Discussion on the Yield of Passive Electronic Labels in RFID Printing
We are a big printing company in Shenzhen China . We offer all book publications, hardcover book printing, papercover book printing, hardcover notebook, sprial book printing, saddle stiching book printing, booklet printing,packaging box, calendars, all kinds of PVC, product brochures, notes, Children's book, stickers, all kinds of special paper color printing products, game cardand so on.
For more information please visit
http://www.joyful-printing.com. ENG only
http://www.joyful-printing.net
http://www.joyful-printing.org
email: info@joyful-printing.net
This paper explores the four printing methods used in passive UHF electronic label printing, and compares the cost and process yield.
Foreword
With the growth of the RFID market, the use of electronic tags has also multiplied, but the real obstacle to the development of the RFID industry is that the price of electronic tags is still high, while the printed electronic tags have a deep cost advantage. Expected by the market.
Printed electronic technology is widely used in soft electronics, organic displays, EMI prevention, paper batteries and RFID. Among them, RFID passive electronic label printing faces the most technical problems.
Printing process
The ink used in RFID passive electronic label printing is commonly known as "conductive silver glue". Due to the use of silver powder materials during printing, the recent increase in the price of raw materials has led to the high cost of silver glue, resulting in the cost of printing electronic tags that originally had the advantage of manufacturing cost. The cost cannot be reduced at one time, but in the long run, the printing type The electronic label is still one of the best solutions for low-cost electronic labels in the future.
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 assembly process of the electronic label printing and the combination of material properties will determine the production method suitable for each electronic label printing.
Screen printing
The printing process of RFID electronic tags adopts the most common example of this kind of method. The screen printing is to scan the ink from the other side of the screen with a doctor blade to press the ink through the screen, and the ink penetrates the pattern on the screen. The mesh gap is adhered to the printed substrate. Screen printing inks have a high viscosity and a printing film thickness of up to 100 μm, while RFID electronic labels have a printed film thickness of only about 8 to 12 μm, 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 RFID 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. The thickness of ink film is much lower than that of the former two. The problem encountered when printing conductive silver glue is the most difficult to overcome. However, if you can overcome various problems, directly put the electronic label. The price competitiveness of printing 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 decade. The printing precision of its large inkjet printing equipment can be up to 50μm. This technology is also the most likely to successfully realize the IC circuit directly in the process of printing. However, the disadvantage is The printing speed is slow, the equipment and ink cost is the highest among all printing processes, and the ink viscosity is the lowest in 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. In addition, the diameter of the silver powder particles is also the key to determine the uniformity of the printing resistance. It is a comparison table of the commercial characteristics of several conductive silver inks on the market. It can be seen from the table that the drying baking temperature and time are higher than the general printing ink. Long, the newly developed conductive silver adhesive has a tendency to be low-temperature, fast-drying, low-energy, and environmentally friendly.
Substrate
In the electronic label printing process, the most neglected part is the substrate of the electronic label. Generally, the type 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 constant of the substrate material will greatly affect the RF impedance of the electronic tag [5], so this factor must be considered when designing the electronic tag antenna.
Corrugated paper When the electronic label is printed on the substrate, the capillary pores of the corrugated paper are quite 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 case, the so-called yield is not only read by the reader, but also the user is more concerned about the application yield. This is the so-called stable reading distance. The key reason for 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 whether the solid content of the ink is uniformly distributed in the ink during printing, the film thickness after printing, and the dielectric coefficient of the printed substrate [7]. Everyone in the printing industry knows that the printed first print to the last printed print, 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 change 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 the adjustment of 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 part. Generally speaking, the accuracy of the letterpress printing is the worst. If it can be adjusted in the future, it can be considered in the process planning and initial equipment construction adjustment. Will effectively improve the yield of the crystallization process.
The life cycle
The printed electronic label life cycle is shorter than the electronic label made by etching, stamping or evaporation, because the silver glue after baking and drying is easily contacted with water molecules or sulfur molecules in the air. Oxidation or vulcanization occurs, and there is discoloration or blackening. If such printed electronic tags are used on goods that are shipped by sea, the oxidized or deuterated phenomenon will be more serious. After the antenna is oxidized, deuterated or vulcanized, the RF performance of the electronic tag will be affected by the depth of the layer, but fortunately, the thickness of the layer is changed to a certain depth, so that the RF impedance is significantly changed.
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 the conductive ink material can break through in the future, the result will be completely changed.
In addition, the cost of inkjet printing is still high in both gravure and letterpress printing technology, but if the equipment investment cost is excluded, the price of conductive ink used in inkjet printing is similar to the price of conductive ink used in gravure and letterpress. The low material loss and stable high yield process characteristics result in the lowest overall production cost.
Since the performance of the printed antenna mainly depends on the two process parameters such as the solid content of the conductive particles of the conductive ink and the thickness of the printed film, and the two parameters can control 74% of the result of the process yield, which shows that the printed passive electronic tag technology is good. The rate will be greatly affected by the properties of the conductive ink material.