JP7720174B2 - Method for manufacturing a smart card, smart card, and conductive particle-containing hot melt adhesive sheet - Google Patents

Description

This technology relates to a method for manufacturing a smart card using a hot-melt adhesive sheet containing conductive particles, and to the smart card itself.

In recent years, smart cards equipped with IC chips have become widespread. One known method for mounting IC chips on smart cards is to use an anisotropic conductive film, which is made by blending conductive particles with a binder containing a crystalline resin (see, for example, Patent Document 1). As noted in Patent Document 1, smart cards equipped with IC chips sometimes use connecting materials such as anisotropic conductive film (ACF) and anisotropic conductive paste (ACP) (see, for example, Patent Document 2).

However, because these technologies rely on contact between conductive particles to achieve conductivity, when smart cards are subjected to reliability tests under high temperature and humidity, the resin can expand, causing a loss of conductivity.

JP 2017-117468 A Patent No. 5964187

This technology was proposed in light of these existing circumstances, and provides a method for manufacturing a smart card that can achieve excellent connection reliability and bending resistance, as well as a smart card and a hot-melt adhesive sheet containing conductive particles.

The method for manufacturing a smart card according to this technology involves placing a conductive particle-containing hot-melt adhesive sheet, which contains solder particles that are a non-eutectic alloy in a binder containing a crystalline polyamide with carboxyl groups, between the card member and the IC chip, and then thermocompression bonding them together.

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 contains solder particles that are a non-eutectic alloy in a binder that includes a crystalline polyamide having a carboxyl group.

The conductive particle-containing hot melt adhesive sheet of this technology contains solder particles, which are a non-eutectic alloy, in a binder containing a crystalline polyamide having carboxyl groups.

This technology uses crystalline polyamide with carboxyl groups to improve the solder wettability of non-eutectic alloys, resulting in excellent connection reliability and bending resistance.

FIG. 1 is a schematic perspective view showing an example of a smart card. FIG. 2 is a top view showing an example of an IC chip area of a card member.

Hereinafter, embodiments of the present technology will be described in detail in the following order with reference to the drawings.
1. Smart Card 2. Smart Card Manufacturing Method 3. Conductive Particle-Containing Hot Melt Adhesive Sheet 4. First Example 5. Second Example

1. Smart Card
The smart card according to the present embodiment includes a card member, an IC chip, and an adhesive layer that bonds the card member and the IC chip, and the adhesive layer contains solder particles that are a non-eutectic alloy in a binder that includes a crystalline polyamide having carboxyl groups. By containing the solder particles that are a non-eutectic alloy in the binder that includes a crystalline polyamide having carboxyl groups, the adhesive layer improves solder wettability and provides excellent connection reliability and bending resistance.

In this specification, a smart card is a card incorporating an integrated circuit (IC) for recording and calculating information (data), and is also called an "IC card (integrated circuit card)" or "chip card." A smart card may also be a dual-interface card with two interfaces, contact and contactless, on a single IC chip, or a hybrid card equipped with a contact IC chip and a contactless IC chip. Other examples include fingerprint authentication cards equipped with a fingerprint authentication element, and cards with a one-time password function that incorporate a battery element and a display element. These IC chips and elements have pads that are electrically connected to the electrode portions on the card member.

Figure 1 is a schematic perspective view showing an example of a smart card, and Figure 2 is a top view showing an example of an IC chip area of a card member. The smart card comprises a card member 10 and an IC chip 20. The card member 10 is a laminate formed by stacking a first substrate, a second substrate with an antenna, and a third substrate in this order. The IC chip 20 has multiple contact terminals 21 on its front surface and electrodes on its back surface, for example, covering the entire surface.

The first substrate, second substrate, and third substrate are each formed, for example, by laminating multiple layers made of resin. Examples of resins that can be used to form each layer include recycled PVC (polyvinyl chloride), PET (polyethylene terephthalate), PET-G, PC (polycarbonate), environmentally friendly biodegradable plastics (one example is PLA (polylactic acid)), and ocean plastics, substrates made from plastic waste collected before it ends up in the ocean. By forming the substrate from multiple layers, it is possible to prevent the rigidity from becoming unnecessarily high compared to a substrate made from a single layer.

