JP2005317490A - Conductive paste and electronic component mounting substrate using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a conductive paste with excellent conductivity, adhesive strength and migration resistance. <P>SOLUTION: This conductive paste contains conductive powder and a binder component. The conductive powder comprises metal powder wherein a surface of copper powder or copper alloy powder is partially covered with silver, and comprises mixed powder of the nearly spherical metal powder and the nearly flat metal powder or single powder of the nearly spherical metal powder and the nearly flat metal powder. The binder component contains a mixture of an epoxy resin and an imidazole compound having a hydroxyl group. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electronic component, a circuit wiring material, an electrode material, a conductive bonding material, a conductive paste used as a conductive adhesive, and an electronic component mounting substrate using the same.

  In order to mount an electronic component on a circuit board or the like, a joining method using lead-containing solder is widely known. However, in recent years, with the growing awareness of environmental issues, lead-free solder and conductive paste that do not contain lead have been attracting attention in place of solder.

  Since the conductive paste contains precious metal, it is more expensive than lead-free solder, but it has many advantages such as lower mounting temperature and flexibility of the joint. As described in Non-Patent Document 1, a conventional conductive paste uses a conductive powder such as gold, silver, copper, carbon, etc., and a binder, an organic solvent, and additives as necessary are added to the paste. It was prepared by mixing with. In particular, it has been generally known to use gold powder or silver powder in a field where high conductivity is required.

  In recent years, conductive pastes generally use silver or copper as a conductive powder from the viewpoints of price, performance, and conductivity. Conductive paste containing silver powder is used for the formation of electrical circuits and electrodes such as printed wiring boards and electronic components because of its good conductivity, but when these are applied with an electric field in a hot and humid atmosphere In addition, silver electrodeposition called migration occurs in the electric circuit or electrode, resulting in a short circuit between electrodes or wiring. Several measures have been taken to prevent this migration, and measures such as applying a moisture-proof paint to the surface of the conductor or adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste have been studied. However, sufficient effects were not obtained. Moreover, in order to obtain a conductor with good conduction resistance, the blending amount of silver powder must be increased, and since silver powder is expensive, the conductive paste is also expensive.

  In order to improve the migration and obtain an inexpensive conductive paste, a conductive paste using silver-coated copper powder has been proposed (for example, see Patent Document 5). However, when silver is coated uniformly and thickly, the effect of improving migration cannot be obtained sufficiently. On the other hand, if the coating is thin, it is necessary to increase the filling amount of the conductive powder in order to ensure good conductivity, and as a result, there is a problem in that the adhesive force (adhesive strength) is reduced due to the decrease in the binder component. .

  Moreover, the electrically conductive paste which uses copper powder as electroconductive powder is also proposed (for example, refer patent document 6). However, since the conductive paste using copper powder has high oxidizability of copper after heat curing, the oxygen contained in the air and the binder reacts with the copper powder to form an oxide film on its surface, making it conductive. Is significantly reduced. Therefore, various additives are added to prevent oxidation of copper powder, and a stable conductive copper paste is disclosed. However, the conductivity is not as good as silver paste, and there is a drawback in storage stability. there were.

  Moreover, the electrically conductive paste which uses the phenol resin for the purpose of improving electroconductivity is also proposed (for example, refer patent document 7). Although this conductive paste has higher conductivity than a conductive paste using an epoxy resin, the by-product generated during the polymerization of the phenol resin forms voids and tends to have a low adhesive force. On the other hand, the conductive paste using epoxy resin has higher adhesive strength than the conductive paste using phenolic resin, but the conductivity tends to be low. There was a need to increase. In other words, the currently used conductive paste does not have a conductive paste that is excellent in conductivity, adhesive strength, workability, and migration resistance, and that can compete with lead solder from the viewpoint of cost.

  Moreover, the following are mentioned as a migration prevention measure disclosed so far. Patent Documents 1 and 2 disclose a conductive paste in which a migration inhibitor is added or pretreated to conductive particles. Examples of the silver-coated copper powder include Patent Document 3 and Patent Document 4.

JP 2001-189107 A JP 2002-161259 A Japanese Patent Publication No. 6-72242 JP-A-10-134636 JP-A-7-138549 JP-A-5-212579 JP-A-6-157946 Electronic Materials, October 1994, pp. 42-46

  This invention is made | formed in view of the subject which the said prior art has, and aims at providing the electrically conductive paste excellent in electroconductivity, adhesive strength, and migration resistance. Another object of the present invention is to provide an electronic component mounting board having good conductivity.

  The invention described in claims 1 to 4 provides a conductive paste that is excellent in conductivity, adhesive strength, and migration resistance.

  The invention according to claim 5 provides an electronic component mounting board having good conductivity.

  As a result of intensive research to achieve the above object, the present inventors have used a predetermined conductive powder and also used a combination of an epoxy resin and an imidazole compound having a predetermined structure as a binder component, thereby providing conductivity and adhesion. The present inventors have found that a conductive paste that can achieve both strength and excellent migration resistance can be obtained, and the present invention has been completed.

  That is, the present invention is a conductive paste containing a conductive powder and a binder component, the conductive powder is made of a metal powder in which the surface of the copper powder or copper alloy powder is partially coated with silver, And it consists of a mixed powder of the substantially spherical metal powder and the flat metal powder, or a single powder of the substantially spherical or flat metal powder, and the binder component contains an epoxy resin and a hydroxyl group. Provided is a conductive paste comprising a mixture with an imidazole compound.

