JP4610215B2 - Conductor paste - Google Patents

Description

  The present invention relates to a conductor paste, and more particularly to a conductor paste that can be suitably used for providing a conductor layer on a ceramic dielectric.

Ceramic materials that can be used as dielectrics for piezoelectric elements and capacitors are known. For example, PZT (Pb (Zr, Ti) O ₃ : lead zirconate titanate), which is a solid solution of lead zirconate (PbZrO ₃ ) and lead titanate (TiZrO ₃ ), has excellent piezoelectric properties. It is used as various piezoelectric elements such as actuators and ultrasonic vibrators. The PZT, barium titanate (BaTiO ₃ ) and the like have a high dielectric constant and are therefore used as a constituent material for the dielectric layer of the capacitor. In these applications, conductor layers such as wiring and electrodes are formed by applying a conductor paste to a ceramic dielectric and firing it.

  The above-mentioned conductor paste generally disperses a metal powder as a conductor component and various subcomponents such as an inorganic binder, a glass frit, and a filler, which are added as necessary, in a predetermined organic medium (vehicle). It is prepared by. For example, a conductor paste whose conductor component is Pt (platinum) is used for applications such as multilayer piezoelectric elements (see, for example, Patent Documents 1 and 2). Further, a conductor component composed of a mixture of a high melting point metal powder such as Pt of 95 (wt%) or more and a low melting point metal powder of 5 (wt%) or less has been proposed (for example, Patent Document 3). (Refer to “wt%” for percentage by weight.) According to such a Pt-based conductor paste, since the melting point of Pt is high and the reactivity with ceramics is low, for example, for the formation of conductor layers such as piezoelectric ceramics fired at a high temperature of 1200 (° C) or higher Therefore, it is also suitable for internal electrodes such as multilayer piezoelectric elements and multilayer capacitors in which a conductor layer is laminated via a plurality of dielectric layers.

In particular, according to the latter technique, since the melting point is lower than that in the case where the conductor component is composed of only Pt, it is dense and adheres to the dielectric even when fired at a relatively low temperature of 1500 (° C.) or less. A conductor layer having high strength (ie, substrate adhesion strength) can be obtained. The refractory metal includes Pd (palladium), Rh (rhodium), and Ru (ruthenium) in addition to Pt, and the low melting point metal includes Au (gold), Ag (silver), Cu ( Copper).
JP-A-11-242913 JP 2001-184942 A JP 2003-281938 A

However, in the conventional conductor paste as described in each of the above publications, the conductor layer is foamed in the process of laminating the conductor layer through a plurality of dielectric layers and repeatedly firing, and the dielectric layer and There is a problem in that the adhesion to the conductor layer is hindered and the substrate adhesion strength becomes insufficient. That is, the conventional conductor paste has a sufficient adhesion strength when the number of firings is small (for example, when the number of firings is only one), but when the firing process is repeated after the conductor layer is formed, the substrate adhesion strength gradually increases. It goes down. For example, Patent Document 2 proposes increasing the film density and increasing the peel strength by using a mixture of spherical Pt and flaky Pt, and Patent Document 3 discloses a refractory metal. It has been proposed to increase the bonding strength by using a low melting point metal together with this, but even in this way, it is possible to maintain a sufficient substrate adhesion strength of 1 (kg / 2mm □) or more after repeated firing treatments. It was difficult. The substrate adhesion strength is determined by soldering a lead wire (for example, tin-plated wire) to a 2 × 2 (mm ² ) rectangular conductor film formed on a ceramic substrate and pulling the lead wire in a direction perpendicular to the substrate. This is a value evaluated by the load when the conductor film peels off at the interface with the substrate.

  Incidentally, as a method for manufacturing a piezoelectric element, a capacitor, and the like, there are a method of performing a baking process for each layer of a conductor layer and a method of performing a baking process collectively after laminating the whole. In the latter, the baking process for forming the internal electrode is performed once, but the baking process is performed again when the external electrode after lamination is provided. Therefore, in any case, resistance to repeated firing is required.

  The present invention has been made against the background of the above circumstances, and an object of the present invention is to provide a conductor paste having sufficiently high substrate adhesion strength even when subjected to repeated firing treatment.

