JP6490781B2 - Anisotropic conductive paste and method for manufacturing electronic substrate - Google Patents

Description

  The present invention relates to an anisotropic conductive paste and a method for manufacturing an electronic substrate.

  In recent years, anisotropic conductive adhesives (anisotropic) have been used to connect flexible boards (flexible wiring boards) and rigid boards (non-flexible wiring boards) and electronic components and wiring boards. A connection method using a conductive film or an anisotropic conductive paste is used. For example, when connecting an electronic component and a wiring board, an anisotropic conductive adhesive is disposed between the electronic component on which the electrode is formed and the wiring board on which the electrode pattern is formed. The electrical connection is ensured by thermocompression bonding with the wiring board.

  As an anisotropic conductive paste, a paste containing a solder powder, a thermosetting resin, a carboxylic acid-based curing agent, an imidazole-based curing agent, and an amine-based curing agent has been proposed (for example, Patent Documents). 1). When the electronic component and the wiring substrate are thermocompression bonded, the electrodes of the electronic component to be connected and the wiring substrate can be soldered together, and conductivity between these electrodes is ensured. On the other hand, in the gap between the electrodes of the electronic component and the gap between the electrodes of the wiring board, the solder component is embedded in the resin component, and insulation between adjacent electrodes is ensured.

JP2013-045650A

When an anisotropic conductive paste as described in Patent Document 1 is used, thermocompression bonding is performed at a high temperature of 180 ° C. or higher in order to react a thermosetting resin such as an epoxy resin and its curing agent. Thus, when thermocompression bonding is performed at a high temperature, a gas (mainly a low-boiling point substance such as water) derived from the wiring board or the electronic component is generated in a temperature region lower than the progress of curing of the epoxy resin. And when this gas is taken in in the low viscosity epoxy resin before hardening, the problem that a void generate | occur | produces arises.
Therefore, in the conventional thermocompression bonding process, as a measure for reducing voids, it is necessary to volatilize a low boiling point substance taken into the wiring board or the electronic component in advance. Specifically, for example, a pre-bake process has been performed on a wiring board or an electronic component at a temperature of 150 ° C. for about 5 to 10 minutes. However, such a pre-baking process requires a processing time of about 5 to 10 minutes, so that it is required to omit the pre-baking process.

  Then, an object of this invention is to provide the manufacturing method of the anisotropic conductive paste which can abbreviate | omit the prebaking process before a thermocompression bonding process, and an electronic substrate.

In order to solve the above problems, the present invention provides the following anisotropic conductive paste and method for producing an electronic substrate.
That is, the anisotropic conductive paste of the present invention contains (A) a solder powder , (B) an epoxy resin, (C) a curing agent, (D) an activator, and (E) a pregelling agent. The (D) activator is at least one selected from the group consisting of an organic acid, an organic acid amine salt, a non-salt organic compound in which a halogen atom is covalently bonded, and an amine activator, The amount of the (E) pregelling agent is 2% by mass to 25% by mass with respect to 100% by mass of the anisotropic conductive paste.

In the anisotropic conductive paste of the present invention, the (B) epoxy resin preferably contains (B1) a bisphenol type epoxy resin that is liquid at 25 ° C. and (B2) a novolac type epoxy resin.
In the anisotropic conductive paste of the present invention, the (E) pregelator is preferably polymethacrylic acid ester-based organic fine particles. Moreover, it is preferable that the polymethacrylic acid ester-based organic fine particles have been subjected to a hydrophilic treatment.

The method for manufacturing an electronic substrate according to the present invention is a method for manufacturing an electronic substrate using the anisotropic conductive paste, the application step of applying the anisotropic conductive paste on a wiring substrate, and the step after the application step A preheating step of performing a heat treatment for 3 seconds to 120 seconds at a temperature of 90 ° C. or higher and 150 ° C. or lower on the wiring substrate; and disposing the electronic component on the anisotropic conductive paste, and placing the electronic component on the wiring substrate And a thermocompression bonding step of thermocompression bonding at a temperature of 130 ° C. or higher and 250 ° C. or lower .
In the method for manufacturing an electronic substrate of the present invention, it is preferable that the temperature of the heat treatment is 100 ° C. or higher and 150 ° C. or lower, and the time of the heat treatment is 3 seconds or longer and 30 seconds or shorter.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the anisotropic conductive paste which can abbreviate | omit the prebaking process before a thermocompression bonding process, and an electronic substrate can be provided.

First, the anisotropic conductive paste of the present invention will be described.
The anisotropic conductive paste of the present invention contains (A) conductive particles, (B) an epoxy resin, (C) a curing agent, (D) an activator and (E) a pregelling agent which will be described below. .

