Conductive-particle-containing hot melt adhesive sheet, smart card manufacturing method, and smart card

Abstract

The present invention provides a conductive-particle-containing hot melt adhesive sheet, a smart card manufacturing method, and a smart card, with which it is possible to obtain, with high production efficiency, an excellent adhesive force. This conductive-particle-containing hot melt adhesive sheet (1) comprises: a binder (2) containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin; and conductive particles (3), the crystalline polyurethane resin content of the binder (2) being 5 mass% to less than 75 mass%, and the melt viscosity of the binder (2) at 155-170℃ being 5,000-50,000 Pa･s.

Description

Conductive particle-containing hot melt adhesive sheet, smart card manufacturing method, and smart card

[0001] This application claims priority from Japanese Patent Application No. 2024-123607, filed on July 30, 2024, which is incorporated herein by reference.

[0002] 2. Description of the Related Art So-called smart cards, such as credit cards, are known in which electrodes of an IC (Integrated Circuit) chip are connected to antenna wiring inside the card member.

[0003] Smart cards are formed, for example, by laminating a film printed with antenna wiring or a film with a surface print, etc., around a plastic plate made of various resins as a core. A recess is formed by milling a portion of the laminated plastic plate or film, and an IC chip is mounted and adhered in this recess, electrically connecting the IC chip to the antenna wiring. Materials such as PVC (Polyvinyl Chloride) and PET (Polyethylene terephthalate) have traditionally been used as card materials for smart cards. Anisotropic conductive films are also used as adhesives for smart cards.

[0004] For example, Patent Document 1 describes the use of an anisotropic conductive film that uses polyester resin and polyamide resin as binder components and non-eutectic solder particles as conductive particles. However, in the technology described in Patent Document 1, within the usable temperature range of the thermocompression bonding process, a metal bond is formed with the connection portion by melting the non-eutectic solder particles, but if the temperature reached by the adhesive sheet exceeds 155°C, the binder's melt viscosity is low, and the binder's repulsive action (springback phenomenon) after thermocompression bonding reduces the adhesive strength, which can result in poor connection between the card member and the IC chip.

[0005] Furthermore, Patent Document 2 describes a latent reactive polyurethane adhesive film containing crystalline polyurethane, an isocyanate as a crosslinking agent, and a conductive filler to accommodate difficult-to-adhere surfaces. However, the technology described in Patent Document 2 involves heating at 120°C and 2.5 bar for 5 minutes and cold pressing at 3.5 bar for 3 minutes to achieve sufficient strength through the reaction in connecting the card member and the IC chip. For this reason, the heating process in the technology described in Patent Document 2 takes time, making it undesirable in terms of production efficiency as an adhesive for mass-produced smart cards.

[0006] Patent No. 6966659 Publication Special Publication No. 2022-515327

[0007] The present technology has been proposed in light of the current situation, and provides a conductive particle-containing hot melt adhesive sheet that can achieve excellent adhesive strength with high production efficiency, a method for manufacturing a smart card, and a smart card.

[0008] The conductive particle-containing hot melt adhesive sheet according to the present technology comprises a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin, and conductive particles, wherein the content of the crystalline polyurethane resin in the binder is 5% by mass or more and less than 75% by mass, and the melt viscosity of the binder at 155 to 170°C is 5,000 to 50,000 Pa·s.

[0009] The method for manufacturing a smart card according to the present technology includes: a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin; and conductive particles. The content of the crystalline polyurethane resin in the binder is 5% by mass or more and less than 75% by mass, and the melt viscosity of the binder at 155 to 170°C is 5,000 to 50,000 Pa·s. The conductive particle-containing hot melt adhesive sheet is interposed between a card member and an IC chip, and the two are thermocompressed together.

[0010] The smart card according to the present technology comprises a card member, an IC chip, and an adhesive layer that bonds the card member and the IC chip, and the adhesive layer is a solidified product obtained after melting the aforementioned conductive particle-containing hot melt adhesive sheet.

[0011] This technology can achieve excellent adhesive strength with high production efficiency when connecting a card member and an IC chip.

[0012] Fig. 1 is a cross-sectional view showing an example of a conductive particle-containing hot melt adhesive sheet. Fig. 2 is a graph illustrating the melt viscosity of a binder to which the present technology is applied. Fig. 3 is a schematic perspective view showing an example of a smart card. Fig. 4 is a top view showing an example of an IC chip region of a card member. Fig. 5 is a perspective view illustrating an example of a step of attaching a conductive particle-containing hot melt adhesive sheet to a connection surface of an IC chip in a method for manufacturing a smart card. Fig. 6 is a cross-sectional view illustrating an example of a step of thermocompression bonding an IC chip and a card member in a method for manufacturing a smart card.

[0013] <Conductive Particle-Containing Hot Melt Adhesive Sheet> Figure 1 is a cross-sectional view showing an example of a conductive particle-containing hot melt adhesive sheet. The conductive particle-containing hot melt adhesive sheet 1 according to this embodiment has a resin layer 4 comprising a binder 2 and conductive particles 3. By adjusting the melt viscosity of the binder 2 at 155 to 170°C to preferably within the range of 5,000 to 50,000 Pa·s, and more preferably within the range of 10,000 to 50,000 Pa·s, it is possible to obtain excellent adhesive strength with high production efficiency when connecting a card member and an IC chip in a smart card, as described below.

[0014] Here, high production efficiency means not only a short time for the thermocompression bonding process but also, for example, a wider usable temperature range in the thermocompression bonding process, thereby improving yield. Furthermore, excellent adhesive strength means that the initial adhesive strength between the card member and the IC chip is good (OK) as evaluated by the method described in the examples below.

