JP2017069189A - Conductive paste and electronic substrate, manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive paste capable of strongly binding a conductive part to a ceramic substrate.SOLUTION: A conductive paste is prepared by combining high melting point metal particles having the melting point over a burning temperature, molten alloy particles melting at the burning temperature and containing an alloy with the melting point of 400°C or less, active metal particles containing an active metal and an organic vehicle. The molten alloy particles may contain Sn and at least one selected from a group consisting of Sn-Ag-Cu alloy particles, Sn-Bi alloy particles and Au-Sn alloy particles. In the active metal particles, the active metal may be Ti and/or Zr. The active metal particles may be at least one selected from a group consisting of titanium hydride particles, titanium boride particles and zirconium hydride particles. The high melting point metal particles may be formed by at least one metal selected from a group consisting of Cu, Ag and Ni or an alloy containing the metal.SELECTED DRAWING: None

Description

  The present invention provides a conductive paste for producing an electronic substrate such as a surface metallized substrate, a via-filled substrate, or a through-hole wall metallized substrate by forming conductive portions such as electrodes and circuits on a ceramic substrate, and using this paste The present invention relates to the obtained electronic substrate (ceramic substrate with a conductive part) and a manufacturing method thereof.

  Conventionally, conductive paste in which metal particles such as Ag, Cu, Ni, and W and glass particles (powder) having a low softening point are mixed in an organic vehicle as a paste material for forming electrodes and circuits on the surface of a ceramic substrate is generally used. Known to. This type of conductive paste is used by printing a predetermined pattern on the substrate surface by screen printing or the like and then heating at a temperature not lower than the softening point of the glass component and not higher than the melting point of the metal in the firing step. That is, in this paste, the glass component melted and softened by heating gets wet with the ceramic substrate, the paste and the substrate are joined, and the metal powder is sintered to form a conductive portion. Such conductive paste containing glass particles has been widely used in the field of the electronics industry for manufacturing electronic components and circuit boards because of its easy handling. However, it cannot be denied that the bonding with the glass component is inferior in terms of bonding strength compared to other bonding methods. In particular, for ceramic substrates such as aluminum nitride substrates and silicon nitride substrates that are often used for heat dissipation of high-power semiconductors, glass components are difficult to wet and it is difficult to obtain sufficient bonding strength. Therefore, in applications that require high reliability, a thin film method by sputtering or a method of attaching a metal foil or metal plate to a substrate using an active metal braze is often used. However, these metallization methods are expensive, and the paste printing method that requires low cost still has a strong demand for improving the bonding strength.

  In Japanese Patent Laid-Open No. 5-226515 (Patent Document 1), an aluminum nitride substrate is obtained by adding a compound of titanium which is an active metal species (titanium hydride) into a conductive paste mainly composed of an Ag-Cu alloy. A metallization method for firmly joining a metallization layer is disclosed. In this document, firing is described as heating in a non-oxidizing atmosphere, an inert atmosphere or a vacuum atmosphere to prevent decomposition and oxidation of the Ag-Cu alloy and titanium hydride. It is fired with.

  In this method, particles of an active metal or a compound thereof are used together with an appropriate melting component (often an Ag—Cu alloy) because the active metal alone hardly reacts with the substrate surface. Therefore, it is easy to flow during firing, and it is difficult to form patterns such as electrodes and wiring, and it is often used for applications such as bonding of metal plates. Furthermore, if the substrate is fired in a vacuum, the substrate and the metallized layer are strongly bonded, and the pattern shape tends to be easily retained. However, the Ag-Cu alloy melted during the firing is shrunk and the edges are turned up or on the substrate. There is a tendency for the pattern to collapse due to being small and round. This tendency is particularly noticeable in firing in a nitrogen atmosphere (non-oxidizing atmosphere), and in firing in a nitrogen atmosphere, the pattern is completely turned up or deformed into a ball shape, and there is a portion that is slightly in contact. The state is barely bonded to the substrate. In the embodiment of this document, it can be presumed that this is the reason why the baking is performed in a vacuum. Therefore, the paste of this document may be able to firmly bond fine pattern shapes such as electrodes and circuits to the substrate by vacuum firing, but the vacuum firing is a batch type and it takes a very long time to raise and lower the temperature. Therefore, productivity is low, and when carrying conveyor type nitrogen firing to improve productivity, the metallized layer shrinks, and it is difficult to maintain fine pattern shapes such as electrodes and circuits.

