Method for manufacturing a conductive pattern on a substrate

Abstract

A method for producing a conductive pattern on a substrate is provided. [Solution] The method comprises the steps of forming an adhesive layer on a substrate in a predetermined pattern, adding conductive solid particles onto the adhesive layer to adhere the particles to the adhesive, heating the particles with electromagnetic radiation having a wavelength in the electromagnetic spectrum range of 600 to 1400 nm, preferably 700 to 1200 nm, so that the temperature of the solid particles exceeds their inherent melting point, and pressing the heated particles against the substrate at a nip to flatten the particles and electrically connect them to form a conductive pattern.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a conductive pattern on a substrate and a method for manufacturing an RFID tag.

Background Art

[0002] It is known to form a conductive pattern on a substrate. Solid conductive particles are formed in a predetermined pattern on the substrate. Then, typically by heating the solid particles by thermal heating in an oven, the solid particles reach a temperature above their melting point. And by pressing the particles at a nip, the particles are flattened and electrically connected to each other to form a conductive pattern.

Summary of the Invention

Problems to be Solved by the Invention

[0003] As a drawback of this method, during the heating process, not only the solid particles but also the substrate absorbs heat. This causes problems such as, for example, when a fiber substrate is heated, it dries out. This results in undesirable dimensional changes in the substrate. Also, if heated to too high a temperature, the fibers may turn brown or even burn. Furthermore, thermal heating has a relatively high energy consumption.

[0004] An object of the present invention is to provide a method for forming a conductive pattern on a substrate that solves at least some of the above problems.

Means for Solving the Problems

[0005] The present invention is a method for manufacturing a conductive pattern on a substrate, forming an adhesive layer in a predetermined pattern on a substrate made of at least one of a cellulose material and a polymer material; adding conductive solid particles on the adhesive layer and attaching the particles to the adhesive; A step of heating the particles with electromagnetic radiation having a wavelength in the range of 600 to 1400 nm, preferably in the range of 700 to 1200 nm, of the electromagnetic spectrum so that the temperature of the solid particles exceeds its intrinsic melting point; A step of flattening the particles and electrically connecting the particles to each other to form a conductive pattern by pressing the heated particles against the substrate at a nip; The method comprises the steps of.

[0006] Further, the present invention is a method for manufacturing an RFID tag, A step of forming an adhesive layer in a predetermined pattern on a substrate made of at least one of a cellulose material and a polymer material; A step of adding conductive solid particles onto the adhesive layer and attaching the particles to the adhesive; A step of heating the particles with electromagnetic radiation having a wavelength in the range of 600 to 1400 nm, preferably in the range of 700 to 1200 nm, of the electromagnetic spectrum so that the temperature of the solid particles exceeds its intrinsic melting point; A step of flattening the particles and electrically connecting the particles to each other to form an antenna by pressing the heated particles against the substrate at a nip; A step of attaching an integrated circuit (IC) to the antenna, establishing an electrical connection between the IC and the antenna, and forming an RFID tag by the antenna and the IC; The method comprises the steps of.

Embodiments for Carrying Out the Invention

[0007] Hereinafter, with reference to some preferred embodiments, a method for manufacturing a conductive pattern on a substrate of the present invention will be described in more detail.

[0008] The method comprises a step of forming an adhesive layer on a substrate in a predetermined pattern. Such an adhesive pattern can be applied by any suitable method as long as it can apply an adhesive pattern on the substrate, for example, inkjet, flexographic printing, letterpress printing, gravure printing, screen printing, spraying, web coating, wheel coating, brushing, etc. Any suitable adhesive can be used as the adhesive according to the purpose. Preferred adhesives include, for example, acrylic adhesives such as styrene / acrylate, styrene / butadiene, or PVAc emulsion. The adhesive may be a starch-based adhesive such as chemical starch.

[0009] Since the adhesiveness of the conductive pattern to the cellulose-based material is very good, the substrate may be a paper or cardboard material. Also, paper or cardboard is biodegradable and recyclable, so it is environmentally friendly. Preferred substrates include cellulose substrates with a basis weight of 30 to 200 gsm. Also, the substrate may be a single substrate or a plurality of substrates.

[0010] Other suitable cellulose substrates include substrates made of microfibrillated cellulose (MFC) or films made of microfibrillated cellulose.

[0011] However, those skilled in the art will understand that other non-conductive substrates such as polyester, taffeta, or nylon are possible. These polymer substrates are particularly suitable for products used in a wet environment, such as, for example, care labels for clothes containing washing instructions. Since these polymers are very sensitive to heat, the present invention is also very suitable for these materials. Also, those skilled in the art will understand that a substrate can be configured by combining a cellulose material and a polymer material.

