JP6769208B2 - Lead-free conductive paste - Google Patents

Description

The present invention relates to a lead-free conductive paste, and more particularly to a lead-free conductive paste used as a material for a conductor formed on a ceramic substrate of an electronic component such as a chip resistor.

As a material for a thick film conductor formed by using the thick film technique, a conductive paste in which a highly conductive conductive powder is dispersed in an organic vehicle together with an oxide powder such as glass frit is generally used. When forming this thick film conductor, the conductive paste is applied to a substrate made of ceramic such as alumina in a desired pattern shape by a coating method such as screen printing, and then fired at 700 to 900 ° C. to make the thickness thicker. The film conductor can be formed on the ceramic substrate.

As the above-mentioned conductive powder, powders having a particle size of 10 μm or less, such as Au, Ag, Pd, and Pt having high conductivity that can be fired in an air atmosphere, are used, and among these, relatively inexpensive Ag powder is used. And Pd powder are mainly used. Further, in order to realize further cost reduction, a conductive paste using Cu has also been proposed. In the conductive powder for such a conductive paste, a fine conductive powder having a particle size of 0.5 μm or less is used for the purpose of thinning or thinning, but the powder tends to aggregate as it becomes finer. Therefore, it is required to improve the dispersibility in order to prevent this and obtain a dense and low resistance conductive film. On the other hand, glass frit generally has a particle size of 1 μm or more in lead borosilicate glass powder or lead aluminoborosilicate glass powder because it is easy to control the softening point and has high chemical durability. Things are used.

In recent years, from the viewpoint of preventing environmental pollution, lead-free electronic components are rapidly advancing, and the adoption of glass frit containing no Pb is required for the above conductive paste. In response to such problems, for example, in Patent Document 1, a conductive paste containing silver powder, glass frit and an organic vehicle as main components, wherein the glass frit is an alkali metal, Bi ₂ O ₃ , SiO ₂ , BaO ₃ , ZnO, Al ₂ O ₃ , and B ₂ O ₃ , and a conductive paste characterized by containing no PbO is disclosed. Further, in Patent Document 2, an oxide powder containing a conductive powder, a SiO _2- B ₂ O _3- Al ₂ O _3- CaO-based glass powder, an Al ₂ O ₃ powder, and a β eucryptite powder is used. A composition for forming a thick film conductor, which is characterized by having and substantially free of lead, is disclosed.

Japanese Patent No. 3964342 Japanese Unexamined Patent Publication No. 2013-122864

As mentioned above, various conductive pastes that do not contain Pb have been proposed, but they are still not sufficient in terms of practical use and cost, and conductive pastes that can be thinned or thinned have been mass-produced. It is hard to say that there is. That is, the conductive paste disclosed in Patent Document 1 has a high softening point of glass of 700 to 900 ° C., which is close to the firing temperature used for electronic parts, and therefore, a conductive film formed by firing at the same temperature. It is considered that the glass cannot be sufficiently melted and the adhesion to the substrate becomes insufficient.

It is described that the composition for forming a thick film conductor disclosed in Patent Document 2 can form a thick film conductor with less solder biting and excellent acid resistance. However, when the content of the conductive powder in the composition is reduced to, for example, 60% by mass or less of the total amount of the conductive paste for cost reduction, the density of the conductive powder in the paste decreases and the particles are sintered together. Is hindered and voids increase, making it difficult to form low resistance conductors. Further, the adhesion and acid resistance may be lowered.

The present invention has been made in view of the above-mentioned circumstances of the conventional lead-free conductive paste, and has the same performance as the conventional conductive paste as an application for electronic parts without containing a lead component that may cause environmental pollution. The purpose is to provide a lead-free and alkali metal-free conductive paste that is suitable for thinning and thinning, and that can reduce the amount of precious metal used and reduce costs. ..

