Application of printing technology in RFID tag manufacturing

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Radio Frequency Identification (Radio Frequency Identification) is a type of smart card. RFID is a way of identifying non-contact two-way communication using radio frequency. It appeared in World War II, began to be used in the 1970s, and began to be used on a large scale in the 1990s. Technology has been widely used in all areas of our lives, such as the simplest access card, bus ride card, campus card and so on. RFID technology is widely recognized in the retail industry as a model of the "future store" model.

In future stores, all items are tagged with RFID. Customers have two exposures to RFID technology in the store: so-called smart shelves and smart checkout counters. Smart shelves, which are equipped with RFID tag scanners on the shelves, can automatically prompt the goods to leave the rack and place the wrong position, solve the problem of timely replenishment and correct loading; the store no longer has a traditional checkout counter, but a Replaced by the smart cashier. The smart checkout can be achieved by a screen mounted at the exit of the RFID tag scanner. When the customer's trolley passes the screen, all purchases in the vehicle are scanned instantaneously, and the smart cashier automatically transfers the total cost of all the goods from the customer's credit card. This makes it easy for customers to checkout and no longer has to wait in line for a long time at the traditional checkout counter.

1. Cost barriers for RFID tags

From the above application mode, we can see that RFID tags bring us more convenient and more efficient consumer life. However, there is still a long way to go before RFID tags can be placed on every item. One of the bottlenecks here is the relatively high cost of RFID tags. For now, the cost of each label has fallen below $1, reaching 20 to 70 cents. This does not matter for high-priced products, but it is considered a cost barrier for many low-priced items such as toothbrushes and pencils. Therefore, in order to fully promote the RFID tag, the manufacturing cost of the tag should be reduced under the premise of ensuring the performance of the tag.

2. Advantages of printing technology in labeling costs

RFlD tags can be divided into three main categories: passive RFID tags, semi-active RFID tags, and active RFID tags. RFID tags on retail packaging are generally passive RFID, which is a passive RFID tag because it needs to receive electromagnetic signals from the reader, induce current, and then send electromagnetic signals to the reader for tagging and reading. Information transfer between devices. The structure of such a label is generally: a substrate, a chip, and an internal antenna (coil). Current coil manufacturing methods include: copper wire winding, chemical etching, electroplating, and direct printing. Among the four methods, the direct printing method is worthy of attention because it has the advantages of high-speed printing of antennas and low cost of consumables, which can significantly reduce the cost of RFID tags.

3. The driving force of conductive ink

Conductive inks are an important driving force in the technology of direct printing antennas. Without the development of conductive inks, there is no application of printing technology in the manufacture of RFID tags. Conductive inks are composed of some conductive particles, resins or more specific raw materials, such as conductive polymers. After the conductive ink is dried on the substrate, the distance between the conductive particles becomes smaller, and the free electrons move in the direction of the applied electric field to form a current, which has good electrical conductivity, so that the ink acts as an antenna. Ink quality is of great significance for improving electrical conductivity and reducing ink consumption. A good conductive ink formulation requires good printability, and has strong adhesion, low resistivity, low curing temperature, and stable electrical conductivity after printing.

4. Research on direct printed antenna technology

Currently, the method of directly printing antennas is still in the research stage. In the antenna printing of RFID tags, the antenna coils of RFID tags with different working frequencies will correspond to different turns, coil thickness and distance between each turn (eg HF band using 13.56MHz chip, usually it requires The number of turns of the coil is 6, and the thickness is about 20 μm.

The UHF band uses 868MHz and 950MHz chips with a coil cross-section thickness of approximately 4μm. Therefore, the thickness of the ink layer to be printed, the width of each line, and the contour of the pattern after drying have strict tolerance ranges (for example, the error of two overlapping overprints must be within 0.1 mm).

When studying the direct printing antenna using silk screen printing, the following beneficial experience is obtained: the hexagonal hole shape is used for the mesh, which is beneficial to the complete transfer of the conductive ink; the conductive ink is better selected from the solvent type ink; and the excellent ink drying is created. Conditions (such as: reducing the wind speed in the oven, the heating temperature is 140 ° C, the heating time is between 30 seconds and 120 seconds), which facilitates the precise shaping of the contour of the printed coil. At present, a rotary screen printing equipment company in Switzerland has created a special production line for smart label printing.

In the study of the gravure printing method for direct printing of RFID tags, the Stuttgart Media University in Germany obtained the following useful conclusions: The best plate making method is the electronic engraving method using diamond, and the resolution is selected at 5080 dpi. At this time, there is almost no jagged edge, and the required unit can be accurately transmitted; the image file format required for front-end plate making uses a bitmap format, so that the graphic information is not easily lost; for the structure of the dot, a special one is required to be different from the conventional one. The open cell of the cell is shown in Figure 2. If a traditional cell is used, the mesh wall between the cells will separate the conductive ink and not form a continuous path; the open cell will not only solve the wall but also solve the problem of dividing the ink into the wall.

Printing technology is involved in the manufacture of RFID tags, which will be a very useful attempt. With the continuous deepening of research on printing process parameters, the continuous improvement of conductive ink formulations will definitely make printing technology play an important role in the manufacture of RFID tags.