JP4893104B2 - Conductive paste and electronic component mounting board using the same - Google Patents

Description

  The present invention relates to a conductive paste used as an electronic component, circuit wiring material, electrode material, conductive bonding material, conductive adhesive, and the like, 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 conventional solder containing lead.

  The conductive paste contains precious metal and is therefore more expensive than lead-free solder, but has many advantages such as lower mounting temperature and flexibility of the joint. Conventional conductive pastes are made by using conductive powders such as gold, silver, copper, carbon, etc., and adding a binder, an organic solvent, and additives as necessary, and mixing them into a paste (for example, non-conductive paste). Patent Document 1). In particular, it has been generally known to use gold powder or silver powder in a field where high conductivity is required.

  Recently, silver or copper is generally used as the conductive powder in the conductive paste from the viewpoint of price, performance, and conductivity. A conductive paste containing silver powder is used for forming electric circuits and electrodes such as printed wiring boards and electronic components because of its good conductivity. However, the conductive paste containing silver powder has a drawback that when an electric field is applied in a high-temperature and high-humidity atmosphere, silver electrodeposition, called migration, occurs in the electric circuit or electrode, causing a short circuit between the electrodes or between the wires. . Several measures have been taken to prevent this migration. For example, measures such as applying a moisture-proof paint to the surface of silver powder, adding a corrosion inhibitor such as a nitrogen-containing compound to the conductive paste, and adding a pH adjuster such as MgO have been studied. It was not obtained (for example, refer to Patent Document 1). 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.

  Furthermore, a conductive paste using copper powder as the conductive powder has also been proposed. 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, a copper paste is disclosed in which various additives are added to prevent oxidation of copper powder and the conductivity is stabilized (see, for example, Patent Document 2), but the conductivity does not reach that of silver paste. In addition, there was a drawback in storage stability.

  In order to improve the migration and obtain an inexpensive conductive paste, a conductive paste using silver-coated copper powder has been proposed (see, for example, Patent Documents 3 and 4). However, when silver is coated uniformly and thickly, the effect of improving migration may not be sufficiently obtained. Conversely, when thinly coated, it is necessary to increase the filling amount of the conductive powder in order to ensure good conductivity, and as a result, there arises a problem that the adhesive strength (adhesive strength) is reduced due to a decrease in the binder component. was there.

  On the other hand, with the increase in mobile devices in recent years, the density of component mounting has been increasing. In order to increase the mounting area, portable devices using a flexible printed wiring board (FPC) are increasing. Since the mounted product using the FPC is likely to be subjected to a large strain due to the large deformation of the FPC, it is required to improve the peeling strength of the connection material.

  In order to improve the peel strength, a conductive paste to which liquid rubber is added, a conductive paste to which a compound having a siloxane skeleton is added, or a conductive paste in which a monofunctional epoxy resin is added to a base resin as an adhesive have been proposed. (For example, refer to Patent Documents 5, 6, and 7). However, when a compound having a liquid rubber or a siloxane skeleton is used, it has a low reactivity, and therefore has a heating time of 30 minutes or more for curing, resulting in a decrease in throughput. In addition, when a monofunctional epoxy resin is used, since the molecular weight is low and volatilization occurs, a void may be generated in the cured product depending on the curing conditions, and the adhesive force may be reduced. In other words, the currently used conductive paste does not have a conductive paste that is excellent in conductivity, peel strength, workability, and migration resistance, and that can compete with lead solder from the viewpoint of cost.

JP 2001-189107 A JP-A-5-212579 JP JP-A-7-138549 JP-A-10-134636 Patent 3265244 JP-A-1-153766 JP 2001-236827 A 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, peeling strength, quick-hardening property, and migration resistance. Another object of the present invention is to provide an electronic component mounting board having good conductivity.

  As a result of intensive research to achieve the above object, the inventors of the present invention use a predetermined conductive powder and use an epoxy resin having a predetermined structure as a binder component. 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, a conductive paste containing conductive powder and a binder component, wherein the conductive powder includes a metal powder in which the surface of copper powder or copper alloy powder is partially coated with silver, and the binder component is bifunctional Provided is a conductive paste comprising the above liquid epoxy resin, wherein the epoxy resin has two or more phenyl glycidyl ether structures in the same molecule and one or more alkylene oxide structures in the same molecule. .