  Thereby, the electrically conductive paste excellent in all electroconductivity, adhesive strength, and migration resistance can be provided.

  Moreover, it is preferable that the compounding ratio (conductive powder: binder component) of the said electrically conductive powder and the said binder component in the said electrically conductive paste is 20: 80-60: 40 by volume ratio.

  Moreover, it is preferable that the mixture ratio of the said imidazole compound in the said electrically conductive paste is 2-18 weight% on the basis of the said binder component whole quantity.

  Furthermore, the imidazole compound in the conductive paste is preferably 2-phenyl-4,5-dihydroxymethylimidazole or 2-phenyl-4-methyl-5-hydroxymethylimidazole.

  The present invention is also an electronic component mounting substrate having a structure in which a substrate and an electronic component are connected by a conductive member, and the conductive member increases the temperature of the conductive paste of the present invention until reaching the maximum temperature. Provided is an electronic component mounting board characterized by being cured by a thermosetting process having a speed of 2 to 20 ° C./min and an oxygen concentration of 20 to 50000 ppm.

  Thereby, the electronic component mounting board | substrate which has favorable electroconductivity can be provided.

  ADVANTAGE OF THE INVENTION According to this invention, the electrically conductive paste excellent in electroconductivity and migration resistance is provided, maintaining predetermined adhesive strength. Moreover, the electronic component mounting board | substrate which has favorable electroconductivity can be provided by using the electrically conductive paste of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. In the following description, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted.

  Since the conductive paste of the present invention has the same degree of conductivity as solder and is excellent in adhesive strength (fixing force), it can be widely used as an alternative material for portions where solder has been used. Of course, it can also be used in fields where adhesiveness is not so required. In other words, electronic components such as passive components and LSI packages, plastic films such as polyimide resin and epoxy resin, and substrates such as glass nonwoven fabric impregnated and cured with plastics such as polyimide resin, epoxy resin and BT resin, alumina It can be used for bonding to a substrate such as ceramics.

  Specifically, as shown in FIGS. 1 and 2, the conductive paste of the present invention can be used to connect passive components that have been conventionally connected with solder, or semiconductor elements that have been connected with solder or an anisotropic conductive film. It can also be applied to the connection of electronic components. In particular, since the conductive paste of the present invention can be connected at a low temperature as compared with solder, it is preferably used when connecting a component having poor heat resistance such as a CCD module. In addition, when connecting a semiconductor element and a substrate with solder, it is necessary to inject an underfill material between the element and the substrate in order to relieve stress generated due to a difference in thermal expansion coefficient between the semiconductor element and the substrate. was there. On the other hand, when connecting with the conductive paste of the present invention, since the resin component has a stress relaxation action, an underfill material is not required and the process can be simplified.

  Moreover, as shown in FIG. 3, the conductive paste of the present invention can be used in combination with solder to connect a semiconductor element and a substrate. Furthermore, as shown in FIG. 4, the conductive paste of the present invention is also used when mounting a substrate as an interposer on which the passive component shown in FIGS. 1 and 2 is mounted on another substrate such as a motherboard. I can do it.

  The conductive paste of the present invention used for such applications contains (A) conductive powder and (B) a binder component, and the (B) binder component contains (b1) an epoxy resin and (b2) a hydroxyl group. It contains a mixture with an imidazole compound. Hereinafter, each component will be described in detail.

[(A) Conductive powder]
(A) The conductive powder used in the present invention is a metal powder (silver-coated copper powder or silver-coated copper alloy powder) in which a part of the copper powder or copper alloy powder is exposed and the surface is substantially coated with silver. It consists of In other words, the surface of the copper powder or copper alloy powder is made of metal powder partially covered with silver. (A) When the conductive powder used is one in which the entire surface is coated with silver without exposing a part of the copper powder or the copper alloy powder, the migration property tends to deteriorate. In addition, when the exposed area of the surface of copper powder or copper alloy powder is too large, there exists a tendency for electroconductivity to fall by oxidation of copper powder. Therefore, the exposed area of the surface of the copper powder or the copper alloy powder is preferably in the range of 1 to 70%, more preferably in the range of 10 to 60% from the viewpoint of migration, oxidation of the exposed portion, conductivity, and the like. A range of 55% is more preferred.

  As the copper powder or the copper alloy powder, it is preferable to use a powder produced by an atomizing method, and the smaller the particle size, the higher the contact probability of the (A) conductive powder and the higher conductivity is preferable. For example, it is preferable to use a powder having an average particle size in the range of 1 to 20 μm, and it is more preferable to use a powder in the range of 1 to 10 μm.

  To coat silver on the surface of copper powder or copper alloy powder, there are methods such as displacement plating, electroplating, electroless plating, etc., high adhesion between copper powder or copper alloy powder and silver, and running cost Since it is inexpensive, it is preferable to coat with displacement plating.

  When the coating amount of silver on the surface of the copper powder or the copper alloy powder is too large, the cost is increased, the migration resistance is lowered, and when it is too small, the conductivity tends to be lowered. Therefore, the coverage of silver is preferably in the range of 5 to 25% by weight (as the weight of silver based on the total weight of copper powder or copper alloy powder and silver) with respect to copper powder or copper alloy powder. The range of 10 to 23% by weight is more preferable.