[(A) component]
As (A) electroconductive particle used for this invention, if it is an electroconductive particle (powder), a well-known thing can be used suitably. Examples of the component (A) include solder powder, inorganic particles (nickel, copper, silver, carbon, etc.), particles having a surface coated with a highly conductive metal (silver, gold, etc.), and organic particles. Examples thereof include particles having a surface coated with a highly conductive metal (silver, gold, etc.). These electroconductive particles may be used individually by 1 type, and 2 or more types may be mixed and used for them.
As this (A) component, it is preferable to use solder powder from a viewpoint of the electroconductivity between electrodes. The solder powder preferably has a melting point of 240 ° C. or lower, more preferably has a melting point of 180 ° C. or lower, and particularly preferably has a melting point of 130 ° C. or higher and 160 ° C. or lower from the viewpoint of low-temperature processing. . On the other hand, this solder powder preferably has a melting point of 180 ° C. or higher from the viewpoint of soldering strength.
Moreover, it is preferable that this solder powder is a lead-free solder powder from a viewpoint of the influence on an environment. Here, the lead-free solder powder refers to a solder metal or alloy powder to which lead is not added. However, it is allowed that lead is present as an inevitable impurity in the lead-free solder powder, but in this case, the amount of lead is preferably 100 mass ppm or less.

  The component (A) is a group consisting of tin (Sn), bismuth (Bi), copper (Cu), silver (Ag), antimony (Sb), indium (In), zinc (Zn), and titanium (Ti). It is preferably a metal or alloy made of at least one metal selected from the group consisting of: For example, tin-based solders include tin-copper such as Sn-0.7Cu; tin-silver such as Sn-3.5Ag; Sn-3.0Ag-0.5Cu, Sn-3.5Ag-0 Tin-silver-copper systems such as .7Cu, Sn-1.0Ag-0.7Cu, Sn-0.3Ag-0.7Cu; Sn-2.5Ag-1.0Bi-0.5Cu, Sn-1.0Ag Tin-silver-bismuth-copper system such as -2.0Bi-0.5Cu; Tin-silver-bismuth-indium system such as Sn-3.5Ag-0.5Bi-8.0In; Sn-1.0Ag-0 Tin-silver-copper-bismuth-indium system such as 7Cu-2.0Bi-0.2In; Tin-bismuth system such as Sn-58Bi; Tin-silver-bismuth system such as Sn-1.0Ag-58Bi; Sn -5.0 Sb tin-antimony system; S Tin-zinc system such as Sn-9Zn; Tin-zinc-bismuth system such as Sn-8.0Zn-3.0Bi; Tin-indium-antimony-zinc system such as Sn-30In-12Sb-3Zn; Sn-56Bi-4Ti Tin-bismuth-titanium system such as Sn-3.5Ag-4Ti; tin-silver-titanium system such as Sn-52In; tin-indium system such as Sn-52In. Examples of the indium-based solder include indium-based metal indium; indium-silver-based such as In-3.0Ag. In addition to the above metals, iron (Fe), nickel (Ni), cobalt (Co), molybdenum (Mo), phosphorus (P), cerium (Ce), Germanium (Ge), silicon (Si), gallium (Ga), aluminum (Al), niobium (Nb), vanadium (V), calcium (Ca), magnesium (Mg), zirconium (Zr), gold (Au), Palladium (Pd), platinum (Pt), lead (Pb), etc. may be contained. Among these, tin-silver-copper and tin-silver are preferred from the viewpoint of solder joint strength. Further, from the viewpoint of low melting point characteristics, tin-bismuth, tin-silver-bismuth, tin-indium, indium, indium-silver, and the like are more preferable.

  The average particle diameter of the component (A) is usually 1 μm or more and 40 μm or less, but is preferably 1 μm or more and 20 μm or less, more preferably 2 μm or more, from the viewpoint of corresponding to an electronic substrate having a narrow soldering pad pitch. More preferably, it is 15 μm or less, and particularly preferably 3 μm or more and 12 μm or less. The average particle size can be measured with a dynamic light scattering type particle size measuring device.

  The blending amount of the component (A) is preferably 15% by mass or more and 40% by mass or less, and more preferably 17% by mass or more and 35% by mass or less with respect to 100% by mass of the anisotropic conductive paste. 20 mass% or more and 30 mass% or less is particularly preferable. If the compounding quantity of (A) component is more than the said minimum, the adhesive strength and electroconductivity of the anisotropic conductive paste obtained can be ensured. On the other hand, if the blending amount of the component (A) is not more than the above upper limit, the insulating property of the obtained anisotropic conductive paste can be ensured.

