Resin composition, method for preparing resin composition, and structure

Abstract

The invention provides an anisotropic conductive adhesive, a method for producing the anisotropic conductive adhesive, and a connection structure, wherein conductive particles can be dispersed by a simple method, and short circuit between electrode terminals of an electronic component can be suppressed. The anisotropic conductive adhesive contains coated conductive particles in which a part of the surfaces of conductive particles are coated with an insulating filler, the insulating filler, and an insulating binder, the coated conductive particles are dispersed in the insulating binder, and the particle diameter of the conductive particles is 7 [mu] m or more. The particle diameter of the insulating filler is 0.02-0.143% of the particle diameter of the conductive particles, and the amount of the insulating filler relative to the conductive particles is 0.78-77% by volume.

Description

This is a divisional application of a patent application with an original filing date of February 27, 2018 (priority date: March 6, 2017), an original application number of 201880013719.5 (international application number: PCT / JP2018 / 007377), and an invention title of "Resin Composition, Method for Producing Resin Composition, and Structure". Technical Field

[0001] The present technology relates to a resin composition, a method for producing a resin composition, and a structure. This application claims priority based on Japanese Patent Application No. 2017-042220 filed in Japan on March 6, 2017, and incorporates this application by reference in this application. Background Art

[0002] In a resin composition containing particles, due to various reasons such as a decrease in performance caused by aggregation, it is necessary for the particles to have high dispersibility (for example, refer to Patent Document 1). In particular, such high dispersibility is strongly required in resin compositions for electronic components, adhesives for electronic components, and the like. The reason is that when the dispersibility of the particles is low, it is difficult to maintain the quality stability of the resin composition.

[0003] As an example of an adhesive for electronic components, there is a circuit connection material, and an anisotropic conductive adhesive therein generally uses an adhesive in which conductive particles are dispersed in an insulating binder (for example, refer to Patent Documents 2 to 4). However, even if the dispersion is achieved immediately after preparation, the conductive particles in the anisotropic conductive adhesive sometimes aggregate. The aggregation of the conductive particles can cause a decrease in the capture efficiency of the conductive particles and a short circuit between the electrode terminals of the electronic component. Therefore, an insulating coating film is sometimes formed on the surface of the conductive particles in advance (for example, refer to Patent Document 2).

[0004] However, if an insulating coating film is formed on the surface of the conductive particles, the production cost tends to increase. In particular, as the particle size of the conductive particles becomes larger, the surface area of the conductive particles also becomes larger, and the difficulty of the technology for forming an insulating coating film on the surface of the conductive particles also increases, and the production cost tends to further increase. Therefore, even when the particle size of the conductive particles is large, it is necessary to uniformly disperse the conductive particles by a simple method and suppress a short circuit between the electrode terminals of the electronic component.

[0005] In addition, even when the particle size of the particles dispersed in the insulating binder is small, it is necessary to uniformly disperse them.

[0006] Prior Art Documents Patent Documents Patent Document 1: Japanese Unexamined Patent Application Publication No. 2015-134887; Patent Document 2: Japanese Patent Application Laid-Open No. 2015-133301; Patent Document 3: Japanese Patent Application Laid-Open No. 2014-241281; Patent Document 4: Japanese Patent Application Laid-Open No. 11-148063. Summary of the Invention

[0007] Problems to be Solved by the Invention In addition, the present technology has been proposed in view of the above-described conventional circumstances, and provides a resin composition capable of uniformly dispersing particles by a simple method, a method for producing the resin composition, and a structure.

[0008] In addition, in the case of an anisotropic conductive adhesive, an anisotropic conductive adhesive, a method for producing the anisotropic conductive adhesive, and a connection structure are provided, which can uniformly disperse conductive particles by a simple method even when the particle diameter of the conductive particles is large, and can suppress short circuits between electrode terminals of electronic components.

[0009] Means for Solving the Problems The resin composition according to the present technology contains coated large-diameter particles in which a part of the surface of large-diameter particles is coated with small-diameter fillers, small-diameter fillers, and an insulating binder, and is obtained by dispersing the coated large-diameter particles. The particle diameter of the large-diameter particles is 2 μm or more, the particle diameter of the small-diameter fillers is 0.02 to 5.0% of the particle diameter of the large-diameter particles, and the amount of the small-diameter fillers relative to the large-diameter particles is less than 156% by volume.

[0010] The method for producing the resin composition according to the present technology includes: Step (A) of obtaining first-coated particles in which the large-diameter particles having an average particle diameter of 2 μm or more are coated with the small-diameter fillers by stirring the large-diameter particles and the small-diameter fillers having a particle diameter of 0.02 to 5.0% of the particle diameter of the large-diameter particles; and Step (B) of obtaining a resin composition in which second-coated particles in which a part of the surface of the large-diameter particles is coated with the small-diameter fillers are dispersed in the insulating binder by stirring the first-coated particles and the insulating binder. In Step (A), the large-diameter particles and the small-diameter fillers are blended such that the amount of the small-diameter fillers relative to the large-diameter particles is less than 156% by volume. It should be noted that in the present invention, the expressions of using particles and fillers are distinguished to facilitate understanding of substances having different sizes.

[0011] The anisotropic conductive adhesive according to the present technology contains coated conductive particles in which a part of the surface of conductive particles is coated with an insulating filler, an insulating filler, and an insulating binder. The coated conductive particles are dispersed in the insulating binder. The particle size of the conductive particles is 7 μm or more, the particle size of the insulating filler is 0.02 to 0.143% of the particle size of the conductive particles, and the amount of the insulating filler relative to the conductive particles is 0.78 to 77% by volume.

[0012] The method for producing an anisotropic conductive adhesive according to the present technology includes: step (A) of obtaining first coated conductive particles in which the conductive particles having an average particle size of 7 μm or more are coated with the insulating filler by stirring the conductive particles and the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles; and step (B) of obtaining an anisotropic conductive adhesive in which second coated conductive particles in which a part of the surface of the conductive particles is coated with the insulating filler are dispersed in the insulating binder by stirring the first coated conductive particles and the insulating binder. In step (A), the conductive particles and the insulating filler are blended such that the amount of the insulating filler relative to the conductive particles is 0.78 to 77% by volume.

[0013] The connection structure according to the present technology is obtained by connecting a first electronic component and a second electronic component through an anisotropic conductive film containing the anisotropic conductive adhesive.

[0014] Advantages of the Invention According to the present technology, by forming partially coated particles in which a part of the surface of large-diameter particles is coated with small-diameter fillers, the large-diameter particles can be uniformly dispersed.

[0015] According to the present technology, even when the particle size of the conductive particles is large, the conductive particles (coated conductive particles in which a part of the surface of the conductive particles is coated with an insulating filler) can be uniformly dispersed by a simple method, and short circuits between electrode terminals of electronic components can be suppressed. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Figure 1 is a cross-sectional view showing an example of the connection structure according to the present embodiment.

[0017] Figure 2 Figure 2 is a view showing an example of a mixture obtained by stirring conductive particles and an insulating filler.

[0018] Figure 3 Figure 3 ​​​​​​It is a diagram showing an example of an anisotropic conductive adhesive obtained by stirring coated conductive particles coated with an insulating filler and an insulating binder.

[0019] Figure 4 Figure 4 It is a diagram showing conductive particles not coated with an insulating filler.

[0020] Figure 5 Figure 5 It is a diagram showing an example of an anisotropic conductive adhesive obtained by stirring conductive particles not coated with an insulating filler and an insulating binder.

[0021] Figure 6 Figure 6 It is a diagram showing an example of a mixture obtained by stirring conductive particles and an insulating filler.

[0022] Figure 7 Figure 7 It is a cross-sectional view schematically showing a first example of partially coated particles to which the present technology is applied.

[0023] Figure 8 Figure 8 It is a cross-sectional view schematically showing a second example of partially coated particles to which the present technology is applied.

[0024] Figure 9 Figure 9 It is a cross-sectional view schematically showing a third example of partially coated particles to which the present technology is applied. Detailed implementation mode

[0025] The present technology improves the dispersibility of large-diameter particles in an insulating binder by forming partially coated particles in which a part of the surface of large-diameter particles is coated with small-diameter fillers. On the other hand, when the entire surface of the large-diameter particles is coated with small-diameter fillers, the amount of small-diameter fillers relative to the large-diameter particles becomes excessive, and there is a tendency for the dispersibility of the large-diameter particles in the insulating binder to decrease.

[0026] Partially coated particles can be obtained by mixing powders of large-diameter particles and small-diameter fillers (preferably only mixing them), coating the surface of the large-diameter particles with small-diameter fillers, and then mixing (kneading) the mixture with a resin composition to peel off a part of the small-diameter fillers on the surface of the coated large-diameter particles. Conversely, if partially coated particles are formed, the amount of small-diameter fillers relative to the large-diameter particles is appropriate, and it can be said that the dispersibility of the large-diameter particles in the insulating binder is high. This is carried out, for example, by using a planetary stirring device or the like and applying high shear (shearing force), whereby the coating of the small-diameter fillers on the surface of the large-diameter particles and partial peeling can be effectively carried out. ​​​​​​​​​​​​

[0027] Hereinafter, the first embodiment will be described.

[0028] [First Embodiment] <Resin Composition> The resin composition according to this embodiment contains partially coated particles in which the surface of large-diameter particles is partially coated with small-diameter fillers, small-diameter fillers, and an insulating binder, and is formed by dispersing the partially coated particles. The diameter of the large-diameter particles is 2 μm or more, the diameter of the small-diameter fillers is 0.02 to 5.0% of the diameter of the large-diameter particles, and the amount of the small-diameter fillers relative to the large-diameter particles is less than 156% by volume. It should be noted that, unless otherwise specified, the expression of 0.02 to 5.0% as described above means 0.02% or more and 5.0% or less.