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 area. The second substrate is disposed between the first substrate and the 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 area 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, 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 area. The metal wire of the antenna pattern 12 can be, for example, a copper wire.

The second substrate preferably has blind grooves or multiple holes in the IC chip area. This allows the resin of the adhesive layer to flow into the grooves and holes, improving adhesion to the adhesive layer. The minimum length of the opening of the grooves and holes is preferably smaller than the average particle diameter of the solder particles. The minimum length of the opening of the grooves and holes is preferably 20% or more of the average particle diameter of the solder particles, more preferably 30% or more, and particularly preferably 40% or more. The maximum length of the opening of the holes is preferably 80% or less of the average particle diameter of the solder particles, more preferably 70% or less, and particularly preferably 60% or less. This makes it easier for the solder particles to fit into the grooves and holes, improving the solder particle capture and achieving excellent electrical connection with the IC chip.

The adhesive layer is interposed between the IC chip area of the opening 11 and the IC chip 20, electrically connecting the IC chip 20 to the first exposed portion 12a and the second exposed portion 12b of the antenna pattern 12.

The smart card according to this embodiment includes an adhesive layer containing solder particles of a non-eutectic alloy in a binder containing a crystalline polyamide having carboxyl groups, thereby improving solder wettability and achieving excellent connection reliability. This is believed to be due to the flux effect of the carboxyl groups present in the crystalline polyamide. As a result, the adhesive layer's elastic modulus is prevented from decreasing due to the addition of a flux compound, resulting in excellent bending resistance. Furthermore, non-eutectic alloy solder particles remain in a semi-molten state for a longer period during thermocompression bonding than eutectic alloy solder particles, allowing for sufficient removal of resin and achieving excellent connection reliability. Furthermore, the smart card according to this embodiment forms a metal bond between the IC chip circuit (conductive portion) and the antenna pattern circuit (conductive portion) through melting of the solder particles. This reduces swelling and elongation due to moisture absorption by the binder during a wet heat test, resulting in excellent connection reliability. This technology can also be applied to general anisotropic joined bodies. The scope of application of this technology is also substantially similar to that of joined body manufacturing methods.

2. Smart card manufacturing method
The method for manufacturing a smart card according to this embodiment involves interposing a conductive particle-containing hot melt adhesive sheet, which contains solder particles that are a non-eutectic alloy in a binder containing a crystalline polyamide having carboxyl groups, between a card member and an IC chip, and then thermocompression bonding the two together, thereby improving solder wettability and achieving excellent connection reliability and bending resistance.

The following describes, with reference to Figures 1 and 2, the application process (A) of applying a conductive particle-containing hot melt adhesive sheet to the connection surface of the IC chip, the placement process (B) of placing the IC chip in the IC chip area of the card member, and the pressure-bonding process (C) of thermocompression-bonding the IC chip and card member.

[Attachment step (A)]
In the attachment step (A), a conductive particle-containing hot melt adhesive sheet is attached to the connection surface (back surface) of the IC chip 20. The attachment step (A) may be a lamination step in which the conductive particle-containing hot melt adhesive sheet is laminated onto the connection surface of the IC chip 20, or may be a temporary attachment step in which the conductive particle-containing hot melt adhesive sheet is attached to the connection surface of the IC chip 20 at a low temperature.

When the attachment process (A) is a lamination process, either a pressure laminator or a vacuum pressure laminator may be used. When the attachment process (A) is a lamination process, a relatively large area can be mounted at once compared to a temporary attachment process. Furthermore, when the attachment process (A) is a temporary attachment process, only minimal changes, such as the installation or modification of tools, are required from the previous equipment, resulting in economic benefits.

In the application step (A), the temperature reached by the conductive particle-containing hot melt adhesive sheet is preferably equal to or higher than the temperature at which the binder flows, but lower than the temperature at which the solder melts. The temperature at which the binder flows may be a temperature at which the melt viscosity of the conductive particle-containing hot melt adhesive sheet 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 to be applied 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 can be measured, for example, using a rotational rheometer (manufactured by TA Instrument) under the following conditions: measurement pressure of 5 g, temperature range of 30 to 200°C, heating rate of 10°C/min, measurement frequency of 10 Hz, measurement plate diameter of 8 mm, and load fluctuation on the measurement plate of 5 g.

