JP2019175664A - Conductive paste and burned body - Google Patents

Abstract

To provide a conductive paste for filling via holes capable of reducing problems such as peeling from a side surface of the via holes when filled in the via holes.SOLUTION: There is provided a conductive paste for filling via holes including (A) a conductive filler with tap density of 4.5 g/cmor more, and (B) a metal powder with melting point of 200°C to 700°C.SELECTED DRAWING: Figure 1c

Description

  The present invention relates to a conductive paste for forming a wiring pattern, an electrode pattern, and the like, and a fired body thereof. Specifically, the present invention relates to a conductive paste for filling via holes in wiring patterns and electrode patterns, and a fired body thereof.

  The conductive paste is used for forming a conductive pattern such as a wiring pattern and an electrode pattern of a printed wiring board, and forming an electrode of an electronic component. In the wiring pattern and the electrode pattern of the printed wiring board, a through hole (via hole) formed in the printed wiring board may be formed for electrical connection between the front surface and the back surface of the printed wiring board. By filling the via hole with the conductive paste, electrical connection between the front surface and the back surface of the printed wiring board can be obtained.

  Patent Document 1 describes a conductive paste comprising a conductive component made of silver powder and a heat shrinkage inhibitor made of aluminum powder dispersed in an organic vehicle. Furthermore, in Patent Document 1, by adding inexpensive aluminum powder as a heat shrinkage inhibitor, no conductive gap is formed between the via conductor and the inner wall of the via hole after firing, and the conductive paste is less likely to form a depression in the via conductor. It is described that can be provided.

JP 2008-147033 A

  In the wiring pattern and electrode pattern of the printed wiring board, via holes formed in the insulating substrate are used for electrical connection between the front and back surfaces of the insulating substrate of the printed wiring board, for example, a ceramic substrate such as an alumina substrate and an aluminum nitride substrate. And filled with conductive paste.

  For example, as shown in FIG. 1 a as a schematic cross-sectional view, a via hole 12 is formed in the substrate 10 of the printed wiring board. As shown in FIG. 1 b, a conductive fired body 20 can be formed inside the via hole by filling the via hole 12 with a conductive paste and firing it. As shown in FIG. 1c, in the printed wiring board, the front surface wiring 22 and the back surface wiring 24 are further formed on the front surface and the back surface of the substrate. The front surface wiring 22 and the back surface wiring 24 can be electrically connected by being in contact with the fired body 20 inside the via hole.

  When the insulating substrate is a ceramic substrate, the volume change of the substrate due to heat is small. Therefore, the shape of the via hole 12 of the ceramic substrate 10 does not change greatly. On the other hand, the volume of the conductive paste filled in the via hole 12 tends to shrink due to drying and / or firing. Therefore, when the conductive paste filled in the via hole 12 is baked, it may be peeled off from the side surface of the via hole. FIG. 1 d schematically shows how the fired body 20 b inside the via hole 12 is peeled off from the side surface of the via hole 12. In that case, the electrical connection between the front surface wiring 22 and the back surface wiring 24 by the fired body 20b inside the via hole 12 may become unstable or the electrical connection may be broken. Further, when the fired body 20b inside the via hole 12 is recessed, the surface of the via hole and the back surface may be recessed. Also in this case, the electrical connection may become unstable or the electrical connection may be broken between the fired body 20b inside the via hole and the front surface wiring 22 and the back surface wiring 24.

  As a conductive paste used for filling a via hole, it has been proposed to use a conductive paste containing a metal component mainly composed of silver and palladium or platinum in order to reduce shrinkage after firing. However, since the specific resistance (electrical resistivity) of palladium and platinum is high, there arises a problem that the resistance value of the via becomes high.

  Therefore, an object of the present invention is to provide a conductive paste for filling a via hole, which can reduce the problem of peeling from the side surface of the via hole when the via hole is filled.

  In order to solve the above problems, the present invention has the following configuration.

