JP2008186590A - High heat and electric conductivity composition, conductive paste, and conductive adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a conductive paste and an adhesive having high electrical conductivity and high thermal conductivity. <P>SOLUTION: The above problems are solved by containing at least a pitch-based graphitized carbon fiber filler having high heat conductivity, a metal fine particle filler, and a binder resin at a prescribed ratio. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention is a conductive composition used for, for example, a conductive paste for filling through holes or via holes in printed wiring boards, and a conductive adhesive for fixing electrical contacts when mounting various semiconductor chips such as LED chips and LD chips. The present invention relates to a conductive composition having high thermal conductivity in addition to electrical conductivity.

In chip mounting and device mounting in the electric / electronic field, the need for heat countermeasure technology (heat dissipation technology) has been greatly increased in response to the trend toward higher mounting density and higher device output.
As one of these heat dissipation techniques, there is a thermal via method that uses a through hole or via hole of a wiring board and penetrates the wiring board to create an escape path for heat generated in the device. These thermal vias are created by filling a hole with a highly thermally conductive material, and a filling method using a metal plating method or a conductive paste has been proposed as a filling method. (For example, Patent Documents 1 to 3)

In light emitting modules using LED chips, it has been proposed to use a conductive paste for forming a wiring circuit on a substrate. (For example, Patent Document 4)
Further, in the case of fixing electrical contacts when various semiconductor chips such as LED chips and LD chips are mounted, a conductive adhesive may be used from the viewpoint of process temperature reduction and stress relaxation. (For example, Patent Documents 5 and 6)

  As these conductive pastes and conductive adhesives, as disclosed in Patent Documents 1 to 6, conventionally, a resin binder in which a metal fine particle filler typified by silver is dispersed at a high ratio has been proposed.

JP 2004-265607 A JP-A-2005-353783 JP 2006-147378 A JP 2006-041290 A JP 2006-241365 A JP 2005-113059 A

  Regarding the above-described method, the metal plating method is generally not preferable because the process is complicated and time-consuming and there are environmental problems of the plating bath waste liquid. Moreover, it is difficult to obtain a high thermal conductivity with a conventional conductive paste or conductive adhesive in which a metal fine particle filler is simply dispersed in a binder resin at a high ratio. The conductive paste of Patent Document 3 is a proposed example that focuses on increasing the thermal conductivity, but is a content that focuses on increasing the mixing ratio of the metal fine particle filler, and this method leads to an increase in paste viscosity, Practicality (hole fillability, printability, etc.) is greatly reduced.

  In the present invention, it is proposed to realize a highly heat conductive conductive composition by using a metal fine particle filler and pitch-based graphitized carbon short fibers in combination. According to this proposal, it is possible to obtain a composition paste and an adhesive that are excellent in practicality without causing a significant increase in viscosity.

The present invention is as follows.
1. As a solid component in the composition, pitch-based graphite having at least an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 200 μm, and a true density of 2.0 to 2.5 g / cc. A highly heat-conductive conductive composition comprising 5 to 80% by weight of a carbonized carbon fiber filler, 15 to 90% by weight of a metal fine particle filler having an average particle size of 0.001 to 30 μm, and 5 to 50% by weight of a binder resin.
2. The high thermal conductive conductive composition according to 1 above, wherein the crystallite size (Lc) in the c-axis direction of the pitch-based graphitized carbon fiber is 20 to 100 nm.
3. The high thermal conductive conductive composition according to any one of the above 1 or 2, wherein the crystallite size (La) in the ab axis direction of the pitch-based graphitized carbon fiber is 30 to 200 nm.
4). A conductive paste for filling a through hole or via hole in a wiring board, or for forming a circuit, comprising the high thermal conductive conductive composition according to 1 above.
5. A conductive adhesive for fixing electrical contacts, comprising the high thermal conductive conductive composition according to 1 above.
6). 10. A conductive adhesive tape or sheet having a thickness of 10 to 1000 μm, comprising the high thermal conductive conductive composition according to 1 above.

  According to the present invention, it is possible to obtain a conductive composition, a conductive paste, and an adhesive excellent in practicality without causing a significant increase in viscosity.

Next, embodiments of the present invention will be described in detail.
The highly heat conductive conductive composition of the present invention has the greatest feature in that pitch-based graphitic carbon fiber is used as a filler as one of its constituent elements.

  Pitch-based graphitized carbon fibers are made of pitch hydrocarbons made of cyclic hydrocarbons such as petroleum and coal, and after undergoing spinning, infusibilization, carbonization firing, and extremely high temperature graphitization treatment, graphitized carbon Various performances as a fiber appear. Although graphitized carbon fiber is not a single crystal, it contains graphite crystals with a number of network structures. The characteristics derived from these crystals include higher electrical conductivity, thermal conductivity, and elasticity than PAN-based carbon fibers. And has a low thermal expansion coefficient comparable to that of ceramics.

The thermal conductivity of graphite crystals is not as good as that of diamond, but is superior to metals such as silver and copper. Since it is a hexagonal crystal, it has anisotropy, and in particular, a value exceeding 600 W / m · K can be expressed in the hexagonal network direction of the graphite crystal.
Therefore, these pitch-based graphitized fibers can be combined with resin materials and other types of materials to increase their thermal conductivity and conductivity, and to improve thermal dimensional stability and mechanical rigidity.

  The pitch-based graphitized carbon fiber used in the present invention preferably has a thermal conductivity in the fiber axis direction of at least 200 W / (m · K) or more, more preferably 300 W / (m · K) or more, and more It is preferably 400 W / (m · K) or more, and most preferably 500 W / (m · K) or more.

