JP2006066163A - Conductive particles for anisotropic conductive film and anisotropic conductive film using them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide conductive particles distributedly used in an anisotropic conductive film. <P>SOLUTION: The conductive particles for the anisotropic conductive film are secondary particles wherein a plurality of primary particles gathered and at least surfaces have conductivity. Furthermore, in the anisotropic conductive film, the conductive the particles for the anisotropic conductive films are dispersed in an insulated resin. The anisotropic conductive film using the conductive particles are easily compressively deformed so that connection resistance fully decreases even in a connection condition at low pressure when connecting electrodes etc. and exhibits excellent connection reliability over a long period without faulty connection. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a conductive particle for an anisotropic conductive film having a novel structure and an anisotropic conductive film using the same.

  In recent years, the area of terminals to be connected and the terminal pitch have become very small in the trend of downsizing and high functionality of electronic devices. For this reason, anisotropic conductive films capable of connecting such terminals are widely used in the electronics mounting field. For example, anisotropic conductive films are used for joining an IC chip and electrodes formed on a flexible printed wiring board (FPC), joining electrodes, and the like.

  An anisotropic conductive film is a sheet-like adhesive in which conductive particles are dispersed in a film-like insulating adhesive. The anisotropic conductive film is sandwiched between connection objects and is heated and pressurized to adhere the connection objects. That is, the sheet-like resin flows by heating and pressurizing, sealing the gaps between the electrodes facing each other, and at the same time, some of the conductive particles are caught between the facing electrodes. An electrical connection is achieved.

  As the conductive particles in the conventional anisotropic conductive film, the surface of a single metal particle such as nickel, gold or solder having an average particle diameter of about 10 μm or a particle made of styrene resin or the like is formed by a conductive layer such as nickel-gold. Coated metal plating resin particles are used (Patent Document 1). However, single metal particles are generally hard materials, and deformation due to pressurization during mounting is small. Therefore, there is a problem that height variations between multiple electrodes on the wiring board cannot be absorbed and poor conduction occurs. It was.

  Moreover, high reliability is required for the anisotropic conductive film. Therefore, environmental resistance is required in addition to conduction / insulation performance, and the performance is evaluated by, for example, a high-temperature and high-humidity test or a heat cycle test. Here, the anisotropic conductive film using single metal particles as conductive particles cannot follow deformation due to thermal expansion or the like of the resin adhesive after mounting and tends to be unstable in connection.

  When metal-plated resin particles are used as conductive particles, the resin particles are soft, so the metal single particles can absorb the height variation between the electrodes when the particles are deformed by the pressure applied during mounting. It is easy compared. However, in an anisotropic conductive film using such resin particles as conductive particles, the conductive particles collapse excessively in a portion where the distance between the electrodes is small, so that the metal coating on the outer surface of the conductive particles There was a problem that cracks and cracks occurred in the metal film without following the deformation, and as a result, conduction by the metal film could not be ensured, resulting in poor conduction.

Therefore, it is possible to prevent the metal particles on the outer surface of the conductive particles from cracking and cracking due to excessive crushing of the conductive particles in the portion where the distance between the electrodes is small, and the conduction by the metal film on the outer surface of the conductive particles is prevented. In order to ensure, an anisotropic conductive film is proposed in which conductive particles are composed of an inner core and an outer layer covering the inner core, and the outer layer is softer than the inner layer (Patent Document 2).
However, in the structure of the conductive particles as in Patent Document 2, since the conductive particles cannot collapse smaller than the inner core, the distance between the upper and lower electrodes cannot be less than the size of the inner core. If there is a variation in the distance between the electrodes, the distance between the electrodes becomes larger than that of the conductive particles in a portion where the distance between the upper and lower electrodes is large, and there is a problem in that connection failure occurs.