  The conductive powder (A) used in the present invention is composed of a mixed powder of the substantially spherical metal powder and the flat metal powder, or a single powder of the substantially spherical or flat metal powder. Here, “substantially spherical metal powder” is a concept including “spherical (true spherical) metal powder”. These metal powders have different combinations and ratios depending on the viscosity of the conductive paste, the coating area, the film thickness, and the specifications and required characteristics of the bonding member.

  For example, in order to improve the conductivity in the planar direction, it is preferable to use a flat metal powder as the conductive powder (A) from the viewpoint of the contact area between the conductive powders, the orientation, and the like. On the other hand, in order to improve the electrical conductivity in the cross-sectional direction, the volume occupied by a single particle in the cross-sectional direction increases. Therefore, it is preferable to use a substantially spherical metal powder as the (A) conductive powder.

  In addition, although the adhesive strength also varies depending on the bonding specifications, in general, in a conductive paste applied smoothly to a base material, (A) when a flat metal powder is used as the conductive powder, There is a tendency to show a higher value than when spherical metal powder is used.

  For example, when a lead frame is bonded to a copper foil using a conductive paste, from the viewpoint of conductivity, adhesive strength, workability, reliability, etc., (A) As a conductive powder, a substantially spherical metal powder and a flat metal It is preferable to use a mixed powder in which the ratio of the powder to the powder is approximately spherical metal powder: flat metal powder in a range of 40:60 to 98: 2. By using such a mixed powder, good results have been obtained.

  (A) When flat metal powder is mainly used as the conductive powder, the viscosity of the conductive paste is high. On the other hand, when substantially spherical metal powder is mainly used, when flat metal powder is mainly used. The viscosity becomes lower and workability is improved.

  In addition, when the viscosity of the conductive paste is the same when the substantially spherical metal powder is mainly used as the conductive powder and when the flat metal powder is mainly used, the ratio of the substantially spherical metal powder is flattened. The ratio of the metal powder can be higher. In other words, when producing a conductive paste having a predetermined viscosity, when (A) a substantially spherical metal powder is mainly used as the conductive powder, the conductive paste in the conductive paste is used more than when a flat metal powder is mainly used. (A) The ratio of conductive powder can be increased.

Furthermore, (A) The substantially spherical metal powder used as the conductive powder has an average particle diameter of 1 to 20 μm in major axis, an aspect ratio of 1 to 1.5, a tap density of 4.5 to 6.2 g / cm ³ , A relative density of 50 to 68% and a specific surface area of 0.1 to 1.0 m ² / g are preferable. On the other hand, the flat metal powder has an average particle diameter of 5 to 30 μm of major axis, an aspect ratio of 3 to 20, a tap density of 2.5 to 5.8 g / cm ³ , a relative density of 27 to 63% and a specific surface area. Is preferably in the range of 0.4 to 1.3 m ² / g.

  Here, for each of the substantially spherical metal powder and the flat metal powder, when the average particle diameter exceeds the upper limit of the above range, (A) the contact probability of the conductive powder tends to decrease, so the conductivity tends to decrease. is there. On the other hand, when the average particle size is less than the lower limit of the above range, the viscosity tends to increase and the adhesive strength tends to decrease. On the other hand, when the aspect ratio exceeds the upper limit of the above range, the viscosity tends to increase and the adhesive strength tends to decrease. On the other hand, when the aspect ratio is less than the lower limit of the above range, the conductivity tends to decrease. Furthermore, when the specific surface area exceeds the upper limit of the above range, the adhesive force tends to decrease. On the other hand, when the specific surface area is less than the lower limit of the above range, the conductivity tends to decrease. Moreover, when the tap density exceeds the upper limit of the above range, the conductivity tends to decrease. On the other hand, when the tap density is less than the lower limit of the above range, the viscosity tends to increase and the adhesive strength tends to decrease.

  In the present invention, the aspect ratio of the metal powder refers to the ratio (major axis / minor axis) of the major axis (μm) and minor axis (μm) of the metal powder particles. This aspect ratio can be measured by the following procedure. First, after putting metal powder particles in a curable resin having a low viscosity and mixing them well, the particles are allowed to settle and the resin is cured as it is to produce a cured product. Next, the obtained cured product is cut in the vertical direction, and the shape of particles appearing on the cut surface is enlarged and observed with an electron microscope. Then, the major axis / minor axis of each particle is obtained for at least 100 particles, and the average value thereof is used as the aspect ratio.

  Here, the minor axis refers to the particle appearing on the cut surface, and a combination of two parallel lines in contact with the outside of the particle is selected so as to sandwich the particle, and the two parallel lines having the shortest distance among these combinations are selected. Distance. On the other hand, the major axis is the distance between two parallel lines that are the longest interval among the two parallel lines that are perpendicular to the parallel line that determines the minor axis, and that is in contact with the outside of the particle. is there. The rectangle formed by these four lines is the size that the particles just fit within.

[(B) Binder component]
In the present invention, the main component of the (B) binder component is (b1) an epoxy resin and (b2) an imidazole compound containing a hydroxyl group. Moreover, the compounding ratio of (A) conductive powder and (B) binder component is a volume ratio with respect to solid content of the conductive paste, and (A) conductive powder: (B) binder component is 20:80 to 60:40. Preferably there is. Furthermore, from the viewpoint of adhesiveness, conductivity, and workability, the (A) conductive powder: (B) binder component is more preferably 30:70 to 50:50. In the blending ratio, when the volume ratio of (A) conductive powder is less than 20% by volume based on the total volume of (A) conductive powder and (B) binder component, conductivity tends to deteriorate, and 60 volume. If it exceeds%, the adhesive force tends to decrease with a decrease in the binder component. In the present invention, the (B) binder component includes the (b1) epoxy resin and the (b2) imidazole compound, and (b3) a curing accelerator contained as necessary and optionally contained. (B4) It shall mean a mixture of curing agents. The constituent materials of the binder component (B) will be described in order.

