JP5454414B2 - Thick film conductor forming composition, thick film conductor formed using the composition, and chip resistor using the thick film conductor - Google Patents

Description

  The present invention relates to a composition for forming a thick film conductor that does not contain lead, and more particularly to a composition for forming a thick film conductor used as an upper surface electrode of a chip resistor. The present invention also relates to a thick film conductor formed using this composition, and further to a chip resistor in which this thick film conductor is applied to at least the upper surface electrode.

  When forming a thick film conductor using thick film technology, a conductive powder with a high conductivity is usually dispersed in an organic vehicle together with an oxide powder such as glass powder to form a paste-like thick film conductor. The composition for forming a thick film conductor is applied to a ceramic substrate such as an alumina substrate in a predetermined shape using a screen printing method or other application means, and is fired at 500 ° C. to 900 ° C. Things have been done.

  Among the materials constituting the thick film conductor forming composition, the conductive powder is made of at least one metal selected from Au, Ag, Pd, and Pt having high conductivity, and has an average particle size of 10 μm or less. Metal powder is used. Among these metals, Ag powder and Pd powder are generally used because they are inexpensive, but Ag powder is used as the main material of conductive powder from the viewpoint of better conductivity. .

  On the other hand, as the glass powder, lead borosilicate or lead aluminoborosilicate, which has been easy to control the softening point and has high chemical durability, has been used. However, from the viewpoint of preventing recent environmental pollution, a composition for forming a thick film conductor that does not contain lead is desired, and a study of lead-free glass powder is being conducted.

  A thick film conductor formed using such a composition for forming a thick film conductor is applied as an electrode of an electronic component such as a chip resistor, a resistor network, or a hybrid IC used in the electronics industry. Among these, as schematically shown in FIG. 1, the chip resistor is made of an alumina substrate, an internal electrode composed of a top electrode, a side electrode and a back electrode formed by a thick film conductor, and a ruthenium oxide thick film. In order to improve solderability on the exposed electrode surface, an intermediate electrode made of Ni plating and Sn—Pb solder plating or Sn substituted for this are provided. External electrodes made of lead-free solder plating of an alloy are further formed by electrolytic plating.

  At present, Ag, which is mainly used as a conductor powder, is a material that is particularly vulnerable to sulfuration. In the chip resistor, the electrode made of an Ag-based thick film conductor is protected by coating with Ni plating or solder plating, and the problem of Ag sulfidation does not occur in normal use. However, when the chip resistor is used under severe conditions such as thermal aging or thermal cycle, a gap is generated at the interface between the protective film made of insulating glass and the solder plating and Ni plating due to stress, or The internal electrode is exposed due to the displacement of the protective film due to a failure in the manufacturing process of the resistor, etc., and the sulfurization of Ag due to sulfur gas in the air occurs, and the electrode is short-circuited. May end up. In particular, in areas where the concentration of sulfur gas in the air is high, such as hot springs where volcanic gas is generated, problems such as short-circuiting of electrodes due to Ag sulfide are likely to occur.

  Also, in the manufacturing process or the mounting process, soldering is performed on electronic components such as chip resistors. If the internal electrodes are exposed at that time, a metal material such as Ag diffuses into the solder. In addition, the conductor portion disappears and solder breakage that breaks may occur. Solder is also being replaced by Sn-Pb eutectic solder such as 63Sn / 37Pb with a lead-free and high Sn content solder, and since the melting point of this Sn-based alloy solder is high, the soldering temperature Tend to be higher. With such a change in solder composition and an increase in soldering temperature, there is also a problem that solder erosion is more likely to occur than before.

  As a method of coping with such a short circuit due to sulfidation or solder erosion of an electrode made of an Ag-based thick film conductor, a method of adding Pd to Ag as a conductor powder is generally performed. For example, Japanese Patent Application Laid-Open No. 2004-250308 uses Bi-based glass powder having excellent acid resistance and prevents addition of 0.3 to 2% by weight of Pd powder in order to prevent sulfuration due to sulfur gas of Ag. Is disclosed. However, for sulfurization, only the discoloration of the Ag-based electrode is observed with the naked eye, and no quantitative discussion has been made on the effect thereof.

  However, the use of Pd powder itself has problems such as an increase in the specific resistance value of the electrode, a decrease in contact strength with the substrate due to a decrease in the film strength of the electrode, and an increase in cost. In JP-A-7-335402, Ag-coated Pd powder is used as an electrode material to improve the denseness of the fired film and to prevent sulfuration. However, the use of such a powder causes a further increase in cost, which is problematic in practical use.

  It has also been studied to prevent electrode sulfidation by devising the structure of the chip resistor. For example, in the technique disclosed in Japanese Patent Laid-Open No. 2002-64003, an Ag-based thick film conductor having a Pd content of 5.0% or more is formed as a protective layer on the upper surface electrode where a gap is likely to occur. Moreover, in the technique of Unexamined-Japanese-Patent No. 2003-224001, the ruthenium resistor layer is formed as a similar protective layer. However, these add a new structure and cause problems in terms of downsizing and cost of the chip resistor.