[0015] In this specification, a smart card is a card incorporating an integrated circuit (IC) for recording and calculating information (data), and is also referred to as an "IC card" or "chip card." A smart card includes, for example, a card member, an IC chip, and an adhesive layer that bonds the card member and the IC chip. A smart card may also be a dual-interface card with a single IC chip that has two interfaces, contact and contactless, or a hybrid card equipped with a contact IC chip and a contactless IC chip. A smart card may also be a fingerprint authentication card equipped with a fingerprint authentication element, or a card equipped with a one-time password function that incorporates a battery element and a display element. These IC chips and elements have pads that are electrically connected to the electrode portions of the card member.

[0016] The lower limit of the thickness of the conductive particle-containing hot melt adhesive sheet 1 (resin layer 4) can be, for example, 10 μm or more, 20 μm or more, 30 μm or more, or 35 μm or more. The upper limit of the thickness of the conductive particle-containing hot melt adhesive sheet 1 can be, for example, 100 μm or less, 80 μm or less, 60 μm or less, 50 μm or less, or 45 μm or less. This allows the conductive particle-containing hot melt adhesive sheet 1 to be suitably used, for example, in the production of smart cards.

[0017] [Binder] Binder 2 contains a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin. The content of the crystalline polyamide resin, crystalline polyester resin, and crystalline polyurethane resin in binder 2 is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more. This allows the melt viscosity of binder 2 at 155 to 170°C to be preferably in the range of 5,000 to 50,000 Pa·s, more preferably in the range of 10,000 to 50,000 Pa·s. Here, crystalline resins such as crystalline polyamide resins, crystalline polyester resins, and crystalline polyurethane resins refer to resins that have a glass transition point and a melting point and contain "crystals" in which molecular chains are regularly arranged. The melt viscosity of the binder can be measured using a viscoelasticity tester in accordance with JIS K 7244-10.

[0018] (Crystalline Polyamide Resin) The crystalline polyamide resin preferably has a carboxyl group at its terminal. Whether the binder 2 contains a crystalline polyamide resin can be confirmed, for example, by observing an endothermic peak during the temperature rise process in differential scanning calorimetry.

[0019] The terminal carboxyl group concentration of the crystalline polyamide resin is not particularly limited and can be, for example, 0.5 mgKOH / g or more, 1.0 mgKOH / g or more, or 2.0 mgKOH / g or more. The terminal carboxyl group concentration of the crystalline polyamide resin can be, for example, 50 mgKOH / g or less, 30 mgKOH / g or less, or 10 mgKOH / g or less. The terminal carboxyl group concentration of the crystalline polyamide resin can be evaluated, for example, in accordance with JIS K 0070-1992 or ISO 2114. Specific examples of commercially available crystalline polyamide resins having carboxyl groups include "HX2592," "HX2519," and "M1276" manufactured by Arkema.

[0020] The content of the crystalline polyamide resin in the binder 2 is preferably 5% by mass or more, more preferably 15% by mass or more, and even more preferably 25% by mass or more. The content of the crystalline polyamide resin in the binder 2 is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0021] The crystalline polyamide resin in the binder 2 may be used alone or in combination of two or more types. When two or more types of crystalline polyamide resins are used in combination, it is preferable that the total amount thereof satisfies the above content range. The content of the crystalline polyamide resin may be based on the total mass of the resin layer 4 excluding the conductive particles 3. In this case, the preferred range of the content of the crystalline polyamide resin is the same as the above-mentioned numerical range.

[0022] The inclusion of crystalline polyamide resin can improve the adhesive strength between the card member and the IC chip, for example, and can also improve the bending resistance of the smart card. Furthermore, when solder particles are used as conductive particles, the solder wettability is improved, resulting in excellent connection reliability. This is thought to be due to the flux effect of the carboxyl groups present in the crystalline polyamide. As a result, the decrease in the elastic modulus of the adhesive layer due to the addition of a flux compound is prevented, and excellent bending resistance is achieved.

[0023] (Crystalline Polyester Resin) The crystalline polyester resin is not particularly limited, and for example, one having a softening point of 100 to 150°C can be used. A specific example of a commercially available crystalline polyester resin is "Aronmelt PES-111EE" manufactured by Toagosei Co., Ltd. Whether or not the binder 2 contains a crystalline polyester resin can be confirmed, for example, by observing an endothermic peak during the temperature rise process in differential scanning calorimetry.

[0024] The content of the crystalline polyester resin in the binder 2 is preferably 5% by mass or more, more preferably 15% by mass or more, and is preferably 40% by mass or less, more preferably 25% by mass or less.

[0025] The crystalline polyester resin in the binder 2 may be used alone or in combination of two or more types. When two or more types of crystalline polyester resins are used in combination, it is preferable that the total amount thereof satisfies the above content range. The content of the crystalline polyester resin may be based on the total mass of the resin layer 4 excluding the conductive particles 3. In this case, the preferred range of the content of the crystalline polyamide resin is the same as the above-mentioned numerical range.

[0026] By including a crystalline polyester resin, for example, the card member and the IC chip can be bonded together at low temperature in a short time.

[0027] (Crystalline Polyurethane Resin) The crystalline polyurethane resin may have a viscosity of 200 to 3000 mmPa·s in a 15% MEK (Methyl Ethyl Ketone) solution, for example. Whether the binder 2 contains a crystalline polyurethane resin can be confirmed, for example, by observing an endothermic peak during the temperature rise process in differential scanning calorimetry.

[0028] The softening point of the crystalline polyurethane resin is preferably 120° C. or lower, more preferably 110° C. or lower. The softening point of the crystalline polyurethane resin is preferably 70° C. or higher, more preferably 80° C. or higher. The softening point of the crystalline polyurethane resin can be measured using a TMA (Thermomechanical Analysis) device in accordance with JIS K 7196, for example, by raising the temperature of a sample from room temperature to 300° C. at a rate of 5° C. / min.

