JP3914206B2 - Conductive fine particles and anisotropic conductive materials - Google Patents

Description

  The present invention relates to conductive fine particles having a low connection resistance value and excellent conductive reliability, and an anisotropic conductive material using the conductive fine particles.

  Conductive fine particles are mixed (kneaded) with a binder resin, an adhesive, etc., for example, anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, anisotropic conductive film It is widely used as an anisotropic conductive material such as an anisotropic conductive sheet.

  These anisotropic conductive materials, for example, in electronic devices such as liquid crystal displays, personal computers, mobile phones, etc., electrically connect substrates or electrically bond small parts such as semiconductor elements to the substrate. In order to do so, it is used by being sandwiched between opposing substrates and electrode terminals.

  Conventionally, metal particles such as gold (hereinafter also referred to as Au), silver (hereinafter also referred to as Ag), nickel (hereinafter also referred to as Ni), etc. are generally used as the conductive fine particles used in the anisotropic conductive material. However, since the metal particles have a large specific gravity and an irregular shape, they tend to exist (disperse) in a non-uniform state in the binder resin and the adhesive, resulting in the anisotropic conductivity obtained. There is a problem of causing unevenness in the conductivity of the material.

  For this reason, instead of metal particles, for example, electroless Ni plating is applied to the surface of non-conductive fine particles such as resin fine particles having a uniform particle diameter and appropriate strength to form a metal plating layer (conductive layer). Conductive fine particles have been used. However, Ni has a problem that the connection resistance is high, and when it is exposed to high temperature and high humidity for a long time, it deteriorates and the connection conductivity is further deteriorated. In order to solve such problems, conductive fine particles have been proposed in which electroless Ni plating is performed on the surface of spherical core particles and an Au plating layer is further formed thereon (for example, Patent Documents). 1).

  However, with the rapid progress and development of electronic devices in recent years, further reduction in connection resistance of conductive fine particles used as anisotropic conductive materials has been demanded.

Japanese Patent Application Laid-Open No. 7-118866 (claims on page 2)

  If the conductive layer is entirely made of Au in order to reduce the connection resistance of the conductive fine particles, the cost becomes very high. Further, when Ag (silver) or Cu (copper) having a lower resistance value than Au is used as the outermost layer of the conductive layer, the resistance value increases due to oxidation, or the Au layer / Ag layer or Au layer / The configuration in which the Cu layer is continuous has a problem of causing migration.

  An object of the present invention is a conductive fine particle in which a Ni layer is formed on the surface of a spherical substrate fine particle and an Au layer is further formed on the outermost layer in view of the above-described situation, and has a low connection resistance and is conductive An object is to provide conductive fine particles having excellent reliability. Another object of the present invention is to provide an anisotropic conductive material having a low connection resistance value and excellent conductive reliability using the conductive fine particles.

In order to achieve the above object, the invention according to claim 1 is a conductive fine particle in which a Ni layer is formed on the surface of a spherical substrate fine particle, and an Au layer is further formed on the outermost layer, wherein the Ni layer It contains at least one metal (M) selected from Ag, Cu, and Co, and at least one metal (M) selected from Ag, Cu, and Co in the Ni layer contains the Ni layer as a sea component. The present invention provides conductive fine particles that exist as a sea-island structure containing metal (M) as an island component .

Further, in the invention described in claim 2 , the Ni layer has a convex portion for projecting the outermost Au layer having an average height falling within a range of 0.5 to 25% with respect to the particle diameter of the base particle. The conductive fine particles according to claim 1 , wherein the convex portions contain at least one metal (M) selected from Ag, Cu and Co.

The invention according to claim 3 provides an anisotropic conductive material using the conductive fine particles according to claim 1 or 2 .

Details of the present invention will be described below.
The conductive fine particles of the present invention are formed by forming a Ni layer on the surface of spherical base fine particles and further forming an Au layer as the outermost layer.