In order to achieve such an object, the gist of the conductor paste of the present invention is (a) a conductor paste containing Pt (platinum) as a main component and a second component Pd (palladium) and a vehicle. Te, (b) said saw including a Ag (silver) of the third metal component is a lower melting point than Pd, (c) the Pt is 50 to 98 (wt% based on the total amount of the conductive component in the conductive paste ) To be included at a rate within the range .

In this way, since Pd is included as the second component in addition to Pt as the conductor component, even if repeated firing treatment is performed, foaming is suppressed and the conductor can maintain sufficiently high substrate adhesion strength. A conductor paste capable of forming a layer is obtained. Further, since the conductor paste contains Ag of the third metal component having a melting point lower than that of Pd, in addition to Pt and Pd, Ag having a melting point lower than those is further contained in the conductor paste. These metal components are easily melted, and high substrate adhesion strength is obtained. Moreover, since the Pt is included at a ratio in the range of 50 to 98 (wt%) with respect to the total amount of the conductive component in the conductor paste, the amount of Pt is determined to be in an appropriate range. Even when foaming is further suppressed and the number of repeated firing treatments is remarkably increased, a conductor paste capable of maintaining sufficiently high substrate adhesion strength can be obtained.

  Incidentally, when Pt is heated to about 700 to 800 (° C.), the gas introduced in the manufacturing process is volatilized. The gas remaining in the conductor layer is considered to be a cause of foaming of the conductor layer. Therefore, in order to escape the generated gas out of the film and suppress foaming, it is preferable that the sintering of the conductor paste does not proceed up to this degassing temperature, while ensuring the strength and conductivity of the conductor layer itself. In this case, it is desirable that the sintering proceeds as much as possible at the maximum holding temperature of the baking treatment (generally, about 1100 to 1400 (° C.)). The second component added to the conductor paste is preferably one that gives such sintering characteristics. As a result of extensive studies by the present inventors, it has been found that Pd has the most appropriate characteristics.

  Here, preferably, the Pt is included in a proportion within a range of 50 to 98 (wt%) with respect to the total amount of the conductive component in the conductor paste. In this way, since the amount of Pt is determined in an appropriate range, a conductive paste that can maintain sufficiently high substrate adhesion strength even when foaming is further suppressed and the number of repeated firing treatments is significantly increased. can get. If Pt is less than 50 (wt%), the high melting point component (Pt) becomes too small, and on the contrary, it becomes easy to foam by repeated firing, and if Pt exceeds 98 (wt%), the amount of Pd becomes too small. Therefore, the effect of addition cannot be sufficiently obtained.

  More preferably, the amount of Pt is included in a proportion within the range of 60 to 95 (wt%) with respect to the total amount of the conductor component. In this way, a conductor paste can be obtained that has a higher substrate adhesion strength and is less likely to have a reduced strength even when repeatedly fired.

  Preferably, the conductor paste includes a third metal component having a melting point lower than that of Pd at a ratio of 90 (wt%) or less with respect to the total amount of Pd and the third metal component. In this way, in addition to Pt and Pd, a metal component having a melting point lower than those is further contained, so that the metal component in the conductor paste is easily melted, and higher substrate adhesion strength is obtained. When the third metal component exceeds 90% (wt%) of the total amount of Pd and the third metal component, it is caused by repeated firing treatment due to oversintering or abnormal grain growth of the third metal component having a low melting point. It becomes easy to foam, and it becomes difficult to maintain the substrate adhesion strength.

  The third metal component is at least one of Au (gold), Ag (silver), and Cu (copper). These are suitable because they have high conductivity and have a reasonably low melting point. For example, the melting point of Ag is 961 (° C.), which is significantly lower than the melting point of Pt 1770 (° C.) and the melting point of Pd 1550 (° C.).

  Preferably, the conductor paste is used for forming a conductor layer on a ceramic dielectric. That is, the use of the conductor paste of the present invention is not particularly limited, but it is difficult to foam even when repeatedly baked, and the substrate adhesion strength can be maintained. It is suitable for dielectric applications that often occur. More preferably, the conductor paste is used for forming a conductor layer of a ceramic piezoelectric body.