  Further, as taught by Japanese Patent Application Laid-Open Nos. 2004-221006 and 2002-324428, it is conceivable to provide a protective layer formed of a conductive carbon paste. However, the carbon protective layer has a problem such as lowering the conductivity of the electrode itself, and it is required to achieve sulfur resistance without providing such a carbon protective layer. The present situation is that effective sulfidation resistance is not achieved in an Ag-based thick film conductor by forming a protective layer with a carbon material or simply adding a carbon material.

  On the other hand, as a countermeasure against solder erosion, a method of adding Pd is generally used for Ag-based electrode materials as described in JP-A No. 2004-327356. However, as a countermeasure against solder erosion, it is necessary to add Pd to about 2 to 20 parts by mass, and as described above, various problems such as an increase in the specific resistance value of the electrode occur. Further, when these additive materials are small, additive materials such as Au, Pd, and Pt may be eroded when soldering to the thick film conductor.

As countermeasures against such solder erosion, as described in JP-A-6-223616, as a thick film conductor forming composition, PbO—SiO ₂ —CaO—Al ₂ O ₃ glass powder and A needle called anorthite (CaAl ₂ Si ₂ O ₈ ) at the time of firing the composition using a dispersion of Al ₂ O ₃ powder, SiO ₂ powder and conductive powder in an organic vehicle There is a method of precipitating a crystalline phase inside a thick film conductor.

  However, in this thick film conductor forming composition, glass powder containing Pb is used, and the presence of this Pb is essential for the formation of anorthite, and the generation of anorthite in the lead-free thick film conductor is immediately performed. It is not a suggestion.

In contrast, Japanese Unexamined 7-97269 and JP-open 2 001-114556 discloses a _{SiO 2 -B 2 O 3 -Al 2} O 3 -CaO based glass powder, the Al ₂ O ₃ powder It is disclosed that anorthite is deposited on a thick film conductor by firing the thick film conductor forming composition. However, in these cases, in order to precipitate a sufficiently large anorthite, the crystallization temperature is high (the softening temperature of the glass is high), so a high temperature of 900 ° C. or higher is required. When the composition for forming a thick film conductor is fired at a temperature of 900 ° C. or higher, the thick film conductor becomes oversintered or the melting point of Ag is low, so the electrode made of the Ag-based thick film conductor becomes an island shape. However, there is a problem that it is difficult to form a homogeneous electrode.

In the Japanese Patent Application Laid-Open No. 2006-228572, the present inventors use a SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder as a glass-based powder, whereby the glass softening temperature. And thus anorthite is uniformly deposited inside the thick film even by firing at less than 900 ° C. By this method, a marked improvement in solder erosion resistance has been recognized. However, as a result of further evaluation and examination by the present inventors, chip resistance was obtained using a thick film conductor forming composition using Ag powder as the main conductive material. When the upper surface electrode of the vessel is formed, and when the chip resistor is used in a special environment with a high concentration of sulfurous gas as described above, it is pointed out that the upper surface electrode may be sulfided over time, Further improvement of the sulfidation resistance is required.

JP 2004-250308 A JP 7-335402 A JP 2003-224001 A JP 2004-221006 A JP 2002-324428 A JP 2004-327356 A JP-A-6-223616 JP-A-7-97269 JP 2001-114556 A JP 2006-228572 A

   An object of the present invention is to provide a lead-free composition for forming a thick film conductor that is excellent in both resistance to sulfidation and resistance to solder corrosion at low cost.

The composition for forming a thick film conductor of the present invention is a composition for forming a thick film conductor comprising a conductive powder, an oxide powder, an additive, and an organic vehicle, and the conductive powder includes at least an Ag powder. And the oxide powder includes SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder and Al ₂ O ₃ powder, and the addition Carbon powder is added as a product.

1 to 10 parts by mass of the carbon powder, 0.1 to 15 parts by mass of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder with respect to 100 parts by mass of the conductive powder, The Al ₂ O ₃ powder is preferably 0.1 to 8 parts by mass.

The composition ratio of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O glass powder is SiO ₂ : 20 to 60% by mass, B ₂ O ₃ : 2 to 25% by mass, Al ₂ O ₃ : 2 to 25% by mass, CaO: 20 to 50% by mass, and Li ₂ O: 0.5 to 6% by mass are preferable.

  In the present invention, 0.1 to 5 parts by mass of at least one selected from Au, Pd and Pt as a conductive powder may be further added to 100 parts by mass of the Ag powder.

The thick film conductor of the present invention is obtained by applying the above thick film conductor forming composition to a ceramic substrate and then firing at a temperature of 500 ° C. or more and less than 900 ° C., and anorthite is uniformly formed inside. It is precipitated, and the Li ₂ O is immobilized on anorthite.