[Placement step (B)]
In the placement process (B), the IC chip 20 is picked up using, for example, a tool equipped with an adsorption mechanism, the IC chip area of the card member 10 is aligned with the IC chip 20, and the IC chip 20 is placed via a hot melt adhesive sheet containing conductive particles.

[Compression bonding step (C)]
In the pressure-bonding step (C), a pressure-bonding device is used to thermocompress the IC chip 20 and the card member 10. The number of thermocompression bonding steps in the pressure-bonding step (C) can be set according to the objects to be connected, and may be one, but preferably multiple. This allows the binder in the conductive particle-containing hot-melt adhesive sheet to be sufficiently removed, and the IC chip 20 and the first exposed portion 12a and the second exposed portion 12b of the antenna pattern 12 can be metallically bonded by melting the solder particles.

The thermocompression bonding temperature in the compression bonding step (C) is preferably such that the temperature reached by the conductive particle-containing hot melt adhesive sheet is equal to or higher than the melting point of the solder particles. Here, melting point refers to the solidus temperature. In other words, the thermocompression bonding temperature in the compression bonding step (C) is preferably such that the temperature reached by the conductive particle-containing hot melt adhesive sheet is equal to or higher than the solidus temperature of the solder particles. Here, the solidus is a curve that shows 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 is preferably 120 to 160°C, more preferably 120 to 155°C, and even more preferably 120 to 150°C. This suppresses thermal shock to the card member 10 and IC chip 20, and prevents deformation of the card member 10.

The smart card manufacturing method according to this embodiment uses a conductive particle-containing hot melt adhesive sheet containing solder particles that are a non-eutectic alloy in a binder containing a crystalline polyamide with carboxyl groups, thereby improving solder wettability and achieving excellent connection reliability. This is thought to be due to the flux effect of the carboxyl groups present in the crystalline polyamide, which prevents a decrease in the adhesive layer's elastic modulus due to the addition of a flux compound and achieves excellent bending resistance. Furthermore, non-eutectic alloy solder particles remain in a semi-molten state for a longer period during thermocompression bonding than eutectic alloy solder particles, allowing for sufficient removal of resin and achieving excellent connection reliability. Furthermore, the smart card manufacturing method according to this embodiment forms a metal bond between the conductive portions of the IC chip and the conductive portions of the antenna pattern by melting the solder particles. This reduces swelling and elongation due to moisture absorption by the binder during a moist heat test, resulting in excellent connection reliability.

<3. Hot melt adhesive sheet containing conductive particles>
The conductive particle-containing hot melt adhesive sheet according to the present embodiment contains solder particles, which are a non-eutectic alloy, in a binder containing a carboxyl-containing crystalline polyamide, thereby improving solder wettability and providing excellent connection reliability and bending resistance.

The lower limit of the thickness of the conductive particle-containing hot melt adhesive sheet is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more. The upper limit of the thickness of the conductive particle-containing hot melt adhesive sheet is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 60 μm or less. This makes it suitable for use in the manufacture of smart cards in which an IC chip is thermocompression bonded to a card member.

[binder]
The binder contains at least a crystalline polyamide having a carboxyl group. The crystalline resin can be confirmed by, for example, observing an endothermic peak during the temperature rise process in differential scanning calorimetry.

The terminal carboxyl group concentration of the crystalline polyamide is preferably 0.5 mgKOH/g or more, more preferably 1.0 mgKOH/g or more, and even more preferably 2.0 mgKOH/g or more. The terminal carboxyl group concentration of the crystalline polyamide may be 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 can be evaluated, for example, in accordance with JIS K 0070-1992 or ISO 2114. Specific examples of commercially available crystalline polyamides having carboxyl groups include "HX2519" and "M1276" manufactured by Arkema Inc.

The carboxyl-containing crystalline polyamide is preferably a copolymer based on lauryllactam (PA12: polyamide 12 or nylon 21) or 11-aminoundecanoic acid (PA11: polyamide 11) as a monomer. Compared to polyamides based on dimer acid, such copolymers have higher crystallinity, higher melt viscosity, and higher rigidity, resulting in excellent connection reliability and bending resistance.