[Component (B)]
As (B) epoxy resin used for this invention, a well-known epoxy resin can be used suitably. The component (B) preferably contains (B1) a bisphenol-type epoxy resin that is liquid at 25 ° C. and (B2) a novolac-type epoxy resin. Thus, by using together (B1) component and (B2) component, adhesive strength can be improved, maintaining the pregel property at the time of preheating. Furthermore, this (B) component may contain other epoxy resins (henceforth (B3) component) other than the said (B1) component and the said (B2) component.

Examples of the component (B1) include bisphenol A type epoxy resins and bisphenol F type epoxy resins. These may be used alone or in combination of two or more.
Examples of the component (B2) include biphenyl novolac type epoxy resins, cresol novolac type epoxy resins, and phenol novolac type epoxy resins. Among these, biphenyl novolac type epoxy resins are preferable from the viewpoints of adhesive strength and insulation. Moreover, these may be used individually by 1 type and may be used in mixture of 2 or more types.
When the component (B1) and the component (B2) are used in combination, the blending amount of the component (B1) is 50% by mass to 90% by mass with respect to 100% by mass of the component (B). Preferably, it is 60 mass% or more and 80 mass% or less.

  As the component (B3), crystalline epoxy resins (tetrakis (glycidyloxyphenyl) ethane, triglycidyl isocyanurate, etc.), biphenyl type epoxy resins, naphthalene type epoxy resins, dicyclopentadiene type epoxy resins, and solid at 25 ° C. And bisphenol type epoxy resin. Among these, from the viewpoint of heat resistance, a crystalline epoxy resin is preferable, and tetrakis (glycidyloxyphenyl) ethane is particularly preferable. Moreover, these may be used individually by 1 type and may be used in mixture of 2 or more types.

  The blending amount of the component (B) is preferably 30% by mass to 75% by mass and more preferably 40% by mass to 65% by mass with respect to 100% by mass of the anisotropic conductive paste. 45 mass% or more and 60 mass% or less is particularly preferable. If the compounding quantity of (B) component is below the said minimum, the adhesive strength of the anisotropic conductive paste obtained can be ensured. On the other hand, if the blending amount of the component (B) is not more than the above upper limit, the viscosity of the obtained anisotropic conductive paste can be lowered, and applicability can be secured.

[Component (C)]
Examples of the curing agent (C) used in the present invention include imidazoles, imidazole derivatives, and epoxy resin amine adduct curing agents. These may be used alone or in combination of two or more. Moreover, it is preferable to use together with at least any one of imidazoles and imidazole derivatives, and an epoxy resin amine adduct type hardening | curing agent from a viewpoint of sclerosis | hardenability and the performance of hardened | cured material.

Examples of the imidazoles include 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2,4-diamino-6- [2′-ethyl-4′-methyl. Imidazolyl- (1 ′)]-ethyl-s-triazine, 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine, 2,4-diamino-6- [ 2'-methylimidazolyl- (1 ')]-ethyl-s-triazine isocyanuric acid adduct, 1-cyanoethyl-2-phenylimidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate, 1-cyanoethyl-2- Undecylimidazole and 2,4-diamino-6- [2'-undecylimidazolyl- (1 ')]-ethyl-s-triazine Etc., and the like. Among these, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine isocyanuric acid adduct, and It is preferable to use 1-cyanoethyl-2-phenylimidazolium trimellitate or the like. These may be used alone or in combination of two or more.
Examples of commercially available imidazoles include 2P4MHZ, 2PHZ-PW, 2E4MZ-A, 2MZ-A, 2MA-OK, 2PZ-CN, 2PZCNS-PW, C11Z-CN, and C11Z-A (manufactured by Shikoku Kasei Kogyo Co., Ltd.). Product name).

The imidazole derivative is derived from imidazoles. Examples of commercially available imidazole derivatives include Sanmide LH-210, Imicure AMI-2, and Imicure HAPI (trade name, manufactured by Air Products).
Examples of the epoxy resin amine adduct-based curing agent include Amicure PN-23, PN-F, MY-24, VDH, UDH, PN-31, and PN-40 (manufactured by Ajinomoto Fine Techno Co., Ltd., trade name), EH-3615S. , EH-3293S, EH-3366S, EH-3842, EH-3670S, EH-3636AS, EH-4346S (trade name, manufactured by ADEKA).

  The blending amount of the component (C) is preferably 5% by mass to 30% by mass, more preferably 7% by mass to 25% by mass with respect to 100% by mass of the anisotropic conductive paste. It is particularly preferably 10% by mass or more and 20% by mass or less. If the compounding quantity of (C) component is more than the said minimum, the sclerosis | hardenability of the anisotropic conductive paste obtained can be ensured. On the other hand, if the amount of component (C) is not more than the above upper limit, the storage stability of the resulting anisotropic conductive paste can be ensured.