  Furthermore, the chip resistor of the present invention is formed on the ceramic substrate, the internal electrode formed on the ceramic substrate, and composed of the top electrode, the side electrode, and the back electrode, and on the ceramic substrate and the top electrode. A chip resistor comprising a resistance film, an insulating glass protective film covering the resistance film, an intermediate electrode made of Ni plating covering the internal electrode, and an external electrode made of solder plating, wherein at least the upper surface electrode is a main resistor It is characterized by comprising only the thick film conductor of the invention.

  The composition for forming a thick film conductor of the present invention provides a lead-free composition for forming a thick film conductor that not only prevents solder erosion but also has excellent sulfidation resistance only by devising the material. be able to.

  By using this composition for forming a thick film conductor, when used for an electrode of an electronic component, particularly a chip resistor, it is possible to prevent sulfuration and solder erosion of Ag which is a conductive material constituting the electrode. Further, since there is no need for a special structural device or use of a special material, there is an effect that it is possible to efficiently and inexpensively provide such an electronic component with less disconnection failure due to sulfidation or solder erosion.

FIG. 1 is a schematic diagram of a chip resistor to which the present invention is applied.

The composition for forming a thick film conductor of the present invention comprises SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder and Al ₂ O ₃ powder, and has a conductive property. By reacting the glass powder and the Al ₂ O ₃ powder during paste firing, a thick film conductor in which anorthite is uniformly deposited inside the thick film conductor can be obtained. When such a thick film conductor is used, a small amount of the noble metal in the thick film conductor is dissolved into the solder, so that the anorthite is exposed in a spine shape on the surface of the thick film conductor. Anorthite is a needle-like crystal, and when this is exposed in a spine shape on the surface of the thick film conductor, the solder does not reach the noble metal due to the surface tension, and the solder erosion does not proceed.

In the present invention, the Al ₂ O ₃ powder is included as the oxide powder in addition to the above glass powder in order to achieve uniform precipitation inside the thick film conductor of anorthite. That is, when Al ₂ O ₃ powder is not mixed with the glass powder, a lot of anorthite is deposited near the interface between the resulting thick film conductor and the ceramic substrate. I can't get it. Therefore, in order to prevent the solder from reaching the noble metal due to the surface tension, the anorthite needs to be uniformly deposited inside the thick film conductor. Further, the length of the anorthite barb exposed by soldering is 1 μm or more, preferably 3 μm or more. In a fine crystal phase having a length of less than 1 μm, the anorthite moves from the thick film conductor into the solder, and the effect of suppressing solder erosion cannot be sufficiently obtained.

Anorthite can also be deposited by firing a mixture of SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO glass powder and Al ₂ O ₃ powder. In this case, however, a high temperature of 900 ° C. or higher is necessary to deposit a sufficiently large anorthite. On the other hand, in the present invention, since Li ₂ O is contained in the glass powder, anorthite can be precipitated even at a lower temperature.

In the present invention, with respect to the conductive powder 100 parts by weight, the Al ₂ O ₃ powder 0.1 to 8 parts by weight, but is preferably 0.5-3 parts by weight. When the Al ₂ O ₃ powder used as the oxide powder is less than 0.1 parts by mass with respect to 100 parts by mass of the conductive powder, the precipitation of anorthite is small and solder erosion is likely to occur. Anorthite is a complex oxide of Si, Al, and Ca. Anorthite does not precipitate unless Al is sufficiently supplied. In addition, the precipitation of anorthite is necessary for exerting sulfidation resistance. That is, even if carbon powder is simply added to the glass powder, the sulfide resistance is not sufficiently exhibited, and the combination of the addition of the carbon powder and the precipitation of anorthite is sufficient to exhibit the sulfide resistance for the first time. Become. On the other hand, when the added amount of Al ₂ O ₃ powder exceeds 8 parts by mass, not only the contact resistance increases, but also the adhesive strength with the ceramic substrate decreases.

The average particle diameter of the Al ₂ O ₃ powder used as the oxide powder is 3 μm or less, preferably 0.5 to 2 μm. When the average particle size of the Al ₂ O ₃ powder exceeds 3 μm, not only is the anorthite difficult to deposit uniformly in the thick film conductor, but also the surface of the thick film conductor becomes rough and the characteristics of the electronic component are measured. The contact resistance with the probe may increase. The shape of the Al ₂ O ₃ powder is not particularly limited, but is preferably spherical or powdery from the viewpoint of uniform mixing with the glass powder and uniform precipitation of anorthite.

In the present invention, the composition ratio of _{SiO 2 -B 2 O 3 -Al 2} O 3 -CaO-Li 2 O glass powder used as the oxide _powder, SiO 2: 20 to 60 wt%, B ₂ O ₃ : 2 to 25 wt%, Al ₂ O _3: 2 to 25 wt%, CaO: 20 to 50 wt%, and Li ₂ O: is preferably 0.5 to 6 wt%.