((B1) Epoxy resin)
The (b1) epoxy resin is preferably a compound having two or more epoxy groups in one molecule, and examples thereof include an epoxy resin derived from bisphenol A, bisphenol F, bisphenol AD, etc. and epichlorohydrin.

  Examples of such compounds include AER-X8501 (trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.), R-301 (trade name, manufactured by Yuka Shell Epoxy Co., Ltd.), YL-980 (which is a bisphenol A type epoxy resin). YDF-170 (trade name) manufactured by Yuka Shell Epoxy Co., Ltd., bisphenol F type epoxy resin, R-1710 (trade name) manufactured by Toto Kasei Co., Ltd., Mitsui Petrochemical Co., Ltd. Product name), phenol novolac type epoxy resin N-730S (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), Quatrex-2010 (product name, manufactured by Dow Chemical Co., Ltd.), YDCN which is a cresol novolac type epoxy resin -702S (trade name, manufactured by Toto Kasei Co., Ltd.), EOCN-100 (Nippon Kayaku Co., Ltd.) (Trade name), EPPN-501 (trade name) manufactured by Nippon Kayaku Co., Ltd., TACTIX-742 (trade name, manufactured by Dow Chemical Co.), VG-3010 (Mitsui Petrochemical Industries, Ltd.) Product name), 1032S (trade name, manufactured by Yuka Shell Epoxy Co., Ltd.), HP-4032 (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), an epoxy resin having a naphthalene skeleton, and alicyclic Epoxy resins EHPE-3150, CEL-3000 (both manufactured by Daicel Chemical Industries, Ltd., trade name), DME-100 (manufactured by Shin Nippon Chemical Co., Ltd., trade name), EX-216L (manufactured by Nagase Chemical Industries, Ltd., Product name), W-100 (manufactured by Shin Nippon Rika Co., Ltd., product name), an aliphatic epoxy resin, ELM-100 (Sumitomo Chemical), an amine type epoxy resin Kogyo Co., Ltd., trade name), YH-434L (manufactured by Toto Kasei Co., Ltd., trade name), TETRAD-X, TETRAC-C (both made by Mitsubishi Gas Chemical Co., Ltd., trade name), Denacol which is a resorcinol type epoxy resin EX-201 (trade name, manufactured by Nagase Kasei Kogyo Co., Ltd.), Denacol EX-211 (trade name, manufactured by Nagase Kasei Kogyo Co., Ltd.), a neopentyl glycol type epoxy resin, Denacol EX, a hexane dinel glycol type epoxy resin -212 (manufactured by Nagase Kasei Kogyo Co., Ltd., trade name), Denacol EX series (EX-810, 811, 850, 851, 821, 830, 832, 841, 861 (all Nagase) Kasei Kogyo Co., Ltd., trade name)), represented by the following general formula (I) Epoxy resins E-XL-24 and E-XL-3L (both manufactured by Mitsui Toatsu Chemical Co., Ltd., trade names)) and the like. These epoxy resins can be used alone or in combination of two or more.

  Moreover, you may include the epoxy compound (reactive diluent) which has only one epoxy group in 1 molecule as an epoxy resin. Although such an epoxy compound is used in the range which does not inhibit the characteristic of the electrically conductive paste of this invention, it is preferable to use it in the range of 0-30 weight% with respect to the epoxy resin whole quantity. Examples of such commercially available epoxy compounds include PGE (trade name, manufactured by Nippon Kayaku Co., Ltd.), PP-101 (trade name, manufactured by Tohto Kasei Co., Ltd.), ED-502, ED-509, ED-509S ( Asahi Denka Kogyo Co., Ltd., trade name), YED-122 (Oilized Shell Epoxy Co., Ltd. trade name), KBM-403 (Shin-Etsu Chemical Co., Ltd. trade name), TSL-8350, TSL-8355, And TSL-9905 (trade name, manufactured by Toshiba Silicone Co., Ltd.).

((B2) Imidazole compound)
The (b2) imidazole compound used in the present invention has a hydroxyl group as a substituent. By using such (b2) imidazole compound in combination with the above (b1) epoxy resin, a conductive paste excellent in both adhesive properties and conductive properties can be obtained. Specific examples of the (b2) imidazole compound are not particularly limited as long as they have a hydroxyl group. For example, 2-phenyl-4-methyl-5-hydroxymethylimidazole (2P4MHZ, manufactured by Shikoku Kasei Co., Ltd.), 2-phenyl-4,5-hydroxymethylimidazole (2PHZ, manufactured by Shikoku Kasei Co., Ltd.) and the like can be mentioned. These can be used alone or in combination of two or more.

  (B2) The blending ratio of the imidazole compound is preferably 2 to 18% by weight based on the total amount of the (B) binder component of the conductive paste. (B2) When the blending ratio of the imidazole compound is less than 2% by weight, sufficient curing cannot be obtained and the adhesive strength tends to decrease, and when it exceeds 18% by weight, workability deteriorates due to the increase in viscosity. Or the unreacted (b2) imidazole compound tends to deteriorate the conductivity.

