JP6600019B2 - Method for manufacturing electronic substrate and anisotropic conductive paste - Google Patents

Description

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

  In recent years, anisotropic conductive adhesives (anisotropic) have been used for connection between flexible boards (wiring boards having flexibility) and rigid boards (wiring boards not having flexibility) and between 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 paste is disposed between the electronic component on which the electrode is formed and the wiring board on which the electrode pattern is formed, and the electronic component and the wiring are connected. The electrical connection is ensured by thermocompression bonding with the substrate.

  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

  In the case of using an anisotropic conductive paste as described in Patent Document 1, the entire electrode surface is not solder-bonded, and a part of the electrode surface is solder-bonded so that conduction between the electrodes can be achieved. Sex is secured. For conductivity, this is sufficient, but it is more preferable that the entire electrode surface is soldered in consideration of, for example, a case where a high-frequency current or a large current flows.

  Then, this invention aims at providing the manufacturing method of the electronic substrate which can produce the electronic substrate which has high connection reliability using an anisotropic conductive paste, and the anisotropic conductive paste used for the method .

In order to solve the above problems, the present invention provides the following method for manufacturing an electronic substrate and anisotropic conductive paste.
That is, the method for manufacturing an electronic substrate according to the present invention is a method for manufacturing an electronic substrate in which an electronic substrate is manufactured by connecting a first wiring substrate and a second wiring substrate or an electronic component using an anisotropic conductive paste. A thermosetting resin composition, wherein the anisotropic conductive paste comprises (A) a solder powder having a melting point of 150 ° C. or less, (B) an epoxy resin, (C) a curing agent, and (D) an activator. The blending amount of the component (A) is more than 50% by weight and 75% by weight or less with respect to 100% by weight of the anisotropic conductive paste, and the blending amount of the thermosetting resin composition Is an application step of applying the anisotropic conductive paste on the first wiring board, and anisotropy, with respect to 100% by mass of the anisotropic conductive paste. The second wiring board or the electronic part on a conductive paste A thermocompression bonding step in which the second wiring board or the electronic component is thermocompression bonded to the first wiring board at a temperature higher than the melting point of the component (A), and the first after the thermocompression bonding process. A thermosetting step of heating the wiring board and the second wiring board or the electronic component to cure the thermosetting resin composition, and the pitch of the electrodes of the first wiring board, and the second The pitch of the electrodes of the wiring board or the electronic component is 60 μm or more and 500 μm or less, respectively, and the total of the thickness of the electrode of the first wiring board and the thickness of the electrode of the second wiring board or the electronic component is 20 μm. The method is characterized by being 100 μm or less.

  An anisotropic conductive paste of the present invention is an anisotropic conductive paste used in the method for producing an electronic substrate, wherein (A) a solder powder having a melting point of 150 ° C. or less, (B) an epoxy resin, (C) A thermosetting resin composition containing a curing agent and (D) an activator, and the blending amount of the component (A) is more than 50% by mass with respect to 100% by mass of the anisotropic conductive paste. The blending amount of the thermosetting resin composition is 25% by mass or more and less than 50% by mass with respect to 100% by mass of the anisotropic conductive paste.

In the present invention, the anisotropic conductive paste means that the electrodes to be connected can be electrically connected to each other, and has conductivity in the vertical direction of the substrate, but is insulative in the surface direction of the substrate in other portions. The paste which can form the anisotropic electrically-conductive material which has this.
In addition, according to the method for manufacturing an electronic substrate of the present invention, the reason why an electronic substrate having high connection reliability can be manufactured using an anisotropic conductive paste is not necessarily clear, but the present inventors are as follows. To guess.

  That is, when the anisotropic conductive paste used in the present invention is thermocompression bonded at a temperature equal to or higher than the melting point of the solder powder, the lead-free solder powders are melted and close to each other, and the surrounding solders Join and grow. Moreover, since the space | interval of the electrodes of an electronic component and a wiring board also becomes short by thermocompression bonding, electrodes can be solder-joined by the molten solder enlarged as mentioned above. Further, the surrounding solder powder gathers on the molten solder, and solder bonding can be performed on the entire surface of the electrode. On the other hand, the amount of solder powder existing in the gap between the electrodes of the wiring board is reduced by collecting the surrounding solder powder by molten solder. As a result, insulation is ensured between the electrodes of the wiring board. As described above, the present inventors speculate that the effects of the present invention are achieved.

