JP2020173990A - Method for producing conductive particle - Google Patents

Abstract

To provide a method for producing a conductive particle that can achieve stable connection resistance when used in an anisotropic conductive adhesive.SOLUTION: The present disclosure relates to a method for producing a conductive particle. The production method includes the steps of forming an electroless plating layer on the surface of a core particle, forming a gold layer on the surface of the electroless plating layer, and forming a tungsten layer by sputtering on the surface of the gold layer.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a method for producing conductive particles. The conductive particles produced by this method are used, for example, in an anisotropic conductive adhesive.

A drive IC is mounted on a liquid crystal and a glass panel for displaying an OLED (Organic Light-Emitting Diode). The method can be roughly divided into two types, COG (Chip-on-Glass) mounting and COF (Chip-on-Flex) mounting. In COG mounting, the driving IC is directly bonded onto the glass panel using an anisotropic conductive adhesive containing conductive particles. On the other hand, in COF mounting, drive ICs are bonded to a flexible tape having metal wiring, and they are bonded to a glass panel using an anisotropic conductive adhesive containing conductive particles. The anisotropy here means that it conducts in the pressurized direction and maintains the insulating property in the non-pressurized direction.

Until now, the wiring on the glass panel has been mainly ITO (Indium Tin Oxide) wiring, but it is being replaced by IZO (Indium Zinc Oxide) for the purpose of improving productivity or smoothness. Further, in recent years, electrodes formed by laminating a plurality of Cu, Al, Ti and the like on a glass panel, and composite multilayer electrodes having ITO or IZO further formed on the outermost surface have been developed. It is necessary to obtain a stable connection resistance with respect to an electrode using such a material having high flatness and high hardness such as Ti.

Patent Document 1 discloses a method for producing conductive fine particles having a base material fine particles and a conductive film formed on the surface thereof, and the conductive film has protrusions raised on the surface. According to this document, conductive fine particles having protrusions on the conductive film are said to have excellent conductive reliability.

Patent Document 2 discloses conductive particles having a base material particles and a nickel-boron conductive layer provided on the surface thereof. According to this document, since the nickel-boron conductive layer has an appropriate hardness, the oxide film on the surface of the electrodes and the conductive particles can be sufficiently eliminated at the time of the member to be connected between the electrodes, and the connection resistance is lowered. It is said that it can be done.

Patent Document 3 discloses conductive particles having resin particles, an electroless metal plating layer covering the surface thereof, and a metal sputter layer excluding Au forming the outermost layer. According to this document, the surface of the resin particles is coated with electroless metal plating to improve the adhesion to the surface of the resin particles, and the outermost layer is a metal sputtered layer, so that good connection reliability can be obtained. It is said that.

Japanese Patent No. 4563110 JP-A-2011-243455 JP 2012-164454

However, according to the study by the present inventors, when a metal sputtered layer having a relatively high hardness is used as the outermost layer like the conductive particles described in Patent Document 3, the conductive particles are deformed by applying a compressive force. As a result, the sputtered metal layer is broken, and there is a problem that the connection resistance is not stable.

The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide a method for producing conductive particles capable of achieving stable connection resistance when used in an anisotropic conductive adhesive.

As a result of diligent studies by the inventors, in order to achieve a stable connection resistance, it is useful to have a structure in which the conductive layer constituting the outermost layer is not easily destroyed even if the conductive particles are compressionally deformed. The present inventors have found that the destruction of the outermost layer at the time of particle deformation can be suppressed by providing a gold layer under the conductive layer constituting the outermost layer, and have completed the following invention.

The present disclosure relates to a method for producing conductive particles. This manufacturing method includes a step of forming an electroless plating layer on the surface of core particles, a step of forming a gold layer on the surface of the electroless plating layer, and a step of forming a tungsten layer on the surface of the gold layer by sputtering. Including.

According to the above manufacturing method, by interposing a gold layer between the electroless plating layer and the tungsten layer, the adhesion between the two can be improved. In addition to this, the gold layer functions as a base layer of the tungsten layer, and even if the conductive particles are compressed and deformed, the tungsten layer can be suppressed from being destroyed. Due to these actions, according to the conductive particles produced by the above-mentioned production method, stable connection resistance can be achieved when used in an anisotropic conductive adhesive.

In the above manufacturing method, it is preferable to form a gold layer by a substitution plating method or an electroless plating method from the viewpoint of further stabilizing the connection resistance. That is, the gold layer formed by the substitution plating method or the electroless plating method has high adhesion to the electroless plating layer, and when a compressive force is applied to the conductive particles, the electroless plating layer and the gold layer are integrally deformed. To do. As a result, the connection resistance becomes more stable.

In the present disclosure, it is preferable that the electroless plating layer is thicker than the gold layer and the gold layer is thicker than the tungsten layer. By adopting such a configuration, it is possible to further suppress the destruction of the tungsten layer during particle deformation. The average particle size of the core particles is, for example, in the range of 1 to 25 μm.

