JPH08298018A - Conductive paste - Google Patents

Abstract

(57) [Summary] [Structure] 70-98% by weight of Ag powder and 0-28% by weight of P
d is a conductive paste composed of 2 to 11% by weight of glass frit, and the composition of the glass frit is 15
-40 wt% PbO and 40-70 wt% Bi ₂ O ₃ and 0
15 wt% SiO ₂ and 0-20 wt% B ₂ O ₃ and 5-10
It consists of wt% In ₂ O ₃ . [Effect] A conductive film that has a strong adhesive strength to a substrate such as a dielectric porcelain, does not peel off due to external stress, has a good external appearance, and has excellent plating resistance and solder resistance. A film is obtained. In particular, it is suitable for forming a terminal electrode of a laminated ceramic capacitor.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a conductive paste,
More specifically, the present invention relates to a conductive paste that is used as a material for a terminal electrode of a laminated ceramic capacitor and has improved adhesive strength with a ceramic.

[0002]

2. Description of the Related Art Conductive pastes are widely used, for example, for forming internal electrodes and terminal electrodes of laminated porcelain (ceramic) capacitors, or for forming conductive films of conductive circuits formed on substrates such as glass and ceramics. The conductive film is formed by applying it to a desired portion by a method such as printing, drying it, and then baking it by a method such as firing.

Such a conductive paste is, for example, silver (A
g) ・ Gold (Au) ・ Platinum (Pt) ・ Palladium (Pd)
-Nickel (Ni) -copper (Cu) -zinc (Zn), etc., or metal powder mixed or alloyed with these, dispersed in an organic vehicle prepared by dissolving an organic binder resin in an organic solvent. In addition, additives such as various dispersants and various glass frits are added as necessary.

As such glass frit, lead silicate glass, lead borosilicate glass, bismuth borosilicate glass, zinc borosilicate glass, cadmium borate glass, etc. are used.

When the terminal electrode of the laminated ceramic capacitor is formed by using the conductive paste, the conductive film formed by the conductive paste has a good conductivity as well as a good external appearance of the conductive film. It is required that the adhesive strength with the dielectric ceramic is strong, and that the conductive film has good plating resistance when electrolytically plating. Further, it is also required that the electrode film after firing has no defects such as voids and has a good sealing property with respect to the plating solution.

Conventionally, a conductive paste for forming a terminal electrode of a laminated porcelain capacitor contains Ag fine powder and PbO 50.
80 wt%, B ₂ O ₃ is 10 to 20 wt%, SiO ₂ is 5
A silver paste prepared by dispersing a low melting point lead borosilicate glass frit having a composition of 15% by weight and ZnO of 1 to 10% by weight in an organic vehicle has been used.

Further, JP-A-58-11565 discloses a noble metal powder and 1 to 30% by weight of a zinc borosilicate glass frit containing an alkali metal and an alkaline earth metal.
A conductive paste has been proposed which is dispersed in an inert organic vehicle. The composition of the glass frit is Zn
O is 30 to 55% by weight, B ₂ O ₃ is 25 to 45% by weight, SiO ₂
5 to 15% by weight, at least one of Li ₂ O, Na ₂ O and K ₂ O is 1 to 10% by weight, MgO, CaO and BaO
It is disclosed that at least one of them is 2 to 20% by weight, CdO is 2 to 8% by weight, and SnO ₂ is ₂ to 10% by weight. According to this, even if the surface of the conductive coating formed by baking the paste is subjected to a metal coating treatment by an electrolytic plating method, it is not deteriorated and the adhesive strength is not impaired.

Further, Japanese Patent Application Laid-Open No. 62-237605 proposes a thick film paste containing palladium and silver as main components, and a glass component and a metal oxide therein, and the glass component contains Pb. It is a ZnO-B ₂ O ₃ -based material that does not contain, and is 1 to 6 per 100 parts by weight of palladium and silver.
It is disclosed that parts by weight are included. According to it
The reliability of the adhesive strength with a non-oxide insulating base such as an aluminum nitride sintered base can be enhanced, and deterioration of the adhesive strength can be suppressed especially at high temperatures.