  ADVANTAGE OF THE INVENTION According to this invention, the anisotropic conductive paste which can produce the electronic substrate which can produce the electronic substrate which has high connection reliability using anisotropic conductive paste, and the anisotropic conductive paste used for the method can be provided.

It is the schematic which shows an example of the 1st wiring board used for this embodiment. It is II-II sectional drawing of FIG. 1 in this embodiment. It is the schematic which shows an example of the 2nd wiring board used for this embodiment. It is IV-IV sectional drawing of FIG. 3 in this embodiment. In this embodiment, it is the schematic which shows an example of the state which has arrange | positioned the 2nd wiring board on anisotropic conductive paste. In this embodiment, it is the schematic which shows an example of the state which thermocompression-bonds a 2nd wiring board to a 1st wiring board. In this embodiment, it is the schematic which shows an example of the state which has arrange | positioned the 2nd wiring board on anisotropic conductive paste. In this embodiment, it is the schematic which shows an example of the state which thermocompression-bonds a 2nd wiring board to a 1st wiring board. 4 is a photograph showing a comb-shaped electrode portion of a rigid substrate in the evaluation substrate obtained in Example 1. FIG. 6 is a photograph showing a comb-shaped electrode portion of a rigid substrate in an evaluation substrate obtained in Comparative Example 1; 2 is a photograph showing a cross-section of a comb-shaped electrode portion on an evaluation substrate obtained in Example 1. FIG. 4 is a photograph showing a cross section of a comb-shaped electrode portion in an evaluation substrate obtained in Comparative Example 1. FIG.

[Anisotropic conductive paste]
First, the anisotropic conductive paste of this embodiment will be described.
The anisotropic conductive paste of the present embodiment is an anisotropic conductive paste used for the electronic substrate manufacturing method of the present embodiment described later. And this anisotropic conductive paste contains (A) a solder powder whose melting point is 150 ° C. or less, which will be described below, and a thermosetting resin composition which will be described below. More than 50 mass% and 75 mass% or less with respect to 100 mass% of the anisotropic conductive paste, and the blending amount of the thermosetting resin composition is 25 mass% or more with respect to 100 mass% of the anisotropic conductive paste. It is less than 50% by mass.
When the blending amount of the component (A) is 50% by mass or less (when the blending amount of the thermosetting resin composition is 50% by mass or more), the obtained anisotropic conductive paste is subjected to thermocompression bonding. The entire surface cannot form a solder joint. On the other hand, when the blending amount of the component (A) exceeds 75% by mass (when the blending amount of the thermosetting resin composition is less than 25% by mass), the anisotropy is not exhibited by the solder bridge. Further, in the obtained anisotropic conductive paste, the blending amount of the component (A) is preferably 50.5% by mass or more and 70% by mass or less from the viewpoint of balancing insulation and connection reliability. More preferably, it is 50.5 mass% or more and 65 mass% or less.

[(A) component]
The (A) solder powder used in the present embodiment has a melting point of 150 ° C. or lower. 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 based such as Sn-9Zn; tin-zinc-bismuth based such as Sn-8.0Zn-3.0Bi; tin-indium-antimony-zinc based 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-bismuth, tin-silver-bismuth, tin-indium, indium, indium-silver, and the like are more preferable from the viewpoint of low melting point characteristics.

  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.

[Thermosetting resin composition]
The thermosetting resin composition used in the present embodiment includes (B) an epoxy resin, (C) a curing agent, and (D) an activator. The acid value of the thermosetting resin composition is preferably from 10 mgKOH / g or higher 55 mg KOH / g, more preferably at most 15 mgKOH / g or more 50mgKOH / g, 30mgKOH / g or more 45 mg KOH / g by particularly preferably less. From the viewpoint of activation of the solder, the acid value is preferably equal to or higher than the lower limit, and from the viewpoint of insulation in the obtained anisotropic conductive paste, the acid value is preferably equal to or lower than the upper limit.