  Thereby, the electrically conductive paste excellent in all of electroconductivity, peeling strength, quick-hardening property, and migration resistance can be provided.

  Moreover, it is preferable that the compounding ratio (conductive powder: binder component) of the said conductive powder and the said binder component in the said conductive paste is 15: 85-60: 40 by volume ratio.

  Moreover, it is preferable that the mixture ratio of the said epoxy resin in the said electrically conductive paste is 5-95 weight% on the basis of the said binder component whole quantity.

  Furthermore, it is preferable that the weight average molecular weight of the said epoxy resin in the said electrically conductive paste is 400-5000.

  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, wherein the conductive member is formed by curing the conductive paste. Provide electronic component mounting boards.

  Moreover, it is preferable that hardening in the said electronic component mounting board | substrate is performed by the thermosetting process whose hardening temperature is 130-220 degreeC and hardening time is 3-20 minutes.

  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 which is excellent in electroconductivity, migration resistance, workability | operativity, etc. is provided, maintaining predetermined peeling strength by hardening for a short time. 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 peeling strength (fixing force), it can be widely used as an alternative material for parts where solder has been used. Of course, it can also be used in fields where adhesiveness is not so required. In other words, impregnating and curing electronic parts such as passive parts and active parts such as LSI packages, plastic films such as polyimide resin and epoxy resin, and substrates such as glass nonwoven fabric with polyimide resin, epoxy resin, BT resin, etc. It can be used for joining with a substrate made of ceramic or ceramics such as alumina.

  Specifically, as shown in FIG. 1 or 2, the conductive paste of the present invention can be used to connect passive components that have been conventionally connected by solder, semiconductor elements that have been connected by solder or anisotropic conductive film, and the like. It can also be applied to the connection of active parts. 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. Also, when connecting the semiconductor element and the substrate with solder, it is necessary to inject an underfill material between the element and the substrate in order to relieve the stress generated by the 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 a substrate as an interposer having the passive components shown in FIGS. 1 and 2 is mounted on another substrate such as a motherboard. Can do.

  The conductive paste of the present invention used for such applications includes (A) conductive powder and (B) a binder component, and the (B) binder component includes an epoxy resin having a predetermined structure. Hereinafter, each component will be described in detail.

[(A) Conductive powder]
The conductive powder (A) 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 coated with silver. Is included. In other words, the surface of the copper powder or copper alloy powder contains 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 exposed portions, 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 diameter, 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, since the volume occupied by single particles in the cross-sectional direction increases, 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, the substantially spherical metal powder used as the conductive powder (A) 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, 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 determined 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 binder component (B) includes an epoxy resin having a predetermined structure. Moreover, the compounding ratio of (A) conductive powder and (B) binder component is a volume ratio with respect to the solid content of the conductive paste, and (A) conductive powder: (B) binder component is 15: 85-60: 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 15% 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, (B) the binder component is (b1) an epoxy resin having a predetermined structure, and (b2) other thermosetting resins contained as necessary (b3). It is intended to mean a mixture of) a curing accelerator, (b4) a curing agent, optionally contained (b5) an additive, and optionally a diluent. The constituent materials of the binder component (B) will be described in order.

((B1) epoxy resin having a predetermined structure)
The (b1) epoxy resin having a predetermined structure is a liquid epoxy resin having two or more functions, and has two or more phenyl glycidyl ether structures in the same molecule and one or more alkylene oxide structures in the same molecule. It is an epoxy resin. By containing such an epoxy resin, a conductive paste having excellent peel strength can be obtained by curing in a short time due to the high reactivity of phenylglycidyl ether and the flexibility of the alkylene oxide chain. Specific examples of the epoxy resin include EXA-4850-150 (Dainippon Ink Chemical Co., Ltd.) and EXA-4850-1000 (Dainippon Ink Chemical Co., Ltd.).
If it has two or more phenyl glycidyl ether structures and one or more alkylene oxide structures in the same molecule, it can be used as an epoxy resin having a predetermined structure (b1) and is described by the following general formula (I). An epoxy resin having a structure is preferable.

