JP5703836B2 - Conductive particles, adhesive composition, circuit connection material, and connection structure - Google Patents

Description

  The present invention relates to a conductive particle and a method for producing the same, an adhesive composition, a circuit connection material, a connection structure, and a circuit member connection method.

  With the advancement of performance and functionality of electronic devices, electronic components mounted inside electronic devices are also becoming more functional, smaller and thinner. These electronic components do not perform their function independently, but perform their functions by being electrically connected to the wiring board. Specifically, it is mounted on a wiring board such as a printed circuit board (PCB) or a flexible circuit board (FPC) by solder or gold wire.

  In the field of flat panel display (FPD), which has been remarkably developed, a mounting method using a circuit connecting material containing conductive particles has been widely adopted in place of the conventional electronic component connecting method using solder. Specific examples of the circuit connecting material include an adhesive composition containing conductive particles and an adhesive component and an anisotropic conductive film obtained by forming the adhesive composition into a film. By interposing a circuit connecting material between a pair of circuit members arranged opposite to each other and heating and pressurizing the whole, circuit electrodes included in each circuit member are electrically connected and the circuit members are bonded to each other. The circuit connection material containing conductive particles has an advantage that even when the number of electrodes to be connected is small and the number of electrodes is large, the electrodes can be connected to each other by a single pressure bonding. In addition, anisotropic conductivity here means conducting in the pressurizing direction and maintaining insulation in the non-pressurizing direction.

  In recent years, the number of drive semiconductors has increased due to the progress of higher image quality, and the pitch between electrodes has been reduced. In addition, from the viewpoint of design, the frame size and the thickness have been reduced, the mounting area and volume have been reduced, and the requirements for the circuit connection material have become more severe. As a connection method using a circuit connecting material, COG (Chip-on-Glass) mounting directly mounted on a glass transparent electrode, or COF (Chip-) for connecting a flexible substrate to a glass substrate after mounting on a flexible substrate. on-Flex) implementation.

  Various conductive particles have been developed so far. For example, Patent Document 1 describes conductive fine particles having a metal sphere made of silver, nickel, copper, tin, aluminum, zinc, or the like as a nucleus. Patent Document 2 describes conductive fine particles in which a resin coat layer is formed on the outer surface of carbon particles. Patent Documents 3 to 5 describe conductive particles obtained by coating the surfaces of resin particles with metal. These conductive particles are properly used according to the application.

  As described above, with the progress of narrowing the pitch between the electrodes of the circuit member in the FPD, there is a high risk that the adjacent electrodes are short-circuited. A short circuit tends to occur when the particle diameter of the conductive particles is too large or when the conductive particles are aggregated in the adhesive component. Circuit connection materials for narrow-pitch electrodes are required to achieve both a reduction in the diameter of the conductive particles and a high filling and high dispersibility in the adhesive component. Conductive particles whose resin particles are coated with metal are advantageous in that they are easily dispersed uniformly in the adhesive component because the volume density is close to that of the adhesive component compared to conductive particles made of metal fine particles (Patent Literature). 3).

  On the other hand, circuit connection materials using metal fine particles as conductive particles have been proposed in fields such as a plasma display (PDP) and a solar cell in which a large current flows through an electrode (Patent Document 6). However, when metal particles such as nickel, silver, and copper are used for the core particles, oxidation proceeds depending on humidity and temperature, connection resistance increases, migration occurs after connection, and adjacent electrodes are short-circuited. there's a possibility that. Migration means electrodeposition in an electric circuit or an electrode, and causes a reduction in connection reliability of the connection structure. This migration is considered to occur when impurities in the adhesive or the metal constituting the electrode are ionized when a voltage is applied.

  Accordingly, conductive particles in which metal particles are coated with a noble metal have been proposed for the purpose of preventing metal oxidation and migration. For example, Patent Document 7 discloses a conductive particle having a metal sphere formed by coating the surface of a metal material with a noble metal as a nucleus. Such conductive particles have a certain effect on metal oxidation and suppression of migration, but need to select a noble metal with low cost.

  Patent Document 8 discloses conductive particles in which the surface of base metal particles is coated with two or more different noble metals and the surface layer is palladium. However, it is necessary to perform the precious metal treatment twice, which not only lengthens the manufacturing process, but also increases the overall cost because two types of expensive precious metals are used.

  Patent Document 9 describes a method of imparting conductivity to an inorganic powder by coating the surface of the inorganic powder such as mica with a metal by chemical plating and further performing electroplating thereon. .

Japanese Patent Laid-Open No. 11-134935 JP-A-10-308121 Japanese Unexamined Patent Publication No. 57-49632 Japanese Patent Laid-Open No. 62-181379 Japanese Unexamined Patent Publication No. 1-224282 Japanese Patent Laid-Open No. 2003-197033 Japanese Patent Laid-Open No. 11-134936 JP-A-2-66101 JP-A-60-181294

  However, conventionally, conductive particles obtained by coating core particles made of a base metal with a noble metal do not always sufficiently eliminate defects due to metal oxidation and migration, and stably achieve excellent connection reliability of the connection structure. There was room for improvement.

  The present invention has been made in view of the above problems, and can maintain the resistance between the electrodes to be connected at a good value for a sufficiently long period of time and can sufficiently suppress the occurrence of migration and achieve excellent connection reliability. And it aims at providing the electrically-conductive particle obtained at low cost.

  Based on the method described in Patent Document 7, the present inventors respectively produced conductive particles obtained by electroless gold plating on the surface of nickel particles, and conductive particles obtained by electroless palladium plating on the surface of nickel particles. did. A circuit connecting material was produced using these conductive particles, and the evaluation test was performed. As a result, it was found that a material containing nickel particles plated with palladium has higher connection resistance and inferior performance than a material containing nickel particles plated with gold. In order to investigate this cause, the present inventors observed nickel particles plated with palladium by SEM (Scanning Electron Microscope). As a result, the palladium layer did not completely cover the nickel particles, and the surface of the conductive particles Nickel particles were exposed. Based on these findings, the inventors have completed the following invention.

  The conductive particles according to the present invention include nickel particles, a nickel layer formed by electroless plating that covers the surface of the nickel particles, and a palladium layer that covers the outer surface of the nickel layer.

  The conductive particles have core particles made of nickel particles, and a nickel layer and a palladium layer are laminated in this order on the surface of the nickel particles. A circuit connection material is produced by dispersing the conductive particles in the adhesive component. By using this circuit connecting material, the resistance between the electrodes to be connected can be maintained at a small value for a sufficiently long period. Further, the conductive particles according to the present invention are less concerned about the occurrence of migration than the conductive particles using silver.