[0029] The minimum activation temperature of the crystalline polyurethane resin is preferably 100°C or lower, more preferably 80°C or lower. The minimum activation temperature of the crystalline polyurethane resin is preferably 40°C or higher, more preferably 50°C or higher. The minimum activation temperature is the temperature at which the crystalline resin re-crystallizes when cooled from a melted state. The minimum activation temperature of the crystalline polyurethane resin can be determined in accordance with EN 12961 by preparing samples and measuring them according to the following procedure. Step 1: Two PVC sheets with a crystalline polyurethane resin layer are allowed to stand for 10 minutes at a predetermined temperature. Here, the "predetermined temperature" is set, for example, between 40°C and 100°C in 5°C increments. Step 2: After standing, the two sheets are bonded together and allowed to stand for 24 hours at 23°C / 50% HR. Step 3: The temperature is set to the predetermined temperature, and the peel strength is measured for multiple samples prepared. For example, when the peel strength of a sample prepared at a temperature showing the highest peel strength, for example 70°C, is taken as 100%, the lowest temperature showing a peel strength of 80% or more is taken as the minimum activation temperature.

[0030] Specific examples of commercially available crystalline polyurethane resins include "HK-6502" manufactured by Henan Huike New Material Technology Co., Ltd., "H306" manufactured by Micacll Co., Ltd., and "H3F3002EH-5" manufactured by Fuwafon Co., Ltd.

[0031] The content of the crystalline polyurethane resin in the binder 2 is preferably 5% by mass or more, more preferably 15% by mass or more, and is preferably less than 75% by mass, more preferably 60% by mass or less.

[0032] The crystalline polyurethane resin in the binder 2 may be used alone or in combination of two or more types. When two or more types of crystalline polyurethane resins are used in combination, it is preferable that the total amount thereof satisfies the above content range. The content of the crystalline polyurethane resin may be based on the total mass of the resin layer 4 excluding the conductive particles 3. In this case, the preferred range of the content of the crystalline polyurethane resin is the same as the above-mentioned numerical range.

[0033] By including a crystalline polyurethane resin, it is possible to prevent a decrease in the melt viscosity of the binder during thermocompression bonding, and to widen the temperature range in which the conductive particle-containing hot melt adhesive sheet 1 can be used.

[0034] (Other Additives) The binder 2 may further contain other resins besides the crystalline polyamide resin, crystalline polyester resin, and crystalline polyurethane resin, as necessary. The other resins can be selected appropriately depending on the purpose, such as crystalline resins and amorphous resins. The crystalline resin is not particularly limited as long as it has a crystalline region, and examples thereof include polyester resins, polyolefin resins, and polyurethane resins. Examples of polyester resins include polyethylene terephthalate resins and polybutylene terephthalate resins. Examples of polyolefin resins include polyethylene resins, polypropylene resins, and polybutylene resins. Examples of amorphous resins include those exemplified in the description of the crystalline resins.

[0035] (Melt Viscosity of Binder) Figure 2 is a graph illustrating the melt viscosity of a binder to which the present technology is applied. In the graph shown in Figure 2, melt viscosity curve A is for the binder to which the present technology is applied, and melt viscosity curve B is for the binder of the conventional technology. Here, the binder of the conventional technology contains 50 to 100 mass% of crystalline polyamide and does not contain a crystalline polyurethane resin.

[0036] By incorporating crystalline polyurethane resin, the binder to which this technology is applied can increase the melt viscosity at high temperatures while leaving the melt viscosity at low temperatures unchanged. This is because the temperature dependency of crystalline polyurethane resin is smaller than that of polyamide resin or polyester resin.

[0037] In the graph shown in Figure 2, there is almost no difference in viscosity between melt viscosity curve A and melt viscosity curve B from room temperature to around 120°C, but at temperatures above that, the difference in viscosity gradually increases as the temperature increases. In melt viscosity curve A, the melt viscosity at 155 to 170°C is preferably in the range of 5,000 to 50,000 Pa s, more preferably in the range of 10,000 to 50,000 Pa s. On the other hand, in melt viscosity curve B, the melt viscosity at 155 to 170°C is 1,000 Pa s or less.

[0038] For example, when the thermocompression bonding is performed four times at 1.0 second intervals under the conditions of 210°C, 90N, and 0.7 seconds described below, the temperature reached by the conductive particle-containing hot melt adhesive sheet 1 is approximately 155°C. When the thermocompression bonding is performed four times at 1.0 second intervals under the conditions of 240°C, 90N, and 0.7 seconds, the temperature reached by the conductive particle-containing hot melt adhesive sheet is approximately 170°C.

[0039] In such a thermocompression bonding process, if the binder exhibits a melt viscosity curve such as melt viscosity curve B, the melt viscosity at 155 to 170°C is low, resulting in a decrease in adhesive strength due to the binder's repulsive action (springback phenomenon) after thermocompression bonding. On the other hand, if the binder exhibits a melt viscosity curve such as melt viscosity curve A, the binder's springback phenomenon after thermocompression bonding can be prevented, preventing a decrease in adhesive strength. Furthermore, if the binder exhibits a melt viscosity curve such as melt viscosity curve A, a stable metal bond can be obtained, resulting in excellent results in various bending resistance tests. Furthermore, if the binder exhibits a melt viscosity curve such as melt viscosity curve A, the usable temperature range in the thermocompression bonding process can be expanded by approximately twice as much as if the binder exhibited melt viscosity curve B, thereby achieving high production efficiency. Furthermore, by adding a thermoplastic crystalline polyurethane resin, rather than a thermosetting resin, to the binder, a conductive particle-containing hot melt adhesive sheet with excellent storage stability and ease of use can be obtained.