  Preferably, the conductor paste is used to form a conductor layer in the production of a laminated dielectric element in which the conductor layer is laminated via a plurality of dielectric layers. In the manufacturing process of such a multilayer dielectric element, the conductor layer is repeatedly subjected to heat treatment, and thus is more suitable as an application target of the conductor paste of the present invention.

Preferably, the conductive paste is baked on the ceramic dielectric by firing in a Pb (lead) atmosphere. The conductor paste of the present invention is suitable for such applications. Since Pt sintering is likely to proceed at a relatively low temperature in a Pb atmosphere, it is easy to foam and it is difficult to maintain the substrate adhesion strength. For example, although a dielectric having a high dielectric constant containing Pb is suitable for an application such as an actuator, such a material is fired in an atmosphere containing Pb, for example, a PZT atmosphere in order to suppress Pb volatilization. Therefore, in particular, in such a high-performance dielectric, it has been strongly desired to suppress foaming. However, according to the present invention, foaming can be suitably suppressed. Note that the PZT atmosphere is an atmosphere containing PbO, ZrO ₂ , TiO ₂ vapor, or Pb-excess PbZrO ₃ vapor and having a low oxygen content. Further, in the PZT atmosphere, the pressure including those vapors is in the range of 8-20 (MPa), preferably in the range of 10-14 (MPa), more preferably in the range of 11-13 (MPa). Further, a high temperature and high pressure atmosphere having a temperature in the range of 800 to 1500 (° C.), preferably in the range of 1000 to 1300 (° C.), more preferably in the range of 1100 to 1300 (° C.) is also included.

  Preferably, the conductor paste is subjected to a firing treatment at a temperature within a range of 1000 to 1500 (° C.). More preferably, the temperature is in the range of 1100 to 1400 (° C.), and most preferably about 1300 (° C.). The firing time is appropriately determined for the time required for sintering the conductor paste. For example, the holding time at the maximum holding temperature is 0.5 to 10 hours, preferably 1 to 7 hours, more preferably 2 ~ About 4 hours.

  Preferably, the conductor paste includes the Pt, Pd, and the third metal component in respective powders or alloys thereof. For example, Pt can be prepared as a single powder, and Pd and the third metal component can be prepared as an alloy. Moreover, you may prepare with the alloy of Pt, Pd, and a 3rd metal component. Further, Pt, Pd, and the third metal component may be prepared as separate powders. For example, an alloy produced by a coprecipitation method or the like can be used.

  In the case of using Pt as a powder, the particle diameter is not particularly limited, but in order to form a dense conductor layer, it is preferable to use a fine powder, for example, the average particle diameter is 2.0 (μm) or less, one layer Preferably, fine powder having an average particle size in the range of 0.1 to 1.0 (μm) is used. In particular, those having a narrow particle size distribution in which the average particle size is in the above range and does not contain particles having a particle size of 10 (μm) or more, preferably 5 (μm) or more are preferable. In addition, when a Pt powder having an average particle size of two or more types, for example, one in the range of 0.1 to 0.5 (μm) and one in the range of 0.6 to 1.0 (μm) is used in combination, a particularly dense conductor layer is obtained. Obtainable. The average particle size used in combination is more preferably 0.1 to 0.3 (μm) and 0.7 to 0.9 (μm). Here, the average particle diameter is an average value of Haywood diameters obtained by image analysis through observation with a scanning electron microscope (SEM).

  Moreover, what was manufactured by the well-known appropriate method can be used for Pt powder used for a conductor paste. Examples of the production method include a reduction precipitation method, a gas phase reaction method, and a gas reduction method. The Pt powder is desirably as highly pure as possible, but may contain a slight amount of a noble metal such as Pd or a base metal such as Ni (nickel).

  The vehicle may be any material as long as it can disperse the metal powder, and a known material used for a conventional conductor paste including a platinum paste can be appropriately used. For example, cellulosic polymers such as ethyl cellulose, ethylene glycol and diethylene glycol derivatives, toluene, xylene, mineral spirits, butyl carbitol, terpineol (also referred to as terpineol), or a combination of two or more thereof. . Among these, ethyl cellulose, terpineol, or a mixed solution of ethyl cellulose and terpineol (preferably the volume ratio is 1: 1) is preferable.

