JP2021143226A - Metal paste and electrode paste for forming end face - Google Patents

Abstract

To provide a metal paste optimal for a conductive resin end face paste, having sufficient strength and electric conductivity for an end face electrode.SOLUTION: A metal paste includes: metal powder; an epoxy resin, a curing agent and a curing accelerator; and a modified urea resin. The epoxy resin is a bifunctional epoxy resin in which an epoxy group is introduced to a terminal of the structural formula of the epoxy resin. The curing accelerator has a melting point of 180°C or higher.SELECTED DRAWING: None

Description

The present invention relates to a conductive resin paste, and more particularly to a conductive resin paste for use in forming end face electrodes of chip components such as resistors, capacitors, and inductors.

In the conventional chip component, a paste firing film of Ag, Cu, Ni or the like is formed on the end face electrode. The surface of the fired film is subjected to Ni plating and Sn plating to complete the end face electrode. This chip component is mounted on the board by soldering to the board. However, if the usage environment of the mounting board is exposed to an environment that is susceptible to thermal expansion and mechanical stress such as thermal stress and vibration, the joint between the soldered board and the chip component body and its end face electrodes May crack and be destroyed.

In order to prevent this crack, an electrode layer made of a heat-curable conductive resin paste is formed on the outside of the end face electrode formed from a paste-fired film of Ag, Cu, Ni or the like, and Ni plating or Sn is formed on the outside. It is known that by applying plating, the stress on the end face electrodes can be relaxed and the occurrence of cracks can be suppressed.
Epoxy resin is mainly used as the thermosetting resin.

By the way, in order to form the structure of the end face electrode as described above on the chip component, the following method is used. Here, the end face electrode of the monolithic ceramic capacitor (MLCC) will be described as an example.
A laminated ceramic sintered body element having a ceramic layer and an internal electrode layer is prepared. An end face base electrode layer in which a metal paste such as Ag, Cu, or Ni is applied to both end faces of this element, fired at a temperature of 700 ° C to 1300 ° C, and the internal electrode layer and the end face electrode are physically bonded by sintering. To form. A thermosetting conductive resin paste is formed on the end face base electrode layer for the purpose of stress relaxation.

Generally, a so-called "Paloma method" is used as a paste immersion end face coating machine. First, one end face on which one of the base end face electrodes of the above-mentioned capacitor element is formed is immersed in a conductive resin paste developed on a surface plate with a film thickness of 600 μm, and the one end face on which the base end face electrode is formed is conductive. Apply the sex resin paste. The chip element is mounted in a through hole provided in the carrier plate, and one element end face is inserted and immersed in a paste coating film developed by a doctor blade on a surface plate to form a base end face electrode. Apply a thermosetting conductive resin paste to the surface.

This is heated in an oven at 150 ° C. for 10 to 30 minutes to form a temporarily cured resin end face electrode. Next, the end face portion of the element is pushed with a pin from the temporarily cured resin end face electrode surface to expose the element on the opposite surface of the carrier plate. The paste was dipped and applied to the other end face of the exposed capacitor element in the same manner, and then heated again in an oven at 150 ° C. for 10 to 30 minutes to form temporarily cured resin end face electrodes at both ends. Obtain a ceramic element.
It is pushed again from the carrier plate with a pin, and the ceramic element having the resin end face electrodes temporarily cured at both ends is collected. This element is heated in an oven at 200 ° C. for 60 minutes to cure the resin end face to obtain a ceramic element in which the resin end face electrode is formed on the base electrode.

Patent Document 1 discloses a technique of a conductive paste for an external electrode, which is improved in stress relaxation by adding rubber particles having an average particle size of 1 μm to 6 μm.

Japanese Unexamined Patent Publication No. 2015-11576

Since the cured product of the thermosetting conductive resin paste contains a cured resin product, the electric conductivity may be inferior. The present invention provides an optimum metal paste for a conductive resin end face paste having sufficient strength and electrical conductivity required for an end face electrode.

The first invention of the present invention contains a metal powder, an epoxy resin, a curing agent, a curing accelerator, and a modified urea resin, and the epoxy resin is introduced into the terminal portion in the structural formula of the epoxy resin. This is a bifunctional epoxy resin, which is a metal paste characterized by having a curing accelerator having a melting point of 180 ° C. or higher.

The second invention of the present invention is a metal paste characterized in that the curing accelerator in the first invention is imidazole.

The third invention of the present invention is a metal paste characterized in that the epoxy equivalent of the epoxy resin in the first and second inventions is 100 [g / eq] or more and 500 [g / eq] or less. ..

The fourth invention of the present invention is a metal paste characterized in that the curing agent in the first to third inventions is a phenol resin.