((B3) curing accelerator)
The (b2) imidazole compound acts as a so-called epoxy resin curing accelerator, but other (b3) curing accelerators may be used in combination. For example, Cureazole, which is an imidazole, 1-cyanoethyl-2-phenylimidazolium trimellitate (2PZ-CNS, manufactured by Shikoku Kasei Co., Ltd.), 2-undecylimidazole (C17Z, manufactured by Shikoku Kasei Co., Ltd.), 2-phenyl Imidazole isocyanuric acid adduct (2PZ-OK, manufactured by Shikoku Kasei Co., Ltd.), organic boron salt compound EMZ · K, TPPK (both manufactured by Hokuko Chemical Co., Ltd., trade name), tertiary amines or salts thereof DBU, U-CAT102, 106, 830, 840, 5002 (both manufactured by San Apro, trade name), dicyandiamide, dibasic acid dihydrazide represented by the following general formula (IV), ADH, PDH, SDH (all Nippon Hydrazine Kogyo Co., Ltd., trade name), reaction product of epoxy resin and amine compound Novacure (trade name) manufactured by Asahi Kasei Kogyo Co., Ltd., which is a microcapsule type curing agent made of

［式中、Ｒ^３はｍ−フェニレン基、ｐ−フェニレン基等の２価の芳香族基、或いは炭素数１〜１２の直鎖又は分岐鎖のアルキレン基を示す。］

[Wherein R ³ represents a divalent aromatic group such as an m-phenylene group or a p-phenylene group, or a linear or branched alkylene group having 1 to 12 carbon atoms. ]

((B4) curing agent)
Furthermore, (b4) a curing agent can be used in combination. As such a hardening | curing agent, what is illustrated by p117-209 of review epoxy resin (epoxy resin technical association) can be used widely. Specifically, for example, H-1 (trade name, manufactured by Meiwa Kasei Co., Ltd.), VR-9300 (trade name, manufactured by Mitsui Toatsu Chemical Co., Ltd.), which is a phenol novolac resin, XL-225, which is a phenol aralkyl resin. (Trade name) manufactured by Mitsui Toatsu Chemical Co., Ltd., p-cresol novolak resin MTPC (trade name, manufactured by Honshu Chemical Industry Co., Ltd.) represented by the following general formula (II), or AL which is an allylated phenol novolac resin -VR-9300 (trade name, manufactured by Mitsui Toatsu Chemical Co., Ltd.), special phenol resin PP-700-300 (trade name, manufactured by Nippon Petrochemical Co., Ltd.) represented by the following general formula (III), and the like. . These can be used alone or in combination of two or more.

［ただし、式（ＩＩ）及び（ＩＩＩ）中、Ｒはメチル基、アリル基などの炭化水素基を示し、ｍは１〜５の整数を示し、Ｒ¹はメチル基、エチル基等のアルキル基を示し、Ｒ^２は水素又は炭化水素基を示し、ｐは２〜４の整数を示す。］

[In the formulas (II) and (III), R represents a hydrocarbon group such as a methyl group or an allyl group, m represents an integer of 1 to 5, and R ¹ represents an alkyl group such as a methyl group or an ethyl group. R ² represents hydrogen or a hydrocarbon group, and p represents an integer of 2 to 4. ]

  (B4) The amount of the curing agent used is such that (b4) the total amount of reactive groups in the curing agent is 0.3 to 1.2 equivalents with respect to 1.0 equivalent of the epoxy group of the epoxy resin. It is preferable that the amount is 0.4 to 1.0 equivalent, and it is particularly preferable that the amount is 0.5 to 1.0 equivalent. When the total amount of the reactive groups is less than 0.3 equivalent, the adhesive force tends to decrease, and when it exceeds 1.2 equivalent, the viscosity of the paste increases and the workability tends to decrease. The reactive group is a substituent having a reactive activity with an epoxy resin, and examples thereof include a phenolic hydroxyl group.

[(C) Additive]
(C) Additives such as a flexible agent, a coupling agent, a surfactant, an antifoaming agent, a toughness improving agent, and an ion trapping agent can be appropriately added to the conductive paste of the present invention as necessary. . Hereinafter, these (C) additives will be described.

  A flexible agent can be used in the conductive paste of the present invention for the purpose of stress relaxation. Examples of the flexible agent include liquid polybutadiene (“CTBN-1300 × 31”, “CTBN-1300 × 9” manufactured by Ube Industries, Ltd., “NISSO-PB-C-2000” manufactured by Nippon Soda Co., Ltd.), and the like. It is done. The flexible agent has an effect of relieving stress generated by bonding the passive component and the electrode on the substrate. Usually, it is preferable to add 0 to 500 parts by weight of the flexible agent when the total amount of the organic polymer compound (such as an epoxy resin) and its precursor is 100 parts by weight.

  In the conductive paste of the present invention, a silane coupling agent (such as “KBM-573” manufactured by Shin-Etsu Chemical Co., Ltd.) or a titanium coupling agent can be used for the purpose of improving the adhesive strength. Moreover, an anionic surfactant, a fluorochemical surfactant, etc. can be used in order to improve wettability. Furthermore, silicone oil or the like can be used as an antifoaming agent. The above-mentioned adhesion improver, wettability improver, and antifoaming agent can be used alone or in combination of two or more, and the amount used is (A) 0 with respect to 100 parts by weight of conductive powder. -10 parts by weight is preferred.