[Component (B)]
As (B) epoxy resin used for this embodiment, a well-known epoxy resin can be used suitably. Examples of such epoxy resins include bisphenol A type, bisphenol F type, biphenyl type, naphthalene type, cresol novolac type, phenol novolac type, and dicyclopentadiene type epoxy resins. These epoxy resins may be used individually by 1 type, and may mix and use 2 or more types. Further, these epoxy resins preferably contain a liquid at normal temperature, and when a solid at normal temperature is used, it is preferably used in combination with a liquid at normal temperature.

  (B) As a compounding quantity of a component, it is preferable that it is 70 to 95 mass% with respect to 100 mass% of thermosetting resin compositions, and it is more preferable that it is 75 to 92 mass%. It is particularly preferably 80% by mass or more and 90% by mass or less. (B) If the compounding quantity of a component is more than the said minimum, the tolerance with respect to a drop impact can be improved. 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 the coating property can be improved.

[Component (C)]
Examples of the curing agent (C) used in the present embodiment 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.
In addition, it is preferable that the thermosetting resin composition used for this embodiment does not inhibit solder aggregation. From this point of view, it is preferable that the thermosetting resin composition does not progress excessively during thermocompression bonding, and it is preferable to select a component (C) that is difficult to cure during thermocompression bonding.

Examples of imidazoles include 2-phenyl-4-methyl-5-hydroxymethylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2,4-diamino-6- [2′-ethyl-4′-methylimidazolyl. -(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-un Decylimidazole, 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 Chemical Industries, etc. , Product name).

Imidazole derivatives are those 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 amount of component (C) is preferably 1% by mass or more and 15% by mass or less, more preferably 2% by mass or more and 10% by mass or less with respect to 100% by mass of the thermosetting resin composition. The content is particularly preferably 3% by mass or more and 6% 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 improved. 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 improved.

[(D) component]
Examples of the (D) activator used in the present embodiment 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 besides 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 the amine, a known amine can be appropriately used. 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.
Aromatic amines include benzylamine, aniline, 1,3-diphenylguanidine and the like. 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.

  Amine-based activators include amines (such as polyamines such as ethylenediamine), amine salts (such as amines such as trimethylolamine, cyclohexylamine, and diethylamine) and organic acid salts and inorganic acid salts such as amino alcohols (hydrochloric acid, sulfuric acid, bromide). 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.

  (D) As a compounding quantity of a component, it is preferable that it is 0.1 to 10 mass% with respect to 100 mass% of thermosetting resin compositions, and is 0.5 to 8 mass%. More preferably, it is more preferably 1% by mass or more and 5% by mass or less. If the blending amount of the component (D) is not less than the lower limit, the active action on the surface of the solder powder can be enhanced. Moreover, if the compounding quantity of (D) component is below the said upper limit, the insulation of the anisotropic conductive paste obtained can be improved.

[Other ingredients]
The thermosetting resin composition used in the present embodiment, if necessary, in addition to the components (B) to (D), a thixotropic agent, a surfactant, a coupling agent, an antifoaming agent, a powder surface treatment agent, You may contain additives, such as a reaction inhibitor and a sedimentation inhibitor. As a compounding quantity of these additives, it is preferable that it is 0.01 mass% or more and 10 mass% or less with respect to 100 mass% of thermosetting resin compositions, and 0.05 mass% or more and 5 mass% or less. More preferably.
In addition, it is preferable that the thermosetting resin composition used for this embodiment does not inhibit solder aggregation. From this viewpoint, it is preferable that the thermosetting resin composition does not contain a thixotropic agent. Moreover, when using a thixotropic agent, it is preferable that the compounding quantity is 2 mass% or less with respect to 100 mass% of thermosetting resin compositions, and it is more preferable that it is 1 mass% or less.

