JP2019206615A - Metallic paste and end surface forming electrode paste - Google Patents

Abstract

To provide a metallic paste optimum for a conductive resin end surface paste having sufficient strength and electric conductivity required for the end surface electrode, even under a conductive resin curing step that undergoes twice of tentative curing steps, and having small viscosity change of a degree of allowing a coating operation for a long term in an end surface coating step, when a metallic paste is used for a conductive resin end surface paste.SOLUTION: A metallic paste includes metallic powder, an epoxy resin, a curing agent, and a curing accelerator, in which the epoxy resin is a bifunctional epoxy resin having an epoxy group introduced at a terminal end part in a structural formula of the epoxy resin, and the melting point of the curing accelerator is 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 parts such as resistors, capacitors, and inductors.

  In a conventional chip component, a paste fired film made of Ag, Cu, Ni or the like is formed on an end face electrode. An end face electrode is completed by applying Ni plating and Sn plating to the surface of the fired film. This chip component is mounted on the substrate by soldering to the substrate. However, when the usage environment of the mounting board is exposed to an environment where thermal expansion or mechanical stress is likely to occur, such as thermal stress or vibration, the soldered board and the chip part body or its end electrode joint May crack and break.

In order to prevent this crack, an electrode layer made of a thermosetting 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, Sn is formed on the outside thereof. It is known that by applying the plating, the stress on the end face electrode is relaxed and the generation of cracks can be suppressed.
As the thermosetting resin, an epoxy resin is mainly used.

By the way, in order to form the end face electrode structure as described above in the chip component, the following method is used. Here, an end face electrode of a multilayer ceramic capacitor (MLCC) will be described as an example.
A multilayer 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, Ni or the like 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 joined by sintering. Form. A thermosetting conductive resin paste is formed on the end face base electrode layer for stress relaxation.

  In general, the so-called “Paloma system” is used as a paste immersion end coating machine. First, one end face of the capacitor element on which one base end face electrode 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 electrically conductive. Apply a functional resin paste. The chip element is mounted in a through-hole provided in the carrier plate, and one end face on which a base end face electrode is formed is inserted and immersed in a paste coating developed on a surface plate with a doctor blade. A conductive resin paste is applied to the substrate.

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 of the element is pushed with a pin from the temporarily cured resin end face electrode surface, and the element is exposed on the opposite surface of the carrier plate. A ceramic having a resin end face electrode formed on both ends of the exposed capacitor element by dip coating in the same manner and heated again in an oven at 150 ° C. for 10 to 30 minutes and temporarily cured at both ends. Get the element.
The ceramic element in which the resin end face electrode which is temporarily hardened on both ends is formed is collected by pushing again from the carrier plate with a pin. 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 external electrodes in which rubber particles having an average particle diameter of 1 μm to 6 μm are added to improve stress relaxation.
In the process of forming the conductive resin end face paste, there are the following problems.
First, in the process of spreading the paste on a surface plate with a blade to form a coating film, when the coating film development and recovery of the paste with a blade and a squeegee are repeated for a long time at room temperature, the viscosity of the resin paste gradually increases. A normal coating shape cannot be obtained. This is because, with a conductive resin paste having a one-pack type composition, polymerization of the resin proceeds gradually with time at room temperature. In a long-time coating operation, a paste having a long pot life at room temperature is desired.

Moreover, in the temporary hardening formation of the end face electrode, as described above, the heat history is given to the resin paste at 150 ° C. twice. In the main curing heat treatment, the end face resin is bonded to the base electrode by curing at 200 ° C. However, at this time, there is a problem that the strength and conductivity cannot be sufficiently obtained in the composition.
This is considered to be because the function of the reaction accelerator to be blended in the composition disappears due to the heat history in the two temporary curings, and the curing promoting action does not function.

JP 2015-1111576 A

  When a metal paste is used for the conductive resin end face paste, the change in viscosity is small enough to allow a long-time application operation in the end face application process, and further in the conductive resin curing process that undergoes two temporary curing processes. In addition, the present invention provides a metal paste that is most suitable for a conductive resin end face paste having sufficient strength and electrical conductivity required for an end face electrode.

  In order to achieve the above object, a first invention of the present invention is a metal paste containing a metal powder, an epoxy resin, a curing agent, and a curing accelerator, and the epoxy resin is at the end in the structural formula of the epoxy resin. The metal paste is a bifunctional epoxy resin into which an epoxy group is introduced, and the melting accelerator has 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.

  3rd invention of this invention is the metal paste characterized by the epoxy equivalent of the epoxy resin in 1st and 2nd invention being 100-500 [g / eq].

  A 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.

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

  According to a seventh aspect of the present invention, there is provided an end face forming electrode paste, wherein the end face forming electrode paste of the chip electronic component is the metal paste according to the first to sixth aspects of the invention.