[0040] [Conductive Particles] The conductive particle-containing hot melt adhesive sheet 1 contains, for example, solder particles as the conductive particles 3. The solder particles may be non-eutectic alloy solder particles or eutectic alloy solder particles, but it is preferable to use non-eutectic alloy solder particles. A non-eutectic alloy refers to an alloy that does not have a eutectic point. Non-eutectic alloy solder particles remain in a semi-molten state for a longer period of time during thermocompression bonding than eutectic alloy solder particles, so they can sufficiently remove resin and achieve excellent connection reliability. The solder particles are preferably an alloy containing two or more elements selected from the group consisting of Sn, Bi, Ag, In, Cu, Sb, Pb, and Zn. The solder particles can be appropriately selected from, for example, Sn-Pb, Pb-Sn-Sb, Sn-Sb, Sn-Pb-Bi, Bi-Sn, Sn-Bi-Cu, Sn-Cu, Sn-Pb-Cu, Sn-In, Sn-Ag, Sn-Pb-Ag, Pb-Ag, etc., as specified in JIS Z 3282-2017 (corresponding international standard: ISO 9453:2014), depending on the terminal material, connection conditions, etc.

[0041] The lower limit of the solidus temperature (melting point) of the solder particles is, for example, preferably 120°C or higher, more preferably 130°C or higher, and even more preferably 135°C or higher. The upper limit of the liquidus temperature of the solder particles may be, for example, 210°C or lower, preferably 200°C or lower, more preferably 195°C or lower, and even more preferably 190°C or lower. Here, the liquidus is a curve showing the relationship between the temperature (melting point) of the liquid phase in equilibrium with the solid phase and the composition of the liquid phase. Furthermore, the upper limit of the solidus temperature of the solder particles is, for example, preferably 155°C or lower, may be 150°C or lower, 145°C or lower, or may be 140°C or lower. Furthermore, a flux compound may be directly bonded to the surface of the solder particles for the purpose of surface activation. Activating the surface can promote metallic bonding with metal wires or electrodes.

[0042] In particular, the solder particles are preferably non-eutectic alloys with a solidus temperature (melting point) of 155°C or lower. For example, the solder particles preferably have a solidus temperature of 150°C or lower and are preferably one or more alloys selected from the group consisting of Sn-Bi-Cu alloy, Sn-Bi-Ag alloy, Sn-Bi alloy, Sn-Pb-Bi alloy, and Sn-In alloy. Specific examples of solder particles include Sn30Bi0.5Cu, Sn30Bi, Sn40Bi, Sn50Bi, Sn58Bi, Sn40Bi0.1Cu, Sn43Pb14Bi, and Sn20In. This allows for excellent connection reliability.

[0043] The lower limit of the content of solder particles in the conductive particle-containing hot melt adhesive sheet 1 is, for example, preferably 20 parts by mass or more, more preferably 40 parts by mass or more, per 100 parts by mass of the binder (or the total mass of all components other than the solder particles) in the conductive particle-containing hot melt adhesive sheet 1. The upper limit of the content of solder particles is, for example, preferably 500 parts by mass or less, more preferably 400 parts by mass or less, and even more preferably 300 parts by mass or less, per 100 parts by mass of the binder (or the total mass of all components other than the solder particles) in the conductive particle-containing hot melt adhesive sheet 1, and may be 200 parts by mass or less, 150 parts by mass or less, 100 parts by mass or less, 80 parts by mass or less, or 70 parts by mass or less.

[0044] If the solder particle content is too low, it is difficult to obtain excellent conductivity. On the other hand, if the solder particle content is too high, it is difficult to obtain sufficient adhesive strength, and the insulation within the IC chip is easily impaired, making it difficult to obtain excellent conductivity reliability. When the solder particles are present in the binder, the volume ratio may be used, and when producing the conductive particle-containing hot melt adhesive sheet 1 (before the solder particles are present in the binder), the mass ratio may be used. The mass ratio can be converted to a volume ratio based on the specific gravity or compounding ratio of the compound.

[0045] The solder particles may be kneaded and dispersed in the resin of the conductive particle-containing hot melt adhesive sheet 1, or may be arranged at a distance from one another, for example, arranged in a regular pattern. Examples of regular arrangements include lattice arrangements such as square lattices, hexagonal lattices, oblique lattices, and rectangular lattices. The solder particles may also be arranged as aggregates in which multiple particles are aggregated. In this case, the arrangement of the aggregates in the plan view of the conductive particle-containing hot melt adhesive sheet 1 may be regular or random, similar to the arrangement of the solder particles described above.

[0046] The average particle diameter of the solder particles is, for example, preferably 70% or more, more preferably 80% or more, and even more preferably 95% or more of the thickness of the conductive particle-containing hot melt adhesive sheet 1. This allows, for example, the solder particles to be more reliably sandwiched between the conductive parts of the IC chip and the conductive parts of the card member during thermocompression bonding of the conductive particle-containing hot melt adhesive sheet 1, thereby easily forming a metal bond.

[0047] The lower limit of the average particle diameter of the solder particles is, for example, preferably 10 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more. The upper limit of the average particle diameter of the solder particles is, for example, preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 40 μm or less. The average particle diameter of the solder particles can be, for example, in the range of 25 to 45 μm. The maximum diameter of the solder particles is, for example, preferably 200% or less of the average particle diameter, more preferably 150% or less of the average particle diameter, and even more preferably 120% or less of the average particle diameter. By having the maximum diameter of the solder particles within the above range, the solder particles can be more reliably sandwiched between the conductive portions of the IC chip and the conductive portions of the card member, and melting of the solder particles can more reliably form a metal bond between the conductive portions.