  In order to develop such a high thermal conductivity in the carbon fiber, it is preferable that the content of graphite crystals in the carbon fiber (hereinafter referred to as graphitization rate) is high, and that the crystallite size is large. It is preferable to realize conduction. This is due to the fact that the heat conduction in the carbon fiber is mainly carried by the phonon conduction.

Regarding the graphitization rate, it is preferable that the true density of the pitch-based graphitized carbon fiber is in the range of 2.0 to 2.5 g / cc as a reflection value.
Regarding the crystallite size, the crystallite size (Lc) in the c-axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably in the range of 20 to 100 nm.
More preferably, the crystallite size (La) in the ab axis direction of the graphite crystal (hexagonal network surface) in the carbon material is preferably in the range of 30 to 200 nm.

  These crystallite sizes can be obtained by the X-ray diffraction method. The Gakushin method is used as an analysis method, and the crystallite size is obtained by using diffraction lines from the (002) plane and the (110) plane of the graphite crystal. Can do.

  Thus, in order to obtain a carbon material with a very high graphitization rate, raw materials such as PAN and rayon are not so preferable as described above, and cyclic hydrocarbons having condensed heterocyclic rings, that is, pitch-based raw materials are used. It is preferable to use a liquid crystal mesophase pitch among them.

As for the form of the carbon material, a spherical or indefinite shape can be used. Especially when a mesophase pitch is used, the growth surface of the graphite crystal is oriented almost in one direction to obtain extremely high thermal conductivity. It is more preferable that it is a fibrous shape that enables the above.
From these things, the pitch-based graphitized carbon fiber using the pitch as a raw material is optimal as the carbon material used in the present invention.

  Examples of raw materials for such pitch-based carbon fibers include condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene, condensed heterocyclic compounds such as petroleum-based pitch and coal-based pitch, and the like. In particular, condensed polycyclic hydrocarbon compounds such as naphthalene and phenanthrene are preferred.

  In particular, an optically anisotropic pitch, that is, a mesophase pitch is preferable. These may be used singly or in appropriate combination of two or more, but the use of mesophase pitch alone can increase the graphitization rate in the graphitization treatment, and consequently The thermal conductivity of the carbon fiber can be improved, which is a preferred embodiment.

  The softening point of the raw material pitch can be determined by the Mettler method, and is preferably in the range of 230 ° C. or higher and 340 ° C. or lower. If the softening point is lower than 230 ° C., fusion between fibers or large heat shrinkage occurs during infusibilization. If the temperature is higher than 340 ° C., the pitch is thermally decomposed in the spinning process, which tends to make the spinning molding difficult. Furthermore, under high temperature spinning conditions, gas components are generated, bubbles are generated inside the spun fibers, leading to strength deterioration, and yarn breakage is likely to occur.

  The raw material pitch is spun by a known melt spinning method or melt blowing method, and then the pitch-based graphitized carbon, which has a relatively short fiber length by various processes of infusibilization, carbonization firing, milling, sieving, and graphitization, and is optimal as a filler Become fiber.

Below, the process regarding pitch-type graphitized carbon fiber manufacture using a melt blow method is demonstrated as an example.
First, the shape of the spinning nozzle is not particularly limited, but those having a ratio of the nozzle hole length to the hole diameter of less than 3 are preferably used, and more preferably about 1.5.

  There are no particular restrictions on the nozzle temperature during spinning, and there is no problem as long as the temperature can maintain a stable spinning state. If the viscosity of the raw material pitch is in an appropriate range, the spinning state is stabilized, that is, the pitch viscosity during spinning is 0.1 to 20 Pa · S, preferably 8 to 16 Pa · S, more preferably 10 to 14 Pa · S. The temperature may be S.

  The pitch fibers drawn out from the nozzle holes are shortened by blowing a gas having a linear velocity of 100 to 10000 m per minute heated to 100 to 370 ° C. in the vicinity of the thinning point. As the gas to be blown, air, nitrogen, argon or the like can be used, but air is preferable from the viewpoint of cost performance.

The pitch fibers are collected on a wire mesh belt, become a continuous mat, and are further cross-wrapped to form a web having a predetermined basis weight (weight per unit area).
The web made of pitch fibers thus obtained has a three-dimensional randomness due to the interlace of the fibers. These webs can be infusibilized by known methods.

  Infusibilization is achieved by applying heat treatment for a certain time at a temperature of about 200 to 300 ° C., for example, using air or a mixed gas obtained by adding ozone, nitrogen dioxide, nitrogen, oxygen, iodine or bromine to air. . Considering safety and convenience, it is desirable to carry out in air.

  The infusible pitch fiber is then fired in a temperature range of 700 to 900 ° C. in a vacuum or in an inert gas such as nitrogen, argon or krypton. Usually, the calcination is performed at low pressure using nitrogen at low cost.

  The web made of infusibilized and fired pitch fibers is further milled and sieved in order to further shorten the fibers and to obtain a predetermined fiber length. For milling, a pulverizer or cutting machine such as a Victory mill, a jet mill, or a high-speed rotary mill is used. In order to perform milling efficiently, a method of cutting fibers in a direction perpendicular to the fiber axis by rotating a rotor to which blades are attached at high speed is appropriate.

  The average fiber length of the fibers generated by milling is controlled by adjusting the number of rotations of the rotor, the angle of the blade, and the like, and can be classified by a combination of the coarseness of the sieve through a sieve.

  The fiber after the milling and sieving is heated to 2300-3500 ° C. and graphitized to obtain a final pitch-based carbon short fiber. Graphitization is performed in a non-oxidizing atmosphere in an Atchison furnace or the like.