A fifth invention of the present invention is a metal paste characterized in that the metal powder in the first to fourth inventions is a silver powder.

The sixth invention of the present invention is a metal paste characterized in that the silver powder in the fifth invention is a mixed powder of spherical silver powder and flake-shaped silver powder.

A seventh aspect of the present invention is an end face forming electrode paste according to any one of the first to sixth inventions, wherein the end face forming electrode paste of the chip electronic component is the metal paste.

The metal paste according to the present invention is an optimum paste as a conductive resin end face paste used for an electrode paste for forming an end face of a chip component, and has sufficient strength and electrical conductivity.

This embodiment is a metal paste containing a metal powder, an epoxy resin, a curing agent, a curing accelerator, and a modified urea resin. The epoxy resin to be used has an epoxy group introduced at the end of the structural formula of the epoxy resin. It is a bifunctional epoxy resin, which is a metal paste characterized by having a curing accelerator having a melting point of 180 ° C. or higher.

Hereinafter, individual components of the metal paste according to the present embodiment will be described.
1) Metal powder As the metal powder, spherical metal powder or flake-shaped metal powder can be used.
The average particle size of the spherical metal powder can be in the range of 0.1 μm to 5 μm. On the other hand, as the flake-shaped metal powder, a powder having a scale diameter of 1 μm to 15 μm can be used.
If the average particle size of the spherical metal powder exceeds 5 μm, the contact of each metal particle in the cured film of the metal paste may be hindered and the conductivity of the cured film may deteriorate. On the other hand, if the average particle size of the spherical metal powder is less than 0.1 μm, the fluidity of the metal paste may deteriorate and the flatness of the coated surface of the metal paste may deteriorate.

If the scale diameter of the flake-shaped metal powder is less than 1 μm, the conductivity of the cured film of the metal paste may deteriorate. If the scale diameter exceeds 15 μm, the flatness of the cured film of the metal paste may deteriorate.
The metal powder is not particularly limited as long as it is in the above size range. The average particle size and scale diameter of the metal powder can be measured by a scanning electron microscope image (SEM image).
The surface of the spherical metal powder may be coated with an organic acid such as stearic acid, and the coating of the spherical metal powder with an organic acid is appropriately selected in consideration of the characteristics of the metal paste.

Further, in the metal paste, a spherical metal powder and a flake-shaped metal powder can be mixed and used. When the spherical metal powder and the flake-shaped metal powder are mixed and used, it is desirable that the ratio of the flake-shaped metal powder to the metal powder is 70% by mass or less. The desirable range of the ratio of the flaky metal powder to the metal powder is 30% by mass to 70% by mass. That is, it is desirable that the notation of spherical metal powder / flake-shaped metal powder is 70/30 to 30/70.
When the ratio of the flake-shaped metal powder to the metal powder exceeds 70% by mass, the fluidity of the metal paste deteriorates and the flatness of the coated surface of the metal paste deteriorates. On the other hand, when the ratio of the flake-shaped metal powder to the metal powder is less than 30% by mass, the conductivity of the cured product of the metal paste may deteriorate.

As the material of the metal powder to be used, conductive powders such as Ag powder, Ni powder, Cu powder, Ag-coated Cu powder, Ag-coated Ni powder, and Ag-coated NiCuZn alloy powder can be used alone or in combination. Ag powder is desirable in consideration of conductivity after resin curing. Further, in order to reduce the cost of precious metals, various coating powders of Ag and Ni powder can be used alone or in combination.

2) Resin The metal paste according to the present embodiment is a thermosetting paste, and includes an epoxy resin, a curing agent, a curing accelerator, and a modified urea resin.
Here, the epoxy resin refers to an uncured epoxy resin contained in a metal paste, and the cured product is referred to as an epoxy resin cured product or simply a cured product.
The choice of epoxy resin and curing agent affects the properties of the cured metal paste. That is, in the metal paste according to the present embodiment, Ni plating or Sn plating is formed on the surface of the resin end face electrode of the cured product by a wet plating method. In order to apply the wet plating, the cured product is required to have chemical resistance.

The epoxy resin that can be used for the metal paste of the present embodiment is a bifunctional group type epoxy resin, and bisphenol A type epoxy resin and bisphenol F type epoxy resin can be used. Of these, it is desirable to use a bisphenol A type epoxy resin as a part of the epoxy resin because the glass transition point of the cured product tends to be high.
Examples of such bisphenol A type epoxy resin include "jER825, jER827, jER828, jER834 (manufactured by Mitsubishi Chemical Corporation)", "EPICLON840, EPICLON850, EPICLON860, EPICLON1050, EPICLON1055 (manufactured by DIC Corporation)".
Further, a modified epoxy resin having bisphenol A and a hydrocarbon skeleton, an ether skeleton, and a glycol skeleton can also be used.