[0029] In this specification, the diameter of the large-diameter particles can be set as the value measured by an image type particle size distribution analyzer (as an example, FPIA-3000: manufactured by Malvern Instruments). Preferably, the number thereof is 1000 or more, and more preferably 2000 or more. In addition, the diameter of the small-diameter fillers can be, for example, observed by an electron microscope and set as the average value of any 100, and the accuracy can be further improved by setting it to 200 or more.

[0030] In addition, the amount (% by volume) of the small-diameter fillers relative to the large-diameter particles can be set as the value obtained by the following formula: Amount (% by volume) of small-diameter fillers (B) relative to large-diameter particles (A) = {(Bw / Bd) / (Aw / Ad)} × 100 Aw: Mass composition (% by mass) of large-diameter particles (A); Bw: Mass composition (% by mass) of small-diameter fillers (B); Ad: Specific gravity of large-diameter particles (A); Bd: Specific gravity of small-diameter fillers (B).

[0031] Figures 7 to 9 Respectively are cross-sectional views schematically showing the first to third examples of the partially coated particles to which this technology is applied. As Figures 7 to 9 shown, the partially coated particles 20 coat a part of the surface of the large-diameter particles 21 with small-diameter fillers. In other words, the partially coated particles 20 have a coated portion 22 coated with small-diameter fillers and an exposed portion 23 where the surface of the large-diameter particles is exposed on their surface. For example, as Figure 7 shown, the exposed portion 23 may exist in a mottled manner as a whole on the surface, or as Figure 8 shown, the exposed portion 23 may be a part, or as Figure 9As shown, the exposed portion 23 may be more than half of the whole. The reason is that: for the first purpose of simply obtaining the dispersibility of the partially coated large-diameter particles obtained by this method, rather than giving priority to obtaining the performance of the large-diameter particles through the coating state.

[0032] For the partially coated particles 20, as long as the resin composition is formed into a film shape and partial coating can be confirmed by surface field observation using an electron microscope or the like. It is preferably to obtain the same result by changing the observation site multiple times. In the case of detailed confirmation, in the cross-section of the partially coated particles 20, it is only necessary to confirm that at least a part of the outermost surface is coated. It should be noted that by observing the same part on the front and back surfaces of the observed film body, it can be confirmed more precisely and simply. If it is this method, it can be distinguished only by determining whether there is partial coating of the large-diameter particles. It is also considered that the determination in the case where the peeled small-particle fillers and the large-diameter particles overlap can be individually determined by adjusting the focal distance.

[0033] The ratio of the coated portion 22 in the partially coated particles 20 can also be confirmed, for example, by surface field observation using an electron microscope or the like after forming the above resin composition into a film shape. Or, the resin composition can be cured or frozen, and the outermost surface of the cross-section of any 100 partially coated particles is observed by an electron microscope, and the average value of the ratio of the coated portions of any 100 partially coated particles is set. The average value of the ratio of the coated portions of the partially coated particles as described above is, for example, only required to be 15% or more and less than 100%, and may also be 30 to 95%.

[0034] In addition, the number ratio of the partially coated particles 20 is 70% or more, preferably 80% or more, and more preferably 95% or more with respect to the whole of the fully coated particles and the partially coated particles. The number ratio of the partially coated particles 20 can, for example, cure or freeze the resin composition, observe any 100 fully coated particles and partially coated particles by an electron microscope, and set it as the number of partially coated particles with respect to any 100 fully coated particles and partially coated particles.

[0035] The large-diameter particles are not particularly limited, and the material is appropriately selected according to the function of the resin composition. For example, in the case of imparting conductivity to the resin composition, conductive particles, metal particles, etc. are selected. In addition, in the case of imparting a spacer function to the resin composition, acrylic rubber, styrene rubber, styrene-olefin rubber, silicone rubber, etc. are selected. If it can be coated and partially coated by combining with small-particle fillers, there is no particular limitation, and it can be an organic substance or an inorganic substance. In addition, it can be particles obtained by combining an organic substance and an inorganic substance, such as resin particles plated with metal. One kind can be used alone, or two or more kinds can be used in combination. If it is one kind alone, the evaluation of dispersibility becomes easy. In the case of two or more kinds, for the same reason, particles with completely different appearances are preferably used.

[0036] The particle size of the large-diameter particles is 2 μm or more. In addition, there is no particular limitation on the upper limit of the particle size of the large-diameter particles. However, for example, in the case where the large-diameter particles are conductive particles, from the viewpoint of the capture efficiency of the conductive particles in the connection structure, it is preferably 50 μm or less, more preferably 20 μm or less.

[0037] The number density of the large-diameter particles in the resin composition can be appropriately adjusted according to the purpose. However, as the lower limit, it is preferably 20 particles / mm 2 or more, more preferably 100 particles / mm 2 or more, even more preferably 150 particles / mm 2 or more. The reason is that when the amount is too small, the adjustment limit of the ratio with the small-particle filler becomes narrow, and reproducibility becomes difficult. In addition, the upper limit is preferably 80,000 particles / mm 2 or less, more preferably 70,000 particles / mm 2 or less, even more preferably 65,000 particles / mm 2As described below, if the number density of large-diameter particles becomes excessively large, it becomes difficult to coat or mix the small-particle-size filler with the resin composition. The number density can be formed into a film shape on the smooth surface of the support and obtained by observation under a surface view. The thickness at this time can be set to 1.3 times or more of the large-diameter particles or 10 μm or more, and the upper limit can be set to 4 times or less of the large-diameter particles, preferably 2 times or less or 40 μm or less. Since this thickness is derived from the resin composition, it is difficult to generally specify, so the range is set as described above. The surface view observation can be performed using an electron microscope such as a metallurgical microscope or SEM. It can be obtained by measuring each large-diameter particle based on the observed image, or by using known image analysis software (as an example, WinROOF (Mitani Corporation)) for measurement. In the case of the resin composition, since it varies depending on the thickness in the case of forming a film shape, it can be specified by the number density in the surface view with a thickness of 1.3 times or 4 times that of the large-diameter particles. It should be noted that in the case of containing a solvent, it is set as the thickness after drying.

[0038] Most of the small-particle-size fillers are dispersed in the insulating binder, and a part covers a part of the surface of the large-diameter particles. As the small-particle-size filler, an insulating filler can be used. As the insulating filler, for example, oxides such as titanium oxide, aluminum oxide, silicon dioxide, calcium oxide, and magnesium oxide, hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate, and barium carbonate, sulfates such as calcium sulfate and barium sulfate, silicates such as calcium silicate, nitrides such as aluminum nitride, boron nitride, and silicon nitride, etc. can be cited. The insulating filler can be used alone or in combination of two or more.

[0039] The upper limit of the particle size of the small-particle-size filler can be set to 14% or less, preferably 0.3% or less, of the large-diameter particles. Or it is preferably 100 nm or less, more preferably 50 nm or less. Since the surface area of the small-particle-size filler relative to the large-diameter particles is not too large, defects such as damage to the surface of the large-diameter particles can be suppressed. In addition, the lower limit of the particle size of the small-particle-size filler is preferably 10 nm or more. Since the surface area of the small-particle-size filler relative to the large-diameter particles is not too small, aggregation of the large-diameter particles can be more effectively suppressed. In the case of being too small, there is a risk of affecting the dispersibility due to an excessive increase in the viscosity of the resin composition.

[0040] According to the relationship between the sizes of the large-diameter particles and the small-particle-size fillers described above, the particle size ratio of the large-diameter particles to the small-particle-size fillers (particle size of the small-particle-size filler / particle size of the large-diameter particles) is 0.02 to 5.0%, preferably 0.02 to 2.5%.

[0041] In addition, the volume ratio of the small-sized filler satisfying the above particle size ratio to the large-sized particles is less than 156% by volume. If this ratio is exceeded, it becomes difficult to easily achieve uniform dispersion in the resin. It should be noted that the lower limit value certainly exceeds 0%, but in addition to the size ratio of the large-sized particles to the small-sized filler, it is also related to their shapes, etc., so it is difficult to generally specify. However, if it is 0.78% or more, there are considered to be no special problems, if it is 3.9% or more, it is preferred, and if it is 7.8% or more, it is more preferred. It should be noted that the upper limit value is preferably 78% by volume or less, and more preferably 39% or less. It should be noted that these values can be appropriately selected according to the relationship between the large-sized particles and the small-sized filler. By satisfying the conditions described above, the dispersibility of the large-sized particles can be made good.

[0042] As the insulating binder (insulating resin), a known insulating binder can be used. As the curable type, a thermosetting type, a photocurable type, a combination of photo- and heat-curing type, etc. can be cited. For example, a photo-radical polymerization type resin containing a (meth)acrylate compound and a photo-radical polymerization initiator, a thermo-radical polymerization type resin containing a (meth)acrylate compound and a thermo-radical polymerization initiator, a thermo-cationic polymerization type resin containing an epoxy compound and a thermo-cationic polymerization initiator, a thermo-anionic polymerization type resin containing an epoxy compound and a thermo-anionic polymerization initiator, etc. can be cited. In addition, a known binder composition can also be used.

[0043] The resin composition may further contain other components other than the partially coated particles, the small-sized filler, and the insulating binder as needed. As other components, for example, solvents (methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, etc.), stress relaxants, silane coupling agents, etc. can be cited.