Further, in mounting using an anisotropic conductive film, connection with a low pressing force is required. For example, when an IC chip is mounted, a pressing force of 1 MPa or less is preferable. However, in mounting with such a low pressing force, the resin particles cannot be sufficiently compressed and deformed, the contact area between the surface of the conductive particles and the electrode does not increase, and connection failure occurs. Therefore, the compressive elastic modulus (20% when the particle diameter is 20% compressively deformed as conductive fine particles that can be easily compressively deformed even under short-time connection conditions at low temperature and low pressure to sufficiently reduce the connection resistance. K value) and the surface of a resin fine particle having a compressive elastic modulus (30% K value) of 30% K / 30% or less both of which is 1.96 × 10 ⁹ N / mm or less and a fracture strain of 20 to 50% Conductive fine particles having a conductive layer formed thereon have been proposed (Patent Document 3).

  However, such conductive fine particles in which a conductive layer is formed on the surface of the resin fine particles are difficult to form a metal layer by securing sufficient adhesion with the resin particles, and require a lot of cost for quality control. It is very expensive.

JP-A-8-115617 (0003, FIG. 1) JP-A-8-193186 (0010) JP 2004-165123 A (0009)

  An object of the present invention is to provide conductive particles that are used by being dispersed in an anisotropic conductive film, which solves the problems in the background art described above. That is, the anisotropic conductive film using the conductive particles easily compresses and deforms even under low-pressure connection conditions when the electrodes are connected and the like, and the connection resistance is sufficiently reduced and connection failure occurs. Without any problem, it exhibits excellent connection reliability over a long period of time. The conductive particles can be manufactured at a low cost. Furthermore, it aims at providing the anisotropic electrically conductive film using the said electroconductive particle.

  As a result of intensive studies, the present inventor has obtained the above problem by using conductive particles characterized in that they are secondary particles in which a plurality of needle-like primary particles are aggregated, and at least the surface has conductivity. Was achieved and the present invention was completed.

  The conductive particles of the present invention are secondary particles in which a plurality of needle-like primary particles are aggregated, and are conductive particles for an anisotropic conductive film having at least a surface of conductivity (Claim 1).

  As one aspect thereof, there may be mentioned conductive particles in which a plurality of needle-like primary particles having at least a surface of conductivity are aggregated to form secondary particles (Claim 2). Further, a conductive layer may be coated on the surface of the secondary particles. Another embodiment is conductive particles in which a plurality of needle-like primary particles are aggregated to form secondary particles, and the surface of the secondary particles is covered with a conductive layer (Claim 4).

  The anisotropic conductive film according to the present invention is an anisotropic conductive film in which these conductive particles are dispersed in an insulating resin.

  FIG. 1 is a conceptual diagram of conductive particles for an anisotropic conductive film according to a preferred embodiment of the present invention. The conductive particles 2 have a plurality of needle-like primary particles 1 connected by weak bonds, and have a bulky structure with elasticity. FIG. 2 shows a state of deformation when a pressing force is applied to the anisotropic conductive film conductive particles of the present invention. (2a) is a conductive particle in a state where no pressing force is applied, and (2b) is a conductive particle in a state where a pressing force is applied. When a pressing force is applied to the conductive particles, it easily deforms and reversibly changes from the structure of FIG. 2 (2a) to the structure of (2b). Therefore, when connecting between electrodes, etc., it can be easily deformed even with a low pressing force, and conductivity can be ensured while absorbing variations in height between connecting electrodes.

  Further, even in an environmental resistance test such as a high-temperature and high-humidity test and a heat cycle test, the elasticity of the conductive particles can sufficiently follow deformation due to thermal expansion of the resin and has high reliability.

  At least the surface of the needle-shaped primary particles having conductivity is coated with metal particles such as gold, silver, copper, nickel and their alloys, needle-shaped ferrite, carbon fiber, carbon nanotube, and tin oxide-based conductive layer. Examples thereof include titanium oxide, aluminum borate coated with a tin oxide based conductive layer, and potassium titanate fiber coated with a tin oxide based conductive layer. Moreover, you may coat | cover a metal layer further by methods, such as plating, on the surface of these primary particles. Furthermore, what formed the electroconductive layer by methods, such as plating, on the surface of non-conductive acicular particle | grains, such as a titanium oxide, an iron oxide, an aluminum borate, a potassium titanate fiber, can also be used as a primary particle.