(Configuration 1)
Configuration 1 of the present invention includes (A) a conductive filler having a tap density of 4.5 g / cm ³ or more, and (B) a metal powder having a melting point of 200 ° C. to 700 ° C. It is a conductive paste.

  If the conductive paste for filling a via hole according to Configuration 1 of the present invention is used, it is possible to reduce the problem of peeling from the side surface of the via hole when the via hole is filled.

(Configuration 2)
Configuration 2 of the present invention is the conductive paste of Configuration 1 further including (C) a glass frit having a linear expansion coefficient α of 60 × 10 ⁻⁷ / ° C. or less.

  According to Configuration 2 of the present invention, the conductive paste has a low linear expansion coefficient α in a predetermined range, so that it is more reliable to reduce the problem of peeling from the side surface of the via hole when filling the via hole. Can be.

(Configuration 3)
Configuration 3 of the present invention is the conductive paste according to Configuration 2 in which (C) the glass frit is a zinc-based glass frit.

  As in configuration 3 of the present invention, (C) by using a zinc-based glass frit as the glass frit, a stable adhesion strength is obtained between the side surface of the via hole and the fired body of the conductive paste in the via hole. Can do.

(Configuration 4)
Configuration 4 of the present invention is the conductive paste according to any one of Configurations 1 to 3, wherein (A) the conductive filler is silver particles.

  According to Configuration 4 of the present invention, since the specific resistance of silver particles is low, a via hole having a low electrical resistance can be formed.

(Configuration 5)
Configuration 5 of the present invention is a fired body of the conductive paste according to any one of Configurations 1 to 4.

  According to Configuration 5 of the present invention, by using a fired body of a predetermined conductive paste for filling via holes, it is possible to reduce the problem that the fired body peels from the side surfaces of the via holes.

  ADVANTAGE OF THE INVENTION According to this invention, the conductive paste for via hole filling which can reduce the malfunction which peels from the side surface of a via hole when it fills a via hole can be provided.

It is a cross-sectional schematic diagram for demonstrating the board | substrate and via hole of a printed wiring board. It is a cross-sectional schematic diagram for demonstrating that the sintered body was formed in the via hole. It is a cross-sectional schematic diagram for demonstrating that the surface wiring and the back surface wiring were formed in the surface and back surface of a printed wiring board. It is a cross-sectional schematic diagram for demonstrating a firing body inside the via hole of a printed wiring board peeling from the side surface of a via hole. It is a plane schematic diagram which shows the pattern for specific resistance measurement of the electroconductive thin film formed using the electroconductive paste. In order to observe the state of peeling of the fired body of the conductive paste from the side surface of the via hole, it is an example of an SEM photograph in which a cross section at the center of the via hole is observed with a scanning electron microscope (SEM) at a magnification of 250 times.

  Embodiments of the present invention will be specifically described below with reference to the drawings. In addition, the following embodiment is a form at the time of actualizing this invention, Comprising: This invention is not limited within the range.

The conductive paste for filling via holes of the present invention includes (A) a conductive filler having a tap density of 4.5 g / cm ³ or more, and (B) a metal powder having a melting point of 200 ° C. to 700 ° C. The conductive paste of the present invention can further contain a predetermined glass frit. By using the conductive paste for filling via holes of the present invention, it is possible to reduce the problem of peeling from the side surfaces of the via holes when filling the via holes.

  Hereinafter, the conductive paste of the present invention will be described in detail.

<(A) Conductive filler>
The via hole filling conductive paste of the present invention includes (A) a conductive filler having a tap density of 4.5 g / cm ³ or more. The tap density is preferably 5 g / cm ³ or more. The upper limit of the tap density is not particularly limited, but varies depending on the material of the conductive filler. From a practical point, for example, the upper limit of the tap density when the conductive filler is silver, is preferably 10 g / cm ³ or less, more preferably 8 g / cm ³ or less, 7 g / cm ³ or less More preferably.

