Discussion on yield of passive RFID printed electronic tags

[Abstract] This article discusses the four printing methods used in passive UHF electronic label printing, and compares and analyzes them from different aspects of cost and process yield.

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 of electronic tags is still high, and printed electronic tags are inherently cost-effective. Expected by the market.

Printed electronic technology is widely used in the fields of soft electronics, organic displays, EMI prevention, paper batteries and RFID. Among them, RFID passive electronic label printing faces the most technical difficulties.

Printing process

The main ink used in RFID passive electronic label printing is commonly known as "conductive silver glue". Due to the need to use silver powder materials for printing, the recent rising price of raw materials has made the cost of silver glue high, which led to the original sibling Xiu Pufei killing the home and climbing the frequency: ⅹ Block the horoscope? Also? ぴ 独 纯 From: ⑹ Jiangmuyingying ?? Yun Qiao stupidly blowing the picture Yanyingying nickname ┑ 淖 罴 呀 饩 龇 Borrow? Arc? / P>

In the printing process, there are four major types of printing transfer inks: screen printing, gravure printing, letterpress printing, and inkjet printing. The characteristics, quality, and cost of each printing process are also different. The consideration of the characteristics of the printed substrate, the process of electronic label printing and the combination of material characteristics will determine the suitability of various electronic label prints.

Screen printing

The printing process of RFID electronic tags? What is the address by borrowing? The screen printing is shown in the screen printing is to conduct conductive ink from the other side of the screen with a scraper to sweep the ink through the screen, and The ink penetrates through the mesh gap of the pattern on the screen and sticks to the printed substrate. The ink viscosity of screen printing is high, and the printing film thickness can be up to 100μm, while the printing film thickness of RFID electronic tags is only about 8 ~ 12μm, and then drying can be achieved by UV, IR and hot air.

Figure 1. Screen printing

Gravure printing

Gravure printing is to fix a patterned thin metal plate (gravure) on a printing reel on a printing machine, transfer it to the printed substrate after being printed with printing ink, as shown in Figure [2]. The ink viscosity of gravure printing is lower than the viscosity of screen printing ink. The ink film thickness is controlled most accurately. It can also meet the film thickness requirements for RFID electronic label printing, and the printing speed is faster. It is a relatively high equipment investment.

Figure 2. Gravure printing

Toppan Printing

In relief printing, a thick rubber plate (embossed) with a pattern is fixed on a printing reel on a printing machine, and transferred to the substrate after being printed with printing ink, as shown in figure [3]. The ink viscosity of letterpress printing is lower than that of gravure printing, and the ink film thickness is much lower than the former two. The difficulties encountered when printing conductive silver paste are the highest and most difficult to overcome. The price competitiveness printed on the carton is unmatched by the first two.

Figure 3. Letterpress printing [3]

Inkjet printing

The development of inkjet printing technology is an emerging technology in the past ten years. The printing accuracy of its large-scale inkjet printing equipment can be up to about 50μm. This technology is also the most likely to successfully implement the IC circuit directly by printing in the process, but the disadvantages are The printing speed is slow, the cost of equipment and ink is the highest in all printing processes, and the viscosity of the ink is the lowest in the four processes, but the accuracy of film thickness control is the highest.

Conductive silver glue ink characteristics

At present, the suppliers of conductive silver adhesives are mainly American and European manufacturers. In Asia, there are Japanese and South Korean manufacturers competing. 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 powder particles is also the key to determine the uniformity of its printing resistance. Table [1] is a comparison table of the commercial characteristics of several conductive silver paste inks on the market. Printing inks are high and long, and the characteristics of the newly developed conductive silver adhesive tend to be low-temperature, quick-drying, low energy consumption, and environmental protection.

Table 1. Comparison of characteristics of commercially available conductive inks [4]

Substrate

In the electronic label printing process, the most easily overlooked part is the substrate of the electronic label (substrate). In general, the types of substrates of passive electronic labels are nothing more than PVC and PET. Coated? Xunzijian⑼ When using the HF frequency band, the dielectric number of the substrate material will greatly affect the RF impedance of the electronic tag [5], so this factor must be taken into account when designing the electronic tag antenna.

When the electronic label is printed on the substrate, the capillary hole of the tile is quite large, and it is irregularly divided? Dazzle? When the conductive ink is printed, the ink will penetrate into the capillary holes, causing the antenna impedance of the electronic tag to be broken down?

Figure 4. The microscopic surface of the tile

Yield

The so-called yield rate is not only whether the finished electronic tag can be read by the reader, but also users are more concerned about the application yield rate, which is the so-called stable reading distance, and the key reason for this yield rate is the finished product. RF impedance. In addition, the adhesion of printed antennas, chip packaging and ink characteristics are important factors that determine the life of such products.