  The pitch-based graphitized carbon fiber filler used in the present invention preferably has a structure in which the graphene sheet is closed by observing the shape of the filler end face with a transmission electron microscope. When the end surface of the filler is closed as a graphene sheet, generation of extra functional groups and localization of electrons due to the shape do not occur, so that the concentration of impurities such as water can be reduced.

  Note that the graphene sheet is closed means that the end of the graphene sheet itself constituting the carbon fiber is not exposed at the end of the carbon fiber, the graphite layer is curved in a substantially U shape, and the curved portion is the end of the carbon fiber. It is in the state exposed to the part.

The pitch-based graphitized carbon fiber filler used in the present invention has a substantially flat observation surface with a scanning electron microscope. Here, “substantially flat” means that the surface does not have severe unevenness like a fibril structure, and when there is intense unevenness on the surface of the filler, the surface area increases upon kneading with the matrix resin. It is desirable that the surface irregularities be as small as possible, since this causes an increase in the viscosity accompanying this and lowers the moldability.
The pitch-based carbon fiber filler described above can be easily obtained by performing graphitization after milling.

  The fiber diameter of the pitch-based graphitized carbon fiber thus obtained is 1 to 30 μm as an average fiber diameter (D1) observed with an optical microscope, more preferably 3 to 20 μm, and further preferably 5 to 15 μm. When the fiber diameter is larger than 30 μm, adjacent fibers are likely to be fused in the infusibilization step. When the fiber diameter is less than 1 μm, the surface area per weight of the pitch-based carbon fiber filler is increased, and the fiber surface is substantially Even if it is flat, the formability may be lowered in the same manner as a fiber having irregularities on the surface, which may be inappropriate in practice. The percentage of the fiber diameter dispersion (S1), which is the dispersion of the fiber diameter with respect to the average fiber diameter (D1) observed with an optical microscope, is preferably in the range of 5 to 18%. More preferably, it is 5 to 15% of range.

  In addition to pitch-based graphitized carbon fibers using the melt blow spinning method described so far, pitch-based graphitized carbon fibers usable in the present invention include pitch-based graphitized carbon fibers obtained by melt spinning. . However, it is more preferable to use the pitch-based graphitized carbon fiber of this method because the melt blow spinning method is more excellent in the productivity and quality (surface properties, appearance, etc.) of the pitch-based graphitized carbon fiber.

  On the other hand, as a pitch-based graphitized carbon fiber whose fiber diameter is smaller and finer than the pitch-based graphitized carbon fiber described so far, for example, in WO 04/031461 pamphlet, a carbon material as a core material, A composite fiber is prepared by a blend spinning method (or conjugate spinning method) using an olefin-based material or the like as a matrix material, and the matrix material is dissolved and removed as a post-treatment, so that a final fiber of about 0.1 to 1 μm is obtained. A technique for obtaining fine graphitized pitch-based carbon fibers having a diameter with high productivity is disclosed, and these can also be suitably used.

Overall, the average fiber diameter of the pitch-based graphitized carbon fiber filler preferably used in the present invention is in the range of about 0.1 to 30 μm.
The aspect ratio represented by the ratio of average fiber length / average fiber diameter is preferably in the range of about 2-100. This is because when the aspect ratio is less than 2, it is difficult to utilize the characteristics of the fiber shape, and when it exceeds 100, the bulk density is lowered, and high-density filling becomes difficult.
The aspect ratio is more preferably in the range of 2 to 60, still more preferably in the range of 3 to 30, and most preferably in the range of 3 to 15.

  On the other hand, the average fiber length of the carbon fiber filler is preferably 200 μm or less. This is necessary for performing various uses such as filling of through holes and via holes, forming fine wiring circuit patterns, and fixing fine electric contacts with high accuracy. The lower limit of the average fiber length is 0.2 μm.

  The carbon fiber filler is subjected to a surface treatment as necessary. These surface treatments include coating of resin, inorganic substances, metal oxides, metals and their fine particles on the surface of carbon fibers, surface activation by introducing hydrophilic functional groups and metal elements, and surface by introducing hydrophobic groups. Its main purpose is to control surface roughness by inactivation and etching.

  Specific surface treatment methods include various coating treatments (dipping coating, spray coating, electrodeposition coating, various plating, plasma CVD, etc.), ozone treatment, plasma treatment, corona treatment, ion implantation treatment, electrolytic oxidation treatment, acid / Examples include alkali and other chemical treatments.

  Further, the carbon fiber filler is subjected to surface treatment as necessary as described above, and then the sizing agent is 0.01 to 10% by weight, preferably 0.1 to 2.5% based on the pitch-based graphitized carbon fiber. It may be added by weight%. As the sizing agent, any commonly used sizing agent can be used. Specifically, an epoxy compound, a water-soluble polyamide compound, a saturated polyester, an unsaturated polyester, vinyl acetate, water, alcohol, glycol are used alone or in a mixture thereof. Can do. Such surface treatment is an effective means when attempting to increase the true density. However, since the excessive sizing agent is added to the heat resistance, this can be carried out according to the required physical properties.

  In the present invention, it is also preferable to form a layer having high electrical conductivity (hereinafter referred to as an electrical conductive layer) on the surface including at least the side surface of the electrical carbon fiber filler. The thickness of the electrically conductive layer is preferably about 0.01 to 10 μm. If the thickness is less than 0.01 μm, the function as an electrically conductive layer is insufficient, and if it exceeds 10 μm, the adhesion to the carbon fiber is lowered, and in some cases, heat conduction may be hindered as a heat resistance component. Yes, not preferred. In addition, the thickness of the light reflection layer is more preferably 0.03 to 5 μm, and further preferably 0.05 to 3 μm.