[(D) component]
Examples of the (D) activator used in the present invention include organic acids, organic acid amine salts, non-dissociative activators, and amine activators. These may be used alone or in combination of two or more. Among these, it is preferable to use an organic acid or an organic acid amine salt from the viewpoint of environmental measures.

Examples of the organic acid include other organic acids in addition to monocarboxylic acid and dicarboxylic acid.
Monocarboxylic acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, capric acid, lauric acid, myristic acid, pentadecylic acid, palmitic acid, margaric acid, stearic acid, tuberculostearic acid Arachidic acid, behenic acid, lignoceric acid, glycolic acid and the like.
Examples of the dicarboxylic acid include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, fumaric acid, maleic acid, tartaric acid, diglycolic acid and the like. Of these, glutaric acid and adipic acid are preferred.
Examples of other organic acids include dimer acid, levulinic acid, lactic acid, acrylic acid, benzoic acid, salicylic acid, anisic acid, citric acid, and picolinic acid.

The organic acid amine salt is an amine salt of the organic acid. As said amine, a well-known amine can be used suitably. Such an amine may be an aromatic amine or an aliphatic amine. These may be used alone or in combination of two or more. As such an amine, an amine having 3 to 13 carbon atoms is preferably used, and a primary amine having 4 to 7 carbon atoms is more preferably used from the viewpoint of the stability of the organic acid amine salt.
Examples of the aromatic amine include benzylamine, aniline, and 1,3-diphenylguanidine. Of these, benzylamine is particularly preferred.
Examples of the aliphatic amine include propylamine, butylamine, pentylamine, hexylamine, heptylamine, octylamine, cyclohexylamine, and triethanolamine.

  Examples of the non-dissociative activator include non-salt organic compounds in which halogen atoms are bonded by a covalent bond. The halogenated compound may be a compound formed by covalent bonding of chlorine, bromine and fluorine, such as chlorinated, brominated and fluoride, but any two or all of chlorine, bromine and fluorine may be used. The compound which has the following covalent bond may be sufficient. In order to improve the solubility in an aqueous solvent, these compounds preferably have a polar group such as a hydroxyl group or a carboxyl group such as a halogenated alcohol or a halogenated carboxyl compound. Examples of the halogenated alcohol include 2,3-dibromopropanol, 2,3-dibromobutanediol, trans-2,3-dibromo-2-butene-1,4-diol, 1,4-dibromo-2-butanol, Brominated alcohols such as tribromoneopentyl alcohol, chlorinated alcohols such as 1,3-dichloro-2-propanol and 1,4-dichloro-2-butanol, fluorinated alcohols such as 3-fluorocatechol, and the like Compounds. Examples of the halogenated carboxyl compound include 2-iodobenzoic acid, 3-iodobenzoic acid, 2-iodopropionic acid, 5-iodosalicylic acid, 5-iodoanthranilic acid, and the like, 2-chlorobenzoic acid, 3-chloro Examples thereof include carboxylated carboxyl compounds such as chloropropionic acid, brominated carboxyl compounds such as 2,3-dibromopropionic acid, 2,3-dibromosuccinic acid and 2-bromobenzoic acid, and the like.

  Examples of the amine activator include amines (polyamines such as ethylenediamine), amine salts (amines such as trimethylolamine, cyclohexylamine, diethylamine, and organic acid salts such as amino alcohols and inorganic acid salts (hydrochloric acid, sulfuric acid, odors). Hydroacid, etc.)), amino acids (glycine, alanine, aspartic acid, glutamic acid, valine, etc.), amide compounds and the like. Specifically, diphenylguanidine hydrobromide, cyclohexylamine hydrobromide, diethylamine salt (hydrochloride, succinate, adipate, sebacate, etc.), triethanolamine, monoethanolamine, etc. And the hydrobromide of the amine.

  The blending amount of the component (D) is preferably 0.1% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less with respect to 100% by mass of the anisotropic conductive paste. More preferably, it is more preferably 1% by mass or more and 3% by mass or less. When the blending amount of the component (D) is equal to or more than the lower limit, an active action on the surface of the solder powder can be secured. Moreover, if the compounding quantity of (D) component is below the said upper limit, the insulation of the anisotropic conductive paste obtained can be ensured.

[(E) component]
The (E) pregelling agent used in the present invention is organic fine particles having good compatibility with the epoxy resin. Moreover, this (E) component can gelatinize an anisotropic electrically conductive paste because an organic fine particle swells when it heats more than predetermined temperature and below the curing temperature of an epoxy resin. The component (E) is preferably polymethacrylate organic fine particles from the viewpoint of suppressing voids. Moreover, it is preferable that the polymethacrylic acid ester-based organic fine particles have been subjected to a hydrophilic treatment. The component (E) may have a core-shell structure.