[0048] Furthermore, when the solder particles are aggregates of a plurality of solder particles, the size of the aggregates may be set to be equal to the average particle size of the solder particles. The size of the aggregates can be determined by observation with an electron microscope or an optical microscope.

[0049] Here, the average particle size is the average value of the major axis diameter of particles measured, for example, at N = 20 or more, preferably N = 50 or more, and more preferably N = 200 or more, in observation images using a metallurgical microscope, optical microscope, electron microscope such as SEM (Scanning Electron Microscope), or the like, and in the case of spherical particles, it is the average value of the diameter of the particles. Alternatively, the observed image may be measured using known image analysis software (such as "WinROOF" manufactured by Mitani Shoji Co., Ltd. or "Azo-kun (registered trademark)" manufactured by Asahi Kasei Engineering Co., Ltd.), or may be measured (N = 1000 or more) using an image-based particle size distribution analyzer (for example, FPIA-3000 (manufactured by Malvern Instruments)). The average particle size determined from the observed image or image-based particle size distribution analyzer may be the average value of the maximum length of the particles. When producing the conductive particle-containing hot melt adhesive sheet 1, it is possible to use manufacturer values ​​such as the particle size (D50) at which the cumulative frequency in the particle size distribution determined by a simple laser diffraction / scattering method is 50%, and the arithmetic mean diameter (preferably on a volume basis).

[0050] The conductive particle-containing hot melt adhesive sheet 1 may further contain additives other than the above-mentioned components, as long as the effects of the present technology are not impaired. For example, nano-sized silica (primary particle diameter of 1 nm or more and less than 1000 nm) may be dispersed in the conductive particle-containing hot melt adhesive sheet 1 to further improve gas barrier properties and elastic modulus. Furthermore, to more uniformly control the height of the solder particles after compression bonding, the conductive particle-containing hot melt adhesive sheet 1 may also be dispersed with spacer particles such as resin particles, rubber particles, silicone rubber particles, silica, etc. of a specified size. The conductive particle-containing hot melt adhesive sheet 1 may also contain a thermosetting resin or a curing agent.

[0051] Furthermore, the conductive particle-containing hot melt adhesive sheet 1 may further include layers other than the resin layer 4, as long as the effects of the present technology are not impaired. Furthermore, the conductive particle-containing hot melt adhesive sheet 1 can also be used for applications other than smart cards, and may be used, for example, as an anisotropic conductive film.

[0052] <Method of Manufacturing a Conductive Particle-Containing Hot Melt Adhesive Sheet> Next, an example of a method of manufacturing a conductive particle-containing hot melt adhesive sheet 1 will be described. The method of manufacturing a conductive particle-containing hot melt adhesive sheet includes a varnish preparation step in which each resin component of the binder is dissolved in a solvent to prepare a varnish, a conductive particle-containing resin composition preparation step in which conductive particles are added to obtain a conductive particle-containing resin composition, and a drying step in which the conductive particle-containing resin composition is applied to a release substrate to a predetermined thickness and dried. Note that when the conductive particles in the conductive particle-containing hot melt adhesive sheet are arranged at intervals or in a regular arrangement, the sheet can be prepared without adding conductive particles, and the conductive particles can be arranged separately by a known method.

[0053] In the step of preparing the varnish, the crystalline polyamide resin, crystalline polyester resin, and crystalline polyurethane resin are dissolved in a solvent. The solvent is not particularly limited and can be appropriately selected depending on the purpose. For example, a mixed solvent of methyl ethyl ketone:toluene:cyclohexanone at a ratio of 50:40:10 (by mass), or a mixed solvent of toluene:ethyl acetate at a ratio of 50:50 (by mass), can be used.

[0054] Furthermore, examples of the release substrate include those having a contact angle with water of 80° or more. Specific examples of the release substrate include silicone-based films, fluorine-based films, silicone-based films, PET, PEN, glassine paper, and the like that have been treated with a release agent such as a fluorine-based release agent. The thickness of the release substrate is not particularly limited and can be appropriately selected depending on the purpose, and can be, for example, 20 to 120 μm.

[0055] The conductive particle-containing hot melt adhesive sheet 1 may also be in the form of a film wound around a core, for example, formed into a tape. The diameter of the core is not particularly limited and can be selected appropriately depending on the purpose, and can be, for example, 50 to 1000 mm. The film length is also not particularly limited; for example, a length of 5 m or more allows for easy trial production using manufacturing equipment, while a length of 1000 m or less does not impose excessive burdens on workability and handling.

[0056] <Smart Card> The smart card according to this embodiment includes a card member, an IC chip, and an adhesive layer that bonds the card member and the IC chip together. The adhesive layer is a solidified product obtained by melting a conductive particle-containing hot-melt adhesive sheet that includes, for example, a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin having a softening point of 90° C. or higher and 120° C. or lower, and solder particles that are a non-eutectic alloy having a solidus temperature of 155° C. or lower. This allows for a stable metal bond with excellent adhesive strength, and excellent results in various bending resistance tests.

[0057] Fig. 3 is a schematic perspective view showing an example of a smart card, and Fig. 4 is a top view showing an example of an IC chip area of ​​a card member. The smart card includes, for example, a card member 10 and an IC chip 20. The card member 10 is, for example, a laminate formed by stacking a first substrate, a second substrate including an antenna, and a third substrate in this order. The IC chip 20 has, for example, multiple contact terminals 21 on its front surface and electrodes on the entire back surface.