  For the electrically conductive layer, a metal material having high electrical conductivity is particularly preferably used, and in particular, a film made of a metal such as silver, copper, gold, nickel, platinum, palladium, tin, or an alloy thereof is preferably used.

  As a method of laminating these electric conductive layers on the carbon fiber surface, electrolytic plating methods for fine particles in fluids using a rotating field such as a barrel plating device and other flow fields, and wet plating methods such as electroless plating , Vacuum vapor deposition, sputtering, ion plating, physical vapor deposition such as laser ablation, film formation by chemical vapor deposition such as plasma CVD, etc., mechanochemical method to fix fine particles based on mechanical impact, rotation Examples thereof include a method using a fluidizer (for example, “Ominitex” manufactured by Nara Machinery Co., Ltd.). Among these, a wet plating method using a fluidized field is particularly preferably used.

  In the barrel plating method, for example, a plating solution and a material to be processed are placed in a rotatable polygonal cylindrical container (barrel), and the electrode provided in the barrel and the material to be processed are brought into contact with the rotation of the barrel. In this case, a plating film is formed on the material to be processed, and is relatively commonly used in the plating process of fine particles. However, the formation of a liquid flow field suitable for electrolytic plating on fine particles can be realized not only by the above-described method of rotating the barrel but also by other methods, for example, forced turbulence generation using a special high-speed stirrer, etc. Etc. can also be used.

  As for the composition of the plating bath, as an example of silver, as a monovalent silver compound as a raw material of silver, silver oxide, silver sulfate, silver citrate, silver nitrate, silver chloride, silver iodide, silver methanesulfonate, etc. These are used after being dissolved in a dilute acid solution or the like, if necessary, and then adjusting the PH value to an appropriate range. Further, polyethylene glycol, polyoxyalkyl ether, polyoxyethylene or the like may be added as a surface conditioner for the purpose of increasing the surface gloss of the film.

Next, a highly thermally conductive composition using these pitch-based graphitized carbon fiber thermally conductive fillers will be described.
The highly heat conductive conductive composition of the present invention comprises at least 5 to 80% by weight of the carbon fiber filler, 15 to 90% by weight of the metal fine particle filler, and 5 to 50% by weight of the binder resin in the total solid component of the composition. Consists of including.

  If the mixing ratio of the carbon fiber filler is less than 5% by weight, the effect of enhancing the thermal conductivity tends to be insufficient, while if it exceeds 80% by weight, there may be a problem in dispersibility and fluidity as a composition. Since it increases, it is not preferable. The mixing ratio of the carbon fiber filler is more preferably 10 to 65% by weight, further preferably 15 to 50% by weight in the total solid component of the composition.

  Various types of metal fine particle fillers are used, and conductive fine particles prepared by a chemical reduction method, an electrolytic method, a dry atomization method, a pulverization method, or the like are preferably used, and have an average particle size of 0.001 to 30 μm. , Fine particles (for example, silver / copper, silver / palladium, silver / tin, etc.) of metals such as silver, copper, gold, platinum, nickel, palladium, and tin and alloys thereof, and at least the surface layer is formed of the metal material. Multi-layer composite fine particles (eg, silver-coated copper) are preferably used.

The metal fine particle filler may be selected in consideration of its average particle diameter, shape, material, etc., but one kind may be used alone, or a plurality of different kinds may be used in combination. .
In addition, regarding the average particle diameter, the particle diameter is 0.1 to 30 μm, more preferably 0.3 to 20 μm, and further preferably 0.5 to 10 μm for the purpose of achieving both high conductivity and high fluidity in the composition. It is preferable to mainly use the metal fine particle filler. In order to improve the filler filling property, for example, it is preferable to use a combination of a plurality of fillers having greatly different average particle sizes (about 10 to 1000 times).
As for the shape, there are a spherical shape, a scale shape, an indefinite shape, a fibrous shape, a radial dendritic shape, and the like, and it is preferable to combine them as necessary.

In addition, it is preferable to mix the mixing rate of a metal fine particle filler in the range of 15 to 90 weight% in all the solid components of a composition. If it is 15% by weight or less, the conductivity of the composition tends to be insufficient, and it becomes difficult to increase the filling rate of the filler as a whole. On the other hand, if it exceeds 90%, the composition tends to be inferior in fluidity and film-forming property, which is not preferable.
In addition, the more preferable mixing ratio of the metal fine particle filler is 25 to 85% by weight, and more preferably 35 to 80% by weight.

  As the resin binder, various types can be used, for example, acrylic resin (methacrylate, acrylate), epoxy resin, polyamide resin, polyamideimide resin, silicone resin, polyimide resin, polyimide silicone resin, urethane resin, melamine resin, Preferable examples include polyester resins (including unsaturated polyesters), phenolic resins (such as novolac type phenolic resins), polyester acrylate resins, silicone polyimide resins, epoxy silicone resins, and acrylic rubber fine particle dispersed epoxy resins. In the case of a curable resin, it is possible to crosslink and cure the resin with moisture, heat, ultraviolet rays, etc. in the air after adding a reaction initiator or a curing agent (curing accelerator) if necessary. is there.

  In applications such as via filling, it is generally necessary to have heat resistance that can cope with the soldering process. Therefore, characteristics such as glass transition temperature are important. Various epoxy resins, polyimide resins, phenol resole resins, cyanate ester resins Etc. are preferably used.