  The spherical base particles are not particularly limited as long as they have an appropriate elastic modulus, elastic deformability, and restoration property, regardless of inorganic or organic, but resin fine particles made of resin are suitable.

  The resin fine particles are not particularly limited. For example, polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, and polybutadiene; acrylic resins such as polymethyl methacrylate and polymethyl acrylate A copolymer resin of acrylate and divinylbenzene, polyalkylene terephthalate, polysulfone, polycarbonate, polyamide, phenol formaldehyde resin, melamine formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin, and the like. These resin fine particles may be used independently and 2 or more types may be used together.

  The average particle diameter of the spherical base particles is preferably 1 to 20 μm. If it is less than 1 μm, it tends to aggregate when forming the Ni layer, making it difficult to form single particles, and if it exceeds 20 μm, it may exceed the range used as an anisotropic conductive material between substrate electrodes. There is. A more preferable average particle diameter is 1 to 10 μm.

  The conductive fine particles of the present invention are those in which a Ni layer is formed on the surface of the substrate fine particles. For the formation of the Ni layer, electroless Ni plating can be suitably used. Furthermore, the conductive fine particles of the present invention are those in which an Au layer is formed on the outermost layer.

  By forming the Au layer as the outermost layer, the resistance value can be reduced and the surface can be stabilized.

  The Au layer can be formed by a known method such as electroless plating, displacement plating, electroplating, or sputtering.

  Although it does not specifically limit as an average film thickness of the said Ni layer, In order to exhibit the electroconductivity required as a conductive connection material, 10 nm-1 micrometer are preferable. When the thickness is less than 10 nm, a portion where the Ni layer is not formed may be formed on the substrate fine particles, or the resistance may be increased. If the thickness exceeds 1 μm, the Ni layer becomes hard and cannot follow the deformation of the substrate fine particles, so that the breakage easily proceeds, the connection electrode is destroyed to prevent the deformation of the substrate fine particles, and the contact area does not increase. In some cases, the connection resistance value becomes high or connection failure is likely to occur. More preferably, it is 10-500 nm.

  Although it does not specifically limit as an average film thickness of the said Au layer, 1-100 nm is preferable. If it is less than 1 nm, the underlying Ni layer cannot be oxidized and the connection resistance value may increase. If the thickness exceeds 100 nm, in the case of substitutional plating, the underlying Ni layer may be eroded and adhesion between the substrate fine particles and the underlying Ni layer may be deteriorated. More preferably, it is 1-50 nm.

  The conductive fine particles of the present invention need to contain at least one metal (M) selected from Ag (silver), Cu (copper), and Co (cobalt) in the Ni layer.

  Since the metal (M) has a resistance value lower than that of Ni, the metal (M) is present in the Ni layer to further reduce the resistance value of the Ni layer. Further, since Ni and metal (M) do not cause migration, they can be stably present in the Ni layer.

In the conductive fine particles of the present invention, the metal (M) in the Ni layer is present as a sea-island structure in which the Ni layer is a sea component and the metal (M) is an island component .

  In the present invention, the sea-island structure means that the sea component and the island component exist in a phase-separated state, and the island component is dispersed in the sea component.

  The dispersed particle diameter in the dispersed state of the metal (M) is preferably 0.1 nm or more. If it is less than 0.1 nm, it may be difficult to obtain the effect of reducing the resistance value due to the presence of the metal (M). Further, when the particle diameter is within 25% with respect to the particle diameter of the substrate fine particles, it may be difficult to disperse in the Ni layer. More preferably, it is 1 nm or more.

  The conductive fine particles of the present invention have a convex portion for projecting the outermost Au layer having an average height within which the Ni layer falls within a range of 0.5 to 25% with respect to the particle diameter of the base fine particles. It is preferable that the convex portion contains a metal (M).

