JP2005019398A - Conductive paste, circuit board, solar cell, and ceramic chip electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thermosetting conductive paste that can forme an electroconductive film having excellent conductivity and adhesive property. <P>SOLUTION: The conductive paste comprises a conductive powder, a binder resin containing a phthalic acid glycidyl ester type epoxy resin, wherein the phthalic acid glycidyl ester type epoxy resin is one or two kinds selected from a group consisting of a phthalic acid glycidyl ester, dihydro phthalic acid glycidyl ester, tetrahydro phthalic acid glycidyl ester, and hexahydro phthalic acid glycidyl ester. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention can form a conductive film excellent in conductivity and adhesiveness for a conductor or electrode of a circuit board or electronic component, or for electromagnetic wave shielding, and further can be used as a conductive adhesive. The present invention relates to a curable conductive paste, and a circuit board, a solar cell, and a chip-type ceramic electronic component formed using the conductive paste.

  A conductive paste in which a conductive powder is dispersed in a resin composition containing a binder resin, a curing agent, and, if necessary, a solvent, a catalyst, and other additives, is applied to the substrate by means of printing or the like. By heat-treating at a temperature of about 300 ° C., the resin is cured and a conductive film is formed.

  As the binder resin, an epoxy resin, a phenol resin, a melamine resin, an alkyd resin, an unsaturated polyester resin, an acrylic resin, an epoxy-modified acrylic resin, or the like is usually used.

  Such resin-based thermosetting conductive pastes are generally used to form printed circuit board jumper circuits and conductor circuits including through-hole conductors, resistors, capacitors, and other electronic components and display elements. In addition to being used for forming a conductive film for electromagnetic wave shielding, it is used as a conductive adhesive for bonding semiconductor elements and electronic components or mounting them on a substrate. Also, in recent years, when forming electrodes for solar cells, particularly those for solar cells that cannot be processed at high temperatures using amorphous silicon semiconductors, or outside chip-type ceramic electronic components such as multilayer ceramic capacitors, multilayer ceramic inductors, multilayer ceramic actuators, etc. Also when forming an electrode, a thermosetting conductive paste is used.

JP-A-6-267784 JP-A-6-37340

  In general, conductive paste is applied according to application methods such as curability, conductivity, adhesiveness, heat resistance, water resistance, environment resistance, and depending on the application, solderability, solder heat resistance, screen printing, etc. Aptitude is also required.

  In recent years, due to the demand for miniaturization and higher density of circuit boards and electronic components, high conductivity is required so that good conductivity is maintained even when a conductor circuit is formed with a finer pattern with a thinner film thickness. Something that shows sex is required. Therefore, for example, when forming a grid electrode of a solar cell, a solder layer is usually formed on the surface of a conductor film formed of a conductive paste in order to reduce resistance. It is complicated. Moreover, since the toxicity of lead contained in solder is still regarded as a problem, it is desired to omit the solder layer coating step by using a conductive paste having higher conductivity.

However, in the conventional thermosetting conductive paste, when the amount of the conductive powder is increased for the purpose of improving the conductivity, the adhesive ratio is greatly lowered because the ratio of the resin is decreased. For this reason, it is difficult to obtain a material having excellent conductivity and adhesiveness, and there is a limit to improving the conductivity. For example, in the case of a commercially available conductive paste, the specific resistance is about 3 × 10 ⁻⁵ Ω · cm at the lowest from the order of 10 ⁻³ Ω · cm, and below that, for example, about 2 × 10 ⁻⁵ Ω · cm. In particular, those having high conductivity of the order of 10 ⁻⁶ Ω · cm have not been obtained.

  Further, external electrodes of chip-type ceramic electronic components such as multilayer ceramic capacitors have been conventionally formed by baking a metal electrode containing glass on a component body at a high temperature, but peeling and cracking are likely to occur due to mechanical impact. There is a problem. For this reason, a resin-based conductive paste with excellent impact resistance is coated on the baked electrode and heat-cured, or the resin-based conductive paste is directly applied to the element body and heat-cured to form an external electrode. Attempts have been made. However, the present condition is that a thermosetting conductive paste excellent in all of conductivity, adhesiveness, solderability, and plating resistance, which can replace the baked electrode, has not been obtained.