  The tap density can be measured as follows. That is, a tap density can be obtained by putting a predetermined weight of conductive filler in a predetermined graduated cylinder and measuring the capacity of the conductive filler after tapping a predetermined number of times with a tapping device. As the predetermined measuring cylinder, one for 10 ml can be used. Further, the predetermined weight of the conductive filler can be 10 g. Further, as a tap condition, a condition of tapping 400 times at a tap speed of 100 times / min at a height of 20 mm can be used. As the tap density measuring device, for example, KRS-406 manufactured by Kuramochi Scientific Instruments can be used. In this specification, the tap density can be a value measured under the above-described conditions.

  The material of the conductive filler is not particularly limited, but metal particles can be used. Examples of the metal type of the metal particles include silver (Ag), gold (Au), copper (Cu), nickel (Ni), palladium (Pd), platinum (Pt), tin (Sn), and alloys thereof. be able to. Note that the conductive filler may be one in which an inorganic material is coated with the above metal material. The conductive filler may be used alone or in combination of two or more.

  In the conductive paste of the present invention, (A) the conductive filler is preferably silver (Ag) particles. Since the specific resistance of the silver particles is relatively low, a via hole having a low electric resistance can be formed because the conductive filler (A) is silver particles.

  The shape of the particles of the conductive filler is not particularly limited, and examples thereof include a spherical shape and a flake shape (flaky shape). The shape of the conductive filler is preferably spherical from the viewpoint of easily releasing the gas generated during firing.

The particle size of the conductive filler is preferably 0.1 to 10 μm, more preferably 1 to 8 μm, and still more preferably 1 to 5 μm. BET specific surface area of the conductive filler is preferably 0.1~5.0m ² / g, more preferably 0.1~1.5m ² / g, more preferably 0.1~0.7m ² / g.

  In general, since the size of the fine particles has a certain distribution, it is not necessary that all the conductive fillers have the above-mentioned particle size, and the particle size (average particle size D50) of the integrated value 50% of all particles is the above-mentioned. It is preferable that the particle size is within a range. The same applies to the dimensions of particles and powders other than the conductive filler described in this specification. The average particle size D50 can be obtained by performing particle size distribution measurement by the microtrack method (laser diffraction scattering method) and obtaining the D50 value from the result of particle size distribution measurement.

<(B) Metal powder>
The conductive paste for filling a via hole of the present invention includes (B) a metal powder having a melting point of 200 ° C to 700 ° C.

  The material of the metal powder can be used without particular limitation as long as it is a powder made of a metal having a melting point of 200 ° C. to 700 ° C. As a material for the metal powder, aluminum (Al), tin (Sn), zinc (Zn), bismuth (Bi) and alloys thereof, and alloys of these metals and silicon (Si) can be used. From the viewpoint of a low melting point and handleability, it is preferable to use aluminum (Al), tin (Sn), zinc (Zn), bismuth (Bi), or an alloy of aluminum (Al) and silicon (Si) as the metal powder. .

  More preferably, the metal powder is a metal powder of an alloy of aluminum and silicon (AlSi alloy). The content of aluminum in the AlSi alloy is preferably 50 to 95% by weight, more preferably 70 to 93% by weight, still more preferably 80 to 90% by weight, and 85 to 90% by weight. It is particularly preferred that The AlSi alloy can contain other metals as long as the effects of the present invention are not hindered. However, in order to ensure the effect of the present invention, it is preferable that the AlSi alloy is composed only of aluminum and silicon in the above-mentioned content ranges except for other metals inevitably mixed.

  The shape of the particles constituting the metal powder is not particularly limited, and examples thereof include an indefinite shape, a spherical shape, and a flake shape (flaky shape).

  The particle size (average particle size D50) of the particles constituting the metal powder is preferably 0.1 to 10 μm, more preferably 0.5 to 8 μm, and still more preferably 1 to 5 μm.

