JP4561574B2 - Conductive paste for multilayer ceramic component terminal electrode - Google Patents

Description

  The present invention relates to a conductor paste for multilayer ceramic component terminal electrodes, and more particularly to a conductor paste for multilayer ceramic component terminal electrodes suitable for forming terminal electrodes of multilayer ceramic components such as capacitors and inductors.

In general, multilayer ceramic parts such as capacitors and inductors are manufactured as follows.
First, unfired ceramic sheets such as dielectrics and magnetic bodies and internal electrode paste layers are alternately stacked to form an unfired laminate, and this laminate is cut and then fired at a high temperature to form a ceramic body (hereinafter referred to as “fired”). , "Element body"). Next, the conductive paste for the laminated ceramic component terminal electrode in which the conductive powder and the inorganic binder powder such as glass are dispersed in the vehicle is dipped, brushed and screened on the terminal surface where the internal electrode is exposed from the element body. It is applied by various methods such as printing. Then, after drying, baking at a high temperature forms a terminal electrode electrically connected to the internal electrode. On the terminal electrode, a nickel plating layer and a tin plating layer made of tin having good solderability or an alloy thereof are sequentially formed as necessary to form a multilayer ceramic component.

  As internal electrode materials, noble metals such as palladium, silver-palladium, and platinum were used, but in addition to resource saving and cost reduction, in order to prevent delamination and cracks due to oxidative expansion of palladium, Base metals such as nickel and copper are being used. For this reason, conductive powders such as nickel, cobalt, and copper, which are easy to form a good electrical connection with the internal electrode material, are also used for the terminal electrode conductor paste. In addition, in order to prevent the base metal contained in the internal electrode and terminal electrode from being oxidized and reducing the conductivity during firing, in a non-oxidizing atmosphere, that is, in an inert atmosphere such as nitrogen or hydrogen-nitrogen. Alternatively, it is performed at a maximum temperature of about 700 to 900 ° C. in a reducing atmosphere.

  In particular, in the case of a conductor paste containing a copper-based conductive powder, it is necessary to use a reduction-resistant glass that is stable even when fired in a non-oxidizing atmosphere as an inorganic binder. In addition, when electroplating is performed on the terminal electrode, the glass component may be altered or dissolved due to the acidity of the electroplating solution, the glass structure may be destroyed, and the adhesive strength with the element body may be greatly reduced. . In addition, when performing electroplating on the terminal electrode, the plating solution that has penetrated into the electrode film from the part where the glass component is melted or the void in the fired film causes a decrease in insulation resistance or the element body. In addition to incurring cracks, the invading plating solution may be heated and gasified during solder reflow to cause a so-called “solder explosion phenomenon” in which molten solder scatters.

Therefore, the glass component of the conductor paste is required to have a plating solution resistance and a characteristic capable of forming a dense fired film, and the use of zinc-based or barium-based glass has been studied ( (See Patent Document 1 and Patent Document 2). In addition, the use of alkali silicate glass has been studied (see Patent Document 3 and Patent Document 4).
Japanese Patent Laid-Open No. 2002-1000052 JP 2003-246644 A JP 2002-25337 A JP 2003-347148 A

  However, in recent years, demands for higher capacity, higher performance, and higher reliability for multilayer ceramic parts have become increasingly severe. In particular, in a small-sized and large-capacity monolithic ceramic capacitor, there is an increasing demand for thinning of the terminal electrode as the size is reduced, and a film thickness of 50 μm or less, and further about 20 μm is required. I came. In order to obtain excellent electrode characteristics equal to or better than those of conventional terminals with such a thin terminal electrode, it is necessary to be denser, have higher adhesion strength to the element body, and have excellent plating solution resistance. .

  Here, when using barium-based or zinc-based glass, a dense fired film structure with few voids is formed when fired together with conductive powder, and the penetration of the plating solution into the electrode film is suppressed. It has been known. In particular, in the case of zinc-based glass, a stronger reaction layer is formed between the glass and the element body, so that the adhesive strength and film strength can be improved and strength deterioration can be prevented. However, the barium-based and zinc-based glasses themselves are not so high in acid resistance, and in order to improve the plating solution resistance of the terminal electrode after firing, it is necessary to form the film more than the thickness.