  Preferably, the conductor paste contains a conductor component at a ratio in the range of 50 to 90 (wt%). In this way, since the proportion of the conductor component is sufficiently increased, the firing shrinkage is small, so that distortion due to firing shrinkage is suppressed, foaming is further suppressed, and the substrate adhesion strength is further increased. A conductive paste that is high and difficult to lower is obtained. If the proportion of the conductor component exceeds 90 (wt%), the wettability of the paste with respect to the ceramic becomes insufficient. The content of the conductor component is more preferably 70 to 90 (wt%), and further preferably 75 to 85 (wt%).

In addition to the conductor component and the vehicle, the conductor paste may contain various inorganic additives as long as the heat resistance and conductivity are not significantly impaired (that is, the characteristics suitable for the application can be maintained). Examples of the inorganic additive include various inorganic oxides, glass powders, fillers, and the like. Such an inorganic additive can function as a binder that melts when the conductive paste is baked onto the ceramic to increase the adhesive strength. In addition, inorganic additives having a specific surface area in the range of 0.5 to 50 (m ² / g) and an average particle size of 2 (μm) or less (particularly preferably 1 (μm) or less) are sufficiently high. It is preferable in order to ensure conductivity.

  The inorganic additive as described above is preferably added within a range of 0.1 to 10 (wt%) of the entire conductor paste. If it does in this way, the adhesive strength with respect to the conductor layer produced | generated from a conductor paste and ceramics can fully be raised, without impairing electroconductivity substantially.

  In addition to the vehicle, the conductor paste can contain various organic additives such as an organic binder and a coupling agent as long as the heat resistance and conductivity are not significantly impaired. Examples of the organic binder include those based on acrylic resin, epoxy resin, phenol resin, alkyd resin, cellulosic polymer, polyvinyl alcohol and the like. Examples of the coupling agent include silicon-based and aluminum-based ones. These are preferably those capable of imparting suitable viscosity and coating film forming ability to the conductor paste. In addition to these, a photopolymerizable compound, a photopolymerization initiator, and the like can be added to form a photocurable conductor paste.

  Further, a surfactant, an antifoaming agent, a plasticizer, a thickener, an antioxidant, a dispersant, a polymerization inhibitor, and the like can be appropriately added to the conductor paste.

  The conductor paste of the present invention is produced by mixing the above-described conductor component and vehicle with an arbitrarily added inorganic additive, organic additive, and the like. It can be carried out using an appropriate kneader such as a roll mill.

  In addition, manufacture of the ceramic dielectric element using the conductor paste of this invention can be performed as follows, for example. That is, first, a ceramic dielectric base material is manufactured by a green sheet molding method or a dry pressure molding method or the like, and a conductive paste is applied to this with a predetermined planar shape in a predetermined thickness dimension. Next, the base materials each coated with the conductive paste are laminated and pressure-bonded to each other. At this time, a conductive paste is applied to the uppermost surface and the lowermost surface of the laminate as necessary. Next, this laminate is fired at a predetermined temperature determined for each type of substrate. This firing temperature is set in a range not exceeding the melting point of Pt. Further, the firing is appropriately selected in the air atmosphere or Pb atmosphere depending on the composition of the substrate. After firing the laminated body, a conductor dielectric for forming an external electrode is applied to the end face, and a ceramic dielectric element can be obtained by generating the external electrode from this conductor paste by firing treatment.

  In addition, the baking process of a laminated body may be performed every time it coats and forms one conductor layer other than performing collectively as mentioned above. For example, the dielectric layer can be formed by applying a dielectric paste on the conductor layer, or laminating and pressing a dielectric raw sheet, and sequentially firing in a PZT atmosphere.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  The typical preparation method of the conductor paste of this invention and the formation method of a conductor film are demonstrated. The conductive paste is prepared as follows by preparing Pt powder, Ag / Pd powder or Pd powder, and a vehicle. As the Pt powder, for example, a commercially available platinum powder can be used. In this example, a powder having an average particle diameter of 0.2 (μm) and a powder having an average particle diameter of 0.8 (μm) are used at a weight ratio of 1: A mixture of 1 was used. As the Ag / Pd powder, for example, a commercially available co-precipitated powder having an average particle size of about 0.5 (μm) within the range of Ag: Pd of 90:10 to 30:70 was used. As the Pd powder, for example, a commercially available powder having an average particle size of about 0.5 (μm) was used. As the vehicle, a mixed solution in which ethyl cellulose and α-terpineol were mixed at a volume ratio of 1: 1 was used. These Pt powder, Ag / Pd powder, Pd powder, and vehicle are weighed and mixed so as to have a predetermined ratio, respectively, and kneaded by, for example, a three-roll mill to obtain a conductor paste.

