JP2007277384A - Electroconductive adhesive - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroconductive adhesive used when bonding a semiconductor element such as an IC and a chip part such as a chip resistor a chip LED (light-emitting diode) to a lead frame, a heat dissipation board, etc., having stress relaxing properties to an FPC board (flexible printed circuit board) and affording a cured product having excellent electroconductivity, adhesiveness, heat and moisture resistances, flexibility and operation efficiency. <P>SOLUTION: The electroconductive adhesive comprises an electroconductive filler (A), a resin binder (B) and an organic solvent (C). In the electroconductive adhesive, the content of the electroconductive filler (A) is 70-90 wt.% based on the whole composition. The resin binder (B) consists essentially of an epoxy resin (b1) which is a liquid at room temperature and further comprises an epoxy resin (b2) which is a solid at room temperature and has 500-10,000 average molecular weight. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a conductive adhesive, and more particularly, a flexible printed circuit board used when bonding a semiconductor element such as an IC and a chip component such as a chip resistor or a chip LED to a lead frame or a heat sink. The present invention relates to a conductive adhesive that has a stress relaxation property for (FPC board) and can be a cured product excellent in conductivity, adhesiveness, heat resistance, moisture resistance, flexibility, and workability.

  In recent years, electronic products incorporating semiconductor elements and chip parts have been reduced in performance and size, and higher density, smaller size, and lower price are required for mounting components and the like. In addition, there are a wide variety of materials for substrates on which components are mounted, and the opportunity to use flexible flexible flexible printed circuit boards (FPC boards) such as polyimide, polyester, polyethylene terephthalate, etc. that can easily create 3D curved surfaces. Is increasing.

  When mounting components on such an FPC board, the heat resistance of the board is low, so the board that can be used is limited in the case of soldering, but by using a conductive adhesive with a low curing temperature The use of conductive adhesives is becoming mainstream because of the advantage that many types of substrates can be applied. Therefore, the conductive adhesive is required to have properties such as heat resistance, stress relaxation, flexibility, workability, and moisture resistance as well as conductivity and adhesiveness.

  The conductive adhesive is generally composed of conductive powder, organic resin (binder), solvent, catalyst, and the like. Gold, silver, copper, carbon or the like is used for the conductive powder, and a thermosetting resin such as epoxy resin or phenol resin, or a thermoplastic resin such as polyester resin or urethane resin is used for the organic resin. . The catalyst is for accelerating the thermosetting reaction of the thermosetting resin, and the solvent is compatible with the organic resin.

  However, when a thermosetting resin such as epoxy resin or phenol resin is used in the conductive adhesive, there is no stress relaxation property that can be accommodated when bonding to the FPC board, and a thermoplastic resin such as polyester resin or urethane resin is used. In such a case, there are disadvantages such as stress relaxation but weak heat resistance.

  For this reason, it has been proposed to improve the organic resin and mix polyvinyl acetal with a thermosetting organic binder (see, for example, Patent Document 1). However, although the conductive paste disclosed here has sufficient adhesion and conductivity for electromagnetic wave noise countermeasures for circuit boards or wiring conductors for circuit boards, it can meet the requirements for FPC boards. The stress relaxation property was not exhibited so much.

  Further, as a thermosetting organic binder, it has been proposed to add an addition reaction type silicone resin to an epoxy resin modified with a butadiene-nitrile copolymer rubber having a terminal carboxylated or aminated (for example, a patent) Reference 2). However, the conductive paste thus obtained has sufficient adhesive strength and conductivity for a relatively rigid circuit board and has storage stability, but is satisfactory for a flexible FPC board such as polyester. Power stress relaxation was not obtained.

Under such circumstances, when mounting a chip component or the like on an FPC board, a conductive adhesive containing an organic resin that exhibits both stress relaxation properties and heat resistance is strongly desired.
JP-A-4-139267 JP-A-5-314812

  In view of the conventional problems, an object of the present invention is used when a semiconductor element such as an IC and a chip component such as a chip resistor and a chip LED are bonded to a lead frame, a heat sink, etc. An object of the present invention is to provide a conductive adhesive that has a relaxation property and can be a cured product excellent in conductivity, adhesiveness, heat resistance, moisture resistance, flexibility, and workability.