If the SiO ₂ content is less than 20% by mass in the composition of the glass powder, Si is not sufficiently supplied, and anorthite is difficult to precipitate, and solder erosion and sulfidation may not be prevented. In addition, the weather resistance, water resistance and acid resistance of the glass in the thick film conductor tend to decrease. On the other hand, when SiO ₂ exceeds 60% by mass, the softening temperature of the glass becomes too high, and the temperature at which anorthite precipitates tends to increase.

When B ₂ O ₃ is less than 2% by mass, the softening temperature of the glass tends to be too high. In addition, the glass of the thick film conductor tends to become brittle. On the other hand, if the B ₂ O ₃ content exceeds 25% by mass, the glass is likely to undergo phase separation, and the weather resistance, water resistance, and acid resistance of the glass in the thick film conductor may be reduced.

In the composition of the glass powder, when Al ₂ O ₃ is less than 2% by mass, anorthite is similarly hardly precipitated, and the glass in the thick film conductor is easily phase-separated. On the other hand, if Al ₂ O ₃ is more than 25% by mass, the softening temperature of the glass becomes too high, and the temperature at which anorthite precipitates may become too high.

  When CaO is less than 20% by mass, the supply of Ca becomes insufficient, and anorthite becomes difficult to precipitate. On the other hand, when CaO exceeds 50 mass%, it will become difficult to vitrify.

Li ₂ O has a function of lowering the softening temperature of the glass. When the content of Li ₂ O is increased, anorthite crystals can be grown correspondingly. Therefore, in the composition of the glass powder, when Li ₂ O is less than 0.1% by mass, anorthite is difficult to precipitate at a low temperature, and the size of the precipitated anorthite tends to be small. On the other hand, if the Li ₂ O content exceeds 10% by mass, the weather resistance, water resistance and acid resistance of the glass may be lowered. Incidentally, Li ₂ O is, if the range of 4-6 wt%, even if a small amount of glass powder contained in the thick film conductor composition for forming erosion soldering of the resulting thick film conductor The adhesive strength can be improved without impairing the properties.

In the composition ratio of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder of the present invention, Li ₂ O is almost taken into the anorthite precipitated during paste firing and immobilized. Is done. Therefore, even if there is a potential difference between the formed electrodes, Li ions do not migrate.

The glass powder used in the present invention is of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O system, but it can also contain other components in its composition, softening point, acid resistance Depending on the above, components such as ZnO, BaO, TiO ₂ , ZrO ₂ , Bi ₂ O ₃ , CuO, and MnO ₂ can be appropriately selected and contained.

In the present invention, the average particle size of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O glass powder is 10 μm or less, preferably 3 to 7 μm. When the average particle size is 10 μm or more, the softening of the glass powder is delayed, and the adhesive strength between the electrode film and the substrate tends to decrease, which is not preferable.

In the present invention, the addition amount of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O glass powder is 0.1 to 15 parts by mass, preferably 100 parts by mass of the conductive powder. 3 to 8 parts by mass. When the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder is less than 0.1 part by mass with respect to 100 parts by mass of the conductive powder, the adhesive strength with the ceramic substrate decreases. End up. Moreover, the material for anorthite precipitation will not be supplied sufficiently. On the other hand, when the amount exceeds 15 parts by mass, not only the resistance value of the thick film conductor becomes high, but also glass floats on the surface of the thick film conductor, plating property, solder wettability, and contact resistance with the probe for characteristic evaluation. However, there is a risk of deterioration.

  As the conductive powder, at least one kind of noble metal powder selected from Au, Ag, Pd and Pt is used. Since the present invention is intended to prevent the sulfurization of Ag, the object of the present invention is a conductive powder containing at least Ag. However, Ag may further include at least one kind of noble metal powder selected from Au, Pd and Pt. The addition of these noble metals has an effect of improving Ag solder resistance and sulfidation resistance as a conductive material. However, although these noble metals are highly resistant to sulfuration, they are expensive noble metals. Therefore, in the present invention, the composition for forming a thick film conductor can be provided at a low cost by reducing the content of such expensive metals. The purpose is to supply. Therefore, in the present invention, only low-cost Ag may be used as the conductive powder, and when it is necessary to further improve the sulfidation resistance, these noble metals, preferably Pd or Pt, particularly Pd from the cost viewpoint. You may add to 0.1-5 mass parts with respect to 100 mass parts of Ag.

  The reason why the sulfurization of Ag is suppressed by the addition of Pd or the like is that the sulfurization of Ag is caused by the diffusion of S from the outside of Ag. If Ag and Pd are alloyed, Ag is alloyed. It is considered that the sulfidation rate decreases as the sulfidation occurs because the alloy portion gradually diffuses from the surface to the sulfide surface and the alloy portion immediately below the sulfide changes to a noble metal rich phase such as Pd.

