Detailed explanation of RFID electronic label die cutting process

RFID electronic tag die-cutting is a crucial process in the production of RFID tags. This process involves cutting the electronic tags into the desired shape and size using specialized die-cutting machines. Precision and accuracy are key factors in ensuring the proper functionality and aesthetic appeal of the RFID tags.

During the die-cutting process, the RFID tags are placed on a cutting die, which is a specialized tool that contains the cutting pattern. The die-cutting machine then applies pressure to the die, cutting through the material and creating the desired shape. The cutting dies are specifically designed to match the shape and size requirements of the RFID tags, ensuring consistency and uniformity throughout the production process.

The RFID tag die-cutting process is carried out with great care and attention to detail. The machines are equipped with advanced technology to maintain high levels of accuracy, minimizing any errors or inconsistencies. This precision is crucial as it directly impacts the performance and reliability of the RFID tags during their application and usage.

Furthermore, the die-cutting process enables efficient production and scalability. With the ability to cut multiple tags simultaneously, manufacturers can achieve high volumes of RFID tag production in a relatively short span of time. This makes the process cost-effective and helps meet the growing demand for RFID tags in various industries.

The manufacturing techniques for RFID antennas in the low-frequency range mainly include coil winding. For ultra-high frequency and high frequency antennas, the main manufacturing methods are etching, electroplating, and printing.

Etching method:

First, print anti-etching ink on the PET film covered with metal foil to protect the antenna circuit from being dissolved during the etching process. Then, the film is baked, etched, and cleaned to obtain the desired antenna pattern.

The advantages of this method are: mature process, high yield in antenna production, and consistent performance of the antennas. The disadvantages are: slow etching process leading to slow production speed, and high cost due to the large amount of copper foil etched away.

Printing method:

The antenna pattern is printed on the PET substrate using conductive silver paste, which is then baked and cured. This method has the advantages of fast production speed and flexibility for small-scale production.

The disadvantages of this method are: 1) the conductivity of conductive silver paste is much lower than copper foil, resulting in higher conductor loss and lower antenna efficiency compared to etching method antennas; 2) poor adhesion of conductive silver paste to PET substrate, leading to lower reliability of the antennas; 3) increase in silver prices, which increases the cost of conductive silver paste and weakens its cost advantage.

Electroplating method:

First, the antenna pattern is directly printed on the PET substrate using conductive silver paste (thinner than printing method) or other electroplating seed layers. Then, the substrate is baked and electroplated to thicken the conductive layer and obtain the finished antenna.

The advantages of this method are: fast production speed, low conductor loss, and good antenna performance. The disadvantage is that the initial equipment investment is large, and it is only suitable for large-scale production.

Vacuum coating method:

First, the reverse pattern of the RFID antenna is printed on the PET substrate using a mask in the printing process. Then, aluminum or copper is coated using vacuum coating method. Finally, the RFID antenna is formed through the demasking process.

The advantages of this method are: fast production speed, relatively low cost; the disadvantage is that the deposited film thickness is approximately 2μm, much lower than the etching and electroplating methods' 18μm. The performance of the antennas is between etching and printing methods. The equipment cost for vacuum coating is around 1 million US dollars, making it suitable for large-scale production, similar to electroplating method.

Some people have also tried printing platinum ink on the PET substrate as a seed layer, followed by electroplating copper. The advantage of this method is that platinum ink is cheaper than conductive ink. However, the plating speed of copper is slower and the deposition thickness is about several micrometers.

In addition, there is a wiring method for high frequency antennas, which involves threading enameled wire (approximately 0.25mm) through an ultrasonic head. The ultrasonic head follows the design pattern during the wiring process, and the enameled wire is bonded ultrasonically to the PVC substrate. This method has good antenna performance and high reliability but is relatively more expensive than etching method.

Die cutting technology introduction

Due to the slow production speed, material waste, and environmental pollution of the mainstream etching method, as well as the high cost and low reliability of the conductive silver paste in the printing method, people have developed new low-cost, high-performance antenna manufacturing methods. Therefore, die cutting technology has been adopted to process adhesive materials for RFID antenna production.

Principle of die cutting technology

Die cutting technology is actually a cutting process. The adhesive material is placed on the die cutting table of the die cutting machine, and pressure is applied according to the pre-designed pattern using a die cutting blade to break and separate the areas corresponding to the blade edge, thereby obtaining the desired shape. The die cutting of the adhesive material usually only cuts through the surface material and adhesive layer, leaving the backing paper and the silicone oil coating on its surface. The die cut labels are ultimately retained on the backing paper.

Die cutting materials

RFID antennas are generally composed of a layer of 18μm thick aluminum or copper and a 100μm thick release paper. The aluminum or copper layer serves as the functional layer on which the pattern shape of the RFID antenna is formed. PET serves as the carrier layer for the antenna pattern, mainly providing mechanical support. The dielectric constant and thickness of the PET substrate also affect the resonant frequency of the antenna. This structure is similar to traditional adhesive structures, but with an additional reinforcement layer. Therefore, the antenna is made in the form of an adhesive structure. The materials used for die cutting have a three-layer structure: release paper or PET (approximately 100μm) with silicone oil, adhesive layer (approximately 20μm), and aluminum foil with a reinforcement layer (approximately 35μm).

Silicone oil is mainly used for easy waste separation, and the reinforcement layer is used to strengthen the aluminum foil for easier waste removal.

Die cutting machine

The die cutting machine mainly completes the die cutting process by controlling the pressure. Its working principle is to use die cutting blades, steel blades, metal molds, and steel wires (or templates engraved on steel plates) to apply a certain pressure through the embossing plate to cut the material into the desired shape.