As a result of diligent research to solve the above problems, the present inventor uses a conductive powder satisfying a predetermined condition in a conductive paste containing a conductive powder, a glass frit, and an organic vehicle as main components. As a result, a thin, dense and low-resistance conductive film can be obtained after firing, so that the same conductive characteristics as the conventional one can be realized with a smaller amount of the conductive component than the conventional one, and thinning and thinning are also possible. It was found that the present invention was completed.

That is, the first lead-free conductive paste of the present invention is a conductive paste containing conductive powder, lead-free glass frit, and an organic vehicle as main components, and the conductive powder has an SEM average particle size of 0. The median diameter D50 of the volume integration measured by the laser diffraction scattering method is 0.1 μm or more and 1.0 μm or less, and the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml. / 100 g or less, 40% by mass or more and 60% by mass or less with respect to 100% by mass of the conductive paste, and 100% by mass of the conductive powder is Pd fine powder having an SEM average particle size of 0.01 μm or more and less than 0.1 μm. It is characterized in that it is further contained in an amount of 0.1% by mass or more and 3.0% by mass or less .
The second lead-free conductive paste of the present invention is a conductive paste containing conductive powder, lead-free glass frit, and an organic vehicle as main components, and the conductive powder has an SEM average particle size of 0. It is .1 μm or more and 1.0 μm or less, the median diameter D50 of the volume integration measured by the laser diffraction scattering method is 0.1 μm or more and 2.0 μm or less, and the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml. / 100 g or less, 40% by mass or more and 60% by mass or less with respect to 100% by mass of the conductive paste, and the glass frit contains 5% by mass or more of SiO ₂ when the total amount of the glass frit is 100% by mass. The main components are 30% by mass or less, B ₂ O ₃ is 9% by mass or more and 20% by mass or less, Al ₂ O ₃ is 5% by mass or more and 20% by mass or less, and Bi ₂ O ₃ is 30% by mass or more and 70% by mass or less. It is a SiO _2- B ₂ O _3- Al ₂ O _3- Bi ₂ O ₃ based glass composed of the same material, and further contains ZrO ₂ in an amount of 0.1% by mass or more and 5% by mass or less, and contains PbO and an alkali metal. It is not included and is characterized in that the softening point is 550 ° C. or higher and 700 ° C. or lower.
The third lead-free conductive paste of the present invention is a conductive paste containing conductive powder, lead-free glass frit, and an organic vehicle as main components, and the conductive powder has an SEM average particle size of 0. The median diameter D50 of the volume integration measured by the laser diffraction / scattering method is 0.1 μm or more and 1.0 μm or less, and the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml. It is / 100 g or less, and is contained in an amount of 40% by mass or more and 60% by mass or less with respect to 100% by mass of the conductive paste. It is characterized in that it is 0.1 μm or more and 1.0 μm or less, and the volume particle size distribution width index SD is 0.3 μm or less.

In the lead-free conductive paste of the present invention described above, it is preferable that the conductive powder is at least one of Au, Ag, Cu, Pd and Pt .

According to the present invention, since it is possible to form a dense and low-resistance conductive film, it is possible to obtain almost the same characteristics as the conventional one even if the conductor is formed thinner or thinner than the conventional one. It will be possible. Therefore, it is possible to reduce the amount of the conductive powder made of an expensive precious metal used for wiring and the like, and as a result, the cost of electronic parts can be suppressed. In addition, not only can electronic components be made thinner and smaller, but also alkali metal is not required, so when used as a top electrode of a chip resistor, for example, the effect on the temperature characteristics of the resistor can be reduced. it can.

It is an SEM photograph of the conductive film made by the conductive paste of the Example of this invention. It is an SEM photograph of a conductive film produced by the conductive paste of the comparative example of this invention. It is a graph which plotted the relationship between the time of immersing the conductive film prepared by the conductive paste of the Example of this invention in a cutting oil containing sulfur, and the area resistance value thereof.