  The main reason why the above effect is obtained is not necessarily clear at the present time, but the present inventors have provided a nickel layer by electroless plating, which is denser and more homogeneous than the direct formation of the palladium layer on the surface of the core particles. This is presumed to be related to easy formation of a palladium layer. In addition to this, it is inferred that it is easy to form a continuous palladium layer on the surface of the nickel layer by electroless plating.

  Since the nickel particles that form the core of the conductive particles are excellent in conductivity and low in cost, according to the present invention, the resistance value between the electrodes to be connected can be sufficiently reduced and the cost can be reduced. In addition, since palladium is less expensive than noble metals such as gold and platinum, conductive particles including a palladium layer are lower in cost than conductive particles using only gold or platinum.

  In addition, the nickel particle here means the metal particle which has nickel as a main component, and means a nickel content 50 mass% or more on the mass reference | standard of a nickel particle. The nickel layer means a metal layer containing nickel as a main component and has a nickel content of 50% by mass or more based on the mass of the nickel layer. The palladium layer means a metal layer containing palladium as a main component and has a palladium content of 50% by mass or more based on the mass of the palladium layer.

  The phosphorus content and boron content of the nickel layer are preferably 7% by mass or less based on the mass of the nickel layer. When the content of these elements is 7% by mass or less, palladium is likely to be uniformly deposited on the surface of the nickel layer, and a dense and homogeneous palladium layer is more easily formed.

  The palladium layer is preferably formed by reduction plating or displacement plating. In this case, the palladium layer covering the nickel layer becomes dense and homogeneous, and the surface exposure of nickel can be sufficiently reduced. In particular, a palladium layer formed by reduction plating is more preferable because it has very few impurities and can completely cover the base (nickel).

  When the surface of the conductive particles according to the present invention is observed with an SEM, the palladium layer preferably covers the entire outer surface of the nickel layer. The conductive particles having such a configuration have almost no phenomenon of ion elution via an oxide and migration, and it is easy to maintain higher connection reliability.

  In the conductive particles according to the present invention, the ratio A / B between the number A of nickel atoms on the surface and the number B of palladium atoms is preferably 1.0 or less from the viewpoint of achieving even better connection reliability. Here, the ratio A / B means a value obtained by analyzing the surface of the conductive particles by ESCA (Electron Spectroscopy for Chemical Analysis, X-ray photoelectron spectroscopy) method.

  From the viewpoint of more reliably preventing nickel exposure, the thickness of the palladium layer is preferably 5 to 100 nm.

  The present invention provides a method for producing conductive particles comprising a step of forming a nickel layer covering the surface of nickel particles by electroless plating and a step of forming a palladium layer covering the surface of the nickel layer. According to this method, it is possible to obtain conductive particles useful for achieving excellent connection reliability at a low cost. Further, in the present invention, by providing the nickel layer, it is possible to reduce the influence of the characteristics of the nickel particles (for example, nickel purity and surface condition) on the formation of the palladium layer. There are advantages.

  In the conventional electroless gold plating, cyan gold plating is mainly used, but a change to plating without cyan is desired from the viewpoint of environmental problems. According to the present invention, conductive particles including a nickel layer and a palladium layer can be produced without using cyan.

  The present invention provides an adhesive composition comprising an adhesive component having adhesiveness and the conductive particles dispersed in the adhesive component. This invention consists of this adhesive composition, and provides the circuit connection material used in order to adhere | attach circuit members and to electrically connect the circuit electrodes which each circuit member has.

  The present invention comprises a pair of circuit members arranged opposite to each other and a cured product of the circuit connection material, and is interposed between the pair of circuit members so that circuit electrodes included in the respective circuit members are electrically connected to each other. A connection structure including a connection portion for bonding the circuit members to each other is provided. In the present invention, the circuit connection material is interposed between a pair of circuit members arranged to face each other, and the whole is heated and pressurized to be formed of a cured product of the circuit connection material. The connection of circuit members is obtained by forming a connection part that bonds the circuit members to each other so that the circuit electrodes of the circuit member are electrically connected to each other. Provide a method.

  According to the present invention, the resistance between the electrodes to be connected can be maintained at a good value for a sufficiently long time, and the occurrence of migration can be sufficiently suppressed to achieve excellent connection reliability. In addition, the conductive particles according to the present invention can be obtained at low cost.

It is sectional drawing which shows typically suitable embodiment of the electrically-conductive particle which concerns on this invention. It is sectional drawing which shows typically suitable embodiment of the circuit connection material which concerns on this invention. It is sectional drawing which shows typically suitable embodiment of the connection structure to which circuit electrodes were connected. It is sectional drawing which shows typically an example of the manufacturing method of a connection structure.

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

(Conductive particles)
A conductive particle 10 shown in FIG. 1 includes nickel particles 1 as core particles, a nickel layer 2 by electroless plating covering the surface of the nickel particles 1, and a palladium layer 3 covering the outer surface of the nickel layer 2.

<Nickel particles>
The particle diameter of the nickel particles 1 is preferably smaller than the interval between the adjacent electrodes from the viewpoint of ensuring the insulation between the adjacent electrodes (see FIG. 3). Further, when the height of the electrodes to be connected varies, the particle diameter of the nickel particles 1 is preferably larger than the variation in height from the viewpoint of obtaining a sufficiently low connection resistance. For these reasons, the particle diameter of the nickel particles 1 is preferably 1 to 200 μm, more preferably 1 to 100 μm, and particularly preferably 20 to 50 μm. Here, the average particle diameter means the median diameter D50 measured by a laser light diffraction / scattering particle size analyzer.

The nickel particles 1 may be produced by either wet or dry methods such as liquid phase reduction deposition, gas phase chemical reaction, and gas evaporation. Specifically, a method of reducing NiO obtained from Ni ₃ S _2, a method of firing nickel carbonyl Ni (CO) ₄ (Mondo method), contacting metal gas with chlorine gas, and continuously supplying metal chloride gas After being generated in the metal chloride gas, a reducing gas such as hydrogen is brought into contact with the metal chloride gas (Japanese Patent Laid-Open No. 10-219313), and Ni (OH) ₂ is reduced with H ₂ gas (Japanese Patent Laid-Open No. 2001-2001). 284603), an atomizing method, a CVD method, and the like.

  The nickel particles 1 mean particles containing nickel as a main component, and may contain metals, oxides, inorganic substances, etc. in addition to nickel. Depending on the method for producing the nickel particles 1, the types and amounts of these inclusions are different, but by forming the nickel layer 2 described later on the surface of the nickel particles 1, there is an influence due to the difference in the types and amounts of these inclusions. It is suppressed and it becomes easy to form a dense and homogeneous palladium layer 3. Therefore, the nickel particles 1 can be selected according to the purpose of the obtained conductive particles 10 such as cost, size, and shape.