  Japanese Patent Application Laid-Open No. 2000-246482 (Patent Document 2) discloses a brazing material paste containing Ag—Cu alloy particles and titanium particles whose surfaces are coated with copper as metal components. In this document, the conventional titanium hydride is decomposed into hydrogen and titanium at about 400 to 500 ° C., and the highly reactive titanium reacts with oxygen and carbon, which are decomposition gases of organic substances contained in the paste. It is described that the joining with the member was hindered.

  In contrast, Patent Document 1 describes that titanium hydride is stable up to 700 ° C. However, anyway, since the firing temperature is as high as about 850 ° C., oxygen, carbon, nitrogen, etc. are used during firing. When exposed to this gas, it could not function sufficiently and was usually fired in a vacuum without the gas.

JP-A-5-226515 (Claims 1 and 2, paragraphs [0005] and [0007], Examples) JP 2000-246482 A (Claim 1, paragraphs [0006] [0017])

  Accordingly, an object of the present invention is to provide a conductive paste capable of firmly bonding a conductive part to a ceramic substrate, an electronic substrate obtained using this paste, and a method for manufacturing the same.

  Another object of the present invention is to provide a conductive paste capable of firmly bonding a fine pattern to a ceramic substrate even when fired in a nitrogen atmosphere, an electronic substrate obtained using this paste, and a method for producing the same. It is in.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have found that high melting point metal particles having a melting point exceeding the firing temperature, molten alloy particles including an alloy having a melting point of 400 ° C. or less, and an active metal containing an active metal It has been found that when a conductive paste combining particles and an organic vehicle is applied or filled on a ceramic substrate and fired, the conductive portion can be firmly bonded to the ceramic substrate, and the present invention has been completed.

  That is, the conductive paste of the present invention includes high melting point metal particles having a melting point exceeding the firing temperature, molten alloy particles containing an alloy that melts at the firing temperature and has a melting point of 400 ° C. or less, and an active metal containing active metal. Includes metal particles and an organic vehicle. The molten alloy particles may contain Sn, and may contain at least one selected from the group consisting of Sn—Ag—Cu alloy particles, Sn—Bi alloy particles, and Au—Sn alloy particles. In the active metal particles, the active metal may be Ti and / or Zr. The active metal particles may be at least one selected from the group consisting of titanium hydride particles, titanium boride particles, and zirconium hydride particles. The refractory metal particles may be formed of at least one metal selected from the group consisting of Cu, Ag and Ni, or an alloy containing this metal. The mass ratio of the refractory metal particles and the molten alloy particles is refractory metal particles / molten alloy particles = about 90/10 to 40/60. The ratio of the active metal particles is about 0.5 to 30 parts by mass with respect to 100 parts by mass in total of the refractory metal particles and the molten alloy particles. The center particle size of the molten alloy particles may be 0.1 to 15 μm. The central particle diameter of the active metal particles is about 1 to 15 μm. The center particle diameter of the refractory metal particles is about 0.01 to 10 μm.

  The present invention also includes an electronic substrate manufacturing method including an attaching step of attaching the conductive paste to a ceramic substrate and a firing step of firing the conductive paste attached to the ceramic substrate to form a conductive portion. . In the firing step, the conductive paste may be fired in a nitrogen atmosphere. In the firing step, the firing temperature is about 800 to 950 ° C.

  The present invention also includes an electronic substrate including a ceramic substrate, a high melting point metal having a melting point equal to or higher than the firing temperature, a molten alloy having a melting point of 400 ° C. or less, and a conductive portion including an active metal. The ceramic substrate may be an alumina substrate, an alumina-zirconia substrate, an aluminum nitride substrate, a silicon nitride substrate, or a silicon carbide substrate. The electronic substrate of the present invention may be a surface metallized substrate, a via-filled substrate, or a through-hole wall surface metallized substrate.

