JP5534745B2 - Conductive fine particles, anisotropic conductive material, and connection structure - Google Patents

Description

The present invention relates to conductive fine particles that are unlikely to break at the interface between the conductive layer and the low-melting-point metal layer, and that can realize high connection reliability, an anisotropic conductive material using the conductive fine particles, and The connection structure.

Conventionally, in an electronic circuit board, ICs and LSIs are connected by soldering electrodes to a printed circuit board. However, soldering cannot efficiently connect the printed circuit board to the IC or LSI. In addition, it is difficult to improve the mounting density of ICs and LSIs by soldering.
In order to solve this problem, a BGA (ball grid array) has been developed in which the solder is made into a spherical shape, so-called “solder balls” that connect the IC or LSI to the substrate. According to this technique, an electronic circuit that achieves both high productivity and high connection reliability can be configured by melting a solder ball mounted on a chip or a substrate at a high temperature and connecting the substrate and the chip.

However, in recent years, since the number of substrates has been increased and multilayer substrates are easily affected by the use environment, there has been a problem that distortion and expansion / contraction occur in the substrates and disconnection occurs in the connection portion between the substrates.

For such a problem, Patent Document 1 discloses that a metal layer (conductive layer) containing a highly conductive metal is formed on the surface of resin fine particles, and further, a metal such as tin is formed on the surface of the metal layer. A conductive fine particle having a low melting point metal layer (solder layer) formed thereon is disclosed. If such conductive fine particles are used, the stress applied to the conductive fine particles by the flexible resin fine particles can be relaxed, and the low melting point metal layer can be formed on the outermost surface to easily conduct conductive connection between the electrodes. it can.

However, when a low melting point metal layer is formed on the surface of the metal layer by a method such as electrolytic plating, the heating during mounting tends to cause breakage such as cracking at the interface between the metal layer and the low melting point metal layer. As a result, there is a problem that the connection reliability of the connection structure and the like obtained due to this is greatly impaired.

JP 2001-220691 A

The present invention relates to conductive fine particles that are unlikely to break at the interface between the conductive layer and the low-melting-point metal layer, and that can realize high connection reliability, an anisotropic conductive material using the conductive fine particles, and An object is to provide a connection structure.

The present invention is a conductive fine particle in which a conductive layer and a low melting point metal layer are sequentially formed on the surface of a substrate fine particle, and is heated between 150 ° C. for 300 hours between the conductive layer and the low melting point metal layer. The conductive fine particles in which the thickness of the intermetallic diffusion layer is 20% or less with respect to the total thickness of the conductive layer and the low melting point metal layer.
The present invention is described in detail below.

As a result of intensive studies, the present invention has been made up of the metal constituting the conductive layer and the low-melting-point metal layer as a factor that causes breakdown at the interface between the metal layer (conductive layer) and the low-melting-point metal layer in the conductive connection between the electrodes. The present inventors have found that a layer made of an intermetallic compound (intermetallic diffusion layer) formed between the metal and the metal to be related is involved. That is, it has been found that the formation of a fragile intermetallic diffusion layer causes the interface to break with the intermetallic diffusion layer as a starting point against external force.
As a result of further intensive studies, the present inventors have determined that the thickness of the intermetallic diffusion layer between the conductive layer and the low melting point metal layer after heating at 150 ° C. for 300 hours is the thickness of the conductive layer and the low melting point metal layer. In order to complete the present invention, it is found that when the thickness is 20% or less with respect to the total thickness, the connection reliability can be greatly improved by suppressing the breakage at the interface between the conductive layer and the low melting point metal layer. It came.

The conductive fine particles of the present invention are conductive fine particles in which a conductive layer and a low-melting-point metal layer are sequentially formed on the surface of the substrate fine particles, and the conductive layer and the low-melting-point metal after heating at 150 ° C. for 300 hours. The thickness of the intermetallic diffusion layer between the layers is 20% or less with respect to the total thickness of the conductive layer and the low melting point metal layer.

The substrate fine particles are not particularly limited, and examples thereof include resin fine particles, inorganic fine particles, organic-inorganic hybrid fine particles, and metal fine particles. As the substrate fine particles, resin fine particles are particularly preferable.