INDUSTRIAL APPLICABILITY According to the present invention, there is provided a method for producing conductive particles capable of achieving a stable connection resistance when used in an anisotropic conductive adhesive.

FIG. 1 is a cross-sectional view schematically showing an example of conductive particles produced by the method according to the present disclosure. FIG. 2 is a cross-sectional view schematically showing an example of an anisotropic conductive film containing the conductive particles shown in FIG. FIG. 3 is a cross-sectional view schematically showing an example of a connection structure in which circuit electrodes are connected to each other. 4 (a) to 4 (c) are cross-sectional views schematically showing an example of a method for manufacturing a connection structure.

Hereinafter, embodiments of the present disclosure will be described in detail. However, the present invention is not limited to the following embodiments.

FIG. 1 is a cross-sectional view showing an embodiment of conductive particles. The conductive particles 10 shown in FIG. 1 include a core particle 1, an electroless plating layer 2a formed on the surface of the core particle 1, a gold layer 2b formed on the surface of the electroless plating layer 2a, and a gold layer. It includes a tungsten layer 5 formed on the surface of 2b. The tungsten layer 5 forming the outermost layer of the conductive particles 10 is formed by sputtering.

The particle size of the conductive particles 10 is generally smaller than the minimum value of the distance between the electrodes of the circuit members to be connected. When the heights of the connected electrodes vary, the average particle size of the conductive particles 10 is preferably larger than the height variation. From this point of view, the average particle size of the conductive particles 10 is preferably 1 to 50 μm, more preferably 2 to 30 μm, and particularly preferably 3 to 25 μm. The "average particle size" as used herein means the median diameter D50 measured by a laser light diffraction / scattering type particle size analyzer.

The material constituting the core particle 1 is not particularly limited, and an organic material, an inorganic material, a metal material, or the like can be used. The average particle size of the core particles is preferably 1 to 50 μm, more preferably 2 to 30 μm, and 3 to 30 μm from the viewpoint of sufficiently securing the contact area between the electrode and the conductive particles and obtaining a stable connection resistance. It is more preferably 25 μm. In order to maintain the insulation between adjacent electrodes, it is preferable that the particle size distribution is sharp. When the particle size distribution is uniform, the insulation reliability between adjacent electrodes is stable. Further, since a force is uniformly applied to the conductive particles 10 when they are sandwiched between the opposing electrodes, stable connection resistance can be obtained, which is preferable. As the core particles having a uniform particle size distribution, organic resin particles or silica particles obtained by synthesis can be preferably used.

Organic resin particles include, for example, acrylic resins such as polymethylmethacrylate and polymethylacrylate, and resins selected from polyolefin resins such as polyethylene, polypropylene, polyisobutylene and polybutadiene. Such organic resin particles can be synthesized by a known method, and are synthesized by suspension polymerization, seed polymerization, precipitation polymerization, or dispersion polymerization.

The core particle 1 is preferably spherical. In particular, particles produced by seed polymerization are preferable because they have a sharp particle size distribution and a small particle size variation. Specifically, the CV value (Coefficient of Variation) of the core particle 1 is preferably 20% or less, more preferably 15% or less, and further preferably 10% or less. In particular, in order to stably connect electrodes having a distance of 10 μm between adjacent electrodes without short-circuit defects, the CV value of the core particle 1 is particularly preferably 5% or less, and most preferably 3% or less. .. For example, if the CV value of particles having an average particle size of 3.0 μm exceeds 20%, a short circuit defect may occur when a driving IC with a narrow pitch electrode having a level of 10 μm is connected.

When an electrode formed on a relatively soft polyimide film or an electrode formed on a brittle glass substrate is used for connection, if the core particle 1 is too hard, the conductive particle 10 may damage the electrode. From this point of view, when the driving IC is directly connected to the electrode formed on the glass substrate such as COG, it is preferable that the core particles 1 are soft. For example, the compression modulus of the core particles 1 obtained while a 20% compression displacement at 200 ° C. (20% K value) is more preferably is preferably 300 kgf / mm ² or less, 200 kgf / mm ² or less .. If the core particle 1 is too soft, it becomes difficult to measure the particle capture rate due to indentation. Therefore, the 20% K value of the core particle 1 at 200 ° C. is preferably 80 kgf / mm ² or more.