  The convex portion causes the outermost Au layer of the conductive fine particles to protrude. That is, the convex portion of the Ni layer appears as a convex portion on the outermost layer of the conductive fine particles.

  When the Ni layer has a convex portion, the convex portion can easily eliminate the binder resin, the adhesive, and the like at the time of connection using the conductive fine particles of the present invention as an anisotropic conductive material. There is an effect of obtaining stability. In addition, it is preferable to contain a metal (M) in the convex portion because the resistance can be further reduced.

  It is preferable that the average height of the protrusions be within a range of 0.5 to 25% with respect to the particle diameter of the base particle. If the average height of the protrusions is less than 0.5% with respect to the particle diameter of the substrate fine particles, it is difficult to obtain the effect of providing the protrusions, and if it exceeds 25%, the protrusions may be easily broken. There is a risk of being deeply cut into the electrode and being damaged.

  Various characteristics of the conductive fine particles in the present invention, for example, the average film thickness of the Ni layer and the Au layer, the sea-island structure, the dispersed particle diameter of the metal (M), the average height of the protrusions, etc. It can be obtained by cross-sectional observation.

  As a method of preparing a sample for performing the cross-sectional observation, conductive fine particles are embedded in a thermosetting resin and cured by heating, and the sample is polished to a specular state that can be observed using a predetermined abrasive paper or abrasive. Methods and the like.

  The measurement is performed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM), and as the magnification, an easily observable magnification may be selected.

  The average film thickness of the Ni layer and the Au layer of the conductive fine particles is a film thickness obtained by measuring 10 randomly selected particles and arithmetically averaging them. In addition, when the film thickness of each electroconductive fine particle has nonuniformity, the maximum film thickness and the minimum film thickness are measured, and let the film thickness be the arithmetic average value.

  The dispersed particle size of the metal (M) is determined by measuring the dispersed particle size of the randomly selected 50 island component metal (M) and arithmetically averaging it. At this time, when the dispersed particles of the metal (M) cannot be regarded as spherical, the major axis and minor axis are measured, and the arithmetic average value is taken as the dispersed particle size.

  The average height of the protrusions is obtained by measuring the heights of the protrusions on the 50 Ni layers selected at random, and calculating the average height thereof to obtain the average height of the protrusions. At this time, it is assumed that the effect of providing the convex portion is obtained, and the one having a height of 0.5% or more with respect to the particle diameter of the base particle is selected as the convex portion.

The Ni layer in the present invention can be formed by, for example, an electroless Ni plating method. As a method for performing the above electroless Ni plating, for example, an electroless Ni plating solution composed of sodium hypophosphite as a reducing agent is bathed and heated according to a predetermined method. Examples include a method of immersing material fine particles and precipitating a Ni layer by a reduction reaction of Ni ²⁺ + H ₂ PO ₂ ⁻ + H ₂ O → Ni + H ₂ PO ₃ ⁻ + 2H ⁺ .

As a method of performing the catalyst application are, for example, the base particle made of a resin, alkali degreasing, acid neutralization, sensitizing the SnCl ₂ solution, an electroless plating pretreatment step consisting of activator bay quenching in PdCl ₂ solution The method of performing etc. are mentioned. Sensitizing is a process of adsorbing Sn ²⁺ ions on the surface of the insulating material, and activating causes a reaction of Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd ^{0 on the} surface of the insulating material. In this process, Pd is used as a catalyst core for electroless plating.

  In addition, as a method for containing the metal (M) in the Ni layer, for example, an electroless Ni containing the metal (M) in a suspended state by dispersing and adding the metal (M) in an electroless Ni plating solution. A method of performing electroless plating by immersing catalyst-supplied substrate fine particles in a plating bath; a substrate provided with a catalyst in an electroless Ni plating bath in which metal (M) ions are added to an electroless Ni plating solution For example, a method of performing electroless plating by immersing fine particles may be used.