  However, in a thick film conductor that is a mixture of a conductive metal component and a glass component, the degree of sulfidation is also influenced by the composition of the thick film conductor, for example, the composition and amount of glass powder added. It is well known that research is being conducted every day to realize low cost and low Pd by study. That is, the present invention has a remarkable effect in that it can provide a composition for forming a thick film conductor that can exhibit sulfidation resistance even when it is composed only of Ag as the conductive powder and Pd is not added. I have it.

  The average particle size of the conductive powder is desirably 10 μm or less from the viewpoint of sinterability. About the shape of electrically conductive powder, arbitrary shapes, such as a granular form and flake shape, can be employ | adopted and can be mixed and used. Among them, the powder diameter of the powdered conductive powder is preferably 0.1 to 2 μm from the viewpoint of sinterability.

The present invention is characterized in that the carbon powder is further added in an amount of 1 to 10 parts by mass, preferably 3 to 7 parts by mass with respect to 100 parts by mass of the conductive powder. Since carbon powder has electrical conductivity, it is a material used as conductive powder in the field of conductive paste in a broad sense. However, in the composition for forming a thick film conductor using the noble metal powder, the mere addition as the conductive material decreases the electrode performance including the original conductor performance or adhesive strength of the obtained thick film conductor, Usually it is not added. In addition, when carbon powder is simply added as a material for a thick film conductor forming composition in which Ag is the main material of the conductor powder but no anosite is formed, sulfuration of Ag is suitably prevented. It is not possible.

According to the inventor's trial and error and experiment, a thick film conductor-forming composition comprising a conductive powder, an oxide powder, and an organic vehicle, the conductive powder containing at least an Ag powder, In the composition for forming a thick film conductor, which contains SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O glass powder and Al ₂ O ₃ powder as an oxide powder, an additive As a result, it was confirmed that the addition of carbon powder further improves the sulfidation resistance of the resulting thick film conductor. After confirming this effect, observation of the cross-sectional structure of the electrode film after firing of the composition for forming a thick film conductor to which carbon powder has been added reveals the following findings.

  That is, the added carbon powder affects the melting behavior of the glass powder in the composition by its action, and when the glass melts and the viscosity decreases, the glass moves to the interface with the ceramic substrate. It suppresses it. As a result, in the cross-sectional observation of the electrode film after firing, acicular anorthite crystals and amorphous glass components are uniformly deposited in a network shape in the matrix of Ag, which is a conductor. It has a characteristic film structure in which oxides are combined. The reason for such a structure is not clear, but when this film structure is exposed to a sulfurizing atmosphere in an electrode film containing Ag, sulfur diffusion occurs in the formation process of silver sulfide that proceeds by diffusion of sulfur from the Ag surface. It is thought that the speed is suppressed. Note that carbon is decomposed as CO by bonding with oxygen during firing, and thus most of the carbon is considered to have disappeared in the film structure after firing.

  The type, shape, and size of the carbon powder used in the present invention are not particularly limited, and general products that are commercially available as carbon ink applications can be used. The average particle size of the carbon powder in such products is often in the range of 0.01 to 0.5 μm. Since it is necessary to disperse uniformly in the paste, it is preferable to use a powder of around 0.1 μm.

  Moreover, regarding the addition amount of carbon powder, it is 1-10 mass parts with respect to 100 mass parts of conductive powder, Preferably it is 3-7 mass parts. When the amount is less than 1 part by mass, the resulting thick film conductor cannot be sufficiently improved in sulfidation resistance. Addition of 10 parts by mass or more is not preferable because the denseness of the fired film is lowered and the adhesive strength with the ceramic substrate is lowered.

  As the organic vehicle that is another material for forming the thick film conductor, a material obtained by dissolving ethyl cellulose, methacrylate, or the like in a solvent such as terpineol, butyl carbitol, or the like can be used.

In the present invention, in addition to the above material powder, various powders conventionally used for the purpose of improving the adhesive strength and solder wettability of the thick film conductor, such as Bi ₂ O ₃ , SiO ₂ , CuO, ZnO, etc. It is possible to add oxide powder such as MnO ₂ .

The thick film conductor of the present invention is fired at a temperature of 500 ° C. or higher and lower than 900 ° C., preferably 820 ° C. to 870 ° C., after applying the above-described composition for forming a thick film conductor of the present invention to a ceramic substrate. The anorthite is uniformly deposited inside, and the Li ₂ O is immobilized on the anorthite.