The resin fine particles are not particularly limited, and include, for example, polyolefin resin, acrylic resin, polyalkylene terephthalate resin, polysulfone resin, polycarbonate resin, polyamide resin, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. Resin fine particles.
The polyolefin resin is not particularly limited, and examples thereof include polyethylene resin, polypropylene resin, polystyrene resin, polyisobutylene resin, and polybutadiene resin. The acrylic resin is not particularly limited, and examples thereof include polymethyl methacrylate resin and polymethyl acrylate resin. These resins may be used alone or in combination of two or more.

The method for producing the resin fine particles is not particularly limited, and examples thereof include a polymerization method, a method using a polymer protective agent, and a method using a surfactant.
The polymerization method is not particularly limited, and examples thereof include emulsion polymerization, suspension polymerization, seed polymerization, dispersion polymerization, and dispersion seed polymerization.

The inorganic fine particles are not particularly limited, and examples thereof include fine particles composed of metal oxides such as silica and alumina. The organic-inorganic hybrid fine particles are not particularly limited, and examples thereof include hybrid fine particles containing an acrylic polymer in an organosiloxane skeleton.
The metal fine particles are not particularly limited, and examples thereof include fine particles made of metals such as aluminum, copper, nickel, iron, gold, and silver. Of these, copper fine particles are preferred. The copper fine particles may be copper fine particles formed substantially only of copper metal, or may be copper fine particles containing copper metal. In addition, when the said base material microparticles | fine-particles are copper microparticles, it is not necessary to form the conductive layer mentioned later.

When the substrate fine particles are resin fine particles, the preferred lower limit of the 10% K value of the fine resin particles is 1000 MPa, and the preferred upper limit is 15000 MPa. If the 10% K value is less than 1000 MPa, the resin fine particles may be destroyed when the resin fine particles are compressed and deformed. When the 10% K value exceeds 15000 MPa, the conductive fine particles may damage the electrode. The more preferable lower limit of the 10% K value is 2000 MPa, and the more preferable upper limit is 10,000 MPa.

The 10% K value is obtained by using a micro compression tester (for example, “PCT-200” manufactured by Shimadzu Corporation), and using a smooth indenter end face of a diamond cylinder having a diameter of 50 μm and a compression speed of 2.6 mN / The compression displacement (mm) when compressed under conditions of seconds and a maximum test load of 10 g can be measured and determined by the following equation.
K value ^{(N / mm 2) = (} 3 / √2) · F · S -3/2 · R -1/2
F: Load value at 10% compression deformation of resin fine particles (N)
S: Compression displacement (mm) in 10% compression deformation of resin fine particles
R: radius of resin fine particles (mm)

The average particle diameter of the substrate fine particles is not particularly limited, but a preferable lower limit is 1 μm and a preferable upper limit is 2000 μm. When the average particle diameter of the above-mentioned substrate fine particles is less than 1 μm, the substrate fine particles are likely to aggregate. When conductive fine particles in which a low melting point metal layer is formed on the surface of the aggregated substrate fine particles are used, a gap between adjacent electrodes can be obtained. May cause a short circuit. When the average particle diameter of the base material fine particles exceeds 2000 μm, the range suitable for connection between electrodes such as a circuit board may be exceeded. The more preferable lower limit of the average particle diameter of the substrate fine particles is 3 μm, and the more preferable upper limit is 1000 μm.
The average particle size of the above-mentioned substrate fine particles is obtained by measuring the particle size of 50 randomly selected substrate fine particles using an optical microscope or an electron microscope and arithmetically averaging the measured particle sizes. Can do.

The coefficient of variation of the average particle diameter of the substrate fine particles is not particularly limited, but is preferably 10% or less. If the coefficient of variation exceeds 10%, the connection reliability of the conductive fine particles may be lowered. The coefficient of variation is a numerical value obtained by dividing the standard deviation obtained from the particle size distribution by the average particle size and expressed as a percentage (%).

The shape of the substrate fine particles is not particularly limited as long as the distance between the opposing electrodes can be maintained, but a true spherical shape is preferable. Further, the surface of the substrate fine particles may be smooth or may have a protrusion.