  In the conductive paste of the present invention, the content of (B) metal powder is preferably 0.01 to 20 parts by weight, more preferably 0.05 to 10 parts by weight with respect to 100 parts by weight of (A) conductive filler. Parts by weight, more preferably 0.1 to 5 parts by weight, and particularly preferably 0.1 to 1 part by weight.

<(C) Glass frit>
The conductive paste for filling via holes of the present invention can further contain (C) glass frit in addition to the above-mentioned predetermined (A) conductive filler and (B) metal powder. However, (C) glass frit is an optional component. Therefore, the conductive paste of the present invention can contain no glass frit. Since the glass frit is an insulator, it is preferable that the conductive paste for filling the via hole does not contain the glass frit in order to obtain a via having a low electric resistance. However, in order to obtain more stable and high adhesion strength between the side surface of the via hole and the sintered body of the conductive paste in the via hole, the via hole filling conductive paste preferably contains glass frit.

When the conductive paste of the present invention further contains glass frit, the glass frit preferably has a linear expansion coefficient α of 60 × 10 ⁻⁷ / ° C. or less, and preferably 50 × 10 ⁻⁷ / ° C. or less. More preferred. Since the conductive paste of the present invention has a low linear expansion coefficient α in a predetermined range, it is possible to more reliably reduce the problem of peeling from the side surface of the via hole when the via hole is filled.

The material of the glass frit contained in the conductive paste of the present invention is not particularly limited as long as it has a predetermined linear expansion coefficient α. Examples of the glass frit having a predetermined linear expansion coefficient α include zinc-based glass frit and aluminum-based glass frit. The zinc-based glass frit is a glass frit containing 30% by mass to 80% by mass of ZnO with respect to 100 parts by mass of the glass frit, preferably 40% by mass to 70% by mass. The zinc-based glass frit may contain oxides such as SiO ₂ , B ₂ O ₃ , Bi ₂ O ₃ , Li ₂ O, Al ₂ O ₃ , and ZrO ₂ as other components. The aluminum-based glass frit is a glass frit containing 5% by mass or more and 50% by mass or less of Al ₂ O ₃ with respect to 100 parts by mass of the glass frit, preferably 5% by mass or more and 30% by mass or less. The aluminum-based glass frit may contain oxides such as SiO ₂ , B ₂ O ₃ , Bi ₂ O ₃ , ZnO, BaO, and CaO as other components.

The glass frit contained in the conductive paste of the present invention is preferably a predetermined zinc-based glass frit. This is because the melting point of the zinc-based glass frit is lower than that of the aluminum-based glass frit. The component composition of the zinc-based glass frit is SiO ₂ —B ₂ O ₃ —ZnO, and the ZnO content is preferably 40 to 70% by weight. When such a zinc-based glass frit is used, the linear expansion coefficient α of the conductive paste can be remarkably reduced. This reduces the difference in firing shrinkage between the conductive paste and the ceramic substrate, so that there is no separation between the side surface of the via hole and the fired body of the conductive paste in the via hole, and more stable and high adhesion. Strength can be obtained.

  The shape of the glass frit particles is not particularly limited, and for example, a spherical shape or an irregular shape can be used.

  The softening point of the glass frit is preferably 300 ° C. or higher, more preferably 400 ° C. or higher and 850 ° C. or lower. More preferably, it is 400 degreeC or more and 700 degrees C or less. Since the softening point of the glass frit is low, the sintering of Ag is promoted, the resistance value is lowered, and the adhesion strength with the ceramic is also improved. The softening point of the glass frit can be measured using a thermogravimetric measuring device (for example, TG-DTA2000SA manufactured by BRUKER AXS).

  The particle size (average particle size D50) of the glass frit is preferably 0.1 to 20 μm, more preferably 0.2 to 10 μm, and most preferably 0.5 to 5 μm.

  In the conductive paste of the present invention, the content of (C) glass frit is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 100 parts by weight with respect to 100 parts by weight of (A) conductive filler. 3 parts by weight, more preferably 0.1 to 1 part by weight.