  The thick film conductor of the present invention is suitably applied as an electrode for electronic components such as resistor networks and hybrid ICs in addition to chip resistors. In particular, the present invention relates to a ceramic substrate, an internal electrode formed on the ceramic substrate, and comprising a top electrode, a side electrode, and a back electrode, a resistance film formed on the ceramic substrate and the top electrode, The present invention is suitably applied to a chip resistor including an insulating glass protective film covering a resistance film, an intermediate electrode made of Ni plating covering the internal electrode, and an external electrode made of solder plating. That is, such a chip resistor may be used in a special environment with a high sulfur concentration, such as a sulfur atmosphere, but in the chip resistor of the present invention, at least the top electrode of the internal electrodes has the thickness of the present invention. It is composed only of membrane conductors, and there is no need to adopt other anti-sulfurization structures, and there is no need to use special conductor powder materials. In such special environments, electrode sulfidation is effectively prevented. The

  An alumina substrate, particularly a high-purity alumina substrate, is used as a ceramic substrate on which a thick film conductor in an electronic component such as a chip resistor is formed, but a zirconia substrate or the like can also be suitably used. . Other constituent elements can be prepared using known materials that have been conventionally known, and thus detailed description thereof is omitted here.

(Composition of glass powder)
Table 1 shows the composition ratio (mass%) of the six types of glass powder. Among these, glass powders A, B, C, and F correspond to the composition range of the present invention. On the other hand, the glass powder D does not contain Li ₂ O, and the glass powder E does not contain CaO, which are outside the composition range of the present invention.

(Preparation of thick film conductor forming composition)
For a conductive powder composed of granular Ag powder having an average particle diameter of 1.5 μm and granular Pd powder having an average particle diameter of 0.1 μm, a glass powder having an average particle diameter of 3 μm and an average particle diameter of the composition shown in Table 1 Paste by mixing 0.5 μm Al ₂ O ₃ powder and carbon powder having an average particle size of 0.1 μm with an organic vehicle obtained by dissolving ethyl cellulose resin in terpineol solution and kneading with a three-roll mill. A thick film conductor forming composition was prepared. The total amount of the conductive powder composed of the Ag powder and the Pd powder is 100 parts by mass, the organic vehicle is 25 parts by mass with respect to 100 parts by mass of the conductive powder, and other materials are with respect to 100 parts by mass of the conductive powder. The mass parts are shown in Table 2.

  The produced composition for forming a thick film conductor was screen-printed on a 96 mass% alumina substrate and dried at 150 ° C. The dried substrate was baked in a belt furnace for 9 minutes at a peak temperature of 850 ° C. for a total of 30 minutes to form a thick film conductor film having a predetermined pattern.

  The film thickness of the obtained thick film conductor was evaluated by measuring a 2.0 mm × 2.0 mm pad using a stylus type film thickness meter.

  The area resistance value was evaluated by measuring the resistance value of a conductor pattern having a width of 0.5 mm and a length of 50 mm with a digital multimeter, and converting the obtained value into an area resistance value.

  Evaluation of solder erosion resistance was performed as follows. First, in a lead-free solder bath having a composition of 96.5 mass% Sn-3 mass% Ag-0.5 mass% Cu maintained at 270 ° C. using a fired thick film conductor having a width of 0.5 mm and a length of 50 mm. Then, after dipping for 10 seconds, this operation was repeated with one operation for measuring the resistance value. Confirm that the solder erosion occurred when the measured resistance value was 1 kΩ or more, and measure the number of repetitions until the solder erosion occurred, that is, until the measured resistance value became 1 kΩ or more. Evaluation of solder erosion resistance was made. The case where the number of repetitions exceeded 12 was judged as good (◯), and the case where it was less than that was judged as bad (x).

  Further, the evaluation of sulfidation resistance was performed as follows. In order to obtain a sulfur atmosphere, a commercially available oil for machine cutting (containing sulfur) is maintained at 80 ° C., and a fired electrode substrate is immersed in this oil and allowed to stand to promote sulfidation. It was. The concentrations of sulfur and chlorine in the machine cutting oil used for the evaluation were 3000 ppm by mass of total sulfur and 23.2% by mass of total chlorine (by ion chromatography).

  Similar to the evaluation of solder erosion resistance, an initial sheet resistance value was measured using a fired thick film conductor having a width of 0.5 mm and a length of 50 mm. The above-mentioned machine cutting oil was kept at 80 ° C., and the thick film conductor fired substrate was immersed in this oil with the electrode exposed, the substrate was taken out every 30 minutes, and the sheet resistance value was measured. . Sulfurization is caused by sulfur in the cutting oil, and the electrode turns black from silver, so the state of sulfidation can be confirmed visually. As a method for determining sulfidation resistance, the time required for the sheet resistance value to become 1 Ω / □ or more after immersion in the oil is confirmed, and the one having a sheet resistance value of less than 1 Ω / □ after 12 hours of immersion is good ( (Circle)) The thing more than 1 ohm / square was made into the defect (x).

  The evaluation of the adhesive strength was performed by using an Sn-plated copper wire having a diameter of 0.65 mm on a thick film conductor having a pattern of 2.0 mm × 2.0 mm, 96.5 mass% Sn-3 mass% Ag-0.5 mass%. Soldering was performed using lead-free solder having a Cu composition, and was pulled and peeled in the vertical direction, and the tensile force at the time of peeling was measured.