  In the present invention, high melting point metal particles having a melting point equal to or higher than the firing temperature, molten alloy particles including an alloy having a melting point of 400 ° C. or lower, active metal particles including an active metal, and an organic vehicle are combined. The conductive portion can be firmly bonded to the ceramic substrate, and in particular, even when baked in a nitrogen atmosphere, it can be firmly bonded to the ceramic substrate without destroying the fine pattern shape.

[Conductive paste]
The conductive paste of the present invention includes high melting point metal particles having a melting point equal to or higher than a firing temperature, molten alloy particles including an alloy having a melting point of 400 ° C. or less, active metal particles including an active metal, and an organic vehicle. . When the conductive paste of the present invention is used, the reason why the conductive portion can be firmly bonded to the ceramic substrate can be estimated as follows. In other words, the molten alloy particles contained in the paste melt at low temperatures and cover the surfaces of the active metal particles, so that the active metal and its compounds are present in the surroundings even at high temperatures (the nitrogen and organic vehicles in the firing atmosphere gas are decomposed). It can be presumed that the reaction with carbon generated in the process is prevented. By such an action, the active metal can maintain its activity up to a high temperature even in a nitrogen atmosphere, and the molten metal component contains the active metal that retains the activity, so that the molten metal wets the ceramic substrate and the active metal and the ceramic substrate. It can be estimated that the metallized film can be turned up and contracted. In addition, since the molten metal literally liquefies and flows, the phenomenon that the pattern turns up or shrinks in a round shape, or on the contrary, the phenomenon that the pattern spreads when it gets too wet with the substrate is completely controlled by such an action alone. It can be estimated that it is impossible. Therefore, in the present invention, the control of the shrinkage and spreading phenomenon as described above is suppressed by adding refractory metal particles separately from the molten metal and the active metal compound. That is, it can be presumed that the molten metal component prevents the excessive flow by getting wet on the surface of the refractory metal particles. Depending on the type of molten metal and refractory metal, it is also possible to suppress fluidization by utilizing the fact that alloying proceeds between the molten metal and refractory metal during firing and the melting point of the molten metal increases. .

(High melting point metal particles)
The metal forming the refractory metal particles is not particularly limited as long as it has a melting point exceeding the firing temperature (for example, exceeding 950 ° C. and not more than 2500 ° C.). Specifically, examples of the metal include Cu, Ag, Ni, W, Mo, Au, Pt, and Pd. These metals can be used alone or in combination of two or more. The metal particles may be a combination of different kinds of metal particles, and may be formed of an alloy in which two or more kinds are combined as long as the melting point is equal to or higher than the firing temperature. Of these metals, at least one metal selected from the group consisting of Cu, Ag and Ni, or an alloy containing this metal is preferred.

  Among these metal particles, Cu particles (melting point 1083 ° C.), Ag particles (melting point) are excellent in conductivity, have a relatively low melting point, and are easily sintered with each other at a firing temperature of 800 to 950 ° C. 960 ° C.), and Cu particles are particularly preferable from the viewpoint of economy.

  The shape of the refractory metal particles is, for example, spherical (true or nearly spherical), ellipsoidal (elliptical sphere), polygonal (polygonal, polygonal, rectangular, etc.), plate-like, etc. (Flat shape, scale shape, flake shape, etc.), rod shape or rod shape, fiber shape, tree needle shape, indefinite shape and the like. The shape of the refractory metal particles is usually spherical, ellipsoidal, polygonal, or indefinite.

  The center particle diameter or average particle diameter (D50) of the refractory metal particles is, for example, 0.01 to 15 μm (for example, 0.01 to 10 μm) from the viewpoint that both the retention of the pattern shape and the adhesion to the ceramic substrate can be achieved. Preferably it is 0.05-10 micrometers (for example, 0.1-7 micrometers), More preferably, it is about 0.3-1 micrometer (especially 0.4-0.8 micrometer). Further, the center particle diameter of the refractory metal particles may be, for example, about 0.01 to 2 μm (particularly 0.05 to 1 μm) in applications where the retention of the pattern shape is important. In important applications, for example, it may be about 0.2 to 10 μm (particularly 0.3 to 8 μm). If the particle size is too small, the economic efficiency is lowered and the dispersibility in the paste may be lowered. If it is too large, the printability and dispersion uniformity of the paste may be lowered.