[0044] As described above, since the resin composition has a large-sized particle diameter of 2 μm or more, the small-sized filler has a particle diameter of 0.02 to 5.0% of the large-sized particle diameter, and the amount of the small-sized filler relative to the large-sized particles is less than 156% by volume, it has high dispersibility.

[0045] In addition, for example, when the resin composition functions as a gasket between the first component and the second component, since the amount of the small-sized filler attached to the large-sized particles is small, a gasket with an approximate diameter of the large-sized particles can be formed. In addition, for example, when the resin composition is made into an anisotropic conductive adhesive in which the large-sized particles are conductive particles and the small-sized filler is an insulating filler, since the amount of the insulating filler attached to the conductive particles is small, excellent conductivity can be obtained.

[0046] In addition, for example, when the resin composition is made into an anisotropic conductive film of an anisotropic conductive adhesive containing large-diameter particles as conductive particles and small-diameter fillers as insulating fillers, since the dispersibility of the conductive particles is very high, the number density (particles / mm 2 ) of the conductive particles in the entire anisotropic conductive film can be made to differ by 15% or less from the number density (particles / mm 2 ) of the conductive particles in a 0.2 mm × 0.2 mm region arbitrarily extracted from the anisotropic conductive film. Here, the difference in the number density is the difference between the maximum value and the minimum value of the number density of the conductive particles in a specified region arbitrarily extracted.

[0047] <Preparation Method of Resin Composition> The preparation method of the resin composition according to the present embodiment has the following steps (A) and (B).

[0048] [Step (A)] In step (A), the first coated particles are obtained by stirring large-diameter particles and small-diameter fillers having a particle size smaller than that of the large-diameter particles. In step (A), in order to suppress the aggregation of the second coated particles obtained in step (B), the large-diameter particles are coated with the small-diameter fillers. In addition, in step (A), as described above, the large-diameter particles and the small-diameter fillers are blended such that the amount of the small-diameter fillers relative to the large-diameter particles is less than 156% by volume. By satisfying the above-described conditions, it is easy to coat the surface of the large-diameter particles with the small-diameter fillers in step (A), and it is easy to separate the small-diameter fillers from the first coated particles in step (B).

[0049] The method for mixing large-diameter particles and small-particle-size fillers can be either a dry method or a wet method, with the dry method being preferred. The reason is that: the method used in known toners and the like can be applied. Examples of the device for mixing large-diameter particles and small-particle-size fillers include planetary stirring devices, vibrators, laboratory mixers, stirring paddles, etc. In particular, from the perspective of coating large-diameter particles with a relatively large average particle diameter with an insulating filler, a planetary stirring device that applies high shear is preferred. The use of media such as ball mills or sand mills is not excluded but not preferred either. The reason is that: if there are substances to be removed in addition to large-diameter particles and small-particle-size fillers, it is also undesirable in terms of productivity. In addition, if the above-mentioned media (balls or beads) are used, the factors affecting the surface state of large-diameter particles or small-particle-size fillers increase, making product design difficult. A planetary stirring device is a stirring device that rotates a container filled with materials (a mixture of large-diameter particles and small-particle-size fillers) while revolving. In the case of a batch method of production in each container, it is also preferred from the perspective of facilitating quality control. That is, it becomes easy to obtain a resin composition in which large-diameter particles and small-particle-size fillers are easily and highly accurately dispersed.

[0050] The large-diameter particles and small-particle-size fillers are the same as the preferred ranges of the large-diameter particles and small-particle-size fillers described in the above anisotropic conductive adhesive. In particular, from the perspective of coating large-diameter particles with small-particle-size fillers in step (A), it is preferred to use large-diameter particles in a dry powder state.

[0051] [Step (B)] In step (B), by mixing the first coated particles and the insulating binder, a resin composition in which the second coated particles and small-particle-size fillers detached from the large-diameter particles in the first coated particles are dispersed in the insulating binder is obtained.

[0052] In step (B), the first coated particles are stirred in an insulating binder, and friction or high shear is applied to the small-sized fillers in the first coated particles with respect to the large-sized particles, whereby the small-sized fillers are detached from the large-sized particles, and partially coated particles (second coated particles) are obtained in which a part of the surface of the large-sized particles is coated with the small-sized fillers. Further, since the small-sized fillers detached from the large-sized particles in the first coated particles are present between the second coated particles, aggregation of the second coated particles can be suppressed. As described above, by performing step (B), aggregation of the second coated particles can be suppressed, and the second coated particles can be dispersed in the insulating binder. At this time, the small-sized fillers are also dispersed. That is, in the present invention, the mixing step is completed with the minimum number of times. For example, as in the conventional case, in order to adjust the viscosity, the small-sized fillers may be added each time, but it can be easily anticipated that it is difficult to obtain reproducibility of the dispersed state. However, by previously adjusting the powder (large-sized particles and small-sized fillers) and blending the resin composition therein, the required amount can be adjusted, and thus it is also desirable from the viewpoints of material cost and production cost. Further, since it is also easy to compare batches having defects in dispersibility, it is also easy to analyze the nonconforming factors, and as described above, there are also advantages in terms of quality control. In addition, in the case of a batch system, there is an advantage that the number of factors to be studied becomes smaller when changing from small-scale development research to large-scale production. Further, for the same reason, from the viewpoints of productivity and quality control, it is also preferable to use the same container and the same planetary stirring device for step (A) and step (B). It is also possible to expect suppression of the influence of contaminants. In the case of mass production, it is only necessary to increase the same device. In other words, it is possible to adapt to small lot sizes and multiple varieties, and it is also possible to adapt to scale expansion. Therefore, it is also easy to adjust production management.

[0053] Further, as in the case of anisotropic conductive connection described later, when a conductive particle as a large-sized particle is held by a terminal, from the viewpoint of maintaining the quality of the surface state of the conductive particle, it is preferable to coat the surface of the large-sized filler with a sufficiently small small-sized filler. That is, it is possible to expect a function of protecting the irregularity of the surface state caused by contact between large-sized particles due to the presence of the coating with the small-sized filler. Further, since the degree of coating is released by mixing (kneading), if a direct force of holding between terminals is applied to the large-sized particles, it is difficult to consider that the partial coating hinders conduction. In addition, in terms of insulation between terminal arrangements, although the large-sized particles maintain high dispersibility, they also maintain partial coating, and thus it is considered that they are in a state where it is easy to avoid a short circuit (caused by connection of large-sized particles). If specific effects are exemplified, in the case where the large-sized particles are conductive particles of resin particles plated with metal, a wider range of choices can be expected for the thickness and material of the plated metal, the hardness of the resin particles, etc., as compared with the prior art. The same can be said for components used by holding them like gaskets.

[0054] The method of stirring the first coated particles and the insulating binder is not particularly limited, and the stirring method in the above-mentioned step (A) can be adopted. In particular, when stirring the first coated particles and the insulating binder, from the viewpoint of detaching the small-sized filler constituting the first coated particles, a stirring method with high shear is preferably applied, such as a stirring method using a planetary stirring device. It is considered that by using a planetary stirring device, in the insulating binder, by applying the friction or high shear between the large-diameter particles and the small-sized filler in the first coated particles, a moderate detachment of the small-sized filler from the large-diameter particles is generated in the first coated particles.

[0055] According to the preparation method having the above step (A) and step (B), a resin composition in which the second coated particles are dispersed in the insulating binder can be obtained by a simple method. It should be noted that this preparation method may further have other steps other than the above step (A) and step (B) as required. It should be noted that, as described above, from the viewpoints of productivity or quality, it is preferable to perform step (A) and step (B) using the same container and the same device (planetary stirring type mixing device).

[0056] <Structural body> The structural body according to this embodiment bonds the first member and the second member with the above resin composition. If the resin composition is a curable resin, it can be cured and fixed, and if it is a binder, it can only adhere. This is an example. For example, the resin composition can be filled in a mold and cured to obtain a molded body. For example, when the resin composition functions as a gasket between the first member and the second member, since the amount of the small-sized filler attached to the large-diameter particles is small, a gasket with an approximate diameter of the large-diameter particles can be formed. In addition, for example, when the resin composition is made into a conductive adhesive in which the large-diameter particles are conductive particles and the small-sized filler is an insulating filler, since the amount of the insulating filler attached to the conductive particles is small, excellent conductivity can be obtained. When an anisotropic conductive adhesive is formed, since the relationship between the terminals and the terminal arrangement functions more complexly, its effect can be further exerted. It should be noted that they can be pre-formed into a thin film body.

[0057] It should be noted that the present invention also includes a structure in which a first article and a second article are connected with a resin composition as an adhesive or an adhesive film, and a method for producing the same. These articles may be electronic components, or have conductivity with a conduction portion (anisotropy is not necessary), but are not limited thereto. In addition, regardless of whether the resin composition has adhesiveness, the present invention also includes a structure obtained by bonding a first article and a second article, and a bonding method thereof. In other words, the present invention is a bonded body of a first article and a second article, or a bonding method for pressing them. In addition, a structure in which only a resin composition or a thin film body thereof is provided on the first article is also included in the present invention. It only needs to be coated on the first article or laminated as a thin film body. If the resin composition is an adhesive, an adhesive layer is formed. An adhesive film can also be formed by forming it on a support.

[0058] Hereinafter, a second embodiment will be described.