  The metal paste according to the present invention is an optimum paste as a conductive resin end face paste used for an electrode face end forming electrode paste. In the chip part end face coating process, the viscosity is such that a long-time coating operation is possible. The change is small, and it has sufficient strength and electrical conductivity required for the end face electrode even under the conductive resin curing step that undergoes two temporary curing steps.

  The present invention is a metal paste containing a metal powder, an epoxy resin, a curing agent, and a curing accelerator, and the epoxy resin to be used is a bifunctional epoxy resin in which an epoxy group is introduced at the terminal portion in the structural formula of the epoxy resin. The metal accelerator is characterized in that the melting accelerator has a melting point of 180 ° C. or higher.

Hereinafter, individual components of the metal paste according to the present invention will be described.
1) Metal powder As the metal powder, spherical metal powder or flaky metal powder can be used.
The spherical metal powder having an average particle size in the range of 0.1 μm to 5 μm can be used. On the other hand, as the flaky metal powder, a powder having a scale diameter of 1 to 15 μm can be used.
When the average particle diameter of the spherical metal powder exceeds 5 μm, the contact of each metal particle in the cured film of the metal paste may be inhibited, and the conductivity of the cured film may be deteriorated. On the other hand, when the average particle size of the spherical metal powder is less than 0.1 μm, the fluidity of the metal paste is deteriorated, and the flatness of the coated surface of the metal paste may be deteriorated.

If the scale diameter of the flaky metal powder is less than 1 μm, the conductivity of the cured film of the metal paste may be deteriorated. If the scale diameter exceeds 15 μm, the flatness of the cured film of the metal paste may be deteriorated.
If it is the range of the above magnitude | sizes, there will be no limitation in particular in a metal powder. The average particle diameter 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.

Furthermore, in the metal paste, a spherical metal powder and a flaky metal powder can be mixed and used. When the spherical metal powder and the flaky metal powder are mixed and used, the ratio of the flaky metal powder to the metal powder is desirably 70% by mass or less. A 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 it is 70/30 to 30/70 in the notation of spherical metal powder / flaky metal powder.
When the ratio of the flaky metal powder in the metal powder exceeds 70% by mass, the fluidity of the metal paste is deteriorated, and the flatness of the coated surface of the metal paste is deteriorated. On the other hand, when the ratio of the flaky metal powder in the metal powder is less than 30% by mass, the conductivity of the cured product of the metal paste may be deteriorated.

  As the material of the metal powder to be used, conductive powder such as Ag powder, Ni powder, Cu powder, Ag-coated Cu powder, Ag-coated Ni powder, Ag-coated NiCuZn alloy powder can be used alone or in combination. In addition, Ag powder is desirable in consideration of the conductivity after resin curing. In addition, various coating powders of Ag and Ni powder can be used alone or in combination because of the reduction of precious metal costs.

2) Resin The metal paste according to the present invention is a thermosetting paste, and includes an epoxy resin, a curing agent, and a curing accelerator.
Here, the epoxy resin refers to an uncured epoxy resin contained in the metal paste, and the cured product is referred to as an epoxy resin cured product or simply a cured product.
The properties of the metal paste cured product are affected by the selection of the epoxy resin and the curing agent. That is, the metal paste according to the present invention forms Ni plating or Sn plating on the surface of the resin end face electrode of the cured product by a wet plating method. In order to perform 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 invention is a bifunctional epoxy resin, and bisphenol A type epoxy resin and bisphenol F type epoxy resin can be used. Among 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 resins include “jER825, jER827, jER828, jER834 (manufactured by Mitsubishi Chemical Corporation)”, “EPICLON 840, EPICLON 850, EPICLON 860, EPICLON 1050, EPICLON 1055 (manufactured by DIC Corporation)”.
A modified epoxy resin having bisphenol A and a hydrocarbon skeleton, an ether skeleton, or 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) and the like.
Such a bisphenol A type epoxy resin may be mixed with an epoxy resin having another structure.

The epoxy resin used in the present invention 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 fluidity of the metal paste. Moreover, when an epoxy equivalent exceeds 500 [g / eq], the bridge | crosslinking of an epoxy resin hardened | cured material will decrease, and the problem that the heat resistance of an epoxy resin falls will arise. However, when the epoxy equivalent is 500 [g / eq] or less, a large number of reacting epoxy groups are contained, and thus a curing reaction (crosslinking reaction of epoxy groups) is frequently performed. If the crosslinking reaction of the epoxy group is insufficient, the cured epoxy resin does not exhibit sufficient characteristics, and as a result, the cured product of the metal paste does not exhibit sufficient curing characteristics.

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

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

The blending ratio of the epoxy resin and the curing agent can be blended by combining the equivalents of the functional groups to 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 blending ratio can be determined by comparing the hydroxyl equivalent of the curing agent with the epoxy equivalent of the epoxy resin. The hydroxyl 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.
In addition, when a hardening | curing agent is solid, such as a powder form, it can melt | dissolve and use in the solvent which can be added to a metal paste.