The average particle size of the component (E) is preferably from 0.1 μm to 5 μm, and more preferably from 0.3 μm to 3 μm. The average particle size can be measured with a dynamic light scattering type particle size measuring device.
Examples of the commercially available component (E) include Zefiac F301, F303, F320, and F351 (trade names such as those manufactured by Aika Kogyo Co., Ltd.).

  The blending amount of the component (E) needs to be 2% by mass or more and 25% by mass or less with respect to 100% by mass of the anisotropic conductive paste. When the compounding amount of the component (E) is less than 2% by mass, the generation of voids cannot be suppressed when the preheating treatment time before the thermocompression bonding process is short. On the other hand, when the blending amount of the component (E) exceeds 25% by mass, the adhesive strength of the obtained anisotropic conductive paste is lowered and the conductivity is insufficient. In addition, from the viewpoint of the balance of voids and electrical conductivity of the obtained anisotropic conductive paste, the amount of the component (E) is 3% by mass or more and 20% by mass or less with respect to 100% by mass of the anisotropic conductive paste. It is more preferable that it is 4 mass% or more and 15 mass% or less.

  The anisotropic conductive paste of the present invention may further contain (F) a thixotropic agent in addition to the components (A) to (E).

[(F) component]
As the (F) thixotropic agent used in the present invention, a known thixotropic agent can be appropriately used. Examples of such thixotropic agents include fatty acid amide, hydrogenated castor oil, olefinic wax, and amorphous silica. Among these, fatty acid amide and amorphous silica are preferable, and amorphous silica is particularly preferable from the viewpoint of difficulty in bleeding of the obtained anisotropic conductive paste. Examples of the amorphous silica include Aerosil R974 and Aerosil 200.
The blending amount of the component (F) is preferably 0.5% by mass or more and 4% by mass or less with respect to 100% by mass of the anisotropic conductive paste. If the compounding quantity of (F) component is more than the said minimum, sufficient thixotropy will be acquired and dripping can fully be suppressed. Moreover, if the compounding quantity of (F) component is below the said upper limit, thixotropy is too high and it does not become a coating defect.

  The anisotropic conductive paste of the present invention is optionally provided with a surfactant, an antifoaming agent, a powder surface treatment agent, a reaction inhibitor, an anti-settling agent in addition to the components (A) to (F). Etc. may be contained. The amount of these additives is preferably 0.01% by mass or more and 10% by mass or less, and 0.05% by mass or more and 5% by mass or less with respect to 100% by mass of the anisotropic conductive paste. It is more preferable.

[Electronic substrate manufacturing method]
Next, the manufacturing method of the electronic substrate of this invention is demonstrated.
The method for manufacturing an electronic substrate of the present invention is a method for manufacturing an electronic substrate using the anisotropic conductive paste of the present invention described above, and a coating step of applying the anisotropic conductive paste on a wiring substrate; A preheating step of performing heat treatment for 3 seconds to 120 seconds at a temperature of 90 ° C. or higher and 150 ° C. or lower with respect to the wiring board after the coating step; and disposing the electronic component on the anisotropic conductive paste; And a thermocompression bonding step of thermocompression bonding to the wiring board.
As the wiring board, a known wiring board such as a printed wiring board can be used. Moreover, as an electronic component, if it has a some electrode, it will not specifically limit, For example, a flexible substrate may be sufficient. Here, the case where the electrodes of a rigid substrate and a flexible substrate are connected using an anisotropic conductive paste will be described as an example.

In the applying step, the anisotropic conductive paste is applied on the rigid substrate.
Examples of the coating apparatus used here include a dispenser, a screen printer, a jet dispenser, and a metal mask printer.
The thickness of the coating film is not particularly limited, but is preferably 50 μm or more and 500 μm or less, and more preferably 100 μm or more and 300 μm or less. When the thickness is less than the lower limit, the adhesive force when the flexible substrate is mounted on the electrode of the rigid substrate tends to be reduced. On the other hand, when the thickness exceeds the upper limit, the paste tends to protrude beyond the connection portion. .