As a method for forming the protrusions on the Ni layer, for example, an electroless Ni plating bath in which the metal (M) is dispersed and added to the above electroless Ni plating solution and the metal (M) is contained in a suspended state. In addition, a method in which electroless plating is performed by immersing the catalyst-supplied substrate fine particles may be mentioned. At this time, the metal (M) is simultaneously taken into the Ni layer to be in a eutectoid state, whereby a Ni layer having a convex portion can be obtained.
In addition, as another method for forming the convex portion on the Ni layer, for example, the formation of the Ni film on the substrate fine particles and the self-decomposition of the plating bath are caused at the same time. Then, by performing electroless plating with an electroless plating solution in which the constituent components are separated into at least two liquids, the growth of the convex portion and the growth of the Ni film are simultaneously performed; Pd is formed on the surface of the substrate fine particles Examples of the process include a method in which Pd is non-uniformly deposited and a plating layer is grown in a portion with a large amount of Pd to provide a convex part; a method in which a convex part is provided on the surface of a substrate fine particle by various methods such as hybridization.

  Next, the anisotropic conductive material of the present invention is produced using the above-described conductive fine particles of the present invention.

  Examples of the anisotropic conductive material include anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, anisotropic conductive film, and anisotropic conductive sheet. The anisotropic conductive material is not limited to this, and any anisotropic conductive material may be used as long as it is manufactured using conductive fine particles.

  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 in an insulating binder resin or an insulating adhesive. , Uniformly mixed and dispersed, for example, anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, etc., in an insulating binder resin or insulating adhesive After the conductive fine particles of the present invention are added to the agent and mixed uniformly to prepare a conductive composition, the conductive composition is uniformly dissolved (dispersed) in an organic solvent as necessary, Alternatively, it is heated and melted and coated on the release treatment surface of a release material such as release paper or release film so as to have a predetermined film thickness, followed by drying or cooling as necessary. Examples of methods include anisotropic conductive films, anisotropic conductive sheets, etc. Corresponding to the type of anisotropic conductive material that may be taken an appropriate manufacturing method. Moreover, it is good also as an anisotropic conductive material by using separately, without mixing insulating binder resin and an insulating adhesive agent, and the electroconductive fine particles of this invention.

  The insulating binder resin is not particularly limited, and examples thereof include vinyl resins such as vinyl acetate resins, vinyl chloride resins, acrylic resins, styrene resins; polyolefin resins, ethylene-acetic acid Thermoplastic resins such as vinyl copolymers and polyamide resins; epoxy resins, urethane resins, acrylic resins, polyimide resins, unsaturated polyester resins, and curable resins composed of these curing agents; styrene-butadiene- Styrene block copolymers, styrene-isoprene-styrene block copolymers, thermoplastic block copolymers such as hydrogenated products thereof; elastomers such as styrene-butadiene copolymer rubber, chloroprene rubber, acrylonitrile-styrene block copolymer rubber (Rubbers) and the like. These insulating binder resins may be used alone or in combination of two or more. The curable resin may be in any curing form such as a room temperature curing type, a thermosetting type, a photocuring type, and a moisture curing type.

  The insulating adhesive is not particularly limited, and examples thereof include an adhesive mainly composed of the insulating binder resin and various known adhesives. . These insulating adhesives may be used alone or in combination of two or more. Moreover, the said insulating binder resin and an insulating adhesive agent may each be used independently, and both may be used together.

  In addition to the insulating binder resin and / or the insulating adhesive and the conductive fine particles of the present invention, the anisotropic conductive material of the present invention is necessary as long as the achievement of the object of the present invention is not hindered. Depending on, for example, extenders, softeners (plasticizers), tackifiers, antioxidants (anti-aging agents), heat stabilizers, light stabilizers, UV absorbers, colorants, flame retardants, One or more of various additives such as organic solvents may be used in combination.