Further, Japanese Patent Publication No. 5-14363 discloses a silver-based conductive paste in which silver powder is dispersed in an organic dispersion medium as a conductivity-imparting component.
4% by weight or less of Bi ₂ O ₃ powder and 0.05 to 0% of CuO powder.
6 wt%, 0.05-0.5 wt% MnO ₂ powder, and
Use a lead borosilicate glass frit with a softening point of 700 ° C or less.
A conductive paste composition has been proposed which is dispersed and contained in an amount of 0.1 to 1.5% by weight. However, the composition of the glass frit is not disclosed. With this conductive paste, the conductor surface after firing does not become a flat surface, but a pattern is formed as if contour lines are running.In such a case, solderability and resistance to melting against solder The property is remarkably improved, and the decrease in adhesive strength after heat aging is reduced.

Furthermore, Japanese Patent Laid-Open No. 4-334007 discloses that
In a ceramic capacitor provided with a ceramic body and an external electrode including a baked electrode layer formed on the outer surface of the ceramic body and composed of a metal and an inorganic binder,
The surface of the baked electrode layer is mainly composed of Pb, Sn, Ag, I
A ceramic capacitor has been proposed in which an alloy layer containing at least one type of n, a Ni plating layer, and a Sn or Sn / Pb plating layer are formed in this order. The alloy layer is formed by electroless and electrolytic plating methods or dipping methods. As a practical alloy, Pb 93.5 wt% / Sn 5 wt% / Ag 1.5 wt% and Pb 92.5 wt% / In 5 wt% / Compositions such as 2.5 wt% Ag are disclosed. According to it, the alloy layer is more flexible than the metal of the baked electrode layer, and easily plastically deforms when subjected to stress even at room temperature,
As it has a high melting point that does not melt during soldering, it has solder heat resistance and solder wettability, but does not crack in the dielectric body even when the capacitor is subjected to thermal shock or mechanical shock, resulting in excellent various characteristics. That is, a highly reliable ceramic capacitor can be obtained.

[0011]

However, since the terminal electrode formed of the above-mentioned conventional silver paste has a high PbO content in the glass frit, the adhesive force with the dielectric ceramic becomes insufficient, and the terminal electrode after baking is not formed. There is a problem in that a defective appearance such as a spherical bulge on the electrode film, a film floating or peeling occurs. Further, when electrolytic plating is performed, the plating solution penetrates between the internal electrodes of the laminated ceramic capacitor and the dielectric ceramics via the terminal electrodes to leave conductive ions, so that the characteristics such as the Q value of the ceramic capacitor are There was a problem that it adversely affected. Furthermore, a phenomenon in which glass frit segregates and floats in layers on the surface of the electrode film is observed, which results in poor solder wettability and heat resistance when soldering on the electrode film, or glass frit or noble metal ( There was also a problem in that a phenomenon called "solder cracking" in which silver) melts into the solder occurs.

Further, the conductive paste having the composition proposed in Japanese Patent Laid-Open No. 58-11565 also causes the ZnO component contained in the glass frit to ooze out by baking, so that the electrode film formed by the conductive paste is not formed. There was a problem of discoloration after plating.

The thick film paste proposed in Japanese Patent Laid-Open No. 62-237605 also has a composition ratio of 1 to 6 parts by weight with respect to 100 parts by weight of palladium and silver. When it is used as an electrode of a component, there is a problem that it is inferior in solder resistance and mechanical strength (fixing force of the electrode film).

Further, even with the conductive paste proposed in Japanese Examined Patent Publication No. 5-14363, CuO is contained in B in the dielectric porcelain.
There is a problem that a large number of microcracks may occur in the dielectric ceramic because of its strong thermochemical reactivity with aTiO ₃ .

Furthermore, the alloy layer disclosed in Japanese Patent Laid-Open No. 4-334007 is formed by a plating method or a dipping method, and is not a base electrode (baking electrode) portion to be metallized in a porcelain portion, so that it is conductive. There is a problem that it cannot be applied to the sex paste. There is also a problem that the characteristics of the capacitor are deteriorated by the intrusion of the plating solution.

The present invention has been completed in order to solve the problems in view of the above circumstances, and its object is to enhance the adhesive strength with a base such as a dielectric porcelain or the like, even if an external force is applied. An object of the present invention is to provide a conductive paste capable of obtaining a conductive film that does not peel off.

Another object of the present invention is to provide a good external appearance,
An object of the present invention is to provide a conductive paste that can obtain a conductive film having excellent resistance to electroplating.