  Such an epoxy resin preferably has a composition containing a polyfunctional epoxy resin having a plurality of epoxy groups from the viewpoint of heat resistance. Examples of the main component of the epoxy resin include glycidyl ether type epoxy resins such as bisphenol F type epoxy resin, bisphenol A type epoxy resin, and bisphenol AD type epoxy resin, glycidyl amine type epoxy resins (tetraglycidyl diaminodiphenylmethane, etc.), glycidyl esters, etc. Type epoxy resin, polyphenol type epoxy resin (phenol novolak type epoxy resin, cresol novolak type epoxy resin, etc.), cycloaliphatic epoxy resin (hexahydronicotinic acid dilysyl ester, vinylcyclohexene dioxide, cyclopentadiene dioxide, icyclic type Epoxy-adi paint, 3,4-epoxy-6-methylcyclohexylmethyl carboxylate, 3,4-epoxycyclohexylmethylcarbo Shireto etc.), an epoxy resin having a naphthalene skeleton, dimer acid diglycidyl ester type epoxy resins, epoxidized butadiene styrene resin or the like is preferably used, and used as a combination of more than one kind of them or two or.

Examples of epoxy resin curing agents or accelerators include various organic phosphine compounds such as novolak-type alkylphenol, triphenylphosphine, and tricyclohexylphosphine, various amine adducts, triethanolamine, trimethylhexamethylenediamine, diaminodiphenylmethane, 2- ( Various amino compounds centered on diamine compounds such as dimethylaminomethyl) phenol, 2,4,6-tris (dimethylaminomethyl) phenol, dicyanamide, imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenimidazole 2-undecylimidazole, 1-cyanoethyl-2-undecylimidazole, 2-phenyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimi Various imidazoles such as sol and 1-cyanoethyl-2-ethyl-4-methylimidazole), acid anhydrides such as tetrahydromethyl phthalic anhydride, hexahydrophthalic anhydride, methyl hymic anhydride, cyclohexanetricarboxylic acid anhydride, Lewis Examples thereof include BF ₃ salts of acid complexes and various blocked isocyanates (such as imidazole blocked isocyanate).

  The mixing ratio of the curing agent (curing accelerator) with respect to the main agent varies depending on the combination, but is approximately 1 to 15 parts by weight, more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the main agent.

  The mixing ratio of the resin binder (main agent + curing agent) is more preferably 5 to 50% by weight, more preferably 6 to 40% by weight, still more preferably 7 to 30% by weight in the total solid components of the composition. %, Most preferably 8-20% by weight. If the mixing ratio of the resin binder is less than 5%, the composition tends to be inferior in fluidity or film-forming property, and if it exceeds 50% by weight, the composition may have insufficient conductivity and thermal conductivity. Many are undesirable.

  In addition to these, if necessary, the composition includes an inorganic ion exchanger (inorganic particles selected from zirconium, bismuth, antimony, aluminum, magnesium), white conductive titanium oxide, and the like from the viewpoint of preventing ion migration. Ceramic filler, acetylene black, carbon black and other graphitic fine particles, dispersants and coupling agents that increase the dispersibility of fine particles, various organic solvents and other solvents that adjust the viscosity suitable for coating, and silicone that increases the surface smoothness of the layer Oil and other leveling agents, surfactants, antioxidants, crosslinking agents, chelating agents, plasticizers, colorants, and the like may be mixed.

  Preferred examples of the solvent include butyl carbitol, butyl carbitol acetate, ethyl carbitol, ethyl carbitol acetate, butyl cellosolve, ethyl cellosolve, γ-butyrolactone, isophorone, glycidyl phenyl ether, and triethylene glycol dimethyl ether. It is done.

The heat conductive electrically conductive composition of the present invention can be produced by kneading the materials listed above with a universal mixing stirrer, kneader or the like.
The viscosity of the composition is preferably about 5 to 500 Pa · S (50 to 5000 poise) at a shear rate of 1.7 (1 / s), for example. If it is less than 5 Pa · S (50 poise), the fluidity is too high, so that the composition may flow out and spread around the portion to be originally formed, and if it exceeds 500 Pa · S (5000 poise), Fluidity tends to be insufficient when pattern printing is performed by filling via holes, screen printing, or the like. The viscosity of the composition under the above conditions is more preferably 5 to 200 Pa · S (50 to 2000 poise), still more preferably 5 to 150 Pa · S (50 to 1500 poise), and most preferably 5 to 100 Pa · S (50 to 1000 Poise).

  These thermally conductive conductive compositions can be preferably used, for example, as a conductive paste for filling through holes or via holes in circuit boards, or for circuit formation, or as a conductive adhesive for fixing electrical contacts.

  For use of conductive paste for filling through-holes or via holes, for example, through-hole patterns can be used for through-holes or via holes provided on copper-laminated laminated substrates such as aramid nonwoven fabric / epoxy, glass nonwoven fabric / epoxy, or prepregs thereof. The holes are locally coated by a method such as screen printing using a mask in which the opening is formed, ink jetting, or the like, and filled into the holes using a squeegee or the like.

The composition is dried and cured by heat treatment under predetermined conditions. However, when the composition is filled in a prepreg, a method in which the composition is fully cured together with the prepreg hot press is also preferably used.
In addition, it is also preferable to perform surface polishing of the hole surface using various abrasives after filling the composition into the through hole or via hole and curing.

  In the use of the conductive paste for forming a circuit, a method of performing pattern printing on various mounting substrates by screen printing, ink jet, or the like, and drying and curing under predetermined conditions is preferable.

  In these applications, a conductive path can be formed in a predetermined pattern, and at the same time, the conductive path can be suitably used as a heat transfer path or a heat transfer circuit. Therefore, it can be used as a conductive paste having higher added value than conventional ones.