  Depending on the purpose, (b1) the epoxy resin may be dissolved in the above-described reactive diluent. To the conductive paste of the present invention, a diluent can be added as necessary in order to make the workability during preparation of the paste composition and the coating workability during use better. As these diluents, organic solvents having a relatively high boiling point such as butyl cellosolve, carbitol, butyl cellosolve, carbitol acetate, dipropylene glycol monomethyl ether, ethylene glycol diethyl ether, and α-terpineol are preferable. The amount used is preferably 0 to 30% by weight based on the total amount of the conductive paste.

  The conductive paste of the present invention further includes a toughness improver such as urethane acrylate, a hygroscopic agent such as calcium oxide and magnesium oxide, an adhesion improver such as an acid anhydride, a nonionic surfactant, and a fluorine-based interface as necessary. A wetting improver such as an activator, an antifoaming agent such as silicone oil, an ion trapping agent such as an inorganic ion exchanger, and the like can be appropriately added.

  The conductive paste of the present invention comprises (A) conductive powder, (B) binder component ((b1) epoxy resin, (b2) imidazole compound, (b3) curing accelerator added as necessary, and (B4) curing agent), and (C) additives such as diluents added as necessary, together with agitator, slab, three rolls, planetary A uniform paste can be obtained by appropriately combining dispersing / dissolving devices such as a mixer and heating, if necessary, mixing, dissolving, pulverizing kneading or dispersing.

  Next, the electronic component mounting substrate of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view showing a preferred embodiment of an electronic component mounting board according to the present invention. As shown in FIG. 1, the electronic component mounting substrate 1 includes a substrate connecting terminal 14 formed on a substrate 12 and an electronic component connecting terminal 18 connected to the electronic component 16 electrically connected by a conductive member 10. It has a connected structure. The conductive member 10 is obtained by curing the above-described conductive paste of the present invention.

  In order to bond the electronic component 16 and the substrate 12 using the conductive paste of the present invention, first, the conductive paste is applied onto the substrate connection terminals 14 of the substrate 12 by a dispensing method, a screen printing method, a stamping method, or the like. Next, the electronic component 16 having the electronic component connection terminal 18 is pressure-bonded to the substrate 12 so that the electronic component connection terminal 18 and the substrate connection terminal 14 are electrically connected via a conductive paste, and then an oven or a reflow furnace. It can be carried out by heating and curing the conductive paste using a heating device such as the above.

  FIG. 5 is a graph showing an example of a thermosetting process for heat-curing the conductive paste. Here, the heating temperature T is preferably 100 to 300 ° C., and the heating time t is preferably 100 to 5000 seconds. And in order to form the electronic component mounting board | substrate 1 using an electrically conductive paste, the temperature increase rate r until it reaches the heating temperature T (When the temperature increase time until it reaches the heating temperature T is x, r Is represented by T / x) at 2 to 20 ° C./min and the oxygen concentration at 20 to 50000 ppm. By such a thermosetting process, the electronic component mounting substrate 1 having a structure in which the substrate 12 and the electronic component 16 are connected by the conductive member 10 can be obtained. Since the electronic component mounting substrate 1 is formed by using the conductive paste of the present invention and curing the conductive paste by the above-described thermosetting process, good electrical conductivity can be obtained.

  In the thermosetting process, when the temperature rising rate r is less than 2 ° C./min, the time for the thermosetting process becomes long, so that it becomes difficult to apply the electronic component mounting substrate 1. On the other hand, when it exceeds 20 ° C./min, a volatile component is generated from the binder component (B) in the conductive paste and voids are formed, so that the adhesive force tends to be reduced. The temperature increase rate r is not necessarily a constant temperature increase rate, and may be appropriately changed within the above range. Also, the oxygen concentration is not practical because it takes a long time to reduce the oxygen concentration to less than 20 ppm with a general-purpose heating device. When the oxygen concentration exceeds 50000 ppm, (A) the oxidation of the conductive powder There exists a tendency for electroconductivity to fall by influence.

  Moreover, the electronic component mounting substrate of this invention is not limited to the structure shown in FIG. 1, For example, you may have the structure shown in FIGS. The electronic component mounting substrate 2 shown in FIG. 2 includes a conductive member 10 in which a substrate connection terminal 14 formed on a substrate 12 and a lead 20 connected to the electronic component 16 are obtained by curing the conductive paste of the present invention. It has the structure electrically connected by.

  The electronic component mounting board 3 shown in FIG. 3 has a structure in which the substrate 12 and the electronic component 16 are connected by combining the conductive paste of the present invention and solder. In the electronic component mounting substrate 3, electronic component connection terminals 18 are formed on the electronic components 16, and solder balls 22 are formed on the electronic component connection terminals 18. And this solder ball 22 and the board | substrate connection terminal 14 formed on the board | substrate 12 are electrically connected by the electrically-conductive member 10 which hardens the electrically conductive paste of this invention, and the electronic component mounting board 3 is formed. Yes.

  Further, the electronic component mounting substrate 4 shown in FIG. 4 has a structure in which the substrate 12 on which the electronic component 16 shown in FIGS. 2 and 3 is mounted is further mounted on another substrate 24. Also here, the connection between the electronic component 16 and the substrate 12 and the connection between the substrate 12 and the substrate 24 are performed by the conductive member 10 formed by curing the conductive paste of the present invention.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto.

  The materials used in Examples, Comparative Examples, and Reference Examples were prepared by the following method or obtained. Example 1 is shown as an example of the production method, but the resin compositions and compounding ratios of other examples, comparative examples, and reference examples are as shown in Tables 1 to 3, and the production method is the same as in Example 1. .

