RFID (Radio Frequency Identification) is a radio frequency identification system, also known as wireless IC tags, electronic tags, inductive electronic chips, inductive cards, non-contact cards, etc. It is a technology that achieves contactless data access through radio waves. It can be combined with data access technology through wireless communication to connect the database system behind it to form a huge and serially connected system. The basic components of its system include RFID tags, RFID readers and antennas. The antenna is a device that receives or radiates the RF signal power of the radio transceiver in the form of electromagnetic waves.
The work flow reader of the RFID system sends a radio frequency signal of a certain frequency through the transmitting antenna. When the radio frequency card enters the working area of ​​the transmitting antenna, an induced current is generated, and the radio frequency card obtains energy to be activated; the radio frequency card encodes its own information and other information through the built-in The antenna is sent out: the system receives the carrier signal sent from the RF card received by the antenna, and transmits it to the reader through the antenna regulator. The reader demodulates and decodes the received signal, and then sends it to the background main system for related processing; The main system judges the legality of the card according to the logical operation, makes corresponding processing and control according to different settings, and issues command signals to control the action of the actuator.
RFID tags
Work flow chart of RFID system
The manufacturing process of RFID electronic tags seems to be simple from the outside. In fact, the design and debugging are still relatively cumbersome. At present, a one-step design cannot be formed, especially the design of the tag antenna and further performance optimization after cooperation with the chip. Adjustment; the production process is also more numerous, and each process link must also be strictly controlled, so that the finished product label can meet the design requirements and customer needs. So how do you use existing equipment to make RFID tags? Here are several methods:
1. Wet embedding method In this workflow, the image is printed on the label surface material first, and then the label backing paper is peeled off. Through the adhesive on the back of the label facestock. Wet embedding (because the adhesive is coated on the embedding and uses release paper, so it is called wet embedding) can be fixed on the back of the label surface material. Then laminate the label facestock with the backing paper. After die cutting, rewinding, and waste disposal, the processing of RFID tags is completed.
2. Dry embedding method The dry embedding method requires a very accurate embedding system. In this workflow, the label image is first printed on the label facestock. Then peel off the label backing paper. Use a servo-driven cutting roller. Cut the dry inlay (because there is no adhesive applied on the inlay. It is called dry inlay because no backing paper is used) into a single inlay. Then use the adhesive on the back of the label surface to fix it on the back of the label surface. Finally, the label surface material with embedded labels is laminated with the label backing paper coated with hot-melt adhesive for the second time. After die-cutting, rewinding, and waste disposal, the processing of RFID tags is completed. When the label facestock and label backing paper are laminated, the adhesive is already cooled.
3. The tape sticking method is used to make UHF RFID tags. The tape sticking method is generally used. This method can directly print conductive ink on the back of the label surface material, but there are two different forms.
(1) The label face material without adhesive is used as the main roll material. In the process of sticking the tape, it is necessary to use conductive ink to print the antenna on the back of the label face material. However, conductive ink is difficult to print on the adhesive layer of the label. The solution is to unwind the label surface material and label backing paper separately. At this time, there is no adhesive on the label surface material, and the conductive ink can be printed smoothly. Then use the spray head to spray conductive adhesive on the back of the label face material. At the same time, the tape attached with adhesive tape is cut into individual pieces by a tape cutting roller controlled by a servo motor, and then attached to the label surface material coated with conductive adhesive on the back side by means of a laminating roller. Next, the label surface material was dried through a hot air drying tunnel to dry the conductive adhesive previously applied. At this time, a wide-width continuous hot-melt adhesive coating nozzle sprays adhesive on the separately unrolled backing paper, and then the backing paper and the label surface material are laminated, and die-cutting, rewinding and waste disposal. Complete the processing of RFID tags.
(2) Self-adhesive material is used as the main roll material. In this process, the label image is printed on the self-adhesive label surface material, and then the backing paper is peeled off. At this time, because of the adhesive layer on the back of the label face material, it is not conducive to the printing of conductive ink. Therefore, first coat a layer of primer on the adhesive layer and dry it, then print the antenna with conductive ink and dry it. At this time, use a spray head to spray conductive adhesive on the back of the label face material to bond the tape. At the same time, the label tape affixed with adhesive tape is cut into individual pieces by a cutting roller controlled by a servo motor, and then affixed to the label surface material coated with conductive adhesive on the back. Next, the label surface material was dried through a hot air drying tunnel to dry the conductive adhesive previously applied. The peeled label base paper is coated with hot melt adhesive, laminated with the label surface material again, and finally die-cut, wound, and discharged, and the processing of the RFID label is completed.