In the conductive fine particles of the present invention, a conductive layer is formed on the surface of the substrate fine particles. The conductive layer serves as a base metal layer.
The metal forming the conductive layer is not particularly limited, and examples thereof include gold, silver, copper, zinc, iron, lead, tin, aluminum, cobalt, indium, nickel, chromium, antimony, bismuth, germanium, and cadmium. . Especially, since it is excellent in electroconductivity, it is preferable that the metal which forms the said conductive layer is gold, copper, or nickel.

The method for forming the conductive layer on the surface of the substrate fine particles is not particularly limited, and examples thereof include an electroless plating method, an electrolytic plating method, a vacuum deposition method, an ion plating method, and an ion sputtering method.

Although the thickness of the said conductive layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 100 micrometers. If the thickness of the conductive layer is less than 0.1 μm, sufficient conductivity may not be obtained. When the thickness of the conductive layer exceeds 100 μm, the flexibility of the conductive fine particles may be lowered. A more preferable lower limit of the thickness of the conductive layer is 0.2 μm, and a more preferable upper limit is 50 μm.
The thickness of the conductive layer is a thickness obtained by observing and measuring a section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging them.

The conductive fine particles of the present invention have a low melting point metal. The low-melting-point metal layer has a role of melting and joining the electrodes by a reflow process and conducting between the electrodes.

The low melting point metal constituting the low melting point metal layer is not particularly limited, but is preferably tin or an alloy containing tin. Examples of the alloy include a tin-silver alloy, a tin-copper alloy, a tin-silver-copper alloy, a tin-bismuth alloy, and a tin-zinc alloy.
Among them, tin, tin-silver alloy, and tin-silver-copper alloy are suitable as the low melting point metal because wettability is excellent for each electrode material.

Furthermore, in order to improve the bonding strength between the low-melting-point metal layer and the electrode, the low-melting-point metal layer includes nickel, copper, antimony, aluminum, zinc, iron, gold, titanium, phosphorus, germanium, tellurium, cobalt, Metals such as bismuth, manganese, chromium, molybdenum, and palladium may be included. Especially, since it is excellent in the effect which improves the joining strength of the said low melting metal layer and an electrode, it is suitable to make the said low melting metal layer contain nickel, copper, antimony, aluminum, and zinc.
The content of the metal in the total of metals contained in the low melting point metal layer is not particularly limited, but a preferable lower limit is 0.0001% by weight and a preferable upper limit is 1% by weight. When the content of the metal in the total of metals contained in the low-melting-point metal layer is within the range of 0.0001 to 1% by weight, the bonding strength between the low-melting-point metal layer and the electrode is further increased. Can be improved.

The tin content in the low melting point metal layer is preferably 40% by weight or more. When the content is less than 40% by weight, the effects of the present invention cannot be sufficiently obtained, and mounting defects may be caused. The tin content in the low melting point metal layer means the ratio of tin to the total of the elements contained in the low melting point metal layer, and the tin content in the low melting point metal layer is the high frequency inductively coupled plasma. It can be measured using an emission spectroscopic analyzer (“ICP-AES” manufactured by Horiba, Ltd.), a fluorescent X-ray analyzer (“EDX-800HS” manufactured by Shimadzu).

Although the thickness of the said low melting metal layer is not specifically limited, A preferable minimum is 0.1 micrometer and a preferable upper limit is 200 micrometers. When the thickness of the low-melting-point metal layer is less than 0.1 μm, it may not be able to be sufficiently bonded to the electrode even when reflowed and melted. When the thickness of the low-melting-point metal layer exceeds 200 μm, Aggregation tends to occur when the melting point metal layer is formed, and the aggregated conductive fine particles may cause a short circuit between adjacent electrodes. The minimum with more preferable thickness of the said low melting metal layer is 0.2 micrometer, and a more preferable upper limit is 50 micrometers.
The thickness of the low-melting-point metal layer is a thickness obtained by observing and measuring the cross section of 10 randomly selected conductive fine particles with a scanning electron microscope (SEM) and arithmetically averaging the measured values. .