The 20% K value of the core particle 1 is measured by the following method using a Fisherscope H100C (manufactured by Fisher Instruments).
1) A slide glass on which a particle sample is placed is placed on a hot plate at 200 ° C., and a weight is applied to the center direction of the particles.
2) The compressive deformation elastic modulus (K20, 20% K value) when the particle sample is deformed by 20% is measured in 50 seconds while applying a load of 50 mN, and then calculated according to the following formula.
K20 (compressive deformation elastic modulus) = (3/2 ^1/2 ) x F20 x S20 ^-3/2 x R- ^{1 / 2}
F20: Load required to deform particles by 20% (N)
S20: Deformation amount (m) of particles at the time of 20% deformation
R: Particle radius (m)

If the electrode is very hard, the core particles 1 may be deformed too much at the time of crimping, and the conductive layer (particularly the tungsten layer 5) may not be sufficiently fitted into the electrode. In this case, the core particle 1 is preferably hard. Specifically, silica particles are preferably used. Silica is a synthetic method typified by the Stöber method, and is preferable because particles having a very sharp particle size distribution and little particle size variation can be obtained. Since the elution of impurities from the core particle 1 lowers the migration resistance, it is preferable that the core particle 1 has a high purity. Specifically, the content of SiO ₂ is preferably 95% by mass or more, more preferably 98% by mass or more, further preferably 99% by mass or more, and 99.9% by mass or more. Most preferably.

The conductive particles 10 shown in FIG. 1 have an electroless plating layer 2a on the surface of the core particles 1. Having the electroless plating layer 2a is preferable because the destruction of the tungsten layer 5 is suppressed at the time of crimping, and a stable connection resistance can be easily obtained. As the electroless plating layer 2a, a metal layer formed by electroless plating is preferably used. The material of the electroless plating layer 2a is not particularly limited, but a metal or alloy used in electroless plating can be applied. Specifically, nickel, copper, palladium, gold, silver, platinum, tin or alloys thereof can be used. Nickel is particularly preferable because of its high practicality. The nickel-plated layer preferably contains phosphorus or boron. As a result, the corrosion resistance of the electroless plating layer 2a is enhanced, it is easy to maintain high insulation properties, the hardness of the electroless plating layer 2a can be increased, and the electric resistance value when the conductive particles 10 are compressed is lowered. It will be easier to keep.

The nickel plating layer as the electroless plating layer 2a may contain other metals to be co-deposited together with phosphorus or boron. Examples of other metals include metals such as cobalt, copper, zinc, iron, manganese, chromium, vanadium, molybdenum, palladium, tin, tungsten, renium, ruthenium and rhodium. By incorporating these metals in the electroless plating layer 2a, the hardness of the electroless plating layer 2a can be increased, and when the conductive particles 10 are highly compressed and pressure-bonded, the protrusions are suppressed from being crushed. It is possible to obtain a low electrical resistance value. When the electroless plating layer 2a is an alloy layer containing copper in addition to nickel, the connection resistance tends to be low, which is preferable. Among other metals that erect together with phosphorus or boron, tungsten having a high hardness itself is preferable. In this case, the nickel content in the electroless plating layer 2a is preferably 85% by mass or more.

When the electroless plating layer 2a is formed by electroless nickel plating, for example, by using a phosphorus-containing compound such as sodium hypophosphite as a reducing agent, phosphorus can be co-deposited and contains a nickel-phosphorus alloy. The electroless plating layer 2a can be formed. Further, by using a boron-containing compound such as dimethylamine borane, sodium borohydride, or potassium borohydride as the reducing agent, boron can be co-deposited and electroless plating containing a nickel-boron alloy is contained. Layer 2a can be formed. Since the nickel-boron alloy has a higher hardness than the nickel-boron alloy, electroless plating is performed from the viewpoint of suppressing the protrusions from being crushed when the conductive particles are highly compressed and pressure-bonded to obtain a lower electric resistance value. Layer 2a preferably contains a nickel-boron alloy.

The thickness of the electroless plating layer 2a is not particularly limited, but is practically preferably 20 nm or more and 500 nm or less, more preferably 30 nm or more and 400 nm or less, particularly preferably 50 nm or more and 300 nm or less, and most preferably 60 nm or more and 200 nm or less. When the thickness of the electroless plating layer 2a is thinner than 20 nm, it is difficult to obtain a continuous electroless plating layer 2a, the electroless plating layer 2a is easily broken during crimping, and the connection characteristics are not stable. On the other hand, when the electroless plating layer 2a is thicker than 500 nm, the formation time of the electroless plating layer 2a becomes very long, the manufacturing cost is high, and the practicality is low. Further, at the time of crimping, the influence of the physical properties of the electroless plating layer 2a becomes dominant over the physical properties of the core particles 1, the electroless plating layer 2a is not sufficiently deformed, the contact area with the electrode becomes small, and the connection resistance is not stable. Is easy to occur.

Electroless plating enables uniform metal coating on the surface of non-conductors, makes it easy to adjust the thickness from several tens of nanometers to several microns, and can form a relatively thick metal layer compared to the sputtering method. There are merits. Further, since a power source is not required as compared with electroplating, a metal layer can be formed with simple equipment, which is preferable. Further, the electroless plating method is a highly practical method because it can be treated in a solution and a large area can be treated. It can also be alloyed by eutectoid with a reducing agent or additive that reduces metal ions. Specifically, in electroless nickel plating, phosphates, hydrazines, boron hydrides, etc. can be used as reducing agents for nickel ions, and nickel-phosphorus alloys, pure nickel, nickel-boron alloys, etc. are obtained, respectively. Be done. In addition, various complexing agents for stabilizing metal ions in the liquid are used, and nickel films having different crystal structures can be obtained depending on the type. Since various properties such as high corrosion resistance, low resistance, malleability, and hardness can be adjusted depending on the alloy ratio or the difference in crystal structure, there is an advantage that the properties can be selected as desired.