In the preheating step, the wiring substrate after the coating step is subjected to a heat treatment for 3 seconds to 120 seconds at a temperature of 90 ° C. to 150 ° C.
The heat treatment in the preheating step may be within the above range, but may be appropriately changed from the viewpoint of workability. For example, the heat treatment temperature is preferably 100 ° C. or higher and 150 ° C. or lower, more preferably 110 ° C. or higher and 140 ° C. or lower, and particularly preferably 120 ° C. or higher and 130 ° C. or lower. The heat treatment temperature is preferably lower than the melting point of the solder powder. The heat treatment time is preferably 3 seconds or longer and 30 seconds or shorter, more preferably 5 seconds or longer and 20 seconds or shorter, and particularly preferably 5 seconds or longer and 10 seconds or shorter.
Moreover, when using the anisotropic conductive paste containing solder powder, it is preferable that the temperature of heat processing shall be 1 degree C or more lower temperature (more preferably 10 degree C or more lower temperature) than melting | fusing point of the said solder powder. .
In the present invention, the pre-bake process before the thermocompression bonding process can be omitted by performing the pre-heating process with a short processing time. That is, conventionally, as a measure for reducing voids, a pre-bake treatment for volatilizing a low-boiling substance taken into a wiring board or an electronic component in advance is necessary. However, when the anisotropic conductive paste of the present invention is used, the anisotropic conductive paste can be pregelled by the preheating step. And even if the gas (mainly low boiling point substances, such as water) originating in a wiring board or an electronic component generate | occur | produces, it can suppress taking in in an epoxy resin. Therefore, even when the prebaking process before the thermocompression bonding process is omitted, the generation of voids can be sufficiently suppressed.

In the thermocompression bonding step, the flexible substrate is disposed on the anisotropic conductive paste, and the flexible substrate is thermocompression bonded to the rigid substrate. Moreover, when using the anisotropic conductive paste containing solder powder, the temperature at the time of thermocompression bonding is set to a temperature that is 1 ° C. higher than the melting point of the solder powder (preferably higher than 10 ° C.). Is preferred.
When the temperature at the time of thermocompression bonding does not satisfy the condition that the temperature is higher by 1 ° C. or more than the melting point of the solder powder, the solder tends not to be sufficiently melted. Therefore, a sufficient solder joint cannot be formed between the flexible substrate and the rigid substrate, and the conductivity between the flexible substrate and the rigid substrate tends to be insufficient.
The temperature during thermocompression bonding is preferably 130 ° C. or higher and 250 ° C. or lower, more preferably 150 ° C. or higher and 240 ° C. or lower, and particularly preferably 180 ° C. or higher and 220 ° C. or lower.
Although the pressure at the time of thermocompression bonding is not particularly limited, it is preferably 0.05 MPa or more and 4 MPa or less, and more preferably 0.1 MPa or more and 3.5 MPa or less. If the pressure is equal to or higher than the lower limit, a sufficient solder joint can be formed between the rigid substrate and the flexible substrate, and the conductivity between the rigid substrate and the flexible substrate can be improved. On the other hand, if the pressure is equal to or lower than the upper limit, it is possible to suppress the rigid substrate from being excessively stressed and reduce the dead space.
In the present invention, as described above, the pressure at the time of thermocompression bonding can be set to a lower pressure range as compared with the case of the method using the conductive filler-based anisotropic conductive paste. Therefore, cost reduction of the apparatus used for a thermocompression bonding process can also be achieved.
Although the time at the time of thermocompression bonding is not particularly limited, it is usually 1 second to 60 seconds, preferably 2 seconds to 20 seconds, and more preferably 3 seconds to 15 seconds.

  Further, the connection method using the anisotropic conductive paste of the present invention is not limited to the connection method described above, and modifications, improvements, etc. within a range where the object of the present invention can be achieved are included in the present invention. is there.

EXAMPLES Next, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited at all by these examples. In addition, the material used in the Example and the comparative example is shown below.
((A) component)
Conductive particles: solder powder, average particle diameter is 12 μm, solder melting point is 139 ° C., solder composition is 42 Sn / 58 Bi
((B1) component)
Epoxy resin A: Mixed liquid epoxy resin of bisphenol F type and bisphenol A type, trade name “EPICRON EXA-830LVP”, manufactured by DIC (component (B2))
Epoxy resin B: biphenyl novolac type epoxy resin, trade name “NC-3000”, manufactured by Nippon Kayaku Co., Ltd. (component (B3))
Epoxy resin C: tetrakis (glycidyloxyphenyl) ethane, trade name “GTR-1800”, manufactured by Nippon Kayaku Co., Ltd. (component (C))
Curing agent A: 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine, trade name “Curazole 2P4MHZ”, curing agent B manufactured by Shikoku Kasei Kogyo Co., Ltd .: imidazole derivative, Product name “Sunmide LH-210”, Air Products Co., Ltd. hardener C: Epoxy resin amine adduct, “Amure PN-F”, Ajinomoto Fine Techno Co., Ltd. (component (D))
Activator A: Adipic acid Activator B: Benzylamine adipate (component (E))
Pregelling agent A: Modified polymethacrylic acid ester fine particles (hydrophilic treatment), trade name “Zefiac F303”, Aika Kogyo Co., Ltd. Pregelling agent B: Polymethacrylic acid ester fine particles, trade name “Zefiac F320”, Aika Kogyo Pregelling agent C: Core-shell type acrylic fine particles, trade name “Zefiac F351”, manufactured by Aika Kogyo Co., Ltd. (component (F))
Thixotropic agent A: Trade name “Gelall D”, Shin Nippon Chemical Co., Ltd. thixotropic agent B: Amorphous silica, trade name “AEROSIL R974”, Nippon Aerosil Co., Ltd. (other ingredients)
Organic fine particles: Multi-layered organic fine particles, trade name “STAPHYLOID AC-3355”, manufactured by Aika Industry Co., Ltd.