<Conductive powder>
Hereinafter, a lead-free conductive paste of a specific example of the present invention will be described in detail. The lead-free conductive paste of one specific example of the present invention contains conductive powder, lead-free glass frit, and an organic vehicle as main components. Of these, the conductive powder is composed of a group of substantially spherical conductive particles, has an SEM average particle size of 0.1 μm or more and 1.0 μm or less, and has a volume integration medium diameter D50 of 0.1 μm or more and 2.0 μm. It is as follows. In the present specification, the SEM average particle diameter is an average value of the particle diameters of any plurality of conductive particles obtained by image analysis of a scanning electron microscope. The medium diameter D50 is the median diameter of the volume integration of the conductive powder measured by using the laser explanatory scattering method.

When the SEM average particle size or the medium diameter D50 is less than 0.1 μm, the conductive powder tends to aggregate, and it becomes difficult to obtain the conductive powder having excellent dispersibility. Further, when the conductive paste is produced, the handleability of the conductive powder is deteriorated and it becomes difficult to handle. Further, the sintering start temperature becomes too low, and the conductor obtained by firing the conductive paste using the sintering start temperature may not be able to maintain the desired pattern shape. On the contrary, when the SEM average particle size is larger than 1.0 μm or the medium diameter D50 is larger than 2.0 μm, the sinterability of the conductive powder is inferior, and it becomes difficult to form a dense conductor after firing. Sufficient continuity may not be obtained.

In addition, the conductive powder has an absorption amount of dibutyl phthalate measured in accordance with JIS K6217-4 of 4 ml / 100 g or more and 8 ml / 100 g or less. When the absorption amount of this conductive powder is less than 4 ml / 100 g, the conductive powder may be packed very densely, but the dispersibility tends to decrease, and the conductive powder agglomerates before the sintering process. Will easily progress and form huge aggregates. As a result, the density of the conductive powder varies during firing, and the conductor formed by the firing may have insufficient conductivity.

On the other hand, when this absorption amount is more than 8 ml / 100 g, it means that there are many voids between the conductive particles, which means that the conductive powder is already agglomerated or the conductive particles having a distorted shape are present. When this conductive powder is used as a conductive paste, the fluidity is impaired. Further, when the conductive powder is agglomerated a lot, the sinterability is inferior, so that a dense conductive film cannot be obtained, it becomes difficult to obtain sufficient conductivity, and the adhesion strength and acid resistance may be lowered.

The conductive paste of one specific example of the present invention contains the above conductive powder in a range of 40% by mass or more and 60% by mass or less with respect to 100% by mass of the conductive paste. When this content is less than 40% by mass, the amount of the conductive powder is too small, and it becomes difficult to form a dense conductor having a thickness of 5 μm or less. On the contrary, when it is more than 60% by mass, it is necessary to print the coating thickness of the conductive paste very thinly in order to form a film having a thickness of 5 μm or thinner, and the film thickness is thin in such a small coating amount. Since it is also necessary to suppress the variation in the film thickness, high-precision printing technology and coating equipment are required, and the manufacturing cost is high. Further, since the amount of reduction of the expensive conductive powder is reduced, it becomes difficult to obtain the cost merit.

The conductive powder contained in the conductive paste of one specific example of the present invention preferably contains one or more of the group consisting of Au, Ag, Cu, Pd and Pt exhibiting high conductivity as a main component. Of these five types of metals, Cu is the cheapest, but since it is easily oxidized, an oxidation resistance treatment step or the like is required, which increases the man-hours. Therefore, among the remaining metals, Ag powder or Pd, which is relatively inexpensive, is used. It is preferable to use a powder, and it is more preferable to contain Ag powder in an amount of 95% by mass or more in 100% by mass of the conductive powder.

