Exploring RFID printed passive electronic label yield

Exploring RFID printed passive electronic label yield

When the conductive ink is printed on, the ink will penetrate into the pores, resulting in uneven distribution of the impedance of the electronic tag antenna. This phenomenon is more serious when the frequency is higher. Adhesion of the printed antenna, chip packaging, and ink characteristics are important factors that determine the longevity of such products.


With the growth of the RFID market, the use of electronic tags is also growing at multiples. However, the real obstacle to the development of the RFID industry is that the price of electronic tags is still high, while printed electronic tags have a cost advantage Seen by the market.

Printed electronic technology is widely used in areas such as soft electronics, organic displays, EMI prevention, paper batteries, and RFID, among which RFID passive electronic label printing faces the most technical challenges.

Printing process

The main ink used in RFID passive electronic label printing is commonly known as "conductive silver glue." Because silver powder is used for printing, the rising cost of raw materials has caused the cost of silver paste to remain high. This has led to the fact that printed electronic tags, which originally had the advantage of manufacturing costs, could not be reduced in time, but in the long run, printing The electronic tag is still one of the best solutions for future low-cost electronic tags.

In the printing process, there are four types of screen printing methods: printing screen, gravure, letterpress, and ink jet printing. The characteristics, quality, and cost of each printing process are different. The characteristics of the printed substrate, the combination of the process and material properties of the electronic label printing, will determine the appropriate production methods for the various electronic label prints.

Screen printing

The RFID electronic label printing process adopts the largest number of examples. Screen printing uses conductive ink from the other side of the screen with a doctor blade to sweep the ink across the screen, and ink penetrates through the screen. The gap of the mesh is adhered to the printed substrate. Screen printing ink viscosity is higher, and the printing film thickness up to 100μm, while the RFID film printed film thickness is only about 8 ~ 12μm can be followed by drying can be UV, IR and hot air to achieve.

Gravure printing

Gravure printing is to engrave a pattern of thin metal plate (indented), fixed on the printing cylinder on the printing press, stained with printing ink and transferred to the printed substrate, as shown in Figure 〔2〕. Gravure printing ink viscosity is lower than the viscosity of screen printing ink, ink film thickness control is most accurate, can also meet the required film thickness requirements for RFID electronic label printing, and the printing speed is faster, very suitable for large-scale printing production, disadvantages The equipment needed to invest is higher.

Toppan Printing

Relief printing is to print a thick plate (embossed) with a pattern on a printing cassette on a printing press and transfer it to the substrate after being coated with printing ink. Relief printing inks have lower ink viscosity than gravure printing. The ink film thickness is also far lower than the former two. The problems encountered when printing conductive silver adhesives are the highest and most difficult to overcome, but if you can overcome various problems, directly use electronic labels. The price competitiveness of printing on cardboard boxes is comparable to the former two.

Inkjet printing

The development of inkjet printing technology is an emerging technology in the past decade. The printing accuracy of large-scale inkjet printing equipment can be as high as about 50 μm. This technology is also most likely to successfully implement IC circuits directly in the printing process, but the disadvantage is that The printing speed is slow, the cost of equipment and ink is also the highest in all printing processes, and the ink viscosity is the lowest of the four processes, and the film thickness control accuracy is the highest.

Conductive silver paste ink characteristics

At present, the suppliers of conductive silver paste are mainly American and European manufacturers. In Asia, Japanese and South Korean manufacturers compete with each other. Their ink characteristics are mainly silver powder components, and the amount of silver powder components determines their conductive impedance characteristics. In addition, the size of the silver particle diameter is also the key to determine the uniformity of the printing impedance. Table 1 shows the comparison of commercial characteristics of several conductive silver adhesive inks on the market. The drying baking temperature and time can be seen from the table. Printing inks are high and long, and the newly developed conductive silver adhesives have the tendency to be low-temperature, fast-drying, low-energy-consuming and environmentally friendly.


In the electronic label printing process, the most easily overlooked part is the substrate for electronic labels. In general, the types of substrates for passive electronic labels are nothing more than PVC, PET, coated white paper, and corrugated paper. However, if it is used in UHF band, the dielectric coefficient of the material of the substrate will greatly affect the RF impedance of the electronic tag [5]. Therefore, it is necessary to consider this factor when designing an electronic tag antenna.

Another corrugated paper is when the electronic label is printed on the substrate, because the pores of the corrugated paper are quite large and irregularly distributed. When the conductive ink is printed on, the ink will penetrate into the pores, resulting in uneven distribution of the impedance of the electronic tag antenna. This phenomenon is more serious when the frequency is higher.

Yield rate

The so-called yield rate is not only whether the finished electronic tag can be read by the reader, but also the user is more concerned with the application yield, which is the so-called stable reading distance, and the key reason that influences the yield rate is the finished product. RF impedance. In addition, the adhesion of the printed antenna, the chip package, and the ink characteristics are important factors that determine the longevity of such products.

Conductive impedance

The characteristics of the RF impedance of the printed RFID tag antenna will be determined by factors such as the ink's solid distribution in the ink, the thickness of the printed film, and the dielectric constant of the printed substrate [7]. Everyone in the printing industry knows that the color difference or film thickness of a printed piece will change by a certain margin. If the quality factor of the substrate adds to the change in the dielectric constant, the result of the addition or offset caused by the variation of the two materials will cause the impedance of the electronic tag printed antenna to exceed the specification and cause defective products. The influence of passive antennas on HF printing is slight, but if UHF printed passive antennas encounter such a situation, the probability of producing defective products will increase significantly. Even if the degree of variation of the previous two process variables is added or offset, the printed impedance of the RFID tag will be different from that of the electronic tag antenna, but the printed UHF tag will still have a different reading distance.


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, and the film thickness after drying is peeled or chipped due to bending stress. It can be improved by adjusting the resin in the ink to improve the adhesion of the ink.

Epitaxial packaging

The yield of the seeding process is mainly determined by the RF characteristics of the package's conductive adhesive and the positioning accuracy of the prints. In general, the precision of letterpress printing is the worst. If the process planning and initial equipment configuration adjustments are considered in the future, It will effectively increase the yield of the seeding process.

Life cycle

The printed electronic label life cycle is shorter than the electronic label made by etching, stamping or evaporation. The reason is that after baking and drying, the silver glue is easily contacted with water molecules or sulfur molecules in the air. Oxidation or vulcanization occurs, and discoloration or blackening occurs. If such printed electronic tags are used on goods that have been shipped by sea, the oxidized or deuterated products will be more serious. After the antenna is oxidized, deuterated, or vulcanized, the RF performance of the tag will be affected by the depth of the change layer, but fortunately, the change in layer thickness to a certain depth will not significantly change the RF impedance.

in conclusion

When the above four printing methods are used in passive UHF electronic label printing, the cost and process yield are different, as shown in Figure [5]. Although the two printing technologies of gravure and letterpress have lower yield, The production cost and production capacity of these two technologies are very competitive, and if the conductive ink material can be broken in the future, the results of figure [5] will completely change.

In addition, the current high cost of ink jet printing is still at the gravure and relief printing technologies. However, if the cost of equipment investment is excluded, the price of conductive ink used in ink jet printing is similar to the price of conductive ink used in gravure and letterpress printing. The process characteristics of low material loss, stable high yield, but the lowest total production costs.

Since the performance of the printed antenna is mainly determined by two kinds of process parameters such as the solid content of conductive particles and the printed film thickness of the conductive ink, these two parameters can control 74% of the results of the process yield, indicating that the printed passive electronic label technology is good. The rate will be strongly influenced by the characteristics of the conductive ink material.

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