Examples of such a modified epoxy resin include "EPICLON EXA-4816, EPICLON EXA-4850, EPICLON TSR-960, EPICLON TSR-601" (manufactured by DIC Corporation).
Such a bisphenol A type epoxy resin and an epoxy resin having another structure may be mixed and used.

The epoxy resin used in the present embodiment preferably has an epoxy equivalent of 100 to 500 [g / eq], and more preferably an epoxy equivalent of 100 to 450 [g / eq]. Here, the epoxy equivalent is a value obtained by dividing the molecular weight of the epoxy resin by the number of epoxy groups contained in one epoxy resin molecule.
When the epoxy equivalent is 500 [g / eq] or less, the molecular weight of the epoxy resin becomes small, which is desirable from the viewpoint of the fluidity of the metal paste. Further, when the epoxy equivalent exceeds 500 [g / eq], the cross-linking of the cured epoxy resin product is reduced, which causes a problem that the heat resistance of the epoxy resin is lowered. However, when the epoxy equivalent is 500 [g / eq] or less, a large amount of reacting epoxy groups is contained, so that a curing reaction (crosslinking reaction of epoxy groups) is often carried out. If the cross-linking reaction of the epoxy group is insufficient, the cured epoxy resin product does not exhibit sufficient properties, and as a result, the cured product of the metal paste does not exhibit sufficient curing properties.

Furthermore, the curing agent also affects the heat resistance and chemical resistance of the epoxy resin cured product.
Further, in order to apply the metal paste with a uniform thickness and smoothly, it is important to select a curing agent and a curing accelerator. The curing agent also affects the storage stability and workability of the metal paste, and it is required that the curing reaction does not occur during storage or application of the metal paste.
The reaction between the epoxy resin and the curing agent, which is required to be cured, reacts with the epoxy group of the epoxy resin and crosslinks between the molecules of the epoxy resin to cure. As the epoxy curing agent, polybasic acid anhydrides such as amine compounds, urea compounds, phenol compounds, pyromellitic anhydrides, and trimellitic anhydrides are known.

In the metal paste according to the present embodiment, the curing agent is preferably a phenol resin because of the resistance of the cured product to the wet plating solution, moisture resistance, and adhesion, and a novolak type phenol resin is more preferable. When a novolak type phenol resin is used as a curing agent, the crosslink density of the epoxy resin cured product is increased, and heat resistance, moisture resistance, and chemical resistance are improved.

The mixing ratio of the epoxy resin and the curing agent can be adjusted by adjusting the equivalent of the functional groups with which the curing agent reacts according to the epoxy equivalent of the epoxy resin. When a phenol resin is used as the curing agent, the compounding ratio can be determined by comparing the hydroxyl equivalent of the curing agent with the epoxy equivalent of the epoxy resin. The hydroxyl group equivalent is a value obtained by dividing the molecular weight of the phenol resin by the number of hydroxyl groups contained in one phenol resin.
When the curing agent is a solid such as powder, it can be used by dissolving it in a solvent that can be added to the metal paste.

Furthermore, when considering the curing reaction between the epoxy resin and the phenol resin, it is found that the curing reaction does not easily proceed even when heated. Therefore, it is necessary to add a curing accelerator that promotes the reaction.
As this curing accelerator, an imidazole compound having a melting point of 180 ° C. or higher is used. Since these are powders in nature and do not evaporate from the paste during the coating operation unlike liquid imidazole, the function of the curing accelerator is exhibited even in the process of curing the metal paste.

Such imidazole compounds having a melting point of 180 ° C. or higher include 2,4-diamino-6- [2'-methylimidazolyl- (1')] ethyl-s-triazine, 2-4-. Diamino-6- [2'-undecylimidazolyl- (1')]-ethyl-s-triazine, 2-4-diamino-6- [2'-ethyl 4'-methylimidazolyl- (1')]-ethyl Examples thereof include −s-triazine, 2-phenyl-4-methyl-5-hydroxymethylimidazole, and 1-methylimidazole.
In addition, they have a promoting action at a temperature of 150 ° C. or higher in the resin curing reaction. These imidazole compounds are in the form of solid powder, and in order to add them to the metal paste, the imidazole compounds can be used by dissolving them in the solvent used for the metal paste.

