With the increasing maturity of RFID (Radio Frequency IdenTIficaTIon) technology and the gradual decline in the price of RFID tags, RFID tags are likely to replace traditional one-dimensional barcodes and two-dimensional codes. If the QR code is an extension of the one-dimensional code label, then the birth of RFID can be called a revolution in the label industry. RFID is a non-contact automatic identification technology that automatically identifies target objects and acquires relevant data through RF signals. It works in a variety of harsh environments without manual intervention. The RFID tag system consists of three main components, namely tags, readers and antennas. Among them, the manufacture and printing of antennas have become more and more "close". Due to the high cost and slow speed of the traditional manufacturing technology copper wire winding process, the metal foil etching process has the disadvantages of low precision, environmental pollution, poor waterproof and folding resistance. Therefore, the direct printing of RFID tag antennas by means of printing is a common method used in the industry in recent years. In fact, flexographic printing, gravure printing, inkjet printing, and screen printing can all be done on the RFID tag antenna, but in many respects, it seems that screen printing is superior to several other printing processes, especially the ink layer. The thickness factor makes screen printing an absolute advantage. In the actual printing process, the thickness of the ink layer is generally required to be more than 20 μm, which is not too difficult for screen printing with an ink layer thickness of 300 μm, but for other printing methods, it is necessary to rely on repeated printing. In order to achieve the desired thickness, this inevitably puts higher demands on the printing accuracy. Therefore, the author believes that screen printing is the most suitable printing process for printing RFID tag antennas. Although screen printing is the most suitable printing process for RFID tag antennas, since the RFID tag antenna is printed with conductive ink, it is in some respects different from traditional screen printing in the printing process. Special attention needs to be paid to the following issues. 1. Determination of antenna structure The antenna mainly plays the role of receiving and transmitting signals in the whole working process of the RFID tag, including four working frequency bands of low frequency, high frequency, ultra high frequency and microwave. Depending on the frequency band, the antenna of the RFID tag can be divided into three basic forms: a coil type, a microstrip patch type, and a dipole type. 2. Determination of printing methods Screen printing methods are generally divided into contact and non-contact. In the contact printing process, the substrate is in direct contact with the screen, and the squeegee moves on the screen for printing, which has the advantage that the screen is not tilted and deformed. In the non-contact printing process, there is a fixed distance between the screen and the substrate, and when the squeegee pushes the slurry through the screen, the screen is tilted and printed on the substrate. Since the screen can immediately rebound after printing, the printed pattern will not be blurred. When a contact-printed RFID tag antenna is used, due to the performance of the conductive ink, smudging is extremely likely to occur, which adversely affects fine printing. Therefore, in order to obtain good printing quality, in actual operation, non-contact printing is often used as the printing method of the RFID tag antenna. 3. Selection of conductive ink The conductive properties of conductive ink are affected by many factors such as the type of conductive material, particle size, shape, filling amount, dispersion state, adhesive type and curing time. The combination of different variables also has different effects on the conductivity. In view of the extremely high electrical conductivity requirements of RFID tag antennas, silver-based conductive inks are preferred. The silver powder for ink is mainly classified into two types of micron and nano grades, and commonly used micron-sized silver powder includes two kinds of flakes and spheres. In order to make the silver powder have good contact between the connecting materials, the flake silver powder is generally used as the main filler, and the nano silver powder is auxiliary. After determining the basic factors such as printing method and antenna structure, the printing process is not smooth. In the process of printing RFID tag antennas by screen printing, there are some inevitable problems, and special examples are given for readers to learn from. 1. Insufficient ink leakage In the process of printing RFID tag antennas by screen printing, this situation is often encountered: local conductivity is good, overall conductivity is poor or no obvious conductivity, and it will be found intermittently when viewed with a magnifying glass. The line, that is, the surface of the substrate has no ink on the surface, which is what we often say is uneven ink leakage. There are many reasons for this phenomenon. For example, if the number of meshes is too high, the ink permeability will be poor. If the mesh is too low, the accuracy of the line will be lowered, which will affect the quality of fine prints. The number is in the range of 200~300 mesh; if the squeegee pressing force is insufficient or the uneven force is applied, the ink leakage will be uneven, and the strength of the screen printing squeegee should be adjusted; the ink viscosity problem is also one of the causes of uneven ink leakage, and the viscosity is too high. The ink penetration is low and cannot be evenly transferred to the substrate. Too low will result in a paste. 2. Electrostatic discharge Electrostatic discharge (ESD) is a huge hidden danger in the electronics manufacturing industry, which seriously affects the development of the industry. Any two phases of solid, liquid, and gas friction will generate static electricity. At the time of printing, the speed, pressure, ink amount, mesh distance, and peeling speed of the substrate of the doctor blade generate static electricity, and the operation of the machine itself generates static electricity. After the static electricity is generated, it will adsorb dust, make the surface of the material dirty or the screen will block the net, causing printing defects; static electricity will also cause drawing or flying phenomenon, which will have a greater impact on the fine film line; excessive electrostatic voltage may be possible Breaking through the air creates a spark that causes a fire. The electrostatic hazard is so great. Due to its invisibility, randomness, potential and complexity, the ESD phenomenon should be based on prevention. The following two measures can be used for protection. 3. Silver powder migration In daily work, there is often a phenomenon in which the product performs well at the factory inspection and the parameters are fully qualified. However, after using the user for a period of time, it is found that some products have increased resistance and even appeared. Short circuit self-pass phenomenon. The reason is that the migration of silver is at work. Silver migration is also the biggest problem affecting the expansion of the application of silver ink. Of course, there is no silver paste that does not undergo silver migration at all, but we can inhibit the migration of silver to some extent by proper treatment of silver powder. Since the silver powder has a catalyst action on the debinding property of the slurry, ultrafine flake silver powder having a particle size of 0.1 to 0.2 μm and an average surface area of ​​2 m 2 /g can be used. The Ag-Pd conductive paste prepared by the airflow spray method has stable electrical conductivity even under the condition of 200 ° C and humidity, and there is little short circuit caused by silver migration. Wireless Charger Car Phone Holder Wireless Charger Car Phone Holder,In Car Phone Holder Wireless Charger,Car Phone Holder And Charger,Phone Car Mount With Wireless Charger Ningbo Luke Automotive Supplies Ltd. , https://www.nbluke.com
The RFID tag antenna of a short-range application system of less than 1 meter generally adopts a coil type antenna structure with simple process and low cost, and its working frequency band is mainly located at low frequency and high frequency. The coil type antenna can be constructed in different ways - either a circular ring or a rectangular ring; the substrate can be made of different materials - either a flexible substrate or a rigid substrate.
The RFID tag antenna of a long-distance application system of more than 1 meter needs to adopt a microstrip patch or dipole type antenna structure, which mainly works in the ultra-high frequency and microwave frequency bands, and the typical working distance is 1 to 10 meters.
During the printing process, the increase in ink resistance due to incomplete drying and thin printing thickness may be encountered. In addition, if the pre-press ink is not sufficiently stirred, the silver is likely to be deposited on the bottom due to the large specific gravity, which may result in low silver content in the upper layer of the ink, increased resistance, high content of the underlying silver, and reduced adhesion. These should all be paid enough attention.
1 venting method. By effectively grounding, the generated static electricity is directly discharged to the earth, thereby eliminating static electricity.
2 neutralization method. The static electricity on the label substrate and the machine is neutralized by releasing static electricity of different polarities.