[Electronic substrate manufacturing method]
Next, the manufacturing method of the electronic substrate of this embodiment is demonstrated based on drawing. FIGS. 1-8 is a figure for demonstrating the manufacturing method of the electronic substrate of this embodiment.
The method for manufacturing an electronic substrate according to this embodiment is a method in which an electronic substrate is manufactured by connecting a first wiring substrate and a second wiring substrate or an electronic component using the anisotropic conductive paste described above.
Moreover, the manufacturing method of the electronic substrate of this embodiment is provided with the application | coating process, thermocompression-bonding process, and thermosetting process which are demonstrated below.

Examples of the electronic component include a chip and a package component.
As the first wiring board and the second wiring board, any of a flexible board having flexibility and a rigid board having no flexibility can be used. Here, a rigid substrate is used as the first wiring substrate, a flexible substrate is used as the second wiring substrate, and the rigid substrate and the flexible substrate are connected using the anisotropic conductive paste described above. An example will be described.

As shown in FIG. 1, the rigid substrate 1 includes a rigid base material 11 as a first base material, a first wiring 12, and a solder resist film 13 as a first insulating film. Further, as shown in FIGS. 1 and 2, a solder resist film 13 is provided at the end portion of the rigid substrate 1 so as to cover the first wiring 12 at the connection portion between the rigid substrate 1 and the flexible substrate 2. It is preferable. This solder resist film 13 can dam the anisotropic conductive paste at the time of thermocompression bonding, so that the solder in the anisotropic conductive paste flows out to the end of the rigid substrate 1 and excessively gathers to form a bridge. Such a problem can be suppressed.
Further, in the rigid substrate 1, as shown in FIG. 1, in the connection portion between the rigid substrate 1 and the flexible substrate 2, a connection area AA in which the solder resist film 13 is not provided in a plan view is formed in the solder resist film 13. It is preferable that it is provided so that it may be surrounded by. The solder resist film 13 outside the connection area AA can dam the anisotropic conductive paste during thermocompression bonding, so that the solder in the anisotropic conductive paste flows out and gathers excessively to form a bridge. Can be suppressed. The connection area AA is preferably rectangular in plan view.
As shown in FIGS. 3 and 4, the flexible substrate 2 includes a flexible substrate 21 as a second substrate, a second wiring 22, and a coverlay 23 as a second insulating film.

In the electronic substrate manufacturing method of the present embodiment, the pitch of the electrodes of the rigid substrate 1 and the pitch of the electrodes of the flexible substrate 2 are required to be 60 μm or more and 500 μm or less, respectively. When the pitch of the electrodes is out of the above range, it is impossible to achieve both high connection reliability and insulation using an anisotropic conductive paste.
Moreover, in the manufacturing method of the electronic substrate of this embodiment, the sum total of the thickness of the electrode of the rigid board | substrate 1 and the thickness of the electrode of the flexible substrate 2 needs to be 20 micrometers or more and 100 micrometers or less. When the total thickness is out of the above range, it is impossible to achieve both high connection reliability and insulation using an anisotropic conductive paste.

In the application step, the anisotropic conductive paste 3 is applied on the rigid substrate 1 as the first wiring substrate.
Examples of the coating device 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 10 μm or more and 500 μm or less, more preferably 20 μm or more and 300 μm or less, and particularly preferably 30 μm or more and 100 μm or less. If thickness is more than the said minimum, the adhesive force of a rigid board | substrate and a flexible substrate can be improved. On the other hand, if the thickness is less than or equal to the above upper limit, the paste can hardly protrude beyond the connection portion.

