JP4936678B2 - Conductive particles and anisotropic conductive materials - Google Patents

Description

The present invention relates to conductive particles and anisotropic conductive materials capable of preventing conduction failure and reducing resistance.

The conductive particles are mixed and kneaded with a binder resin or an adhesive, for example, an anisotropic conductive paste, an anisotropic conductive ink, an anisotropic conductive adhesive, an anisotropic conductive film, Widely used as anisotropic conductive materials such as anisotropic conductive sheets.

These anisotropic conductive materials are used to electrically connect circuit boards to each other, for example, in electronic devices such as liquid crystal displays, personal computers, and mobile phones, and to electrically connect small components such as semiconductor elements to the circuit board. For this reason, it is used by being sandwiched between circuit boards and electrode terminals facing each other.

As conductive particles used in such anisotropic conductive materials, conventionally, a metal plating layer is formed as a conductive layer on the surface of non-conductive particles such as resin particles having a uniform particle size and appropriate strength. Conductive particles are used. However, when the circuit boards are electrically connected using such an anisotropic conductive material, a binder resin or the like is sandwiched between the conductive layer on the surface of the conductive particles and the circuit board, and the conductive particles and the circuit board. In some cases, the connection resistance between them and the like increases. In particular, with rapid progress and development of electronic devices in recent years, there has been a demand for further reduction in connection resistance between conductive particles and circuit boards.

For the purpose of reducing connection resistance, conductive particles having protrusions on the surface are disclosed (for example, see Patent Document 1). This conductive particle ensures that the protrusion and the circuit board are connected by the protrusion breaking through the binder resin or the like existing between the conductive layer on the surface of the conductive particle and the circuit board (resin eliminability). Thus, the connection resistance between the conductive particles and the circuit board is reduced.

However, even when conductive particles having protrusions on such a surface are used, an effect more than resin exclusion cannot be obtained, and the effect of reducing connection resistance is insufficient.
JP 2000-243132 A

An object of this invention is to provide the electroconductive particle and anisotropic conductive material which can reduce a resistance value while preventing a conduction defect in view of the said present condition.

The present invention is a conductive particle used for electrical connection of a circuit board , comprising a base particle and a conductive layer containing nickel or a nickel alloy formed on the surface of the base particle , the conductive layer Is a conductive particle having protrusions made of aggregates of massive fine particles having an average particle diameter of 50 to 300 nm on the surface, and the density of the protrusions is 25 to 50 with respect to one conductive particle. .
The present invention is described in detail below.

As a result of intensive studies, the present inventors have used conductive particles having predetermined protrusions as conductive particles used for electrical connection of a circuit board or the like, thereby eliminating the resin and ensuring the conductive particles and the circuit board. In addition to being able to contact with the circuit board at the time of conductive connection, by changing the contact between the conductive particles and the circuit board, etc., from the point contact to the surface contact by crimping between the circuit boards, It has been found that the circuit board and the conductive particles can be reliably conductively connected and the connection resistance can be reduced, and the present invention has been completed.

The electroconductive particle of this invention is an electroconductive particle which consists of a base material particle and the electroconductive layer containing the nickel or nickel alloy formed in the surface of the said base material particle.

The substrate particles are not particularly limited, and may be those using an inorganic material or an organic material as long as they have an appropriate elastic modulus, elastic deformability, and restoration property. And since it is excellent in the restoring property, it is preferable that it is a resin particle using a resin.

The resin constituting the resin particles is not particularly limited. For example, polyolefins such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyvinylidene chloride, polytetrafluoroethylene, polyisobutylene, polybutadiene; polymethyl methacrylate, polymethyl acrylate Acrylic resin such as acrylate and divinylbenzene, polyalkylene terephthalate, polysulfone, polycarbonate, polyamide, phenol formaldehyde resin, melanin formaldehyde resin, benzoguanamine formaldehyde resin, urea formaldehyde resin and the like. These resins may be used alone or in combination of two or more.