  The shape of the nickel particles 1 is not particularly limited, but is preferably close to a sphere in order to ensure insulation between adjacent electrodes and to ensure conduction stability between opposing electrodes. For example, when flat nickel particles 1 are used, even if the average particle size is sufficiently smaller than the distance between adjacent electrodes, the nickel particles 1 arranged between the electrodes have long sides in the direction between the adjacent electrodes. When arranged in a facing state, the insulation between adjacent electrodes tends to be insufficient. In addition, a plurality of conductive particles 10 are arranged between the opposing electrodes to ensure conduction. However, when flat conductive particles 10 are present, the state of contact with the electrodes and the state of penetration are different for each particle, so that conduction is stable. Tend to be insufficient. Since the conductive particles 10 are in contact with the electrodes in the same state, the shape of the nickel particles 1 forming the core particles is preferably a sphere.

  Further, the surface shape of the nickel particles 1 may be smooth, but it is preferable that there are irregularities. Since the uneven portion is easy to sink into the electrode and the contact area between the electrode and the conductive particles 10 increases, the stability of the conduction resistance increases.

<Nickel layer>
The nickel layer 2 is formed by electroless plating and is made of a material mainly composed of nickel. The nickel layer 2 is for covering at least a part or the whole of the surface of the nickel particle 1, and preferably covers the whole surface of the nickel particle 1 as shown in FIG. Electroless plating is suitable for forming a sufficiently dense and homogeneous nickel layer 2 on the surface of the nickel particles 1.

  The phosphorus content and boron content of the nickel layer are preferably 15% by mass or less on the basis of the mass of the nickel layer 2. Generally, in electroless nickel plating, a phosphorus-based or boron-based reducing agent is used, but phosphorus and boron elements are taken into the nickel layer 2 depending on plating conditions. When the content of these elements is 15% or less by mass, palladium is likely to be deposited on the surface of the nickel layer. Furthermore, in order to make it easier to form a dense and homogeneous palladium layer, the content of these elements is preferably 10% by mass or less, more preferably 7% by mass or less. Most preferably, it is not more than% mass.

  Phosphorus and boron are co-deposited in the nickel layer 2 depending on the type of reducing agent used in the electroless plating, and the characteristics of the nickel layer 2 change depending on the phosphorus content and boron content. That's fine. For example, the lower the phosphorus content in the nickel layer 2, the lower the electrical resistance, and there is a tendency to obtain magnetic conductive particles 10. On the other hand, the higher the phosphorus content, the higher the hardness and the more easily conductive particles 10 can be obtained.

  The thickness of the nickel layer 2 is not particularly limited as long as the surface of the nickel particles 1 is sufficiently covered, but is preferably 5 nm or more and 100 nm or less. If the thickness of the nickel layer 2 is 5 nm or more, the entire surface of the nickel particles 11 can be covered relatively easily. On the other hand, if the thickness of the nickel layer 2 is 100 nm or less, the electroless nickel plating time can be shortened, so that the manufacturing process can be shortened, resources can be saved, and the amount of waste liquid can be reduced. When the thickness of the nickel layer 2 exceeds 100 nm, the difference between the average particle diameter of the conductive particles 10 as the final form provided with the palladium layer 3 and the average particle diameter of the nickel particles 1 increases. As the difference between these average particle diameters increases, the circuit connection material tends not to exhibit the desired performance sufficiently, and, for example, problems such as the balance between connection between electrodes and insulation are likely to occur.

<Palladium layer>
The palladium layer 3 is made of a material whose main component is palladium. The palladium layer 3 is for covering at least part or all of the surfaces of the nickel particles 1 and the nickel layer 2, and preferably covers the entire outer surface of the nickel layer 2 as shown in FIG. 1.

  The conductive particles 10 having the palladium layer 3 have almost no phenomenon of ion elution via an oxide or migration, and it is easy to maintain higher connection reliability. The reason why palladium is suitable as the metal for covering the nickel layer 2 is as follows. First, since palladium is a noble metal, it is less likely to be oxidized than base metal or copper, and even when exposed to high temperature and high humidity, electrical resistance is unlikely to increase. Palladium can be alloyed with phosphorus or the like, and the content thereof can be arbitrarily set. The palladium layer containing phosphorus is higher in hardness than the pure palladium layer not containing phosphorus (see “Surface Technology P651, Vol55, No10, 2004”). When the hardness of the palladium layer 3 is increased, the conductive particles 19 can easily sink into the electrode surface, and the conduction performance can be further improved. The content of the palladium layer 3 other than palladium is not particularly limited, and can be appropriately set according to the purpose of the conductive particles 10.

  The conductive particles 10 preferably have a ratio A / B of the number A of nickel atoms to the number B of palladium atoms of 1.0 or less from the viewpoint of achieving even better connection reliability. A / B is more preferably 0.8 or less, and particularly preferably 0.6 or less. In addition to being dense and homogeneous, the palladium layer 3 having an A / B of 0.6 or less has very little nickel exposure on the surface, and it is possible to suppress defects caused by nickel elution at a higher level.

  On the other hand, when A / B exceeds 1.0, a large amount of nickel atoms are present on the surface of the conductive particles 10, and the surface states of the nickel particles 1 and the nickel layer 2 change (oxidation, alloying, crystallization). Easy to get dirty, etc.). The palladium layer 3 with A / B exceeding 1.0 cannot be said to be sufficiently homogeneous. For example, a state in which granular palladium precipitates are sparsely adhered to the surface of the nickel particles 1 or granular palladium precipitates are present. It may be in a state of being in close proximity. In particular, the latter seems to form a continuous layer of palladium precipitates by observation with an SEM or the like, and this also seems to cover the surfaces of the nickel particles 1 and the nickel layer 2. However, nickel is likely to elute between the palladium precipitate grains, and problems due to nickel oxidation and migration are likely to occur.

  The thickness of the palladium layer 3 is preferably 5 to 100 nm. When the thickness of the palladium layer is less than 5 nm, the conductivity tends to be insufficient. On the other hand, if the thickness of the palladium layer 2 exceeds 100 nm, the elasticity of the entire conductive particle 10 tends to be insufficient. If the elasticity of the conductive particles 10 as a whole is insufficient, the circuit connection material obtained by dispersing the conductive particles 10 is sandwiched between a pair of electrodes, and thermocompression bonding or the like is performed in the vertical direction (the direction in which the pair of electrodes face each other). When crushed, the force with which the palladium layer 3 is sufficiently pressed against the electrode surface due to the elasticity of the conductive particles 10 becomes insufficient. Therefore, the contact area between the palladium layer 3 and the electrode is reduced, and the effect of improving the connection reliability between the electrodes is reduced. Further, the thicker the palladium layer 3 is, the higher the cost is, which is not economically preferable. When the palladium layer 3 is formed by electroless plating (reduction plating or displacement plating), the thickness of the palladium layer 3 can be arbitrarily set by appropriately changing the amount of plating solution.