  In the present specification and claims, the center particle diameter means an average particle diameter measured using a laser diffraction / scattering particle size distribution measuring apparatus.

  The melting point of the refractory metal particles may be a melting point equal to or higher than the firing temperature, and may be, for example, more than 950 ° C. and 2500 ° C. or less, preferably 955 to 2000 ° C., more preferably 960 to 1500 ° C. (especially 980 ˜1200 ° C.). If the melting point is too low, it may be difficult to form a fine pattern.

  The refractory metal particles can be produced by a conventional method, for example, by various production methods such as a wet reduction method, an electrolysis method, an atomization method, and a water atomization method.

(Molten alloy particles)
The molten alloy particles include an alloy that melts at a firing temperature and has a melting point of 400 ° C. or less, and melts and fluidizes during firing at a paste firing temperature or less, thereby improving the bondability between the conductive portion and the ceramic substrate. It can be improved. The melting point of an alloy having a melting point of 400 ° C. or lower may be 400 ° C. or lower, for example, 80 to 400 ° C., preferably 100 to 300 ° C. (eg 120 to 280 ° C.), more preferably 150 to 250 ° C. (particularly 200 ° C. ~ 240 ° C).

  The molten alloy particles only need to contain an alloy having a melting point of 400 ° C. or lower, but from the viewpoint of fluidity, it is preferable to contain particles formed only of an alloy having a melting point of 400 ° C. or lower.

  Examples of alloy particles having a melting point of 400 ° C. or lower include Sn—Bi alloy particles, Sn—Pb alloy particles, Sn—Zn—Bi alloy particles, Au—Sn alloy particles, Sn—Ag—Cu alloy particles, Sn— Examples thereof include Cu alloy particles, Sn—Sb alloy particles, Au—Sn alloy particles, Au—Ge alloy particles, and Zn—Al—Ge alloy particles. Such alloy particles may be solder powder used for solder paste or the like, for example, Sn-58Bi (melting point: about 140 ° C.), Sn-37Pb (melting point: 183 ° C.), Sn-8Zn-3Bi (melting point: about 190 ° C), Au-90Sn (melting point about 220 ° C), Sn-3Ag-0.5Cu (melting point about 220 ° C), Sn-0.7Cu (melting point about 230 ° C), Sn-5Sb (melting point about 235 ° C), Au-20Sn (melting point: about 280 ° C), Au-12Ge (melting point: 356 ° C), Zn-5Al-0.1Ge (melting point: 382 ° C), or the like may be used. These alloy particles can be used alone or in combination of two or more.

  Among these alloy particles, an alloy particle containing Sn is preferable from the viewpoint of fluidity. Furthermore, Sn-Bi alloy particles such as Sn-58Bi, Sn-Ag-Cu alloy particles such as Sn-3Ag-0.5Cu, Au— Au—Sn alloy particles such as −20Sn are preferable, and they are excellent in fluidity, and can improve the bondability between the conductive part and the ceramic substrate to a high degree, so that Sn—Bi alloy particles and Sn—Ag—Cu alloy particles having a low melting point are used. Is preferred. Furthermore, an alloy containing a metal (Cu, Ag, etc.) that forms the refractory metal particles from the viewpoint that the wettability (affinity) with the refractory metal particles can be improved and the pattern shape can be easily maintained by adjusting the fluidity. For example, Sn—Ag—Cu alloy particles are particularly preferable.

  As long as the molten alloy particles do not impair the effects of the present invention, in addition to alloy particles having a melting point of 400 ° C. or lower (first molten alloy particles), alloy particles having a melting point of higher than 400 ° C. and lower than the firing temperature (Second molten alloy particles) may further be included. By combining with the second molten alloy particles, the fluidity of the first molten alloy particles can be adjusted, and both the bondability between the substrate and the conductive portion and a fine pattern shape can be achieved.

  The melting point of the second molten alloy particles is, for example, more than 400 ° C. and 880 ° C. or less, preferably 500 to 850 ° C., more preferably about 700 to 800 ° C.