Further, an object of the present invention is that when used for forming a terminal electrode of a laminated ceramic capacitor, it has a good external appearance,
It has excellent adhesive strength with dielectric porcelain and plating resistance against electrolytic plating, and also has excellent solder wettability and heat resistance. Furthermore, there are no defects such as voids in the electrode film, and good sealing performance against plating liquid. Another object of the present invention is to provide a conductive paste suitable for forming a terminal electrode of a laminated ceramic capacitor, which can obtain a different electrode film.

[0019]

The conductive paste of the present invention comprises 70 to 98% by weight (excluding 98% by weight) of Ag powder and 0 to 28% by weight (excluding 0% by weight) of Pd powder. And 2 to 11% by weight of glass frit, the composition of the glass frit is 15 to 40% by weight of PbO, 40 to 70% by weight of Bi ₂ O ₃ and 0 to 15% by weight (however, 0% by weight is included). (Excluding) SiO ₂ , 0 to 20% by weight (excluding 0% by weight) B ₂ O ₃ and 5 to 10% by weight In ₂ O ₃ .

[0020]

The conductive film obtained by the conductive paste of the present invention has In ₂ O as the composition component of the glass frit.
By adding In (indium) using ₃ (indium oxide), the film becomes mechanically more flexible than a conductive film made of an Ag-Pd alloy that does not contain In, and easily receives stress even at room temperature. It becomes a conductive film that can be plastically deformed. Further, In is Pd when baking the conductive paste.
At the same time, it diffuses into a ceramic substrate such as a dielectric porcelain to enhance the adhesive strength. Therefore, a conductive paste is obtained in which a conductive film that does not peel off from the substrate even when an external force is applied is obtained.

Therefore, when the conductive paste of the present invention is used for forming a terminal electrode of a laminated ceramic capacitor, the electrode film has a characteristic of buffering the external stress on the dielectric ceramic, and as a result, The adhesive strength with the terminal electrode can be improved, the terminal electrode can be prevented from peeling off from the dielectric ceramic, and the plating resistance can be excellent.

Further, the conductive film obtained by the conductive paste of the present invention has a higher melting point than the conductive film not containing In because it contains In.
An electrode film that does not melt even when soldering can be obtained, and heat resistance and solder resistance are also excellent.

According to the results of detailed investigations and examinations by the present inventor regarding the above-described In addition effect, the effect is almost proportional to the In addition amount in the range shown in the above composition components, It was found that the improvement effect cannot be obtained when the amount exceeds the limit.

According to the conductive paste of the present invention, A
By selecting the composition ratio of the g powder and the Pd powder, it is possible to obtain a conductive film having a good external appearance and excellent plating resistance against electrolytic plating. Moreover, by selecting the composition ratio of the glass frit and the Pd powder, the solder wettability becomes excellent, and furthermore, the electrode film is free from defects such as voids and has a good sealing property against the plating solution. Become.

As a result, when the conductive paste of the present invention is used for forming a terminal electrode of a laminated ceramic capacitor, the external shape is good, the adhesive strength with the dielectric ceramic and the plating resistance to electrolytic plating are excellent, and the solder is used. It has excellent wettability and heat resistance, and furthermore, there are no defects such as voids in the electrode film, and an electrode film with good sealing properties against the plating solution can be obtained. Impact resistance can be significantly improved.

[0026]

EXAMPLES The conductive paste of the present invention will be described in detail below based on specific examples.

In the following examples, the terminal electrode of the laminated ceramic capacitor will be described as an application example of the conductive paste, but the use of the conductive paste of the present invention is not necessarily limited to this, and glass, ceramics, etc. It is also applicable to various applications in which a conductive paste is generally used, such as a conductive circuit of a printed wiring board using the above substrate, a microswitch contact portion, an electrode portion of various electronic parts, and the like.

The metal powder of the conductive paste of the present invention includes
70 to 98% by weight (excluding 98% by weight) of Ag (silver) powder and 0 to 28% by weight (excluding 0% by weight) of Pd (palladium) powder are used. It is preferable to set the composition ratio of these metal powders in the above range from the viewpoints of connectivity with internal electrodes, solder wettability, and heat resistance. When the Ag powder content is less than 70% by weight, the laminated ceramic capacitor chip is used as a substrate. When soldering, the Sn in the solder diffuses into the Pd in the terminal electrode and the adhesive strength of the conductive film deteriorates, so-called solder nicking tends to occur. Since the amount of glass frit added is reduced, the adhesive strength and solder heat resistance tend to deteriorate.