［ただし、式（Ｉ）中、Ｒ_１、Ｒ_２はそれぞれ水素原子又は炭素数１〜１２のアルキル基を表し、Ｒ_３は炭素数１〜１２のアルキレン基又は炭素数３〜１２のシクロアルキレン基を表し、ｎは１〜２０の整数を表す。］

[In the formula (I), R ₁ and R ₂ each represent a hydrogen atom or an alkyl group having 1 to 12 carbon atoms, and R ₃ represents an alkylene group having 1 to 12 carbon atoms or a cycloalkylene having 3 to 12 carbon atoms. Represents a group, and n represents an integer of 1 to 20. ]

  Examples of the alkyl group having 1 to 12 carbon atoms include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, sec-butyl group, tert-butyl group, and n-pentyl. Examples thereof include chain or branched alkylene groups such as a group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecyl group and n-dodecyl group.

  Examples of the alkylene group having 1 to 12 carbon atoms include methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene group, decamethylene group, undecamethylene group. , A chain-like or branched alkylene group such as a dodecamethylene group, a propylene group, an ethylmethylene group, or a dimethylmethylene group.

  Examples of the cycloalkylene group having 3 to 12 carbon atoms include cyclopropylene group, cyclobutylene group, cyclopentylene group, cyclohexylene group, cycloheptylene group, cyclooctylene group, cyclononylene group, and cyclodecylene group.

  In the present invention, the blending ratio of the epoxy resin having the predetermined structure (b1) is preferably 5 to 95% by weight based on the total amount of the binder component (B). Furthermore, it is more preferable that it is 20 to 70 weight% on the basis of (B) binder component whole quantity from the surface of adhesiveness, electroconductivity, and workability | operativity. In the blending ratio, when the blending ratio of the epoxy resin having the predetermined structure (b1) is less than 5% by weight based on the total amount of the (B) binder component, the peeling strength tends to decrease, and exceeds 95% by weight. In this case, the viscosity increases and workability decreases, or it is necessary to use a solvent in combination to reduce the viscosity, and the peeling strength tends to decrease with the generation of voids during curing.

  In the present invention, (b1) the epoxy resin having a predetermined structure preferably has a molecular weight of 400 to 5,000. Furthermore, the molecular weight is more preferably 600 to 3000 from the viewpoint of adhesiveness and workability. When the molecular weight is less than 400, the peel strength tends to decrease, and when it exceeds 5000, the viscosity increases and workability decreases, or it is necessary to use a solvent in combination to reduce the viscosity, With the generation of voids during curing, the peel strength tends to decrease. In addition, in this specification, a weight average molecular weight means the weight average molecular weight calculated | required from gel permeation chromatography (GPC) and converted with standard polystyrene.

((B2) Other thermosetting resins)
There is no restriction | limiting in particular as another thermosetting resin, For example, an epoxy resin, an acrylic resin, cyanate resin, its precursor, etc. are mentioned. Among these, an epoxy resin is preferable because it is excellent in heat resistance and adhesiveness, and can be made into a liquid state by using a solvent as appropriate, so that the workability is excellent. The said resin can be used individually or in combination of 2 or more types.
When an epoxy resin is used as the thermosetting resin, it is preferable to use a curing agent and a curing accelerator in combination. The 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 and the like and epichlorohydrin.

  Examples of such a compound 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, trade name), phenol novolac type epoxy resin N-730S (trade name, manufactured by Dainippon Ink & Chemicals, Inc.), Quatrex-2010 (trade 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 Co., Ltd.) Company name, trade 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 cycloaliphatic epoxy Resin EHPE-3150, CEL-3000 (both manufactured by Daicel Chemical Industries, Ltd., trade name), DME-100 (produced by Shin Nippon Chemical Co., Ltd., trade name), EX-216L (produced by Nagase Chemical Industries, Ltd., product) Name), W-100 which is an aliphatic epoxy resin (product name) manufactured by Shin Nippon Chemical Co., Ltd., ELM-100 which is an amine type epoxy resin (Sumitomo Chemical) Made by Kogyo Co., Ltd., trade name), YH-434L (made 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-212, a hexanediol type epoxy resin (Nagase Kasei Kogyo Co., Ltd., trade name), Denacol EX series (EX-810, 811, 850, 851, 821, 830, 832, 841, 861 (all Nagase Chemical Industries) Product name)), epoxy tree represented by the following general formula (II) E-XL-24, E-XL-3L (both Mitsui Toatsu Chemicals Co., Ltd., trade name) and the like can be mentioned), 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) When using other thermosetting resin, it is preferable that the mixture ratio is 5-95 weight% on the basis of (B) binder component whole quantity of an electrically conductive paste. (B2) When the blending ratio of the other thermosetting resin is less than 5% by weight, the viscosity tends to increase and the workability tends to decrease, and when it exceeds 95% by weight, the peel strength decreases. Tend.