In the conductive paste of one specific example of the present invention, Pd fine powder finer than the conductive powder may be added separately from the conductive powder, whereby the effect of suppressing sulfurization of the conductor can be obtained. In this case, the amount of the Pd fine powder added is preferably 0.1% by mass or more and 3.0% by mass or less with respect to 100% by mass of the conductive powder. If this amount is less than 0.1% by mass, the effect of sulfidation resistance becomes insufficient, which is not preferable. On the contrary, even if more than 3.0% by mass is added, the sulfide resistance effect is not further improved, but rather the sintering of the above-mentioned main component conductive powder is hindered and the resistance value of the conductor is increased. In addition, the cost merit is reduced by the amount of Pd fine powder added, which is not preferable. The Pd fine powder preferably has an SEM average particle size of 0.01 μm or more and less than 0.1 μm. If the particle size is less than 0.01 μm, agglomeration of Pd fine powder is likely to occur, the composition of the film may become non-uniform, and the characteristics may vary. On the contrary, if the particle size is 0.1 μm or more, the sinterability is lowered. In some cases.

<Glass frit>
The glass frit used in the conductive paste of one specific example of the present invention contains SiO ₂ of 5% by mass or more and 30% by mass or less, B ₂ O ₃ of 9% by mass or more and 20% by mass or less, and Al ₂ O ₃ of 5% by mass. It is a SiO _2- B ₂ O _3- Al ₂ O _3- Bi ₂ O ₃ system glass composed of 20% by mass or less and Bi ₂ O ₃ is 30% by mass or more and 70% by mass or less. It is preferable that ZrO ₂ is contained in an amount of 0.1% by mass or more and 5% by mass or less, PbO and an alkali metal are not contained, and the softening point is 550 ° C. or more and 700 ° C. or less.

If the amount of SiO ₂ contained in the glass frit is less than 5% by mass, the acid resistance of the conductor obtained by firing the conductive paste containing the same may decrease, which is not preferable. On the contrary, when it is more than 30% by mass, the softening point of the conductive paste containing it becomes too high, the glass frit may not be sufficiently softened at the time of firing, and the adhesion strength may be lowered, which is not preferable.

When B ₂ O ₃ contained in the glass frit is less than 9% by mass, the fluidity of the glass component is lowered, the glass component does not sufficiently reach the interface between the conductor and the substrate during firing, and the conductor adheres. It is not preferable because the property and acid resistance may decrease. On the other hand, if it is more than 20% by mass, the glass frit becomes easily dissolved in water, and the acid resistance of the conductor obtained by firing the conductive paste containing the glass frit may decrease, which is not preferable.

When the amount of Al ₂ O ₃ contained in the glass frit is less than 5% by mass, the glass component is likely to crystallize, and the crystallized glass component has low adhesion strength with the substrate. It is not preferable because the adhesion strength of the obtained conductor may be low. On the contrary, if it is more than 20% by mass, the softening point may be high, which is not preferable.

When Bi ₂ O ₃ contained in the glass frit is less than 30% by mass, the softening point of the conductive paste containing the Bi ₂ O ₃ may be high, which is not preferable. On the contrary, when it is more than 70% by mass, the softening point of the conductive paste becomes too low, and the conductor obtained by firing the conductive paste containing this may be remelted at the time of reflow, which is not preferable.

When ZrO ₂ contained in the glass frit is less than 0.1% by mass, the effect of improving the acid resistance of the conductive paste containing the ZrO ₂ may not be obtained, which is not preferable. On the contrary, even if it is more than 5% by mass, not only the effect of improving the acid resistance of the conductive paste containing this is hardly changed, but also the content of other components is relatively lowered, so that the conductive paste This is not preferable because the adhesion strength and acid resistance of the paste may decrease.

If the softening point of the glass frit is lower than 550 ° C., after the conductive powder is sintered, the glass component may flow out from the sintered conductor onto the substrate, causing problems such as deterioration of adhesion. It is not preferable because it exists. On the contrary, when the softening point is higher than 700 ° C., the temperature is too high and the interface bonding between the conductor and the substrate does not proceed sufficiently, the adhesion strength is lowered, or the glass component having low fluidity at the time of sintering is the conductive powder. It is not preferable because it may hinder sintering or reduce the denseness of the conductor obtained by firing and increase the resistance value.