When the Pd powder content exceeds 28% by weight, solder scoring tends to occur as in the case where the Ag powder content is less than 70% by weight.

The shape of these powders is preferably spherical, flake-shaped, or powder-like, and if spherical, their specific surface areas and tap densities are in the ranges of 0.05 to 10 m ² / g and 1.0 to 5.0 g / cm ² , respectively. If it is flake-like, 0.1-10.0 m ² / g and 1.0-15.0 g, respectively
/ Cm ² range, if powdery, 5.
In the range of 0 to 30.0 m ² / g and 0.1 to 10.0 g / cm ² , the dispersibility and mixing characteristics are good, the appearance shape of the conductive paste coating film is good, and stable conductive characteristics are easily obtained. It is preferable in terms.

The combination of the spherical powder and the flake powder is set within a weight ratio of 1: 1 to 1: 3, preferably 1: 1.5 to 1: 2. However, it is preferable in that the shape of the electrode film after applying and baking the conductive paste becomes good. If the amount of spherical powder is larger than the above range, the shape of the electrode film tends to sag, while if the amount of flake-shaped powder is large, the shape of the electrode film tends to be easily scraped.

The glass frit is used to improve the adhesion between the ceramic substrate such as a dielectric ceramic and the terminal electrode and the solder heat resistance of the electrode film, and its composition ratio is 2
The range of up to 11% by weight is preferable in terms of solder properties such as solder wettability and heat resistance, and adhesive strength. 2 glass frit
If it is less than 11% by weight, the adhesive strength tends to be low and the heat resistance tends to deteriorate, while if it exceeds 11% by weight, the solder wettability tends to deteriorate.

In the conductive paste of the present invention, the composition of the glass frit is 20 to 40% by weight of PbO and 40% by weight.
~ 70 wt% Bi ₂ O ₃ and 0 to 15 wt% (excluding 0 wt%) SiO ₂ and 0 to 20 wt% (excluding 0 wt%)
B ₂ O ₃ ) and 5 to 10% by weight of In ₂ O ₃ .

PbO (lead oxide) is used for improving solder wettability, heat resistance and adhesive strength, and its properties are improved by setting the component ratio in the glass frit to 15 to 40% by weight. When the PbO content is less than 15% by weight, the glass component tends to increase and the solder wettability tends to deteriorate, while when it exceeds 40% by weight, the glass component tends to decrease and the solder resistance tends to deteriorate.

Bi ₂ O ₃ (bismuth oxide) is also used for improving solder wettability and heat resistance / adhesive strength, and its characteristics are improved by setting the component ratio in the glass frit to 40 to 70% by weight. Becomes This Bi ₂ O ₃
If less than 40% by weight, the effect of improving the above properties tends to be insufficient, whereas if more than 70% by weight, the effect of further improving the above properties tends not to be obtained. .

SiO ₂ (silicon dioxide) is used for improving the heat resistance, and by setting the component ratio in the glass frit to 0 to 15% by weight (excluding 0% by weight), the solder wettability and the heat resistance are improved. Will be good. This SiO
_{When 2} is 0 weight, the above-mentioned effects cannot be obtained, while 15
If it exceeds 5% by weight, SiO ₂ may be deposited on the surface of the terminal electrode during baking, which may deteriorate the solder wettability.

B ₂ O ₃ (boron oxide) is used for improving the heat resistance of the solder, and the heat resistance of the solder can be improved by adjusting the component ratio of the glass frit to 0 to 20% by weight (excluding 0% by weight). Will be good. If the B ₂ O ₃ content is 0 weight, the above-mentioned effects cannot be obtained. On the other hand, if it exceeds 20 weight%, vitrification in the glass frit use temperature range tends to be difficult.

In ₂ O ₃ (indium oxide) is used for strengthening the adhesive strength between the terminal electrode (electrode film) and the ceramic substrate such as a dielectric ceramic as described above, and its component ratio in the glass frit is adjusted. Adhesive strength becomes good by setting it as 5-10 weight%. This In ₂ O ₃ is 5
If it is less than 10% by weight, no sufficient effect tends to be obtained, while if it exceeds 10% by weight, further improvement in adhesive strength tends not to be expected.

