Analysis and Discussion on the Efficient Printing Method of New RFID Consumables
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When the conductive ink is printed, the ink will penetrate into the capillary, resulting in uneven distribution of the impedance of the electronic tag antenna. This phenomenon becomes more serious when the frequency is higher. The adhesion of printed antennas, chip packaging and ink characteristics are important factors in determining the life of such products.
Foreword
With the growth of the RFID market, the use of electronic tags has also grown exponentially. But the real obstacle to the development of the RFID industry is that the price cost of electronic tags is still high, and the printed electronic tags are well-received by the market.
Printed electronic technology is widely used in soft electronics, organic displays, EMI prevention, paper batteries and RFID. Among them, RFlD passive electronic label printing faces the most technical problems.
Printing process
The ink used in RFlD passive electronic label printing is commonly known as "conductive silver glue". Because of the need to use silver powder during printing, and the recent rising prices of raw materials, the cost of silver plastics remains high, resulting in the cost of printed electronic tags that originally had the advantage of manufacturing cost. The cost can not be reduced at one time, but in the long run The electronic label is still one of the best solutions for future low-cost electronic labels.
In the printing process, there are four types of printing inks, such as screen printing, gravure, letterpress and inkjet. The printing process characteristics, quality and cost are also different. The characteristics of the printed substrate, the process of electronic label printing and the combination of material properties will determine the various electronic label printing. Suitable production method.
Screen printing
The printing process of RFJD electronic label adopts the most cases of this kind of scheme. The screen printing is to press the conductive ink from the other side of the screen to the screen by the scraper, and the ink penetrates the net of the pattern on the screen. The gap is glued onto the printed substrate. Screen printing inks have a high viscosity and a printing film thickness of up to 100um, while RFID electronic labels have a printed film thickness of only about 8-12um, and then dried by UV, IR and hot air.
Gravure printing
In gravure printing, a metal plate (intaglio) engraved with a pattern is fixed on a printing plate on a printing machine, and the printing ink is applied to the substrate to be printed. The ink viscosity of gravure printing is lower than that of screen printing ink. The ink film thickness control is the most accurate. It can also meet the film thickness requirements of RFlD electronic label printing, and the printing speed is faster, which is very suitable for mass printing production. The equipment that needs to be invested is relatively expensive.
Toppan Printing
Letterpress printing is a rubber thick plate (embossing) with a pattern attached to a printing plate on a printing machine, and transferred to a substrate after being applied with printing ink. The ink viscosity of letterpress printing is lower than that of gravure printing, and the film thickness of ink is much lower than the former two, and the problem encountered when printing conductive silver glue is the most difficult to overcome, but if it can overcome various problems. The price competitiveness of printing electronic labels directly on cardboard boxes is not comparable to the former two.
Inkjet printing
The development of inkjet printing technology is an emerging technology in the past ten years. The printing precision of its large inkjet printing equipment can be up to 50um. This technology is also the most likely to successfully realize the lC circuit directly in the process of printing, but the disadvantage is Printing speed is slow. The cost of equipment and ink is also the highest among all printing processes, while the ink viscosity is the lowest of the four processes, and the film thickness control accuracy is the highest.
Conductive silver glue ink characteristics
At present, the suppliers of conductive silver glue are mainly American and European manufacturers, while in Asia there are Japanese and South Korean manufacturers. The ink characteristics are mainly silver powder components, and the amount of silver powder determines the characteristics of its conductive impedance.
Substrate
In the electronic label printing process, the most neglected part is the sub-label of the electronic label. Generally, the type of the substrate of the passive electronic label is nothing more than PVC, PET, coated white paper, corrugated paper, etc. However, if it is to be used in the UHF band, the dielectric coefficient of the substrate material will greatly affect the RF impedance of the electronic tag, so this factor must be considered when designing the electronic tag antenna.
When corrugated paper is used to print electronic labels on the substrate, the capillary pores of the corrugated paper are relatively large and irregularly distributed. When the conductive ink is printed, the ink will penetrate into the capillary, resulting in uneven distribution of the impedance of the electronic tag antenna. This phenomenon becomes more serious when the frequency is higher.
Yield
In this so-called yield, in addition to whether the finished electronic label can be read by the reader, and the user is more concerned about the application yield, which is the so-called stable reading distance, and the key reason for affecting the yield is the finished product. RF impedance. In addition, the adhesion of printed antennas, chip packaging and ink characteristics are important factors in determining the life of such products.
Conductive impedance
The characteristics of the RF impedance of the printed electronic tag antenna will be determined by factors such as whether the solid content of the ink is uniformly distributed in the ink during printing, the film thickness after printing, and the dielectric constant of the printed substrate. Everyone in the world knows that the first print printed to the last printed one, the color difference or film thickness will have a certain degree of change. If the quality factor of the substrate is added to the change in the dielectric constant, the result of the addition or the offset between the two changes will cause the electronic tag printed antenna impedance to exceed the specifications and cause defective products. The effect of passive antennas printed on HF is relatively minor, but if this happens in UHF printed passive antennas, the chance of producing defective products will increase. Even if the result of the change or the degree of variation of the former two process variables does not cause the printed impedance of the electronic tag antenna to exceed the specification, the printed UHF electronic tag may result in different reading distances.
Adhesion
When the substrate is made of a smooth and firm material, the ink may be easily peeled off after drying, especially when the semi-finished product or the finished product is curled, the film thickness after drying is peeled or chipped due to bending stress, but this case The adhesion of the ink can be improved by adjusting the resin in the ink.
Phytocrystalline package
The yield of the crystallization process is mainly determined by the RF characteristics of the packaged conductive paste and the positioning accuracy of the printed parts. Generally speaking, the accuracy of the letterpress printing is the worst. If it can be planned in the future, and the initial equipment construction adjustment is taken into consideration. Will effectively improve the yield of the crystallization process.
The life cycle
Printed electronic label life cycle is shorter than electronic labels made by etching, stamping or evaporation, because the silver glue after baking is in contact with water molecules or sulfur molecules in the air. It is prone to oxidation or vulcanization, but it is discolored or blackened. If such a printed electronic tag is used, it will be more oxidized or eroded when it is attached to goods that will be shipped by sea. After the antenna is oxidized, oscillated or vulcanized, the RF performance of the electronic tag will be affected by the depth of the changing layer, but fortunately, the thickness of the changing layer is to a certain depth, so that the RF impedance is obvious. Variety.
in conclusion
When the above four printing methods are used for passive UHF electronic label printing, the cost and process yield are different. Although the yield of the two printing technologies of gravure and letterpress is low, the production cost and productivity of these two technologies are different. However, it is very competitive, and if there is a breakthrough in conductive ink materials in the future, the results will be completely changed. Printing cost and yield comparison In addition, the cost of inkjet printing is still high in gravure and letterpress printing technology, but if the equipment investment cost is excluded, the price of conductive ink used in inkjet printing, and gravure and letterpress use The price of conductive inks is similar, and the process characteristics of low material loss and stable high yield make the overall production cost the lowest. Since the performance of the printed antenna mainly depends on the solid content of the conductive particles of the conductive ink and the film thickness of the printed film, and the two parameters can control 74% of the process yield results, which shows the printing passive electronic tag technology. The yield will be strongly influenced by the properties of the conductive ink material.