  Furthermore, acicular particles having no electrical conductivity can also be used as the primary particles. Examples include titanium oxide, iron oxide, aluminum borate, and potassium titanate fiber. In this case, a plurality of these primary particles are aggregated to form secondary particles, and then a conductive layer is coated on the surface to form conductive particles.

  It is more preferable that the surface is covered with a conductive layer after a plurality of needle-like primary particles having at least the surface conductivity are aggregated to form secondary particles, thereby improving the conductivity and reliability. Furthermore, by covering the conductive layer, the bonds between the primary particles are strengthened, and in subsequent processes, the conductive particles are less likely to be pulverized when stirring and mixing with the adhesive resin solution (return to the original primary particles). It also has the effect of becoming difficult).

As the conductive layer covering the surfaces of the secondary particles and the primary particles, metals such as gold, silver, copper, nickel, and alloys thereof, and tin oxide-based materials can be used.
These materials may be used alone or in combination. From the viewpoints of conductivity and reliability, the material that covers the outermost layer is more preferably gold, and the conductive layer can be formed by a method such as plating.

  As a method of collecting a plurality of primary particles into secondary particles, a general granulation technique such as spray drying (spray drying) or freeze drying (freeze drying) can be used. When the primary particles are plated in the liquid phase and dried and recovered, secondary particles having an appropriate size can be formed by selecting the type and amount of the surface treatment agent added to the reaction solution. In this case, since the formation of secondary particles and the formation of the conductive layer can be performed simultaneously, the process can be simplified, which is more preferable.

Surface treatment agents added to the reaction solution include fatty acid salts, alkyl sulfate esters, polyoxyethylene alkyl ethers, anionic materials such as polycarboxylic acids, cationic materials such as alkyltrimethylammonium salts and alkyldimethylbenzyl salts, poly Nonionic materials such as oxyethylene alkyl ether, fatty acid ester, polyethylene glycol, fatty acid alkanol or amide can be used. When an anionic or cationic material is used, if the counter ion contains impurity ions such as Na ⁺ and Cl ⁻ , electromigration tends to occur. Therefore, it is preferable to add a step of washing and removing the counter ions after collecting the secondary particles.

The primary particles have a needle shape. This is because when a plurality of acicular particles are aggregated, bulky secondary particles with many voids can be formed, and they can be easily deformed even with a low pressing force. Here, the needle shape is defined as a particle having a ratio of particle diameter to length (aspect ratio) of 3 or more. In the case of particles having a non-circular cross section, the aspect ratio is obtained using the maximum length of the cross section as a diameter. However, it is not always necessary to have a straight shape, and even if there are some bends or branches, it can be used without any problem. Moreover, what formed many needle | hooks by connecting many fine particles can be used preferably.
The higher the particle diameter / length ratio (aspect ratio), the more bulky secondary particles can be formed. Therefore, the aspect ratio is preferably 5 or more. More preferably, it is 10 or more.

  In addition, when conductive particles are dispersed in an insulating resin and used as an anisotropic conductive film, the distance between the electrodes is small, in the so-called fine pitch connection, the size of the conductive particles is larger than the distance between adjacent electrodes. If it is too large, the electrodes in the horizontal direction are connected to each other, resulting in poor insulation. Therefore, it is necessary to reduce the size of the conductive particles as secondary particles. In order to obtain such secondary particles, it is necessary to reduce the size of the primary particles. However, since the aspect ratio is reduced when only the length of the primary particles is reduced, the smaller one is preferable. Specifically, the diameter of the primary particles is preferably 1 μm or less (Claim 6).

  The particle size of the conductive particles needs to be not more than the space width between adjacent electrodes. Furthermore, it is preferable that it is 1/2 or less of the space width between adjacent electrodes since the insulation is improved. In applications where an anisotropic conductive film is generally used, the inter-electrode space width is in the range of 10 to 1000 μm. Moreover, the particle size of electroconductive particle needs to be below the thickness of an anisotropic conductive film. If the particle size is larger than the thickness of the anisotropic conductive film, there will be a problem in the production process such that the particles jump out of the film surface and cannot be wound well in a reel form, and there is a problem of particle oxidation. Accordingly, the particle diameter of the conductive particles is preferably not more than the thickness of the anisotropic conductive film and not more than ½ of the inter-electrode space width. Furthermore, if the particle size of the conductive particles is too small, the amount of deformation at the time of mounting pressurization becomes small, so it becomes difficult to absorb the height variation of the electrodes, and the lower limit of the particle size is 2 μm. Accordingly, the particle diameter of the conductive particles is preferably 2 μm to 50 μm.