When using alkali-silicate glass, the acid resistance of the glass itself is high, so that the plating solution resistance of the terminal electrode is improved to some extent, but a large amount of alkali metal component must be added to lower the glass softening point. There is. Therefore, the fluidity of the glass component is increased and the glass component is soaked into the element body, which tends to cause a decrease in element body strength and generation of cracks. Moreover, if the fluidity of the glass component is high, glass floats on the surface of the terminal electrode, and the plating property and the soldering property are deteriorated.
On the other hand, in order to solve such problems, the content of the alkali metal component is reduced, and when an alkaline earth metal or the like is blended as a flux for lowering the softening point, the film of the terminal electrode is deteriorated due to poor fluidity. Density decreases. Then, the plating solution penetrates from the pores in the terminal electrode film, and electrode peeling occurs at the thin portion of the edge portion (hereinafter referred to as “corner portion”) of the terminal surface of the element body. The problem arises.

In addition, the conductor paste containing the copper-based conductive powder needs to be fired in a non-oxidizing atmosphere as described above. Therefore, there is a problem that the firing and removal of the vehicle component are not easily performed, and residual carbon, which is a decomposition product of the vehicle component, is generated in the terminal electrode film. In particular, when the flowability of the glass component at a low temperature is high, the glass softens and flows in the initial stage of the firing stage, creating a film structure that is too dense and trapping the vehicle component, which increases the residual carbon. there were.
Residual carbon reduces part of the ceramic derivative in the subsequent high-temperature firing stage, which may cause deterioration of the element body and cracks. Further, there is a problem that gasification occurs at the high temperature firing stage to generate blisters in the terminal electrode film, and a phenomenon that a part of the terminal electrode film swells in a dome shape occurs.

  The present inventors say that when the terminal electrode is electroplated using an acidic plating solution, the acid resistance of the glass itself is high, and the denseness of the terminal electrode film after firing is sufficient. When the conditions are not satisfied at the same time, it is considered that sufficient plating solution resistance that can cope with the thinning of the terminal electrode cannot be obtained, and the reliability of the multilayer ceramic component is lowered. Therefore, by using a glass that has low solubility in the plating solution and that exhibits appropriate fluidity in the firing step, the plating solution resistance of the terminal electrode film after firing is greatly improved and good. Various film density, adhesive strength, and plating properties were found, and various studies were made on the composition of the glass component.

  An object of the present invention is to provide a conductor paste for a laminated ceramic component terminal electrode capable of forming a terminal electrode that is dense, has high adhesive strength with an element body, is excellent in plating solution resistance, and can be used for thinning. There is to do.

In order to solve the above problems, the invention according to claim 1 is a conductor paste for a multilayer ceramic component terminal electrode,
The main component is a conductive powder containing copper, glass powder and vehicle, and the content of each component in the glass powder is 7 to 12% by weight of SiO ₂ , 11 to 15% by weight of Al ₂ O ₃ , and B ₂ O _3. 15 to 28% by weight, BaO 25 to 45% by weight, CaO 5 to 15% by weight, ZnO 7 to 25% by weight, SiO ₂ + B ₂ O ₃ 25 to 35% by weight.

The invention according to claim 2 is the conductor paste for the multilayer ceramic component terminal electrode according to claim 1,
The weight ratio of the content of each component in the glass powder satisfies the following formulas (1) and (2).
0.25 ≦ Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) ≦ 0.35 (1)
0.1 ≦ CaO / (CaO + BaO) ≦ 0.4 (2)

  The glass powder contained in the conductor paste for a laminated ceramic component terminal electrode of the present invention has sufficient acid resistance as a characteristic of the glass itself, and has fluidity that exhibits an appropriate behavior in the firing stage. Therefore, the terminal electrode of the multilayer ceramic component formed using the conductor paste for the multilayer ceramic component terminal electrode of the present invention has few pores and blisters, and is excellent in denseness and adhesion to the element body. Further, even if the terminal electrode is made thin, it exhibits excellent plating solution resistance, and does not cause problems such as a decrease in adhesive strength and solder explosion due to penetration of the plating solution. Further, the present invention provides a highly reliable multilayer ceramic component which does not cause a decrease in solderability due to glass floating and electrode peeling (particularly peeling at a corner).