[0058] The card member 10 is constructed by laminating, for example, a first substrate, a second substrate, and a third substrate in this order. Examples of resins that make up each layer include recycled PVC (polyvinyl chloride), PET (polyethylene terephthalate), PET-G, PC (polycarbonate), environmentally friendly biodegradable plastics (e.g., PLA (polylactic acid)), and ocean plastics, which are substrates made from plastic waste collected before it ends up in the ocean. By constructing the substrate from multiple layers, it is possible to prevent the rigidity from becoming unnecessarily high compared to a single-layer construction.

[0059] The first substrate has an opening 11 corresponding to the shape of the IC chip 20, and the opening 11 exposes the second substrate, forming an IC chip region. The second substrate is disposed between the first substrate and a third substrate, and has an antenna pattern 12 that wraps around its outer periphery multiple times within a layer made of, for example, resin. Furthermore, the second substrate is cut away in the IC chip region facing the opening 11 to correspond to the back surface of the IC chip 20, for example, so that a portion of the embedded antenna pattern is exposed, thereby forming a recess. That is, the recess in the second substrate corresponds to the shape of the opening 11, and a first exposed portion 12a and a second exposed portion 12b of the antenna pattern 12 are formed in the IC chip region. The metal wire of the antenna pattern 12 can be, for example, a copper wire.

[0060] The adhesive layer is interposed between the IC chip region of the opening 11 and the IC chip 20, and electrically connects the IC chip 20 to the first exposed portion 12a and the second exposed portion 12b of the antenna pattern 12. For example, the solder particles as the conductive particles 3 form an intermetallic compound (solder joint) with the Au-plated IC chip 20 side, and also form an intermetallic compound with the Cu wire on the card member 10 side.

[0061] <Method for Manufacturing a Smart Card> Next, an example of a method for manufacturing a smart card will be described. The method for manufacturing a smart card according to this embodiment includes, for example, a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin, and conductive particles. The content of the crystalline polyurethane resin in the binder is 5% by mass or more but less than 75% by mass, and the melt viscosity of the binder at 155 to 170°C is 5,000 to 50,000 Pa·s. A conductive particle-containing hot-melt adhesive sheet is interposed between a card member and an IC chip, and the two are thermocompression-bonded. This prevents the binder from springing back after thermocompression bonding, preventing a decrease in adhesive strength. Furthermore, a stable metal bond can be obtained, resulting in excellent results in various bending resistance tests. Furthermore, the usable temperature range in the thermocompression bonding process can be expanded, resulting in high production efficiency.

[0062] Specific examples of methods for manufacturing smart cards will be described below with reference to Figures 3 to 6. The method for manufacturing smart card 50 includes, for example, step A of attaching conductive particle-containing hot melt adhesive sheet 1 to the connection surface of IC chip 20, step B of placing IC chip 20 in the IC chip area of ​​card member 10, and step C of thermocompression bonding IC chip 20 and card member 10 together.

[0063] [Step A] Figure 5 is a perspective view illustrating an example of a step in the manufacturing method of a smart card of attaching a conductive particle-containing hot melt adhesive sheet 1 to the connection surface of an IC chip 20. In step A, as shown in Figure 5, for example, the conductive particle-containing hot melt adhesive sheet 1 is attached to the connection surface (back surface) of the IC chip 20. As described above, the conductive particle-containing hot melt adhesive sheet 1 is attached to the connection surface of the IC chip 20 with the resin layer 4 facing the IC chip 20, i.e., with the second layer 3 facing the card member 10.

[0064] The conductive particle-containing hot melt adhesive sheet 1 can be shaped to cover the first exposed portion 12a and the second exposed portion 12b of the antenna pattern 12 on the card member 10 and have a cutout in the center, as shown in Figure 5, for example.

[0065] Process A may be a lamination process in which the conductive particle-containing hot melt adhesive sheet 1 is laminated onto the connection surface of the IC chip 20, or may be a temporary attachment process in which the conductive particle-containing hot melt adhesive sheet 1 is attached to the connection surface of the IC chip 20 at a low temperature.

[0066] When process A is a lamination process, a pressure laminator or a vacuum pressure laminator may be used. By using process A as a lamination process, a relatively large area can be mounted at once compared to a temporary attachment process. Furthermore, when process A is a temporary attachment process, only minimal changes such as the installation or modification of tools from the previous equipment are required, which is economically advantageous.

[0067] In step A, the temperature reached by the conductive particle-containing hot melt adhesive sheet 1 is preferably equal to or higher than the temperature at which the binder flows but lower than the temperature at which the solder particles (conductive particles 3) melt. The temperature at which the binder flows may be, for example, a temperature at which the melt viscosity of the conductive particle-containing hot melt adhesive sheet 1 is 100 to 1,000,000 Pa·s, preferably 1,000 to 100,000 Pa·s. This allows the conductive particle-containing hot melt adhesive sheet 1 to be attached to the connection surface of the IC chip 20 while maintaining the shape of the solder particles. The melt viscosity of the conductive particle-containing hot melt adhesive sheet 1 can be measured, for example, using a rotational rheometer (manufactured by TA Instrument) under the following conditions: a measurement pressure of 5 g, a temperature range of 30 to 200°C, a heating rate of 10°C / min, a measurement frequency of 10 Hz, a measurement plate diameter of 8 mm, and a load fluctuation on the measurement plate of 5 g.

[0068] [Step B] In step B, for example, the IC chip 20 is picked up using a tool equipped with a suction mechanism, and as shown in FIG. 5, the IC chip area of ​​the card member 10 is aligned with the IC chip 20, and the IC chip 20 is placed via the conductive particle-containing hot melt adhesive sheet 1.