In the thermocompression bonding step, the flexible substrate 2 as the second wiring substrate is disposed on the anisotropic conductive paste 3, and the flexible substrate 2 is thermocompression bonded to the rigid substrate 1 at a temperature higher than the melting point of the component (A). .
If the temperature at the time of thermocompression bonding does not satisfy the condition that the melting point of the component (A) is higher than the melting point, the solder cannot be sufficiently melted and sufficient solder bonding between the rigid substrate 1 and the flexible substrate 2 is achieved. Cannot be formed, and the conductivity between the rigid substrate 1 and the flexible substrate 2 becomes insufficient. The temperature at the time of thermocompression bonding is preferably 5 ° C. or more higher than the melting point of component (A), more preferably 10 ° C. or more higher than the melting point of component (A), and higher than the melting point of component (A). It is particularly preferable that the temperature is 30 ° C. or higher.
The pressure during thermocompression bonding is not particularly limited, but is preferably 0.05 MPa or more and 3 MPa or less, more preferably 0.2 MPa or more and 2 MPa or less, and particularly preferably 0.5 MPa or more and 1.5 MPa or less. preferable. If the pressure is equal to or higher than the lower limit, a sufficient solder joint can be formed between the rigid substrate 1 and the flexible substrate 2, and the conductivity between the rigid substrate 1 and the flexible substrate 2 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 1 from being excessively stressed and to reduce the dead space.
In the present embodiment, as described above, the pressure at the time of thermocompression bonding can be set to a lower pressure range as compared with the conventional method. 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.

As one form of said thermocompression-bonding process, as shown in FIG.5 and FIG.6, it is preferable to satisfy | fill the following conditions (x1)-(x3).
Condition (x1): When the flexible substrate 2 is disposed on the anisotropic conductive paste 3, the end portion of the flexible substrate 2 and the solder resist film 13 overlap in plan view.
Condition (x2): When the flexible substrate 2 is disposed on the anisotropic conductive paste 3, the end portion of the rigid substrate 1 and the coverlay 23 do not overlap in plan view.
Condition (x3): During thermocompression bonding, the heat tool 4 used for thermocompression bonding overlaps over the entire connection area AA in plan view.
When the conditions (x1) and (x2) are satisfied, the pressure by the heat tool 4 is not directly applied to the anisotropic conductive paste 3 at the time of thermocompression bonding. Further, a weir with the solder resist film 13 is formed outside the connection area AA, and it is possible to reliably prevent the anisotropic conductive paste 3 from flowing outside the connection area AA during thermocompression bonding. Furthermore, since the thermocompression bonding is performed over the entire area of the connection area AA according to the condition (x3), the solder joint can be more reliably formed.

As another form of said thermocompression-bonding process, as shown in FIG.7 and FIG.8, it is preferable to satisfy | fill the following conditions (y1)-(y3).
Condition (y1): When the flexible substrate 2 is disposed on the anisotropic conductive paste 3, the end portion of the flexible substrate 2 and the solder resist film 13 overlap each other in plan view.
Condition (y2): When the flexible substrate 2 is disposed on the anisotropic conductive paste 3, the end portion of the rigid substrate 1 and the cover lay 23 overlap each other in plan view.
Condition (y3): In thermocompression bonding, the heat tool 4 used for thermocompression bonding and the connection area AA overlap in plan view, but the peripheral edge of the connection area AA does not overlap with the heat tool 4.
When the conditions (y1) and (y2) are satisfied, the pressure by the heat tool 4 is not directly applied to the anisotropic conductive paste 3 at the time of thermocompression bonding. In addition, a weir is formed by the solder resist film 13 outside the connection area AA, and it is possible to reliably prevent the anisotropic conductive paste 3 from flowing outside the connection area AA during thermocompression bonding. Furthermore, as shown in FIG. 8, the flexible substrate 2 is deformed by the condition (y3), and this allows air bubbles in the anisotropic conductive paste 3 to escape from the peripheral portion of the connection area AA. Therefore, it can be more reliably suppressed than the voids in the anisotropic conductive paste 3.

In the thermosetting step, the rigid substrate 1 and the flexible substrate 2 after the thermocompression bonding step are heated to cure the thermosetting resin composition.
As the heating furnace, a known heating furnace can be appropriately used.
As heating conditions, the heating temperature is preferably 100 ° C. or higher and 150 ° C. or lower, more preferably 110 ° C. or higher and 135 ° C. or lower, and particularly preferably 120 ° C. or higher and 130 ° C. or lower. When the heating temperature is within the above range, the thermosetting resin composition can be sufficiently cured, and there is little adverse effect on the electronic component mounted on the electronic substrate.
The heating time is preferably 10 minutes or more and 2 hours or less, more preferably 15 minutes or more and 1 hour or less, and particularly preferably 20 minutes or more and 40 minutes or less. When the heating time is within the above range, the thermosetting resin composition can be sufficiently cured, and there is little adverse effect on the electronic components mounted on the electronic substrate.