((B3) curing accelerator)
In the present invention, (b3) a curing accelerator may be used in combination. For example, azoles such as cureazole, 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine (2MZA, manufactured by Shikoku Kasei Co., Ltd.), 1-cyanoethyl-2- Phenylimidazolium trimellitate (2PZ-CNS, manufactured by Shikoku Chemicals Co., Ltd.), 2-undecylimidazole (C17Z, manufactured by Shikoku Chemicals Co., Ltd.), 2-phenylimidazole isocyanuric acid adduct (2PZ-OK, Shikoku Chemicals Co., Ltd.) 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.) organic boron salt compound EMZ · K, TPPK (both made by Hokuko Chemical Co., Ltd., trade name) DBU, U-CAT102, 106, 830, 840, 5002 (both manufactured by Sun Apro, trade name), dicyandiamide, and dibasic acid dihydrazide represented by the following general formula (III) , PDH, SDH (all manufactured by Nippon Hydrazine Kogyo Co., Ltd., trade name), NovaCure (trade name, manufactured by Asahi Kasei Kogyo Co., Ltd.) which is a microcapsule type curing agent made of a reaction product of an epoxy resin and an amine compound. . These can be used alone or in combination of two or more.

［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. ]

  (B3) When using a hardening accelerator, it is preferable that the mixture ratio is 2-18 weight% on the basis of (B) binder component whole quantity of an electrically conductive paste. (B3) When the blending ratio of the curing accelerator 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 is poor due to increase in viscosity. Or the unreacted (b3) curing accelerator tends to deteriorate the conductivity.

((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 (IV), 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 (V), and the like. . These can be used alone or in combination of two or more.

［ただし、式（IV）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の整数を示す。］

[However, in formula (IV), R shows hydrocarbon groups, such as a methyl group and an allyl group, and m shows the integer of 1-5. ]

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

[In the formula (V), R ¹ represents an alkyl group such as a methyl group or an ethyl group, R ² represents hydrogen or a hydrocarbon group such as a methyl group or an allyl group, and p represents an integer of 2 to 4. Show. ]

  When (b4) the curing agent is used, the amount used thereof is 0.3 to 1.2 with respect to (b1) 1.0 equivalent of the epoxy group of the epoxy resin and (b4) the total amount of reactive groups in the curing agent. The amount is preferably an equivalent amount, more preferably 0.4 to 1.0 equivalent, and particularly preferably 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.

((B5) Additive)
If necessary, additives (b5) 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. . Hereinafter, these (b5) additives will be described.

  In the binder component (B) of the present invention, a flexible agent can be used for the purpose of stress relaxation. Examples of the flexible agent include liquid polybutadiene (“CTBN-1300 × 31”, “CTBN-1300 × 9”, “ATBN-1300 × 16” manufactured by Ube Industries, Ltd. “NISSO-PB-C” manufactured by Nippon Soda Co., Ltd. -2000 "). The flexible agent has an effect of relieving stress generated by bonding the passive component and the electrode on the substrate.

  In the binder component of the present invention, a coupling agent such as a silane coupling agent (“KBM-573” manufactured by Shin-Etsu Chemical Co., Ltd.) or a titanium coupling agent is used for the purpose of improving adhesive strength. be able to. In addition, for the purpose of improving wettability, a surfactant such as an anionic surfactant or a fluorosurfactant can be used. Furthermore, silicone oil or the like can be used as an antifoaming agent.

  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 above-mentioned 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 used alone or in combination of two or more. (B5) When using an additive, it is preferable that the mixture ratio is 0.5 to 60 weight% on the basis of (B) binder component whole quantity of an electrically conductive paste. (B5) When the blending ratio of the additive is less than 0.5% by weight, the effect of improving the characteristics due to the addition tends to be difficult to obtain, and when it exceeds 60% by weight, the curability of the thermosetting resin is lowered. Tend to.