  As a result of intensive studies to achieve the above object, the present inventor has included silver powder as a conductive filler, an organic binder composed of an epoxy resin that is liquid at room temperature, and a solvent for diluting the organic binder. Based on a conductive adhesive, by blending a specific amount of conductive filler with a solid epoxy resin having a specific average molecular weight in this organic binder at room temperature, various properties such as adhesive strength and electrical resistance The present inventors have found that the stress relaxation property for the FPC board can be exhibited without impairing the present invention, and have completed the present invention.

  That is, according to the first invention of the present invention, in the conductive adhesive containing the conductive filler (A), the resin binder (B), and the organic solvent (C), the inclusion of the conductive filler (A) The amount is 70 to 90% by weight based on the whole composition, and the resin binder (B) is mainly composed of an epoxy resin (b1) that is liquid at room temperature, and further has an average molecular weight of 500 to 10,000. There is provided a conductive adhesive characterized by containing a solid epoxy resin (b2) at a certain room temperature.

According to the second invention of the present invention, there is provided a conductive adhesive according to the first invention, wherein the conductive filler (A) is silver powder.
Furthermore, according to the third invention of the present invention, in the first or second invention, the content of the conductive filler (A) is 75 to 85% by weight based on the entire composition. A conductive adhesive is provided.

On the other hand, according to the fourth invention of the present invention, in the first invention, the content of the resin binder (B) is 4 to 30% by weight with respect to the entire composition. An agent is provided.
According to a fifth aspect of the present invention, in the first aspect, the epoxy resin (b1) which is liquid at room temperature contains either an imidazole or a phenol novolac compound as a curing agent. A conductive adhesive is provided.
According to the sixth invention of the present invention, in the first invention, the content of the epoxy resin (b2) solid at room temperature is 5 to 50% by weight with respect to the resin binder (B). A conductive adhesive is provided.
Further, according to the seventh invention of the present invention, in the first or sixth invention, the average molecular weight of the epoxy resin (b2) solid at room temperature is 800 to 6,000, An adhesive is provided.

On the other hand, according to the eighth aspect of the present invention, there is provided the conductive adhesive according to the first aspect, wherein the organic solvent (C) is an alkylene glycol alkyl ether.
According to the ninth invention of the present invention, in the first or seventh invention, the content of the organic solvent (C) is 1 to 20% by weight based on the entire composition, A conductive adhesive is provided.
Furthermore, according to a tenth aspect of the present invention, in any one of the first to ninth aspects, the present invention is used for bonding a chip component to a flexible printed circuit board and has sufficient stress relaxation properties. A conductive adhesive is provided.

  Since the conductive adhesive of the present invention is used for bonding a semiconductor element such as an IC or a chip component such as a chip resistor or chip LED and a lead frame or a heat sink, flexibility can be obtained. Bonding can be performed on a flexible FPC board, and the stability of conduction and high adhesive strength can be ensured. In addition, since both of the resins constituting the resin binder (a liquid epoxy resin at room temperature and a solid epoxy resin) react during the mounting operation, a high thermal strength is also obtained.

  Hereinafter, the conductive adhesive of the present invention will be described in detail.

1. Conductive adhesive The conductive adhesive of the present invention is a conductive adhesive containing a conductive filler (A), a resin binder (B), and an organic solvent (C). The amount is 70 to 90% by weight based on the whole composition, and the resin binder (B) is mainly composed of an epoxy resin (b1) that is liquid at room temperature, and further has an average molecular weight of 500 to 10,000. It contains a solid epoxy resin (b2) at a certain room temperature.

(A) Conductive filler The conductive filler is an essential component in the present invention, such as metal powder having conductivity such as silver, gold, copper, and carbon. These shapes are not particularly limited, and may be flaky, spherical, or indefinite.

  Among the conductive metal powders in the present invention, silver powder is particularly preferable. As the silver powder, scaly (flakes) and spherical simple substances or a mixture thereof can be used. If it is an electroconductive adhesive which mix | blended the mixture of spherical silver powder and flaky silver powder, it may not only be excellent in printability but can also reduce the electrical resistance (sheet resistance value) of an adhesive film to 300 mΩ or less, for example.

  As the silver powder, pure silver not containing lead is usually used, but an alloy with tin, bismuth, indium, palladium or the like may be adopted. However, the second component such as tin is desirably 5% by weight or less.