Conductive impedance

The characteristics of the RF impedance of the printed electronic tag antenna will be divided according to whether the solid content of the ink is uniform during printing? Yan Mo Tuan? Small Decide [7], and everyone in the printing industry knows that the color difference or film thickness of the first printed part to the last printed part will have a certain range of changes. If the quality factor of the substrate is added to the change in the dielectric? S number, the result of the addition or offset of the two changes will cause the impedance of the electronic label printed antenna to exceed the specifications and produce defective products. The impact of the passive antenna printed on HF is relatively slight, but if this situation is encountered in the passive antenna printed on UHF, the probability of defective products will increase greatly. Even if the result of the addition or cancellation of the variation of the first two process variables does not make the electronic tag antenna print impedance exceed the specifications, it will still produce a different reading distance for the printed UHF electronic tag.
Adhesion

When the substrate is smooth and tight? The ink may be easily peeled off after drying, especially when it is in a semi-finished product or finished product? Yun? Neon roasting? Slightly 鬖 ?? ず Chu 蛲 淝? ΑΧ ???? ?? Sui Zhiyue Weishan 栌 沎 銎 颺 Fashion? 髡 髡? Hammer to accept poverty ?? N ink adhesion.

Implant package

The yield of the implant process is mainly determined by the RF characteristics of the encapsulated conductive adhesive and the positioning accuracy of the printed parts. In general, the accuracy of letterpress printing is the worst. If it can be considered in the process planning and initial equipment construction adjustment in the future, Will effectively improve the yield of the N implant process.

The life cycle

The life cycle of printed electronic labels is shorter than that of electronic labels made by etching, stamping or evaporation. The reason is that the silver paste after baking and drying is very easy to contact with water molecules or sulfur molecules in the air. Oxidation or vulcanization occurs, and there is discoloration or blackening. If this type of printed electronic label is used and affixed to goods that will be transported by sea, the phenomenon of oxidation or carbonization will be more serious. After the antenna is oxidized, oxidized or vulcanized, the RF performance of the electronic tag will be affected by the depth of its changing layer, but fortunately, the thickness of the changing layer will not change significantly until the thickness of the layer reaches a certain depth. .

in conclusion

When the above four printing methods are used for passive UHF electronic label printing, their costs and process yields are different. As shown in Figure [5], although the yields of the two intaglio and letterpress printing technologies are low, but The production cost and production capacity of these two technologies are very competitive, and if the conductive ink material can have a breakthrough in the future, the results of Figure [5] will be completely improved.

Figure 5. Comparison of printing cost and yield

In addition, the cost of inkjet printing is still higher than that of 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, and The process characteristics of low material loss and stable high yield, on the contrary, make the overall production cost the lowest.

Because the performance of the printed antenna mainly depends on the two process parameters such as the solid content of the conductive particles and the printed film thickness of the conductive ink, and these two parameters can control 74% of the results that affect the yield of the process, as shown in Figure [6]. This shows that the yield of printed passive electronic label technology will be deeply affected by the characteristics of conductive ink materials.

Figure 6. Yield factor of printed electronic label process ?? / P>

references

[1] Helmut Kipphan, Handbook of Print Media, 2001, Berlin: Springer, pp.57.
[2] Helmut Kipphan, Handbook of Print Media, 2001, Berlin: Springer, pp. 48.
[3] Helmut Kipphan, Handbook of Print Media, 2001, Berlin: Springer, pp. 47.
[4] Chen Lijuan and Zhang Haojun, Characteristic Analysis of Commercial Conductive Ink, Zhenglong RFID Research Quarterly Report 2005Q4, Zhenglong Co., Ltd., 2005, pp.13.
[5] Siden, J .; Olsson, T .; Koptioug, A .; Nilsson, H.-E .; Reduced Amount of Conductive Ink with Gridded Printed Antennas, Polymers and Adhesives in Microelectronics and Photonics, Polytronic 2005. 5th International Conference on 23-26 Oct. 2005, pp.86? 89.
[6] Chen Lijuan, Du Jinming, Smart Carton Characteristic Analysis, Zhenglong RFID Research Quarterly Report 2005Q3, Zhenglong Co., Ltd., 2005, pp.08.
[7] Robert J. Weber, Introduction to Microwave Circuits: Radio Frequency and Design Applications, IEEE Press Series on RF and Microwave Technology 2001, pp.21.
[8] Zhang Haojun, Du Jinming, Discussion on the Application of Mainstream Printing Technology to RFID, Zhenglong RFID Research Quarterly Report 2006Q3, Zhenglong Co., Ltd., 2006, pp.26.
[9] Zhang Haojun, Du Jinming, Discussion on the Application of Mainstream Printing Technology to RFID, Zhenglong RFID Research Quarterly Report 2006Q3, Zhenglong Co., Ltd., 2006, pp.28.

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