As a method of forming the electroless plating layer 2a, after the surface of the core particles 1 is catalytically treated, the above-mentioned catalyst is activated and the electroless plating treatment is performed, so that the surface of the core particles 1 is electroless plated layer 2a. To form. Precious metals are mainly used as the catalyst that serves as the precipitation point of electroless plating, and palladium, gold, silver, platinum and the like are preferably used. Palladium is mainly used as a catalyst. The core particles 1 are immersed in a solution containing palladium ions, and the palladium ions are adsorbed on the surface of the core particles 1. After that, the core particles 1 in which palladium ions are adsorbed on the surface are immersed in a reducing solution (activating solution) in which a reducing agent for palladium ions is dissolved, and palladium ions are reduced to precipitate palladium, which is a reaction precipitation of electroless plating. Let it be a point. It is preferable to dissolve the palladium ion as a normal complex because the stability of the treatment liquid is increased.

The gold layer 2b is formed on the surface of the electroless plating layer 2a. Since the gold layer 2b is formed, even if the conductive particles 10 are compressionally deformed during crimping, the tungsten layer 5 of the outermost layer is less likely to be broken, and the connection resistance is stabilized. As a method for forming the gold layer 2b, a sputtering method, an electroless plating method, a CVD method, or the like can be adopted. The method of forming a metal layer on the surface of the particles by sputtering will be described later. From the viewpoint of ensuring adhesion to the electroless plating layer 2a, an electroless plating method is preferably used for the gold layer 2b. As the electroless plating method for forming the gold layer 2b, a substitution plating method can be selected. The substitution plating method is a method of forming a metal layer by utilizing the difference in ionization tendency of metal ions, and the object to be plated (metal B) is placed in a solution in which the metal ion A'of the metal A to be precipitated is dissolved. This is a method in which the metal ion A'receives the electrons generated when the metal B is ionized (dissolved) by immersion and precipitates as the metal A. Specifically, when the electroless nickel layer is applied to the electroless plating layer 2a and the substitution gold plating method is applied to the formation of the gold layer 2b, the electroless nickel plating layer and the substitution gold plating layer (gold layer 2b) Is preferable because it has high adhesion. The replacement gold plating solution contains a complexing agent for gold ions and gold ions, a stabilizer, a pH adjuster, and the like, and the gold ions preferably exist as a gold complex.

After the gold layer 2b is formed by the substitution gold plating method, the thickness of the gold layer 2b may be further increased by the electroless gold plating method. In the replacement gold plating method, the gold layer 2b is precipitated while dissolving the underlying electroless plating layer 2a, so that pinholes are generated in the gold layer 2b and the metal of the underlying electroless plating layer 2a is the surface of the gold layer 2b. May spread to. In this case, since there is a concern that the adhesion between the tungsten layer 5 and the gold layer 2b, which will be described later, may be deteriorated, the electroless gold plating layer is formed on the surface of the substitution gold plating layer so that the metal of the electroless plating layer is not exposed. , The surface of the gold layer 2b can be obtained, the adhesion between the tungsten layer 5 and the gold layer 2b becomes very high, and stable connection resistance can be obtained, which is more preferable.

The thickness of the gold layer 2b is preferably thinner than that of the electroless plating layer 2a. If the gold layer 2b is thicker than the electroless plating layer 2a, the gold layer 2b is easily deformed during crimping, so that the force for sufficiently pressing the tungsten layer 5 described later against the electrode is weakened, and it is difficult to obtain a stable connection resistance. Become. Further, if the gold layer 2b is thicker than the electroless plating layer 2a, the practicality is lowered in terms of cost. Specifically, the thickness of the gold layer 2b is preferably 5 nm or more and 70 nm or less, more preferably 10 nm or more and 60 nm or less, further preferably 13 nm or more and 50 nm or less, and most preferably 15 nm or more and 40 nm or less. If the thickness of the gold layer 2b is thinner than 5 nm, it is difficult to form it as a continuous layer, and the tungsten layer 5 comes into contact with not only the gold layer 2b but also the electroless plating layer 2a, and the tungsten layer 5 is destroyed during crimping. It becomes difficult to suppress. Further, from the viewpoint of suppressing the destruction of the tungsten layer 5 during crimping, the gold layer 2b is more preferably 10 nm or more.

The tungsten layer 5 is formed on the surface of the gold layer 2b. As described above, the tungsten layer 5 is formed by a sputtering method. In the sputtering method, the rare gas element ionized by applying a high voltage collides with the target, and the target atom pops out and repeatedly collides with the particle surface at high speed. Therefore, the nucleation density at the time of forming the tungsten layer 5 is increased. It becomes extremely dense and can evenly coat the particle surface with a small amount of metal. Therefore, in the sputtering method, the metal thin film required to uniformly cover the entire surface of the particles can be thinned.