According to the different die cutting base plates and cutting mechanisms, die cutting machines can be divided into flatbed die cutting, flatbed rotary die cutting, and rotary die cutting machines.

RFID antenna die cutting solution

Analysis of RFID antenna die cutting characteristics

(1) Mold requirements:

1) Although we use adhesive structures to make our antennas, the face material is aluminum or copper, which is prone to blade wear. For non-metal materials, etching molds can generally die cut around 200,000 times, but for metals, they need to be repaired or discarded after about 20,000 times. Therefore, choosing better mold materials and performing heat treatment on the blade edge can improve its hardness.

2) RFID antenna patterns are relatively fine and complex, with small spacing, generally around 1mm line width. Therefore, we choose high-precision etching blades or engraving molds, usually with single-peaked blade edges, with inclined faces facing outward and no slant faces facing inward to ensure a straight 1 mm line width.

Analysis of Difficulties in Waste Disposal for RFID Antenna

The intricate and complex patterns of RFID antenna layouts make it exceptionally challenging to dispose of waste during die-cutting. This is also the difficulty encountered in die-cutting antennas. Specifically, there are several characteristics (using the reference antenna provided by NXP as an example, as shown in Figure 5):

1. Closed-loop structure: In general, dipole antennas have a closed-loop structure, such as a T-shaped matching structure or inductive coupling structure, to match the impedance conjugate with the chip. These impedance matching structures are essentially closed circular loops, making direct waste disposal nearly impossible.

2. In order to adjust the real part of the antenna, the T-shaped matching structure is only connected to the radiating part of the antenna in the middle. The other parts of the T-shaped structure have a gap with the radiating part of the antenna. This gap is perpendicular to the bending line and the normal layout direction, making waste disposal difficult.

3. To miniaturize dipole antennas, bending line techniques are commonly used. The spacing between the bending lines is usually around 1mm-2mm, and the bending height is approximately 8mm. These slender bending lines are challenging to dispose of as waste. After adding the reinforcement layer, we found that the gap of one end of the bending line can be directly disposed of as waste, while the gap of the other end is not easily disposed of.

4. Similarly, for miniaturization purposes, there may also be folding structures at the end of the antenna, which is equivalent to half a closed loop, posing significant difficulties for waste disposal.

Adhesive Die-cutting Waste Disposal Solution

To address the intricate and complex nature of RFID antennas, we propose a two-step die-cutting and waste disposal solution for antenna manufacturing. We divide the antenna into two main parts: internal patterns and frame patterns. The frame pattern is a regular pattern that can be directly disposed of as waste, while the internal pattern is more challenging to dispose of. We separate the internal pattern into individual patterns and use adhesive to stick and dispose of them. Refer to the diagram below:

1) Principle of adhesive waste disposal:

Adhesive waste disposal is mainly based on the relative strength of adhesive force to achieve waste disposal. As shown in Figure 7, the purple parts represent the parts to be disposed of, which are individual "islands." The parts to be retained are connected as a whole. The adhesive tape is attached to the parts to be disposed of. When the adhesive tape passes through the "islands," due to the relatively small area of the "islands," the adhesive force between the adhesive tape and the "islands" is greater than the adhesive force between the "islands" and the release paper, causing the "islands" to be transferred to the adhesive tape. When the adhesive tape passes through the parts to be retained, the area of the parts to be retained is relatively large, and the adhesive force of the adhesive tape to the "islands" is smaller than the adhesive force between the parts to be retained and the release paper. Hence, the parts to be retained continue to stay on the release paper. As a result, the separated "islands" are carried away by the adhesive tape, while the retained pattern layer remains on the release paper, thereby achieving waste disposal.

2) Flowchart and pattern evolution during waste disposal:

Refer to the diagram below for the specific process.

Taking the reference antenna provided by NXP as an example, Figure 9 shows the step-by-step evolution of the antenna pattern during die-cutting.

3) Implementation process:

According to the adhesive waste disposal solution, we selected two 300mm-wide flat bed die-cutting machines, two composite machines, one laminating machine, and one stripping machine.

Laminating is responsible for adhering the tape to the aluminum foil on the release paper, while the stripping machine collects the adhesive tape with waste material. Due to the effect of silicone oil on the release paper, the adhesion between the aluminum foil and the release paper is weak (peel strength exceeding 50g is considered excessive), and the adhesive force of general adhesive tapes can reach more than 100g. Thus, adhesion is generally not a problem. The width of the adhesive tape is generally narrower than the maximum width of waste material.

Comparison of Performance between Die-cut Antennas and Etched Antennas

(1) Edge Neatness: Die-cut antennas have very smooth edges as they are mechanically cut. On the other hand, etched antennas produced through chemical etching have uneven edges due to the lateral etching effect. Please refer to the diagram below for more details:

(2) Production Speed: The speed of a die-cutting machine is three times per second. Assuming the die has three patterns and the machine operates for 12 hours a day, we can produce 400,000 antennas per day. This production speed is not only much higher than that of etching method but also faster than the printing method.

(3) Pattern Precision: The precision of etching can reach up to 0.2 mm, making it suitable for direct chip-on-antenna applications. Die-cutting has a precision of approximately 0.5 mm, and therefore, an interconnection between the antenna and chip needs to be accomplished through module transfer.

(4) Pattern Consistency: Etched antenna patterns are firmly bonded to the PET substrate, while the patterns on die-cut antennas, due to the silicone oil on the release paper, are not fixed and may shift, causing distortion. Therefore, minimizing human intervention is crucial during the production process.