  The average particle size of the silver powder is not particularly limited. For example, for a circuit board such as a semiconductor, the average particle size is 30 μm or less, preferably 20 μm or less, and particularly preferably 5 μm or less. When fine spherical silver powder is used, the thixo ratio increases, so that it is suitable for a printing press, but is not suitable for an automatic coating apparatus. However, when scaly silver powder is mixed with spherical silver powder, the thixotropy ratio is appropriately lowered, and a conductive adhesive suitable for an automatic coating apparatus is obtained. Therefore, it is preferable to select silver powder as appropriate according to the method of applying the conductive adhesive.

  The conductive filler is blended in an amount of 70 to 90% by weight based on the total amount of the composition. If the silver powder is less than 70% by weight, sufficient electrical conductivity cannot be obtained, and if it exceeds 90% by weight, the adhesive strength is remarkably lowered and the role as an adhesive is not achieved. A preferable blending ratio of silver powder is 72 to 88% by weight, particularly 75 to 85% by weight.

(B) Resin binder The resin binder is an essential component used in the present invention to disperse the conductive filler and adhere it to a substrate or the like to form a cured product. In the present invention, the epoxy resin (b1) which is liquid at room temperature is the main component, and the epoxy resin (b2) which is solid at room temperature having a specific average molecular weight is blended therein.

  Moreover, the compounding ratio of the resin binder is set within a range of 4 to 30% by weight with respect to the total amount of the composition. If the resin binder is less than 4% by weight, sufficient adhesion cannot be obtained, and if it exceeds 30% by weight, the electrical conductivity is remarkably lowered. A particularly preferable blending ratio of the resin binder is in the range of 10 to 25% by weight.

(B1) Epoxy resin that is liquid at room temperature In the present invention, the epoxy resin that is liquid at room temperature includes all epoxy resins that are fluid at room temperature, as long as they are mainly used for casting or bonding electronic materials. Can be used and there is no particular limitation.

  Examples of the epoxy resin that is liquid at room temperature are those having a viscosity of not more than 300 poise at 25 ° C., such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, novolac glycidyl ether, epoxidized soybean oil, 3,4- Examples thereof include epoxy resins having a structure such as epoxy-6-methylcyclohexylmethylcarboxylate, 3,4-epoxycyclohexylmethylcarboxylate, and tetraglycidyldiaminodiphenylmethane. Among these, those having a viscosity of 10 to 250 poise at 25 ° C. are preferable. Moreover, these epoxy resins may be used alone or in combination of two or more.

  Moreover, since the object of adhesion is mainly an electronic material, it is desirable that ionic impurities including chlorine ions are 800 ppm or less. Moreover, these epoxy resins may be used alone or in combination of two or more. The epoxy resin may be blended with a curing agent (curing accelerator) and may be blended with a known thermosetting resin such as a phenol resin or an unsaturated polyester resin within a range not impairing the object of the present invention. .

  As an epoxy resin curing agent (curing accelerator), particularly if it can cause a curing reaction quickly with an epoxy resin during heating (60 to 300 ° C.) and satisfy long-term storage stability at room temperature. There is no limit.

In the present invention, either imidazoles or phenol novolac compounds can be used. Examples of imidazoles include 2-ethyl-4-methylimidazole, 2-phenyl-4,5-dihydroxymethylimidazole, 2-phenyl-4-methyl. Examples include -5-hydroxymethylimidazole and 2-heptadecylimidazole. In addition, dicyandiamide, acid anhydride-based tetrahydromethylphthalic anhydride, hexahydrophthalic anhydride, methyl hymic anhydride, BF ₃ salt of Lewis acid complex, and the like can be used. These may be used alone or in combination. Since these curing agents (curing accelerators) have different performance depending on the type, the amount of the curing agent (curing accelerator) cannot be defined, but is appropriately determined in consideration of the epoxy resin and the stoichiometric composition.

  For example, the curing reaction between an epoxy resin and 2-ethyl-4-methylimidazole is known to be represented by the following chemical reaction formula, and 2-ethyl-4-methylimidazole is used alone as a curing (acceleration) agent. When used, the amount is considered to be 2 to 6 parts by weight per 100 parts by weight of the epoxy resin. In addition, in the present invention, those which are recognized to have a curing accelerating action, such as amine salts and block isocyanates, can also be used.

(B2) Epoxy resin solid at room temperature As the epoxy resin solid at room temperature used in the present invention, any epoxy resin solid at room temperature can be used as long as the average molecular weight is 500 to 10,000, and there is no particular limitation. In the present invention, semi-solid materials are also included in the solid epoxy resin at room temperature.