Although it does not specifically limit as an average particle diameter of the said base particle, A preferable minimum is 1 micrometer and a preferable upper limit is 20 micrometers. If it is less than 1 μm, for example, it is likely to aggregate when electroless plating is performed, and it may be difficult to form single particles. If it exceeds 20 μm, it may exceed the range used for circuit boards and the like as anisotropic conductive materials. is there.
In addition, the average particle diameter of the said base particle shall measure a particle diameter about 50 base particles chosen at random, and shall mean these arithmetically.

It does not specifically limit as metals other than nickel which form the nickel alloy which comprises the said conductive layer, For example, zinc, iron, lead, tin, copper, cobalt, antimony, bismuth etc. are mentioned.
Moreover, it does not specifically limit as a nonmetal which forms the nickel alloy which comprises the said conductive layer, For example, phosphorus, boron, etc. are mentioned. These non-metals are generally contained in a reducing agent or the like in the plating solution used when forming the conductive layer.

The conductive layer has a preferred lower limit of phosphorus content of 2% and a preferred upper limit of 8%. As a result, the hardness of the protrusions to be described later becomes moderate, and it is possible to effectively prevent conduction failure and reduce the resistance value.

The conductive layer has protrusions made of aggregates of massive fine particles on the surface.
In the conductive particles of the present invention, the protrusions are composed of aggregates of massive fine particles, so that the protrusions sandwich an anisotropic conductive material using the conductive particles of the present invention between circuit boards and the like. It becomes a soft protrusion that collapses by crimping at conductive connection. As a result, it breaks through the binder resin or the like in the anisotropic conductive material existing between the circuit board and the conductive particles of the present invention (resin eliminability), and the protrusion is crushed on the surface of the circuit board and the tip is Since the surface is flattened, the conductive particles of the present invention and the circuit board or the like are brought into surface contact, thereby preventing conduction failure and reducing the resistance value.

Although it does not specifically limit as thickness of the said conductive layer, A preferable minimum is 10 nm and a preferable upper limit is 500 nm. When the thickness is less than 10 nm, desired conductivity may not be obtained. When the thickness exceeds 500 nm, the conductive layer may be easily peeled due to a difference in thermal expansion coefficient between the base particle and the conductive layer.
Note that the thickness of the conductive layer is a thickness obtained by measuring ten randomly selected particles and arithmetically averaging them.

The average particle diameter of the massive fine particles is not particularly limited, but a preferred lower limit is 50 nm and a preferred upper limit is 300 nm. If the thickness is less than 50 nm, the strength of the projection portion is remarkably inferior, and the projection may be damaged when the conductive particles of the present invention are kneaded with a binder resin or the like. The protrusion may not collapse when a substrate or the like is crimped.

The average height of the protrusions is not particularly limited, but a preferable lower limit is 3% of the average particle diameter of the base particles, and a preferable upper limit is 17% of the average particle diameter of the base particles. If the average particle diameter of the base material particles is less than 3%, sufficient resin exclusion may not be obtained. If the average particle diameter of the base material particles exceeds 17%, protrusions may be formed on the circuit board or the like. There is a risk of digging deep and damaging the circuit board.

The density of the protrusions is not particularly limited, but the preferred lower limit is 25 and the preferred upper limit is 50 for one conductive particle. If the number is less than 25, depending on the direction of the conductive particles, the protrusions may not contact the circuit board. If the number exceeds 50, the protrusions overlap each other, and the conductive particles and the circuit board may be connected during conductive connection. When crimped, the protrusions may be difficult to collapse.
In the conductive particles of the present invention, if the number of projections made of aggregates of the above-mentioned massive fine particles is 25 to 50 with respect to one conductive particle, the conductive particles have projections not composed of aggregates. However, in this case, it is preferable that the projections made of aggregates of massive fine particles that characterize the present invention occupy 50% or more of the total projections.