The lower limit of the melting point of the carboxyl-containing crystalline polyamide is preferably 70°C or higher, more preferably 80°C or higher, and even more preferably 90°C or higher. The upper limit of the melting point of the carboxyl-containing crystalline polyamide is preferably 150°C or lower, more preferably 140°C or lower, and even more preferably 130°C or lower. If the melting point of the carboxyl-containing crystalline polyamide is too high, the viscosity of the binder will not decrease sufficiently, resulting in insufficient resin removal and poor conductive properties. If the melting point of the carboxyl-containing crystalline polyamide is too low, the hardness during press-out will tend to be insufficient. The melting point can be measured, for example, by differential scanning calorimetry (DSC).

The lower limit of the weight-average molecular weight of the crystalline polyamide having carboxyl groups is preferably 5,000 or more, more preferably 8,000 or more, even more preferably 10,000 or more, and most preferably more than 10,000. The upper limit of the weight-average molecular weight of the crystalline polyamide having carboxyl groups is preferably 100,000 or less, more preferably 50,000 or less, and even more preferably 30,000 or less. If the weight-average molecular weight of the crystalline polyamide having carboxyl groups is too small, the binder may not cure sufficiently, resulting in problems such as increased resistance in bending tests. The weight-average molecular weight Mw can be measured, for example, by gel permeation chromatography (GPC) and expressed as a value converted into the molecular weight of standard polystyrene.

Furthermore, the carboxyl group-containing crystalline polyamide preferably has a melt volume flow rate (MVR) of 2 to 50 cm ³ /10 min, more preferably 3 to 30 cm ³ /10 min, and even more preferably 5 to 10 cm ³ /10 min, measured at a temperature of 160°C and a load of 2.16 kg. If the melt volume flow rate is too high, the hardness at press-out tends to be insufficient, and bending properties tend to deteriorate. The melt volume flow rate can be measured in accordance with the provisions of JIS K7210:1999, "Method for determining the melt flow rate of thermoplastic plastics."

By including at least a crystalline polyamide with carboxyl groups in the binder, 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, and as a result, the decrease in elastic modulus of the adhesive layer due to the addition of flux compounds is prevented, resulting in excellent bending resistance.

The binder may also contain other components as needed. These other components can be selected appropriately depending on the purpose, such as crystalline resins or amorphous resins. There are no particular restrictions on crystalline resins, as long as they have crystalline regions, and examples include polyester resins, polyolefin resins, and polyurethane resins. Examples of polyester resins include polyethylene terephthalate resins and polybutylene terephthalate resins, while examples of polyolefin resins include polyethylene resins, polypropylene resins, and polybutylene resins. Examples of amorphous resins include those exemplified in the description of crystalline resins. Among these, it is preferable to include a crystalline polyester resin as an additional component, from the viewpoint of adhesion at low temperatures and in a short time.

The proportion of crystalline polyamide having carboxyl groups in the binder is preferably 10 to 100 wt%, more preferably 30 to 100 wt%, and even more preferably 50 to 100 wt%. This allows the flux effect to be achieved even with low-temperature compression bonding at 160°C or less, improving solder wettability and achieving excellent connection reliability. However, in the case of low-temperature, short-time compression bonding, such as for card applications, if the proportion of crystalline polyamide having carboxyl groups in the binder is 10 wt% or less, it becomes difficult to achieve a sufficient flux effect.

Furthermore, the binder preferably has a melt volume flow rate (MVR) measured at a temperature of 160°C under a load of 2.16 kg that is similar to that of the carboxyl-containing crystalline polyamide. That is, the melt volume flow rate (MVR) is preferably 2 to 50 cm ³ /10 min, more preferably 3 to 30 cm ³ /10 min, and even more preferably 5 to 10 cm ³ /10 min. If the melt volume flow rate is too high, the hardness during press-out tends to be insufficient, and the bending properties tend to deteriorate.

[Solder particles]
The solder particles are not particularly limited as long as they are non-eutectic alloys, but are preferably alloys containing two or more elements selected from the group consisting of Sn, Bi, Ag, In, Cu, Sb, Pb, and Zn. Examples of solder particles include 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, and Pb-Ag, as defined in JIS Z 3282-2017 (corresponding international standard: ISO 9453:2014). These solder particles can be appropriately selected depending on the terminal material and connection conditions. Non-eutectic alloy solder particles remain semi-molten for a longer period of time during thermocompression bonding compared to eutectic alloy solder particles, allowing for sufficient removal of resin and achieving excellent connection reliability. In this specification, the term "non-eutectic alloy" refers to an alloy that does not have a eutectic point.