  An object of the present invention is to provide a thermosetting conductive paste capable of forming a conductive film having excellent conductivity and adhesion. Further, it is a further object to provide a conductive paste that can have appropriate coating properties, heat resistance, water resistance, environmental resistance, solderability, solder heat resistance, and can be used for various applications as required. And

  The present inventors have continued intensive studies on the conductive paste. As a result, it was found that the above-described object can be achieved by using a composition described later, and the present invention has been completed.

  That is, the conductive paste according to the present invention is a conductive paste containing at least a conductive powder and a binder resin containing a phthalic acid-based glycidyl ester type epoxy resin, and this phthalic acid-based glycidyl ester type epoxy. The resin is a glycidyl ester of phthalic acid represented by the following formula 1, a glycidyl ester of dihydrophthalic acid represented by the following formula 2, a glycidyl ester of tetrahydrophthalic acid represented by the following formula 3, or a formula 4 And one or more selected from the group consisting of glycidyl esters of hexahydrophthalic acid.

  The conductive paste according to the present invention preferably contains 5 to 50 parts by weight of binder resin with respect to 100 parts by weight of conductive powder.

The conductive paste according to the present invention may further contain a curing agent, and in Formulas 1 to 4, at least one of R ₁ and R ₂ is CH ₃ , C ₂ H ₅ , C ₃ H _7. or it is preferably _C 4 _{H 9.}

  In the conductive paste according to the present invention, the phthalic acid glycidyl ester type epoxy resin is selected from the group consisting of dimethyl glycidyl phthalate, methyl glycidyl glycidyl phthalate, diethyl glycidyl phthalate, dipropyl glycidyl phthalate, and dibutyl glycidyl phthalate. It is preferably 1 type or 2 types or more, and preferably 1 type or 2 types or more selected from the group consisting of diglycidyl phthalate, diglycidyl hexahydrophthalate, diglycidyl tetrahydrophthalate, diglycidyl methyl tetrahydrophthalate. .

  Furthermore, the conductive paste according to the present invention may further contain another resin as a binder resin.

According to the thermosetting conductive paste according to the present invention, a conductive film having excellent conductivity and adhesion can be formed.

As the conductive powder, powders of metals such as silver, gold, platinum and palladium, and alloys containing these metals, such as silver-copper alloys and silver-palladium-copper alloys, are used. Moreover, what coat | covered these metals or alloys on the surface of inorganic powders, such as a metal, a metal compound, glass, a ceramic, carbon, and organic powders, such as resin, can also be used. In particular, a silver-based conductive powder having a low specific resistance, that is, a silver powder, an alloy powder containing silver as a main component, or a silver-coated powder is desirable. These conductive powders may be used as a mixture of two or more. The shape is not particularly limited, such as spherical, flaky, dendritic or fibrous. The conductive powder can also be used after being surface-treated with various fatty acids or a coupling agent by a conventional method.

  As the phthalic acid-based glycidyl ester type epoxy resin, glycidyl ester or alkyl glycidyl of phthalic acid and hydrogenated phthalic acid, that is, dihydrophthalic acid, tetrahydrophthalic acid, hexahydrophthalic acid as represented by the above formulas 1 to 4 Examples of the phthalic acid and hydrogenated phthalic acid may be alkyl-substituted products such as methyltetrahydrophthalic acid. The phthalic acid ester type epoxy resin as referred to in the invention contains glycidyl ester of these alkyl phthalic acid or alkyl hydrogenated phthalic acid. The position of the two carboxyl groups of the phthalic acid or hydrogenated phthalic acid may be any of -ortho position (phthalic acid), -meta position (isophthalic acid), and -para position (terephthalic acid). .

  Examples of phthalic acid ester type epoxy resins that are relatively easily available include diglycidyl phthalate, dimethyl glycidyl phthalate, diglycidyl hexahydrophthalate, diglycidyl tetrahydrophthalate, and diglycidyl methyl tetrahydrophthalate.