  Examples of the epoxy resin that is solid at room temperature include epoxy resins having structures such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether, and novolak glycidyl ether. Moreover, these epoxy resins may be used alone or in combination of two or more.

  Moreover, if the object of adhesion is an electronic material, it is desirable that ionic impurities including chlorine ions are 800 ppm or less. Moreover, these epoxy resins may be used alone or in combination of two or more.

  Furthermore, the shape of the epoxy resin that is solid at room temperature is not particularly limited, but is preferably a powder or granular material having an average particle size of 0.1 to 0.5 mm. If the average particle size is less than 0.1 mm, dispersibility in the epoxy resin that is liquid at room temperature is good, but pulverization may be necessary. If the average particle size exceeds 0.5 mm, it is uniformly mixed with other components. There are cases where it is not possible.

  The average molecular weight of the epoxy resin solid at room temperature must be 500 to 10,000, preferably 800 to 6,000, more preferably 1000 to 5,500. Epoxy resins having an average molecular weight of less than 500 are generally liquid at room temperature, and when an epoxy resin having an average molecular weight of more than 10,000 is used, the stickiness of the conductive adhesive increases, making it unsuitable for application by printing or the like. It is.

  Compared to epoxy resins that are solid at room temperature, epoxy resins that are solid at room temperature have difficulty in handling during preparation of the composition and application properties of adhesives. As rarely used. However, when the epoxy group of the epoxy resin that is solid at room temperature is applied to a substrate and heated, the liquid epoxy resin cures at room temperature and then reacts with the curing agent blended in the liquid epoxy resin at room temperature. Gradually form a cured product. Therefore, since the crosslinking density is lowered when the resin binder is cured, flexibility can be maintained in the cured epoxy resin.

  The content of the epoxy resin solid at room temperature is desirably 50% by weight or less based on the resin binder (B). If the amount of the epoxy resin solid at room temperature exceeds 50% by weight, sufficient adhesive strength may not be obtained. On the other hand, if it is less than 5% by weight, desired stress relaxation properties may not be obtained. The amount of the epoxy resin (b2) is preferably 5 to 50% by weight, more preferably 25 to 50% by weight, and most preferably 30 to 45% by weight.

(C) Organic solvent In this invention, an organic solvent is a component which functions as a diluent, and is mix | blended with a resin binder in order to improve the printability and applicability | paintability of a conductive adhesive.

  The organic solvent is preferably compatible with both the epoxy resin (b1) that is liquid at room temperature and the epoxy resin (b2) that is solid at room temperature, but it is sufficient that the organic solvent is compatible with either of these. Examples thereof include alkylene glycol alkyl ethers such as ethylene glycol monomethyl ether (also known as butyl cellosolve), ethylene glycol monoethyl ether, ethyl 2-hydroxypropanoate, diethylene glycol monobutyl ether, and triethylene glycol dimethyl ether. In addition, a monoepoxy compound used as a solvent for the epoxy resin can also be used.

  The organic solvent is preferably blended in an amount of 1 to 20% by weight, particularly 3 to 10% by weight, based on the total amount of the composition. When the organic solvent is less than 1% by weight, the viscosity of the conductive adhesive is increased, and printability and applicability may be deteriorated. Conversely, when the amount exceeds 20% by weight, the viscosity is too low. It may cause sagging or a decrease in adhesive strength during printing and application.

2. Preparation of Conductive Adhesive The conductive adhesive of the present invention is a resin in which an epoxy resin (b1) that is liquid at room temperature containing a conductive filler (A) and a curing agent is mixed with an epoxy resin (b2) that is solid at room temperature. A binder (B) and an organic solvent (C) are prepared, and these are mixed and kneaded uniformly.

  The blending procedure of each component is not particularly limited, but first, a liquid epoxy resin (b1) at room temperature and a solid epoxy resin (b2) at room temperature are mixed to prepare a resin binder (B), and then an organic solvent (C It is preferable that the conductive filler (A) is gradually added and kneaded uniformly.

  In order to mix the components, for example, a known kneader such as a ceramic three-roll kneader may be used and stirred until a uniform composition is obtained at a relatively low temperature. Although depending on the kind of the curing agent and curing accelerator, the curing reaction of the epoxy resin proceeds at a temperature exceeding 50 ° C.