To form the end face electrode of a chip component in which the metal paste according to the present embodiment is used, the metal paste is applied to one end face of the chip component, temporarily cured at 150 ° C. for 10 to 30 minutes, and then the other end face. A metal paste is applied to the metal paste, temporarily cured under the same conditions, and then cured at 200 ° C. The curing accelerator used for the metal paste according to the present embodiment has a melting point of 180 ° C. or higher. At a temporary curing temperature of about 150 ° C., it acts slowly while retaining its function, and curing at 200 ° C., which is higher than the melting point, can sufficiently promote the cross-linking reaction between the epoxy resin and the phenol curing agent.

The mixing ratio of the curing accelerator may be determined in consideration of the epoxy equivalent and the like, and in the case of the epoxy resin having an epoxy equivalent of 100 to 500 [g / eq] used in the metal paste according to the present embodiment, the epoxy resin and the curing are cured. When the total amount of the agent is 100 parts by weight, it can be added in the range of 0.3 parts by weight to 5 parts by weight with respect to 100 parts by weight. If the amount of the curing accelerator added is less than 0.3 parts by weight, the curing reaction may not be accelerated, and if the amount of the curing accelerator exceeds 5 parts by weight, the shape of the cured product may be deformed.

By selecting these epoxy resins, curing agents, and curing accelerators, the metal paste is sufficiently cured even after temporary curing while maintaining the storage stability and workability of the metal paste, and the cured product of the metal paste is the glass of the epoxy resin cured product. It is possible to raise the transition point and exhibit chemical resistance and the like.

Further, the metal paste according to the present embodiment contains a modified urea resin.
This modified urea resin is a modified product of urea urethane or urea resin and polyamide, and is a polymer obtained by copolymerizing urea with urethane or polyamide, and is a polymer of BKY-410, BYK-411, BYK-415, BYK-420. , BYK-425, BYK-430, BYK-431 (all manufactured by Big Chemie Co., Ltd.).

The content of the modified urea resin in the metal paste is preferably 0.1% by mass or more and 2% by mass or less, and more preferably 0.1% by mass or more and 1.0% by mass or less.
When the content of the modified urea resin in the metal paste is less than 0.1% by mass, the effect of reducing the resistance value of the cured product of the metal paste is weak, the resistance value cannot be reproducibly and stably reduced, and the resistance value is high. Sometimes. On the other hand, if the modified urea resin is excessively contained, the strength of the cured product may decrease.

In general, the modified urea resin has an effect of preventing deformation such as the shape of the coated surface of the metal paste dripping. However, in the present embodiment, it has been found that the inclusion of the modified urea resin has an unexpected effect of lowering the resistance value of the cured product. When the modified urea resin is contained, the resistance value of the cured product can be reduced to 1/2 or less than the resistance value of the cured product.

The metal paste according to the present embodiment can be produced by mixing a metal powder, an epoxy resin, a curing agent, a curing accelerator, and a modified urea resin.
In order to obtain a metal paste by mixing the raw materials of the metal paste, a three-roll mill, a self-revolution mixer, or the like, which is a known method for producing a paste, can be used.
The content of the metal powder contained in the metal paste is 60% by mass to 95% by mass, and is preferably 70% by mass to 90% by mass from the viewpoint of the coatability of the metal paste, the adhesion of the cured metal paste, and the electrical characteristics.

Various solvents can be added to the metal paste in order to adjust the viscosity of the paste.
The solvent is preferably a solvent that sufficiently dissolves the resin and has a boiling point of about 200 ° C. to 250 ° C. in terms of coating workability. In particular, monoterpene alcohols are desirable because they can suppress an increase in the chixo ratio of the paste and are effective in stabilizing the coating shape. Especially terpineol and dihydroterpineol are desirable.

Further, a known defoaming agent or dispersant can be added to the metal paste. Furthermore, various coupling agents such as silane and titanium can be added in order to improve adhesion and dispersibility.

The obtained metal paste can be applied to the end face of the chip component and cured to form a resin end face electrode. A metal paste is applied to one end face on both sides of the chip part and temporarily cured at 150 ° C. × 10 minutes to 30 minutes, and a metal paste is applied to the other end face of the chip part at 150 ° C. × 10 minutes to 150 ° C. A resin end face electrode can be formed by temporarily curing in 30 minutes and then curing at 200 ° C. Further, the surface of the resin end face electrode can be subjected to Ni plating or Sn plating by a chemical plating method.

Hereinafter, the present invention will be further described with reference to Examples.
(1) Metal powder Silver powder was used as the metal powder. Spherical silver powder and flaky silver powder were used in a weight ratio of 50/50. The average particle size of the spherical silver powder used was 0.2 μm as measured by a 2000-fold SEM image. The scale diameter of one flaky silver powder was 10 μm as measured by a 2000-fold SEM image. The surface of the flake-shaped silver powder is coated with stearic acid.