(Examples 1-3, Comparative Examples 1-3)
As shown in Table 2, the ratio (mass ratio) of Ag powder to Pd powder was 99.3: 0.7, the amount of carbon powder added was 4.0 parts by mass with respect to 100 parts by mass of the conductive powder, and Al ₂ Using the addition amount of O ₃ powder and glass powders A, B, C, D, E, the addition amount is in the range of 3.0 to 5.0 parts by mass, and the combination of the materials and the addition amount are changed. A paste-like thick film conductor forming composition was prepared. Table 2 shows the results of the film thickness, sheet resistance value, adhesion strength, solder erosion resistance, and sulfidation resistance of the measured thick film conductor and their evaluation.

  The thick film conductor obtained by using the glass powder A of Example 1 with an addition amount of 5.0 parts by mass should be disconnected with a sheet resistance of 10Ω / □ or less even if immersed in solder 12 times. There was no solder erosion resistance. In addition, with respect to sulfidation resistance, the sheet resistance after immersion in sulfur-containing oil for 12 hours was 1Ω / □ or less, and the sulfidation resistance was also excellent. The adhesive strength was 58N, which was sufficient for use as an electrode for chip resistors.

  Using the glass powder B of Example 2 and using the thick film conductor obtained by adding 4.0 parts by mass, and the glass powder C of Example 3, using 3.0 parts by mass. Similar results and evaluations were obtained for the thick film conductors.

The thick film conductor obtained by using the glass powder D which is outside the composition range of the present invention of Comparative Example 1 and does not contain Li ₂ O and the addition amount thereof is 5.0 parts by mass is immersed in the fourth solder bath. The sheet resistance was 1 kΩ / □ or more, and the solder corrosion resistance was poor. In addition, regarding the sulfidation resistance, the sheet resistance after immersion for 2 hours in the oil was 1Ω / □ or more, and the sulfidation resistance was also inferior.

In the thick film conductor obtained by using the composition using the glass powder not containing Li ₂ O as in Comparative Example 1, the anorthite sufficiently precipitates in the thick film conductor at a firing temperature of less than 900 ° C. Since it does not grow, not only the Ag of the thick film conductor but also Pd is completely eaten by the solder. From this, it is understood that Li ₂ O promotes the precipitation and growth of anorthite. In addition, it is understood that the precipitation of anorthite is necessary for the development of sulfidation resistance.

  Similarly, the thick film conductor obtained by using the glass powder E which is outside the composition range of the present invention of Comparative Example 2 and the addition amount is 5.0 parts by mass is immersed in the solder bath for the second time. Was 1 kΩ / □ or more, and the sheet resistance after immersion for 1.5 hours in the oil was 1Ω / □ or more, which was inferior in both solder erosion resistance and sulfidation resistance.

  Even in the thick film conductor obtained using the composition using the glass powder not containing CaO as in Comparative Example 2, Ca is not supplied, and anorthite does not precipitate in the thick film conductor, so that it is eroded by solder. It is understood that neither the effects of sulfidity nor sulfidation resistance are exhibited.

The glass powder A in the composition range of the present invention of Comparative Example 3 was used and the addition amount was 5.0 parts by mass, but the thick film conductor obtained without adding the Al ₂ O ₃ powder was 2 By the immersion in the solder bath for the second time, the sheet resistance value was 1 kΩ / □ or more, the sheet resistance value after immersion for 8 hours in oil was 1Ω / □ or more, and both the solder corrosion resistance and the sulfidation resistance were inferior.

As in Comparative Example 3, in the thick film conductor obtained by using a composition that does not contain Al ₂ O ₃ powder as the oxide powder material and only consists of glass powder, anorthite is uniformly deposited in the thick film conductor. However, it is understood that it concentrates on the interface between the thick film conductor and the alumina substrate, and neither of the effects of solder erosion resistance and sulfidation resistance is exhibited.

(Examples 4-6, Comparative Example 4)
In Example 4, Example 5, Example 6, and Comparative Example 4, glass powder F that is the composition range of the present invention was used. The glass powder F is intended to further improve the conductor properties in addition to the glass composition within the scope of the present invention. Bi ₂ O ₃ , CuO, and MnO ₂ are added in the amounts shown in Table 2. The addition amount of glass F was set to 6.3 parts by mass, the ratio of Ag and Pd (mass ratio) was 99.3: 0.7, and the addition amount of carbon powder was changed from 0 to 6.0 parts by mass. .

  As a result, in the thick film conductors made using these glass materials, the resistance to solder erosion does not increase even when immersed in a solder bath 12 times, and good results are obtained. It was. Moreover, also about adhesive strength, all exceeded 60N, and it is thought that the addition effect of said additive material appeared.

  However, with respect to sulfidation resistance, in all of Examples 4 to 6, the area resistance value after immersion for 12 hours in oil was less than 1 Ω / □, and the increase in area resistance value was suppressed, but no carbon powder was added. In a comparative example 4, the sheet resistance value was 1 Ω / □ or more after 3.5 hours of oil immersion, and the sulfur resistance was poor.