The lower limit of the solidus temperature (melting point) of the solder particles is 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 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 that shows the relationship between the temperature (melting point) of the liquid phase in equilibrium with the solid phase and the composition of the liquid phase. The upper limit of the solidus temperature of the solder particles may be 155°C or lower, preferably 150°C or lower, more preferably 145°C or lower, and even more preferably 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 and electrodes.

The solder particles preferably have a solidus temperature (melting point) of 155°C or less, preferably 150°C or less, and are one or more types 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.

The lower limit of the mass ratio range of the amount of solder particles to be blended is preferably 20 parts by mass or more, more preferably 40 parts by mass or more, and even more preferably 80 parts by mass or more, per 100 parts by weight of binder. The upper limit of the mass ratio range of the amount of solder particles to be blended is 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 weight of binder.

If the amount of solder particles is too small, excellent conductivity will not be achieved, while if the amount is too large, sufficient adhesive strength will not be achieved and the insulation within the IC chip will be easily impaired, making it difficult to achieve excellent conductivity reliability. When the solder particles are present in the binder, the volume ratio may be used, and when producing a hot melt adhesive sheet containing conductive particles (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 of the compound or the compounding ratio.

The solder particles may be kneaded and dispersed in the resin of the conductive particle-containing hot melt adhesive sheet, or may be arranged in a spaced-apart state. This arrangement may be regular. Examples of regular arrangements include lattice arrangements such as square lattice, hexagonal lattice, oblique lattice, and rectangular lattice. The solder particles may also be arranged as aggregates in which multiple particles are aggregated. In this case, the arrangement of the aggregates in a planar view of the conductive particle-containing hot melt adhesive sheet may be regular or random, similar to the arrangement of the solder particles described above.

The average particle size of the solder particles is preferably 70% or more of the thickness of the conductive particle-containing hot melt adhesive sheet, more preferably 80% or more, and even more preferably 95% or more. This allows the solder particles to be easily sandwiched between the conductive parts of the IC chip and the conductive parts of the card member during thermocompression bonding, resulting in a metallic bond.

The lower limit of the average particle diameter of the solder particles is 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 preferably 50 μm or less, more preferably 45 μm or less, and even more preferably 40 μm or less. The maximum diameter of the solder particles can be 200% or less of the average particle diameter, preferably 150% or less of the average particle diameter, and 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 sandwiched between the conductive parts of the IC chip and the conductive parts of the card member, and a metallic bond can be formed between the conductive parts by melting the solder particles.

The solder particles may also be in the form of agglomerates of multiple solder particles. In the case of agglomerates of multiple solder particles, the size of the agglomerates may be set to be equal to the average particle size of the solder particles described above. The size of the agglomerates can be determined by observation using an electron microscope or optical microscope.

Here, the average particle size refers to the average major axis diameter of particles measured, for example, with 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, or electron microscope such as a scanning electron microscope (SEM). In the case of spherical particles, it refers to the average diameter of the particles. It may also be a measurement value obtained by measuring the observation image using known image analysis software (such as "WinROOF" from Mitani Shoji Co., Ltd. or "Azo-kun (registered trademark)" from Asahi Kasei Engineering Co., Ltd.), or a measurement value (N=1000 or more) using an image-based particle size analyzer (e.g., FPIA-3000 (Malvern Instruments)). The average particle size determined from the observation image or image-based particle size analyzer can be the average maximum length of the particles. When producing a conductive particle-containing hot melt adhesive sheet, 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).

[Other additives]
In addition to the binder and solder particles described above, various additives can be blended into the conductive particle-containing hot melt adhesive sheet as long as they do not impair the effects of the present technology. For example, nano-sized silica (primary particle diameter of 1 nm or more and less than 1000 nm) may be dispersed to improve gas barrier properties and elastic modulus. Furthermore, resin particles, rubber particles, silicone rubber particles, silica, etc. of a specified size may be dispersed as spacer particles to maintain a constant height of the solder particles after compression bonding. Furthermore, thermosetting resins and curing agents may be added as long as they do not impair the effects of the present technology.