  Conventionally, most epoxy resins used in conductive pastes are of glycidyl ether type such as bisphenol type, and the adhesiveness is greatly reduced when the blending ratio of the conductive powder is increased. However, when the phthalic acid ester type epoxy resin was used as in the present invention, surprisingly, the blending ratio of the conductive powder was increased. Also, the decrease in adhesiveness can be suppressed to a very small level. Therefore, by using such a phthalic acid ester type epoxy resin as a binder resin, a conductive film having extremely high conductivity can be formed without impairing other characteristics as a conductive paste such as adhesiveness and coatability. .

According to the present invention, a conductive film having a specific resistance value of 2 × 10 ⁻⁵ Ω · cm or less can be formed, and a highly conductive conductive film having a specific resistance value smaller than 1 × 10 ⁻⁵ Ω · cm is also provided. It becomes possible to form.

In particular, in Formulas 1 to 4, when at least one of the substituents R ₁ and R ₂ of the glycidyl group is a methyl group, an ethyl group, a propyl group, or a butyl group, an extremely excellent conductivity improving effect is obtained. Preferably, dimethyl glycidyl phthalate, methyl glycidyl glycidyl phthalate, diethyl glycidyl phthalate, dipropyl glycidyl phthalate, dibutyl glycidyl phthalate or the like is used.

  These phthalic acid ester type epoxy resins are usually low molecular weight monomers, but those obtained by reacting in advance into a polymer having a low degree of polymerization may be used.

  Depending on the application and required characteristics, other resin components may be further blended as the binder resin. Examples of other resin components include butyral resin, acrylic resin, methacrylic resin, acrylic styrene resin, modified acrylic resin, glycidyl methacrylate, melamine resin, alkyd resin, polyester resin, phenoxy resin, urethane resin, phenol resin, vinyl resin, cellulose Examples include various thermosetting resins such as derivatives and thermoplastic resins. Epoxy resins other than phthalic acid ester type epoxy resins, for example, bisphenol A type epoxy resins, bisphenol F type epoxy resins, novolac epoxy resins, glycidylamine type resins, alicyclic epoxy resins and the like may be used in combination. The mixing ratio of the phthalic acid-based glycidyl ester type epoxy resin and the other resin is desirably about 100: 0 to 40:60 by weight. When there are more other resins than this, it is difficult to obtain the effect of improving conductivity.

  The blending ratio of the binder resin is 5 to 50 parts by weight with respect to 100 parts by weight of the conductive powder. When the amount exceeds 50 parts by weight, the resistance value increases. When the amount is less than 5 parts by weight, the resistance value increases due to a decrease in the strength of the cured film. The optimum range is 5 to 30 parts by weight with respect to 100 parts by weight of the conductive powder.

  If desired, the conductive paste of the present invention may contain a curing agent. As the curing agent, an acid anhydride-based curing agent, an amine-based curing agent, a phenol resin-based curing agent and the like that are usually used in an epoxy resin composition are used. Particularly preferred are acid anhydride curing agents. You may mix and use 2 or more types of hardening | curing agents as needed. A compounding quantity is about 1-100 weight part with respect to 100 weight part of binder resin. A curing accelerator may be used in combination.

  When the phthalic acid ester type epoxy resin is in a liquid state at room temperature, it is not essential to use a solvent, but a solvent is blended as necessary in order to adjust the coating property of the paste. As the solvent, for example, known solvents such as alcohol solvents, ester solvents, ether solvents, ketone solvents, hydrocarbon solvents, fatty acid solvents, reactive diluents and the like are used.

  In addition, additives that are usually blended as necessary, for example, surfactants, antifoaming agents, plasticizers, thixotropic agents, dispersants, inorganic fillers and the like may be added as appropriate. By these, the properties such as heat resistance, water resistance, environmental resistance, flexibility, solderability, solder heat resistance, etc. of the coating property and the conductive film to be formed can be adjusted appropriately and applied to various applications. It becomes possible to do.