[0069] [Step C] Figure 6 is a cross-sectional view illustrating an example of a step of thermocompression bonding the IC chip 20 and the card member 10 in the manufacturing method of the smart card 50. In step C, the IC chip 20 and the card member 10 are thermocompression bonded using a bonding device 30. In step C, the number of thermocompression bonding operations can be set depending on the objects to be connected. For example, one operation may be performed, but multiple operations are preferable. Specifically, for example, four thermocompression bonding operations are preferably performed at 1.0-second intervals under conditions of 210 to 240°C, 90 N, and 0.7 seconds. This allows the binder in the conductive particle-containing hot melt adhesive sheet 1 to be sufficiently removed, and the IC chip 20 and the first exposed portion 12a and second exposed portion 12b of the antenna pattern 12 can be more reliably metal-bonded by melting the solder particles.

[0070] The thermocompression bonding temperature in step C, which is the temperature reached by the conductive particle-containing hot melt adhesive sheet 1, is preferably equal to or higher than the melting point of the solder particles (conductive particles 3). Here, the melting point refers to the solidus temperature. That is, the thermocompression bonding temperature in step C, which is the temperature reached by the conductive particle-containing hot melt adhesive sheet 1, is preferably equal to or higher than the solidus temperature of the solder particles. Here, the solidus is a curve showing the relationship between the temperature (melting point) of the liquid phase in equilibrium with the solid phase and the composition of the solid phase. Specifically, the temperature reached by the conductive particle-containing hot melt adhesive sheet 1 is preferably 120 to 190°C, more preferably 140 to 180°C, and even more preferably 155 to 170°C. This further suppresses thermal shock to the card member 10 and the IC chip 20, and more effectively prevents deformation of the card member 10.

[0071] In this example, a conductive particle-containing hot melt adhesive sheet containing solder particles was prepared, and a smart card was fabricated using this sheet. The initial adhesive strength between the card member and the IC module (IC chip) in the smart card was then evaluated, and the smart card was subjected to a wrapping (bending) test and a bending (bending) test. Note that the present technology is not limited to these examples.

[0072] [Preparation of solder particles] Metal materials were placed in a heated container in a predetermined compounding ratio, melted, and then cooled to obtain a solder alloy. Powder was prepared from the solder alloy using an atomization method, and the powder was classified to obtain solder particles with the following composition: Type 3 (25-45 μm, IPC standard J-STD 005) Sn-40Bi (non-eutectic, solidus temperature: 139°C, liquidus temperature: 167°C)

[0073] [Preparation of Conductive Particle-Containing Hot Melt Adhesive Sheet] The following compounds were prepared for the conductive particle-containing hot melt adhesive sheet. Platamid HX2592 (Arkema, crystalline polyamide resin having carboxyl groups) Aronmelt PES-111EE (Toagosei, crystalline polyester resin, softening point: 125°C) dissolved in 25 / 75 solids / cyclohexanone HK-6502 (Henan Huike New Material Technology, crystalline polyurethane resin, minimum activation temperature: 55-60°C, softening point: 100°C, melt viscosity: 200-300mPa) H306 (Micacll, crystalline polyurethane resin, minimum activation temperature: 60-70°C, softening point: 90°C, melt viscosity: 300-800mPa) H3F3002EH-5 (Fuwafon, crystalline polyurethane resin, softening point: 100°C, melt viscosity: 700-800mPa) Elitel UE3210 (amorphous polyester resin manufactured by Unitika Ltd.) Septon 4033 (styrene-based thermoplastic elastomer manufactured by Kuraray Co., Ltd.)

[0074] Examples 1 to 9, Comparative Examples 1 to 4 The compounds shown in Tables 1 and 2 were mixed and stirred to the prescribed solid content (parts by mass) to obtain a mixed varnish. Subsequently, approximately 100 parts by mass of solder particles per 100 parts by mass of the mixed varnish solids were added to the resulting mixed varnish to obtain a conductive particle-containing resin composition. The resulting conductive particle-containing resin composition was applied to a 50 μm-thick PET film so that the average thickness after drying would be 40 μm, and the film was dried at 70°C for 5 minutes and then at 120°C for 5 minutes to produce a single-layer conductive particle-containing hot melt adhesive sheet.

[0075] [Melt Viscosity of Binder] The melt viscosity of the binder of the mixed varnish was measured at 155°C and 170°C using a viscoelasticity tester HAAKE MARS60 (Thermo Fisher Scientific Co., Ltd.) In Tables 1 and 2, binders with a melt viscosity of 5,000 to 50,000 Pa s at 155°C or 170°C were rated "OK," and other cases were rated "NG."

[0076] [Fabrication of Smart Card] A dual interface PVC card (manufactured by Shoei Printing Co., Ltd.) with Cu wires was used as the card member. The Cu wires were exposed in the IC chip area of ​​this card member 10. A 6-pin IC module (manufactured by Wisecard Co., Ltd.) was used as the IC chip.

[0077] A conductive particle-containing hot-melt adhesive sheet was laminated to the connection surface of the IC module at 3 bar. The IC module with the conductive particle-containing hot-melt adhesive sheet attached was then placed on the IC chip area of ​​the card member, and thermocompression bonding was performed four times at 1.0-second intervals using an OM-ICB01-S adhesive tape manufactured by Optoscience, at 210°C, 90 N, and 0.7 seconds, or at 240°C, 90 N, and 0.7 seconds, to produce a smart card.

[0078] [Initial Adhesion Strength Between Card Member and IC Module] In accordance with ISO 24789-2 5.4 "Adhesion of ICM to card-push test," the initial adhesion strength between the card member (PVC card) and the IC module of a smart card was evaluated. An initial adhesion strength of 100 N or more was evaluated as "OK," and an initial adhesion strength of less than 100 N was evaluated as "NG." The results are shown in Tables 1 and 2.