The low melting point metal layer may have a close contact layer on the conductive layer side.
The adhesion layer is preferably formed by displacement plating. As a result, the adhesion between the conductive layer and the low-melting-point metal layer is greatly improved, so that it is possible to effectively prevent the occurrence of poor bonding due to the exposure of the conductive layer after the primary mounting.

The metal forming the adhesion layer is preferably tin, but may contain an element other than tin, or may be an alloy of tin and another metal. The said alloy is not specifically limited, For example, a tin-copper alloy, a tin-silver alloy, a tin-bismuth alloy, a tin-zinc alloy, a tin-indium alloy etc. are mentioned.

The above displacement plating is a method of immersing an object to be plated in a plating solution containing a metal salt solution, and using the difference in ionization tendency between the substrate metal of the object to be plated and the metal ion in the displacement plating solution, This is a method for precipitating ions. For example, by immersing a substrate fine particle on which a conductive layer made of a metal having a high ionization tendency is formed in a plating solution containing metal ions having a low ionization tendency, the metal having a high ionization tendency is dissolved and the ionization tendency is low. An adhesion layer made of metal can be formed.
The above displacement plating is a plating method different from electroplating in which a base metal of an object to be plated is energized as a cathode in a plating solution containing metal ions, and a metal film is deposited on the surface. Is different from electroless reduction plating in which metal ions in the plating solution are chemically reduced and deposited to form a metal film on the surface of the base metal.

The substitution plating solution used in the substitution plating step is not particularly limited as long as it contains metal ions, and examples thereof include those containing tin ions and silver ions. In addition, it is preferable that the concentration of metal ions is appropriately changed according to the material of the conductive layer.
In addition, various acids, complexing agents, and other additives are added to the above replacement plating solution for the purpose of lowering the potential of the base metal and allowing precipitation of metal ions in the plating solution, which has a higher ionization tendency than the base metal. An agent may be added. Furthermore, various counter ions such as sulfate ions, nitrate ions, halide ions may be contained as counter ions of the metal ions.

In the conductive fine particles of the present invention, the upper limit of the thickness of the intermetallic diffusion layer between the conductive layer and the low melting point metal layer after heating at 150 ° C. for 300 hours is the thickness of the conductive layer and the thickness of the low melting point metal layer. It is 20% with respect to the sum total. This means that there is very little contact in atomic units between the metal constituting the conductive layer and the metal constituting the low melting point metal layer when the conductive fine particles are produced. Thereby, formation of an intermetallic diffusion layer can be suppressed, destruction of the interface can be prevented, and conductive fine particles having high connection reliability can be obtained.
When the thickness of the intermetallic diffusion layer exceeds 20% with respect to the total of the thickness of the conductive layer and the low melting point metal layer, the interface breaks from the intermetallic diffusion layer. The preferable lower limit of the thickness of the intermetallic diffusion layer is 1% of the total thickness of the conductive layer and the low melting point metal layer, and the preferable upper limit is 16.7 of the total thickness of the conductive layer and the low melting point metal layer. %.
In the present invention, the “intermetallic diffusion layer” refers to a layer made of an “intermetallic compound” in which a metal element constituting the conductive layer and a metal element constituting the low melting point metal layer are combined. The thickness of the intermetallic diffusion layer can be measured using a scanning electron microscope (FE-SEM, manufactured by HORIBA, Ltd.) by performing electron micrograph photography and element beam analysis.

The method for producing the conductive fine particles of the present invention is not particularly limited as long as the above-described intermetallic diffusion layer can be obtained. For example, the conductive fine particles containing copper by electroless plating on the surface of the substrate fine particles are used. A method having a step of forming a layer and a step of forming a low melting point metal layer made of tin or an alloy of tin and another metal on the conductive layer is preferable.
Moreover, after performing the process of forming the contact | adherence layer containing a tin etc. by displacement plating on the said conductive layer, further, by forming the layer which consists of an alloy of tin or tin, and another metal, low melting-point metal A layer may be formed.

In the method for producing conductive fine particles of the present invention, a conventionally known method can be used in the step of forming the conductive layer containing the metal such as copper. In addition, as the step of forming the adhesion layer, the above-described method can be used.