Further, 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 accelerates the reaction.
As the curing accelerator, an imidazole compound having a melting point of 180 ° C. or higher is used. Since these are powders and do not evaporate from the paste during application work like liquid imidazole, the function of a curing accelerator is exhibited even in the process of curing the metal paste.

Examples of the imidazole compound 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 -S-triazine, 2-phenyl-4-methyl-5-hydroxymethylimidazole, 1-methylimidazole can be mentioned.
Further, they function to accelerate at a temperature of 150 ° C. or higher in the resin curing reaction. These imidazole compounds are in the form of a solid powder, and can be used by dissolving the imidazole compound in a solvent used for the metal paste in order to be added to the metal paste.

  The end surface electrode of the chip component using the metal paste according to the present invention is formed by applying the metal paste to one end surface of the chip component, pre-curing at 150 ° C. for 10 to 30 minutes, and then forming the other end surface. A metal paste is applied, pre-cured under the same conditions, and then cured at 200 ° C. The curing accelerator used for the metal paste according to the present invention is 150 ° C. by setting the melting point to 180 ° C. or higher. At a temporary curing temperature of about a degree, it functions slowly while leaving a function, and curing at 200 ° C. above the melting point can sufficiently promote the crosslinking reaction between the epoxy resin and the phenol curing agent.

  The blending ratio of the curing accelerator may be determined in consideration of an epoxy equivalent and the like. In the case of an epoxy resin having an epoxy equivalent of 100 to 500 [g / eq] used in the metal paste according to the present invention, the epoxy resin and the curing agent. The total amount of 100 parts by weight can be added in the range of 0.3 to 5 parts by weight. When the addition amount of the curing accelerator is less than 0.3 parts by weight, the curing reaction may not be promoted, and when 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 has sufficient storage stability and workability, and is sufficiently cured even after temporary curing. The cured metal paste is a glass of epoxy resin cured product. The transition point can be increased and chemical resistance and the like can be exhibited.

The metal paste according to the present invention can be produced by mixing a metal powder, an epoxy resin, a curing agent, and a curing accelerator. In order to obtain the metal paste by mixing the raw materials of the metal paste, a three-roll mill or a self-revolving mixer that is a known paste manufacturing method 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 applicability of the metal paste, the adhesion of the metal paste cured product, 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 coating workability. In particular, monoterpene alcohols are preferable because they can suppress an increase in the thixotropy ratio of the paste and are effective in stabilizing the coating shape. In particular, terpineol and dihydroterpineol are desirable.
Moreover, a well-known antifoamer and a dispersing agent can also be added to a metal paste. Furthermore, various coupling agents such as silane and titanium can be added 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 component and temporarily cured at 150 ° C. × 10 minutes to 30 minutes, and a metal paste is applied to the other end surface of the chip component, and 150 ° C. × 10 minutes to A resin end face electrode can be formed by temporarily curing in 30 minutes and then curing at 200 ° C. Further, Ni plating or Sn plating can be applied to the surface of the resin end face electrode by chemical plating.

The present invention will be further described below using examples.
Table 1 shows the metal powder and organic composition used.
(1) Metal powder The silver powder shown in Table 1 was used for the metal powder. Spherical silver powder and flaky silver powder were used in a weight ratio of 50/50. The average particle diameter of the spherical silver powder used was 0.2 μm as measured by SEM image. The flaky diameter of one flaky silver powder was 10 μm as measured by SEM image. The surface of the flaky silver powder is coated with stearic acid.

(2) Organic composition A bisphenol A type epoxy resin having an epoxy equivalent of 184 [g / eq] and a long-chain hydrocarbon-modified bisphenol A type epoxy resin having an epoxy equivalent of 403 [g / eq] were used as the epoxy resin.
A phenol novolac resin having a hydroxyl equivalent weight of 105 was used as the curing agent. Since this phenol resin is solid, it was used after dissolving in terpineol with a solid content of 30 wt%. The epoxy resin and the curing agent were blended so that the epoxy equivalent and the hydroxyl equivalent were equivalent.
As the curing accelerator, the compounds shown in Table 1 were used, and the amounts added were compared for comparison.

(3) Paste preparation A metal paste was obtained by adding 80% by mass of a metal powder, an epoxy resin, a curing agent, and a curing accelerator and kneading with a three-roll mill. When a bisphenol A type epoxy resin having an epoxy equivalent of 184 [g / eq] was used as the epoxy resin, the content of the epoxy resin in the metal paste was set to 10% by mass. When using a long-chain hydrocarbon-modified bisphenol A type epoxy resin having an epoxy equivalent of 403 [g / eq], the content of the epoxy resin in the metal paste was set to 14% by mass. In addition, 0.16 mass% of hardening accelerators were added in any metal paste.