  Although it will not specifically limit if it has such melting | fusing point as 2nd molten alloy particle, Since affinity with 1st molten alloy particle can be improved, the metal contained in 1st molten alloy particle is used. The alloy particle containing is preferable, and the alloy particle containing the metal (Cu, Ag etc.) which forms a refractory metal particle from the point which can improve wettability with a refractory metal particle is also preferable. Among these, it is particularly preferable that the first and second molten alloy particles are formed of an alloy containing a metal (Cu, Ag, etc.) that forms refractory metal particles. Preferred second molten alloy particles include an alloy containing Cu and / or Ag (for example, an Ag—Cu alloy), for example, a silver brazing material 72Ag-28Cu (melting point: about 780 ° C.) widely used as a brazing paste. Is mentioned.

  The mass ratio of the first molten alloy particles and the second molten alloy particles can be selected from the range of the former / the latter = 100/0 to 10/90, and when both particles are combined, for example, 90/10 to 20 / 80, preferably 70/30 to 30/70, more preferably about 60/40 to 40/60. If the ratio of the second molten alloy particles is too large, the bonding force between the substrate and the conductive portion may be reduced.

  The molten alloy particles can be produced by a so-called atomizing method in which gas, air, water, or the like is sprayed on a molten alloy to pulverize and cool and solidify instantaneously to form powder. Among these methods, particles produced by a water atomizing method in which water is sprayed may be used from the viewpoint that micron-order alloy particles close to a true sphere can be produced.

  As the shape of the molten alloy particles, for example, spherical (true spherical or substantially spherical), ellipsoid (elliptical sphere), polygonal shape (polygonal shape such as polygonal pyramid shape, tetragonal shape, rectangular parallelepiped shape, etc.), plate shape ( Flat, scale or flake), rod or rod, fiber, and indefinite shape. The shape of the molten alloy particles is usually spherical, ellipsoidal, polygonal, indeterminate.

  The center particle diameter (D50) of the molten alloy particles is, for example, about 0.1 to 15 μm, preferably about 0.5 to 10 μm, more preferably about 1 to 7 μm (particularly 3 to 6 μm). If the particle size is too small, the yield in producing the particles may be significantly reduced and the cost may be significantly increased. On the other hand, if the particle size is too large, the ratio of one particle size at the time of fine pattern formation increases, the uniformity within the pattern decreases, and there are problems such as pattern chipping, voids, and uneven bonding with the substrate. May occur. Further, when printing with a mesh screen, there is a risk of mesh clogging.

  The mass ratio of the refractory metal particles and the molten alloy particles is, for example, refractory metal particles / molten alloy particles = 90/10 to 40/60, preferably 85/15 to 45/55, and more preferably 80/20 to It is about 50/50 (particularly 75/25 to 60/40). If the ratio of the molten alloy particles is too large, the fluidity of the molten alloy cannot be suppressed, and the pattern edge is easily turned up due to firing shrinkage or oozes out of the pattern. On the other hand, when the ratio of the molten alloy particles is too small, there is a possibility that a good bonding cannot be obtained because the solid-liquid contact interface serving as a reaction field between the ceramic substrate and the active metal component is reduced.

(Active metal particles)
Examples of the active metal contained in the active metal particles include Ti, Zr, and Hf, which are Group 4A metals of the periodic table. These active metals can be used alone or in combination of two or more. Of these active metals, Ti and / or Zr are preferable, and Ti is particularly preferable because of its excellent activity in the firing step and improvement of the bonding force between the ceramic substrate and the conductive portion.

  The active metal particles only need to contain an active metal and may be formed of the active metal alone, but are preferably formed of a compound containing an active metal from the viewpoint of excellent activity in the firing step. .

As the compound containing the active metal is not particularly limited, for example, titanium compounds [e.g., titanium boride _(TiB 2), titanium hydride _(TiH 2), titanium sulfide _(TiS 2), titanium tetrachloride (TiCl ₄₎ Etc.], zirconium compounds [eg zirconium boride (ZrB ₂ ), zirconium hydride (ZrH ₂ ), zirconium sulfide (ZrS ₂ ), zirconium tetrachloride (ZrCl ₄ ), zirconium hydroxide (Zr (OH) _4, etc.) ], Hafnium compounds [for example, hafnium boride (HfB ₂ ), hafnium hydride (HfH ₂ ), hafnium sulfide (HfS ₂ ), hafnium tetrachloride (HfCl ₄ ) and the like. Of these, titanium hydride (TiH ₂ ), titanium boride (TiB ₂ ), and zirconium hydride (ZrH ₂ ) are preferable because of their excellent activity in the firing step.