The production process case of RFID electronic tags takes Zhongshan Dahua Intelligent Technology Co., Ltd. as an example. A typical electronic tag production process flow diagram includes three main parts:
1) Various raw materials → compound into the base material of the antenna → antenna design + etching → finished product of the antenna;
2) Antenna product → IC chip placement → solder chip → interlayer packaging → test count → core material finished product;
3) Core material finished product + pattern design + system board + printing + double-sided tape → compound die cutting → test counting etc. → finally get the finished electronic label.
The generation and elimination of static electricity of RFID electronic tags are uneven in quality on the market. Many of them cannot be used when they are bought back. It turns out that the circuit is broken. In fact, this situation often occurs in the production of RFID electronic tags, the main reason is that the circuit of the tag is burned by static electricity during the printing process.
1. The generation of static electricity In the printing process of RFID tags, static electricity often occurs. When printing, generally static electricity is first generated from the paper feed roller, and then passes through a series of other sticks and equipment, so that the static electricity accumulates more and eventually reaches the voltage that breaks the label circuit. In general, in label printing, there are two ways to generate static electricity: one is pressing and friction electrification; the other is contact and separation electrification.
1) When contacting and separating solids of two different materials in contact and separation in a short time, the transfer of electrons is easy to occur. In this way, the positively charged electrons are lost and the negatively charged electrons are obtained. At this time, there is a contact potential difference between the two materials. During label printing, the printing material first enters the paper conveying part of the printing machine from the roll paper. When the printing machine is running, the printing material and the equipment are constantly in contact and separation, and static electricity is generated. Then the printing material is gripped by the teeth and printed quickly around the surface of the cylinder, and then peeled off from the impression cylinder. The contact distance between the printing material and the impression cylinder suddenly increases, causing the original potential difference to increase tens of times instantaneously, thereby accumulating a large amount of static charge. Generally, in label printers, the highest potential difference of static electricity can reach 5000V ~ 1000V. Ordinary objects are very sensitive to the voltage of 500V, and the circuit of the RFID electronic tag is relatively precise, so it is easily burned under the action of static electricity.
2) Squeeze and friction electrification. As everyone knows, on the printing press, the label printing material rotates with the cylinder through the suction nozzle, and the plate and the plate reciprocate, relying on the contact pressure of the cylinder and the plate to complete the transfer of graphics. The substrate is squeezed strongly by the printing plate and the cylinder at the same time. In the state of high-speed operation, the plates, paper, rollers, ink, etc. rub against each other violently, and static electricity is generated.
2. Elimination of static electricity In order to prevent static electricity in RFID electronic label printing, the following methods can generally be used to remove static electricity in RFID label printing.
1) Install an active static eliminator to eliminate static charge on the surface of the substrate through high-voltage discharge. This is the most effective method. However, passive static eliminators such as ropes cannot be installed. This will reduce the static voltage to a certain extent, but the voltage may pass to the printed material to the ground, and it is easy to burn the RFID circuit.
2) Install constant temperature and humidity devices in the printing workshop. This can maintain the temperature and humidity balance in the workshop. Under the environment of low temperature and high humidity, static electricity is not easy to generate. This is just an auxiliary method.
3) Improve the anti-shock performance of the RFID circuit. This step should be taken into account when printing the circuit.
RFID electronic label printing method RFID printing is very different from traditional label printing. From the definition of RFID, intelligence refers to the radio frequency circuit composed of chips, antennas, etc .; and the label is the commercialization of radio frequency circuits by the label printing process. From a printing perspective, the emergence of RFID will bring higher gold content to traditional label printing. The chip layer of RFID can be encapsulated and printed with materials such as paper, PE, PET and even textiles to make stickers, paper cards, hang tags or other types of tags. The chip is the key to RFID and is determined by its special structure , Can not withstand the pressure of the printing machine, so, in addition to inkjet printing, generally use the process of printing the surface layer first, and then compound with the chip layer, die cutting process. The antenna has three manufacturing technologies: etching method, coil winding method and printed antenna. Among them, RFID conductive ink printed antenna is a new technology developed in recent years.
1) The printing method of the antenna The printed antenna directly prints the conductive circuit on the insulating substrate with conductive ink to form the antenna and the circuit. 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.