In the glass frit, the volume integration medium diameter D50 measured by the laser diffraction scattering method is 0.1 μm or more and 1.0 μm or less, and the volume particle size distribution width index SD obtained by the following formula 1 is 0.3 μm or less. Is preferable.
[Equation 1]
SD = (D84-D16) / 2

Here, D84 and D16 are particles at points where the volume particle size distribution cumulative curves are 84% and 16%, respectively, when the volume particle size distribution cumulative curve is obtained with the total volume of the particle groups sampled as the measurement target as 100%. Indicates the diameter (μm). When the SD is larger than 0.3 μm, it means that the proportion of coarse particles having a particle size of more than 1.3 μm increases, and the increase of the coarse particles hinders the sintering of the conductive paste and is used in firing. It is not preferable because the number of voids generated in the obtained conductor may increase and the adhesion and acid resistance may decrease.

The glass frit is preferably contained in the conductive paste in an amount of 0.1% by mass or more and 5% by mass or less. If this content is less than 0.1% by mass, it may be difficult for the glass to spread on the joint surface between the conductor and the substrate, and sufficient adhesion may not be obtained. On the contrary, if it exceeds 5% by mass, the ratio of the conductive powder becomes too small, the area resistance value of the fired conductor becomes high, and it becomes difficult to form an electroplating film on the fired conductor, which is not preferable. During the glass frit, CaO, BaO, ZnO, TiO ₂ , V ₂ O for the purpose of improving the wettability between the glass and the substrate, improving the adhesion between the substrate and the conductive film, and further improving the oxidation resistance of the conductive film. Ingredients such as ₅ may be added up to a total of 3% by mass.

<Organic vehicle>
As the organic vehicle used in the conductive paste of one specific example of the present invention, a conventional cellulose derivative such as ethyl cellulose or an acrylic resin such as methacrylate dissolved in an organic solvent such as tarpineol or butyl carbitol can be used. The amount of the organic vehicle to be blended is not particularly limited, and an amount suitable for printing may be added in the same blending amount as before.

Hereinafter, the present invention will be further described with reference to Examples, but the scope of the present invention is not limited by these Examples.

1. 1. Main Raw Materials (1) Conductive Powder As conductive powder, four types of Ag powders A, B, C and D having different sizes were prepared. The average particle size of each SEM of these four types of Ag powder is the maximum in the lateral direction with respect to any 500 of the Ag powder imaged using a scanning electron microscope (JSM-6360L manufactured by JEOL Ltd.). It was calculated by measuring the length as a diameter and arithmetically averaging them. The medium diameter D50 is a volume integrated medium diameter D50 measured using a laser diffraction / scattering type particle size distribution measuring device (MICROTRAC HRA 9320X-100 manufactured by Nikkiso Co., Ltd.). The absorption amount was measured according to JIS K6217-4 (2008) using an absorption amount measuring device (manufactured by Asahi Research Institute, S-500). These values are shown in Table 1 below.

(2) Glass frit As the glass frit, seven types of SiO _2- B ₂ O _3- Al ₂ O _3- Bi ₂ O ₃ system lead-free glass frit a, b, c, d, e, f and g having different compositions are used. I prepared it. These 7 types of glass frit contain 4 types of oxides SiO ₂ , B ₂ O ₃ , Al ₂ O ₃ and Bi ₂ O ₃ as essential additives as main components, and ZrO ₂ , CaO and BaO in addition. Contains one or more of these as sub-ingredients. The medium diameter D50 of these seven types of glass frit was measured in the same manner as the above-mentioned conductive powder, and the volume particle size distribution width index SD was measured based on the above-mentioned formula 1. Further, the softening point was measured according to JIS R3103-1. The measurement results are shown in Table 2 below together with the composition.