  The active metal particles containing these active metals can be used alone or in combination of two or more, and at least one selected from the group consisting of titanium hydride particles, titanium boride particles and zirconium hydride particles is preferred.

  Examples of the shape of the active metal particle include, for example, a spherical shape (true spherical shape or substantially spherical shape), an elliptical shape (elliptical spherical shape), a polygonal shape (polygonal shape such as a polygonal pyramid shape, a rectangular parallelepiped shape, a rectangular parallelepiped shape, etc.) Flat, scale or flake), rod or rod, fiber, and indefinite shape. The shape of the active metal particles is usually spherical, ellipsoidal, polygonal, indefinite or the like.

  The central particle diameter (D50) of the active metal particles is, for example, about 0.1 to 15 μm (for example, 1 to 15 μm), preferably about 0.5 to 10 μm, and more preferably about 1 to 7 μm (particularly 3 to 6 μm). A smaller particle size is preferable in terms of paste uniformity. However, if the particle size is too small, the yield in the production of particles is remarkably lowered, and the economy may be lowered. On the other hand, if the particle size is too large, the ratio of one particle size at the time of forming a fine pattern increases, and the uniformity within the pattern decreases, so there are problems such as pattern chipping, voids, and uneven bonding with the substrate. It is likely to occur. In addition, when printing on a mesh screen, mesh clogging may occur.

  The ratio of the active metal particles is 0.5 to 30 parts by mass, preferably 1 to 20 parts by mass, more preferably 2 to 10 parts by mass (particularly 2 parts) with respect to 100 parts by mass in total of the refractory metal particles and the molten alloy particles. .5 to 5 parts by mass). If the ratio of the active metal particles is too small, the bondability with the ceramic substrate may be lowered. On the other hand, if the amount is too large, the metallized film or the filled via itself may become brittle.

(Organic vehicle)
The organic vehicle may be a conventional organic vehicle used as an organic vehicle of a conductive paste containing metal particles, for example, an organic binder and / or an organic solvent. The organic vehicle may be either an organic binder or an organic solvent, but is usually a combination of an organic binder and an organic solvent (dissolved material of an organic binder with an organic solvent).

The organic binder is not particularly limited. For example, thermoplastic resins (olefin resins, vinyl resins, acrylic resins, styrene resins, polyether resins, polyester resins, polyamide resins, cellulose derivatives, etc.), And thermosetting resins (thermosetting acrylic resins, epoxy resins, phenol resins, unsaturated polyester resins, polyurethane resins, etc.). These organic binders can be used alone or in combination of two or more. Of these organic binders, resins that burn out easily during the baking process and have a low ash content, such as acrylic resins (polymethyl methacrylate, polybutyl methacrylate, etc.), cellulose derivatives (nitrocellulose, ethyl cellulose, butyl cellulose, cellulose acetate) Etc.), polyethers (polyoxymethylene, etc.), rubbers (polybutadiene, polyisoprene, etc.), etc. are widely used. From the viewpoint of thermal decomposability, poly (meth) acrylate and poly (meth) acrylate butyl Poly (meth) acrylic acid C _1-10 alkyl esters such as

The organic solvent is not particularly limited as long as it is an organic compound that imparts an appropriate viscosity to the paste and can be easily volatilized by drying after the paste is applied to the substrate. Good. Examples of such organic solvents include aromatic hydrocarbons (such as paraxylene), esters (such as ethyl lactate), ketones (such as isophorone), amides (such as dimethylformamide), and aliphatic alcohols (such as octanol and decanol). , Diacetone alcohol, etc.), cellosolves (such as methyl cellosolve, ethyl cellosolve), cellosolve acetates (such as ethyl cellosolve acetate, butyl cellosolve acetate), carbitols (such as carbitol, methyl carbitol, ethyl carbitol), carbitol Acetates (ethyl carbitol acetate, butyl carbitol acetate), aliphatic polyhydric alcohols (ethylene glycol, diethylene glycol, dipropylene glycol, butanediol, triethylene glycol) Coal, glycerin, etc.), alicyclic alcohols [eg, cycloalkanols such as cyclohexanol; terpene alcohols such as terpineol and dihydroterpineol (monoterpene alcohols, etc.)], aromatic alcohols (eg, metacresol), Aromatic carboxylic acid esters (dibutyl phthalate, dioctyl phthalate, etc.), nitrogen-containing heterocyclic compounds (dimethyl imidazole, dimethyl imidazolidinone, etc.) and the like can be mentioned. These organic solvents can be used alone or in combination of two or more. Among these organic solvents, alicyclic alcohols such as terpineol and C _1-4 alkyl cellosolve acetates such as butyl carbitol acetate are preferable from the viewpoint of fluidity of the paste.