  The particle size of the conductive particles is directly measured by a method such as CCD microscope observation. The maximum diameter of the particles is defined as the particle diameter of the particles, and the measurement is performed by the following method. That is, the particle is projected on the XY axis, and the projection length is measured. When the XY axis is rotated, the length of the particle projected at a certain angle becomes maximum, and the projection length at this time is the maximum diameter.

  The conductive particles of the present invention are preferably bulky, that is, the more voids, the easier the deformation even with a low pressing force. Apparent particle density is used as an evaluation index of the bulkiness. Here, the apparent particle density is a density when the volume of the outer periphery of the particle having irregularities on the surface. That is, a crack on the particle surface, a narrow dent at the entrance, and an open cavity are calculated by adding to the volume of the particle, and measurement is performed using a liquid that does not wet the particle surface. Also called lyophobic particle density. In order to achieve the object of the present invention, it is preferable that the apparent particle density of the secondary particles is 80% or less of the true density of the primary particles, since it is easily deformed even at a low pressing force during mounting. . More preferably, it is 50% or less, More preferably, it is 30% or less.

  The anisotropic conductive film is manufactured by dispersing the conductive particles thus prepared in an insulating resin. As the insulating resin, any of various compounds having film-forming properties and adhesiveness can be used, and examples thereof include thermoplastic resins, curable resins, and liquid curable resins, and particularly preferable are acrylic resins and epoxy resins. Resin, fluorine resin, phenol resin and the like. Conductive particles are dispersed in a solution obtained by dissolving these insulating resins in a solvent to obtain a dispersion solution. Then, the dispersion solution is applied with a roll coater to form a thin film, and then the solvent is dried. A film-like anisotropic conductive film is obtained by removing by the above. Although the thickness of a film | membrane is not specifically limited, Usually, it is 10-50 micrometers.

  The compounding quantity of electroconductive particle is selected from the range of 0.01-30 volume% with respect to the total volume of an anisotropic conductive adhesive, and uses properly by use. In order to prevent a short circuit of an adjacent circuit due to excessive conductive particles, the content is more preferably 0.01 to 10% by volume.

The present invention provides conductive particles dispersed in an anisotropic conductive film and an anisotropic conductive film using the same. The anisotropic conductive film using the conductive particles of the present invention easily compresses and deforms even under low-pressure connection conditions when the electrodes are connected, and the connection resistance is sufficiently reduced and connection failure occurs. Without any problem, it exhibits excellent connection reliability over a long period of time.

  Next, the best mode for carrying out the invention will be described by way of examples. The examples are not intended to limit the scope of the invention.

(Preparation of conductive particles)
Acicular titanium oxide particles (diameter: 0.27 μm, length: 5.2 μm, aspect ratio: 19, true specific gravity 4.4 g / ml, FT-3000 manufactured by Ishihara Sangyo) coated with a tin oxide-based conductive layer are primary. Used as particles. When electroless nickel / cobalt alloy plating is performed on these particles, polyethylene glycol is dissolved at a concentration of 0.5 g / l in the plating solution, and the primary particles are treated in this solution for 10 minutes to produce primary particles. The surface of the particles was plated with a nickel-cobalt alloy and simultaneously formed into secondary particles. The obtained secondary particles were filtered through a stainless mesh cartridge filter having a pore diameter of 37 μm to remove excessive particles, and washed and recovered to obtain conductive particles. The apparent particle density of the obtained conductive particles was 1.1 g / ml, and the apparent particle density of secondary particles / true density of primary particles = 25%.

