TW201330953A - Sintering type conductive paste - Google Patents

Abstract

Provided is a micro-particle silver powder which can copy with thinning of electrode or circuit, which is a novel silver powder having a low thermal shrinkage rate at 500 DEG C. The present invention provides a sintering type conductive paste characterized by containing 30 ppm to 1000 ppm of Si.

Description

Silver powder for sintered conductive paste

The present invention relates to a silver powder suitable for use in a sintered conductive paste, and particularly relates to a silver powder which can be applied to a sintered conductive paste for a solar cell electrode.

The conductive paste is a fluid composition in which a conductive filler is dispersed in a vehicle containing a resin binder and a solvent, and is widely used for formation of an electric circuit and formation of an external electrode of a ceramic capacitor.

Such a conductive adhesive is a resin-hardened type in which a conductive filler is pressed by curing of a resin to ensure conduction, and a sintered type in which an organic component is volatilized by high-temperature sintering and a conductive filler is sintered to ensure conduction.

Among them, the sintered conductive paste is generally a paste composition in which a conductive filler (metal powder) and a glass frit are dispersed in an organic vehicle, and the organic vehicle liquid is volatilized by sintering at 400 to 800 ° C. The conductive filler is sintered to ensure conduction. At this time, the glass frit has a function of adhering the conductive film to the substrate, and the organic vehicle serves as an organic liquid medium for making the metal powder and the glass frit a printable.

In the silver powder used in the sintered conductive paste, for example, Patent Document 1 discloses that an aqueous solution containing a reducing agent is added to an aqueous reaction system containing silver particles to reduce and precipitate silver particles, thereby obtaining 500. The heat shrinkage ratio at ° C is 5 to 15%, the heat shrinkage ratio at 600 ° C is 10 to 20%, the average particle diameter D ₅₀ is 5 μm or less, the tap density is 2 g/cm ³ or more, and the BET specific surface area is 5 m. Spherical silver powder below ² /g.

Patent Document 2 proposes a silver powder having a heat shrinkage ratio of from 4 to 15% at 410 ° C, preferably from 10 to 20% at 500 ° C, specifically, the average particle diameter D ₅₀ It is 2 μm or less.

In recent years, in order to reduce the thickness of the electrode or the circuit, the silver powder used in the sintered conductive paste is generally a silver powder which requires fine particles and has a sharp particle size distribution. Therefore, a new technology corresponding to this has been proposed.

For example, in the patent document 3 (JP-A-2005-48237), it is proposed to add an alkali or a complex compound to an aqueous solution containing a silver salt, and to add a hydroquinone or the like to the aqueous solution containing the silver complex compound. The phenol is used as a reducing agent to reduce and precipitate the micronized highly dispersible spherical silver powder of 0.6 μm or less, thereby obtaining fine silver powder, and it is proposed to obtain a fine particle silver powder having a monodisperse dispersity which is closer to the aggregation of the powder particles. The method.

Further, in Patent Document 4 (JP-A-2010-70793), it is proposed to mix an aqueous solution of silver nitrate with ammonia water and react it to obtain an aqueous solution of an ammonia silver complex, which is a particle of a seed nucleus and an imine compound. In the presence of the ammonia silver complex solution aqueous solution and the reducing agent aqueous solution, the silver particles are reduced and precipitated, thereby obtaining spherical silver powder having an average particle diameter of 0.1 μm or more and less than 1 μm, and having a sharp particle size distribution and high dispersibility. The method.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2006-2228

Patent Document 2: Japanese Laid-Open Patent Publication No. 2007-270334

Patent Document 3: Japanese Laid-Open Patent Publication No. 2005-48237

Patent Document 4: Japanese Laid-Open Patent Publication No. 2010-70793

The conductive adhesive is sintered at different temperatures depending on the substrate to be coated or the application used. When the conductive filler at the sintering temperature, that is, the thermal shrinkage of the silver powder is inferior to the substrate, the substrate ( There is a possibility that peeling or warpage, deformation, cracking, or the like is likely to occur between the substrate and the silver film. In particular, when the silver powder is fine particles, the heat shrinkage ratio tends to increase, so that the difference in heat shrinkage action between the substrate (substrate) and the silver powder becomes large, and peeling between the substrate (substrate) and the silver film is more likely to occur. , warping or deformation, cracking, etc.