2) Screen printing RFID tags RFID printing is mainly based on screen printing. In smart label printing, conductive ink is used, and the better screen for printing conductive ink is nickel foil perforated screen. It is a high-tech wire mesh, not a wire mesh woven from ordinary metal or nylon wire. It is a foil mesh drilled from nickel foil. The mesh is hexagonal. It can also be made into a circle by electrolytic forming. Hole shape. The entire screen is flat and even, which can greatly improve the stability and precision of the imprint. It is used for printing high-tech products such as conductive ink, wafers and integrated circuits. Up to 0.01mm. You can also choose 61 ~ 100T / mm screen solvent plate printing, printing conductive ink and drying at 60 ℃.
Advantages of screen printing RFID
3) Offset printing RFID label offset printing is the most common method. Its printing materials are wide, fast and efficient. The application of offset printing to coil printing has the advantages of efficiency, precision and resolution, but the thickness of the offset ink film is small, which does not meet the requirements of circuit printing. Of course, this can be done by repeatedly printing many times, but this poses a new challenge for the registration control of fine lines. The new, better conductive ink can also achieve the required impedance performance at a smaller thickness .
4) Flexo printing RFID label flexo printing is a direct printing method. It is made of flexible photosensitive resin with a thickness of 1 to 5 mm and is printed on roll paper. It has fast speed and high efficiency. The viscosity of the ink is between 0.01 and 0.1 Pa.s. Water-based ink, solvent-based ink and UV-curable ink can be used. However, the resolution of flexo printing is low, usually about 60L / cm, fine printing can reach 80L / cm, and the thickness of the ink film is 6 ~ 8μm, which is suitable for the requirements of antenna printing.
With the development of thin plate technology, the resolution and printing accuracy of flexographic printing have also been continuously improved. The shortcoming is that there is a printing pattern on the edge of the print, which is caused by the deformation of the printing plate due to the pressure of the printing process. The appearance of imprints makes the traces on the edges of the lines irregular, which will affect the accuracy of the ink adhesion and the impedance of the lines, and it is easy to produce waste products.
5) Gravure printing RFID tag gravure printing has high printing durability and a wide range of printing materials. The viscosity of the ink is about 10 ~ 50mPa.s, mainly solvent-based ink. The resolution is related to the engraving of the anilox cavity. The laser engraving can reach 1000L / cm, and the ink film thickness is between 8 and 12μm. However, due to its excessive printing pressure, there are difficulties in RFID antenna printing.
6) Inkjet printing RFID tag inkjet printing is the fastest growing printing method in recent years, and its versatility is unmatched by other printing methods. This pressureless method can spray digital information from the computer directly onto any shape of material. The ink system is relatively complicated. The ink used can be water-based, hot-melt type, or UV-curable type, and its viscosity is about 10mPa.s. However, there is a deviation of the inkjet position in inkjet printing, and small ink droplets that affect the printing quality will appear in the blank part, causing an edge effect.
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7) Comprehensive printing of RFID tags uses a combination of printing technology and gold plating to produce wireless tag (RFID tag) antenna patterns. No etching is used, which means that the material can be prevented from being cut off, so the wireless tag antenna can be produced at a lower cost.
The manufacturing process of the wireless tag antenna is as follows:
1) First, use water-soluble special ink, using printing technology or inkjet technology, draw the antenna pattern on the flexible substrate that has formed the antenna pattern using PET and other methods;
2) Then put the flexible bottom plate into the plating solution to plate copper. After the above process, a copper film can be formed on the wiring pattern drawn with special ink. The special ink used here refers to a solution prepared by dissolving two metals into particles with a particle size of tens of nanometers and dissolving in water;
This method does not etch the copper foil, that is, the "subtraction" process, but only places the material on the bottom plate, so it is usually called the "addition" method. Moreover, the copper wiring itself is formed by electroplating technology and does not require high-temperature sintering such as heat treatment. Therefore, a flexible base material with low heat resistance can be used. The resistance between the two ends of the antenna is less than 0.4Ω. Although it is very large in terms of bulk copper, there is no problem as a wireless tag antenna. For the processing accuracy of wiring, printing technology is used in the initial process, and a wiring interval of 80 μm can be achieved. However, the inkjet technology produces droplets, so the accuracy is slightly reduced, and the wiring interval is slightly wider.
RFID printing is both a category of label printing and a type of circuit printing. The production process has strict requirements on printing, precise printing position, and strict ink adhesion. For example, the thickness of the conductive paste film and the number of conductive particles are strictly controlled, and the size of the printing resolution must be considered. The selection of printing process can be comprehensively considered from the aspects of printing volume, surface properties of printing materials, adhesion properties of ink or printing materials, cost, characteristics of process and so on. For the printing field, printing technology can be used to produce RFID antennas, which brings new development opportunities to the printing industry.
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