(Method for producing conductive particles)
Next, a method for manufacturing the conductive particles 10 will be described. The conductive particles 10 are manufactured through a step S1 of forming a nickel layer 2 covering the surface of the nickel particles 1 by electroless plating and a step S2 of forming a palladium layer 3 covering the surface of the nickel layer 2.

<Step of forming a nickel layer (S1)>
This step is a step of forming the nickel layer 2 on the surface of the nickel particles 1 by electroless plating. Thereby, the mother particle which consists of the nickel particle 1 and the nickel layer 2 which covers at least one part or the whole of the surface is manufactured. Examples of components constituting the electroless nickel plating solution include water-soluble nickel salts such as nickel sulfate and nickel chloride, reducing agents such as sodium hypophosphite, sodium borohydride, dimethylamine borane and hydrazine, citric acid And amino acids such as tartaric acid, hydroxyacetic acid, malic acid, lactic acid, gluconic acid and glycine, amines such as ethylenediamine and alkylamine, and other complexing agents such as ammonium, EDTA and pyrophosphoric acid.

  Further, during the electroless plating reaction, the nickel layer 2 can be adjusted by strictly adjusting the plating solution composition such as sodium hypophosphite (hypophosphorous acid / sodium hydroxide) as the pH, complexing agent, and reducing agent. The mother particles can be obtained while controlling the phosphorus content therein. For example, the nickel layer 2 having a phosphorus content of 0.1 to 15% by mass can be formed by adjusting the pH of the electroless nickel plating solution to a range of 2 to 12.

  After the electroless plating is completed, it is preferable to perform water washing efficiently in a short time. The shorter the washing time, the more difficult it is to form an oxide film on the nickel surface, so the formation of the palladium layer 3 is more advantageous. Usually, after completion of electroless plating, filtration is performed using a membrane filter or the like. In this case as well, it is preferable to perform filtration quickly in order to prevent nickel oxidation.

<Step of forming a palladium layer (S2)>
This step is a step of manufacturing the conductive particles 10 by forming the palladium layer 3 on the surface of the mother particles obtained in the step S1. Although it does not specifically limit as a formation method of the palladium layer 3, Electroplating, electroless plating, vapor deposition, etc. are mentioned. Among these, it is preferable to form by electroless plating reduction plating or displacement plating. In this case, the palladium layer 3 covering the nickel layer 2 becomes dense and homogeneous, and the surface exposure of nickel can be sufficiently reduced. In general, when a palladium layer is formed on the surface of nickel particles or a nickel layer by electroless plating, a homogeneous layer may not be formed depending on the state of the nickel surface (oxidation, alloying, crystallinity, dirt, etc.). In addition, the formation state of the palladium layer is influenced by the compatibility with the electroless palladium plating solution. Therefore, it is necessary to select an electroless palladium plating solution, a plating method, or a nickel surface pretreatment according to the state of the nickel surface.

  Among the electroless platings, the palladium layer 3 formed by reduction plating is more preferable because it has very few impurities and can completely cover the mother particles (nickel). In reduction plating, palladium ions are reduced and deposited by a reducing agent, so that a power source is not required, and it is suitably used for plating a large number of independent objects such as fine particles at a time. Moreover, when forming the palladium layer 3 by reduction plating, the palladium concentration and physical property of the palladium layer 3 can be changed with a reducing agent or an additive. For example, when a reducing agent containing phosphorus is used, phosphorus is co-deposited in the palladium layer 3. Further, when formic acid, formate, hydrazine, or the like is used as a reducing agent, a highly pure palladium layer 3 close to pure palladium can be obtained. The palladium layer 13 containing phosphorus is inferior in resistance to pure palladium but is hard. These differences can be appropriately selected according to the use of the conductive particles 10.

  When the palladium layer 3 is formed by reduction plating, the thickness of the palladium layer 3 can also be controlled by adjusting the amount of the plating solution. Specifically, the plating thickness after deposition can be calculated in advance from the concentration of palladium ions contained in the plating solution used. For this reason, useless palladium and a reagent are not used, and cost reduction is possible.

  On the other hand, when the palladium layer 3 is formed by displacement plating, due to the difference in ionization tendency, dissolution of nickel constituting the mother particle and precipitation of palladium occur simultaneously, which is excellent in terms of adhesion between the mother particle and the palladium layer 3. .

(Analysis of plating layer)
An atomic absorption photometer can be used for component analysis of the palladium layer 3. For example, there is a method in which a solution obtained by dissolving the conductive particles 10 with an acid or the like is analyzed using an atomic absorption photometer to measure and calculate a metal ion concentration. Further, the palladium layer 3 may be analyzed using an ICP emission analyzer. When an ICP emission analyzer is used, it is possible to quantify impurities simultaneously with qualitative analysis. Further, the phosphorus concentration in the palladium layer 3 can be quantified using EDX (Energy Dispersive X-ray Spectroscopy). In addition, since EDX measurement at a low magnification obtains information from a plurality of particles, EDX measurement at a high magnification is preferable.

(Particle observation)
A scanning electron microscope (SEM, Scanning Electron Microscope) can be used for observing the plating film (nickel layer 2, palladium layer 3) covering the core particles. The plated film surface can be confirmed from the image.

(Circuit connection material)
An adhesive composition is prepared by dispersing the conductive particles 10 prepared as described above in an adhesive component. As the circuit connection material, the paste-like adhesive composition may be used as it is, or an anisotropic conductive film obtained by forming this into a film may be used. An anisotropic conductive film 50 shown in FIG. 3 is obtained by dispersing conductive particles 10 in an adhesive component 20.

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

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

  Specific examples of the circuit member include chip components such as an IC chip (semiconductor chip), a resistor chip, a capacitor chip, and a driver IC, and a rigid package substrate. These circuit members are provided with circuit electrodes, and generally have many circuit electrodes. Specific examples of the other circuit member to which the circuit member is connected include a flexible tape substrate having metal wiring, a flexible printed wiring board, and a wiring substrate such as a glass substrate on which indium tin oxide (ITO) is deposited. Can be mentioned. Examples of the material of the substrate include inorganic materials such as semiconductors, glass substrates, and ceramics; organic materials such as polyimide, polycarbonate, and polyester sulfone; and materials obtained by combining these inorganic materials and organic materials.

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

  The connection part 50a includes a cured product 20a of an adhesive component contained in the circuit connection material, and the conductive particles 10 dispersed therein. In the connection structure 100, the circuit electrode 32 and the circuit electrode 42 facing each other are electrically connected via the conductive particles 10. More specifically, as shown in FIG. 3, the conductive particles 10 are in direct contact with both the circuit electrodes 32 and 42. On the other hand, in the lateral direction, insulation is maintained by the presence of the cured product 20a having insulation. Therefore, if the anisotropic conductive film 50 is used, it is possible to improve the insulation reliability at a narrow pitch of 10 μm level. In addition, when the position shift of the circuit electrode 32 or the circuit electrode 42 occurs at the time of connection, repair is possible even after the adhesive component is cured.