In a crystalline germanium type solar cell, an n-type diffusion layer is formed on a tantalum substrate (p type) to form a pn junction, and an oxide film is interposed on the inner surface side of the tantalum substrate (p type) and an inner surface electrode is laminated, and The anti-reflection film is laminated on the photosensitive surface side (surface side) of the n-type diffusion layer, and the silver paste is printed and sintered to form a silver electrode. Considering the thermal destruction of the ruthenium substrate, the silver paste is generally sintered at around 500 ° C. An electrode is formed.

Accordingly, the present invention provides a fine-grained particulate silver powder which can be used for an electrode or a circuit, which is a new silver powder which has a low heat shrinkage rate at 500 ° C and can suppress a difference in heat shrinkage action between a substrate (substrate) and silver powder. Further, it is a silver powder which is applicable as a conductive filler in a sintered conductive paste, and is particularly suitable as a silver powder of a conductive filler in a sintered conductive paste for a solar cell electrode.

The present invention provides a silver powder for a sintered conductive paste characterized by containing cerium (Si) of 30 ppm to 1000 ppm.

The silver powder for a sintered conductive paste of the present invention contains cerium (Si) 30 ppm to 1000 ppm by adding a cerium (Si) compound, whereby not only fine silver powder can be produced, but also a shrinkage ratio of 15.0 at 500 ° C can be obtained. %the following. Therefore, the difference in heat shrinkage operation between the substrate (substrate) and the silver powder can be suppressed, so that it can be applied as a conductive filler used in the sintered conductive paste. Among them, since the shrinkage ratio at 500 ° C can be suppressed, it is particularly suitable as a conductive filler used for a sintered conductive paste for a solar cell electrode. However, the use of the silver powder for a sintered conductive paste proposed by the present invention is not limited to the use of a solar cell electrode.

Hereinafter, the present invention will be described based on examples of the embodiments of the present invention, but the present invention is not limited to the embodiments described below.

<本银粉>

The silver powder for a sintered conductive paste of the present embodiment (hereinafter referred to as "the present silver powder") is characterized by containing bismuth (Si).

Features of the invention are further described below.

(矽 content)

The silver powder preferably contains cerium (Si) of 30 ppm to 1000 ppm. When cerium is contained in this range, not only the BET specific surface area can be controlled in the range of 0.8 m 2 /g to 3.0 m 2 /g, but also the shrinkage ratio at 500 ° C can be made 15.0% or less.

From this point of view, the content of bismuth (Si) in the present silver powder is more preferably 40 ppm or more or 700 ppm or less, and particularly preferably 50 ppm or more or 600 ppm or less.

The method of adjusting the content of the bismuth (Si) of the present silver powder may be exemplified by adjusting the type and amount of the hydrazine compound added during the production process.

Further, the content of bismuth (Si) in the present silver powder is the content of cerium (Si) contained in the interior of the silver powder particles or physically or chemically adsorbed on the surface of the particles. Specifically, the amount of cerium (Si) remaining after sufficient washing of the filtrate after the silver powder is washed with pure water is 40 μS/cm or less. The ruthenium (Si) removed by this cleaning does not have the function of the sintering inhibitor and does not contribute to the heat shrinkage rate of the silver powder, and therefore must be removed from the bismuth (Si) content of the silver powder.

Therefore, the content of cerium (Si) in the silver powder is a content of cerium (Si) measured by a measuring apparatus after the conductivity of the filtrate obtained by washing the silver powder with pure water is sufficiently washed at 40 μS/cm or less.

(specific surface area)

The BET specific surface area (SSA) of the present silver powder is preferably from 0.8 m 2 /g to 3.0 m 2 /g.