The conductive particle-containing hot melt adhesive sheet of this embodiment contains solder particles, which are a non-eutectic alloy, in a binder containing a crystalline polyamide with carboxyl groups, thereby improving solder wettability and achieving excellent connection reliability. This is thought to be due to the flux effect of the carboxyl groups present in the crystalline polyamide, which prevents a decrease in the adhesive layer's elastic modulus due to the addition of a flux compound and achieves excellent bending resistance. Furthermore, 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, allowing for sufficient removal of resin and achieving excellent connection reliability. Furthermore, the conductive particle-containing hot melt adhesive sheet of this embodiment forms a metal bond between the conductive portions of the IC chip and the conductive portions of the antenna pattern through the melting of the solder particles. This reduces swelling and elongation due to moisture absorption by the binder during a wet heat test, resulting in excellent connection reliability. The sheet can also be used for applications other than smart cards, such as an anisotropic conductive film.

[Method for producing a conductive particle-containing hot melt adhesive sheet]
The method for producing 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 solder 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 solder particles in the conductive particle-containing hot melt adhesive sheet are arranged at intervals or in a regular pattern, the sheet can be prepared without adding solder particles, and the solder particles can be arranged by a separate known method.

There are no particular restrictions on the solvents used for each resin component and they can be selected appropriately depending on the purpose. For example, a mixed solvent of methyl ethyl ketone: toluene: cyclohexanone in a 50:40:10 (mass ratio) or a mixed solvent of toluene: ethyl acetate in a 50:50 (mass ratio) can be used.

Releasable substrates include those with a contact angle with water of 80° or greater. Specific examples of releasable substrates include silicone-based films, fluorine-based films, silicone-based films, and PET, PEN, and glassine paper that have been treated with a release agent such as a fluorine-based release agent. There are no particular restrictions on the thickness of the releasable substrate, and it can be selected appropriately depending on the purpose, but a thickness of 20 μm to 120 μm is preferred.

The conductive particle-containing hot melt adhesive sheet may also be molded into a tape and supplied as a film roll wound around a core. There are no particular restrictions on the diameter of the core and it can be selected appropriately depending on the purpose, but a diameter of 50 to 1000 mm is preferable. There are also no particular restrictions on the film length, but a length of 5 m or more allows for trial production using manufacturing equipment, and a length of 1000 m or less does not impose too great a burden on workability and handling.

4. First Example
In this example, a conductive particle-containing hot melt adhesive sheet containing solder particles was prepared, and a smart card was produced using this sheet. The smart card was then evaluated for solder wettability, bending test, and connection reliability. However, this example is not limited to these.

[Preparation of solder particles]
The metal materials were placed in a heated container in a predetermined compounding ratio, melted, and then cooled to obtain a solder alloy. Powder was produced from the solder alloy by atomization, and the powder was classified to have a particle size in the range of 20 to 38 μm, obtaining solder particles with the following composition.
・Type 4 Sn-40Bi (non-eutectic, solidus temperature: 139°C, liquidus temperature: 167°C)
・Type 4 Sn-58Bi (eutectic, solidus temperature/liquidus temperature: 138℃)

[Preparation of conductive particle-containing hot melt adhesive sheet]
The following resins were prepared:
PES111EE (crystalline polyester, manufactured by Toagosei Co., Ltd.) -> dissolved at a solid content/cyclohexanone ratio of 25/75; HX2519 (crystalline polyamide having carboxyl groups, manufactured by Arkema Inc., terminal carboxyl group concentration 6.56 mgKOH/g, melting point 109°C, MVR 8 cm ³ /10 min, weight average molecular weight 12,000);
UE3500 (amorphous polyester resin, manufactured by Unitika Ltd.)
N-5196 (Nippon Polyurethane Industry Co., Ltd., a polyurethane elastomer with a polycarbonate backbone)

As shown in Table 1, the above resins were mixed and stirred to the specified solid content (parts by mass) to obtain a mixed varnish. Next, 45 parts by mass of conductive 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 conductive particle-containing hot melt adhesive sheet.