  As the adhesive component 20, a mixture of a heat-reactive resin and a curing agent is used, and specifically, a mixture of an epoxy resin and a latent curing agent is preferable.

  Epoxy resins include bisphenol type epoxy resins derived from epichlorohydrin and bisphenol A, F, AD, etc., epoxy novolac resins derived from epichlorohydrin and phenol novolac or cresol novolac, and naphthalene type epoxy resins having a skeleton containing a naphthalene ring. , Various epoxy compounds having two or more glycidyl groups in one molecule such as glycidylamine, glycidyl ether, biphenyl, and alicyclic can be used alone or in admixture of two or more.

These epoxy resins, impurity ions ^(Na +, Cl ^-, etc.) and, it is preferable to use a high purity which is reduced to 300ppm or less hydrolyzable chlorine and the like. This makes it easier to prevent electromigration.

  Examples of the latent curing agent include imidazole series, hydrazide series, boron trifluoride-amine complex, sulfonium salt, amine imide, polyamine salt, dicyandiamide, and the like. In addition, an energy ray curable resin such as a mixture of a radical reactive resin and an organic peroxide or ultraviolet rays is used for the adhesive.

  To the adhesive component 20, butadiene rubber, acrylic rubber, styrene-butadiene rubber, silicone rubber, or the like can be mixed in order to reduce stress after adhesion or to improve adhesion.

  In order to make the adhesive composition into a film, it is effective to blend a phenoxy resin and a thermoplastic resin such as a polyester resin and a polyamide resin into the composition. These film-forming polymers are also effective in stress relaxation when the reactive resin is cured. In particular, when the film-forming polymer has a functional group such as a hydroxyl group, the adhesiveness is improved, which is more preferable.

  The film is formed by dissolving or dispersing an adhesive composition composed of an epoxy resin, acrylic rubber, a latent curing agent, and a film-forming polymer in an organic solvent to form a peelable substrate (separator film). ) And then removing the solvent below the activation temperature of the curing agent. The organic solvent used at this time is preferably an aromatic hydrocarbon-based and oxygen-containing mixed solvent in terms of improving the solubility of the material.

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

(Method for manufacturing connection structure)
Next, a method for manufacturing the connection structure 100 will be described. FIG. 4 is a process diagram showing a schematic cross-sectional view of an embodiment of a method for manufacturing a connection structure. In the present embodiment, the anisotropic conductive film 50 is thermally cured to finally manufacture the connection structure 100.

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

  Next, pressure is applied in the directions of arrows A and B in FIG. 4A to temporarily fix the anisotropic conductive film 50 to the first circuit member 30 (FIG. 4B). Although the pressure at this time will not be restrict | limited especially if it is a range which does not damage a circuit member, Generally it is preferable to set it as 0.1-30.0 MPa. Moreover, you may pressurize, heating, and let heating temperature be the temperature which the anisotropic conductive film 50 does not harden | cure substantially. In general, the heating temperature is preferably 50 to 100 ° C. These heating and pressurization are preferably performed in the range of 0.1 to 2 seconds.

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

  The connection part 50a is formed by hardening of the adhesive component 20, and the connection structure 100 as shown in FIG. 3 is obtained. The connection conditions are appropriately selected depending on the application to be used, the adhesive composition, and the circuit member. In addition, when what is hardened | cured with light is used as the adhesive component 20, what is necessary is just to irradiate the anisotropic conductive film 50 with an actinic ray or an energy ray suitably. Examples of the active light include ultraviolet light, visible light, and infrared light. Examples of energy rays include electron beams, X-rays, γ rays, and microwaves.

  As mentioned above, although suitable embodiment of the manufacturing method of the electrically-conductive particle 10 and the electrically-conductive particle 10 which concerns on this invention was described in detail, this invention is not limited to the said embodiment. For example, as a modified example of the conductive particles 10, conductive particles further including another conductive layer (for example, a gold layer) covering the surface of the palladium layer 3 can be cited.

  Hereinafter, the present invention will be described by way of examples.

(Conductive particles 1)
100 g of nickel particles having an average particle diameter of 20 μm, 30 g / L of nickel sulfate, 20 g / L of citric acid, 30 g / L of sodium hypophosphite, 11.3 g / L of sodium hydroxide, plating stabilizer: 16.6 ml / L, It was poured into 300 ml of 80 ° C. water adjusted to pH 6.4 and stirred for 5 minutes. Then, it filtered with the membrane filter (made by Millipore) 3 micrometers in diameter, and obtained the mother particle 1 which has an electroless nickel layer 5 nm thick on a nickel particle.

  The obtained mother particles 1 were quickly put into 200 ml of 35 ° C. water adjusted to palladium chloride: 3 g / L (palladium: 2 g / L), hydrochloric acid 25 ml / L, and citric acid 20 g / L, and stirred for 5 minutes. Then, filtration and water washing were performed 3 times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by crushing. Through the above operation, conductive particles 1 having a palladium layer having a thickness of 10 nm on the surface of mother particles 1 were obtained.

(Conductive particles 2)
100 g of nickel particles having an average particle diameter of 10 μm were added to 300 ml of 70 ° C. water adjusted to pH = 5.2 by dissolving sodium citrate: 20 g / L and plating stabilizer: 16.6 ml / L, and stirred. did. Then, using a metering pump, the plating solution a and the plating solution b were added simultaneously and in parallel at 10 ml / min while maintaining the pH of the solution in which the nickel particles were dispersed at 5.2. Then, it filtered with the membrane filter (made by a Millipore company) with a diameter of 3 micrometers, and obtained the mother particle 2 which has an electroless nickel layer 5 nm thick on a nickel particle. As plating solution a, a solution adjusted to nickel sulfate 224 g / L, sodium citrate: 40 g / L was used, and as plating solution b, sodium hypophosphite: 220 g / L, sodium hydroxide: 85 g / L The liquid used was used.