(2) Organic composition (including resin component)
A bisphenol A type epoxy resin having an epoxy equivalent of 189 [g / eq] was used as the first epoxy resin, and a polypropylene glycol diglycidyl ether having an epoxy equivalent of 184 [g / eq] was used as the second epoxy resin. ..
The ratio of the first epoxy resin to the second epoxy resin was 7: 3.

A phenol novolac resin having a hydroxyl group equivalent of 105 was used as the curing agent. Since this phenol resin is a solid, it was used after being dissolved in terpineol with a solid content of 30% by mass. The epoxy resin and the curing agent were blended so that the epoxy equivalent and the hydroxyl group equivalent were equivalent.
As the curing accelerator, powdered 2-phenyl-4-methyl-5-hydroxymethylimidazole was used.

BYK-411 manufactured by Big Chemie Co., Ltd. was used as the modified urea resin.
As the solvent, a solvent soluble in an epoxy resin having a boiling point of about 200 ° C. to 240 ° C. was used. Tarpineol (TPO) was used as the monoterpene alcohol.

(3) Paste Preparation To obtain a metal paste, 80 parts by weight of a metal powder, an epoxy resin, a curing agent, a curing accelerator, and a modified urea resin were added and kneaded with a three-roll mill. The total amount of the first epoxy resin and the second epoxy resin was 11 parts by weight, and 0.16 parts by weight of the curing accelerator was added. Further, a predetermined amount of modified urea resin is added, diluted appropriately with tarpineol as a solvent, and the viscosity is measured using a viscometer shown below so that the viscosity at 10 rpm is in the range of 20 to 30 Pa · s. It was adjusted.

(4) Viscosity measurement The viscosity was measured using a "Brookfield HBT rotational viscometer".
The viscosity was laterally determined under the condition that the share rate of 10 rotations / minute (10 rpm) was "4s-1".

[Characteristic evaluation]
The results of the following characteristic evaluation are also shown in Table 1.
<Measurement of resistivity>
Regarding the metal pastes of Examples and Comparative Examples, a "U-shaped pattern" having a length of 60 mm, a width of 0.6 mm, and a thickness of 30 μm was used on a 1-inch square, 1 mm-thick alumina substrate using a 200-mesh stainless steel screen. Printing was performed, dried in the air at 150 ° C. for 30 minutes, and then cured at 200 ° C. for 60 minutes to form an external electrode.
The thickness of the pattern was determined by averaging the numerical values of three points measured so as to intersect the pattern with a "surface roughness shape measuring machine" manufactured by Tokyo Seimitsu Co., Ltd. After curing, the resistivity was measured by the 4-terminal method using a multimeter LCR meter.

In the above metal paste, 0.5 parts by weight of the modified urea resin was added to prepare the metal paste according to Example 1, and the specific resistance was measured.
The results are shown in Table 1.

In the above metal paste, 1.0 part by weight of the modified urea resin was added to prepare the metal paste according to Example 2, and the specific resistance was measured.
The results are shown in Table 1.

In the above metal paste, 2.0 parts by weight of the modified urea resin was added to prepare the metal paste according to Example 3, and the specific resistance was measured.
The results are shown in Table 1.

(Comparative Example 1)
The metal paste according to Comparative Example 1 was prepared without adding the modified urea resin, and the above specific resistance was measured.
The results are shown in Table 1.

The cured product of the metal paste of Examples 1 to 3 containing the modified urea resin within the range of the present invention has a resistance value lower than 1/2 as compared with Comparative Example 1 not containing the modified urea resin. I understand.

Claims (7)

Contains metal powder, epoxy resin, curing agent, curing accelerator, and modified urea resin.
The epoxy resin is a bifunctional epoxy resin in which an epoxy group is introduced at the terminal portion in the structural formula of the epoxy resin.
A metal paste characterized in that the melting point of the curing accelerator is 180 ° C. or higher. The metal paste according to claim 1, wherein the curing accelerator is imidazole. The metal paste according to claim 1 or 2, wherein the epoxy equivalent of the epoxy resin is 100 [g / eq] or more and 500 [g / eq] or less. The metal paste according to any one of claims 1 to 3, wherein the curing agent is a phenol resin. The metal paste according to any one of claims 1 to 4, wherein the metal powder is a silver powder. The metal paste according to claim 5, wherein the silver powder is a mixed powder of a spherical silver powder and a flake-shaped silver powder. An electrode paste for forming an end face, wherein the electrode paste for forming an end face of a chip electronic component is the metal paste according to any one of claims 1 to 6.