer limited 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 antennas, the printing industry will continue to develop more advanced printing technologies, thereby promoting the rapid development of the printing industry itself.
With the development of conductive ink 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.
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