The sputtering method is not particularly limited, but a bipolar sputtering method, a magnetron sputtering method, a reactive sputtering method, a laser sputtering method, an RF (radio frequency) sputtering method and the like can be applied. In order to form a uniform sputter layer on the particle surface, it is preferable that the particles are constantly rotating or rolling with respect to the target because the particles do not aggregate with each other. As such a sputtering method, a barrel sputtering method can be preferably used. The barrel sputtering method consists of a rotating barrel that houses the particles and a target that is fixed on the axis of rotation of the rotating barrel facing the inner wall of the rotating barrel. The particles are stored in the rotating barrel, and the rotating barrel rotates or oscillates. This is a method in which the particles are constantly rotated or rolled to form a uniform sputter layer on the surface of the particles. As a barrel shape that suppresses agglomeration of particles, the one adopted in the polygonal ballu sputtering apparatus described in Japanese Patent No. 3620842 is preferable.

The tungsten layer 5 is preferably a continuous film so that the underlying electroless plating layer 2a or gold layer 2b is not exposed. When the underlying gold layer 2b is exposed, when the exposed surface comes into contact with the electrode surface, the conductive layer does not sufficiently dig into the electrode surface and stable connection resistance tends not to be obtained.

The thickness of the tungsten layer 5 is not particularly limited, but is preferably thinner than the gold layer 2b from the viewpoint of cost and stability of connection resistance. Tungsten is a hard metal, so if it is thicker than necessary, it will easily break during compressive deformation and will easily worsen the connection resistance. Although it depends on the thickness of the underlying gold layer 2b, the thickness of the tungsten layer 5 is preferably 5 nm or more and 60 nm or less, more preferably 10 nm or more and 50 nm or less, further preferably 13 nm or more and 40 nm or less, and most preferably 15 nm or more and 30 nm or less.

In order to confirm the thickness and continuity of the tungsten layer 5, the cross section of the conductive particles 10 may be observed. For cross-section processing, a method of curing the conductive particles 10 with an epoxy resin and polishing, or a method of processing with a focused ion beam can be used. The cross section can be observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The thickness of the tungsten layer 5 and its variation can be calculated from cross-sectional observation. Further, as a method for evaluating the density of the tungsten layer 5 or the degree of exposure of the underlying layer (electrolytic plating layer 2a and gold layer 2b), in addition to the above-mentioned method of observing with a scanning electron microscope, X-ray photoelectron spectroscopy is used. There is a method of calculating the element ratio of the outermost layer (tungsten layer 5) by using an apparatus (XPS: X-ray Photoelectron Spectroscopy). XPS analysis is the best than cross-section observation because it can obtain information on a region of several nanometers below the metal surface, and by measuring a sample in which conductive particles 10 are spread, information can be obtained as the sum of many particles. It is preferable to be able to obtain a lot of information on the surface of the outer layer.

According to the above embodiment, the following effects are achieved. Since the conductive particles 10 are provided with the electroless plating layer 2a on the surface of the core particles 1, the tungsten layer 5 is more stable than the case where the tungsten layer 5 is directly formed on the surface of the core particles 1 by a sputtering method. Easy to form. Further, by providing the electroless plating layer 2a, the weight (volume specific gravity) of the particles is larger than that of the core particles 1, the efficiency of rolling or stirring in the barrel is increased, and the aggregation of the particles is suppressed. Therefore, there is an advantage that the tungsten layer 5 is easily formed uniformly.

<Glue conductive adhesive>
An anisotropic conductive adhesive is prepared by dispersing the above conductive particles 10 in the adhesive component. As the circuit connection material, a paste-like anisotropic conductive adhesive may be used as it is, or an anisotropic conductive film obtained by molding the paste-like anisotropic conductive adhesive into a film may be used. The anisotropic conductive film 50 shown in FIG. 2 is formed by dispersing the conductive particles 10 in the adhesive component 20.

As the adhesive component 20, for example, a mixture of a thermosetting resin and a curing agent is used. Preferred adhesives include, for example, a mixture of an epoxy resin and a latent curing agent, and a mixture of a radically polymerizable compound and an organic peroxide. It is effective to blend a thermoplastic resin such as a phenoxy resin, a polyester resin, a polyamide resin, a polyester resin, a polyurethane resin, an acrylic resin, or a polyester urethane resin into the heteroconductive film.

The thickness of the anisotropic conductive film 50 is relatively determined in consideration of the particle size of the conductive particles and the characteristics of the adhesive composition, but is preferably 1 to 100 μm. If it is less than 1 μm, sufficient adhesiveness cannot be obtained, and if it exceeds 100 μm, a large amount of conductive particles are required to obtain conductivity, which is not realistic. For this reason, the thickness is more preferably 3 to 50 μm.