[Smart card creation]
A laminate consisting of a first substrate, a second substrate with an antenna, and a third substrate was prepared as a card member. In the IC chip area of this card member, a Cu wire was exposed from the PVC substrate. A test chip module (12 mm x 13 mm, gold-plated) was also prepared as an IC chip.

A conductive particle-containing hot melt adhesive sheet was laminated to the connection surface of the chip module at 3 bar. The chip module with the conductive particle-containing hot melt adhesive sheet attached was then placed on the IC chip area of the card member and thermocompressed three times at 215-230°C for 1.0 seconds at 2.5 bar to produce a smart card. Note that under these thermocompression conditions, the temperature reached by the conductive particle-containing hot melt adhesive sheet was approximately 150-165°C.

[Evaluation of solder wettability]
The chip module was removed from the smart card, and the resin adhering to the chip module and Cu wire was removed with acetone. The gold plating of the chip module and the Cu wire were then inspected for solder adhesion. A rating of "OK" was given when solder was present, and a rating of "NG" was given when solder was not present.

[Bending test evaluation]
In accordance with ISO 10373-1 5.8, a bending force was applied periodically to the smart card with a specified strength and direction. After 4,000 cycles of bending, the Q value of the smart card was measured using a resonance frequency checker MP300CL3 (manufactured by Micropross). A decrease in the Q value of 50% or more was evaluated as "NG," and any other evaluation was evaluated as "OK."

[Evaluation of connection reliability]
After the high temperature and high humidity test (left for 72 hours in an environment of 50°C and 93% RH) conforming to ISO 24789-2, the Q value of the smart card was measured using a resonance frequency checker MP300CL3 (manufactured by Micropross). A decrease in the Q value of 50% or more was evaluated as "NG", and any other evaluation was evaluated as "OK".

Table 1 shows the formulation of the conductive particle-containing hot melt adhesive sheets for Examples 1-2 and Comparative Examples 1-3, as well as the evaluation of the solder wettability of the smart card, the bending test results, and the connection reliability evaluation.

Comparative Example 1 did not achieve excellent connection reliability because it used eutectic alloy solder particles. This is thought to be because the solder particles reached the eutectic point and liquefied during thermocompression bonding, preventing the resin from being fully removed. Comparative Example 2 used a flux compound without a crystalline polyamide having carboxyl groups, which reduced the elastic modulus of the adhesive layer and prevented excellent bending resistance. Comparative Example 3 did not use a crystalline polyamide having carboxyl groups or a flux compound, resulting in poor solder wettability and poor bending resistance.

On the other hand, Examples 1 and 2 used crystalline polyamide with carboxyl groups and non-eutectic alloy solder particles, resulting in excellent connection reliability and bending resistance. 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 flux compounds was prevented, and excellent bending resistance was achieved.

5. Second Example
As in the previous examples, a conductive particle-containing hot melt adhesive sheet containing solder particles was prepared, and a smart card was produced using this sheet. The smart card was then evaluated for solder wettability, bending test, and connection reliability.

The solder particles were prepared in the same manner as in the previous examples, and solder particles with the following composition were obtained. The preparation of a conductive particle-containing hot melt adhesive sheet, the preparation of a smart card, the evaluation of solder wettability, the evaluation of a bending test, and the evaluation of connection reliability were also carried out in the same manner as in the previous examples.
・Type 4 Sn-17Bi (non-eutectic, solidus temperature: 157°C, liquidus temperature: 205°C)
・Type 4 Sn-30Bi (non-eutectic, solidus temperature: 139°C, liquidus temperature: 183°C)

Table 2 shows the formulations of the conductive particle-containing hot melt adhesive sheets for Examples 1-3, Comparative Examples 1-5, and Reference Example 1, as well as the evaluation of the solder wettability of the smart cards, the evaluation of the bending test, and the evaluation of the connection reliability. In Reference Example 1, a chip module with a conductive particle-containing hot melt adhesive sheet attached was placed on the IC chip area of the card member, and a smart card was produced using a reflow oven. The peak temperature of the reflow temperature profile was set so that the temperature reached by the conductive particle-containing hot melt adhesive sheet would be approximately 150°C.