  The heat conductive conductive composition can be coated on, for example, an appropriate substrate to form a heat conductive conductive resin layer. In addition, a self-supporting thermally conductive conductive resin sheet can be produced by coating the substrate on a peelable substrate or by sandwiching the substrate between two substrates, and forming the layer and then separating the substrate. In addition, when the self-supporting thermally conductive conductive resin sheet is a sticky sheet, etc., it is manufactured without peeling the substrate as necessary, and the substrate is peeled off in actual use, etc. This method is also preferably used.

  Coating can be performed by various known techniques, and examples thereof include gravure coating, knife coating, die coating, slit die coating, bar coating, screen printing (printing through a mask pattern), and an inkjet method.

  In addition, according to techniques such as screen printing and ink jet, it can be formed in a pattern only at the necessary location on the substrate, so it can be used for filling through holes or via holes, for forming wiring circuits, for fixing electrical contacts, etc. It can be particularly preferably used.

In addition, it is preferable that the thickness of a heat conductive conductive resin layer is about 5-1000 micrometers. If the thickness is less than 5 μm, the heat transport capability as the heat conductive layer is often insufficient, and if it exceeds 1000 μm, the uniform formation and adhesion of the layer are reduced, and the flexibility and flexibility of the layer are reduced. This is not preferable because the number of cases increases.
The thickness of the resin layer is more preferably 20 to 700 μm, still more preferably 30 to 500 μm, and most preferably 40 to 300 μm.

The thermal conductivity of these thermally conductive conductive resin layers can be measured by methods such as the probe method, hot disk method, laser flash method, etc. Among them, the probe method is particularly preferable.
The higher the value of the thermal conductivity of the heat conductive conductive resin layer, the better. Of course, in the present invention, it is preferably at least 3 W / (m · K) or more. The thermal conductivity is more preferably 5 W / (m · K) or more, further preferably 8 W / (m · K) or more, and most preferably 10 W / (m · K) or more.

  The thermal conductivity often shows different values depending on the measurement technique, and the difference tends to increase particularly in the range of several W / (m · K) to several tens of W / (m · K). In the present invention, the measurement is performed by the probe method, and in the performance comparison with the prior art, the comparison is made not by the thermal conductivity value by the other but by the thermal conductivity value measured by the probe method. Should be.

  On the other hand, regarding the electrical conductivity of these thermally conductive conductive resin layers, the specific resistance value is required to be at least 1 × 10E-2 (Ω · cm) or less, preferably 1 × 10E-3 ( Ω · cm) or less. The specific resistance value of the heat conductive conductive resin layer is more preferably 5 × 10E-4 (Ω · cm) or less, further preferably 1 × 10E-4 (Ω · cm) or less, and most preferably 5 × 10E−. 5 (Ω · cm) or less.

A conductive adhesive tape or sheet having a thickness of 10 to 1000 μm prepared using the highly heat conductive conductive composition of the present invention is also very useful.
These tapes or sheets are prepared by laminating a layer made of the above composition (hereinafter referred to as a conductive layer) on a suitable substrate by a known coating method, etc., and drying and solidifying (curing). I can do things. It is possible to create conductive tapes and sheets that are integrated with the substrate by coating, drying and solidifying on substrates such as plastic and ceramic films, nonwoven fabrics and woven fabrics that adhere well to the conductive layer. It is also possible to form a self-supporting conductive tape or sheet by forming the layer on a peelable substrate or sandwiching the substrate and drying and solidifying only the conductive layer. In the latter case, the tape and the sheet are not peeled off from the peelable substrate, and the peelable substrate is peeled off and used in actual use. Further, a method of preparing these tapes and sheets in a semi-cured state (B stage) and performing the main curing in actual use is also preferably used.
Furthermore, by using such a sheet as a dry film resist, it can also be used for filling through holes or via holes in electronic mounting boards.

Examples are shown below, but the present invention is not limited to these techniques.
(1) Average fiber diameter of pitch-based graphitized carbon fiber:
The graphitized pitch-based carbon fiber was photographed with 10 fields of view under an optical microscope at a magnification of 400 times, and the dimensions were determined from the enlarged photograph image.
(2) Average fiber length of pitch-based graphitized carbon fiber:
The graphitic carbon fiber pitch was obtained by photographing 10 visual fields under an optical microscope. The magnification was appropriately adjusted according to the fiber length.
(3) True density of pitch-based graphitized carbon fiber:
It calculated | required using the specific gravity method.
(4) Crystal size:
Obtained by X-ray diffraction, the crystal size in the thickness direction of the hexagonal mesh surface is obtained using diffraction lines from the (002) plane, and the crystal size in the growth direction of the hexagonal mesh surface is obtained by using diffraction lines from the (110) plane. Asked. In addition, the request was made in accordance with the Gakushin Law.
(5) Thermal conductivity of pitch-based graphitized carbon fiber:
The resistivity of the fiber after graphitization treatment prepared under the same conditions except for the pulverization step was measured, and the relationship between the thermal conductivity and the electrical resistivity disclosed in JP-A-11-117143 is represented by the following formula (1 )
[Equation 1]
C = 1272.4 / ER-49.4 (1)
Here, C represents the thermal conductivity (W / m · K) of the fiber after graphitization, and ER represents the electrical specific resistance μΩm of the same fiber.
(6) Thermal conductivity of the composition:
Measurement was performed by a probe method using a thermal conductivity measuring device “QTM-500” manufactured by Kyoto Electronics. The composition was coated on a reference plate to a thickness of 0.3 mm, heat-dried at 60 ° C. for 30 minutes, and then heat-cured at 130 ° C. for 2 hours as a sample.
(7) Electrical conductivity of the composition:
Using a resistivity meter “Loresta GP” manufactured by Dia Instruments, the resistivity was measured. A sample was prepared by coating the composition on a 50 μm-thick polyimide film with a thickness of 0.3 mm, thermally drying at 60 ° C. for 30 minutes, and then thermally curing at 130 ° C. for 1 hour.
(8) Through-hole filling test 50 mm through-holes with diameters of 0.6 mm, 0.4 mm, and 0.2 mm are provided by laser processing on a 1 mm-thick glass nonwoven fabric / epoxy copper-clad laminate cut into 15 cm squares, and screen By filling the through-holes with the heat conductive conductive composition of each example by printing, and after thermally drying at 60 ° C. for 30 minutes and then thermosetting at 130 ° C. for 1 hour, the laminate was cleaved and The cross-section of the through hole was observed to evaluate whether or not the composition was filled uniformly without any defects.