  The predetermined ratio is, for example, 80 (wt%) of the total amount of the conductor component, that is, Pt powder and Ag / Pd powder or Pd powder, 20 (wt%) of the vehicle, and 100 (wt) of the total of the conductor component and the vehicle. %). The constituent ratio of the conductor component is, for example, about 95 (wt%) for Pt, about 3.5 (wt%) for Pd, and about 1.5 (wt%) for Ag.

  Next, for example, a PZT piezoelectric ceramic substrate having a thickness of about 0.5 (mm) was prepared, and the conductor paste prepared as described above was applied to the surface to form a conductor film. The conductor paste is applied using, for example, a well-known screen printing method, and the application thickness is about 4 (μm).

  Next, the formed coating film is subjected to a drying treatment at, for example, 100 (° C.) for about 15 minutes using, for example, a far infrared dryer, thereby volatilizing the volatile component in the vehicle, that is, terpineol. Thereafter, for example, in an electric furnace, the baking treatment was performed by maintaining the maximum temperature of about 1300 (° C.) for about 2 hours. As a result, ethyl cellulose, which is a residual component in the vehicle, that is, the organic component in the coating film is burned out, and the conductive powder is melted and bonded to each other. It is formed. In addition, the baking process was performed by, for example, raising the temperature from room temperature to the maximum temperature in about 6 hours, allowing to stand for about 2 hours, and then allowing to cool. The conductor layer after firing is densified to such an extent that the conductor components are alloyed or the mutual grain boundaries cannot be observed.

  The characteristic evaluation results of the conductor layer thus obtained will be described below. Table 1 below shows the composition, firing temperature, and properties of the conductor pastes of various examples evaluated together with the comparative examples. The production conditions not listed in Table 1 are all the same. For example, the vehicle amount is 20 (wt%). Further, the composition of the conductor component is such that Pt is in the range of 37.5-100 (wt%), Pd is in the range of 0-43.75 (wt%), Ag is in the range of 0-18.75 (wt%), and Ag: Pd is 100. The range was from 0 to 0: 100. FIG. 1 and FIG. 2 in which a part thereof is enlarged show the conductor component compositions of Examples 1 to 13 and Comparative Examples 1 to 4 in a triangular diagram. In FIG. 1 and FIG. 2, a range surrounded by three dot-and-dash lines of Pt amounts 50 (wt%) and 98 (wt%), and Pd amount 10 (wt%) with respect to the total amount of Pd and Ag (that is, The inner region indicated by the white arrow from these alternate long and short dash lines (including the Pt-Pd line where the Ag amount is zero) is the composition range in which the effect of the present invention is remarkably obtained. In FIGS. 1 and 2, the third metal component is Ag, but the same triangular diagram can be applied to other low melting point metals such as Au and Cu.

  In Table 1 above, what is shown in parentheses in the Pd and Ag columns of the composition column is the constituent ratio of Pd and Ag in each composition. In addition, the firing temperature was a constant temperature of 1300 (° C.) in the examples and comparative examples for evaluating the difference in composition, but in addition, 1100 to 1400 (° C.) in order to evaluate the influence of the firing temperature. The temperature was also evaluated within the range. The evaluation items are the surface roughness of the conductor layer, the substrate adhesion strength, and the foamed state. The surface roughness is evaluated as an index of film quality change, and is an Ra value measured by a surface roughness meter “Surfcom (registered trademark)” manufactured by Tokyo Seimitsu Co., Ltd. In addition, the foamed state is X when a large number of foams are observed by microscopic observation, slightly when, for example, about 1 to 2 foams are observed in 200 (μm) squares, and no foaming is observed. The ones marked with ○ The x level cannot be used, but the intermediate Δ level is determined to be usable depending on the required characteristics.