[0059] [Second Embodiment] <Anisotropic Conductive Adhesive> The anisotropic conductive adhesive according to the present embodiment contains coated conductive particles (second coated conductive particles described later) in which a part of the surface of conductive particles is coated with an insulating filler, an insulating filler, and an insulating binder, and disperses the coated conductive particles in the insulating binder. It should be noted that in the following description, the coated conductive particles obtained by stirring conductive particles having an average particle diameter of 7 μm or more and an insulating filler are referred to as "first coated conductive particles". In addition, the coated conductive particles in which a part of the surface of the first coated conductive particles is coated with an insulating filler obtained by stirring the first coated conductive particles and an insulating binder are referred to as "second coated conductive particles".

[0060] The anisotropic conductive adhesive can be either a film-like anisotropic conductive film (ACF: Anisotropic Conductive Film) or a paste-like anisotropic conductive paste (ACP: Anisotropic Conductive Paste). The anisotropic conductive film is preferred from the viewpoint of easy handling, and the anisotropic conductive paste is preferred in terms of cost.

[0061] Hereinafter, the second coated conductive particles (conductive particles, insulating filler), insulating binder, and other components that can be further contained, which constitute the anisotropic conductive adhesive, will be described.

[0062] [Conductive Particles] There is no particular limitation on the material of the conductive particles. For example, metal particles such as nickel, copper, gold, silver, and palladium, resin particles coated with metal on the surface of resin particles, etc. can be cited. As the resin particles in the resin particles coated with metal, for example, particles of epoxy resin, phenolic resin, acrylic resin, acrylonitrile-styrene resin, benzoguanamine resin, divinylbenzene-based resin, and styrene-based resin can be used. The conductive particles can be used alone or in combination of two or more.

[0063] The particle size of the conductive particles is 7 μm or more. In addition, there is no particular limitation on the upper limit of the particle size of the conductive particles, but from the viewpoint of the capture efficiency of the conductive particles in the connection structure, it is preferably 50 μm or less, for example. The particle size of the conductive particles can be measured using an image-based particle size distribution analyzer (as an example, FPIA-3000: manufactured by Malvern). It is desired to measure 1000 or more, preferably 2000 or more, and obtain the result.

[0064] [Insulating filler] Insulating inorganic particles can be used as the insulating filler. For example, oxides such as titanium oxide, aluminum oxide, silicon dioxide, calcium oxide, and magnesium oxide, hydroxides such as calcium hydroxide, magnesium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, magnesium carbonate, zinc carbonate, and barium carbonate, sulfates such as calcium sulfate and barium sulfate, silicates such as calcium silicate, nitrides such as aluminum nitride, boron nitride, and silicon nitride, etc. can be cited. The insulating filler can be used alone or in combination of two or more.

[0065] Regarding the relationship between the size (particle size) of the conductive particles and the insulating filler, since the surface area of the insulating filler relative to the conductive particles is very small, it is easy to coat and separate the insulating filler from the surface of the conductive particles. Thus, if the first-coated conductive particles are stirred in the insulating binder, the insulating filler separated from the conductive particles in the first-coated conductive particles exists between the second-coated conductive particles, so the aggregation of the second-coated conductive particles can be suppressed. Therefore, the second-coated conductive particles can be uniformly dispersed in the insulating binder.

[0066] Specifically, the upper limit of the particle size of the insulating filler is preferably 1000 nm or less, more preferably 50 nm or less. Since the surface area of the insulating filler relative to the conductive particles is not too large, defects such as damage to the surface of the conductive particles can be suppressed. In addition, the lower limit of the particle size of the insulating filler is preferably 10 nm or more. Since the surface area of the insulating filler relative to the conductive particles is not too small, the aggregation of the conductive particles can be more effectively suppressed. The particle size of the insulating filler can be obtained based on the observation results of an electron microscope or the like.

[0067] Based on the relationship between the sizes of the conductive particles and the insulating filler described above, the particle size ratio of the insulating filler to the conductive particles (particle size of the insulating filler / particle size of the conductive particles) is 0.02 to 0.143%, preferably 0.02 to 0.10%.

[0068] In addition, the number ratio of the insulating filler satisfying the above particle size ratio to the conductive particles, that is, the amount of the insulating filler relative to 1 conductive particle is 0.78 to 77% by volume, preferably 3.9 to 38.7% by volume, and more preferably 7.7 to 15.5% by volume. By satisfying the conditions as described above, good dispersibility of the conductive particles can be achieved.

[0069] [Insulating Binder] As the insulating binder (insulating resin), the insulating binder used in known anisotropic conductive adhesives can be used. As the curable type, a thermosetting type, a photocurable type, a combination of light and heat curable type, etc. can be cited. For example, a photo radical polymerization type resin containing a (meth)acrylate compound and a photo radical polymerization initiator, a thermo radical polymerization type resin containing a (meth)acrylate compound and a thermo radical polymerization initiator, a thermo cationic polymerization type resin containing an epoxy compound and a thermo cationic polymerization initiator, a thermo anionic polymerization type resin containing an epoxy compound and a thermo anionic polymerization initiator, etc. can be cited.

[0070] Hereinafter, as a specific example, a thermo anionic polymerization type insulating binder containing a film-forming resin, an epoxy resin, and a latent curing agent will be described.

[0071] The film-forming resin is preferably a resin having an average molecular weight of about 10,000 to 80,000. As the film-forming resin, various resins such as epoxy resins, modified epoxy resins, polyurethane resins, and phenoxy resins can be cited. Among these, from the viewpoints of film-forming state, connection reliability, etc., phenoxy resin is preferred. The film-forming resin can be used alone or in combination of two or more.

[0072] As the epoxy resin, there is no particular limitation, and for example, naphthalene type epoxy resin, biphenyl type epoxy resin, phenolic resin type epoxy resin, bisphenol type epoxy resin, stilbene type epoxy resin, triphenylmethane type epoxy resin, phenol aralkyl type epoxy resin, naphthol type epoxy resin, dicyclopentadiene type epoxy resin, triphenylmethane type epoxy resin, etc. can be cited. The epoxy resin can be used alone or in combination of two or more.

[0073] As latent curing agents, for example, imidazole-based, hydrazide-based, aminated imides, dicyandiamide, or acid generators such as antimony-based, phosphorus-based, and fluorine-based ones can be cited. They can be used alone or in combination of two or more. Among these, it is suitable to use microcapsule-type curing agents in which the surface of imidazole compound particles is coated with a polymer curing product such as a polyurethane-based or polyester-based one. In addition, a masterbatch-type curing agent in which the microcapsule-type curing agent is dispersed in a liquid epoxy resin can also be used.

[0074] [Other components] The anisotropic conductive adhesive may further contain other components in addition to the second coated conductive particles and the insulating binder as needed. As other components, for example, solvents (methyl ethyl ketone, toluene, propylene glycol monomethyl ether acetate, etc.), stress relaxants, silane coupling agents, etc. can be cited. In addition, the anisotropic conductive adhesive may further contain an insulating filler detached from the conductive particles in the first coated conductive particles.

[0075] As described above, the particle diameter of the conductive particles of the anisotropic conductive adhesive is 7 μm or more, the particle diameter of the insulating filler is 0.02 to 0.143% of the particle diameter of the conductive particles, and the amount of the insulating filler relative to the conductive particles is 0.78 to 77% by volume. When the first coated conductive particles are stirred in the insulating binder, the conductive particles in the first coated conductive particles are detached. Therefore, there are cases where the second coated conductive particles with the coated insulating filler remaining on the particle surface are obtained, and the above-described remaining state can be confirmed by a known observation method (electron microscopes such as SEM or TEM). Whether the adhesive is obtained by the method of the present invention can be confirmed based on the remaining state of the insulating filler and the dispersion state of the conductive particles as described above.

[0076] Since the insulating filler detached from the conductive particles in the first coated conductive particles exists between the second coated conductive particles, the anisotropic conductive adhesive can suppress the aggregation of the second coated conductive particles. Therefore, the second coated conductive particles can be dispersed in the insulating binder, and short circuits between the electrode terminals of the electronic components can be suppressed. In addition, in the anisotropic conductive adhesive, the insulating filler detached from the conductive particles in the first coated conductive particles due to the stirring of the first coated conductive particles and the insulating binder uniformly exists in a constant ratio near the second coated conductive particles. In the anisotropic conductive adhesive as described above, the dispersion state of the second coated conductive particles shows a high correlation with the region where the insulating filler exists, and the conductive particle capture rate can be stabilized.

[0077] In addition, in the present technology, by simply coating an insulating filler on relatively large conductive particles of 7 μm or more and causing it to separate when kneaded into an insulating binder, an effect of sufficiently suppressing short circuits can be obtained even without previously performing an insulation treatment on the surface (conductive layer) of the conductive particles. That is, there are no traces of insulation treatment on the conductive layer of the conductive particles other than the insulating filler that remains in a small amount without separating. Therefore, the processability of the conductive particles is excellent, and it is also advantageous in terms of cost. In the design of the anisotropic conductive adhesive, since the parameters are fewer, there is also an advantage in development. It should be noted that by using conductive particles that have been previously subjected to an insulation treatment by a known method, the performance can also be improved or the design freedom can be increased by using conductive particles with more excellent insulation properties. Therefore, the present technology does not exclude the method of using conductive particles whose surfaces (conductive layers) have been previously subjected to an insulation treatment.

[0078] <Preparation method of anisotropic conductive adhesive> The preparation method of the anisotropic conductive adhesive according to the present embodiment has the following processes (A) and (B).

[0079] [Process (A)] In process (A), the first coated conductive particles are obtained by stirring conductive particles having an average particle diameter of 7 μm or more and an insulating filler having a particle diameter of 0.02 to 0.143% of the particle diameter of the conductive particles. In process (A), in order to suppress the aggregation of the second coated conductive particles obtained in process (B), the conductive particles are coated with the insulating filler. In addition, in process (A), as described above, the conductive particles and the insulating filler are blended so that the amount of the insulating filler relative to the conductive particles is 0.78 to 77% by volume. By satisfying the above conditions, it is easy to coat the insulating filler on the surface of the conductive particles in process (A), and it is easy to separate the insulating filler in the first coated conductive particles in process (B).