<Resin component>
The conductive paste of the present invention can contain a resin component. The resin component joins (A) the conductive filler and (B) the metal powder in the conductive paste. The resin component is burned off when the conductive paste is fired. Although it does not specifically limit as a resin component, For example, a thermoplastic resin or a thermosetting resin can be used.

  Examples of the thermoplastic resin include cellulose resins such as ethyl cellulose and nitrocellulose, acrylic resins, alkyd resins, saturated polyester resins, butyral resins, polyvinyl alcohol, and hydroxypropyl cellulose. Examples of the thermosetting resin include epoxy resins, urethane resins, vinyl ester resins, silicone resins, phenol resins, urea resins, melamine resins, unsaturated polyester resins, diallyl phthalate resins, and polyimide resins. These resins may be used alone as a resin component, or two or more kinds may be mixed and used. As the resin component contained in the conductive paste of the present invention, an ethyl cellulose resin can be preferably used.

  In the conductive paste of the present invention, the content of the resin component is preferably 0.2 to 30 parts by weight, more preferably 0.5 to 5 parts by weight with respect to 100 parts by weight of the (A) conductive filler. Part. When the content of the resin component in the conductive paste is within the above range, the printability of the conductive paste on the substrate is improved, and a fine pattern can be formed with high accuracy.

<Other ingredients>
The conductive paste of the present invention may contain a solvent for viscosity adjustment and the like. Examples of the solvent include alcohols such as methanol, ethanol and isopropyl alcohol (IPA), organic acids such as ethylene acetate, aromatic hydrocarbons such as toluene and xylene, N-methyl-2-pyrrolidone (NMP) and the like. N-alkylpyrrolidones, amides such as N, N-dimethylformamide (DMF), ketones such as methyl ethyl ketone (MEK), terpineol (TEL), butyl carbitol (BC) and butyl carbitol acetate (BCA) Can be mentioned.

  The content of the solvent is not particularly limited. The content of the solvent can be adjusted to an appropriate viscosity for the conductive paste. In general, in order to obtain a conductive paste having an appropriate viscosity, the content of the solvent is preferably 1 to 50 parts by weight, more preferably 2 to 20 parts per 100 parts by weight of the (A) conductive filler. Part by weight, more preferably 5 to 10 parts by weight.

The viscosity of the conductive paste of the present invention is preferably 50 to 700 Pa · s (shear rate: 4.0 sec ⁻¹ ), more preferably 100 to 300 Pa · s (shear rate: 4.0 sec ⁻¹ ). . By adjusting the viscosity of the conductive paste to this range, the printability and / or workability of the conductive paste to the via hole on the ceramic substrate is improved, and the conductive paste is uniformly transferred to the via hole on the ceramic substrate. It becomes possible to print.

  The conductive paste of the present invention may contain other additives such as a dispersant, a rheology modifier, and / or a pigment.

  The conductive paste of the present invention may further contain a plasticizer and / or an antifoaming agent.

  The conductive paste of the present invention can be produced by mixing the above-described components using, for example, a likai machine, a pot mill, a three-roll mill, a rotary mixer, or a twin screw mixer.

  The conductive paste of the present invention is used for general conductive pastes, for example, formation of electronic component circuits and electrodes, bonding of electronic components to a substrate, through-hole mounting, via filling, and heat sink formation. Etc. can be used. For example, it can be used for forming a conductor circuit of a printed wiring board. When the via paste is filled with the conductive paste of the present invention, the problem of peeling from the side surface of the via hole can be reduced. Therefore, the conductive paste of the present invention can be particularly preferably used for filling via holes.

  The conductive paste of the present invention can be used for filling via holes as follows. That is, first, the conductive paste of the above-described embodiment is applied to a portion of a ceramic substrate (for example, an alumina substrate or an aluminum nitride substrate) where via holes are formed. The application method is arbitrary, and can be applied using a known method such as dispensing, jet dispensing, stencil printing, screen printing, pin transfer, or stamping. From the viewpoint of simplicity, the coating method is preferably screen printing.