According to the electronic substrate manufacturing method of the present embodiment as described above, an electronic substrate having high connection reliability can be manufactured using an anisotropic conductive paste.
The manufacturing method of the anisotropic conductive paste and the electronic substrate of the present invention is not limited to the above-described embodiment, and modifications, improvements, etc. within the scope that can achieve the object of the present invention are included in the present invention. It is.

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)
Solder powder: average particle size is 12 μm (particle size range: 5 μm to 20 μm), solder melting point is 139 ° C., solder composition is 42 Sn / 58 Bi
((B) component)
Epoxy resin A: Liquid epoxy resin, trade name “ZX-1059”, Nippon Steel & Sumikin Chemical Co., Ltd. epoxy resin B: Biphenyl novolac type epoxy resin, trade name “NC-3000”, Nippon Kayaku Co., Ltd. epoxy resin C: Tetrakis ( Glycidyloxyphenyl) ethane, trade name “GTR-1800”, manufactured by Nippon Kayaku Co., Ltd. (component (C))
Curing agent: 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine, trade name “Cureazole 2MZA-PW”, manufactured by Shikoku Kasei Kogyo Co., Ltd. (component (D))
Activator A: Adipic acid Activator B: Benzylamine adipate (other ingredients)
Thixo: Brand name “Gelall D”, manufactured by Shin Nippon Rika Co., Ltd.

[Example 1]
60% by mass of epoxy resin A, 20% by mass of epoxy resin B, 10% by mass of epoxy resin C, 5% by mass of curing agent, 2% by mass of activator A, 2% by mass of activator B, and 1% by mass of thixotropic agent are charged into a container. After preliminary mixing, the mixture was dispersed and mixed at room temperature using three rolls to obtain a thermosetting resin composition.
Then, with respect to 49.5 mass% of obtained thermosetting resin compositions, 50.5 mass% of solder powder was put into a 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) was prepared, and the obtained anisotropic conductive paste was applied to a metal mask on the comb-shaped electrode of the rigid substrate. It apply | coated with the printing machine (thickness: 0.05 mm). A flexible substrate (line width: 100 μm, pitch: 200 μm, copper thickness: 12 μm) is placed on the anisotropic conductive paste, and a thermocompression bonding apparatus (manufactured by Ohashi Seisakusho Co., Ltd.) is used at a temperature of 190 ° C. and a pressure of 1 MPa. Then, the flexible substrate is thermocompression bonded to the rigid substrate under the condition of the bonding time of 10 seconds (thermocompression process), and then subjected to a heat treatment at a temperature of 120 ° C. for 30 minutes (thermosetting process). A substrate (evaluation substrate) was produced. Table 1 shows the heating conditions in the thermocompression bonding step and the thermosetting step.

[Example 2]
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.
A rigid substrate (evaluation substrate) with a flexible substrate was produced in the same manner as in Example 1 except that the obtained anisotropic conductive paste was used. Table 1 shows the heating conditions in the thermocompression bonding step and the thermosetting step.

[Comparative Example 1]
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.
Next, a rigid substrate (base material: FR-4, line width: 100 μm, pitch: 200 μm, copper thickness: 18 μm) was prepared, and the obtained anisotropic conductive paste was applied to a metal mask on the comb-shaped electrode of the rigid substrate. It apply | coated with the printing machine (thickness: 0.05 mm). The rigid substrate after coating is preheated at a temperature of 130 ° C. for 6 seconds, and then a flexible substrate (line width: 100 μm, pitch: 200 μm, copper thickness: 12 μm) is formed on the anisotropic conductive paste. Using a thermocompression bonding device (manufactured by Ohashi Seisakusho Co., Ltd.), a flexible substrate is thermocompression bonded to a rigid substrate (thermocompression process) under conditions of a temperature of 180 ° C., a pressure of 3 MPa, and a crimping time of 15 seconds. A rigid substrate (evaluation substrate) was prepared. The heating conditions in the thermocompression bonding process are shown in Table 1.