  The conductive adhesive obtained in this way exhibits an excellent effect when used for bonding a chip component to a flexible printed circuit board. The method of use is not particularly limited, and varies depending on the type of curing agent in the resin binder. For example, the adhesive composition is applied onto a substrate, and a component such as a semiconductor chip is placed thereon. What is necessary is just to let it harden | cure for 20 to 180 minutes in 300 degreeC oven. If it is less than 50 ° C. or less than 20 minutes, the adhesive is not sufficiently cured. On the other hand, if it exceeds 300 ° C. or exceeds 180 minutes, the resin component may be decomposed.

  EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited to these examples. In addition, each sample of Examples 1-12 and Comparative Examples 1-8 was prepared by mixing and kneading the following materials. The sample of the obtained conductive adhesive was evaluated by the method shown below.

[material]
(A) Conductive filler (silver powder) Scale-like silver powder (trade name: TC-25A, manufactured by Tokuru Chemical Laboratory Co., Ltd., average particle size: 1.45 μm)

(B) Resin binder (b1) Epoxy resin that is liquid at room temperature Bisphenol A diglycidyl ether type epoxy resin (trade name: Epicoat 828, manufactured by Japan Epoxy Resin Co., Ltd., viscosity: 135 poise at 25 ° C.)
(B2) Epoxy resin solid at room temperature (b2-1) Epicoat 1004 (Japan Epoxy Resin Co., Ltd., average molecular weight of about 1,600)
(B2-2) Epicoat 1010 (Japan Epoxy Resin Co., Ltd., average molecular weight of about 5,500)
(B2-3) Epicoat 1256 (Japan Epoxy Resin Co., Ltd., average molecular weight of about 50,000)

(C) Organic solvent (triethylene glycol dimethyl ether, deer special grade, manufactured by Kanto Chemical Co., Inc.)

[Sample evaluation]
(1) Measurement of sheet resistance value A conductive adhesive was applied by screen printing in a rectangular shape having a width of 2 mm and a length of 5 mm so as to overlap the electrodes between the electrodes 2 mm apart on the alumina substrate. The sample (conductive adhesive) was allowed to stand in an oven at 150 ° C. for 30 minutes to cure, cooled to room temperature, and the resistance value between the electrodes was measured. When the average value measured at 10 points was less than 500 mΩ, it was judged as good (◯), when it was 500-10000 mΩ, it was acceptable (Δ), and when it was 10000 mΩ or more, it was judged as impossible (×).

(2) Measurement of adhesive strength A sample (conductive adhesive) was applied to a 2.5 cm square copper substrate by screen printing. A 1.5 mm square silicon chip was placed and allowed to stand in an oven at 150 ° C. for 30 minutes to cure the conductive adhesive and cooled to room temperature. Thereafter, a force was applied to the silicon chip from the horizontal direction with respect to the substrate, and the force when the silicon chip was peeled was measured as the adhesive strength. When the average value measured at 10 points was 25N (Newton) or more, it was judged as good (◯), and when it was less than 25N, it was judged as impossible (x).

(3) Measurement of heat resistance strength A sample (conductive adhesive) was applied on a 2.5 cm square copper substrate by screen printing. A 1.5 mm square silicon chip was placed and allowed to stand in an oven at 150 ° C. for 30 minutes to cure the conductive adhesive and cooled to room temperature. Thereafter, the substrate is allowed to stand for 30 seconds on a hot plate heated to 260 ° C., and a force is applied to the silicon chip from the horizontal direction against the substrate while being heated. As measured. If the average value measured at 10 points was 5N or more, it was judged as good (◯), and if it was less than 5N, it was judged as impossible (x).

(4) Stress relaxation property A sample (conductive adhesive) is applied to a 5 cm square polyester flexible printed circuit board at a distance of 2.5 mm and applied to two places, and a chip resistor is adhered thereon, and then placed in an oven at 180 ° C. It was left for 60 minutes and cured. Thereafter, the temperature is returned to room temperature, and the polyester substrate is gradually wound around a cylinder having a cross-sectional circle radius of 10 mm. If the chip resistance is not peeled off from the polyester substrate at that time, it is good (○). ) Impossible (x) if peeled off at two or more locations.

(5) Printability When the samples (1), (2), and (3) are prepared, those that can be printed without problems by screen printing are good (◯), and those that are slightly wrinkled are acceptable ( (Triangle | delta)) and the thing which remarkable twist generate | occur | produced was made into the defect (x).