[Example 1]
Epoxy resin A 35 parts by mass, epoxy resin B 15 parts by mass, epoxy resin C 5 parts by mass, curing agent A 5 parts by mass, curing agent B 5 parts by mass, curing agent C 5 parts by mass, activator A 1 part by mass, activator B 1 part by mass, thixotropic agent A 1 part by mass, 2 parts by mass of thixotropic agent B, and 3 parts by mass of pregelling agent A are charged into a container, premixed with a stirrer, and then mixed and dispersed at room temperature using a three roll to obtain a resin composition. It was.
Then, with respect to 78 mass parts of obtained resin compositions, 25 mass parts of electroconductive particles were thrown into the container, and the anisotropic conductive paste was prepared by mixing for 2 hours with a kneader.
Next, a rigid substrate (base material: FR-4, line width: 100 μm, pitch: 200 μm, copper thickness: 18 μm) is prepared, and the obtained anisotropic conductive paste is used as a dispenser on the comb-shaped electrode of the rigid substrate. (Thickness: 0.2 mm). Then, the rigid substrate after coating is preheated at a temperature of 130 ° C. for 10 seconds, and then a flexible substrate (line width: 100 μm, pitch: 200 μm, copper thickness: 12 μm) is formed on the anisotropic conductive paste. Place the flexible substrate on the rigid substrate using a thermocompression bonding apparatus (manufactured by Advancel) at a temperature of 180 ° C., a pressure of 1.0 MPa, and a bonding time of 15 seconds. (Evaluation substrate) was prepared.

[Examples 2-6 and Comparative Examples 1-3]
An anisotropic conductive paste was obtained in the same manner as in Example 1 except that each material was blended according to the composition shown in Table 1.
Further, a rigid substrate with a flexible substrate (evaluation substrate) was produced in the same manner as in Example 1 except that the obtained anisotropic conductive paste was used.

<Evaluation of anisotropic conductive paste>
Evaluation of the anisotropic conductive paste (void, adhesive strength, conductivity, initial bonding failure rate) was performed by the following method. The obtained results are shown in Table 1.
(1) Void The evaluation substrate is observed with a measurement microscope (“STM6” manufactured by Olympus), and the area of the portion where the rigid substrate and the flexible substrate overlap in the evaluation substrate and the area of the location where bubbles are present are measured. The ratio of bubbles [(area of the area where bubbles exist) / (area of the overlapping part) × 100%] was measured. Voids were evaluated according to the following criteria.
○: The ratio of bubbles is 10% or less.
(Triangle | delta): The ratio for which a bubble accounts is 20% or less exceeding 10%.
X: The ratio for which a bubble accounts is more than 20%.
(2) Adhesive strength (peel strength)
Using a testing machine (“Dage4000” manufactured by Dage), pulling the flexible substrate at a test speed of 50 mm / min with the angle of the flexible substrate relative to the rigid substrate in the evaluation substrate being 90 degrees, peel strength at that time ( Unit: N / mm) was measured. And the adhesive strength was evaluated according to the following criteria.
○: Peel strength is 0.8 N / mm or more.
Δ: Peel strength is 0.6 N / mm or more and less than 0.8 N / mm.
X: Peel strength is less than 0.6 N / mm.
(3) Conductivity The resistance value of the evaluation substrate was measured using a digital multimeter (“34410A” manufactured by Agilent Technologies). In addition, the resistance value was measured by connecting terminals to the electrode of the rigid substrate and the electrode of the flexible substrate, respectively. If the resistance value is measured as a measurement standard, it can be seen that the circuit is conductive and it can be determined that the circuit can be formed. The conductivity was evaluated according to the following criteria.
○: Resistance value is 100 mΩ or less.
Δ: Resistance value exceeds 100 mΩ.
X: Resistance value is too high to measure.
(4) Initial bonding failure rate Ten evaluation boards for the continuity test were prepared, and the continuity test was performed on each evaluation board. The ratio (number of unmeasurable / number of test pieces) to the number of times (number of unmeasurable) that the continuity evaluation result for the number of evaluation boards (number of test pieces) was “x” was evaluated as the initial bonding failure rate. .