[Comparative Example 2]
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.
A rigid substrate (evaluation substrate) with a flexible substrate was produced in the same manner as in Example 1 except that the obtained anisotropic conductive paste was used. Table 1 shows the heating conditions in the thermocompression bonding step and the thermosetting step.

<Evaluation of anisotropic conductive paste>
The anisotropic conductive paste was evaluated (conductivity, insulation, solder joint) by the following method. The obtained results are shown in Table 1. Note that Comparative Example 2 was not evaluated for solder joints.
(1) Conductivity The resistance value of the evaluation board was measured using a digital multimeter (“34410A” manufactured by Agilent Technologies). In addition, the terminal was connected to the electrode of the rigid board | substrate and the electrode of the flexible board | substrate, respectively, and resistance value was measured. 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.
X: Resistance value is too high to measure.
(2) Insulation The insulation resistance value (unit: Ω) was measured when a voltage of 15 V was applied to the comb electrode portion of the evaluation substrate using a high resistance meter (manufactured by Agilent). Insulation was evaluated according to the following criteria.
A: The insulation resistance value is 1.0 × 10 ¹⁰ Ω or more.
×: Insulation resistance value is less than 1.0 × 10 ⁸ Ω.
(3) Solder bonding The flexible substrate was peeled from the evaluation substrate, and the comb-shaped electrode portion of the rigid substrate was visually observed. The photograph which shows the part of the comb-shaped electrode of the rigid board | substrate in the evaluation board | substrate obtained in Example 1 is shown in FIG. Moreover, the photograph which shows the part of the comb-shaped electrode of the rigid board | substrate in the evaluation board | substrate obtained by the comparative example 1 is shown in FIG.
Moreover, the part of the comb-shaped electrode of the evaluation substrate was cut, and the cross section of the part was observed with a magnifier. A photograph showing a cross section of the comb-shaped electrode portion of the evaluation substrate obtained in Example 1 is shown in FIG. Moreover, the photograph which shows the cross section of the part of the comb-shaped electrode in the evaluation board | substrate obtained by the comparative example 1 is shown in FIG.
And the solder joint was evaluated according to the following criteria.
A: Solder was wet to 90% or more of the surface area of the electrode surface.
Δ: The solder was wet to 50% or more and less than 90% of the surface area of the electrode surface.
X: The solder was wet to less than 50% of the surface area of the electrode surface.

As is apparent from the results shown in Table 1 and FIGS. 9 to 12, when the evaluation board was produced by the method for producing an electronic board of the present invention (Examples 1 and 2), the electrical conductivity, the insulation, and the solder joint Were all good results. Therefore, according to the method for manufacturing an electronic substrate of the present invention, it was confirmed that an electronic substrate having high connection reliability can be manufactured using an anisotropic conductive paste.
On the other hand, when the blending amount of the component (A) in the anisotropic conductive paste is too small (Comparative Example 1), only a part of the electrode surface is soldered and the entire electrode surface is soldered. I found out that it was not done. Moreover, when there were too many compounding quantities of (A) component in anisotropic conductive paste (comparative example 2), it turned out that insulation is inadequate.

  The method for producing an electronic board 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.

DESCRIPTION OF SYMBOLS 1 ... Rigid board | substrate 11 ... Rigid base material 12 ... First wiring 13 ... Solder resist film 2 ... Flexible board 21 ... Flexible base material 22 ... Second wiring 23 ... Coverlay 3 ... Anisotropic conductive paste 4 ... Heat tool AA ... Connection area

Claims (6)