  The conductive paste is applied to the substrate by various means such as screen printing, transfer printing, dipping, brush coating, and application using a dispenser. As the substrate, in addition to a resin such as a printed wiring board, various materials such as ceramic, glass, silicon semiconductor, and compound semiconductor can be used. Since the electrically conductive paste of this invention has moderate flexibility, it can respond also to a flexible substrate. Moreover, it can also be used for the purpose of an electrode, an adhesive agent, circuit protection, etc. by apply | coating on the conductor circuit, dielectric material, and resistor which were formed on these base | substrates.

  The conductive paste applied on the substrate or the like is heat-treated by a known method to cure the resin (conductive paste), thereby obtaining a conductive film. The optimum heat treatment condition varies depending on the combination of the resin and the curing agent, but is performed at a temperature of 250 ° C. or lower, preferably 100 ° C. to 200 ° C.

  The electrically conductive paste of this invention and the electrically conductive film using the same can be used for various uses. Typical application examples include use for printed circuit board jumper circuits, through-hole conductors, additive circuits, etc., use for touch panel conductor circuits, use for resistance terminals, use as electromagnetic shielding, Examples thereof include adhesion and use as a conductive adhesive for mounting a semiconductor element or electronic component on a substrate.

  Moreover, the conductive paste of the present invention is suitable for use as a back electrode, a surface electrode, or a collecting electrode of a solar cell.

  For example, in the case of a solar cell using amorphous silicon, a high temperature treatment cannot be performed. Therefore, generally, a resin-based silver paste is heat-treated at a low temperature (for example, about 100 ° C. to 300 ° C.) to form a silver electrode containing a resin. A grid (current collecting) electrode that is formed and further has a specific resistance lowered by covering the surface thereof with solder is used (Patent Document 2 and others described above). When an electrode is formed using the conductive paste of the present invention, an electrode having a specific resistance smaller than that of a conventional solder-coated silver electrode can be obtained. That is, by using the conductive paste of the present invention, it is possible to obtain a high-performance curable electrode that does not require solder coating and has high conductivity. Thereby, the process of electrode formation is simplified, and there is no problem of environmental contamination due to the use of lead solder.

  In the case of a solar cell capable of high-temperature processing, a grid electrode is generally used in which the surface of a high-temperature firing type silver electrode is covered with solder. Since the conductive film obtained by heat-treating the conductive paste of the present invention has a lower resistance than the solder, it can be used as a substitute for the solder portion of the conventional solder-coated silver electrode, so that a higher-performance high-temperature fired mold An electrode can be obtained.

  In addition, the conductive paste of the present invention can be used as an external electrode of a chip-type ceramic electronic component such as a multilayer ceramic capacitor, a multilayer ceramic inductor, or a multilayer ceramic actuator by being cured by heat treatment.

  For example, external electrodes of conventional chip-type ceramic electronic components can be obtained by baking a high-temperature firing type electrode on a component body and coating a thermosetting conductive paste on the component body, or a thermosetting conductive paste directly on the body. Is formed by a method of applying and heat-curing, and solder plating is applied if necessary. The conductive paste of the present invention can be used as an alternative to a conventional thermosetting conductive paste.

  Further, solder is conventionally used for mounting a chip-type ceramic electronic component on a substrate, but instead of this, the conductive paste of the present invention may be used as a conductive adhesive.

  In addition, the above-mentioned use is an illustration, The electroconductive paste of this invention is not limited to the use which concerns, It can be used for the various uses by which electroconductivity and adhesiveness are requested | required.

  Using the conductive pastes of Examples 1 to 16 (shown in Table 1) and Comparative Examples 1 to 4 (shown in Table 2), specific resistance measurement tests and cross-cut tests were performed.

First, each component shown in Table 1 and Table 2 was mixed and kneaded with a three-roll mill to produce a conductive paste. All compounding amounts are parts by weight. The flaky silver powder has a specific surface area of about 1 m ² / g and an average particle size of 8 μm, the spherical silver powder has a specific surface area of about 0.8 m ² / g, and the curing agent is an acid anhydride. System curing agent (in the table, curing agent (i)) and phenol resin curing agent (same curing agent (ii)) were used. Moreover, the numerical value of each component in a table | surface represents the weight part of each component with respect to 100 weight part of electroconductive powders (flaky silver powder, spherical silver powder).