[0080] The method of stirring the conductive particles and the insulating filler can be either a dry method or a wet method, and the dry method is preferred. Examples of the device for stirring the conductive particles and the insulating filler include a planetary stirring device, a vibrator, a laboratory mixer, a stirring paddle, etc. In particular, from the viewpoint of coating conductive particles with a relatively large average particle diameter with an insulating filler, a planetary stirring device that applies high shear is preferred. A planetary stirring device is a stirring device in which a container containing materials (a mixture of conductive particles and an insulating filler) rotates while revolving.

[0081] The conductive particles and the insulating filler are the same as the preferred ranges of the conductive particles and the insulating filler described in the above anisotropic conductive adhesive. In particular, from the viewpoint of coating the conductive particles with the insulating filler in step (A), it is preferable to use conductive particles in a dry powder state.

[0082] [Step (B)] In step (B), by stirring the first coated conductive particles and the insulating binder, an anisotropic conductive adhesive in which the second coated conductive particles and the insulating filler detached from the conductive particles in the first coated conductive particles are dispersed in the insulating binder is obtained.

[0083] In step (B), by stirring the first coated conductive particles in the insulating binder, friction or high shear is applied to the insulating filler in the first coated conductive particles with respect to the conductive particles, whereby the insulating filler detaches from the conductive particles, and a coated conductive particle (second coated conductive particle) in which a part of the surface of the conductive particles is coated with the insulating filler is obtained. In addition, since the insulating filler detached from the conductive particles in the first coated conductive particles exists between the second coated conductive particles, aggregation of the second coated conductive particles can be suppressed. As described above, by performing step (B), aggregation of the second coated conductive particles can be suppressed, and the second coated conductive particles can be dispersed in the insulating binder.

[0084] The method of stirring the first coated conductive particles and the insulating binder is not particularly limited, and the stirring method in the above step (A) can be adopted. In particular, when stirring the first coated conductive particles and the insulating binder, from the viewpoint of detaching the insulating filler constituting the first coated conductive particles, a stirring method applying high shear, for example, a stirring method using a planetary stirring device, is preferable. By using a planetary stirring device, friction or high shear is applied between the conductive particles and the insulating filler in the first coated conductive particles, whereby detachment of the insulating filler from the conductive particles sometimes occurs in the first coated conductive particles.

[0085] According to the production method having the above step (A) and step (B), an anisotropic conductive adhesive in which the second coated conductive particles are dispersed in the insulating binder is obtained by a simple method. By using this anisotropic conductive adhesive, short circuits between electrode terminals of electronic components can be suppressed. It should be noted that if steps (A) and (B) are carried out in the same container and the same device (planetary stirring type mixing device), it is preferable both from the viewpoint of the man-hours in production and from the viewpoint of quality control for preventing contamination.

[0086] It should be noted that this production method may further have other steps other than the above step (A) and step (B) as needed.

[0087] <Anisotropic Conductive Film> The anisotropic conductive film according to this embodiment contains the above-described anisotropic conductive adhesive, and the above-described second coated conductive particles are dispersed in the adhesive layer containing the insulating binder. For example, the number density (number / mm 2 ) of the second coated conductive particles in the entire anisotropic conductive film (e.g., 1.0 mm × 1.0 mm) and the number density (number / mm 2 ) of the second coated conductive particles in a narrow area (e.g., 0.2 mm × 0.2 mm) arbitrarily extracted from the anisotropic conductive film are preferably 15% or less, more preferably 10% or less, and further more preferably substantially the same (as an example, within 5%). In addition, when used in the form of an anisotropic conductive paste for connection, as an example, it is preferable to obtain the same dispersibility as described above. This can be confirmed by forming a layer on a smooth surface such as a support.

[0088] As described above, since the difference between the number density of the second coated conductive particles in the entire anisotropic conductive film and the number density of the second coated conductive particles in an arbitrarily extracted narrow area of the anisotropic conductive film is small, it can be confirmed that the second coated conductive particles are uniformly dispersed throughout the film. Therefore, the conductive particle capture rate is stable, and conduction failure or short circuit can be suppressed. When the second coated conductive particles are uniformly dispersed throughout the film, there is an effect that the man-hour for the quality inspection of the anisotropic conductive film itself can also be reduced. The reason is that in the case of uniform dispersion, it becomes easy to detect irregular aggregation. Therefore, the effect is further exerted especially when the length is 10 m or more. In addition, if the anisotropic conductive film has a length of 10 m or more, preferably 50 m or more, the connection is continuously performed, so there is also an effect of reducing the cost of the manufacturing method of the connection structure. There is no particular upper limit for the length, and from the viewpoint of minimizing the improvement of the connection device or handling, it is preferably 5000 m or less, more preferably 1000 m or less, and further more preferably 600 m or less.

[0089] In addition, as shown in the present invention, in the case of a relatively large particle size with a conductive particle diameter of 7 μm or more, it is suitable for connecting an electronic component to be connected to a material whose surface is not as smooth as glass, such as a ceramic substrate (a material having irregularities on the surface). In addition, as described above, by uniformly dispersing relatively large conductive particles, even if the electronic component to be connected has irregularities, it is difficult to be affected by capture due to the flow of the resin during connection. The reason is that in the case of conductive particle aggregation, since the terminal surface for capturing the conductive particles through the irregularities is not constant, there is a risk that the capture state for each terminal is no longer maintained constant.

[0090] The particle density of the second coated conductive particles in the anisotropic conductive film is not particularly limited as long as it can coexist conduction reliability and short-circuit suppression. As an example, if it is too small, it becomes difficult to satisfy the conduction reliability. Therefore, it is preferably 20 particles / mm 2 or more, more preferably 100 particles / mm 2 or more. In addition, as an upper limit, if it is too large, the risk of short circuit increases. Therefore, as an example, it is preferably 3000 particles / mm 2 or less, more preferably 2000 particles / mm 2 or less, and even more preferably 1000 particles / mm 2 or less. They can be appropriately adjusted as long as they are connected to the terminal size of the conductive particle diameter. In addition, in the case of using an anisotropic conductive paste, as an example, it is also preferably the same as above. This can be confirmed by forming a layer on a smooth surface such as a support.

[0091] The upper limit of the area occupancy rate of the second coated conductive particles in the anisotropic conductive film in a plan view is preferably 80% or less, more preferably 75% or less, and even more preferably 70% or less. The reason for achieving the high area occupancy rate as described above is that although it also depends on the ratio of the thickness and particle diameter of the anisotropic conductive film, high uniformity is maintained even though the second coated conductive particles are mixed in the insulating resin. Even with the high area occupancy rate as described above, the risk of short circuit can be avoided, which can be said to be one of the features of the present invention. In addition, in the case of using it in the form of an anisotropic conductive paste for connection, as an example, it is preferably to obtain the same dispersibility as above. This can be confirmed by forming a layer on a smooth surface such as a support.

[0092] In addition, although the lower limit of the area occupancy rate of the second coated conductive particles in the anisotropic conductive film in a plan view also depends on the ratio of the thickness and particle diameter of the anisotropic conductive film, as an example, if it is larger than 0.2%, the minimum conduction performance can be ensured. In practical terms, it is preferably larger than 5%, and more preferably larger than 10%. In addition, in the case of using an anisotropic conductive paste, as an example, it is also preferably the same as above. This can be confirmed by forming a layer on a smooth surface such as a support.

[0093] The area occupancy ratio of the second coated conductive particles in the anisotropic conductive film can be calculated based on observations using an optical microscope, a metal microscope, or an electron microscope such as SEM. It can be measured using known image analysis software (as an example, WinROOF (Mitsutani Shoko Co., Ltd.) can be cited). In addition, the calculation area of the area occupancy ratio can be the same as an example of the area for obtaining the number density, or can be obtained using a larger area (for example, 2 mm × 2 mm or 5 mm × 5 mm). In addition, when used in the form of an anisotropic conductive paste for connection, as an example, it is preferable to obtain the same dispersibility as described above. This can be confirmed by forming a layer on a smooth surface such as a support.

[0094] As a method for forming the anisotropic conductive film, for example, a method of forming and drying an anisotropic conductive adhesive using a coating method can be cited. The thickness of the anisotropic conductive film, for example, the lower limit can be the same as the particle size, and preferably can be set to 1.3 times or more the particle size or 10 μm or more. For example, the upper limit can be set to 40 μm or less or 2 times or less the particle size. In addition, the anisotropic conductive film can be formed on a release film.

[0095] <Connection structure> The connection structure according to the present embodiment connects the first electronic component and the second electronic component through the above-described anisotropic conductive film. For example, as Figure 1 shown, the connection structure 1 connects the first electronic component 5 having the first terminal row 4 including a plurality of terminals 4a and the second electronic component 7 opposite to the first terminal row 4 and having the second terminal row 6 including a plurality of terminals 6a through the conductive particles (second coated conductive particles) 3 in the anisotropic conductive film 2.