<Connection structure>
The connection structure 100 shown in FIG. 3 includes a first circuit member 30 and a second circuit member 40 that face each other, and is located between the first circuit member 30 and the second circuit member 40. , A connecting portion 50a for connecting these is provided.

The first circuit member 30 includes a circuit board (first circuit board) 31 and a circuit electrode (first circuit electrode) 32 formed on the main surface 31a of the circuit board 31. The second circuit member 40 includes a circuit board (second circuit board) 41 and a circuit electrode (second circuit electrode) 42 formed on the main surface 41a of the circuit board 41.

Specific examples of circuit members include IC chips (semiconductor chips), resistor chips, capacitor chips, chip components such as driver ICs, and rigid type package substrates. These circuit members are provided with circuit electrodes, and are generally provided with a large number of circuit electrodes. Specific examples of the other circuit member to which the circuit member is connected include a flexible tape substrate having metal wiring, a flexible printed wiring board, and a wiring board such as a glass substrate on which ITO or IZO is vapor-deposited. Examples of the material of the substrate include inorganic substances such as semiconductors, glass substrates and ceramics; organic substances such as polyimide, polycarbonate and polyester sulfone; and materials obtained by combining these inorganic substances and organic substances.

According to the anisotropic conductive film 50, the circuit members can be connected to each other efficiently and with high connection reliability. Therefore, the anisotropic conductive film 50 is suitable for COG mounting or COF mounting on a wiring board of a chip component provided with a large number of fine connection terminals (circuit electrodes).

The connecting portion 50a includes a cured product 20a of an adhesive component contained in the circuit connecting material, and conductive particles 10 dispersed therein. Then, in the connection structure 100, the opposite circuit electrodes 32 and the circuit electrodes 42 are electrically connected via the conductive particles 10. More specifically, as shown in FIG. 3, the conductive particles 10 are in direct contact with both the circuit electrodes 32 and 42. On the other hand, in the lateral direction, the insulating property is maintained by the presence of the cured product 20a having the insulating property.

<Manufacturing method of connection structure>
Next, a method of manufacturing the connection structure 100 will be described. 4 (a) to 4 (c) are process diagrams showing an embodiment of a method for manufacturing a connection structure by a schematic cross-sectional view. In the present embodiment, the anisotropic conductive film 50 is thermosetting, and finally the connection structure 100 is manufactured.

The anisotropic conductive film 50 cut to a predetermined length is placed on the main surface 31a of the circuit member 30 (FIG. 4A). At this stage, the separator film 52 remains on one surface of the anisotropic conductive film 50.

Next, pressure is applied in the directions of arrows A and B in FIG. 4A to temporarily fix the anisotropic conductive film 50 to the first circuit member 30 (FIG. 4B). The pressure at this time is not particularly limited as long as it does not damage the circuit member, but is generally preferably 0.1 to 30.0 MPa. Further, the pressure may be applied while heating, and the heating temperature is set to a temperature at which the anisotropic conductive film 50 does not substantially cure. The heating temperature is generally preferably 50 to 100 ° C. These heating and pressurization are preferably performed in the range of 0.1 to 2 seconds.

After peeling off the separator film 52, as shown in FIG. 4C, the second circuit member 40 is anisotropically conductive so that the second circuit electrode 42 faces the side of the first circuit member 30. Place on film 50. Then, while heating the anisotropic conductive film 50, the whole is pressurized in the directions of arrows A and B in FIG. 4 (c). The heating temperature at this time is a temperature at which the adhesive component 20 can be cured. The heating temperature is preferably 60 to 180 ° C, more preferably 70 to 170 ° C, and even more preferably 80 to 160 ° C. If the heating temperature is less than 60 ° C., the curing rate tends to be slow, and if it exceeds 180 ° C., unwanted side reactions tend to proceed. The heating time is preferably 0.1 to 180 seconds, more preferably 0.5 to 180 seconds, and even more preferably 1 to 180 seconds.

The connecting portion 50a is formed by curing the adhesive component 20, and the connecting structure 100 as shown in FIG. 3 is obtained. The connection conditions are appropriately selected depending on the intended use, the adhesive composition, and the circuit member. When an adhesive component 20 that is cured by light is used, the anisotropic conductive film 50 may be appropriately irradiated with active rays or energy rays. Examples of the active light beam include ultraviolet rays, visible light, and infrared rays. Examples of energy rays include electron beams, X-rays, γ-rays, microwaves, and the like.

Hereinafter, the present disclosure will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
(1) Preparation of conductive particles <Preparation of core particles>
27 g of spherically crosslinked acrylic particles having an average particle size of 20 μm were prepared. 27 g of the crosslinked acrylic particles were dispersed in a 3% aqueous potassium hydroxide solution, and the mixture was stirred for 10 minutes. Then, the crosslinked acrylic particles were taken out by filtration using a membrane filter (manufactured by Merck & Co., Inc.) having a diameter of 3 μm. The crosslinked acrylic particles taken out were washed with water. As a result, crosslinked acrylic particles whose surface was adjusted were obtained.