  The obtained composition was applied to a 10 mm × 10 mm square pattern on a glass substrate so that the thickness of the cured film was 20 μm, and was heat-treated at a temperature of 180 ° C. for 30 minutes to cure the resin. . The specific resistance values of the cured coating are also shown in Tables 1 and 2.

  Next, each composition was applied in a square pattern on a copper foil / paper phenolic resin substrate and subjected to a heat treatment at a temperature of 180 ° C. for 30 minutes to cure the resin. A cross-cut test was performed on the cured coating by cutting into 1 mm-interval grids with a cutter knife, applying a cellophane tape, and peeling it off. The film after peeling was observed. The film with almost no film peeling was marked with ◯, the film with no peeling was marked with ◎, and the film with the underlying copper foil visible was marked with x, and the results are shown in Tables 1 and 2. Indicated.

Other materials used in the examples are:
Dimethyl glycidyl phthalate: Epicron 200 manufactured by Dainippon Ink, Inc.
Diglycidyl hexahydrophthalate (i): Epicoat 190p manufactured by Japan Epoxy Resin Co., Ltd.
Diglycidyl hexahydrophthalate (ii): Epicoat 191p manufactured by Japan Epoxy Resin Co., Ltd.
Bisphenol A type epoxy resin: Epicoat 828 manufactured by Japan Epoxy Resin Co., Ltd.
Bisphenol F type epoxy resin: Epicoat 807 manufactured by Japan Epoxy Resin Co., Ltd.
Glycidyl methacrylate (low molecular weight): Average molecular weight 2,000
Glycidyl methacrylate (high molecular weight): Average molecular weight 20,000
It is.

As shown in Table 1 and Table 2, the specific resistance value of the example was smaller than that of the comparative example, and the result of the cross-cut test was also good, confirming the remarkable effects of the present invention.

Claims (10)

A conductive paste containing at least conductive powder and a binder resin containing a phthalic acid-based glycidyl ester type epoxy resin,
The phthalic acid-based glycidyl ester type epoxy resin is glycidyl ester of phthalic acid represented by the following formula 1, glycidyl ester of dihydrophthalic acid represented by the following formula 2, and glycidyl tetrahydrophthalic acid represented by the following formula 3. A conductive paste that is one or more selected from the group consisting of esters or glycidyl esters of hexahydrophthalic acid represented by the following formula 4.

  The conductive paste according to claim 1, wherein 5 to 50 parts by weight of the binder resin is blended with 100 parts by weight of the conductive powder.   The conductive paste according to claim 1 or 2, further comprising a curing agent. The conductivity according to any one of claims 1 to 3, wherein in formulas 1 to 4, at least one of R ₁ and R ₂ is CH ₃ , C ₂ H ₅ , C ₃ H ₇ or C ₄ H _9. Sex paste.   The phthalic acid-based glycidyl ester type epoxy resin is one or more selected from the group consisting of dimethyl glycidyl phthalate, methyl glycidyl glycidyl phthalate, diethyl glycidyl phthalate, dipropyl glycidyl phthalate, and dibutyl glycidyl phthalate, Item 5. A conductive paste according to Item 4.   The phthalic acid-based glycidyl ester type epoxy resin is one or more selected from the group consisting of diglycidyl phthalate, diglycidyl hexahydrophthalate, diglycidyl tetrahydrophthalate, and diglycidyl methyl tetrahydrophthalate. The electrically conductive paste as described in any one of thru | or 3.   The conductive paste according to claim 1, further comprising another resin as the binder resin. A circuit board provided with a conductive film having a specific resistance of 2 × 10 ⁻⁵ Ω · cm or less, obtained by applying the conductive paste according to claim 1 to a substrate and heat-treating the substrate.   The solar cell provided with the electrode formed using the electrically conductive paste in any one of Claim 1 thru | or 7. A chip-type ceramic electronic component comprising an electrode formed using the conductive paste according to claim 1.