(Shape evaluation test)
After mixing 10.0 g of Acrysilap SY-105 (trade name of Kanae Co., Ltd.) and 0.01 g of 2,2′-azobis (isobutyronitrile) per 0.01 g of the obtained conductive particles A liquid composite material for shape evaluation was prepared by uniformly dispersing through 10 minutes of centrifugal stirring and 10 minutes of defoaming. Next, after applying this composite material on a glass plate using a doctor knife (gap 25 μm), heating and drying at 100 ° C. for 30 minutes and curing the resin, the conductive particles are uniform. A film for shape evaluation dispersed in was prepared.
And the microscope image of the surface of the said film | membrane was taken in into the computer using the CCD camera connected to the microscope, the image analysis was performed with the computer, and the particle size of the secondary particle was measured. The obtained secondary particles had a particle size of 10 μm.

(Preparation of coating solution)
As an insulating resin, an epoxy resin having an average molecular weight of 39000 (Epicoat YL6954 manufactured by JER Co., Ltd.) and a naphthalene type epoxy resin having an average molecular weight of 320 (manufactured by Dainippon Ink & Chemicals, Inc., HP4032) introduced with a biphenyl skeleton, A microcapsule type imidazole curing agent (manufactured by Asahi Kasei Epoxy Co., Ltd., Novacure HX3941) was used at a weight ratio of 50/40/10, and these were dissolved in cyclohexanone to prepare a solution having a solid content of 50%. The conductive particles are uniformly added to the solution so that the filling rate represented by the ratio of the total solid content (conductive particles + resin) is 1% by volume, and then stirred using a centrifugal mixer. Dispersion was performed to prepare a coating solution for the anisotropic conductive film.

(Production of anisotropic conductive film)
The coating solution prepared above was applied onto a release-treated PET film using a roll coater, dried at 60 ° C. for 10 minutes, and solidified to form a 35-micron-thick anisotropic conductive film. Obtained.

(Connection resistance evaluation)
A flexible printed wiring board (FPC) having an electrode region in which electrodes having a width of 50 μm and a length of 18 μm are arranged at intervals of 100 μm is prepared, and the manufactured anisotropic conductive film is overlaid on the electrode region of the FPC Then, while heating to 60 ° C., the FPC and the anisotropic conductive film were temporarily bonded by pressing with a pressing force of 1 MPa for 10 seconds. Next, a glass substrate with an ITO film deposited on one side is stacked with the ITO film in contact with the anisotropic conductive film and heated for 10 seconds with the three types of pressing forces shown in Table 1 while heating to 200 ° C. And thermally bonded. The resistance value between two adjacent electrodes that are conductively connected via the anisotropic conductive film and the ITO film is measured using a digital multimeter, and ½ of this measured value is measured in the thickness direction of the anisotropic conductive film. Connection resistance was used.

(Insulation resistance evaluation)
A flexible printed wiring board (FPC) having an electrode region in which electrodes having a width of 50 μm and a thickness of 18 μm are arranged at intervals of 100 μm is prepared, and the manufactured anisotropic conductive film is overlaid on the electrode region of the FPC. The FPC and the anisotropic conductive film were temporarily bonded by pressing for 10 seconds with a pressing force of 1 MPa while heating to 60 ° C. Next, the glass substrate on which the ITO film was not deposited was overlapped so that the glass substrate was in contact with the anisotropic conductive film, and was heated and pressed under the same conditions as in the connection resistance evaluation to be thermally bonded. The resistance value between two adjacent electrodes was measured at an applied voltage of 25 V using an insulation resistance meter to obtain the insulation resistance in the surface direction of the anisotropic conductive film. The insulation resistance of 1 GΩ or more was evaluated as ◯, and 1 GΩ or less as x.

(Heat and humidity resistance test)
The FPC-glass substrate assembly was put into a high-temperature and high-humidity tank set at 80 ° C. to 95%, taken out after 500 hours, and connection resistance and insulation resistance were measured again in the same manner as described above. The results are shown in Table 1. In addition, connection resistance represents 10Ω or less as ◯, 10 to 100Ω as Δ, and 100Ω or more as ×, and insulation resistance as 1GΩ or more as ○, and 1GΩ or less as ×.