[Example 1]
70 parts by weight of YDF-170 (manufactured by Toto Kasei Co., Ltd., trade name of bisphenol F type epoxy resin, epoxy equivalent = 170), and PP-101 (trade name of alkylphenyl glycidyl ether, produced by Toto Kasei Co., Ltd., epoxy equivalent = 230) 20 parts by weight and 10 parts by weight of 2P4MHZ (trade name of imidazole compound having a hydroxyl group, manufactured by Shikoku Kasei Co., Ltd.) were mixed, and a binder component was prepared by passing three rolls three times.

  Next, spherical copper powder (trade name SFR-Cu, manufactured by Nippon Atomizing Co., Ltd.) having an average particle diameter of 5.1 μm prepared by the atomizing method was washed with dilute hydrochloric acid and pure water, and then 80 g of AgCN and 75 g of NaCN per liter of water. Substrate plating is performed so that the coating amount of silver is 18% by weight with respect to the spherical copper powder (the weight of silver is 18% by weight based on the total weight of the spherical copper powder and silver). Washed with water and dried to obtain silver-plated copper powder.

Thereafter, 750 g of the silver-plated copper powder obtained above and 3 kg of zirconia balls having a diameter of 5 mm are placed in a 2 liter ball mill container, and rotated for 40 minutes. ^3. The surface of spherical copper powder having a relative density of 93%, a specific surface area of 0.26 m ² / g, an aspect ratio of 1.3 and an average particle size of major axis of 5.5 μm is partially coated with silver. A conductive powder A was obtained which was a substantially spherical silver-coated copper powder (metal powder) (a part of the surface of the spherical copper powder was exposed). In addition, when the ratio of the exposed area of the surface of the spherical copper powder at this time was measured with a scanning Auger electron spectrometer, it was 20% based on the total area of the surface of the silver-plated copper powder.

  Next, with respect to 100 parts by weight of the binder component obtained above, 330 parts by weight of substantially spherical silver-coated copper powder (conductive powder A) (volume ratio of the conductive powder A based on the total volume of the conductive powder A and the binder component: 30 volume%) was added and mixed, and after passing three rolls three times, a conductive paste was obtained by performing defoaming treatment at 500 Pa or less for 10 minutes using a vacuum stirrer.

[Examples 2 to 8, Comparative Examples 1 to 3 and Reference Examples 1 to 4]
As above-mentioned, except having set it as the composition shown in Tables 1-3, it carried out similarly to Example 1, and obtained the electrically conductive paste of Examples 2-8, Comparative Examples 1-3, and Reference Examples 1-4. The details of the materials shown in Tables 1 to 3 are as follows. Moreover, the unit of the compounding quantity of each material in Tables 1-3 is a weight part (however, the numerical value in the parenthesis of conductive powder A and silver powder is based on the total volume of conductive powder A or silver powder and a binder component. The volume ratio (unit: volume%) of the conductive powder A or the silver powder is shown.

YL-980: trade name of bisphenol A type epoxy resin, manufactured by Yuka Shell Epoxy Co., Ltd .;
EX-212: Trade name of neopentyl glycol type epoxy resin, manufactured by Nagase Chemical Industries, Ltd .;
2PHZ: trade name of 2-phenyl-4,5-hydroxymethylimidazole which is an imidazole compound having a hydroxyl group, manufactured by Shikoku Kasei Co., Ltd .;
C17Z: trade name of 2-undecylimidazole which is a hydroxyl group-free imidazole compound, manufactured by Shikoku Kasei Co., Ltd .;
2MZA: trade name of 2,4-diamino-6- (2′-methylimidazolyl (1 ′))-ethyl-s-triazine, which is a hydroxyl group-free imidazole compound, manufactured by Shikoku Kasei Co., Ltd .;
1B2PZ: trade name of 1-benzyl-2-phenylimidazole which is a hydroxyl group-free imidazole compound, manufactured by Shikoku Kasei Co., Ltd .;
Silver powder (TCG-1): trade name, manufactured by Tokuri Chemical Laboratory Co., Ltd.

(Evaluation of volume resistivity, adhesive strength and migration resistance)
The characteristics of the conductive pastes according to Examples 1 to 8, Comparative Examples 1 to 3 and Reference Examples 1 to 4 were measured by the following method. The results are summarized in Tables 1 to 3.
(1) Volume resistivity: 1 × 50 × 0.03 mm The above conductive paste was heated to 180 ° C. at a rate of 4 ° C./min at an oxygen concentration of 1000 ppm, and further heated at 180 ° C. for 1 hour. Then, a test piece was prepared, and the volume resistivity was measured by the four probe method.
(2) Adhesive strength (adhesive strength): About 0.5 mg of a conductive paste was applied on a Sn-plated copper plate, a 2 × 2 × 0.25 mm Ag-plated copper chip was pressure-bonded thereon, and the above (1 ) Was heated and cured by the heating process. The shear strength at 25 ° C. was measured with a bond tester (manufactured by DAGE, 2400) at a shear rate of 500 μm / sec and a clearance of 100 μm.
(3) Migration resistance: The conductive paste was screen-printed on a glass plate using a metal mask having a thickness of 100 μm, heated to 180 ° C. at a rate of temperature increase of 4 ° C./min at an oxygen concentration of 1000 ppm, and further 180 The electrodes 30 (12 mm × 2 mm, spacing between the electrodes 2 mm) shown in FIG. 6 were produced by heat treatment at 0 ° C. for 1 hour to cure. Next, as shown in FIG. 7, the filter paper 34 was arrange | positioned between the electrodes 30 formed on the glass plate 32, and the ion-exchange water 36 was dripped on the filter paper 34 (No. 5A). Thereafter, as shown in FIG. 8, 10V is applied in the circuit in which the electrode 30, the power source 38, the resistor 40, and the recorder 42 are connected, and the inter-electrode leakage current after voltage application is relative to the initial value (immediately after voltage application). The time to change by 10% was measured. In order to keep the shape of the ion-exchanged water 36 constant, a filter paper 34 is disposed between the electrodes 30, and the ion-exchanged water 36 is replenished every 10 minutes to prevent drying. The longer the leakage current change time (minute) measured in this way, the better the migration resistance.