In the conductive particles of the present invention, a gold layer is preferably formed on the surface of the conductive layer. By applying a gold layer to the surface of the conductive layer, it is possible to prevent oxidation of the conductive layer containing nickel (alloy), reduce connection resistance, stabilize the surface, and the like.

The method for forming the gold layer is not particularly limited, and examples thereof include conventionally known methods such as electroless plating, displacement plating, electroplating, reduction plating, and sputtering.

Although it does not specifically limit as thickness of the said gold layer, A preferable minimum is 1 nm and a preferable upper limit is 100 nm. When the thickness is less than 1 nm, it may be difficult to prevent oxidation of the conductive layer containing nickel (alloy), and the connection resistance value may increase. When the thickness exceeds 100 nm, the gold layer becomes nickel (alloy). ) Layer may be eroded and adhesion between the substrate particles and the conductive layer containing nickel (alloy) may be deteriorated.

Although it does not specifically limit as a method to manufacture the electroconductive particle of this invention, For example, it can manufacture by the electroless-plating method.
The electroless plating method involves roughening the surface by etching the base particles with an alkaline solution such as an aqueous sodium hydroxide solution, and then applying a catalyst to the surface of the base particles and then containing a plating stabilizer. A nickel stabilizer containing a plating stabilizer and sodium hypophosphite (reducing agent) is added to the base material particle dispersion, and the surface of the base material provided with a catalyst is reduced by the following reaction formula. In this method, a conductive layer containing nickel (alloy) is deposited by reaction.
Ni ²⁺ + H ₂ PO ₂ ⁻ + H ₂ O → Ni + H ₂ PO ₃ ⁻ + 2H ⁺

Here, during etching, the surface of the base material particles is made extremely rough by vigorously etching with an alkaline solution such as a high concentration sodium hydroxide aqueous solution to increase the adhesion amount of palladium or the like as the catalyst. By reducing the amount of the plating stabilizer in the material particle dispersion and destabilizing the plating solution at the time of the plating reaction, it is possible to form protrusions composed of aggregates of minute massive particles.
Alkaline solution for etching when the concentration of the alkali solution for etching the surface of the substrate particles is A (wt%) and the concentration of the plating stabilizer in the substrate particle dispersion is B (mol / L) The concentration A of B may be increased, or the concentration B of the plating stabilizer in the base particle dispersion may be reduced as much as possible, but the ratio (A / B) of A and B is represented by the following formula (1) In the case of the above range, it is possible to produce the conductive particles of the present invention having protrusions composed of aggregates of massive fine particles with extremely high efficiency.
Step 1 of etching the surface of the base particles using an alkaline solution, Step 2 of applying a catalyst to the surface of the etched base particles, and a base particle dispersion containing a plating stabilizer in nickel or A step of adding a plating solution containing a nickel alloy and a plating stabilizer to form a conductive layer on the surface of the base material particles provided with a catalyst. When the concentration of the alkaline solution of 1 is A (% by weight) and the concentration of the plating stabilizer in the base particle dispersion in the above step 3 is B (mol / L), the ratio of A to B (B / A The manufacturing method of the electroconductive particle which satisfy | fills following formula (1) is also one of this invention.
5.0 × 10 ⁻⁷ <B / A <3.0 × 10 ⁻⁶ (1)

As a method for performing the catalyst application, for example, acid neutralization and sensitizing in a tin dichloride (SnCl ₂ ) solution are performed on base particles etched with an alkaline solution, and a palladium dichloride (PdCl ₂ ) solution is then provided. The method of performing the electroless-plating pre-processing process which performs activating in is mentioned.
Sensitizing is a process in which Sn ²⁺ ions are adsorbed on the surface of an insulating material, and activating is a reaction represented by Sn ²⁺ + Pd ²⁺ → Sn ⁴⁺ + Pd ⁰ on the surface of an insulating material. In this process, palladium is used as a catalyst core for electroless plating.