[0079] [Wrapping Test] In accordance with ISO 24789-2 5.3 "Adhesion of ICM to Wrapping Test," a periodic bending force was applied to the smart card at a specified strength and direction. Then, for the smart card after 10 cycles of bending test, the Q value was measured using a resonance frequency checker MP300CL3 (manufactured by Micropross). If no Q value signal was detected, the evaluation was "NG," i.e., the smart card's bending resistance was judged to be poor. Otherwise, the evaluation was "OK," i.e., the smart card's bending resistance was judged to be good. The results are shown in Tables 1 and 2.

[0080] [Bending Test] In accordance with ISO 10373-1 Dynamic Bending Stress, a periodic bending force was applied to the smart card at a specified strength and direction. Then, for the smart card after 4000 cycles of bending test, the Q value was measured using a resonance frequency checker MP300CL3 (manufactured by Micropross). If no Q value signal was detected, the evaluation was "NG," i.e., the smart card's bending resistance was judged to be poor. Otherwise, the evaluation was "OK," i.e., the smart card's bending resistance was judged to be good. The results are shown in Tables 1 and 2.

[0081]

[0082]

[0083] In Comparative Example 1, the content of crystalline polyurethane resin was zero, so the melt viscosity of the binder was too low, causing a springback phenomenon in the adhesive layer during high-temperature compression bonding at 240°C, resulting in gaps (floating) between the solder particles and the connection.In the wrapping test and bending test, signals could not be obtained due to unstable connections, and sufficient adhesive strength was not obtained.

[0084] In Comparative Example 2, the content of crystalline polyurethane resin was too high, so the melt viscosity of the binder was too high, and the binder could not be sufficiently removed during low-temperature compression bonding at 210°C.In addition, the solder particles were unable to form a sufficient metal bond with the connection, so no signals could be obtained in the wrapping test or bending test, and sufficient adhesive strength was not obtained.

[0085] In Comparative Examples 3 and 4, because a styrene-based thermoplastic elastomer was added, the melt viscosity of the binder showed a melt viscosity curve similar to that when a crystalline polyurethane resin was added, but sufficient adhesive strength to PVC was not obtained, and no signals could be obtained in the wrapping test or bending test.

[0086] On the other hand, in Examples 1 to 9, because the content of the crystalline polyurethane resin was within a predetermined range, the melt viscosity of the binder could be maintained within a predetermined range whether the bonding was performed at 210°C or 240°C, and the binder could be sufficiently removed. Furthermore, the springback phenomenon of the binder after thermocompression bonding could be prevented, resulting in excellent adhesive strength. It was also found that the usable temperature range could be expanded to 210-240°C compared to Comparative Examples 1 and 2, and high production efficiency could be achieved.

[0087] REFERENCE SIGNS LIST 1 Conductive particle-containing hot melt adhesive sheet, 2 Binder, 3 Conductive particles, 4 Resin layer, 10 Card member, 11 Opening, 12 Antenna pattern, 12a First exposed portion, 12b Second exposed portion, 20 IC chip, 21 Contact terminal, 30 Crimping device, 40 Adhesive layer, 50 Smart card

Claims

1. A conductive particle-containing hot melt adhesive sheet comprising: a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin; and conductive particles, wherein the content of the crystalline polyurethane resin in the binder is 5% by mass or more but less than 75% by mass; and the melt viscosity of the binder at 155 to 170°C is 5,000 to 50,000 Pa·s.

2. The conductive particle-containing hot melt adhesive sheet according to claim 1, wherein the binder has a melt viscosity of 10,000 to 50,000 Pa·s at 155 to 170°C.

3. The conductive particle-containing hot melt adhesive sheet according to claim 1 or 2, wherein the softening point of the crystalline polyurethane resin is 120°C or lower.

4. A conductive particle-containing hot melt adhesive sheet according to claim 1 or 2, wherein the content of the crystalline polyamide resin, the crystalline polyester resin, and the crystalline polyurethane resin in the binder is 80 mass% or more.

5. The conductive particle-containing hot melt adhesive sheet according to claim 1 or 2, wherein the content of the crystalline polyamide resin in the binder is 15 to 50 mass %.

6. The conductive particle-containing hot melt adhesive sheet according to claim 1 or 2, wherein the content of the crystalline polyester resin in the binder is 15 to 25% by mass.

7. The conductive particle-containing hot melt adhesive sheet according to claim 1 or 2, wherein the conductive particles are solder particles that are a non-eutectic alloy having a solidus temperature of 155°C or less.

8. A method for manufacturing a smart card, comprising: a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin; and conductive particles, wherein the content of the crystalline polyurethane resin in the binder is 5% by mass or more but less than 75% by mass; and the melt viscosity of the binder at 155 to 170°C is 5,000 to 50,000 Pa·s; the conductive particle-containing hot melt adhesive sheet is interposed between a card member and an IC chip, and the two are thermocompressed together.

9. A smart card comprising: a card member; an IC chip; and an adhesive layer that bonds the card member and the IC chip, wherein the adhesive layer is a solidified product obtained by melting the conductive particle-containing hot melt adhesive sheet described in claim 1 or 2.

10. A smart card comprising: a card member; an IC chip; and an adhesive layer that bonds the card member and the IC chip, wherein the adhesive layer is a solidified product obtained after melting a conductive particle-containing hot melt adhesive sheet that comprises a binder containing a crystalline polyamide resin, a crystalline polyester resin, and a crystalline polyurethane resin having a softening point of 90°C or higher and 120°C or lower, and solder particles that are a non-eutectic alloy having a solidus temperature of 155°C or lower.

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