2. Preparation of Conductive Paste The conductive pastes of Samples 1 to 19 were prepared by changing the combination of the above four types of Ag powder, Pd fine powder, and seven types of glass frit. Specifically, first, 80% by mass of tarpineol and 20% by mass of ethyl cellulose were mixed to prepare an organic vehicle. Next, when the total amount of the conductive paste is 100% by mass, the addition amounts of one Ag powder selected from the above four types and the Pd fine powder having an SEM average particle size of 0.02 μm are shown in Tables 3 and 4. The amount of glass frit selected from 7 types is 1.0% by mass, and the balance is weighed so that it becomes the above organic vehicle, and 3 roll mills (Buehler stock) are used. A conductive paste of each sample was prepared by mixing using SDY-300) manufactured by the company.

3. 3. Evaluation of various characteristics (3-1) Evaluation of conductivity (area resistance value)
The conductor pastes of Samples 1 to 13 prepared above are printed on a 96% alumina substrate using a screen printing machine so as to form a conductor pattern having a width of 0.5 mm and a length of 50 mm, and a belt-type drying furnace is used. After drying at 150 ° C. for 5 minutes, the film was fired at a peak temperature of 850 ° C. for 9 minutes for a total of 30 minutes using a belt furnace to form a conductor film for evaluation on an alumina substrate. The thickness of the obtained conductor film was measured using a stylus type surface roughness meter (SURFCOM 480A, manufactured by Tokyo Seimitsu Co., Ltd.).

Next, the resistance value (Rt) of the conductor film was measured using a digital multimeter (manufactured by ADVANTEST Co., Ltd., R6781E), and the thickness (t), width (W), and length of the conductor film measured above were measured. From (L), the area resistance value (Rs) when converted to a film thickness of 5 μm was calculated from the following formula 2 and the conductivity was evaluated.
[Equation 2]
Rs = Rt × W / L × t / 5

(3-2) Adhesion evaluation (adhesion strength)
The conductive pastes of Samples 1 to 13 were printed on a 96% alumina substrate so as to have a square shape of 2 mm in length × 2 mm in width and a thickness of 5 μm after firing, and under the same conditions as in the case of the above-mentioned conductivity evaluation. Heat treatment was performed to prepare a conductor film for evaluation of adhesion. Next, electroplating is performed for 2 minutes at a current density of 5 × 10 ^-3 A / mm ² using a plating solution prepared by adding water to 280 g of nickel sulfate, 60 g of nickel chloride, and 40 g of boric acid to make a total amount of 1 L. A nickel plating film was formed on the conductor film having a length of 2 mm and a width of 2 mm.

A Sn-plated copper wire having a diameter of 0.65 mm was soldered onto the obtained nickel-plated film using a lead-free solder having a composition of 96.5 mass% Sn-3 mass% Ag-0.5 mass% Cu. Using a load measuring device (MODEL 2152HTP manufactured by Aiko Engineering Co., Ltd.), pull the alumina substrate at a speed of 80 mm / min in the vertical direction, measure the maximum load until the conductor film peels off from the substrate, and measure the maximum load. Adhesion was evaluated as the initial adhesion strength.

(3-3) Acid resistance evaluation (adhesion strength)
A conductor film was prepared on a 96% alumina substrate using the conductive pastes of Samples 1 to 13 in the same manner as in the case of the above adhesion evaluation. This was immersed in 5% sulfuric acid at a liquid temperature of 25 ° C. for 5 minutes, then taken out, washed, and sufficiently dried to prepare a conductor film for acid resistance evaluation. Nickel plating and Sn-plated copper wire were soldered onto the conductor film for acid resistance evaluation in the same manner as in the case of adhesion evaluation described above, and the adhesion strength was measured in the same manner to evaluate acid resistance. .. Table 3 below shows the types and amounts of Ag powder added, the amount of Pd fine powder added, and the types of glass frit using the evaluation results of the above conductivity evaluation, adhesion evaluation, and acid resistance evaluation. Further, SEM photographs of the surfaces of the conductor film prepared from the conductive pastes of Sample 1 and Sample 11 are shown in FIGS. 1 and 2, respectively.