When the BET specific surface area of the present silver powder is from 0.8 m 2 /g to 3.0 m 2 /g, it can be a silver powder which is applicable as a conductive filler of a sintered conductive paste, and particularly suitable for use as a sintered conductive material for a solar cell electrode. The silver powder of the conductive filler of the gel, which can correspond to the thinning of the electrode or the circuit.

Therefore, from this viewpoint, the BET specific surface area of silver powder is preferably 0.8m2 / g or more than 3.0m ² / g or less, which is more preferably 1.0m ² / g or more than 2.8m ² / g or less, which Laid Preferably, it is 2.65 m ² /g or less.

Further, the method of adjusting the BET specific surface area may be a method of adjusting the type and amount of the telluride added during the production process, or adjusting the concentration or amount of the silver nitrate aqueous solution, or adjusting the concentration or the amount of the reducing agent solution.

(particle shape)

The particle shape of the present silver powder is not particularly limited, but is preferably a spherical shape or a spherical shape. Further, as the conductive paste user, it is preferred to process the spherical particles or the spherical particles into flaky particles, and it is preferable that the spherical particles or the spherical particles and the flaky particles are used. Mixture.

(D50)

The D50 of the silver powder, that is, the D50 of the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement is preferably 0.50 μm to 1.50 μm.

If the D50 of the present silver powder is from 0.50 μm to 1.50 μm, fine lines can be easily formed when the conductive paste is printed.

Therefore, from this viewpoint, the D50 of the present silver powder is preferably 0.50 μm or more or 1.50 μm or less, more preferably 0.70 μm or more or 1.20 μm or less, and particularly preferably 0.90 μm or more.

The D50 may be adjusted by adjusting the type and amount of the telluride added during the manufacturing process, or adjusting the concentration or amount of the silver nitrate aqueous solution, or adjusting the concentration or amount of the reducing agent solution.

(heat shrinkage rate)

As described above, the present silver powder has a ruthenium substrate which is not caused by shrinkage of silver powder which is generated when sintering is performed at 500 ° C from the viewpoint of adhesion to a ruthenium substrate used in a solar cell. The shrinkage ratio of the present silver powder at 500 ° C is preferably 15.0% or less, more preferably 4.0% or more or 14.0% or less, and particularly preferably 12.0% or less.

In the present silver powder, the shrinkage ratio of the silver powder at 500 ° C can be adjusted by adjusting the type and amount of the telluride added during the production process.

<Method>

Next, a preferred method of producing the present silver powder will be described.

An example of the method for producing the present silver powder is a method in which a telluride is added and reduced before or after a reducing agent is added to a silver solution such as silver nitrate.

Specifically, the wrong agent can be added to silver nitrate or the like. After the silver aqueous solution is added, the hydrazine compound is added and stirred before or after the addition of the reducing agent, and then a dispersing agent may be added as needed, and the silver particles are reduced and precipitated while stirring, and then filtered, washed, and dried to produce This silver powder.

Here, the telluride may be a sulfonate such as a decane coupling agent or the like in addition to a citrate such as sodium citrate or potassium citrate. From the viewpoint of the effect of reducing the atomization and the heat shrinkage rate, it is preferably not cerium oxide (SiO2) but a ceric acid salt such as sodium citrate or potassium citrate.

Further, as the aqueous silver solution such as silver nitrate, an aqueous solution or slurry containing any one of silver nitrate, a silver salt complex and a silver intermediate can be used.

Further, examples of the complexing agent include ammonia water, an ammonium salt, a chelate compound, and the like.

Examples of the reducing agent include aqueous solutions containing ascorbic acid, sulfite, alkanolamine, hydrogen peroxide, formic acid, ammonium formate, sodium formate, glyoxal, tartaric acid, sodium hypophosphite, and boron hydride metal salts. , dimethylamine borane, hydrazine, hydrazine compound, hydroquinone, pyrogallol, glucose, gallic acid, formalin, anhydrous sodium sulfite, and rongalite.