  The obtained mother particles 2 were adjusted to palladium chloride: 6.55 g / L (palladium: 4.0 g / L), hydrochloric acid 25 ml / L, and citric acid 20 g / L, and quickly charged into 35 ° C. water: 200 ml. Stir for minutes. Then, filtration and water washing were performed once. When the mother particles 2 after substitution palladium plating were analyzed by atomic absorption, it was confirmed that a palladium layer having a thickness of 10 nm was formed. The mother particles 2 after substitution palladium plating were put into an electroless reduced palladium plating solution at 60 ° C. in which 200 ml of water, plating solution c: 75 ml, and plating solution d: 75 ml were mixed, and stirred for 5 minutes. Japanese Patent No. 3035763 was referred to for the composition of the plating solution c and the plating solution d. As the plating solution c, a solution prepared by mixing palladium: 20 g / L, sodium citrate: 250 g / L, ethylenediamine: 50 g / L and adjusting the pH to 6.0 was used. The palladium described above is a weight converted value as metallic palladium. As the plating solution d, a solution prepared by adjusting sodium formate: 100 g / L to pH 6.0 with sodium hydroxide and / or sulfuric acid was used. Then, filtration and water washing were performed 3 times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by crushing. Through the above operation, conductive particles 2 having a palladium layer with a thickness of 30 nm on the surface of the mother particles 2 were produced. This palladium layer is obtained by displacement palladium plating and reduced palladium plating.

(Conductive particles 3)
100 g of nickel particles having an average particle diameter of 5 μm were added to 300 ml of 70 ° C. water adjusted to pH = 6.0 by dissolving sodium citrate: 20 g / L and plating stabilizer: 16.6 ml / L and stirred. . Then, using a metering pump, plating solution a and plating solution b were added simultaneously and in parallel at 10 ml / min while maintaining the pH of the solution in which nickel particles were dispersed at 6.0. Then, it filtered with the membrane filter (made by Millipore) 3 micrometers in diameter, and obtained the mother particle 3 which has an electroless nickel layer 10 nm thick on a nickel particle.

  The obtained mother particles 3 were quickly put into an electroless palladium plating solution at 70 ° C. in which 400 ml of water, plating solution c: 150 ml, and plating solution d: 150 ml were mixed, and stirred for 5 minutes. Then, filtration and water washing were performed 3 times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by crushing. Through the above operation, conductive particles 3 having a palladium layer with a thickness of 20 nm on the outermost surface of base particles 3 were produced.

(Conductive particles 4)
The nickel particles were operated in the same manner as the conductive particles 2 except that 100 g of nickel particles having an average particle diameter of 5 μm were used, the dropping time of the electroless nickel plating solutions a and b was increased, and the pH was maintained at 5.5. Base particles 4 having an electroless nickel layer of 20 nm thereon were obtained.

  The obtained mother particles 4 were immediately dispersed in a 70 ° C. bath in which 50 g / L of sodium citrate was dissolved. Then, using a metering pump, the plating solution e and the plating solution f were added simultaneously and in parallel to the liquid in which the mother particles 4 were dispersed at 10 ml / min, and electroless palladium plating was performed on the mother particles 4. . As the plating solution e, a solution adjusted to palladium: 20 g / L, sodium citrate: 50 g / L, ethylenediamine 20 g / L, pH 6.0 was used. In the plating solution e, palladium is dissolved in an ion or complex state, and the amount of palladium “20 g / L” is a weight-converted value as metallic palladium. As the plating solution f, a solution obtained by adjusting sodium hypophosphite: 1.0 mol / L to pH 6.0 with sodium hydroxide was used. The sampled particles were analyzed with an atomic absorption photometer to adjust the palladium film thickness. The addition of the electroless plating solution was stopped when the palladium film thickness reached 60 nm. When the reaction stopped, the pH was 6.0. After completion of the addition, filtration and washing with water were performed three times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by crushing. Through the above operation, conductive particles 4 having a 60 nm-thick palladium layer on nickel particles were produced.

(Conductive particles 5)
100 g of nickel particles having an average particle size of 2 μm were used, the dropping time of the electroless nickel plating solutions a and b was increased, and the pH was maintained at 6.4. Base particles 5 having an electroless nickel layer of 100 nm were obtained.

  The obtained mother particles 5 were immediately dispersed in a 70 ° C. bath in which 50 g / L of sodium citrate was dissolved. Then, using a metering pump, the plating solution e and the plating solution fh were added simultaneously and in parallel to the liquid in which the mother particles 5 were dispersed at 20 ml / min, and electroless palladium plating was performed on the nickel particles. The sampled particles were analyzed with an atomic absorption photometer to adjust the palladium film thickness. When the palladium film thickness reached 100 nm, the addition of the electroless plating solution was stopped. When the reaction stopped, the pH was 6.0. After completion of the addition, filtration and washing with water were performed three times. After vacuum drying at 40 ° C. for 7 hours, aggregation was broken by crushing. By the above operation, conductive particles 5 having a palladium layer with a thickness of 100 nm on nickel particles were produced.

(Conductive particles 6)
10 g of nickel particles having an average particle size of 10 μm were stirred in 300 ml of 50% hydrochloric acid for 10 minutes, filtered and washed three times to obtain mother particles 6. The mother particles 6 were stirred in 300 ml of water in which a reducing agent was dissolved for 1 hour, filtered and washed three times to produce conductive particles 6 with improved electrical characteristics.

(Conductive particles 7)
Instead of the electroless nickel plating treatment, the same operation as the conductive particle 2 was performed except that the mother particle 7 obtained by stirring with 300 ml of water for 10 minutes and performing filtration was used to obtain the conductive particle 7. The obtained particles were darker gray than the conductive particles 2. When the obtained conductive particles 7 were observed using an SEM without vapor deposition, several hundred nanometers of palladium fine particles were sparsely adhered to the surface of the nickel particles, and most of the surface of the nickel layer was exposed. Further, when the mother particles 7 sampled after the substitution palladium plating were similarly observed by SEM, only a few hundreds of nanometers of palladium particles adhered to the surface of the mother particles 7, and the surface of the mother particles 7 was almost the same. Since it was exposed, it turned out that substitution palladium plating to the mother particle 7 was not completed. The mother particles 7 were put into the electroless palladium plating solution in which the palladium plating solutions c and d were dissolved, and after 3 minutes, a silvery foreign matter was generated in the plating bath, and the palladium plating solution was decomposed. It was.

(Conductive particles 8)
Instead of the electroless nickel plating solutions a and b, the plating solutions g and h are used, the pH is adjusted to 4.0, and the mother particles 8 having an electroless plating nickel layer with a thickness of 10 nm on the nickel particles A conductive particle 8 was obtained by performing the same operation as that of the conductive particle 3 except that the above was prepared. As the plating solution g, a solution prepared in nickel sulfate: 450 g / L and sodium citrate: 116 g / L was used, and as the plating solution h, a solution prepared in sodium hypophosphite: 150 g / L was used.

  The obtained conductive particles 8 were darker gray than the conductive particles 3. When the conductive particles 8 were analyzed with an atomic absorption photometer, the amount of palladium that can form a palladium layer equivalent to a thickness of 20 nm was detected on the outermost surface of the nickel particles, but the outermost surface was observed in the observation using the SEM. In this case, palladium particles having a diameter of several hundreds of nanometers were independently attached to each other, and the nickel layer was exposed in half of the entire particle surface. The palladium thus deposited did not substantially cover the nickel layer, and a continuous palladium film was not obtained.