[0096] There are no special restrictions on the first electronic component and the second electronic component, and they can be appropriately selected according to the purpose. As the first electronic component, for example, a flexible substrate (FPC: Flexible Printed Circuits), a transparent substrate, etc. can be cited. If the transparent substrate is a substrate with high transparency, there are no special limitations, and a glass substrate, a plastic substrate, etc. can be cited. In addition, as the second electronic component, for example, a camera module, an IC (Integrated Circuit) module, an IC chip, etc. can be cited. The second electronic component can be a functional module equipped with a sensor. In a camera module, from the viewpoint of excellent electrical insulation and thermal insulation, a ceramic substrate is sometimes used. The ceramic substrate or the functional module has advantages such as excellent dimensional stability under miniaturization (for example, 1 cm 2 or less).

[0097] <Preparation method of connection structure> The manufacturing method of the connection structure according to this embodiment includes pressing the first electronic component 5 having the first terminal row 4 and the second electronic component 7 having the second terminal row 6 opposite to the first terminal row 4 through the above-mentioned anisotropic conductive film. Thus, the first terminal row 4 and the second terminal row 6 can be connected by the conductive particles 3.

[0098] The first electronic component 5 and the second electronic component 7 are the same as the first electronic component 5 and the second electronic component 7 in the above-mentioned connection structure. In addition, the anisotropic conductive adhesive is also the same as the above-mentioned anisotropic conductive adhesive. Example

[0099] Hereinafter, a first embodiment of the present technology will be described.

[0100] [Experimental Example 1] [Production of Anisotropic Conductive Adhesive (Resin Composition)] 1 g of conductive particles with an average particle size of 3 μm (large-diameter particles, Ni-plated (thickness: 115 nm), resin core, specific gravity: 3.44 g / cm 3 ) and 0.5 g (78.2 vol% relative to the conductive particles) of silica filler with an average particle size of 10 nm as an insulating filler (small-particle-size filler, product name: YA010C, specific gravity: 2.2 g / cm 3 ) were put into a planetary stirring device (product name: THINKYMIXER, manufactured by THINKY Corporation) and stirred for 5 minutes to produce a mixture of conductive particles and insulating filler.

[0101] Regarding the number ratio of the insulating filler, it was evaluated according to any one of "appropriate amount", "excess", and "insufficient amount". Specifically, the case where the number ratio of the silica filler to the conductive particles, that is, the amount of the silica filler relative to the conductive particles, was in the range of more than 1.56 vol% and less than 156 vol% was evaluated as "appropriate amount". In addition, the case where the amount of the silica filler relative to the conductive particles exceeded 156 vol% was evaluated as "excess". Furthermore, the case where the amount of the silica filler relative to the conductive particles was less than 1.56 vol% was evaluated as "insufficient amount".

[0102] The mixture of conductive particles and insulating filler and an insulating binder containing the following various components were put into a planetary stirring device (product name: THINKYMIXER, manufactured by THINKY Corporation) and stirred for 1 minute to produce an anisotropic conductive adhesive.

[0103] The insulating binder uses a binder obtained by diluting, adjusting, and mixing 20 g of epoxy resin (EP828: manufactured by Mitsubishi Chemical Corporation), 30 g of phenoxy resin (YP-50: manufactured by Nippon Steel & Sumitomo Metal Chemicals Co., Ltd.), and 50 g of a curing agent (Novacure 3941HP, manufactured by Asahi Kasei Corporation) with toluene.

[0104] [Fabrication of Anisotropic Conductive Film (Film Body)] The anisotropic conductive adhesive is coated on a PET film and dried in an oven at 80°C for 5 minutes to form an adhesive layer containing the anisotropic conductive adhesive on the PET film. Thus, an anisotropic conductive film with a thickness of 12 μm (4 times the particle diameter of the large-diameter particles) is obtained. It should be noted that the adjustment is made according to the number density of conductive particles in the anisotropic conductive film being approximately 5000 particles / mm 2 .

[0105] [Experimental Example 2] An anisotropic conductive film is fabricated in the same manner as in Experimental Example 1, except that the blending amount of the insulating filler is changed to 0.15 g (23.5 vol% with respect to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation is performed.

[0106] [Experimental Example 3] An anisotropic conductive film is fabricated in the same manner as in Experimental Example 1, except that the blending amount of the insulating filler is changed to 0.05 g (7.8 vol% with respect to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation is performed.

[0107] [Experimental Example 4] An anisotropic conductive film is fabricated in the same manner as in Experimental Example 1, except that the insulating filler is not blended to fabricate the anisotropic conductive adhesive, and evaluation is performed.

[0108] [Experimental Example 5] An anisotropic conductive film is fabricated in the same manner as in Experimental Example 1, except that the blending amount of the insulating filler is changed to 1 g (156 vol% with respect to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation is performed.

[0109] [Experimental Example 6] An anisotropic conductive film is fabricated in the same manner as in Experimental Example 1, except that the blending amount of the insulating filler is changed to 0.01 g (1.56 vol% with respect to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation is performed.

[0110] [Presence or Absence of Insulating Filler] The cross-section of the conductive particles in the anisotropic conductive film was observed with a scanning electron microscope to confirm whether an insulating filler was attached to the surface of the conductive particles. The case where the insulating filler was attached to the surface of the conductive particles was evaluated as "yes", and the case where it was not attached was evaluated as "no". The results are shown in Table 1.

[0111] [Difference in number density of conductive particles] Evaluate the number density (number / mm 2 ) of the conductive particles in the entire anisotropic conductive film (1.0 mm × 1.0 mm) and the difference from the number density (number / mm 2 ) of the conductive particles in a 0.2 mm × 0.2 mm area randomly extracted from 10 parts of the anisotropic conductive film. The evaluation criteria are shown below. A or B is preferred. The results are shown in Table 1. It should be noted that the difference in number density is the difference between the maximum and minimum values of the number density of the conductive particles in the specified area randomly extracted.

[0112] A: The number density difference is 10% or less B: The number density difference is greater than 10 and 15% or less C: The number density difference exceeds 15% (greater than 15%) [Fabrication of connection structure] Using the fabricated anisotropic conductive film, a flexible substrate (copper wiring: line / space (L / S) = 25 μm / 25 μm, terminal height: 8 μm, polyimide thickness: 25 μm) and an ITO solid glass (solid glass) (thickness: 0.7 mm) were heated and pressed (180 °C, 2 MPa, 20 s) with a heating and pressing component to obtain a connection structure.

[0113] [Initial resistance value] Using a digital multimeter (manufactured by Yokogawa Electric Corporation), the conduction resistance value of the connection structure when a current of 1 mA flows through it was measured by the four-terminal method. The evaluation that the conduction resistance value of the connection structure is less than 2.0 Ω was recorded as "OK", and the evaluation that the conduction resistance value is 2.0 Ω or more was recorded as "NG". In Experimental Examples 1 to 3, all were OK.

[0114] [Resistance value after connection reliability test] After the connection structure was placed in an atmosphere of 60 °C and a relative humidity of 95% for 1000 hours, the conduction resistance value of the connection structure was measured by the same method as the initial resistance value. The evaluation criterion was that the evaluation that it was less than 5.0 Ω was recorded as "OK", and the evaluation that the conduction resistance value was 5.0 Ω or more was recorded as "NG". In Experimental Examples 1 to 3, all were OK.

[0115] [Number of conductive particles captured] For the connection structure samples, confirm that a sufficient number of conductive particles are captured by the opposing terminals in Experimental Examples 1 to 3. Additionally, when comparing the replenishment states between Experimental Examples 1 to 3 and Experimental Examples 4 to 6, Experimental Examples 1 to 3 show a tendency for the capture numbers of each bump to be uniform.

[0116] [Short circuit] Fabricate the same connection structure as the sample used in the evaluation of the initial resistance value, and evaluate whether a short circuit occurs between adjacent terminals. When the short circuit incidence rate is 50 ppm or less, the evaluation is counted as "OK", and when the short circuit incidence rate exceeds 50 ppm, the evaluation is counted as "NG". In Experimental Examples 1 to 3, all are OK.

[0117] [Table 1] In Experimental Examples 1 to 3, it is known that by setting the amount of the insulating filler having a particle size of 0.02% or more and 5.0% or less of the particle size of the conductive particles with respect to the amount of the conductive particles to be more than 1.56 vol% and less than 156 vol%, and stirring the conductive particles and the insulating filler, the difference in the number density of the conductive particles (second-coated conductive particles) in the anisotropic conductive film can be reduced. In particular, from Experimental Examples 1 to 3, it is known that if it is set to 7.8 to 78.2 vol%, a good state is obtained. That is, it is known that the dispersibility of the conductive particles is good.

[0118] In Experimental Examples 1 to 3, when observing the SEM image of the conductive particles in the film cross section, the coating state of the insulating filler can be confirmed. It should be noted that in the second-coated conductive particles in the insulating binder obtained as described above, there is a case where a part of the coating of the insulating filler remains. The remaining coating of the insulating filler on the surface of the conductive particles can be confirmed by observing the second-coated conductive particles according to Experimental Examples 1 to 3 using an electron microscope (SEM).

[0119] Additionally, in Experimental Examples 1 to 3, it is known that a short circuit between the electrode terminals of the electronic component can be suppressed. Furthermore, in Experimental Examples 1 to 3, it is known that the conductive particle capture rate is good, and the evaluations of the initial resistance value and the resistance value after the reliability test are also good. It should be noted that in Experimental Examples 1 and 2, in particular, it is known that the dispersibility of the conductive particles is better.

[0120] In Experimental Example 4 in which an insulating filler having a particle size of 0.02 to 5.0% of the particle size of the conductive particles was not blended, it was found that the difference in the number density of the conductive particles could not be reduced. That is, in Experimental Example 4, it was found that the dispersibility of the conductive particles was poor. In addition, in Experimental Example 4, it was found that the short circuit between the electrode terminals of the electronic component could not be suppressed and the capture rate of the conductive particles was poor. In addition, in Experimental Example 4, it was found that when compared with Examples 1 to 3, the evaluation of the initial resistance value and the resistance value after the reliability test was poor.