The conductive paste of the present invention is used by dispersing the metal powder and the glass frit having the above composition ratios in an organic vehicle in which an organic binder resin is dissolved in an organic solvent. As characteristics of this organic vehicle, it is required that the viscosity and viscosity suitability of the conductive paste obtained by using the organic vehicle can be controlled, that a good coating shape be obtained, and that an appropriate dry film strength be obtained. .

Organic vehicles that can be used in the conductive paste of the present invention include organic binders such as acrylic resins, phenol resins, alkyd resins, rosin esters, ethyl cellulose, methyl cellulose, ethyl hydrocellulose, PVA (polyvinyl alcohol), polyvinyl butyrate, etc. For example, the resin may be dispersed in an organic solvent such as α-terpineol, BCA (butyl carbitol acetate) or benzyl alcohol.

Above all, it is preferable to use ethyl cellulose as the organic binder resin, since the binder resin of the ceramic green sheet is usually acrylic resin, so that it is completely dissolved in a petroleum ether solvent which is insoluble in this resin. Moreover, it is preferable to use a petroleum ether-based solvent as the organic solvent, because it sufficiently dissolves ethyl cellulose, which is a chain molecule and has a high binding ability.

In order to disperse the metal powder and the glass frit in the organic vehicle, it is preferable to use a roll mill, a planetary mixer or the like, and a roll mill is particularly preferable because uniform dispersion can be carried out efficiently in a short time.

The ratio of the mixture of the metal powder and the glass frit dispersed in the organic vehicle is in the range of 70 to 85% by weight of the conductive paste and 15 to 30% by weight of the organic vehicle in total. It is preferable to adjust the amount to be 100% by weight from the viewpoint of improving the rheology of the conductive paste and the outer shape of the conductive film.

In order to form a conductive film with the conductive paste of the present invention, the conductive paste is formed into a desired shape on the surface of a dielectric ceramic, glass, ceramic or the like, which is a substrate, by a method such as dipping (immersion) or printing. And a thickness to form a paste film, which is dried and then baked by a method such as baking to form a conductive film.

In forming the conductive film as described above, the thickness of the paste film is preferably set in the range of 30 to 150 μm, whereby a conductive film having a good appearance and uniform characteristics can be easily obtained. Become. Drying is preferably carried out in a drying oven at a temperature of 130 to 180 ° C. for a time of about 5 to 15 minutes, which allows the shape of the paste film to be controlled, resulting in a good appearance and good adhesion to the substrate. It is easy to obtain a conductive film that is strong and has a dense structure. If this drying is performed in an oxygen (O ₂ ) atmosphere, the strength of the paste coating after drying is improved, which is more suitable. For baking, use a firing furnace (tunnel furnace) if firing.
It is preferable to carry out at a temperature of 00 to 900 ° C. for about 30 to 60 minutes, whereby Ag in the conductive film can be sintered, so that the appearance shape is good and the adhesive strength to the substrate is high.
It becomes easy to obtain a conductive film having a dense structure and excellent plating resistance and solder resistance. If this firing is also performed in an atmosphere of O _2, the binder removal in the paste coating proceeds, and a good conductive film can be obtained, which is more preferable.

Specific examples will be shown below. 80 wt% Ag powder and 18 wt% Pd powder were prepared as the metal powder of the conductive paste, and 2 wt% glass frit having the composition components shown in Table 1 was prepared.

[0047]

[Table 1]

A solution in which 25% by weight of ethyl cellulose as an organic binder resin was dissolved in a petroleum ether solvent (liproin) which is an organic solvent was prepared as an organic vehicle.

Then, the above-mentioned Ag powder, Pd powder and glass frit were mixed, respectively, and the solid content thereof was 78% by weight.
And 22% by weight of the above organic vehicle are mixed, and each is kneaded in a planetary mixer for 90 minutes and then 45 in a three-roll mill.
After being dispersed for a minute, the viscosity was adjusted with the above organic solvent to prepare conductive pastes A to G using glass frits having the composition components shown in Table 1. The conductive pastes A, B, F, and G are comparative examples.

These conductive pastes were applied to a laminated ceramic capacitor chip made of a BaTiO ₃ -based dielectric by a dipping method, dried at 150 ° C., baked at a baking temperature of 800 ° C. for 40 minutes and sintered, respectively. Capacitor samples A to G were prepared by forming terminal electrodes of the laminated ceramic capacitor with the conductive pastes A to G.