  Hereinafter, the conductor paste for multilayer ceramic component terminal electrodes according to the present invention (hereinafter referred to as “conductor paste”) will be described in detail. The conductive paste in the present embodiment is mainly composed of conductive powder containing copper, glass powder, and vehicle.

  The conductive powder containing copper used in the present invention may be copper powder, copper alloy powder or mixed powder of these and other conductive metals, and metal oxide, glass, A metal-inorganic composite powder in which an inorganic material such as ceramic is present, a metal-inorganic composite powder in which a metal oxide, glass, ceramic powder, or other metal powder is coated with copper can also be used.

The glass powder used in the present invention, the content of each _component, SiO 2 7 to 12 _{wt%, Al} 2 O 3 _{11~15 wt%, B} 2 O 3 _15~28 wt%, BaO 25 to 45 weight %, CaO 5-15 wt%, ZnO 7-25 wt%, SiO ₂ + B ₂ O ₃ 25-35 wt%.
Moreover, it is preferable to satisfy | fill following formula (1) and (2).
0.25 ≦ Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) ≦ 0.35 (1)
0.1 ≦ CaO / (CaO + BaO) ≦ 0.4 (2)

  Hereinafter, each component contained in the glass powder will be described in detail.

SiO ₂ is a glass-forming oxide and greatly affects acid resistance. When the content of SiO ₂ exceeds 12%, glass floating tends to occur, and the plating property is deteriorated. If it is less than 7.0%, the acid resistance is lowered, and the glass component is easily dissolved when immersed in the plating solution.

B ₂ O _{3 is} also a glass-forming oxide and is a component that improves fluidity. If the content exceeds 28%, the acid resistance tends to decrease. If it is less than 15%, the fluidity is lowered and the film density of the terminal electrode is lowered.

Al ₂ O ₃ is an intermediate oxide and greatly affects acid resistance. If its content exceeds 15%, it tends to devitrify during the cooling process during glass production. Acid resistance falls that it is less than 11%.

  BaO is a glass-modified oxide that stabilizes the glass and improves fluidity. When the content exceeds 45%, the acid resistance decreases. If it is less than 25%, glass floats and the plating property is lowered.

  CaO is also a glass-modified oxide that stabilizes the glass and improves acid resistance. When the content exceeds 15%, the glass transition point rises rapidly. If it is less than 5.0%, the acid resistance decreases.

  ZnO is also a glass-modified oxide, which stabilizes the glass and adjusts the crystallization temperature. When the content exceeds 25%, the acid resistance is remarkably deteriorated. If it is less than 7.0%, the fluidity is lowered and the film density of the terminal electrode is lowered.

The total amount of SiO ₂ and B ₂ O ₃ is a factor that adjusts the fluidity in the firing stage. If it exceeds 35%, the fluidity becomes too high and glass floating tends to occur, and the terminal electrode tends to have poor plating properties and blisters. If it is less than 25%, the fluidity is lowered and the film density of the terminal electrode is lowered.

The value represented by Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) is one of the important factors affecting the acid resistance. If it is less than 0.25, the acid resistance decreases, and it becomes impossible to suppress the dissolution of the glass component during immersion of the plating solution. If it exceeds 0.35, the fluidity is lowered and the film density of the terminal electrode is lowered.

  In the present invention, the value represented by CaO / (CaO + BaO) is also an important factor that affects acid resistance. If it is less than 0.1, the acid resistance is lowered, and the glass component is dissolved when the plating solution is immersed. If it exceeds 0.4, the wettability between the glass component and the element body deteriorates, so that electrode peeling tends to occur at the corners of the multilayer ceramic component.

  In addition, the glass powder may contain a small amount of other oxides such as alkali metal, strontium, manganese, copper, tin, iron, or cobalt within a range not affecting the properties.

  Although the magnitude | size of glass powder is not specifically limited, Usually, a thing with an average particle diameter of 0.1-10 micrometers is used. In addition, when glass floating tends to occur on the surface of the terminal electrode, it can be prevented by adjusting the particle size of the glass powder. Therefore, the glass powder of the present invention preferably has an average particle size of 0.5 to 5 μm, more preferably 1 to 4 μm.