  After applying a conductive paste to a predetermined place on an alumina substrate or an aluminum nitride substrate, the substrate is put into a firing furnace or the like. And the electrically conductive paste apply | coated on the board | substrate is baked at 500-1000 degreeC, More preferably, it is 600-1000 degreeC, More preferably, it is 600-900 degreeC. Thereby, the conductive filler contained in the conductive paste is sintered, the metal powder is oxidized, the solvent component contained in the conductive paste is evaporated at 300 ° C. or less, and the resin component is burned out at 400 ° C. to 600 ° C. Then, a fired body of the conductive paste is formed inside the via hole. Since the obtained fired body can ensure adhesion to the side surface of the via hole, the problem that the fired body peels from the side surface of the via hole can be reduced.

  The reason why the fired body of the conductive paste of the present invention ensures adhesion to the side surface of the via hole can be inferred as follows. However, the present invention is not limited to this reasoning.

  The fired body of the conductive paste of the present invention contains a predetermined (A) conductive filler and a predetermined (B) metal powder. Since the tap density of the conductive filler is high, it is considered that heat shrinkage during firing can be suppressed. Moreover, it is considered that the high tap density of the conductive filler contributes to lowering the specific resistance of the sintered body in the via hole. In addition, it is considered that the predetermined metal powder contained in the conductive paste of the present invention melts at the melting point, oxidizes during firing, forms an oxide, and expands in volume. Therefore, even if the volume of the conductive filler is thermally contracted, it is considered that the volume change of the fired body can be suppressed by the presence of the metal powder. As a result, it is considered that the firing step can be completed without impairing the adhesion with the side surface of the via hole formed during firing. For this reason, the material of the metal powder (B) is a powder made of a metal having a melting point of 200 ° C. to 700 ° C., but a melting point of 600 ° C. or less is preferable because volume expansion during firing occurs faster. Moreover, considering that it is preferable that the volume expansion of the metal powder (B) occurs after the resin component contained in the conductive paste is burned out, the material of the metal powder is a powder made of a metal having a melting point of 450 ° C. to 600 ° C. It is particularly preferred.

  Further, when the conductive paste of the present invention contains a predetermined (C) glass frit, it is considered that the glass frit can assist the adhesion with the side surface of the via hole.

  From the foregoing, it can be said that the use of the conductive paste of the present invention can reduce the problem that the fired body is peeled off from the side surface of the via hole in the firing step. However, the present invention is not limited to the above reasoning.

  Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

[Manufacture of conductive paste]
Tables 2 to 4 show the blending of the materials of Examples and Comparative Examples. The compounding ratio shown by Tables 2-4 is a weight part with respect to 100 weight part of (A) electroconductive filler.

<(A) Conductive filler>
(A) As a conductive filler, the following three types of silver particles A1, A2 and A3 were used in the formulations shown in Tables 2 to 4.
Silver particles A1: Silver particles with a tap density of 6.7 g / cm ³ (average particle diameter D50: 3 μm, particle shape: spherical)
Silver particle A2: Silver particle having a tap density of 5.3 g / cm ³ (average particle diameter D50: 5 μm, particle shape: spherical)
Silver particle A3: Silver particle having a tap density of 4.1 g / cm ³ (average particle diameter D50: 1 μm, particle shape: spherical)

  The tap density of the silver particles A1, A2 and A3 was measured as follows. That is, 10 g of silver particles was put into a measuring cylinder (for 10 ml) and tapped 400 times with a tapping device. The tap was performed at a tap speed of 100 times / minute with a height of 20 mm. After tapping, the capacity of the silver particles was measured by reading the scale of the graduated cylinder. The tap density was obtained from the charged amount of silver particles and the capacity after tapping. For the measurement, KRS-406 manufactured by Kuramotsu Scientific Instruments was used as a tap density measuring device.

<(B) Metal powder>
(B) Six types of metal powders B1 to B6 shown in Table 1 were used as metal powders in the formulations shown in Tables 2 to 4.