[0121] In Experimental Example 5 in which an insulating filler having a particle size of 0.02 to 0.5% of the particle size of the conductive particles was 156% by volume relative to the amount of the conductive particles, it was found that the difference in the number density of the conductive particles could not be reduced. That is, in Experimental Example 5, it was found that since the number ratio of the insulating filler having a particle size of 0.02 to 0.5% of the particle size of the conductive particles was excessive, the dispersibility of the conductive particles was poor. In addition, in Experimental Example 5, it was found that the short circuit between the electrode terminals of the electronic component could not be suppressed and the capture rate of the conductive particles was poor. In addition, in Experimental Example 5, it was found that when compared with Examples 1 to 3, the evaluation of the initial resistance value and the resistance value after the reliability test was poor.

[0122] In Experimental Example 6 in which an insulating filler having a particle size of 0.02 to 0.5% of the particle size of the conductive particles was 1.57% by volume relative to the amount of the conductive particles, it was found that the difference in the number density of the conductive particles could not be reduced. That is, in Experimental Example 6, it was found that since the number ratio of the insulating filler having a particle size of 0.02 to 0.5% of the particle size of the conductive particles was insufficient, the dispersibility of the conductive particles was poor. In addition, in Experimental Example 6, it was found that when compared with Examples 1 to 3, the short circuit between the electrode terminals of the electronic component could not be suppressed and the capture rate of the conductive particles was poor.

[0123] Hereinafter, a second embodiment of the present technology will be described.

[0124] [Example 1] [Production of Anisotropic Conductive Adhesive] 1 g of conductive particles having an average particle size of 20 μm (Au plating (outer layer, thickness 34 nm) / Ni plating (inner layer, thickness 200 nm), resin core, specific gravity 1.4 g / cm 3 ) and 0.5 g (38.7% by volume relative to the conductive particles) of silica filler having an average particle size of 10 nm as an insulating filler (product name: YA010C, specific gravity 2.2 g / cm 3 ) were put into a planetary stirring device (product name: THINKYMIXER, manufactured by THINKY Corporation) and stirred for 5 minutes to produce a mixture of conductive particles and an insulating filler.

[0125] Regarding the number ratio of the insulating filler, it is evaluated according to any one of "appropriate amount", "excess", and "insufficient amount". Specifically, the case where the number ratio of the silica filler to the conductive particles, that is, the amount of the silica filler relative to the conductive particles, is in the range of 0.78 to 77% by volume is evaluated as "appropriate amount". In addition, the case where the amount of the silica filler relative to the conductive particles exceeds 77% by volume is evaluated as "excess". Furthermore, the case where the amount of the silica filler relative to the conductive particles is less than 0.78% by volume is evaluated as "insufficient amount".

[0126] The mixture of the conductive particles and the insulating filler and the insulating binder containing the following various components are put into a planetary stirring device (product name: THINKYMIXER, manufactured by THINKY Corporation), and stirred for 1 minute to produce an anisotropic conductive adhesive.

[0127] As the insulating binder, a binder obtained by diluting and mixing 20 g of epoxy resin (EP828: manufactured by Mitsubishi Chemical Corporation), 30 g of phenoxy resin (YP-50: manufactured by Nippon Steel & Sumikin Chemical Co., Ltd.), and 50 g of curing agent (Novacure 3941HP, manufactured by Asahi Kasei Corporation) with toluene is used.

[0128] [Fabrication of Anisotropic Conductive Film] The anisotropic conductive adhesive is coated on a PET film and dried in an oven at 80°C for 5 minutes to form an adhesive layer containing the anisotropic conductive adhesive on the PET film. Thus, an anisotropic conductive film with a thickness of 25 μm is obtained. It should be noted that the number density of the conductive particles in the anisotropic conductive film is adjusted to be about 300 particles / mm 2 for adjustment.

[0129] [Presence or Absence of Insulating Filler] The cross-section of the conductive particles in the anisotropic conductive film is observed with a scanning electron microscope to confirm whether an insulating filler is attached to the surface of the conductive particles. The case where the insulating filler is attached to the surface of the conductive particles is evaluated as "present", and the case where it is not attached is evaluated as "absent". The results are shown in Table 2.

[0130] [Difference in Number Density of Conductive Particles] The number density (particles / mm 2 ) of the conductive particles in the entire anisotropic conductive film (1.0 mm × 1.0 mm) and the number density (particles / mm 2) The difference is as follows. The evaluation criteria are shown below. A or B is preferred. Note that the difference in number density is the difference between the maximum and minimum number densities of the conductive particles in a randomly extracted specified area. The results are shown in Table 2.

[0131] A: The difference in number density is 10% or less B: The difference in number density is greater than 10 and 15% or less C: The difference in number density exceeds 15% (greater than 15%) [Fabrication of the connection structure] Using the fabricated anisotropic conductive film, a flexible substrate (copper wiring: line / space (L / S) = 100 μm / 100 μm, terminal height: 12 μm, polyimide thickness: 25 μm) and an alumina ceramic substrate (gold / tungsten wiring: line / space (L / S) = 100 μm / 100 μm, wiring height: 10 μm, substrate thickness: 0.4 mm) are heated and pressed (180 °C, 1 MPa, 20 s) by a heating and pressing member to obtain a connection structure.

[0132] [Initial resistance value] Using a digital multimeter (manufactured by Yokogawa Electric Corporation), the conduction resistance value of the connection structure when a current of 1 mA flows is measured by the four-terminal method. An evaluation of "OK" is given when the conduction resistance value of the connection structure is less than 1.0 Ω, and an evaluation of "NG" is given when the conduction resistance value is 1.0 Ω or more. The results are shown in Table 2.

[0133] [Resistance value after the connection reliability test] After the connection structure is placed in an atmosphere of 60 °C and a relative humidity of 95% for 1000 hours, the conduction resistance value of the connection structure is measured by the same method as the initial resistance value. The evaluation criteria are the same as those for the initial resistance value. The results are shown in Table 2.

[0134] [Number of conductive particles captured] For the connection structure sample, the number of conductive particles captured by the opposing terminals is calculated, and the average value of the number of conductive particles captured is obtained based on a total of 150 terminals. The average value is evaluated according to the following criteria. The evaluation criteria are shown below. A or B is preferred. The results are shown in Table 2.

[0135] A: 5 or more B: 3 - 4 C: Less than 2 [Short circuit] Fabricate a connection structure identical to the sample used in the evaluation of the initial resistance value, and evaluate whether there is a short circuit between adjacent terminals. When the short circuit incidence rate is 50 ppm or less, the evaluation is recorded as "OK", and when the short circuit incidence rate exceeds 50 ppm, the evaluation is recorded as "NG". The results are shown in Table 2.

[0136] [Example 2] An anisotropic conductive film was fabricated in the same manner as in Example 1, except that the blending amount of the insulating filler was changed to 0.15 g (11.6% by volume relative to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation was performed.

[0137] [Example 3] An anisotropic conductive film was fabricated in the same manner as in Example 1, except that the blending amount of the insulating filler was changed to 0.05 g (3.9% by volume relative to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation was performed.

[0138] [Comparative Example 1] An anisotropic conductive film was fabricated in the same manner as in Example 1, except that the anisotropic conductive adhesive was fabricated without blending an insulating filler, and evaluation was performed.

[0139] [Comparative Example 2] An anisotropic conductive film was fabricated in the same manner as in Example 1, except that the blending amount of the insulating filler was changed to 1.0 g (77.3% by volume relative to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation was performed.

[0140] [Comparative Example 2] An anisotropic conductive film was fabricated in the same manner as in Example 1, except that the blending amount of the insulating filler was changed to 0.01 g (0.77% by volume relative to the conductive particles) to fabricate the anisotropic conductive adhesive, and evaluation was performed.

[0141] [Table 2] In the embodiments, it is known that by setting the amount of the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles to 0.78 to 77% by volume with respect to the amount of the conductive particles and stirring the conductive particles and the insulating filler, the difference in the number density of the conductive particles (second-coated conductive particles) in the anisotropic conductive film can be reduced. In particular, according to the embodiments, if it is set to 3.9 to 38.7% by volume, a good state is obtained. That is, it is known that the dispersibility of the conductive particles is good. In addition, in the embodiments, it is known that short circuits between the electrode terminals of the electronic component can be suppressed. Further, in the embodiments, it is known that the capture rate of the conductive particles is good, and the evaluation of the initial resistance value and the resistance value after the reliability test is also good. In particular, in Embodiments 1 and 2, it is known that the dispersibility of the conductive particles is even better.

[0142] In the embodiments, by stirring the conductive particles and the insulating filler, as Figure 2 shown, the first-coated conductive particles 10 are obtained. Then, by stirring the first-coated conductive particles 10 in the insulating binder, the silica filler detaches from the conductive particles in the first-coated conductive particles 10, as Figure 3 shown, the second-coated conductive particles 11 are obtained. In addition, the detached silica filler exists between the second-coated conductive particles 11. Thereby, aggregation of the second-coated conductive particles 11 is suppressed, and the second-coated conductive particles 11 can be uniformly dispersed in the insulating binder. It should be noted that in the second-coated conductive particles 11 in the insulating binder obtained as described above, there is a case where a part of the coating of the insulating filler remains. The remaining coating of the insulating filler on the surface of the conductive particles can be confirmed by observing the second-coated conductive particles 11 according to Embodiments 1 to 3 using a scanning electron microscope (SEM).