Examples of the dispersant include a fatty acid, a fatty acid salt, a surfactant, an organic metal, a chelating agent, a protective colloid, and the like.

<Use>

The silver powder is suitable for use as a conductive paste, and is particularly suitable as a silver powder for a sintered conductive paste.

The sintered conductive paste can be prepared, for example, by mixing the present silver powder with a glass frit in an organic vehicle.

In this case, examples of the glass frit include lead-free borosilicate glass or lead-free glass such as zinc borosilicate.

Further, as the resin binder, for example, any resin binder can be used. It is preferable to use, for example, one or more compositions selected from the group consisting of epoxy resins, polyester resins, enamel resins, urea resins, acrylic resins, and cellulose resins.

The silver powder has a heat shrinkage ratio of 15.0% or less at 500 ° C, and is excellent in compatibility with a ruthenium substrate in a solar cell. Therefore, the conductive paste using the silver powder is preferably used in an electrode of a solar cell. However, it is not limited to this use.

<Description of statement>

In the present specification, when the expression is "X to Y" (X, Y is an arbitrary number), the meaning of "X or more Y or less" is included when there is no particular limitation, and "the preferred system is greater than X" or " Preferably, it is less than the meaning of Y".

In addition, the meaning of "better than X" or "better than Y" is also included when the performance is "X" or above (X is any number) or "Y" (Y is any number).

(Example)

Hereinafter, the present invention will be described in more detail based on the following examples and comparative examples.

Regarding the silver powder obtained in the examples and comparative examples, The characteristics were evaluated by the methods shown below.

(1) 矽 (Si) content

It is washed with pure water to have a conductivity of 40 μS/cm or less, and an ICP emission spectroscopic analyzer (iCAP6300DUO) manufactured by Thermo Fisher Scientific Co., Ltd. is used according to JIS H 1061:1998 (a quantitative method for bismuth in copper and copper alloys). 8. ICP emission spectrometry, for the silver powder (sample) thus washed, the strontium content was measured.

(2) BET specific surface area (SSA)

Using the specific surface area measuring device (Monosorb MS-18) manufactured by QUANTACHROME Co., Ltd., according to JIS R 1626:1996 (measurement method of specific surface area according to gas adsorption BET method of fine ceramic powder), "6.2 flow method (3.5) single point The BET specific surface area (SSA) was measured. In this case, a mixed gas of a helium gas of a carrier gas and nitrogen of an adsorbent gas is used.

(3) D50

0.2 g of silver powder (sample) was placed in 50 mL of IPA and dispersed by irradiation with ultrasonic waves (3 minutes), and then D50 of volume-based particle size distribution was measured by a particle size distribution measuring apparatus (Microtrac MT-3000EXII) manufactured by Nikkiso Co., Ltd. .

(4) Heat shrinkage rate

0.2 g of silver powder (sample) was used, and 493 kg of pressure was applied to form 3.8mm cylindrical shape. Using a thermomechanical analyzer (TMA) (EXSTAR6000TMA/SS6200) manufactured by Seiko Instruments Co., Ltd., the line in the longitudinal direction of the molded body was measured at a temperature rise temperature of 5 ° C /min in an air atmosphere while applying a pressure of 98 mN. Shrinkage ratio (%) to obtain a heat shrinkage ratio (%) at 500 °C.

<Example 1>

50 mL of a silver nitrate aqueous solution having a silver concentration of 400 g/L was dissolved in 1 L of pure water to prepare a silver nitrate aqueous solution, and 60 mL of ammonia water having a concentration of 25% by mass was added thereto and stirred to obtain an aqueous ammonia silver complex solution.

Next, 8 mL of a gelatin aqueous solution having a concentration of 5 g/L was added to an aqueous solution of ammonia silver complex at 30 ° C and stirred, and a sodium citrate solution (52 to 57%) was added in an amount of 0.10% by mass relative to silver (Wako Pure Chemical Industries Co., Ltd.) The mixture was stirred and mixed with 1 L of a 11.9 g/L hydrazine aqueous solution to thereby reduce and precipitate the silver particles.