  Since this invention consists of the above-mentioned structure, it can obtain the electroconductive fine particles with a low connection resistance value and excellent electrical conductivity reliability. Further, it has become possible to obtain an anisotropic conductive material having a low connection resistance value and excellent conductive reliability using the conductive fine particles.

Hereinafter, the conductive fine particles of the present invention will be described with reference to the drawings.
In the conductive fine particles shown in FIG. 1, a Ni layer 2 is formed on the surface of the substrate fine particles 1, and an Au layer 3 is further formed on the outermost layer. The Ni layer 2 contains at least one metal (M) 4 selected from Ag, Cu, and Co.
In addition, at least one metal (M) 4 selected from Ag, Cu, and Co in the Ni layer 2 has a sea-island structure in which the Ni layer 2 is a sea component and the metal (M) 4 is an island component. .

  FIG. 2 is an enlarged schematic view of a part of the cross section of the conductive fine particles in which the Ni layer has convex portions. In the conductive fine particles shown in FIG. 2, the Ni layer 6 is formed on the surface of the substrate fine particles 5, and the Au layer 7 is further formed on the outermost layer. Further, the Ni layer 6 contains a metal (M) 8 and has a sea-island structure in which the Ni layer 6 is a sea component and the metal (M) 8 is an island component. Further, the Ni layer 6 has a convex portion for projecting the outermost Au layer 7, and a state in which the convex portion contains a metal (M) 8 is shown.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, this invention is not limited to a following example.

Example 1
(Production of conductive fine particles in which the Ni layer has a convex portion and Cu is contained in the convex portion)
A base particle composed of a copolymer resin of tetramethylolmethane tetraacrylate and divinylbenzene having an average particle diameter of 5 μm is coated with alkali degreasing, acid neutralization, sensitizing in SnCl ₂ solution, and activation in PdCl ₂ solution. An electrolytic plating pretreatment process was performed.
Electroless Ni plating was performed by immersing the base material fine particles subjected to the electroless plating pretreatment step in an electroless Ni plating bath in which Cu fine powder dispersed in a building bath and heated according to a predetermined method. “Top Nicolon MX” manufactured by Okuno Pharmaceutical Co., Ltd. was used as the electroless Ni plating bath, and fine particles having a particle diameter of 40 nm were used as the Cu fine powder.
Thereafter, the surface was further plated with Au by a displacement plating method to obtain conductive fine particles.
The obtained electroconductive fine particles had a Ni plating film thickness of 80 nm and an Au plating film thickness of 40 nm.
When the cross section was observed with a transmission electron microscope (TEM) manufactured by JEOL Datum, the Ni layer had a convex portion, and the Ni layer contained Cu (metal (M)). Further, Cu has a sea-island structure in which the Ni layer is a sea component and Cu is an island component, and it was confirmed that the dispersed particle diameter of Cu is 40 nm. Moreover, the average height of the convex part of Ni layer was 200 nm, and was 4% with respect to the particle diameter of base-material microparticles | fine-particles.

(Example 2)
(Preparation of conductive fine particles with smooth Ni layer and Cu)
The electroless plating pretreatment step was performed in the same manner as in Example 1.
Electroless Ni plating was performed by immersing the substrate fine particles subjected to the electroless plating pretreatment step in a building bath and an electroless Ni plating bath to which heated Cu ions were added according to a predetermined method. “Top Nicolon MX” manufactured by Okuno Pharmaceutical Co., Ltd. was used as the electroless Ni plating bath, and Cu ₂ P ₂ O ₇ .3H ₂ O was used as the Cu ion.
Thereafter, the surface was further plated with Au by a displacement plating method to obtain conductive fine particles.
The obtained electroconductive fine particles had a Ni plating film thickness of 80 nm and an Au plating film thickness of 40 nm.
When the cross section was observed with a transmission electron microscope (TEM) manufactured by JEOL Datum, the Ni layer was smooth and contained Cu (metal (M)) in the Ni layer. Further, Cu has a sea-island structure in which the Ni layer is a sea component and Cu is an island component, and the state of Cu is indefinite and the size thereof is uneven.