[0012] The method further comprises a step of adding conductive solid particles onto the adhesive layer pattern and attaching the particles to the adhesive. The solid particles can be applied by several different methods, but the present invention is not limited to a specific application method. For example, the application step may include spraying the solid particles onto the adhesive, dipping the substrate into a particle bed to attach the particles onto the adhesive pattern, or electrostatic transfer.

[0013] The conductive solid particles are preferably made of a solder material of a non-eutectic alloy. However, alloys containing tin and bismuth or tin only are most preferred. Since tin and bismuth are lead-free, they are more environmentally friendly.

[0014] Also, tin and bismuth have a relatively low melting temperature and better conductivity.

[0015] The method also includes at least one heating step. The heating is performed by heating the solid particles with electromagnetic radiation having a wavelength in the range of 600 - 1400 nm, preferably in the range of 700 - 1200 nm, such that the temperature of the solid particles exceeds their respective melting points.

[0016] The energy emission of the electromagnetic radiation is in the range of 1.5 - 2.8 MW / μm·m 2 of the range.

[0017] Tests have shown that these short-wavelength electromagnetic radiations are very suitable for heating and melting the solid solder particles of the non-eutectic alloy. In this region, the radiation excites combinations of molecular vibrations and overtones. This means that in this part of the electromagnetic spectrum, since the molar absorptivity is typically low, many polymer compounds do not have strong absorbance and are difficult to heat when irradiated with such short-wavelength electromagnetic radiations. These short-wavelength electromagnetic radiations have the potential to selectively heat materials with strong absorbance in this part of the spectrum, and their inherent energy density enables high speeds while the underlying substrate can avoid damage by transmitting the radiation. These short-wavelength electromagnetic radiations are also known as near-infrared light (NIR). The electromagnetic radiation may be directly irradiated simultaneously on the surface of the substrate facing the solid particles, or on the back surface of the substrate opposite to the solid particles, or on both sides of the substrate.

[0018] Therefore, paper, fiber-based substrates, and the most common plastic packages do not significantly absorb radiation at these short wavelengths. This means that there is very little excessive heating of the substrate that would indirectly have an adverse effect on substrates made of paper, cardboard, polyester, and nylon.

[0019] This method also includes a step of pressing the heated particles against the substrate. The pressing is performed by a nip, and the surface temperature of the nip is lower than the inherent melting temperature of the particles. By pressing with the nip, the particles are flattened and electrically connected to each other to form a conductive pattern.

[0020] It is preferable to perform this pressing soon after radiation heating so that the particles remain in a nearly molten state. This causes the previously melted material to solidify as a substantially continuous conductive pattern.

[0021] The nip may be a non-heated nip. However, it is preferable to heat the nip surface to a temperature slightly lower (for example, about 30 to 60 °C) than the specific melting temperature. Thereby, for example, before pressing the melt against the substrate, it is possible to prevent solidification on the way. The nip solidifies the molten material in front of the originally solid conductive particles as a substantially continuous conductive layer arranged within a predetermined pattern, rather than as separate particles at this stage.

[0022] This method may include embodiments of one or more additional heating steps. These additional heating steps may be arranged before and / or after the short-wavelength electromagnetic radiation irradiation step.

[0023] The additional heating step may be infrared (IR) heating with a wavelength of 1500 nm or more.

[0024] As the IR source, a 2×2 kW IR lamp or a 4×2 kW IR lamp is preferable. As a preferred embodiment, there is one that irradiates IR with a wavelength of 1500 nm or more after electromagnetic radiation in the wavelength range of 600 to 1400 nm.

[0025] The additional heating step may be thermal heating in an oven. The temperature of the oven is less than 200 °C.

[0026] Since the conductor can have geometric attributes of various shapes and sizes, the additional heating step can be suitably used. Different combinations of heating steps can heat all different geometric shapes in different ways. For example, as one heating method, first, a narrow shape or edge of a solid pattern may be heated, but as another heating method, first, the center of a solid pattern may be heated. Therefore, in the electromagnetic radiation heating step (wavelength 600 to 1400 nm) of the present invention, it may be beneficial to use IR and / or thermal heating in combination to obtain a well-balanced and uniform heating profile for various geometric shapes.

[0027] In a preferred embodiment of the present invention, the formed conductive pattern is an antenna, preferably an antenna for an RFID tag.