27 g of surface-adjusted crosslinked acrylic particles are adjusted to pH 1.0, and after adding HS201 (trade name, manufactured by Hitachi Kasei Co., Ltd.), which is a palladium catalyst, to 100 mL of a palladium-catalyzed solution containing 20% by mass, the temperature is 30 ° C. Was stirred for 30 minutes. Next, after filtering with a membrane filter (manufactured by Merck & Co., Inc.) having a diameter of 3 μm, the palladium catalyst was adsorbed on the surface of the crosslinked acrylic particles by washing with water. Then, the crosslinked acrylic particles were added to the 0.5 mass% dimethylamine borane solution adjusted to pH 6.0, and the mixture was stirred at 60 ° C. for 5 minutes. As a result, the palladium catalyst was fixed and crosslinked acrylic particles having an activated surface were obtained.

<Formation of electroless nickel plating layer>
The surface was activated and 27 g of crosslinked acrylic particles were dispersed in 1000 mL of water heated to 70 ° C. To this dispersion, 1 mL of a 1 g / L bismuth nitrate aqueous solution was added as a plating stabilizer, and then 100 mL of an electroless nickel plating solution having the following composition was added dropwise at a dropping rate of 5 mL / min. After 10 minutes had passed from the end of the dropping, the dispersion was filtered and the filtrate was washed with water. Then, the filtrate was dried in a vacuum dryer at 80 ° C. In this way, particles (nickel-plated particles) having an electroless nickel-plated layer (nickel-phosphorus alloy layer) having a thickness of 80 nm were obtained. The obtained nickel-plated particles weighed 30 g. The surface of the obtained nickel-plated particles was smooth.
(Electroless nickel plating solution)
-Nickel sulfate: 400 g / L
-Sodium hypophosphite: 150 g / L
・ Sodium tartrate ・ Dihydrate: 120 g / L
・ Bismuth nitrate aqueous solution (1 g / L): 1 mL / L

<Formation of gold layer>
Next, a gold plating solution having the following composition was prepared, and the pH was adjusted to 6 with sodium hydroxide. 30 g of the nickel-plated particles were ultrasonically applied in 100 mL of pure water heated to 60 ° C. and dispersed. Using this plating solution, nickel-plated particles were subjected to substitution gold plating treatment under the condition of a liquid temperature of 60 ° C. until the average thickness was 20 nm. After filtration, the plated particles were washed with 100 mL of pure water for 60 seconds. As a result, conductive particles in which a gold layer (thickness 20 nm) was formed on the outside of the electroless nickel plating layer were obtained.
(Replacement Au plating solution)
-Ethylenediaminetetraacetic acid tetrasodium: 0.03 mol / L
-Trisodium citrate: 0.04 mol / L
-Potassium gold cyanide: 0.01 mol / L
・ PH: 6

<Formation of tungsten layer>
Next, we prepared a polygonal barrel sputtering device in which a stainless steel barrel with a hexagonal cross section and an internal diagonal length of 200 mm, a sputtering target placed inside the barrel, and a vacuum device for depressurizing the inside of the barrel were connected. did. In the barrel, 2 g of conductive particles in which a nickel layer and a gold layer were formed in this order on the surface of the crosslinked acrylic particles were placed, and tungsten was placed as a target for sputtering in the barrel. After depressurizing the inside of the barrel to 9 × 10 ^-4 Pa or less, argon was flowed at a constant flow velocity so that the inside of the barrel became 2 Pa. Then, the barrel was rotated forward and inverted at ± 75 °, and the outer peripheral portion of the barrel was stamped to roll, stir, and vibrate the conductive particles. Subsequently, a voltage was applied to the target and tungsten sputtering was performed for 30 minutes to form a continuous tungsten layer having a thickness of 10 nm. The inside of the barrel was returned to atmospheric pressure, and conductive particles having a tungsten layer as the outermost layer were taken out.

(2) Preparation of heteroconductive film 20 g of phenoxy resin [manufactured by Union Carbide Co., Ltd., trade name PKHC, weight average molecular weight 45000] is added to toluene (boiling point 110.6 ° C., SP value 8.90) / acetate by mass ratio. It was dissolved in a mixed solvent of ethyl (boiling point 77.1 ° C., SP value 9.10) = 50/50 to prepare a solution having a solid content of 40% by mass.

Butyl acrylate (hereinafter referred to as BA) (50 parts by mass), ethyl acrylate (hereinafter referred to as EA) (30 parts by mass), acrylonitrile (hereinafter referred to as AN) (20 parts by mass), and glycidyl methacrylate (hereinafter referred to as GMA) (3 parts by mass). ) Is co-polymerized with 50 g of acrylic rubber (weight average molecular weight: 500,000) dissolved in a mixed solvent of toluene (boiling point 110.6 ° C.) / ethyl acetate (boiling point 77.1 ° C.) = 50/50 by mass ratio. , A solution having a solid content of 40% by mass.