(3-4) Sulfurization resistance evaluation (adhesion strength)
For the conductive pastes of Samples 14 to 19, a conductive film for evaluation of sulfurization resistance was prepared in the same manner as in the case of the above-mentioned evaluation of conductivity. Sulfidation resistance evaluation, the acceleration evaluation by soaking the Kakushirube film in cutting oil retained sulfur (S) in 80 ° C. containing 0.3 mass%, and before immersion area resistance value R _S0, dipping after 1 hour from the start, after 2 hours passed, and the sheet resistance after 3 hours have passed R _{S1, R S2,} and was calculated in the same manner as the R _S3 conductivity evaluation. The evaluation results are shown in Table 4 below together with the type and amount of Ag powder added, the amount of Pd fine powder added, and the type of glass frit. Further, FIG. 3 shows a graph plotting the relationship between the immersion time and the area resistance value.

4. Evaluation Results The conductor film prepared from the conductive pastes of Samples 1 to 10 satisfying the requirements of the present invention has sufficient adhesion with an initial adhesion strength of 20.9 N or more, and is as thin as 3.7 to 5.1 μm. It can be seen that despite the film thickness, the area resistance value is 8.7 mΩ / □ or less, which is sufficient conductivity. In particular, the conductive pastes of Samples 1, 3, 5, and 6 using a glass frit having a preferable composition and having an appropriate amount of Ag added to the conductive powder have an extremely high adhesion with an initial adhesion strength of 42.3 N or more. In addition, the area resistance value was 6.7 to 6.9 mΩ / □ at a thickness of 3.9 to 4.1 μm, showing good conductivity. In addition, these samples obtained extremely high adhesion strength of 23.7 to 28.4N in the acid resistance evaluation.

Furthermore, from the results of Sample 1 and Sample 3, it was confirmed that when Pd fine powder was added within the range of the present invention, there was no significant difference in conductivity, adhesion and acid resistance. Further, from the results of Sample 2 and Sample 3, it was confirmed that when the addition amount of Ag powder, which is a conductive powder, is small, the conductor film forming ability is inferior, the area resistance value is increased, and the initial strength and the adhesion strength are also lowered. .. On the other hand, from the results of Sample 3 and Sample 4, when the amount of Ag powder, which is a conductive powder, is increased, it becomes slightly difficult to make the conductor film sufficiently thin, and even if the amount of Ag powder added is further increased, the area resistance It was confirmed that the effects of improving the value, initial strength, and adhesion strength were almost saturated.

Further, from the results of Sample 3 and Sample 7, it was confirmed that the adhesion and acid resistance were lowered by increasing the diameter of the glass frit out of the preferable range. Further, from the results of Sample 3 and Samples 8 to 10, it was confirmed that the adhesiveness was lowered because a part of the composition of the glass frit was out of the preferable range. In particular, Samples 9 and 10 in which B ₂ O ₃ and ZrO _{2 which} are effective in acid resistance are less than the preferable range are inferior in acid resistance, so they should be used for products that are not treated with an acidic liquid such as plating. It was confirmed that it was preferable. Further, from the results of Samples 14 to 19, it was confirmed that the sulfurization resistance effect can be obtained by adding the Pd fine powder. It was confirmed that the effect was almost saturated when the amount of Pd fine powder added was 3.0% by mass with respect to the amount of Ag added of 100% by mass.

The conductive pastes of the samples 11 to 13 that do not meet the requirements of the present invention have an area resistance value of 15.0 mΩ / □ or more, which is sufficient because the shape of the conductive powder is too large or the amount of absorption is too large. It can be seen that conductivity is not obtained. In particular, it was confirmed that the conductive paste of Sample 11 using Ag powder having an SEM average particle size too large has a high area resistance value and is significantly inferior in adhesion because the Ag powder cannot be sufficiently sintered.