(Examples 7 and 8)
Examples 7 and 8 are the series of Example 5, and the addition amounts of Al ₂ O ₃ powder are 0.5 parts by mass and 3.0 parts by mass, respectively.

  As a result, regarding the resistance to solder erosion, no increase in the sheet resistance value was observed even when immersed in the solder bath 12 times, and good results were obtained. After 12 hours, the sheet resistance value was less than 1 Ω / □, and good results were obtained. Further, the adhesive strength was also high.

Example 9
Example 9 is also a series of Example 5 in which the conductive powder is composed only of Ag powder without adding Pd powder.

  As a result, regarding the resistance to solder erosion, no increase in the sheet resistance value was observed even when immersed in the solder bath 12 times, and good results were obtained. The sheet resistance value was less than 1Ω / □, and good results were obtained. Further, the adhesive strength was also high.

(Comparative Examples 5-7)
In Comparative Example 5, Comparative Example 6, and Comparative Example 7, 1.0 parts by mass of Al ₂ O ₃ powder was added using glass powder E that does not contain CaO and is outside the composition range of the present invention, and no carbon powder was used. This is a thick film conductor obtained by using the composition to be added, and the effect of Pd addition in this composition was confirmed by changing the ratio of Ag powder to Pd powder in the composition. In both cases, Pd powder that improves solder erosion resistance and sulfidation resistance is added, but there is no precipitation of anorthite and there is no special crystal structure due to the addition effect of anorthite and carbon. The comparative example thick film conductors were inferior in solder erosion resistance.

  Regarding the sulfidation resistance, for Comparative Example 7 in which the addition amount of Pd powder is 7.0 parts by mass with respect to 100 parts by mass of Ag powder, an increase in sheet resistance value 12 hours after oil immersion is suppressed. Although sulfidation resistance was exhibited, the sulfidation resistance was inferior when the Pd content was less than that.

  In Example 9 within the scope of the present invention, the composition of only Ag is obtained and sulfidation resistance is obtained even when no Pd powder is added, and the effect is fully understood by comparison with Comparative Example 5. Further, it is understood from the comparison with the composition having a high content of Pd in Comparative Example 7 that even in the present invention, the equivalent sulfur resistance can be obtained even if the content of Pd is suppressed to 1/10 or less. .

  As described above, by using the composition for forming a thick film conductor according to the present invention, it is possible to realize sulfidation resistance and solder erosion resistance at low cost, and suppress short-circuiting of electrodes due to Ag sulfidation. It is possible to provide a thick film conductor forming composition that can simultaneously achieve both suppression of short-circuiting of electrodes due to solder erosion of noble metal material containing Ag during soldering. Therefore, a chip capable of exhibiting stable performance even when placed in a special environment such as a sulfur atmosphere by using the thick film conductor formed by using the thick film conductor forming composition of the present invention. Since electronic components such as resistors are provided at low cost, it can be said that the present invention greatly contributes to the field of electronic components including chip component manufacturers.

Claims (6)

A composition for forming a thick film conductor comprising a conductive powder, an oxide powder, an additive, and an organic vehicle, wherein the conductive powder includes at least an Ag powder, and the oxide powder includes SiO _2- B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder and Al ₂ O ₃ powder are contained, and carbon powder is added as the additive. A composition for forming a thick film conductor. 1 to 10 parts by mass of the carbon powder, 0.1 to 15 parts by mass of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O-based glass powder with respect to 100 parts by mass of the conductive powder, The composition for forming a thick film conductor according to claim 1, wherein the Al ₂ O ₃ powder is 0.1 to 8 parts by mass. The composition ratio of the SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —CaO—Li ₂ O glass powder is SiO ₂ : 20 to 60% by mass, B ₂ O ₃ : 2 to 25% by mass, Al ₂ O. _3: 2 to 25 wt%, CaO: 20 to 50 wt%, and Li ₂ O: 0.5 to 6% by mass, according to claim 1 or thick film conductor forming composition according to 2.  4. The conductive powder according to claim 1, wherein 0.1 to 5 parts by mass of at least one selected from Au, Pd, and Pt is added to 100 parts by mass of the Ag powder. A composition for forming a thick film conductor. The thick film conductor-forming composition according to any one of claims 1 to 4 is applied to a ceramic substrate, and then fired at a temperature of 500 ° C or higher and lower than 900 ° C. The thick film conductor is characterized in that the Li ₂ O is deposited on the anorthite.   The ceramic substrate, an internal electrode formed on the ceramic substrate and including a top electrode, a side electrode, and a back electrode, a resistance film formed on the ceramic substrate and the top electrode, and an insulation covering the resistance film A chip resistor comprising a glass protective film, an intermediate electrode made of Ni plating covering the internal electrode, and an external electrode made of solder plating, wherein at least the upper surface electrode is made only from the thick film conductor according to claim 5. A chip resistor, characterized in that it is configured.

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