30 g of an epoxy resin [bisphenol A type epoxy resin, oiled shell epoxy Co., Ltd., trade name Epicoat 828 (EP-828), epoxy equivalent 184) was used as it was.

The latent curing agent is a master batch in which a microcapsule type curing agent having an average particle size of 5 μm, which has an imidazole modified product as a core and whose surface is coated with polyurethane, is dispersed in a liquid bisphenol F type epoxy resin. A mold curing agent (manufactured by Asahi Kasei Kogyo Co., Ltd., trade name Novacure 3941, active temperature 125 ° C.) was used.

The resin component is 100 and the latent curing agent is 30 in terms of solid mass ratio. Further, 3% by volume of conductive particles are blended and dispersed, and the PET resin film having a thickness of 50 μm is coated with a coating device. By hot air drying at ℃ for 3 minutes, an anisotropic conductive film having an adhesive layer thickness of 20 μm was obtained.

(3) Preparation of Circuit Connector Using the anisotropic conductive film obtained as described above, the semiconductor chip and the glass substrate with the IZO circuit were connected as follows. First, an adhesive surface of an anisotropic conductive film was attached onto a glass substrate with an IZO circuit, and then heated and pressurized for 5 seconds at 70 ° C. and 0.5 MPa for temporary connection. Then, the PET resin film was peeled off, the glass substrate with the IZO circuit was aligned, and the semiconductor chip was placed on the anisotropic conductive film. Next, heating and pressurization were performed from above the semiconductor chip for 10 seconds under the conditions of 190 ° C. and 40 gf / bump to make the main connection.

(4) Evaluation of the connection structure The conduction resistance test of the obtained connection structure was performed as follows. The evaluation procedure is the same for other examples and comparative examples described later.

(Conduction resistance test)
Regarding the conduction resistance between the chip electrode (bump) / glass electrode (IZO), after the initial value of the conduction resistance and the moisture absorption and heat resistance test (after leaving for 100 hours, 500 hours and 1000 hours under the conditions of temperature 85 ° C. and humidity 85%). The value of was measured for 20 samples, and the average value thereof was calculated. From the obtained average value, the conduction resistance was evaluated according to the following criteria. The results are shown in Table 1. It can be said that the conduction resistance is good when the criteria of A or B below are satisfied after 500 hours of the moisture absorption and heat resistance test.
A: Mean value of conduction resistance is less than 2Ω B: Mean value of conduction resistance is 2Ω or more and less than 5Ω C: Mean value of conduction resistance is 5Ω or more and less than 10Ω D: Mean value of conduction resistance is 10Ω or more and less than 20Ω E: Conduction resistance The average value of is 20Ω or more

(Examples 2 to 6)
Conductive particles of Examples 2 to 6 were prepared in the same manner as in Example 1 except that the thickness of the tungsten layer was adjusted as shown in Table 1. Using the conductive particles thus obtained, respectively, the anisotropic conductive film and the connecting structure according to Examples 2 to 6 were prepared and a conduction resistance test was conducted in the same manner as in Example 1.

(Example 7)
An electroless nickel plating layer and a replacement gold plating layer were formed on the surface of the crosslinked acrylic particles having an average particle size of 20.0 μm in the same manner as in Example 1. Next, crosslinked acrylic particles having the above-mentioned replacement gold plating layer as the outermost layer were put into the electroless gold plating solution HGS-2000 (product name, manufactured by Hitachi Kasei Co., Ltd.) heated to 60 ° C. Plating was performed until the plating layer became 20 nm. Next, a continuous tungsten layer having a thickness of 10 nm was formed on the surface of the gold layer in the same manner as in Example 1. Using the conductive particles thus obtained, the anisotropic conductive film and the connection structure according to Example 7 were produced and a conduction resistance test was conducted in the same manner as in Example 1.

(Comparative Example 1)
Conductive particles having an electroless nickel plating layer (innermost layer) and a tungsten layer (outermost layer) were produced in the same manner as in Example 1 except that the replacement gold plating layer was not formed. Using the obtained conductive particles, an anisotropic conductive film and a connection structure according to Comparative Example 1 were prepared and a conduction resistance test was conducted in the same manner as in Example 1.

1 ... core particles, 2a ... electroless plating layer, 2b ... gold layer, 5 ... tungsten layer, 10 ... conductive particles

Claims (4)

The process of forming an electroless plating layer on the surface of core particles,
The step of forming a gold layer on the surface of the electroless plating layer and
A step of forming a tungsten layer on the surface of the gold layer by sputtering, and
A method for producing conductive particles, including. The method for producing conductive particles according to claim 1, wherein the gold layer is formed by a displacement plating method or an electroless plating method. The method for producing conductive particles according to claim 1 or 2, wherein the electroless plating layer is thicker than the gold layer, and the gold layer is thicker than the tungsten layer. The method for producing conductive particles according to any one of claims 1 to 3, wherein the average particle size of the core particles is 1 to 25 μm.

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