[0143] In Comparative Example 1 in which the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles is not blended, it is known that the difference in the number density of the conductive particles cannot be reduced. That is, in Comparative Example 1, it is known that the dispersibility of the conductive particles is poor. In addition, in Comparative Example 1, it is known that short circuits between the electrode terminals of the electronic component cannot be suppressed, and the capture rate of the conductive particles is poor. In Comparative Example 1, as Figure 4 shown, by using the conductive particles (unprocessed particles) 12 not coated with the silica filler, as Figure 5 shown, a plurality of conductive particles 12 are connected and aggregated in the insulating binder.

[0144] In Comparative Example 2 where the amount of the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles is set to more than 77.3% by volume (more than 77%) with respect to the amount of the conductive particles, it can be seen that the difference in the number density of the conductive particles cannot be reduced. That is, in Comparative Example 2, it can be seen that since the number ratio of the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles is excessive, the dispersibility of the conductive particles is poor. In addition, in Comparative Example 2, it can be seen that the short circuit between the electrode terminals of the electronic component cannot be suppressed and the conductive particle capture rate is poor. In addition, in Comparative Example 2, it can be seen that the evaluation of the initial resistance value and the resistance value after the reliability test are both poor. In Comparative Example 2, it can be seen that after mixing the conductive particles and the silica filler, for example, as Figure 6 shown, partially formed are coated conductive particles 13 in which two conductive particles are coated with the silica filler.

[0145] In Comparative Example 3 where the amount of the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles is set to 0.77% by volume (less than 0.78% by volume) with respect to the amount of the conductive particles, it can be seen that the difference in the number density of the conductive particles cannot be reduced. That is, in Comparative Example 3, it can be seen that since the number ratio of the insulating filler having a particle size of 0.02 to 0.143% of the particle size of the conductive particles is insufficient, the dispersibility of the conductive particles is poor. In addition, in Comparative Example 3, it can be seen that the short circuit between the electrode terminals of the electronic component cannot be suppressed and the conductive particle capture rate is poor.

[0146] Symbol Explanation 1 Connection structure, 2 Anisotropic conductive film, 3 Conductive particle, 4 First terminal row, 5 First electronic component, 6 Second terminal row, 7 Second electronic component, 10 First coated conductive particle, 11 Second coated conductive particle, 12 Conductive particle, 13 Coated conductive particle, 20 Partially coated particle, 21 Large-diameter particle, 22 Coated portion, 23 Exposed portion.

Claims

1. A resin composition comprising: coated large-diameter particles in which a part of the surface of large-diameter particles is coated with small-diameter fillers and an exposed portion is present on the surface of the large-diameter particles, small-diameter fillers, and an insulating binder, which is formed by dispersing the above-mentioned coated large-diameter particles, wherein the diameter of the above-mentioned large-diameter particles is 2 μm or more, the diameter of the above-mentioned small-diameter fillers is 0.02% or more and 5.0% or less of the diameter of the above-mentioned large-diameter particles, and the amount of the above-mentioned small-diameter fillers relative to the above-mentioned large-diameter particles is 7.8 to 78.2% by volume.

2. A resin composition comprising: coated large-diameter particles in which the surface of large-diameter particles is coated with small-diameter fillers, small-diameter fillers, and an insulating binder, which is formed by dispersing the above-mentioned coated large-diameter particles, wherein the number-average diameter of the above-mentioned large-diameter particles is 2 μm or more and 20 μm or less, the number-average diameter of the above-mentioned small-diameter fillers is 0.02% or more and 0.143% or less of the number-average diameter of the above-mentioned large-diameter particles and is 10 nm or more, and the amount of the above-mentioned small-diameter fillers relative to the above-mentioned large-diameter particles is 11.6 to 38.7% by volume.

3. A method for preparing a resin composition, comprising: Step (A), in which large-diameter particles having a number-average diameter of 2 μm or more and 20 μm or less and small-diameter fillers having a number-average diameter of 0.02% or more and 0.143% or less of the number-average diameter of the above-mentioned large-diameter particles and being 10 nm or more are stirred to obtain first-coated particles in which the above-mentioned large-diameter particles are coated with the above-mentioned small-diameter fillers; and Step (B), in which a mixture of the above-mentioned first-coated particles obtained in the above-mentioned step (A) and the above-mentioned small-diameter fillers and an insulating binder are stirred to obtain a resin composition in which second-coated particles in which the surface of the above-mentioned large-diameter particles is coated with the above-mentioned small-diameter fillers are dispersed in the above-mentioned insulating binder, in the above-mentioned step (A), the large-diameter particles and the small-diameter fillers are blended such that the amount of the above-mentioned small-diameter fillers relative to the above-mentioned large-diameter particles is 11.6 to 38.7% by volume, and in the above-mentioned step (B), the amount of the above-mentioned small-diameter fillers relative to the above-mentioned large-diameter particles is also 11.6 to 38.7% by volume.

4. An anisotropic conductive adhesive comprising: coated conductive particles in which the surface of conductive particles is coated with insulating fillers, insulating fillers, and an insulating binder, wherein the above-mentioned coated conductive particles are dispersed in the above-mentioned insulating binder, the number-average diameter of the above-mentioned conductive particles is 7 μm or more and 20 μm or less, the number-average diameter of the above-mentioned insulating fillers is 0.02 to 0.143% of the number-average diameter of the above-mentioned conductive particles and is 10 nm or more, and the amount of the above-mentioned insulating fillers relative to the above-mentioned conductive particles is 11.6 to 38.7% by volume.

5. A method for preparing an anisotropic conductive adhesive, comprising: Step (A), in which conductive particles having a number average particle diameter of 7 μm or more and 20 μm or less and an insulating filler having a number average particle diameter of 0.02 to 0.143% of the number average particle diameter of the conductive particles and 10 nm or more are stirred to obtain first coated conductive particles in which the conductive particles are coated with the insulating filler; and Step (B), in which a mixture of the first coated conductive particles obtained in the above step (A) and the insulating filler and an insulating binder are stirred to obtain an anisotropic conductive adhesive in which the first coated conductive particles having the surface coated with the insulating filler are dispersed in the insulating binder, In the above step (A), the conductive particles and the insulating filler are blended such that the amount of the insulating filler relative to the conductive particles is 11.6 to 38.7% by volume, In the above step (B), the amount of the insulating filler relative to the conductive particles is also 11.6 to 38.7% by volume.

6. An adhesive composition containing a resin composition, which contains: coated large-diameter particles in which a part of the surface of large-diameter particles is coated with a small-diameter filler, the small-diameter filler, and an insulating binder, Dispersed the above coated large-diameter particles, The number average particle diameter of the above large-diameter particles is 2 μm or more and less than 20 μm, The number average particle diameter of the above small-diameter filler is 0.02% or more and 2.5% or less of the number average particle diameter of the above large-diameter particles, the amount of the above small-diameter filler relative to the above large-diameter particles is 23.5 to 78.2% by volume, and the above large-diameter particles and the above small-diameter filler are contained in the above volume ratio, The number density (particles / mm) of the large-diameter particles in the entire film with a thickness set to 4 times that of the above large-diameter particles 2 ) and the number density (particles / mm) of the large-diameter particles in a 0.2 mm × 0.2 mm region arbitrarily extracted from the film 2 ) differ by 10% or less, The surface of the above coated large-diameter particles has a coated portion coated with the small-diameter filler and an exposed portion where the surface of the above large-diameter particles is exposed. When the resin composition is cured or frozen and the outermost surface of an arbitrary 100 cross-sections of the coated large-diameter particles is observed by an electron microscope, the average value of the ratio of the coated portion of the coated large-diameter particles is 15% or more, and when an arbitrary 100 coated particles in which a part or all of the surface of the above large-diameter particles is coated are observed by an electron microscope, the number ratio of the above coated large-diameter particles is 70% or more.

7. A method for preparing a resin composition, which has: Step (A), in which large-diameter particles having a number average particle diameter of 2 μm or more and less than 20 μm and a small-diameter filler having a number average particle diameter of 0.02% or more and 2.5% or less of the number average particle diameter of the large-diameter particles are stirred to obtain first coated particles in which the large-diameter particles are coated with the small-diameter filler; and Step (B), in which a mixture of the first coated particles and the small-diameter filler obtained by stirring in the above step (A) and an insulating binder are stirred to obtain a resin composition in which second coated particles in which a part of the surface of the large-diameter particles is coated with the small-diameter filler are dispersed in the insulating binder, In the above step (A), the large-diameter particles and the small-diameter filler are blended such that the amount of the small-diameter filler relative to the large-diameter particles is 23.5 to 78.2% by volume. In the above step (B), a mixture containing the large-diameter particles and the small-diameter filler in the volume ratio of step (A) and an insulating binder are stirred. The number density (number / mm) of the large-diameter particles in the entire film having a thickness of 4 times that of the above resin composition is 2 ) and the number density (number / mm) of the large-diameter particles in a 0.2 mm × 0.2 mm region arbitrarily extracted from the film is 2 ) The difference is 10% or less. The surface of the coated large-diameter particles has a coated portion coated with the small-diameter filler and an exposed portion where the surface of the large-diameter particles is exposed. When curing or freezing the resin composition and observing the outermost surface of any 100 cross-sections of the coated large-diameter particles by electron microscopy, the average value of the proportion of the coated portion of the coated large-diameter particles is 15% or more, and when observing any 100 coated particles in which a part or all of the surface of the large-diameter particles is coated by electron microscopy, the number proportion of the coated large-diameter particles is 70% or more.

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