(Conductive particles 9)
Instead of the electroless nickel plating treatment, nickel particles were stirred in 300 ml of 50% hydrochloric acid for 10 minutes, and the mother particles 9 obtained by performing filtration and washing three times were used. Operation was performed to obtain conductive particles 9.

  After a while after the electroless palladium plating solutions e and f were dropped, it started to appear that foreign matter shining in silver was floating on the surface of the solution in which nickel particles were dispersed. In addition, when the conductive particles 9 were observed with an SEM, there were particles that were not particles in which palladium was deposited. The conductive particles on which palladium was deposited also had a portion where palladium was deposited on the surface of the mother particles 9 and a portion where palladium was not deposited, and the mother particles 9 were exposed. When the deposited palladium portion was magnified 10,000 times, palladium fine particles of several hundred nm were densely deposited on the surface of the mother particle 9, but it was not a dense and continuous deposited film.

  In addition, palladium pieces abnormally deposited on portions other than the mother particles 9 were also observed, and it could not be said that the nickel particles were substantially covered with palladium. Further, when the conductive particles 9 were analyzed with an atomic absorption spectrophotometer, the amount of palladium that can form a palladium layer corresponding to a thickness of 30 nm on the outermost surface of the nickel particles was detected for calculation. An amount of palladium sufficient to form a palladium layer was not obtained. It is considered that the palladium in the added electroless palladium plating solution is precipitated other than the surface of the mother particle 9 due to the decomposition of the plating solution. It is considered that since the plating solution was continuously added without being densely deposited on the surface of the mother particle 9, the palladium ion concentration in the bath increased and the decomposition reaction of the plating solution started.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to this. In addition, each compounding ratio was put together in Table 1, and was described. Table 1 shows the ratio of each material with respect to the total mass of the adhesive composition in mass%.

(Example 1)
<Production of circuit connection material>
20 g of phenoxy resin [trade name PKHC, weight average molecular weight 45000, manufactured by Union Carbide Co., Ltd.], toluene (boiling point 110.6 ° C., SP value 8.90) / ethyl acetate (boiling point 77.1 ° C., SP Value 9.10) = dissolved in a 50/50 mixed solvent to obtain a solution having a solid content of 40% by mass.

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

  30 g of an epoxy resin (bisphenol A type epoxy resin, manufactured by Yuka Shell Epoxy Co., Ltd., trade name Epicoat 828 (EP-828), epoxy equivalent 184) was used as a stock solution.

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

  The resin component 100 and the latent curing agent 30 are blended in a solid weight ratio, and further, 3% by volume of the conductive particles 1 are blended and dispersed, and applied to a PET resin film having a thickness of 50 μm using a coating apparatus. A circuit connection material having an adhesive layer thickness of 20 μm was obtained by hot-air drying at 3 ° C. for 3 minutes.

(Example 2)
A circuit connection material was obtained through the same process as in Example 1 except that the conductive particle 2 was used instead of the conductive particle 1 and the same material as in Example 1 was used.

(Example 3)
A circuit connection material was obtained through the same process as in Example 1 except that the conductive particle 3 was used instead of the conductive particle 1 and the same material as in Example 1 was used.

Example 4
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 4 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Example 5)
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 5 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Comparative Example 1)
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 6 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Comparative Example 2)
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 7 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Comparative Example 3)
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 8 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Comparative Example 4)
A circuit connection material was obtained through the same steps as in Example 1 except that the conductive particles 9 were used instead of the conductive particles 1 and the same material as in Example 1 was used.

(Metal film thickness measurement)
In the measurement of the palladium film thickness, each particle was dissolved in 50% by volume aqua regia, and then solids were removed by filtration with a 0.2 μm diameter filter (Millipore), and an atomic absorption photometer Z-5310 (Co., Ltd.) was obtained. After the amount of each metal was measured using a Hitachi product name) or an ICP (inductively coupled plasma) emission spectrometer P4010 (Hitachi product name), the thickness was converted.

  Next, in the measurement of the thickness of the electrolessly plated nickel layer, a thin piece of the metal layer portion of the conductive particles is cut out with a focused ion beam, and a transmission electron microscope HF-2200 (product name, manufactured by Hitachi, Ltd.) is used. The thickness of the nickel layer was measured by observing the cross section of the plating layer.

(Observation of conductive particles)
In the observation of the conductive particles, the conductive particles were uniformly spread on the conductive tape, the excess conductive particles were blown off with an air gun, and then observed with an electron microscope without vapor deposition. For the electron microscope, S4700 (product name, manufactured by Hitachi, Ltd.) was used, and observation was performed at 5000 times or more.

(Particulate boiling test)
1 g of each of the conductive particles 1 to 9 was collected and dispersed in 50 g of pure water. Next, the sample was put into a 60 ml pressure vessel and left at 100 ° C. for 10 hours. Thereafter, the dispersion solvent of the conductive particles was filtered with a 0.2 μm filter, and each metal ion in the filtrate was measured with an atomic absorption photometer. The amount of boiled out (measured ion value) was determined by the following formula.

(Component analysis)
A thin piece of the metal layer portion of the conductive particles is cut out with a focused ion beam, and observed with a transmission electron microscope HF-2200 (product name, manufactured by Hitachi, Ltd.) over 100,000 times. The component analysis of each area | region of the plating layer was conducted. The concentration of nickel, palladium and phosphorus in each region was calculated from the obtained values.

  Furthermore, an ESCA analyzer, AXIS-165 type (Shimadzu Corporation / Kratos product name) was also used for component analysis of each region of the palladium plating layer. Each mother particle before disposing the insulating fine particles was fixed to an indium foil, and component analysis of the surface of the plating layer was performed while removing the palladium plating layer by Ar etching. The Ar etching rate was 5 nm / min, component analysis was performed every minute of Ar etching, and this was repeated to calculate the components in each region of the plating layer.

(Production of circuit connection body)
Using circuit connection materials according to Examples 1 to 5 and Comparative Examples 1 to 4, flexible circuit boards (FPCs) having 500 copper circuits having a line width of 50 μm, a pitch of 100 μm, and a thickness of 18 μm are 180 ° C. and 15 MPa at 3 MPa. It was heated and pressurized for 2 seconds and connected over a width of 2 mm. At this time, after pasting the adhesive surface of the circuit connecting material on one FPC in advance, it was heated and pressurized for 5 seconds under the conditions of 70 ° C. and 0.5 MPa, and then the PET resin film was peeled off. Connected to the other FPC.

