JP2019207762A - Metallic paste and end surface forming electrode paste - Google Patents

Abstract

To provide a conductive resin paste capable of alleviating stress generated by vibration or temperature change of a cured material by substituting an epoxy resin having a soft skeleton at a constant rate relative to a content of the epoxy resin contained in a conductive resin 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, the epoxy resin contains a bisphenol A skeleton, and is formed of a first epoxy resin of the bifunctional epoxy resin in which an epoxy group is introduced at a terminal part in the structural formula of the epoxy resin and a second epoxy resin in which a main chain in the structural formula is polyglycol and both terminal parts of the structural formula are provided with an epoxy group, 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, the following method is used to form the end face electrode structure as described above in the chip component. 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. However, in the technique disclosed in Patent Document 1, the cured product of the electrode conductive paste satisfies the bending elasticity as a bulk, but the thinnest portion of the cured product of the electrode conductive paste of the MLCC end face electrode is 10 μm or less. When rubber particles having an average particle diameter of 1 μm to 6 μm are used, the thinnest portion of the cured product of the electrode conductive paste is caused by cracks in the cured product of the electrode conductive paste due to partial deviation of the bending elastic modulus. May occur.

JP 2015-1111576 A

  Conductivity that can relieve the stress generated by vibrations and temperature changes in cured products by replacing the epoxy resin contained in the conductive resin paste with a certain percentage of the epoxy resin with a flexible skeleton. A functional resin paste is provided.

  Under such circumstances, the first invention of the present invention is a metal paste containing metal powder, an epoxy resin, a curing agent, and a curing accelerator, and the epoxy resin is epoxy at the end in the structural formula of the epoxy resin. A bifunctional epoxy resin into which a group is introduced, wherein the epoxy resin includes a bisphenol A skeleton, and an epoxy group is introduced into a terminal portion in the structural formula of the epoxy resin. The epoxy resin and the main chain in the structural formula are polyglycols, and are composed of a second epoxy resin having epoxy groups at both ends of the structural formula, and the melting accelerator has a melting point of 180 ° C. or higher. It is a metal paste characterized by this.

  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.

  According to the present invention, the epoxy resin contained in the metal paste according to the present invention, which is a conductive resin paste, is an epoxy resin in which an epoxy resin having a flexible skeleton with respect to its content is replaced at a certain ratio. Thus, the cured product has a function of relieving stress generated by vibration or temperature change, thereby bringing about an effect of suppressing the occurrence of cracks in the chip component and the like, and has a remarkable industrial effect.

  The present invention is a metal paste containing a metal powder, an epoxy resin, a curing agent, and a curing accelerator, the epoxy resin to be used contains a bisphenol A skeleton, and an epoxy group is introduced into the terminal of the structural formula of the epoxy resin. A first epoxy resin comprising a bifunctional epoxy resin, a main chain in the structural formula being polyglycol, and a second epoxy resin having epoxy groups at both ends of the structural formula, wherein the curing accelerator Is characterized by having 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 to 5 μm can be used. On the other hand, the flaky metal powder can be a powder having a scale diameter of about 1 μm to 15 μm.
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.

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 or the like 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 first epoxy resin that can be used in 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.

  The second epoxy resin that can be used for the metal paste of the present invention is a bifunctional epoxy resin, and has a polyglycol skeleton in the main chain in the structural formula instead of a bisphenol skeleton. Since the second epoxy resin does not have a benzene ring in the skeleton, the bending elastic modulus of the cured epoxy resin can be lowered, and the cured metal paste is given flexibility.

  As such a second epoxy resin, there is polypropylene glycol diglycidyl ether, and DER732 and DER736 (manufactured by Olin Corporation) are known.

  The blending ratio of the first epoxy resin and the second epoxy resin is the blending ratio of the first epoxy resin: the second epoxy resin, and is 90: 10-40: 60. When the blending ratio of the second epoxy resin is less than 10, the bending elastic modulus of the metal paste cured product is high, and when the ratio of the second epoxy resin exceeds 60, the adhesive strength decreases.

The first epoxy resin and the second epoxy resin used in the present invention preferably have 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 and cured on the end face of the chip component 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.
(1) Metal powder Silver powder 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] is used for the first epoxy resin, and a polypropylene glycol diester having an epoxy equivalent of 184 [g / eq] is used for the second epoxy resin. Glycidyl ether was used.
The ratio of the first epoxy resin to the second epoxy resin was 8: 2 in Example 1, 7: 3 in Example 2, and 5: 5 in Example 3. In Comparative Example 1, only the first epoxy resin was used without adding the second 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, 2-phenyl-4-methyl-5-hydroxymethylimidazole was used.
As the solvent, a solvent that is soluble in an epoxy resin having a boiling point of about 200 ° C. to 240 ° C. was used. Turpineol (TPO) was used as the monoterpene alcohol.

(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. The total amount of the first epoxy resin and the second epoxy resin was 11% by mass, and 0.16% by mass of a curing accelerator was added.
Dilution adjustment was appropriately performed with a solvent terpineol, and the viscosity at a rotation speed of 10 rpm was adjusted to be in a range of 20 to 30 Pa · s by viscosity measurement using a viscometer shown below.

(4) Viscosity measurement Viscosity was measured using "Brookfield HBT rotational viscometer".
In addition, the viscosity was 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 specific resistance>
About the metal paste of an Example and a comparative example, U-shaped pattern printing of length 60mm, width 0.6mm, and thickness 30micrometer using a 200 mesh stainless steel screen on an alumina substrate of 1 inch square and thickness 1mm. And dried in 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 obtained from an average of three numerical values measured so as to intersect with the pattern using a “surface roughness shape measuring instrument” manufactured by Tokyo Seimitsu Co., Ltd. After curing, the specific resistance was measured by a four-terminal method using a multimeter LCR meter.

<Measurement of adhesion strength>
The paste of Example and Comparative Example was printed on a 1 mm square, 1 mm thick alumina substrate with a 2 mm square pad, and a 1.5 mm square silicon chip was placed thereon and cured at 200 ° C. for 60 minutes. It was. Thereafter, the adhesive surface was pushed from the side surface with a push-pull gauge, and the value when the silicon chip was peeled was read.

<Measurement of flexural modulus>
Four heat-resistant tapes were stacked on a Teflon (registered trademark) plate and pasted so as to surround an area of 10 mm × 50 mm, and the pastes of Examples and Comparative Examples were applied and cured at 200 ° C. for 60 minutes. After curing, the test piece was peeled off from the Teflon (registered trademark) plate to obtain a sample for bending test.
Each specimen was measured for flexural modulus using an autograph made by Shimadzu Science.
Further, the test piece was held in the atmosphere at 150 ° C. and thermally deteriorated to measure the flexural modulus.

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,
The epoxy resin contains a bisphenol A skeleton and a first epoxy resin composed of a bifunctional epoxy resin in which an epoxy group is introduced at a terminal portion in the structural formula of the epoxy resin, and a main chain in the structural formula is a polyglycol And comprising a second epoxy resin having an epoxy group at both ends of the structural formula,
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.