  Such glass powder may be obtained by any method such as a melt quench method, a sol-gel method, or an atomization method. For example, it can be produced by an ordinary method in which raw material compounds of each component are mixed, melted, quenched, and pulverized. In this case, it is preferable to perform coarse pulverization using a stamp mill or the like and then wet pulverization using a ball mill or a planetary ball mill or dry pulverization using a planetary ball mill or jet mill to obtain a predetermined particle size. In addition to this, it is also possible to produce by spraying and calcination method, spray pyrolysis method, or calcination of raw powder containing component elements, and then pyrolyzing and vitrifying the material powder dispersed in the gas phase can do. These methods are preferable because a fine glass particle having a uniform particle size can be obtained and it is not necessary to perform a separate pulverization treatment.

  The vehicle used in the present invention is not particularly limited, and an organic binder, a solvent and the like which are usually used as a vehicle for silver paste are appropriately selected and blended. For example, as organic binders, celluloses, acrylic resins, phenol resins, alkyd resins, rosin esters, etc., and as solvents, alcohol-based, ether-based, ester-based, hydrocarbon-based organic solvents, water, and mixed solvents thereof Is mentioned. In addition, plasticizers that are usually added, dispersants such as higher fatty acids and fatty acid esters, interfacial lubricants, and the like can be appropriately blended. The blending amount of the vehicle is not particularly limited, and is an appropriate amount capable of retaining the inorganic component in the paste, and is appropriately adjusted according to the use and application method.

  In addition to the above-mentioned components, the conductive paste of the present invention usually contains inorganic components, for example, metal oxides such as alumina, silica, copper oxide, manganese oxide, barium titanate, and titanium oxide, and the same quality as the derivative layer. The ceramic powder, montmorillonite and the like can be appropriately added depending on the purpose.

  Hereinafter, the present invention will be specifically described based on examples.

First, the glass powder which concerns on Examples 1-5 was prepared with the following procedures.
Each component was weighed so as to have an oxide composition as shown in Table 1, mixed well, then put into a platinum crucible, melted in the atmosphere at 1400 ° C. for 60 minutes, then allowed to flow out onto graphite and air-cooled. The glass obtained in this manner was pulverized by a stamp mill and then wet pulverized using a planetary ball mill to obtain a glass powder having an average particle size of 3.3 μm.
Similarly, each component was weighed with an oxide composition as shown in Table 1, and glass powders according to Comparative Examples 1 to 6 were prepared.

  The glass transition point Tg which shows the thermal characteristic of each obtained glass powder was measured using the differential thermal analyzer. The measurement results are shown in Table 1.

In addition, the acid resistance of each glass powder, which is one of the indicators of the plating solution resistance of the terminal electrode after firing, was examined as follows.
A paste in which 10 parts by weight of glass powder was dispersed in 3 parts by weight of an organic vehicle in which an acrylic resin binder was dissolved in benzyl alcohol was prepared, printed on a flat plate made by sintering barium titanate, and dried. Thereafter, it was baked at 800 ° C. in a nitrogen atmosphere having an oxygen concentration of about 5 ppm to form a glass film having a thickness of about 20 μm. Thereafter, the substrate on which the glass film was formed was immersed in an acidic organic tin plating bath having a pH of about 4 for 2 hours, and the residual ratio (% by weight) of the glass film was measured from the change in weight before and after the immersion. The above were evaluated as ◯, 10-30% as △, and less than 10% as x. The measurement results are shown in Table 1.

Then, the conductor paste was produced in the following procedures, and the terminal electrode according to each example and comparative example was formed.
An electrode paste was prepared by kneading 100 parts by weight of copper powder (average particle size 4 μm, flakes) and 10 parts by weight of glass powder together with 40 parts by weight of a vehicle in which an acrylic resin binder was dissolved in terpineol, using a roll mill. The obtained electrode paste is applied to the terminal surface of a barium titanate-based multilayer ceramic capacitor body having an outer diameter of 2.0 mm × 1.2 mm × 1.2 mm having a nickel internal electrode so that the fired film thickness is 40 μm. After applying by dipping method and drying, it was baked at 860 ° C. in a nitrogen atmosphere having an oxygen concentration of 5 ppm to form a terminal electrode.