In Comparative Example 4, the thermocompression temperature was below the solidus temperature, which is thought to be why the solder particles did not melt. In Comparative Example 5, the thermocompression temperature was too high, which caused the card surface in contact with the conductive particle-containing hot melt adhesive sheet to melt, lowering the position of the embedded Cu wire. As a result, the solder-connected solder particles were stretched downward, causing cracks, and it is thought that excellent bending resistance could not be achieved.

In Reference Example 1, the binder's melt volume flow rate (MVR) was relatively low, so when connecting using a reflow oven without applying any weight, the solder particles were unable to provide electrical continuity, and the solder wettability evaluation, bending test evaluation, and connection reliability evaluation all received an "NG" rating.

In Example 3, excellent connection reliability and bending resistance were achieved by using crystalline polyamide with carboxyl groups and non-eutectic alloy solder particles. This is thought to be due to the flux effect of the carboxyl groups present in the crystalline polyamide. As a result, a decrease in the elastic modulus of the adhesive layer due to the addition of flux compounds was prevented, and excellent bending resistance was achieved.

10 Card member, 11 Opening, 12 Antenna pattern, 12a First exposed portion, 12b Second exposed portion, 20 IC chip, 21 Contact terminal

Claims (16)

a conductive particle-containing hot melt adhesive sheet containing solder particles that are a non-eutectic alloy in a binder containing a crystalline polyamide having a carboxyl group is interposed between the card member and the IC chip, and the card member and the IC chip are thermally and pressure-bonded ;
A method for producing a smart card, wherein the crystalline polyamide is a copolymer based on lauryllactam or 11-aminoundecanoic acid . The method for manufacturing a smart card according to claim 1, wherein the binder further contains a crystalline polyester resin. The method for manufacturing a smart card according to claim 1 or 2, wherein the proportion of the crystalline polyamide in the binder is 50 to 100 wt %. A method for manufacturing a smart card according to any one of claims 1 to 3, wherein the solidus temperature of the solder particles is 155°C or less. A method for manufacturing a smart card according to any one of claims 1 to 4, wherein the solder particles are an alloy containing two or more elements selected from the group consisting of Sn, Bi, Ag, In, Cu, Sb, Pb, and Zn. A method for manufacturing a smart card according to any one of claims 1 to 5, wherein the content of the solder particles is 40 to 400 parts by weight per 100 parts by weight of the binder. A method for manufacturing a smart card according to any one of claims 1 to 6, wherein the average particle diameter of the solder particles is 70% or more of the thickness of the conductive particle-containing hot melt adhesive sheet. The method for manufacturing a smart card described in any one of claims 1 to 7, wherein the temperature reached by the conductive particle-containing hot-melt adhesive sheet during the thermocompression bonding is 120 to 160°C. a card member, an IC chip, and an adhesive layer that adheres the card member and the IC chip together;
the adhesive layer contains solder particles that are a non-eutectic alloy in a binder that contains a crystalline polyamide having a carboxyl group,
A smart card in which the crystalline polyamide is a copolymer based on lauryllactam or 11-aminoundecanoic acid . The solder particles are a non-eutectic alloy and are contained in a binder containing a crystalline polyamide having a carboxyl group .
The conductive particle-containing hot melt adhesive sheet, wherein the crystalline polyamide is a copolymer based on lauryllactam or 11-aminoundecanoic acid . The conductive particle-containing hot melt adhesive sheet according to claim 10, wherein the binder further contains a crystalline polyester resin. The conductive particle-containing hot melt adhesive sheet according to claim 10 or 11, wherein the proportion of the crystalline polyamide in the binder is 50 to 100 wt %. The conductive particle-containing hot melt adhesive sheet according to any one of claims 10 to 12, wherein the solidus temperature of the solder particles is 155°C or less. The conductive particle-containing hot melt adhesive sheet according to any one of claims 10 to 13, wherein the solder particles are an alloy containing two or more elements selected from the group consisting of Sn, Bi, Ag, In, Cu, Sb, Pb, and Zn. The conductive particle-containing hot melt adhesive sheet according to any one of claims 10 to 14, wherein the content of the solder particles is 40 to 400 parts by weight per 100 parts by weight of the thermoplastic resin. 16. The conductive particle-containing hot melt adhesive sheet according to claim 10, wherein the average particle diameter of the solder particles is 70% or more of the thickness of the conductive particle-containing hot melt adhesive sheet.