Next, 8 mL of a gelatin aqueous solution having a concentration of 5 g/L was added to the reduced slurry and stirred, and the silver particles were filtered, washed with water until the conductivity of the filtrate became 40 μS/cm or less, and then dried to obtain silver powder (sample).

<Example 2>

Silver powder (sample) was obtained in the same manner as in Example 1 except that the amount of the sodium citrate solution was changed to 0.50% by mass with respect to silver.

<Example 3>

The sodium citrate solution was changed to a potassium citrate solution (27 to 29%) (manufactured by Wako Pure Chemical Industries, Ltd.), and the amount of the addition was changed to 0.10% by mass with respect to silver, and the other examples were the same as those in Example 1. Silver powder (sample) was obtained in the same manner.

<Example 4>

Silver powder (sample) was obtained in the same manner as in Example 3 except that the amount of the potassium citrate solution was changed to 0.25 mass% with respect to silver.

<Example 5>

Silver powder (sample) was obtained in the same manner as in Example 3 except that the amount of the potassium citrate solution was changed to 0.50% by mass with respect to silver.

<Example 6>

Silver powder (sample) was obtained in the same manner as in Example 3 except that the amount of the potassium citrate solution was changed to 0.60% by mass with respect to silver.

<Example 7>

The sodium citrate solution was changed to a decane coupling agent (organic decane, KBM-603, manufactured by Shin-Etsu Chemical Co., Ltd.), and the amount of addition was changed to 0.25 mass% with respect to silver, and otherwise the same as in the first embodiment. And get silver powder (sample).

<Comparative Example 1>

Silver powder (sample) was obtained in the same manner as in Example 1 except that sodium citrate solution was not added.

<Comparative Example 2>

The sodium citrate solution was changed to copper (II) nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.), and the amount of addition was changed to 0.02% by mass based on silver, and the same manner as in Example 1 was used. And get silver powder (sample).

<Comparative Example 3>

Silver powder (sample) was obtained in the same manner as in Comparative Example 2 except that the amount of addition of copper (II) nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was changed to 0.04% by mass with respect to silver.

<Comparative Example 4>

Silver powder (sample) was obtained in the same manner as in Comparative Example 2 except that the amount of addition of copper (II) nitrate trihydrate (manufactured by Wako Pure Chemical Industries, Ltd.) was changed to 0.08 mass% with respect to silver.

<Comparative Example 5>

Silver powder was obtained in the same manner as in Example 1 except that the sodium citrate solution was changed to sodium hydrogencarbonate (manufactured by Wako Pure Chemical Industries, Ltd.), and the amount of the addition was changed to 0.10% by mass based on the amount of silver. ).

The silver powder (sample) obtained in the examples and the comparative examples was in the form of a sphere.

From the results of the examples and the tests conducted so far, it has been found that when the telluride is added to the silver complex salt solution, the silver powder particles can be formed into fine particles. Although the detailed mechanism is still unclear, it can be considered as follows: Since the telluride is a nucleus in which silver particles grow, a reduction precipitation reaction is carried out, so that the particle diameter can be controlled by controlling the number of nuclei to achieve atomization of the silver powder particles.

Further, it was found that the shrinkage ratio at 500 ° C when the crucible entered the inside or the surface of the silver powder particles was lower than when the crucible was not present or when the copper entered.

Claims (4)

A silver powder for a sintered conductive paste containing cerium (Si) in an amount of 30 ppm to 1000 ppm. The silver powder for a sintered conductive paste according to claim 1, wherein the specific surface area measured by the BET method is from 0.8 m ² /g to 3.0 m ² /g. The silver powder for a sintered conductive paste according to claim 1 or 2, wherein a D50 of a volume-based particle size distribution measured by a laser diffraction scattering particle size distribution measurement is 0.50 μm to 1.50 μm. . The silver powder for a sintered conductive paste according to any one of claims 1 to 3, wherein the shrinkage ratio at 500 ° C is 15.0% or less.