Further, in the method for producing conductive particles of the present invention, the reaction rate is remarkably increased by increasing the temperature of the reaction system, adjusting the pH, etc. in the process of increasing the amount of catalyst attached to the surface of the base material particles. By speeding up, it is possible to effectively produce the protrusions made of aggregates of massive fine particles.

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

Specific examples of the anisotropic conductive material of the present invention include, for example, anisotropic conductive paste, anisotropic conductive ink, anisotropic conductive adhesive layer, anisotropic conductive film, anisotropic conductive sheet and the like. Is mentioned.

The resin binder is not particularly limited, and an insulating resin is used. For example, 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, polyimide resins, unsaturated polyester resins, and curable resins composed of these curing agents; styrene-butadiene-styrene block copolymer Polymers, thermoplastic block copolymers such as styrene-isoprene-styrene block copolymers and hydrogenated products thereof; elastomers such as styrene-butadiene copolymer rubber, chloroprene rubber, acrylonitrile-styrene block copolymer rubber (rubbers) ) And the like. These resins may be used alone or in combination of two or more.
Further, the curable resin may be any curable type of room temperature curable type, heat curable type, photo curable type, and moisture curable type.

In addition to the conductive particles of the present invention and the resin binder described above, the anisotropic conductive material of the present invention includes, for example, a bulking agent and a softening agent (if necessary) within a range not impairing the achievement of the problems of the present invention. Additives such as plasticizers), adhesive improvers, antioxidants (anti-aging agents), heat stabilizers, light stabilizers, UV absorbers, colorants, flame retardants, organic solvents, etc. Good.

The method for producing the anisotropic conductive material of the present invention is not particularly limited. For example, the conductive particles of the present invention are added to an insulating resin binder, and are uniformly mixed and dispersed. A method of using a conductive paste, anisotropic conductive ink, anisotropic conductive adhesive, etc., adding the conductive particles of the present invention to an insulating resin binder, and uniformly dissolving (dispersing), or , Heat-dissolve, and apply to the release treatment surface of the release material such as release paper and release film to have a predetermined film thickness, and perform drying and cooling as necessary, for example, anisotropic For example, an appropriate manufacturing method may be employed in accordance with the type of anisotropic conductive material to be manufactured.
Moreover, it is good also as an anisotropic conductive material by using separately, without mixing an insulating resin binder and the electroconductive particle of this invention.

According to the present invention, it is possible to provide conductive particles and an anisotropic conductive material capable of preventing conduction failure and reducing the resistance value.

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
(Conductive layer formation process)
10 g of base particles made of a copolymer resin of tetramethylol methane tetraacrylate and divinylbenzene having an average particle diameter of 3 μm are subjected to alkali etching with 5% by weight sodium hydroxide aqueous solution, acid neutralization, and sensitizing in a tin dichloride solution. went. Then, the electroless-plating pretreatment which consists of activation in a palladium dichloride solution was performed, the base particle which adhered palladium to the particle | grain surface after filtration washing was obtained.
The obtained base particles are diluted with 1500 mL of water, 0.005 mmol of bismuth nitrate and 0.006 mmol of thallium nitrate are added as plating stabilizers, and the pH is adjusted with 10% by weight sulfuric acid water and 2N aqueous sodium hydroxide solution. The mixture was adjusted to 5.7 to form a slurry, and the liquid temperature was set to 26 ° C.
To this slurry, nickel sulfate 450 g / L 40 mL, sodium hypophosphite 150 g / L and sodium citrate 116 g / L mixed solution 80 mL, water 280 mL, plating stabilizer, bismuth nitrate 0.02 mmol, nitric acid 0.024 mmol of thallium was added, and the pre-reaction plating solution whose pH was adjusted to 9.3 with 28 wt% aqueous ammonia was added through a metering pump at an addition rate of 80 mL / min.
Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating pre-process was performed.
Next, 180 mL of nickel sulfate 450 g / L, 440 mL of a mixed solution of sodium hypophosphite 150 g / L and sodium citrate 116 g / L, plating stabilizer, bismuth nitrate 0.3 mmol, thallium nitrate 0.36 mmol The late reaction plating solution was added through a metering pump at an addition rate of 27 mL / min.
Then, it stirred until pH became stable, it confirmed that hydrogen foaming stopped, and the electroless-plating late process was performed.
Next, the plating solution was filtered, the filtrate was washed with water, and then dried with a vacuum dryer at 80 ° C. to obtain conductive particles having a conductive layer having protrusions on the surface.