(Comparative Example 1)
The electroless plating pretreatment step was performed in the same manner as in Example 1.
Electroless Ni plating was performed by immersing the base material fine particles subjected to the electroless plating pretreatment step in an electroless Ni plating bath heated and heated according to a predetermined method. As the electroless Ni plating bath, “Top Nicolon MX” manufactured by Okuno Pharmaceutical Co., Ltd. was used.
Thereafter, the surface was further plated with Au by a displacement plating method to obtain conductive fine particles.
The obtained electroconductive fine particles had a Ni plating film thickness of 80 nm and an Au plating film thickness of 40 nm.
When the cross section was observed with a transmission electron microscope (TEM) manufactured by JEOL Datum, the Ni layer was smoothly plated.

(Production of anisotropic conductive material (anisotropic conductive film))
As a binder resin, 100 parts by weight of an epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd .: “Epicoat 828”), 3 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene are sufficiently dispersed and mixed using a planetary stirrer. On the mold film, it was applied at a constant thickness so that the thickness after drying was 10 μm, and toluene was evaporated to obtain an adhesive film containing no conductive fine particles.
Further, 100 parts by weight of an epoxy resin (manufactured by Yuka Shell Epoxy Co., Ltd .: “Epicoat 828”), 3 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as binder resin in Example 1, Example 2 or Comparative Example 1 The obtained conductive fine particles are added and sufficiently dispersed and mixed using a planetary stirrer to obtain a binder resin dispersion, and then a certain thickness is obtained so that the thickness after drying is 7 μm on the release film. Then, it was applied and the toluene was evaporated to obtain an adhesive film containing conductive fine particles. In addition, the addition amount of electroconductive fine particles was set so that content in an anisotropic conductive film might be 200,000 pieces / cm < ² >.
An adhesive film containing no conductive fine particles was laminated to the obtained adhesive film containing conductive fine particles at room temperature to obtain a 17 μm thick anisotropic conductive film having a two-layer structure.

(Measurement of connection resistance)
Using the obtained anisotropic conductive film, it was sandwiched between flexible printed circuit boards having a 200 × 200 μm bonded wiring pattern, and the connection resistance value was measured in a thermocompression-bonded state.
These results are shown in Table 1.

  From Table 1, it can be seen that those containing metal (M) in the Ni layer have a low connection resistance value.

  According to the present invention, it is possible to provide conductive fine particles having a low connection resistance value and excellent conductive reliability, and an anisotropic conductive material.

In one Example in the electroconductive fine particles of this invention, it is a schematic diagram of the cross section of electroconductive fine particles. It is the schematic diagram which expanded a part of cross section of the electroconductive fine particle in which Ni layer had the convex part in the other Example in the electroconductive fine particle of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base particle 2 Ni layer 3 Au layer 4 At least 1 type of metal (M) chosen from Ag, Cu, and Co
5 Substrate fine particles 6 Ni layer 7 Au layer 8 At least one metal (M) selected from Ag, Cu and Co

Claims (3)

Conductive fine particles in which a Ni layer is formed on the surface of spherical substrate fine particles and an Au layer is further formed on the outermost layer, and at least one metal selected from Ag, Cu and Co in the Ni layer (M) and at least one metal (M) selected from Ag, Cu and Co in the Ni layer exists as a sea-island structure in which the Ni layer is a sea component and the metal (M) is an island component. Conductive fine particles characterized by the above. The Ni layer has a convex portion for projecting the outermost Au layer having an average height falling within a range of 0.5 to 25% with respect to the particle diameter of the base particle, and Ag, Cu are formed on the convex portion. The conductive fine particles according to claim 1 , comprising at least one metal (M) selected from Co and Co. An anisotropic conductive material comprising the conductive fine particles according to claim 1 .

Images