The step of forming the low-melting-point metal layer is not particularly limited, but the low-melting-point metal fine particles containing tin or an alloy of tin and another metal are brought into contact with the substrate fine particles on which the conductive layer is formed, and shear compression is performed. In the case of using a method (dry coating method) having a step of forming a low melting point metal layer by melting the low melting point fine metal particles, the conductive fine particles of the present invention can exhibit particularly excellent effects. .

Examples of the dry coating method include a method using a theta composer (manufactured by Tokuju Kogakusho Co., Ltd.). The theta composer includes a vessel having an elliptical cavity, and a rotor that is separately rotated on the same axis as the vessel in the cavity. A shear compressive force can be applied in the gap in the vicinity where the minor axis of the cavity and the major axis of the rotor coincide. Conductive fine particles in which a low-melting-point metal layer is formed on the surface of the conductive layer of the base particle by repeatedly melting and softening the low-melting-point metal fine particle by this shear compression and attaching the low-melting-point metal fine particle to the base particle. Can be manufactured.

The average particle diameter of the low melting point metal fine particles used when forming the low melting point metal layer is not particularly limited, but the preferred lower limit is 0.1 μm and the preferred upper limit is 100 μm. When the average particle diameter of the low melting point metal fine particles is less than 0.1 μm, the low melting point metal fine particles are likely to aggregate, and it may be difficult to form the low melting point metal layer. When the average particle diameter of the low melting point metal fine particles exceeds 100 μm, it may be difficult to form a low melting point metal layer without being melted and softened during shear compression. The average particle size of the low-melting-point metal fine particles is obtained by measuring the particle sizes of 50 low-melting-point metal fine particles selected at random using an optical microscope or an electron microscope, and arithmetically averaging the measured particle sizes. Can be sought.
Moreover, it is preferable that the average particle diameter of the said low melting metal fine particle is 1/10 or less of the average particle diameter of the said base particle. When the average particle size of the low-melting-point metal fine particles exceeds 1/10 of the average particle size of the substrate fine particles, the low-melting-point metal fine particles adhere to the conductive layer of the substrate fine particles and form a film during shear compression. May not be possible.

An anisotropic conductive material can be produced by dispersing the conductive fine particles of the present invention in a binder resin. Such an anisotropic conductive material is also one aspect of the present invention.

Examples of the anisotropic conductive material of the present invention include anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, anisotropic conductive film, and anisotropic conductive sheet.

The binder resin is not particularly limited, but an insulating resin is used, and examples thereof include a vinyl resin, a thermoplastic resin, a curable resin, a thermoplastic block copolymer, and an elastomer.
Although the said vinyl resin is not specifically limited, For example, a vinyl acetate resin, an acrylic resin, a styrene resin etc. are mentioned.
Although the said thermoplastic resin is not specifically limited, For example, polyolefin resin, ethylene-vinyl acetate copolymer, a polyamide resin etc. are mentioned.
Although the said curable resin is not specifically limited, For example, an epoxy resin, a urethane resin, a polyimide resin, an unsaturated polyester resin etc. are mentioned. The curable resin may be a room temperature curable resin, a thermosetting resin, a photocurable resin, or a moisture curable resin. The curable resin may be used in combination with a curing agent.
The thermoplastic block copolymer is not particularly limited. For example, styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, hydrogenated product of styrene-butadiene-styrene block copolymer, styrene -Hydrogenated product of isoprene-styrene block copolymer.
The elastomer is not particularly limited, and examples thereof include styrene-butadiene copolymer rubber and acrylonitrile-styrene block copolymer rubber.
These resins may be used alone or in combination of two or more.

In addition to the conductive fine particles of the present invention and the above-mentioned binder resin, the anisotropic conductive material of the present invention is, for example, an extender, a plasticizer, and improved adhesiveness within a range that does not hinder the achievement of the present invention. Agents, antioxidants, heat stabilizers, light stabilizers, ultraviolet absorbers, colorants, flame retardants, organic solvents, and the like.