(Production Examples 1 to 5 of conductive member and evaluation thereof)
The characteristics of the conductive members (cured products of the conductive paste) of Production Examples 1 to 5 produced by the following procedure were measured by the following method. The results are summarized in Table 4.
(1) Volume resistivity: 1 × 50 × 0.03 mm of the conductive paste of Example 1 was heated to 180 ° C. at an oxygen concentration and a heating rate shown in Table 4 (Production Examples 1 to 5), and further A test piece was prepared by heat treatment at 180 ° C. for 1 hour, and volume resistivity was measured by a four-terminal method.
(2) Adhesive strength (adhesive strength): About 0.5 mg of the conductive paste of Example 1 was applied onto a Sn-plated copper plate, and a 2 × 2 × 0.25 mm Ag-plated copper chip was pressure-bonded thereon, Furthermore, it heated up to 180 degreeC with the oxygen concentration and temperature increase rate which were shown in Table 4 (Preparation Examples 1-5), and also heat-processed at 180 degreeC for 1 hour, and was adhere | attached. The shear strength at 25 ° C. was measured with a bond tester (manufactured by DAGE, 2400) at a shear rate of 500 μm / sec and a clearance of 100 μm.

  As mentioned above, although this invention has been demonstrated, according to the electrically conductive paste which concerns on this invention, it becomes possible to aim at the improvement of electroconductivity, maintaining predetermined adhesive strength. Therefore, when the conductive paste according to the present invention is used as a conductive adhesive for surface mounting an electronic component, good conductivity can be obtained with a smaller amount of conductive powder than the conventional product. Furthermore, since the conductive paste according to the present invention can obtain good conductivity and adhesive strength in a well-balanced manner with a smaller amount of conductive powder than conventional products, the reliability of the product can be improved. Moreover, according to the electrically conductive paste of this invention, generation | occurrence | production of migration can fully be suppressed.

  Furthermore, as is clear from the results shown in Table 4, in the thermosetting process for thermosetting the conductive paste of the present invention, by setting the temperature rising rate to 2 to 20 ° C./min and the oxygen concentration to 20 to 50000 ppm, The conductive member which is the cured product can obtain particularly excellent conductivity and adhesive strength (Production Examples 1 to 3). Therefore, when the electronic component mounting substrate is manufactured, the conductive paste of the present invention is used, and an electronic component mounting substrate having good conductivity can be obtained by performing a thermosetting process under the above conditions.

1 is a schematic cross-sectional view showing a preferred embodiment of an electronic component mounting board according to the present invention. It is a schematic cross section which shows other suitable one Embodiment of the electronic component mounting board | substrate of this invention. It is a schematic cross section which shows other suitable one Embodiment of the electronic component mounting board | substrate of this invention. It is a schematic cross section which shows other suitable one Embodiment of the electronic component mounting board | substrate of this invention. It is a graph which shows an example of the thermosetting process for heat-hardening the electrically conductive paste of this invention. It is a schematic plan view which shows the electrode for evaluating migration resistance. It is a schematic cross section which shows the electrode for evaluating migration resistance. It is a figure which shows the electric circuit for evaluating migration resistance.

Explanation of symbols

1, 2, 3, 4 ... Electronic component mounting board, 10 ... Conductive member, 12, 24 ... Substrate, 14 ... Substrate connection terminal, 16 ... Electronic component, 18 ... Electronic component connection terminal, 20 ... Lead, 22 ... Solder ball .

Claims (5)

A conductive paste containing conductive powder and a binder component,
The conductive powder is made of metal powder in which the surface of copper powder or copper alloy powder is partially coated with silver, and a mixed powder of the substantially spherical metal powder and the flat metal powder, Or, it is made of a single powder of the metal powder having a substantially spherical or flat shape,
The conductive paste is characterized in that the binder component contains a mixture of an epoxy resin and an imidazole compound having a hydroxyl group.   2. The conductive paste according to claim 1, wherein a mixing ratio of the conductive powder and the binder component is 20:80 to 60:40 by volume ratio.   The conductive paste according to claim 1 or 2, wherein a blending ratio of the imidazole compound is 2 to 18% by weight based on the total amount of the binder component.   The imidazole compound is 2-phenyl-4,5-dihydroxymethylimidazole or 2-phenyl-4-methyl-5-hydroxymethylimidazole, according to any one of claims 1 to 3. Conductive paste. An electronic component mounting substrate having a structure in which a substrate and an electronic component are connected by a conductive member,
The conductive member according to any one of claims 1 to 4, wherein the conductive paste has a rate of temperature increase of 2 to 20 ° C / min until reaching the maximum temperature, and an oxygen concentration of 20 to 50000 ppm. An electronic component mounting board characterized by being cured by a thermosetting process.

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