  In Table 1, “first firing” means the first firing for generating a conductor layer, and firing is performed in an air atmosphere. In addition, “repetitive heat treatment” simulates a firing process repeatedly applied for lamination, and is heat-treated in a PZT atmosphere. In any case, the treatment temperature was set to the firing temperature shown in Table 1.

  In FIGS. 1 and 2, the circled numbers correspond to the numbers of the examples shown in Table 1, and the white circled numbers correspond to the numbers of the comparative examples. In addition, since Examples 4-6 have the same composition as Example 3, they are not described in the triangular diagram.

  As shown in Table 1, in Examples 1 to 13, the surface roughness after the first firing was about 0.14 to 0.18 (μm) Ra, and after about 3 repeated heat treatments, about 0.14 to 0.22 (μm) Ra. The surface roughness was relatively good. On the other hand, in Comparative Examples 1 to 4, the surface roughness after the first firing was about 0.16 to 0.18 (μm) Ra, which was slightly worse than the examples, and after two repeated heat treatments, 0.22 to 0.26 (μm ) Remarkably bad results were obtained compared to Ra and the examples. That is, in the examples, the film quality change is small, but in the comparative example, the film quality change is significant. In particular, in the range where the Pt amount is 62.5 to 95 (wt%) and Pd / (Ag + Pd) is 30 (wt%) or more, the initial surface roughness is 0.17 (μm) Ra or less, and after three heat treatments It can be seen that the surface roughness is kept at a very good value of 0.17 (μm) Ra or less, and the film quality change is further reduced. In Example 2, the amount of Pt is large. In Example 9, the ratio of Ag to Pt is large. In Example 13, the amount of Pt is small. Therefore, the film quality is likely to change compared to other examples. it is conceivable that.

  In Examples 1 to 13, the substrate adhesion strength after the first firing was relatively high, about 1.7 to 2.2 (kg / 2mm □), and about 1.1 to 2.0 (kg / 2mm □) even after the third heat treatment. It has sufficient strength. Further, in the range where the film quality change is small, it has a strength of 1.8 (kg / 2mm □) or more even after the heat treatment is repeated three times, and is particularly suitable for an application where the firing treatment is repeated. On the other hand, in Comparative Examples 1 to 4, it has a relatively high strength of about 1.8 to 1.9 (kg / 2mm □) after the first firing, but 0.4 to 0.5 (kg / 2mm □) after the third heat treatment. The strength is significantly reduced. Therefore, since the minimum required strength of 1 (kg / 2mm □) or more cannot be ensured, the applications shown in Comparative Examples 1 to 4 cannot be used in applications where the firing process is repeated after the formation of the conductor layer. I understand that. In addition, if this intensity | strength is about 2.0 (kg / 2mm □) or more, it can be said that it has sufficient intensity | strength for any present use. Further, if it is 1.0 (kg / 2mm □) or more, preferably 1.3 (kg / 2mm □) or more, it can be said that it has sufficient strength in most applications, depending on the required specifications.

  3 to 5 evaluate the relationship between the composition and the firing temperature and the substrate adhesion strength from the data shown in Table 1. FIG. In each figure, the width from the minimum value to the maximum value of the strength after the first firing and after 1 to 3 heat treatments is indicated by a bar, and the numbers of the examples and comparative examples are circled numbers and white circles. Expressed in numbers. In most embodiments, the minimum value is the value after the third heat treatment, and the maximum value is the value after the first firing.

  In FIG. 3 showing the relationship with the Pt amount, a strength of 1 (kg / 2mm □) or more can be secured in the range of 50 to 98 (wt%), but the Pt amount is smaller or larger than that. As a result, the tendency of the substrate adhesion strength to decrease is apparent. It can be seen that when the amount of Pt is in the range of about 60 to 95 (wt%), the strength change due to repeated heat treatment is extremely small, which is particularly suitable for applications in which the firing treatment is repeated. Note that FIG. 3 shows only Pd: Ag of 7: 3 and fired at 1300 (° C.) for easy evaluation of the Pt amount.