The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive fine particles of the present invention are added to the binder resin, and the mixture is uniformly mixed and dispersed. Examples thereof include a method for producing an anisotropic conductive ink, an anisotropic conductive adhesive, and the like. Further, the conductive fine particles of the present invention are added to the binder resin and uniformly dispersed or dissolved by heating, and a predetermined film thickness is applied to a release treatment surface of a release material such as release paper or release film. For example, a method for producing an anisotropic conductive film, an anisotropic conductive sheet or the like by coating may be used.
Moreover, it is good also as an anisotropic conductive material by using separately the said binder resin and the electroconductive fine particles of this invention, without mixing.

A connection structure using the conductive fine particles of the present invention or the anisotropic conductive material of the present invention is also one aspect of the present invention.

The connection structure of the present invention is a conductive connection structure in which a pair of circuit boards are connected by filling the pair of circuit boards with the conductive fine particles of the present invention or the anisotropic conductive material of the present invention. is there.

According to the present invention, conductive fine particles that are less likely to be broken at the interface between the conductive layer and the low-melting-point metal layer and can realize high connection reliability, and anisotropic conductive materials using the conductive fine particles And a connection structure can be provided.

2 is an electron micrograph of a cross section of conductive fine particles obtained in Example 1 before heating. 2 is an electron micrograph of a cross section after heating of the conductive fine particles obtained in Example 1. FIG. 2 is an electron micrograph of a cross section of conductive fine particles obtained in Comparative Example 1 before heating. 4 is an electron micrograph of a cross section of conductive fine particles obtained in Comparative Example 1 after heating. 2 is a chart showing element beam analysis measurement results before heating of the conductive fine particles obtained in Example 1. FIG. 2 is a chart showing element beam analysis measurement results after heating the conductive fine particles obtained in Example 1. FIG. 6 is a chart showing element beam analysis measurement results of conductive fine particles obtained in Comparative Example 1 before heating. 4 is a chart showing element beam analysis measurement results after heating the conductive fine particles obtained in Comparative Example 1. FIG.

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

Example 1
A copper layer having a thickness of 10 μm was formed by electroplating on the surface of resin fine particles (average particle diameter of 240 μm) made of a copolymer of tetramethylolmethane tetraacrylate and divinylbenzene to obtain substrate fine particles.
Subsequently, substitution plating was performed on 90 g of the obtained copper layer forming substrate fine particles using 500 g of a tin plating solution (plating solution temperature 20 ° C.) having the following composition, and a thickness of 0. A 5 μm tin layer was formed.

(Tin plating solution composition)
15 g of tin sulfate
Methanesulfonic acid 75g
Thiourea 45g
365g of water

Next, resin fine particles on which a copper layer and a tin layer were formed and 165 g of tin 96.5 silver 3.5 alloy fine particles (particle size distribution: 5 to 15 μm) were put into a Theta composer (manufactured by Tokuju Kogakusha Co., Ltd.) and mixed. . Thereby, the tin 96.5 silver 3.5 alloy fine particles were adhered to the resin fine particles on which the copper layer and the tin layer were formed and formed into a film to form a tin 96.5 silver 3.5 alloy layer having a thickness of 25 μm. Conductive fine particles were obtained. When mixing using a theta composer, the rotating container (vessel) was rotated in reverse at 35 rpm and the rotating blade (rotor) was rotated in reverse at 3500 rpm so that the shear compression force was applied. The mixing time was 300 minutes.

(Example 2)
In Example 1, conductive fine particles were produced in the same manner as in Example 1 except that copper fine particles (average particle size 260 μm) were used instead of resin fine particles (average particle size 240 μm) and no copper layer was formed. .

(Example 3)
In Example 1, instead of tin 96.5 silver 3.5 alloy fine particles (particle size distribution 5-15 μm), tin 96.5 silver 3.0 copper 0.5 alloy fine particles (particle size distribution 5-15 μm) were used. Conductive fine particles were produced in the same manner as in Example 1 except that they were used.

Example 4
In Example 1, tin 42.0 bismuth 58.0 alloy fine particles (particle size distribution 5 to 15 μm) were used in place of tin 96.5 silver 3.5 alloy fine particles (particle size distribution 5 to 15 μm). Conductive fine particles were produced in the same manner as in Example 1.