A method for manufacturing an electronic substrate, wherein an electronic substrate is manufactured by connecting a first wiring substrate and a second wiring substrate or an electronic component using an anisotropic conductive paste,
The anisotropic conductive paste comprises (A) a solder powder having a melting point of 150 ° C. or less, and (B) an epoxy resin, (C) a curing agent, and (D) a thermosetting resin composition containing an activator. Contains,
The blending amount of the component (A) is more than 50% by mass and 75% by mass or less with respect to 100% by mass of the anisotropic conductive paste,
The amount of the thermosetting resin composition is 25% by mass or more and less than 50% by mass with respect to 100% by mass of the anisotropic conductive paste,
The component (C) is at least one selected from the group consisting of imidazoles, imidazole derivatives, and epoxy resin amine adduct curing agents,
The amount of the component (C) is 1% by mass to 6% by mass with respect to 100% by mass of the thermosetting resin composition,
An application step of applying the anisotropic conductive paste on the first wiring board;
The second wiring board or the electronic component is disposed on the anisotropic conductive paste, and the second wiring board or the electronic component is placed on the first wiring board at a temperature higher than the melting point of the component (A). A thermocompression bonding process for thermocompression bonding;
The first wiring board and the second wiring board or the electronic component after the thermocompression bonding step are heated under a condition where the heating temperature is 100 ° C. or higher and 130 ° C. or lower and the heating time is 10 minutes or longer and 2 hours or shorter. A thermosetting step of heating and curing the thermosetting resin composition,
The pitch of the electrodes of the first wiring board and the pitch of the electrodes of the second wiring board or the electronic component are 60 μm or more and 500 μm or less, respectively.
The sum of the thickness of the electrode of said 1st wiring board and the thickness of said 2nd wiring board or the electrode of said electronic component is 20 micrometers or more and 100 micrometers or less. The manufacturing method of the electronic board characterized by the above-mentioned. In the manufacturing method of the electronic substrate of Claim 1,
The first wiring board includes a first base material, a first wiring, and a first insulating coating,
The first insulating coating is provided so as to cover the first wiring at an end portion of the first wiring board at a connection portion between the first wiring board and the second wiring board or the electronic component. A method of manufacturing an electronic substrate. In the manufacturing method of the electronic substrate of Claim 1,
The first wiring board includes a first base material, a first wiring, and a first insulating coating,
In the first wiring substrate, the first insulating coating is not provided in a plan view at the connection portion between the first wiring substrate and the second wiring substrate or the electronic component. A method for manufacturing an electronic substrate, comprising: a connection region surrounded by a substrate. In the manufacturing method of the electronic substrate of Claim 3,
The second wiring board includes a second base material, a second wiring, and a second insulating film,
The said thermocompression-bonding process satisfy | fills the following conditions (x1)-(x3). The manufacturing method of the electronic substrate characterized by the above-mentioned.
Condition (x1): When the second wiring board is disposed on the anisotropic conductive paste, the end portion of the second wiring board and the first insulating coating overlap in plan view.
Condition (x2): When the second wiring board is disposed on the anisotropic conductive paste, the end of the first wiring board does not overlap the second insulating film in plan view.
Condition (x3): At the time of thermocompression bonding, the heat tool used for thermocompression bonding overlaps over the entire region of the connection region in plan view. In the manufacturing method of the electronic substrate of Claim 3,
The second wiring board includes a second base material, a second wiring, and a second insulating film,
The said thermocompression-bonding process satisfy | fills the following conditions (y1)-(y3). The manufacturing method of the electronic substrate characterized by the above-mentioned.
Condition (y1): When the second wiring board is disposed on the anisotropic conductive paste, the end portion of the second wiring board and the first insulating coating overlap in plan view.
Condition (y2): When the second wiring board is disposed on the anisotropic conductive paste, the end portion of the first wiring board and the second insulating coating overlap in plan view.
Condition (y3): In thermocompression bonding, the heat tool used for thermocompression bonding and the connection region overlap in plan view, but the peripheral edge of the connection region does not overlap with the heat tool. An anisotropic conductive paste used in the method for manufacturing an electronic substrate according to any one of claims 1 to 5,
(A) a solder powder having a melting point of 150 ° C. or less, and (B) an epoxy resin, (C) a curing agent, and (D) a thermosetting resin composition containing an activator,
The blending amount of the component (A) is more than 50% by mass and 75% by mass or less with respect to 100% by mass of the anisotropic conductive paste,
The anisotropic conductive paste, wherein the blending amount of the thermosetting resin composition is 25% by mass or more and less than 50% by mass with respect to 100% by mass of the anisotropic conductive paste.