As is clear from the results shown in Table 1, when the anisotropic conductive paste of the present invention was used (Examples 1 to 6), voids were generated even when the pre-bake treatment before the thermocompression bonding step was omitted. It was confirmed that the material can be sufficiently suppressed and has sufficient adhesive strength and electrical conductivity. Therefore, according to the anisotropic conductive paste of this invention, it was confirmed that the prebaking process before a thermocompression bonding process can be skipped.
On the other hand, when the anisotropic conductive paste containing no pregelling agent is used (Comparative Examples 1 and 3), it is found that a void problem occurs when the prebaking process before the thermocompression bonding step is omitted. It was. Moreover, when there were too many compounding quantities of the pregelling agent (comparative example 2), it turned out that the problem of electroconductivity generate | occur | produces.

[Example 7]
A rigid substrate with a flexible substrate (evaluation substrate) was prepared in the same manner as in Example 2 except that the rigid substrate after coating was preheated at 90 ° C. for 3 seconds.
[Example 8]
A rigid substrate with a flexible substrate (evaluation substrate) was prepared in the same manner as in Example 2 except that the rigid substrate after coating was preheated at a temperature of 150 ° C. for 120 seconds.
[Example 9]
A rigid substrate with a flexible substrate (evaluation substrate) was prepared in the same manner as in Example 2 except that the rigid substrate after coating was preheated at 90 ° C. for 120 seconds.
[Example 10]
A rigid substrate with a flexible substrate (evaluation substrate) was produced in the same manner as in Example 2 except that the rigid substrate after coating was preheated at a temperature of 150 ° C. for 3 seconds.

<Evaluation of electronic substrate manufacturing method>
Evaluation of the manufacturing method of the electronic substrate (void, adhesive strength, conductivity, initial bonding failure rate) was performed by the same method as the evaluation of the anisotropic conductive paste described above. The obtained results are shown in Table 2. Table 2 shows the heat treatment temperature and heat treatment time in the preheating step. For reference, the results of Example 2 are also shown in Table 2.

  As is clear from the results shown in Table 2, if the heat treatment temperature in the preheating step is 90 ° C. or more and 150 ° C. or less and the heat treatment time is 3 seconds or more and 120 seconds or less (Examples 7 to 10), In the case of using the anisotropic conductive paste, it was confirmed that even when the pre-bake treatment before the thermocompression bonding step is omitted, the generation of voids can be sufficiently suppressed and the adhesive strength and conductivity are sufficient.

  The anisotropic conductive paste of the present invention can be suitably used as a technique for connecting wiring boards (for example, a flexible board and a rigid board) or a technique for connecting an electronic component and a wiring board.

Claims (6)

(A) a solder powder , (B) an epoxy resin, (C) a curing agent, (D) an activator, and (E) a pregelling agent,
The (D) activator is at least one selected from the group consisting of an organic acid, an organic acid amine salt, a non-salt organic compound in which a halogen atom is covalently bonded, and an amine activator,
The anisotropic conductive paste characterized in that the compounding amount of the (E) pregelling agent is 2% by mass or more and 25% by mass or less with respect to 100% by mass of the anisotropic conductive paste. The anisotropic conductive paste according to claim 1 ,
The anisotropic conductive paste, wherein the (B) epoxy resin contains (B1) a bisphenol-type epoxy resin that is liquid at 25 ° C. and (B2) a novolac-type epoxy resin. In the anisotropic conductive paste according to claim 1 or 2 ,
The anisotropic conductive paste, wherein the pregelling agent (E) is polymethacrylate organic fine particles. In the anisotropic conductive paste according to claim 3 ,
The anisotropic conductive paste, wherein the polymethacrylate organic fine particles are subjected to a hydrophilic treatment. A method for producing an electronic substrate using the anisotropic conductive paste according to any one of claims 1 to 4 ,
An application step of applying the anisotropic conductive paste on the wiring board;
A preheating step of performing a heat treatment for 3 seconds to 120 seconds at a temperature of 90 ° C. or more and 150 ° C. or less to the wiring board after the coating step;
A thermocompression bonding step of placing an electronic component on the anisotropic conductive paste, and thermocompression bonding the electronic component to the wiring board at a temperature of 130 ° C. or higher and 250 ° C. or lower ;
A method for manufacturing an electronic substrate, comprising: In the manufacturing method of the electronic substrate of Claim 5 ,
The temperature of the said heat processing is 100 degreeC or more and 150 degrees C or less, The time of the said heat processing is 3 seconds or more and 30 seconds or less. The manufacturing method of the electronic substrate characterized by the above-mentioned.