[Experimental Example 1] (Preparation of pitch-based graphitized carbon fiber)
A pitch made of a condensed polycyclic hydrocarbon compound was used as a main raw material. The optical anisotropy ratio was 100%, and the softening point was 283 ° C. Using a spinneret having a diameter of 0.2 mm, heated air was ejected from the slit at a linear velocity of 5000 m / min, and the pitch pitch carbon fibers having an average fiber diameter of 15 μm were drawn by pulling the melt pitch. The spun fibers were collected on a belt to form a mat, and a web made of pitch-based carbon fibers having a basis weight of 320 g / m ² by cross-wrapping.

  The web was infusibilized by increasing the temperature from 175 ° C. to 280 ° C. in air at an average temperature increase rate of 7 ° C./min. After firing the infusible web at 800 ° C. in a nitrogen atmosphere, milling or the like is performed, fibers having an average fiber length of about 40 μm (hereinafter referred to as carbon fiber A), fibers having an average fiber length of about 120 μm (hereinafter, referred to as carbon fiber A). Sieve into carbon fiber B). Thereafter, it was graphitized by heat treatment at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere. The average fiber diameter was 9.7 μm. The percentage of the fiber diameter dispersion to the average fiber diameter was 14%. The true density was 2.18 g / cc.

Using a transmission electron microscope, the pitch-based graphitized carbon fiber was observed at a magnification of 1,000,000 times and magnified on a photograph at 4 million times. It was confirmed that the graphene sheet was closed on the end face of the pitch-based graphitized carbon fiber. Further, the surface of the pitch-based graphitized carbon fiber observed with a scanning electron microscope at a magnification of 4000 times was smooth with no large irregularities.
The crystallite size in the c-axis direction of the graphite crystal obtained by the X-ray diffraction method of the pitch-based graphitized carbon fiber was 33 nm. The crystallite size in the ab axis direction was 57 nm.

Moreover, the single yarn was extracted from the graphitized web heat-treated at 3000 ° C. in an electric furnace in a non-oxidizing atmosphere, and the electrical specific resistance was measured. However, it was 2.2 μΩ · m. The thermal conductivity obtained using the following formula (1) was 530 W / m · K.
[Equation 2]
C = 1272.4 / ER-49.4 (1)
(ER indicates the electrical resistivity, and the unit here is μΩ · m)

[Experimental example 2] (Electrically conductive layer formation on carbon fiber surface)
The surface of the pitch-based graphitized carbon fiber (carbon fiber A, carbon fiber B) prepared in Experimental Example 1 was coated with silver as an electrically conductive layer. Electrolytic plating using a liquid flow field was used for the silver coating.
Prior to the electrolytic plating, the carbon fiber surface was subjected to a surface treatment with ozone using an ozone treatment apparatus manufactured by Iwasaki Electric Co., Ltd.

  The plating solution used was composed of 3 g / L silver oxide, 1 g / L polyethylene glycol having a molecular weight of 5000, and the like. The plating solution 9L and carbon fiber 50 g were put in a tabletop super vibration α-1 type stirring tester manufactured by Nippon Techno Co., Ltd., and five copper foils were immersed in the plating solution at regular intervals as a cathode. As an anode, a tin plate is immersed in a container containing a plating solution, and the vibration motor of the stirring tester is driven to generate a violent turbulent flow field around the cathode, while maintaining a predetermined input current. A silver film was formed on the surface of each of the carbon fibers A and B by electrolytic plating. The silver film had an average thickness of about 2 μm, and the film was uniformly formed on the entire surface including the end face portion of the carbon fiber.

[Example 1]
20% by weight of carbon fiber A prepared in Experimental Example 1, 30% by weight of silver fine particles having an average particle diameter of about 8 μm, 30% by weight of flaky silver fine particles having an average particle diameter of about 1.5 μm, and 20% by weight of the following resin binder. In addition, 2 parts by weight of ethylene glycol monoethyl ether acetate as a diluent solvent was mixed, and vacuum defoaming was performed using a planetary mixer for 30 minutes to produce a thermally conductive composition.

As a resin binder, 50 parts by weight of a polyglycidylamine type epoxy resin as a main agent, 50 parts by weight of a novolak type alkylphenol resin as a curing agent, and 1.5 parts by weight of 2-phenyl-4,5-dihydroxymethylimidazole as a curing accelerator The composition was as follows.
The specific resistance value of this heat conductive conductive composition was 1 × 10E-4 (Ω · cm), and the heat conductivity was 7.2 W / (m · K).
Moreover, about the hole filling test, the favorable result was obtained about each hole diameter of 0.2 mm, 0.4 mm, and 0.6 mm.

[Example 2]
A thermally conductive composition was produced in exactly the same manner as in Example 1 except that the carbon fiber B prepared in Experimental Example 1 was used instead of the carbon fiber A used in Example 1.
The specific resistance value of this heat conductive conductive composition was 3 × 10E-5 (Ω · cm), and the heat conductivity was 9.5 W / (m · K).
Moreover, about the hole filling test, the favorable result was obtained about each hole diameter of 0.4 mm and 0.6 mm. In the 0.2 mm diameter, some portions were insufficiently filled.