(Gold plating process)
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 5, B = 7.33 * 10 < ^-6 >, B / A = 1.5 * 10 < ^-6 >.

(Example 2)
Example 1 except that the concentration of the aqueous sodium hydroxide solution for etching was changed to 10% by weight, and the amount of stabilizer added to the slurry in the first electroless plating step was changed to 0.0125 mmol of bismuth nitrate and 0.015 mmol of thallium nitrate. In the same manner as above, conductive particles having a conductive layer having protrusions on the surface were obtained.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 10, B = 1.83 * 10 < ^-5 >, B / A = 1.8 * 10 < ^-6 >.

(Example 3)
Conductive particles having a conductive layer having protrusions on the surface were obtained in the same manner as in Example 1 except that the concentration of the aqueous sodium hydroxide solution for etching was changed to 10% by weight.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 10, B = 7.33 * 10 < ^-6 >, B / A = 7.3 * 10 < ^-7 >.

Example 4
Example 1 except that the concentration of the sodium hydroxide aqueous solution for etching was changed to 10% by weight, and the amount of the stabilizer added to the slurry in the first electroless plating process was changed to 0.02 mmol of bismuth nitrate and 0.024 mmol of thallium nitrate. In the same manner as above, conductive particles having a conductive layer having protrusions on the surface were obtained.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 10, B = 2.93 * 10 < ^-5 >, B / A = 2.9 * 10 < ^-6 >.

(Comparative Example 1)
After the electroless plating pretreatment step on the substrate particles, the same procedure as in Example 1 was carried out except that the amount of stabilizer added to the slurry in the previous electroless plating step was changed to 0.0125 mmol of bismuth nitrate and 0.015 mol of thallium nitrate. Thus, conductive particles having a conductive layer having protrusions on the surface were obtained.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 5, B = 1.83 * 10 < ^-5 >, B / A = 3.7 * 10 < ^-6 >.

(Comparative Example 2)
After the electroless plating pretreatment step on the substrate particles, the same procedure as in Example 1 was performed except that the amount of stabilizer added to the slurry in the previous electroless plating step was changed to bismuth nitrate 0.02 mmol and thallium nitrate 0.024 mmol. Thus, conductive particles having a conductive layer were obtained.
Thereafter, the surface was further plated with gold by a displacement plating method to obtain conductive particles.
In addition, about the value prescribed | regulated in this specification, they are A = 5, B = 2.93 * 10 < ^-5 >, B / A = 5.9 * 10 < ^-6 >.

<Evaluation>
The following evaluation was performed about the electroconductive particle obtained in Examples 1-4 and Comparative Examples 1-2. The results are shown in Table 1.