  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 comprises (A) conductive powder, (B) binder component ((b1) epoxy resin having a predetermined structure, added as necessary (b2) other thermosetting resin, added as necessary (B3) curing accelerator, (b4) curing agent added if necessary, and (b5) additive added if necessary), diluent added if necessary, etc. , Lump or divide and combine as appropriate a dispersing / dissolving device such as a stirrer, slab, three rolls, planetary mixer, etc., and if necessary, mix by heating, mixing, dissolving, pulverizing kneading or dispersing, etc. It can be obtained as a uniform paste.

  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. The conductive paste can be heated and cured using a heating device such as the above.

  In the thermosetting process for heating and curing the conductive paste of the present invention, the heating temperature T is preferably 130 to 220 ° C., and the heating time t is preferably 3 to 20 minutes. 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 said thermosetting process, when heating temperature T is less than 130 degreeC, hardening | curing becomes inadequate and there exists a tendency for peeling strength to fall or for electroconductivity to fall. When heating temperature T exceeds 220 degreeC, since a volatile component volatilizes from the (B) binder component in an electrically conductive paste, and a void is formed, there exists a tendency for peeling strength to fall. On the other hand, when the heating time t is less than 3 minutes, the curing is insufficient and the peeling strength is lowered, or the conductivity tends to be lowered. When the heating time t is 20 minutes or longer, the thermosetting process takes a long time and the throughput is deteriorated, making it difficult to apply in manufacturing the electronic component mounting substrate 1.

  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. Then, the solder balls 22 and the board connection terminals 14 formed on the board 12 are electrically connected by the conductive member 10 formed by curing the conductive paste of the present 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 the examples and comparative 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 blending ratios of other examples and comparative examples are as shown in Table 1 or 2, and the production method is the same as in Example 1.

[Example 1]
10 parts by weight of EXA-4850-150 (manufactured by Dainippon Ink & Chemicals, Inc.), 80 parts by weight of YDF-170 (manufactured by Tohto Kasei Co., Ltd., trade name of bisphenol F type epoxy resin, epoxy equivalent = 170), and 2MZA (Brand name of imidazole derivative made by Shikoku Kasei Co., Ltd.) 10 parts by weight 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 10 mm were put into a 2 liter ball mill container, rotated for 8 hours, and the tap density by tapping 1000 times was 3.79 g / cm. ^{3. The} surface of flat copper powder having a relative density of 48%, a specific surface area of 0.77 m ² / g, an average aspect ratio of 5.2, and an average particle diameter of major axis of 7.7 μm is partially coated with silver. Conductive powder A which was flat silver-coated copper powder was obtained. Five particles of the obtained flat silver-coated copper powder were taken out, analyzed quantitatively with a scanning Auger electron spectrometer, and examined for the exposed area of copper. The average was 41% in the range of 10 to 60%. It was.

In the present invention, the tap density, relative density, and specific surface area are values measured according to the following method.
Tap density: A value obtained by filling a graduated cylinder with conductive particles and tapping 100 times with a stroke of 25 mm and dividing the volume by weight Relative density: A value obtained by dividing the tap density by the true density of the conductive particles Specific surface area: BET Calculated from the amount of nitrogen adsorption by the method

  Next, with respect to 100 parts by weight of the binder component obtained above, 514 parts by weight of flat 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: 40 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 5]
As described above, the conductive pastes of Examples 2 to 8 and Comparative Examples 1 to 5 were produced by the same method as in Example 1. The details of the materials shown in Table 1 or 2 are as follows. Moreover, the unit of the blending amount of each material in Table 1 or 2 is parts by weight (however, the numerical values in parentheses of conductive powder A and silver powder are based on the total volume of conductive powder A or silver powder and binder component) The volume ratio (unit: volume%) of the conductive powder A or the silver powder is shown.