  Also, in FIG. 4 showing the relationship with the amount of Pd / (Ag + Pd), a strength of 1 (kg / 2mm □) or more can be secured in the range where the amount of Pd is 10 (wt%) or more. It is clear that when the amount of Pd is smaller than that, the substrate adhesion strength tends to decrease. In particular, it can be seen that when the amount of Pd is in the range of about 20 (wt%) or more, there is almost no decrease in strength due to repeated heat treatment, which is suitable for applications where the firing treatment is repeated. FIG. 4 also shows only the case where the Pt amount is 95 (wt%) and the baking treatment is performed at 1300 (° C.) for the purpose of evaluating the Pd amount.

  In addition, in FIG. 5 showing the relationship with the firing temperature, a high strength of 1.5 (kg / 2 mm □) or more is maintained even when firing treatment and repeated heat treatment are performed at any temperature between 1100 and 1400 (° C.). It was confirmed that Moreover, in the range tested, the strength tends to increase as the firing temperature increases, and it is presumed that the firing temperature is preferably higher in the range not exceeding the melting point of Pt. In FIG. 5, for the evaluation of the firing temperature, only data with a Pt amount of 95 (wt%) and a Pd / (Ag + Pd) amount of 70 (wt%) are shown.

  Returning to Table 1, with respect to the evaluation results of the foamed state, the conductor paste of this example had no or no foaming even after the heat treatment was repeated three times, and the evaluations of ◯ to Δ were obtained. On the other hand, in all of the comparative examples, a large number of foaming occurred, and the evaluation was x. Photomicrographs of the substrate surface are shown in FIGS. In these figures, the lateral width corresponds to 300 (μm). FIG. 6 shows the X level where many foams are observed, FIG. 7 shows the Δ level where foaming is slightly present, and FIG. 8 shows the ○ level where no foaming is observed. In FIG. 7 at the Δ level, spherical objects observed at several places such as the lower center are foamed portions. The presence / absence and degree of foaming influence the substrate adhesion strength, and it is clear from Table 1 that the foam with less foaming has high strength and the foam with much foam has low strength. Further, in the range where the film quality change is small, all are maintained at the level ◯ even after repeated heat treatment, and it is found that foaming is extremely difficult to occur and is particularly suitable for applications where the firing treatment is repeated.

  As described above, in this embodiment, since Pd is included as the second component in addition to Pt as the conductor component, even if repeated baking treatment is performed, foaming is suppressed and the substrate adhesion is sufficiently high. A conductor paste capable of forming a conductor layer capable of maintaining strength can be obtained.

  In particular, foaming is further suppressed when the amount of Pt is within the range of 50 to 98 (wt%) or when Ag is contained in a proportion of 90% (wt%) or less with respect to the total amount of Pd and Ag. There is an advantage that a conductor paste that can maintain higher strength even after repeated heat treatment can be obtained.

  As mentioned above, although this invention was demonstrated in detail with reference to drawings, this invention can be implemented also in another aspect, A various change can be added in the range which does not deviate from the main point.

3 is a triangular diagram showing the conductor component composition shown in Table 1. FIG. It is a figure which expands and shows the area | region where Pt in FIG. 1 is 90 (wt%) or more. 3 is a graph showing the relationship between the amount of Pt in Table 1 and the substrate adhesion strength. 3 is a graph showing the relationship between the amount of Pd / (Pd + Ag) in Table 1 and the substrate adhesion strength. It is the graph showing the relationship between the calcination temperature in Table 1, and board | substrate adhesion strength. It is a microscope picture of the conductor layer surface where many foaming has appeared. It is a microscope picture of the conductor layer surface in which foaming is seen slightly. It is a microscope picture of the conductor layer surface in which foaming does not exist.

Claims (4)

A conductive paste containing Pt (platinum) as a main component and a second component, Pd (palladium), and a vehicle,
The look containing a Ag (silver) of the third metal component is a lower melting point than Pd,
Pt is contained in a proportion within the range of 50 to 98 (wt%) with respect to the total amount of conductive components in the conductor paste. The conductor paste according to claim 1 , comprising Ag of the third metal component in a proportion of 90 wt% or less with respect to the total amount of Pd and Ag. 3. The conductor paste according to claim 1 or 2 , which is used for forming a conductor layer on a ceramic dielectric. 4. The conductive paste according to claim 3 , wherein the conductive paste is baked on the ceramic dielectric by firing in a Pb (lead) atmosphere.