<(C) Glass frit>
As the glass frit, the following four types of glass frit C1 to C4 were used in the formulations shown in Tables 2 to 4.
Glass frit C1: Zinc-based glass frit (component composition: SiO ₂ —B ₂ O ₃ —ZnO, ZnO content: 50 to 60% by weight, linear expansion coefficient α: 40 × 10 ⁻⁷ / ° C., average particle size 1. 1μm, softening point 635 ° C)
Glass frit C2: Zinc-based glass frit (component composition: SiO ₂ —B ₂ O ₃ —ZnO, ZnO content: 60 to 70 wt%, linear expansion coefficient α: 40 × 10 ⁻⁷ / ° C., average particle diameter 2 μm, (Softening point 660 ° C)
Glass frit C3: Aluminum-based glass frit (component composition: SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ , Al ₂ O ₃ , content: 5 to 30% by weight, linear expansion coefficient α: 51 × 10 ⁻⁷ / ℃, average particle size 2μm, softening point 775 ℃)
Glass frit C4: Aluminum-based glass frit (component composition: SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ , Al ₂ O ₃ , content: 5 to 30% by weight, linear expansion coefficient α: 53 × 10 ⁻⁷ / ℃, average particle size 2μm, softening point 800 ℃)

<Resin component>
In the conductive pastes of Examples and Comparative Examples, ethyl cellulose resin (manufactured by Dow Chemical, product name: Etcel (STD-45)) was blended as a resin component. In Tables 2-4, the compounding quantity of ethylcellulose resin is shown.

<Solvent>
The conductive pastes of Examples and Comparative Examples of the present invention were mixed with butyl carbitol (manufactured by Daishin Chemical Co., Ltd., product name: butyl carbitol) as a solvent. Tables 2 to 4 show the blending amounts of butyl carbitol.

Next, the conductive pastes of Examples and Comparative Examples were manufactured by mixing the materials of the above-described predetermined weight ratio with a planetary mixer, further dispersing with a three-roll mill, and forming a paste. The viscosity of the obtained conductive pastes of Examples and Comparative Examples was 110 to 150 Pa · s (shear rate: 4.0 sec ⁻¹ ). In all cases, the viscosity was such that the conductive paste could be printed in the via hole.

[Measurement of wiring resistivity]
The specific resistance (electric resistivity) of the conductive films obtained by firing the conductive pastes of Examples and Comparative Examples was measured. This specific resistance can be said to be the same value as the specific resistance of the fired body when the conductive paste is embedded and fired in the via hole.

  The specific resistances of the examples and comparative examples were measured by the following procedure. That is, an alumina substrate having a width of 20 mm, a length of 20 mm, and a thickness of 1 mm was prepared. A pattern made of a conductive paste as shown in FIG. 2 was printed on this substrate using a 325 mesh stainless steel screen.

  Next, the patterns made of the conductive pastes of Examples and Comparative Examples applied on the substrate were baked at 850 ° C. for 10 minutes and the total baking time was 60 minutes to obtain a sample for measuring specific resistance. Specifically, a substrate having a predetermined pattern printed on its surface was baked under the above conditions in the atmosphere using a baking furnace (mesh belt type continuous furnace manufactured by Koyo Thermo System Co., Ltd.). The film thickness of the conductive film pattern after firing was measured.

  The electric resistance of the conductive film pattern (see FIG. 2) of the specific resistance measurement sample obtained by heating the conductive pastes of the example and the comparative example is 4 terminals using a multimeter type 2001 manufactured by Toyo Corporation. Measured by the method. The specific resistance of the conductive film was calculated from the obtained electric resistance value and the pattern shape and film thickness obtained by measuring the electric resistance value. The measurement results of the conductive film patterns of the conductive pastes of Examples and Comparative Examples are shown in the “specific resistance of wiring” column of Tables 2 to 4.