EXA-4850-150: Bifunctional liquid epoxy resin, trade name of epoxy resin having two or more phenylglycidyl ether structures in the same molecule and one or more alkylene oxide structures in the same molecule, molecular weight 900, large Made by Nippon Ink Chemical Co., Ltd .;
EXA-4850-1000: Bifunctional liquid epoxy resin, trade name of epoxy resin having two or more phenylglycidyl ether structures in one molecule and one or more alkylene oxide structures in the same molecule, molecular weight 700, large Made by Nippon Ink Chemical Co., Ltd .;
YDF-170: trade name of bisphenol F type epoxy resin, manufactured by Toto Kasei Co., Ltd .;
YL-980: trade name of bisphenol A type epoxy resin, manufactured by Yuka Shell Epoxy Co., Ltd .;
2MZA: trade name of 2,4-diamino-6- [2′-methylimidazolyl- (1 ′)]-ethyl-s-triazine, which is an imidazole derivative, manufactured by Shikoku Kasei Co., Ltd .;
2PZ-CN: trade name of 1-cyanoethyl-2-phenylimidazole which is an imidazole derivative, manufactured by Shikoku Kasei Co., Ltd .;
BEO-60E: trade name of flexible epoxy resin, manufactured by Shin Nippon Rika Co., Ltd .;
XB-4122: trade name of flexible epoxy resin, manufactured by Asahi Ciba Co., Ltd .;
CTBN-1300X31: trade name of carboxy-modified acrylonitrile butadiene rubber, manufactured by Ube Industries, Ltd .;
Silver powder (TCG-1): Trade name, manufactured by Tokuri Chemical Laboratory.

(Evaluation of volume resistivity, peel strength and migration resistance)
The characteristics of the conductive pastes according to Examples 1 to 8 and Comparative Examples 1 to 5 were measured by the following method. The results are summarized in Tables 1 and 2.

(1) Volume resistivity: The above-mentioned conductive paste formed to 1 × 50 × 0.03 mm was heat-treated at 200 ° C. for 10 minutes in a reflow furnace to produce a test piece, and the volume resistivity was measured by a four-terminal method. .

(2) Adhesive strength (adhesive strength): A conductive paste is applied on a printed wiring board with copper foil to a size of 10 × 50 × 0.1 mm, and a flexible printed wiring board of 10 × 50 × 0.03 mm ( FPC) (copper foil film thickness: 18 μm, polyimide film film thickness: 12 μm) was pressure-bonded at 300 gf, and further heat-cured and adhered by the heating process of (1) above. After curing, the FPC was cut to a width of 10 mm, the printed wiring board with copper foil was fixed, the FPC was peeled off at a peeling speed of 50 mm / min, pulled up at 90 °, and peel strength at 25 ° C. was measured with a push-pull gauge.

(3) Migration resistance: The conductive paste is screen-printed on a glass plate using a metal mask having a thickness of 100 μm, and is heated and cured by the heating process of (1) above, whereby the electrode 30 (12 mm × 12 mm) shown in FIG. 2 mm, 2 mm between electrodes). Next, as shown in FIG. 6, 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). After that, as shown in FIG. 7, 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.

  As described above, the present invention has been described. However, according to the conductive paste according to the present invention, it is possible to achieve both a predetermined peeling strength and conductivity by curing in a short time. Therefore, when the conductive paste according to the present invention is used for a flexible printed wiring board as a conductive adhesive for surface mounting electronic components, the impact resistance and the migration suppression effect are superior to those of conventional products. Reliability can be increased. Moreover, when producing an electronic component mounting board, while using the electrically conductive paste of this invention and performing said thermosetting process, the electronic component mounting board which has favorable electroconductivity can be obtained.

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 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 an electric circuit diagram for evaluating migration resistance.

Explanation of symbols

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

Claims (6)

A conductive paste containing conductive powder and a binder component,
Wherein the conductive powder is, the front surface is partially coated with silver, include a metal powder of copper powder or copper alloy powder,
The binder component includes a bifunctional or higher liquid epoxy resin,
A conductive paste, wherein the epoxy resin has two or more phenyl glycidyl ether structures in the same molecule and one or more alkylene oxide structures in the same molecule.   The conductive paste according to claim 1, wherein a mixing ratio of the conductive powder and the binder component is 15:85 to 60:40 in volume ratio.   The conductive paste according to claim 1 or 2, wherein a blending ratio of the epoxy resin is 5 to 95% by weight based on the total amount of the binder component.   The electrically conductive paste of any one of Claims 1-3 whose weight average molecular weights of the said epoxy resin are 400-5000.   An electronic component mounting substrate having a structure in which a substrate and an electronic component are connected by a conductive member, wherein the conductive member is obtained by curing the conductive paste according to any one of claims 1 to 4. Mounting board.   The electronic component mounting substrate according to claim 5, which is cured by a thermosetting process at a curing temperature of 130 to 220 ° C. and a curing time of 3 to 20 minutes.

Images