(1) Measurement of connection resistance value An anisotropic conductive material was produced by the following method using the obtained conductive particles, and the connection resistance value between the electrodes was measured.
100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as a resin binder resin are sufficiently mixed using a planetary stirrer. Then, it was applied on the release film so that the thickness after drying was 10 μm, and toluene was evaporated to obtain an adhesive film.
Subsequently, 100 parts by weight of an epoxy resin (“Epicoat 828” manufactured by Yuka Shell Epoxy Co., Ltd.), 2 parts by weight of trisdimethylaminoethylphenol, and 100 parts by weight of toluene as a resin binder resin were obtained. Adhesive film containing conductive particles after adding the particles and mixing well using a planetary stirrer, applying to the release film so that the thickness after drying is 7 μm, and evaporating toluene Got. In addition, the compounding quantity of electroconductive particle was set so that content in a film might be 50,000 pieces / cm < ² >.
The obtained adhesive film and an adhesive film containing conductive particles were laminated at room temperature to obtain a 17 μm thick anisotropic conductive film having a two-layer structure.
The obtained anisotropic conductive film was cut into a size of 5 × 5 mm. After affixing this to approximately the center of an aluminum electrode having a width of 200 μm, a length of 1 mm, a height of 0.2 μm, and an L / S of 20 μm having a lead wire for resistance measurement, a glass substrate having an ITO electrode is obtained. After aligning the electrodes so that they overlap each other, they were bonded together.
The bonded portion of this glass substrate was thermocompression bonded under pressure bonding conditions of 10N and 100 ° C., and then the connection resistance value between the electrodes was measured.
In addition, a reliability test (held at 80 ° C. in a high-temperature and high-humidity environment of 95% RH for 1000 hours) was performed on the prepared test piece, and then the connection resistance value between the electrodes was measured.

(2) Average particle diameter of massive fine particles The obtained conductive particles were observed with a scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation at a magnification of 10,000 times to examine the particle diameter of the massive fine particles. The average particle diameter of the massive fine particles was determined by measuring the particle diameters of the 20 confirmed massive fine particles and arithmetically averaging them.

(3) Average height of protrusions The obtained conductive particles were observed with a scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation at a magnification of 10,000 times to examine the height of the protrusions.
The height of the protrusion was measured by measuring the height appearing as a protrusion from the reference surface of the conductive layer forming the outermost surface of the conductive particles. At this time, it is assumed that a protrusion having a thickness of 100 nm or more is selected as the protrusion as an effect of providing the protrusion.
The average height of the protrusions was measured for 20 confirmed protrusions, and the average of the protrusions was calculated as the average height of the protrusions.

(4) Presence density of projections The obtained conductive particles were observed with a scanning electron microscope (SEM) manufactured by Hitachi High-Technologies Corporation at a magnification of 10,000 times to examine the density of projections.
As for the density of the protrusions, the number of protrusions per one conductive particle was counted by counting the number of protrusions of 100 nm or more as protrusions, assuming that the effect of providing protrusions was obtained for 20 randomly selected particles. Converted to a number, it was defined as the density of protrusions.

(5) Measurement of phosphorus content Using EDX (Energy Dispersing X-ray analyzer: manufactured by JEOL Datum Co., Ltd.), the cross section of the conductive particles is cut out with a focused ion beam, and in the conductive layer The phosphorus content was measured by analyzing the components of each of the above.

According to the present invention, it is possible to provide conductive particles and an anisotropic conductive material capable of preventing conduction failure and reducing the resistance value.

2 is a SEM photograph of conductive particles obtained in Example 1. 2 is a SEM photograph of conductive particles obtained in Example 2. 4 is a SEM photograph of conductive particles obtained in Comparative Example 1.

Claims (4)

Conductive particles used for electrical connection of a circuit board,
Consisting of base particles and a conductive layer containing nickel or a nickel alloy formed on the surface of the base particles,
The conductive layer is 3 to 17% of the average height average particle diameter of the base particles, an average particle diameter of Ri Do from aggregates of massive particles of 50 to 300 nm, when conductive connection across the circuit board has a surface projections Ru collapsed by crimping,
Conductive particles, wherein the density of protrusions is 25 to 50 with respect to one conductive particle. The conductive particles according to claim 1, wherein the base particles are resin particles. The conductive particle according to claim 1, further comprising a gold layer formed on the surface of the conductive layer. An anisotropic conductive material comprising the conductive particles according to claim 1 dispersed in a resin binder.