(6) Comprehensive evaluation If all the above four items were good (◯), it was judged as acceptable (◯), and even if there was at least one defect (x), it was judged as unacceptable (x).

(Examples 1-12)
Using the silver powder component, epoxy resin component that is liquid at room temperature, epoxy resin component that is solid at room temperature with an average molecular weight of 500 to 10,000, and an organic solvent component as raw materials, blended according to the weight ratio in Tables 1 and 2, and bonded An agent composition was prepared and kneaded using a three-roll kneader to obtain a conductive adhesive of the present invention. The epoxy resin that is liquid at room temperature was blended with a novolak type phenol resin as a curing agent and 2-phenyl-4,5-dihydroxymethylimidazole as a curing accelerator.
Using the obtained adhesive composition as a sample, the sheet resistance value, the adhesive strength, and the heat resistance strength were measured by the above-described methods, and the stress relaxation property was judged and comprehensive evaluation was performed. The results are shown in Tables 1 and 2.

(Comparative Examples 1-8)
In Table 3, except that the solid epoxy resin component is not used or increased at room temperature having an average molecular weight of 500 to 10,000, or that the blending amount of the silver powder component is reduced or increased as compared with the examples. Each component was mix | blended according to the weight ratio of, and the conductive adhesive for a comparison was obtained. Further, a similar experiment was conducted when a solid epoxy resin component was used at room temperature with an average molecular weight exceeding 10,000 (Comparative Example 6).
Using the obtained adhesive composition as a sample, the sheet resistance value, the adhesive strength, and the heat resistance strength were measured by the above-described methods, and the stress relaxation property was judged and comprehensive evaluation was performed. The results are also shown in Table 3.

"Evaluation"
In Comparative Examples 1 and 2, the sheet resistance value was large because the blending amount of silver powder was as small as 65% by weight, and in Comparative Examples 7 and 8, the sheet resistance was too large as 92% by weight of silver powder. Although the value was small, the adhesive strength and heat resistance were reduced, and neither of them could be used as a conductive adhesive.
Moreover, since the comparative example 3 did not mix | blend a solid epoxy resin component at room temperature, stress relaxation property was disqualified, and the comparative examples 4 and 5 increased too much the amount of solid epoxy resin components at room temperature. In addition, the adhesive strength was lowered, and none of them could be used as a conductive adhesive.
Moreover, since the comparative example 6 used the solid epoxy resin component at room temperature exceeding the average molecular weight 10,000, printability was disqualified.

  On the other hand, since Examples 1-12 are silver powder, the epoxy resin component solid at room temperature, and the compounding quantity of each component is the range of this invention, sheet resistance value, adhesive strength, heat resistance strength, stress relaxation property All of these were good, and the conductive adhesive was excellent in overall evaluation.

Claims (10)

In the conductive adhesive containing the conductive filler (A), the resin binder (B), and the organic solvent (C),
The content of the conductive filler (A) is 70 to 90% by weight with respect to the entire composition, and the resin binder (B) is mainly composed of an epoxy resin (b1) that is liquid at room temperature, and is further averaged. A conductive adhesive comprising a solid epoxy resin (b2) at room temperature having a molecular weight of 500 to 10,000.   The conductive adhesive according to claim 1, wherein the conductive filler (A) is silver powder.   2. The conductive adhesive according to claim 1, wherein the content of the conductive filler (A) is 75 to 85% by weight with respect to the entire composition.   The conductive adhesive according to claim 1, wherein the content of the resin binder (B) is 4 to 30% by weight with respect to the entire composition.   The conductive adhesive according to claim 1, wherein the epoxy resin (b1) which is liquid at room temperature contains either an imidazole or a phenol novolac compound as a curing agent.   The conductive adhesive according to claim 1, wherein the content of the epoxy resin (b2) solid at room temperature is 5 to 50% by weight with respect to the resin binder (B).   The conductive adhesive according to claim 1 or 6, wherein the average molecular weight of the epoxy resin (b2) solid at room temperature is 800 to 6,000.   The conductive adhesive according to claim 1, wherein the organic solvent (C) is an alkylene glycol alkyl ether.   The conductive adhesive according to claim 1 or 8, wherein the content of the organic solvent (C) is 1 to 20% by weight based on the entire composition.   The conductive adhesive according to claim 1, wherein the conductive adhesive is used for bonding a chip component to a flexible printed circuit board and has sufficient stress relaxation properties.