[0028] According to another aspect of the present invention, a method for manufacturing an RFID tag is provided. This embodiment is the same as the above embodiment, but further includes a step of attaching an integrated circuit (IC) or a microchip to the conductive pattern, i.e., the antenna, to establish an electrical connection between the IC and the antenna, and forming an RFID tag with the antenna and the IC.

[0029] The IC can be attached to the antenna in various ways. In the first embodiment, an adhesive is applied between the IC and the antenna pad area, and the IC is pressed against the RFID antenna to attach the IC to the antenna. In the second embodiment, the IC is attached by soldering.

[0030] Compared with the prior art, there are several advantages to the method of the present invention. · Since the substrate absorbs less heat, the risk of damage to the substrate is low. · Since the heat is directed to where it is needed, the energy consumption is reduced. · Even when additional heat is required, the energy consumption is reduced by the heating process of the present invention. · According to the method of the present invention, a heat-sensitive substrate can be used. · Substrates made of cellulose and / or polymers do not significantly absorb these short-wavelength radiations. Since it has been shown that heating and cooling of the substrate can increase the stress in the substrate and cause cracks or the like, the above advantages mean that unnecessary heating of the substrate is significantly reduced.

[0031] The present invention has been described based on several preferred embodiments. However, it is obvious that those skilled in the art can conceive of additional embodiments and modifications within the scope described in the claims.

[0032] For example, the present invention can be applied not only to the manufacture of antennas for RFID tags. For example, it will be apparent to those skilled in the art that the method of the present invention can also be applied when manufacturing other conductive patterns such as printed wiring, conductors for flexible batteries, displays, sensors, heaters, and the like.

Claims

1. A method for manufacturing a conductive pattern on a substrate, comprising: forming an adhesive layer in a predetermined pattern on a substrate made of at least one of a cellulose material and a polymer material; adding conductive solid particles onto the adhesive layer and attaching the particles to the adhesive; heating the particles with electromagnetic radiation having a wavelength in the range of 600 to 1400 nm, preferably in the range of 700 to 1200 nm, of the electromagnetic spectrum such that the temperature of the solid particles exceeds its intrinsic melting point; flattening the particles by pressing the heated particles against the substrate at a nip, electrically connecting the particles to each other to form a conductive pattern; at least one additional heating step of heating the particles to a temperature below 200°C, the additional heating step being infrared heating by infrared radiation with a wavelength of the IR source of 1500 nm or more.

2. The method according to claim 1, wherein the additional heating step is thermal heating in an oven at a temperature below 200°C.

3. The energy emission of the electromagnetic radiation is within the range of 1.5 to 2.8 MW / μm·m ２ The method according to claim 1 or 2

4. The method according to any one of claims 1 to 3, wherein the solid particles are made of a non-eutectic alloy.

5. The method according to claim 4, wherein the non-eutectic alloy contains tin, preferably tin and bismuth.

6. The method according to any one of claims 1 to 5, wherein the substrate is made of paper or paperboard material.

7. The method according to any one of claims 1 to 5, wherein the substrate is made of polyester or nylon.

8. The method according to any one of claims 1 to 7, wherein the conductive pattern is an antenna.

9. The method according to claim 8, further comprising a step of attaching an integrated circuit (IC) to the antenna to establish an electrical connection between the IC and the antenna, and forming an RFID tag by the antenna and the IC.

10. A method for manufacturing an RFID tag, comprising: forming an adhesive layer in a predetermined pattern on a substrate made of at least one of a cellulose material and a polymer material; adding conductive solid particles onto the adhesive layer and attaching the particles to the adhesive; heating the particles with electromagnetic radiation having a wavelength in the range of 600 to 1400 nm, preferably in the range of 700 to 1200 nm, of the electromagnetic spectrum such that the temperature of the solid particles exceeds its intrinsic melting point; Pressing the heated particles against the substrate at the nip to flatten the particles and electrically connect the particles to each other to form an antenna; Attaching an integrated circuit (IC) to the antenna to establish an electrical connection between the IC and the antenna and forming an RFID tag with the antenna and the IC; At least one additional heating step of heating the particles to a temperature below 200° C., the additional heating step being infrared heating by infrared heating in which the wavelength of the IR source is 1500 nm or more; A method comprising the steps of: **Claim 11** The method according to claim 10, wherein the integrated circuit (IC) is attached by being pasted on and pressed against the antenna. **Claim 12** The method according to claim 10, wherein the integrated circuit (IC) is attached by soldering.