(Comparative Example 1)
In the same manner as in Example 1, a copper layer and a tin layer were formed on the surface of resin fine particles (average particle size 240 μm) made of a copolymer of tetramethylolmethane tetraacrylate and divinylbenzene.
Next, a tin 96.5 silver 3.5 alloy layer having a thickness of 25 μm was formed by electroplating on the surface of the resin fine particles on which the obtained copper layer and tin layer were formed, and conductive fine particles were obtained.

<Evaluation>
The following evaluation was performed about the electroconductive fine particles obtained by the Example and the comparative example. The results are shown in Table 1.

(1) Intermetallic diffusion layer thickness measurement About the obtained conductive fine particles, using a scanning electron microscope (FE-SEM, manufactured by HORIBA, Ltd.), the thickness of the conductive fine particles before and after heating at 150 ° C. for 300 hours was measured. An electron micrograph of the cut surface was taken, and at the same time, element beam analysis was performed. Next, the thickness of the intermetallic diffusion layer was measured from the length of the copper element and the tin element mixed on the straight line in the thickness direction of the conductive fine particles. The thickness of the intermetallic diffusion layer was determined by performing the same thickness measurement 10 times and calculating the average thickness. Table 1 shows the thickness ratio of the thickness of the intermetallic diffusion layer to the total thickness of the copper layer, the tin layer, and the alloy layer.
The electron micrograph before heating of the conductive fine particles obtained in Example 1 is shown in FIG. 1, the electron micrograph after heating is shown in FIG. 2, and the electron micrograph before heating of the conductive fine particles obtained in Comparative Example 1 is shown. FIG. 3 shows an electron micrograph after heating.
5 shows the results of element beam analysis before heating of the conductive fine particles obtained in Example 1, FIG. 6 shows the results of element beam analysis after heating, and FIG. 6 shows the results of the element fine particle analysis before heating of the conductive fine particles obtained in Comparative Example 1. FIG. 7 shows the result of element beam analysis in FIG. 8, and FIG. 8 shows the result of element beam analysis after heating.

(2) Reliability evaluation After the obtained conductive fine particles were heated at 150 ° C. for 300 hours, 112 pieces were mounted on a silicon chip having a copper electrode, and placed in a reflow furnace set at 270 ° C. to be melted. Next, a silicon chip on which conductive fine particles were mounted was mounted on a substrate having a copper electrode, and was put into a reflow furnace set at 270 ° C. and melted to obtain a connection structure.
A drop strength test of the obtained connection structure was performed according to JEDEC standard JESD22-B111. It dropped until the disconnection of the connection structure was confirmed, and the number of drops until the disconnection occurred was obtained. Even when the number of drops exceeded 150 times, the case where the wire was not broken was evaluated as ◯, and when the wire was broken below 150 times, the case was evaluated as x.

According to the present invention, conductive fine particles that are less likely to be broken at the interface between the conductive layer and the low-melting-point metal layer and can realize high connection reliability, and anisotropic conductive materials using the conductive fine particles And a connection structure can be provided.

Claims (6)

Conductive fine particles in which a conductive layer and a low melting point metal layer composed of tin or an alloy of tin and other metals are sequentially formed on the surface of the base fine particles,
The low-melting-point metal layer has an adhesion layer made of tin or an alloy of tin and another metal formed by displacement plating on the conductive layer side,
Between the conductive layer and the low melting point metal layer after heating at 150 ° C. for 300 hours ,
The thickness of the intermetallic diffusion layer made of an intermetallic compound formed between the metal constituting the conductive layer and the metal constituting the low melting point metal layer is the sum of the thickness of the conductive layer and the thickness of the low melting point metal layer. 1 to 20% of the conductive fine particles. 2. The conductive fine particle according to claim 1, wherein the conductive layer is made of copper. The conductive fine particles according to claim 1, wherein the substrate fine particles are resin fine particles. The conductive fine particles according to claim 1, wherein the substrate fine particles are copper fine particles. An anisotropic conductive material, wherein the conductive fine particles according to claim 1, 2, 3, or 4 are dispersed in a binder resin. A connection structure comprising the conductive fine particles according to claim 1, 2, 3 or 4, or the anisotropic conductive material according to claim 5.