As primary particles, linear nickel fine particles (nickel fine particles having an average particle diameter of 200 nm connected in a linear form. Diameter: 0.2 μm, length: 3 μm to 15 μm, true density: 8.8 g / ml) were used. When gold plating is performed on the particles, polyethylene glycol is dissolved at a concentration of 0.5 g / l in the plating solution, and the primary particles are treated in the solution heated to 80 ° C. for 10 minutes. Secondary particles were formed at the same time when gold was plated on the surface of the secondary particles. The obtained secondary particles were filtered through a stainless mesh cartridge filter having a pore diameter of 37 μm to remove excessive particles, and washed and recovered to obtain conductive particles. The apparent particle density of the obtained conductive particles was 1.5 g / ml, and the apparent particle density of secondary particles / true density of primary particles = 17%. When the shape evaluation test was performed in the same manner as in Example 1, the particle size of the obtained conductive particles was 10 μm.
Thereafter, an anisotropic conductive film was prepared in the same manner as in Example 1, and a connection resistance evaluation, an insulation resistance evaluation, and a heat and moisture resistance test were performed. The results are shown in Table 1.

[Comparative Example 1]
Connection was made in the same manner as in Example 1 except that nickel / gold coated resin particles (Sekisui Chemical Co., Ltd., Micropearl AU-205) having a particle size of 5 μm, in which no secondary particle forming step was added, were used as conductive particles. Resistance evaluation, insulation resistance evaluation, and heat / moisture resistance tests were performed. The results are shown in Table 1.

[Comparative Example 2]
Evaluation of connection resistance and insulation resistance in the same manner as in Example 1 except that nickel particles (Inco Type 123 manufactured by Inco Tokyo Nickel Co., Ltd.) having a particle size of 3 μm to 7 μm with no secondary particle forming step added were used as the conductive particles. Evaluation, heat and humidity resistance tests were conducted. The results are shown in Table 1.

  The results in Table 1 show that when mounted with anisotropic conductive films using conductive particles of Examples of the present invention (Examples 1 and 2), connection resistance and insulation even when mounted with a low pressing force of 0.35 MPa. It shows excellent resistance and maintains its performance after humidity and heat resistance tests. On the other hand, Comparative Examples 1 and 2 outside the scope of the present invention show good connection resistance when mounted at a high pressure of 3.5 MPa, but when mounted at a pressure of 0.7 MPa or less, they are connected in a heat / humidity test. Resistance increases. As is apparent from this result, by using the conductive particles of the present invention example, an anisotropic conductive film having good connection resistance and high reliability can be obtained even at a low pressing force.

It is a conceptual diagram which shows the form of the electroconductive particle of this invention. It is a conceptual diagram which shows the form at the time of pressurization of the electroconductive particle of this invention. It is a figure which shows the form of the anisotropic electrically conductive film using the electroconductive particle of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Primary particle 2 ... Conductive particle (secondary particle)
3 ... Insulating resin

Claims (9)

  A conductive particle for an anisotropic conductive film, which is a secondary particle in which a plurality of needle-shaped primary particles are aggregated, and at least the surface has conductivity.   Conductive particles for an anisotropic conductive film, characterized in that a plurality of needle-like primary particles having at least a surface of conductivity are aggregated to form secondary particles.   The conductive particle for anisotropic conductive film according to claim 2, wherein a surface of the secondary particle is coated with a conductive layer.   A conductive particle for an anisotropic conductive film, wherein a plurality of needle-like primary particles are aggregated to form secondary particles, and the surface of the secondary particles is coated with a conductive layer.   5. The conductive particle for anisotropic conductive film according to claim 1, wherein the ratio (aspect ratio) of the diameter and length of the primary particles is 5 or more.   The conductive particle for anisotropic conductive film according to any one of claims 1 to 5, wherein the diameter of the primary particle is 1 µm or less.   The conductive particles for anisotropic conductive film according to any one of claims 1 to 5, wherein the secondary particles have a particle size of 2 µm to 50 µm.   The conductive particle for anisotropic conductive film according to any one of claims 1 to 7, wherein the apparent particle density of the secondary particles is 80% or less of the true density of the primary particles.   An anisotropic conductive film, wherein the conductive particles for the anisotropic conductive film according to claim 1 are dispersed in an insulating resin.

Images