In addition, the dilution was adjusted appropriately with the solvent terpineol, and the viscosity at 10 rpm was adjusted by viscosity measurement using a viscometer shown below so that the viscosity at 20 rpm was in the range of 20-30 Pa · s.
<Viscosity measurement>
The viscosity was measured using a “Brookfield HBT rotational viscometer”.
In addition, the viscosity was determined under the condition that the share rate of 10 rotations / minute (10 rpm) was 4 [s ⁻¹ ].

(4) End surface coating An end surface coating machine MS-100 (manufactured by Product) was used. The prepared paste was applied to MLCC bare chips having a chip size of 2012 M (JIS C5101-221-2006) under the conditions shown in Table 2.
The procedure for forming the copper external electrode on the MLCC is shown below.

·procedure;
1. Copper external electric coating:
A copper external electrode paste (TE-3025; manufactured by Sumitomo Metal Mining Co., Ltd.) was dip-coated on one end face of the bare chip and dried in an oven at 120 ° C. for 10 minutes. Next, the other end face of the bare chip was similarly dip coated and dried under the condition of 120 ° C. × 10 min. The dried product was baked using a belt firing furnace in a nitrogen atmosphere under a condition of 900 ° C. × 10 min (in-out 60 min, BBO 300 ppm) in a nitrogen atmosphere, and a base electrode forming chip provided with a copper base electrode layer was obtained. Obtained.
2. Capacity measurement of base electrode forming chip;
The “capacitance” and “tan δ measurement (1 kHz)” of the chip produced by the capacitance meter were measured.
<Capacitance measurement of base electrode forming chip>
The capacitance and tan δ were measured (1 kHz) with a capacitance meter.
3. Metal paste application;
The conductive resin paste shown in Table 1 was dip-coated on one end face of the chip formed with the copper base electrode layer prepared in 1 above under the application conditions shown in Table 2, and dried in an oven at 150 ° C. for 30 minutes. . Next, dip-apply in the same manner on the other end surface of the chip, and after drying at 150 ° C. × 30 min, the chip is removed from the carrier plate, placed on an Al ₂ O ₃ substrate and cured under the conditions of 200 ° C. × 60 min, and on the copper base A chip (MLCC element) having a conductive resin end face was produced.

[Characteristic evaluation]
<Pot life (measurement of viscosity over time)>
The paste was held in a constant temperature bath at 25 ° C., and the change in viscosity with time was confirmed.
The sample was stored in a constant temperature bath at 25 ° C., and after 72 hours, the viscosity value exceeded 2 times was evaluated as “X”, and the others were evaluated as “◯”.

<Volume resistance value>
An electrode pattern having a width of 0.6 mm and a length of 600 mm was printed on an alumina substrate.
This test substrate was put into an oven maintained at 150 ° C. and dried for 30 minutes. After drying, the substrate was taken out and once returned to room temperature.
Next, this substrate was put into an oven held at 200 ° C., heat-treated for 60 minutes, and cured to produce a cured conductive paste film.
The resistance value in the electrode pattern of the obtained conductive paste cured film was measured using a digital multimeter.
The film thickness was determined using a Surfcom surface roughness meter (manufactured by Tokyo Seimitsu Co., Ltd.), and the volume resistance value (unit: Ωcm) was determined from the film thickness.
Those having a volume resistance value of 1.0 × 10 ⁻³ Ωcm or more were evaluated as conductive “x”.

<Capacitance, tan δ measurement>
About the MLCC element which formed the conductive resin end surface on the copper base produced by the method shown in the above “procedure”, the capacitance and tan δ were measured using a capacitance meter (Hewlett-Packard 4278A).
The measurement frequency was 1 kHz.
30 MLCC elements were measured with respect to the paste composition, and the average value was obtained.
An average value of a capacitance lower than 90% with respect to the design capacitance value of 1 μF of the MLCC element was designated as “x”. The tan δ was defined as “x” when the tan δ was 1.5 times or more of the value of tan δ measured only with the copper base electrode.
The above evaluation results are also shown in Table 1.

Claims (7)

Metal paste containing metal powder, epoxy resin, curing agent and curing accelerator,
The epoxy resin is a bifunctional epoxy resin in which an epoxy group is introduced at a terminal portion in the structural formula of the epoxy resin,
A metal paste, wherein the curing accelerator has a melting point of 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 an epoxy equivalent of the epoxy resin is 100 to 500 [g / eq].   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 silver powder.   6. The metal paste according to claim 5, wherein the silver powder is a mixed powder of spherical silver powder and flaky silver powder.   An electrode paste for forming an end surface, wherein the electrode paste for forming an end surface of a chip electronic component is the metal paste according to any one of claims 1 to 6.