  Next, a nickel plating film and a tin plating film were sequentially formed on the terminal electrode by electroplating, and the film density, blister, plating property, and electrode peeling were evaluated in the following manner.

As for the film density, the cross section (surface perpendicular to the terminal surface) of each terminal electrode is observed with a scanning electron microscope, and the porosity is less than 0.6% ○, 0.6% or more and less than 3% Δ3 % Or more was evaluated as x.
The blister was evaluated as ◯ when no blister was detected on the surface of the terminal electrode, Δ when the blister generation rate was less than 30%, and × when 30% or more.
The plating property was evaluated as ○ when the continuous plating film was formed on the surface of the terminal electrode, and × when it was discontinuous. In addition, when there is glass floating, the plating film tends to be discontinuous.
In the electrode peeling, the case where the terminal electrode was completely adhered to the corner portion of the element body was marked with ◯, and the case where the terminal electrode was peeled was marked with x.

As can be seen from Table 1, regarding Comparative Example 1, the contents of SiO ₂ , Al ₂ O ₃ and CaO are small, and SiO ₂ + B ₂ O ₃ , Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) The values of CaO / (CaO + BaO) are also small, and the acid resistance is remarkably lowered. Respect Comparative Example _2, the content of B 2 _{O 3} is _large, the value of SiO _{2 +} B 2 _{O 3} is _large, the value of _{Al 2 O 3 / (Al 2} O 3 + SiO 2 + B 2 O 3) is decreased In addition, a large number of blisters are generated and the plating property is remarkably lowered. Regarding Comparative Example 3, the value of SiO ₂ + B ₂ O ₃ is small, and voids are generated in the terminal electrode after firing, resulting in a decrease in film density. Regarding Comparative Example 4, the contents of Al ₂ O ₃ and BaO are small, the values of SiO ₂ + B ₂ O ₃ and CaO / (CaO + BaO) are large, and Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O). The value of ₃ ) is small, the acid resistance is lowered, and electrode peeling occurs. With respect to Comparative Example 5, the content of Al ₂ O ₃ is small, the value of Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) is also small, and a large number of blisters are generated and the plating property is increased. Is significantly reduced. Regarding Comparative Example 6, the content of Al ₂ O ₃ and BaO is small, and the values of SiO ₂ + B ₂ O ₃ and CaO / (CaO + BaO) are increased, while Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B). The value of ₂ O ₃ ) is small, and the plating property is remarkably lowered.

On the other hand, in the glass powder of the composition of the present invention, the content of each component is 7 to 12% by weight of SiO _2, 11 to 15% by weight of Al ₂ O _3, 15 to 28% by weight of B ₂ O _{3, and} 25 to 45% by weight of BaO. %, CaO 5 to 15 wt%, ZnO 7 to 25 wt%, SiO ₂ + B ₂ O ₃ 25 to 35 wt%, and further satisfy the following formulas (1) and (2).
0.25 ≦ Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) ≦ 0.35 (1)
0.1 ≦ CaO / (CaO + BaO) ≦ 0.4 (2)
Therefore, it has excellent acid resistance, and by using the glass powder, it is possible to form a terminal electrode that is dense, has high adhesion strength with the element body, has excellent plating solution resistance, and can be used for thinning. The

Claims (2)

The main component is a conductive powder containing copper, glass powder and vehicle, and the content of each component in the glass powder is 7 to 12% by weight of SiO ₂ , 11 to 15% by weight of Al ₂ O ₃ , and B ₂ O _3. 15 to 28% by weight, BaO 25 to 45% by weight, CaO 5 to 15% by weight, ZnO 7 to 25% by weight, SiO ₂ + B ₂ O ₃ 25 to 35% by weight Conductor paste for electrodes. 2. The conductor paste for a multilayer ceramic component terminal electrode according to claim 1, wherein the weight ratio of the content of each component in the glass powder satisfies the following formulas (1) and (2).
0.25 ≦ Al ₂ O ₃ / (Al ₂ O ₃ + SiO ₂ + B ₂ O ₃ ) ≦ 0.35 (1)
0.1 ≦ CaO / (CaO + BaO) ≦ 0.4 (2)