  Note that four samples with the same conditions were prepared as specific resistance measurement samples, and the measured values were obtained as an average value of the four samples. When the specific resistance is 4.5 μΩ · cm or less, it is acceptable to use the conductive paste for filling via holes. When the specific resistance is 4.0 μΩ · cm or less, the conductive paste can be favorably used for filling via holes. When the specific resistance is 3.5 μΩ · cm or less, the conductive paste can be used particularly well for filling via holes. When the specific resistance is 3.0 μΩ · cm or less, the conductive paste can be used extremely well for filling via holes.

  As is apparent from Tables 2 to 4, the specific resistance of the conductive films formed using the conductive pastes of Examples 1 to 15 of the present invention is 2.4 μΩ · cm (Example 7) to 3.5 μΩ · cm. It was the range of (Example 9). Therefore, it can be said that the conductive paste of the example of the present invention has a specific resistance value that can be used particularly well for filling via holes. As is clear from Table 4, the specific resistances of the conductive films formed using the conductive pastes of Comparative Examples 1 to 4 were all 3.5 μΩ · cm or less. Therefore, it can be said that the conductive pastes of Comparative Examples 1 to 4 have no problem in terms of specific resistance.

[Presence of peeling after via filling]
The through-holes (via holes, diameter 250 μm) of the ceramic substrate having a thickness of 270 μm were filled with the conductive pastes of Examples and Comparative Examples by screen printing. The conductive paste filled in the via hole was kept at 850 ° C. for 10 minutes and fired for a total firing time of 60 minutes, thereby forming a fired body in the via hole. Specifically, a substrate having a predetermined pattern printed on the surface thereof was baked in the atmosphere under the above-described temperature and heating time conditions using a baking furnace (mesh belt type continuous furnace manufactured by Koyo Thermo System Co., Ltd.).

  In order to observe the state of peeling of the fired body from the side surface of the via hole, a cross section at the substantially center of the via hole was observed with a scanning electron microscope (SEM) at a magnification of 250 times. FIG. 3 shows an example of a SEM photograph of the cross section of the via hole for observing the state of peeling of the fired body from the side surface of the via hole. If any part of the fired body is peeled off from the side of the via hole (as shown in the photo on the right in Fig. 3), enter "Yes" in the "Presence of peeling after filling via" column in Tables 2-4. did. When it was not observed that the fired body was peeled off from the side surface of the via hole (as shown in the left photograph of FIG. 3), “None” was entered in the “Presence or absence of peeling after via filling” column.

  As is clear from Tables 2 to 4, in the fired body of the via hole formed using the conductive pastes of Examples 1 to 15 of the present invention, no peeling from the side surface of the via hole was observed. Therefore, it can be said that the use of the conductive paste of the present invention can reduce the problem of peeling from the side surface of the via hole when the via hole is filled.

  On the other hand, as is clear from Table 4, it was observed that at least a part of the fired body of the via hole formed using the conductive pastes of Comparative Examples 1 to 4 was peeled from the side surface of the via hole. Therefore, when the conductive pastes of Comparative Examples 1 to 4 are used, it can be said that there is a high possibility that a problem of peeling from the side surface of the via hole occurs when the via hole is filled.

DESCRIPTION OF SYMBOLS 10 Board | substrate 12 Via hole 20, 20b Fired body 22 Front surface wiring 24 Back surface wiring

Claims (5)

(A) a conductive filler having a tap density of 4.5 g / cm ³ or more;
(B) A conductive paste for filling via holes, comprising metal powder having a melting point of 200 ° C. to 700 ° C. (C) The electrically conductive paste of Claim 1 which further contains the glass frit whose linear expansion coefficient (alpha) is 60x10 < ^-7 > / degrees C or less.   The conductive paste according to claim 2, wherein (C) the glass frit is a zinc-based glass frit.   The conductive paste according to any one of claims 1 to 3, wherein (A) the conductive filler is silver particles.   The fired body of the conductive paste according to any one of claims 1 to 4.