[Example 3]
Instead of the carbon fiber A used in Example 1, the same as in Example 1 except that the carbon fiber A prepared in Experimental Example 2 (the surface of the carbon fiber A in Experimental Example 1 coated with silver) was used. Thus, a heat conductive conductive composition was produced.
The specific resistance value of this heat conductive conductive composition was 5 × 10E-5 (Ω · cm), and the heat conductivity was 7.9 W / (m · K).
Moreover, about the hole filling test, the favorable result was obtained about each hole diameter of 0.2 mm, 0.4 mm, and 0.6 mm.

[Example 4]
Instead of the carbon fiber A used in Example 1, the same as in Example 1 except that the carbon fiber B prepared in Experimental Example 2 (the surface of the carbon fiber B of Experimental Example 1 coated with silver) was used. Thus, a heat conductive conductive composition was produced.
The specific resistance value of this heat conductive conductive composition was 1 × 10E-5 (Ω · cm), and the heat conductivity was 10.3 W / (m · K).
Moreover, about the hole filling test, the favorable result was obtained about each hole diameter of 0.4 mm and 0.6 mm. In addition, in the 0.2 mm diameter, a part with insufficient filling was observed.

[Comparative Example 1]
40% by weight of silver fine particles having an average particle diameter of about 8 μm, 40% by weight of flaky silver fine particles having an average particle diameter of about 1.5 μm, 20% by weight of the following resin binder, and ethylene glycol monoethyl ether acetate 2 as a diluent solvent. Part by weight was mixed and vacuum degassed while mixing for 30 minutes using a planetary mixer to produce a heat conductive conductive composition.

As a resin binder, 50 parts by weight of a polyglycidylamine type epoxy resin as a main agent, 50 parts by weight of a novolak type alkylphenol resin as a curing agent, and 1.5 parts by weight of 2-phenyl-4,5-dihydroxymethylimidazole as a curing accelerator The composition was as follows.
The specific resistance value of this thermally conductive conductive composition is 4 × 10E-5 (Ω · cm), which is not significantly different from Examples 1 to 4, and the hole filling test is 0.2 mm, 0.4 mm, 0 Good results were obtained for each hole diameter of 0.6 mm, but the thermal conductivity was 5.1 W / (m · K), which was a considerably low value compared to Examples 1 to 4.

[Example 5] (Preparation of conductive adhesive film)
After further diluting the thermally conductive conductive composition of Example 1 with a diluting solvent, a film of polyparaphenylene terephthalamide with a thickness of 6.5 μm (trade name “Aramika” manufactured by Teijin Advanced Films Ltd.) was applied by a gravure coating method. After coating with a dry film thickness of 40 μm and heat treatment at 70 ° C. for 30 minutes, a polyester film with a thickness of 25 μm with one side coated with a silicone release agent was laminated. The coating layer is in a semi-cured state (B stage state). The conductive film can be integrated with other substrates by peeling the polyester film, laminating it with another substrate, and performing vacuum hot pressing. A film was obtained.

[Example 6] (Preparation of conductive adhesive sheet)
The heat conductive conductive composition of Example 2 was prepared without adding any diluent solvent, and this was die-coated on a polyester film having a thickness of 125 μm, and then between two rolls having a gap fixed at about 250 μm. It was sandwiched with a polyester film having a thickness of 25 μm and heat-treated at 60 ° C. for 1 hour with the polyester film laminated on the coating surface. The thickness of the coating layer was about 100 μm, and it was in a semi-cured state (B stage state), and could be used as a self-supporting conductive adhesive sheet by peeling the polyester films on both sides.

  Since the high thermal conductivity conductive composition of the present invention provides high conductivity and high thermal conductivity, it is possible to form a thermal conduction path (circuit) in addition to the formation of the conductive path (circuit). It can be widely applied as a heat dissipation countermeasure technology in various applications including electronic mounting boards.

Claims (9)

  As a solid component in the composition, pitch-based graphite having at least an average fiber diameter of 0.1 to 30 μm, an aspect ratio of 2 to 100, an average fiber length of 0.2 to 200 μm, and a true density of 2.0 to 2.5 g / cc. High thermal conductivity conductive material comprising 5 to 80% by weight of carbonized carbon fiber filler, 15 to 90% by weight of metal fine particle filler having an average particle size of 0.001 to 30 μm, and 5 to 50% by weight of a binder resin. Sex composition.   The highly heat conductive conductive composition according to claim 1, wherein the crystallite size (Lc) in the c-axis direction of the pitch-based graphitized carbon fiber is 20 to 100 nm.   The highly thermally conductive conductive composition according to claim 1, wherein the crystallite size (La) in the ab axis direction of the pitch-based graphitized carbon fiber is 30 to 200 nm.   A conductive paste for filling a through hole of a wiring board, comprising the highly thermally conductive conductive composition according to claim 1.   A conductive paste for filling a via hole of a wiring board, comprising the highly thermally conductive conductive composition according to claim 1.   A conductive paste for forming a circuit, comprising the highly thermally conductive conductive composition according to claim 1.   A conductive adhesive for fixing electrical contacts, comprising the highly heat conductive conductive composition according to claim 1.   A conductive adhesive tape having a thickness of 10 to 1000 μm, comprising the highly thermally conductive conductive composition according to claim 1.   A conductive adhesive sheet having a thickness of 10 to 1000 μm, comprising the highly thermally conductive conductive composition according to claim 1.