  Further, the above-mentioned FPC and glass (surface resistance 20Ω / □) on which a thin layer of ITO was formed were heated and pressurized at 180 ° C. and 3 MPa for 15 seconds to be connected over a width of 1.5 mm. At this time, temporary connection was made to ITO glass in the same manner as described above.

(Conduction resistance test)
The performance of the circuit connection materials according to Examples 1 to 5 and Comparative Examples 1 to 4 was evaluated by conducting a conduction resistance test of the circuit connection body obtained as described above. It is important that the circuit connection material (anisotropic conductive film) has high insulation resistance between chip electrodes and low conduction resistance (connection resistance) between electrodes to be connected. Regarding the conduction resistance between the electrodes to be connected, the average value of 14 samples was measured. The circuit connection material was evaluated based on the initial conduction resistance value and the conduction resistance value after each of the moisture absorption heat resistance test and the temperature cycle test. The hygroscopic heat resistance test here refers to a test in which the circuit connector is left for 1000 hours under conditions of a temperature of 85 ° C. and a humidity of 85% to evaluate the resistance. The temperature cycle test refers to a test in which the circuit connection body is left under the condition of repeating the temperature change of −40 ° C. to 100 ° C. for 100 cycles and its resistance is evaluated.

(High temperature and high humidity exposure test)
1 g each of conductive particles 1 to 9 was put in a glass beaker having a capacity of 100 ml, and these glass beakers were left in a tank having a temperature of 85 ° C. and a humidity of 85% for 120 hours. Thereafter, the surface of the conductive particles was observed using SEM, and the amount of oxide (rust) was evaluated.

Table 1 shows the evaluation results.

  The electroconductive particles 1-5 which concern on Examples 1-5 provide the electroless nickel plating layer in the surface of nickel particle, and provide the palladium layer in the outermost surface. As shown in Table 1, these conductive particles maintained a low resistance both after the moisture absorption heat test and after the temperature cycle test. As for the conductive particles 1 to 5, the result after the high-temperature and high-humidity test on the conductive particles themselves was little changed from that before the test, and only a small amount of rust was observed only in the conductive particles 1, but there was no rust and the conductive particles themselves. It can be seen that the reliability of is high.

  In addition, when the conductive particles 1 to 5 are observed with an SEM, the outermost surface is substantially covered with palladium, and the surface of the underlying nickel particles and the nickel plating layer is extremely small. Also in the ESCA analysis, it is confirmed that the palladium concentration on the outermost surface of the conductive particle surface is high.

  On the other hand, in the connection structures according to Comparative Examples 1 to 4, the connection reliability decreased after the moisture absorption heat test and the temperature cycle test. That is, the conductive particles 6 to 9 used in Comparative Examples 1 to 4, respectively, increased in conduction resistance after the test. In the SEM observation after the high-temperature and high-humidity test on the conductive particles themselves, the conductive particles 6 not provided with the palladium layer had a particularly large amount of rust, and the surface of the underlying nickel particles was not observed. Further, the conductive particles 7 to 9 also had a lot of surface rust. It is suggested that the cause of the decrease in the connection resistance is rust on the surface of the conductive particles.

In addition, the conductive particles 7 and 9 tried to provide a palladium layer directly on the surface of the nickel particles, but abnormal precipitation occurred during the plating operation or foreign substances (palladium pieces) dropped during washing. Palladium plating was not done. Also in SEM observation, the conductive particles 7 and 9 were not covered sufficiently with the nickel particles because the fine palladium particles with a size of several hundreds of nanometers adhered to the outermost surface or were continuously arranged. The ESCA analysis also showed that the outermost surface of the conductive particles had a high ratio to nickel, and the nickel was exposed much. Thus, the exposure of the nickel surface causes rust and reduces the conduction resistance.

  Moreover, when the boiling test result is seen, the conductive particles 6 to 9 having the most exposed nickel on the outermost surface have a large amount of elution of nickel, and correlate with the occurrence of rust and a decrease in conduction resistance.

  Note that palladium, which is a noble metal, has almost no elution. It is clear that the example with low nickel elution shows good results, and the comparative example with high nickel elution has low connection reliability.

  Palladium is relatively inexpensive and practical among noble metals, but it is still more expensive than nickel, which is used in large numbers as conductive particles for anisotropic conductive films, so it is desirable to reduce the amount of palladium used as much as possible. On the other hand, if nickel is exposed a lot, connection reliability tends to decrease. Reduction plating is preferable because the base can be completely covered with the deposited metal and the purity of the deposited metal is high. Particularly preferred is a substitution reduction type having good adhesion and covering properties.

  In the present invention, an electroless nickel plating layer is provided on the surface of nickel particles produced by melting, vapor phase reduction, electroreduction, etc., and a palladium layer is provided thereon to obtain conductive particles with very little nickel exposure. It is done. As shown in the comparative example, if the nickel particles produced by the above method are directly plated with palladium, a dense and uniform palladium layer with little nickel exposure cannot be obtained. The cause of this is not clear, but it will be revealed in the future.

  According to the present invention, the resistance between the electrodes to be connected can be maintained at a good value for a sufficiently long time, and the occurrence of migration can be sufficiently suppressed to achieve excellent connection reliability. In addition, the conductive particles according to the present invention can be obtained at low cost.

  DESCRIPTION OF SYMBOLS 1 ... Nickel particle, 2 ... Nickel layer, 3 ... Palladium layer, 10 ... Conductive particle, 20 ... Adhesive component, 20a ... Hardened | cured material of an adhesive component, 30, 40 ... Circuit member, 32, 42 ... Circuit electrode, 50 ... anisotropic conductive film (circuit connection material), 100 ... connection structure.

Claims (7)

Nickel particles,
A nickel layer by electroless plating covering the surface of the nickel particles;
A palladium layer covering the outer surface of the nickel layer;
Equipped with a,
A phosphorus content of 0.5-4.0% by mass Rushirubeden particles of the nickel layer. The conductive particle according to claim 1, wherein the palladium layer covers the entire outer surface of the nickel layer. The conductive particle according to claim 1 or 2 , wherein a ratio A / B of the number A of nickel atoms and the number B of palladium atoms on the surface of the conductive particle is 1.0 or less. The electroconductive particle as described in any one of Claims 1-3 whose thickness of the said palladium layer is 5-100 nm. An adhesive component having adhesiveness;
The conductive particles according to any one of claims 1 to 4 , which are dispersed in the adhesive component,
An adhesive composition comprising: A circuit connection material comprising the adhesive composition according to claim 5 and used for bonding circuit members together and electrically connecting circuit electrodes of the respective circuit members. A pair of circuit members disposed opposite to each other;
It consists of the hardened | cured material of the circuit connection material of Claim 6 , and the said circuit members are adhere | attached so that the circuit electrodes which intervene between the said pair of circuit members and each circuit member has may be electrically connected. A connection,
A connection structure comprising:

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