Regarding the conductive paste of Sample 11, the adhesion strength was so low that it could not be measured in the adhesion evaluation, so the acid resistance was not evaluated. The Ag powder of the conductive paste of Sample 12 has an appropriate SEM average particle size, but the particle size of D50 is large, so that it is considered that a lot of aggregation occurs. Therefore, it is considered that many gaps are generated and voids are involved, resulting in poor adhesion and acid resistance.

The Ag powder used for the conductive paste of sample 13 in which the SEM particle size and the particle size of D50 are appropriate but the absorption amount is too high has been conventionally judged to be a preferable conductive powder, but it is different from a liquid such as the absorption amount evaluation. It is considered that many gaps are formed by cross-linking in a mixed state. Therefore, it is considered that sufficient values could not be obtained in any of the conductivity, adhesion, and acid resistance. It can be seen that the conductive film of FIG. 1 is formed more densely than the conductive film of FIG.

When each of Au powder, Cu powder, Pd powder, and Pt powder was used instead of Ag powder as the conductive powder, the same evaluation as above was performed. As long as the requirements of the present invention are satisfied, the above In all of the above evaluation items, the same results as in the case of the above Ag powder were obtained.

Claims (4)

A conductive paste containing a conductive powder, a lead-free glass frit, and an organic vehicle as main components. The conductive powder has an SEM average particle size of 0.1 μm or more and 1.0 μm or less, and is subjected to a laser diffraction scattering method. The median diameter D50 of the volume integration measured using the above is 0.1 μm or more and 2.0 μm or less, and the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml / 100 g or less, based on 100% by mass of the conductive paste. Pd fine powder containing 40% by mass or more and 60% by mass or less and having an SEM average particle size of 0.01 μm or more and less than 0.1 μm is 0.1% by mass or more and 3.0% by mass with respect to 100% by mass of the conductive powder. A lead-free conductive paste, which is further contained below . A conductive paste containing a conductive powder, a lead-free glass frit, and an organic vehicle as main components. The conductive powder has an SEM average particle size of 0.1 μm or more and 1.0 μm or less, and is subjected to a laser diffraction scattering method. The median diameter D50 of the volume integration measured using the above is 0.1 μm or more and 2.0 μm or less, the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml / 100 g or less, and the conductive paste is 100% by mass. are contained 40 wt% to 60 wt% or less, the glass frit, when the glass frit total volume of 100 wt%, SiO ₂ is 30 mass% or more and 5 mass% or _less, B 2 _{O 3} is 9% by weight or more 20 wt% or less, _Al 2 _{O 3} is 20 mass% or more and 5 mass% or less, _Bi 2 _{O 3} is formed of a material mainly containing less than 70 mass% 30 mass% _SiO 2 _-B 2 _{O 3} - Al ₂ O _3- Bi ₂ O ₃ glass, further containing ZrO ₂ in an amount of 0.1% by mass or more and 5% by mass or less, not containing PbO and alkali metals, and having a softening point of 550 ° C or more and 700 ° C or less. A lead-free conductive paste characterized by that. A conductive paste containing a conductive powder, a lead-free glass frit, and an organic vehicle as main components. The conductive powder has an SEM average particle size of 0.1 μm or more and 1.0 μm or less, and is subjected to a laser diffraction / scattering method. The median diameter D50 of the volume integration measured using the above is 0.1 μm or more and 2.0 μm or less, and the absorption amount of dibutyl phthalate is 4 ml / 100 g or more and 8 ml / 100 g or less, based on 100% by mass of the conductive paste. The glass frit is contained in an amount of 40% by mass or more and 60% by mass or less , and the volume integrated medium diameter D50 measured by the laser diffraction / scattering method is 0.1 μm or more and 1.0 μm or less, and the volume particle size distribution width. A lead-free conductive paste having an index SD of 0.3 μm or less . The lead-free conductive paste according to any one of claims 1 to 3, wherein the conductive powder is at least one of Au, Ag, Cu, Pd and Pt.