Using the tensile compression tester SV51-E-50MV manufactured by Imada Seisakusho Co., Ltd., these capacitor samples were tested for adhesion strength and tensile strength of the terminal electrode under the conditions of a tensile compression speed of 0.5 mm / sec. It was measured. As the evaluation criteria for these, the adhesive strength of 2.0 kgf or more and the tensile strength of 2.0 kgf or more were considered good.

Regarding the occurrence of electrode film peeling due to external stress, a tensile compression tester SV51-E-50MV, also manufactured by Imada Seisakusho Co., Ltd., was used.
Under the condition of 0.5 mm / sec, the number of occurrence of peeling was examined and evaluated for each of 20 samples.

With respect to the plating resistance of the electrode film, the terminal electrode of each capacitor sample was Sn plated on the Ni plating.
The plating was performed by electrolytic plating, and the Q value of the capacitor before and after the plating was measured, and the change was obtained and evaluated. And the Q value after plating is 1,000 or more and the Q value before and after plating
A value change within 2,000 was considered good.

Further, the solder wettability and solder resistance of the electrode film were evaluated by a dipping method using Pd / Ag eutectic solder containing 3% of Ag. The solder wettability evaluation conditions are a temperature of 230 ± 5 ° C., a time of 4 ± 1 seconds, good (OK) if the terminal electrode part is covered by 90% or more of the solder, and poor (NG) if it is less than that. ). The soldering resistance evaluation conditions were a temperature of 270 ± 5 ° C., a time of 10 ± 5 seconds, and good (OK) if the solder nick of the terminal electrode portion was less than 25%, and bad (>). NG).

The results are summarized in Table 2. Those marked with * in the sample column indicate that the sample is outside the scope of the present invention.

[0056]

[Table 2]

From the results shown in Table 2, in the samples using the conductive pastes C to E of the present invention, the fixing strength and the tensile strength of the terminal electrode are large, no film peeling due to stress occurs, and the plating resistance is high. It is understood that all of the properties, solder wettability, and solder resistance are good, and an extremely excellent electrode film can be obtained as a terminal electrode of a laminated ceramic capacitor.

On the other hand, in the samples A and B using the conductive pastes A and B, the amount of In ₂ O ₃ added was larger than the range of the present invention, and therefore, compared with those in the range of the present invention. The effect of improving the adhesive strength was not particularly observed, but on the other hand, it was found that the solder wettability was poor.

Sample F using conductive pastes F and G
In the case of G, the adhesive strength and the tensile strength were insufficient, the occurrence of electrode film peeling was observed, and it was found that the adhesive strength was inferior because the amount of In ₂ O ₃ added was less than the range of the present invention. Furthermore, it was also inferior in solder resistance.

Sample C using the conductive paste of the present invention
It was also confirmed that each of the electrode films of to E had good appearance and no defects such as voids in the electrode film, and the electric characteristics of the capacitor were good and stable.

[0061]

As described above in detail, according to the present invention, A
In ₂ as a glass frit in g-Pd conductive paste
By adding O ₃ and containing In, the adhesive strength with a base such as a dielectric porcelain is increased, and a conductive paste is obtained that can be obtained as a conductive film that does not peel off from the base even when an external force is applied. I was able to.

Further, according to the present invention, the appearance shape is good,
It was possible to provide a conductive paste that can obtain a conductive film having excellent resistance to electroplating.

Further, when the conductive paste of the present invention is used for forming a terminal electrode of a laminated ceramic capacitor, for example, the external shape is good, the adhesive strength with the dielectric ceramic and the resistance to electrolytic plating are excellent, and It also has excellent solder wettability and heat resistance, and it has no defects such as voids in the electrode film, and has good sealing properties against the plating solution.This prevents peeling due to external stress. As a result, it was possible to obtain a laminated porcelain capacitor with stable characteristics against electrolytic plating or soldering.

Claims (1)

[Claims] 1. 70 to 98% by weight (excluding 98% by weight) of Ag powder, 0 to 28% by weight (excluding 0% by weight) of Pd powder, and 2 to 11% by weight of glass frit. The composition of the glass frit is 15 to 40% by weight of PbO, 40 to 70% by weight of Bi ₂ O ₃ and 0 to 1
5% by weight (except 0% by weight) of SiO ₂ and 0-2
0% by weight (excluding 0% by weight) B ₂ O ₃ and 5-1
An electrically conductive paste comprising 0% by weight of In ₂ O ₃ .