  When combining an organic binder and an organic solvent, the ratio of the organic binder is, for example, 1 to 200 parts by weight, preferably 10 to 100 parts by weight, and more preferably about 30 to 80 parts by weight with respect to 100 parts by weight of the organic solvent. Yes, about 5 to 80% by mass, preferably 10 to 50% by mass, and more preferably about 15 to 40% by mass with respect to the whole organic vehicle.

  The volume ratio of the organic vehicle is, for example, about 10 to 80% by mass, preferably about 20 to 75% by mass, and more preferably about 30 to 70% by mass with respect to the entire volume of the conductive paste. The mass ratio of the organic vehicle is, for example, 1 to 200 parts by mass, preferably 5 to 150 parts by mass, more preferably 100 parts by mass with respect to 100 parts by mass of the conductive component (the total amount of the refractory metal particles, molten alloy particles and active metal particles). About 10 to 100 parts by mass.

(Other ingredients)
The conductive paste may further contain a conventional additive as long as the effects of the present invention are not impaired. Conventional additives include, for example, inorganic binders (such as glass frit), curing agents (such as curing agents for acrylic resins), colorants (such as dyes and pigments), hue improvers, dye fixing agents, gloss imparting agents, metals Corrosion inhibitors, stabilizers (antioxidants, UV absorbers, etc.), surfactants or dispersants (anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc.), dispersion Stabilizers, viscosity modifiers or rheology modifiers, humectants, thixotropic agents, leveling agents, antifoaming agents, bactericides, fillers and the like can be mentioned. These other components can be used alone or in combination of two or more. The ratio of the other components can be selected according to the type of the component, and is usually about 10% by mass or less (for example, 0.01 to 10% by mass) with respect to the entire conductive paste. Furthermore, the conductive paste of the present invention may not contain an inorganic binder such as glass frit.

[Electronic substrate manufacturing method]
The electronic substrate (ceramic substrate with a conductive part) of the present invention is subjected to an attaching step of attaching the conductive paste to a ceramic substrate, and a firing step of firing the conductive paste attached to the ceramic substrate to form a conductive part. can get.

  In the attaching process, the method of attaching the conductive paste can be selected according to the type of the electronic substrate. In the case of a surface metallized substrate or through-hole wall surface metallized substrate, the conductive paste is applied to the surface of the substrate or the inner wall of the through hole (through hole). In the via-filled substrate, a conductive paste may be filled into the front and back through holes (via filling). Since the conductive paste of the present invention does not shrink during firing, the shape can be maintained after firing regardless of the type of electronic substrate.

  Examples of the conductive paste application and filling methods include screen printing, ink jet printing, intaglio printing (eg, gravure printing), lithographic printing, offset printing, flexographic printing, and the like. And a direct press-fitting method such as a spin coating method, a dipping method, a roll press-fitting method, a squeegee press-fitting method, and a press press-fitting method. Of these methods, the screen printing method and the like are preferable.

  The paste adhered to the substrate may be naturally dried before firing, or may be dried by heating. The heating temperature can be selected according to the type of the organic solvent, and is, for example, about 50 to 200 ° C, preferably about 80 to 180 ° C, and more preferably about 100 to 150 ° C. The heating time is, for example, about 1 minute to 3 hours, preferably about 5 minutes to 2 hours, and more preferably about 10 minutes to 1 hour.

  In the firing step, the firing temperature may be equal to or higher than the sintering temperature of the refractory metal particles in the conductive paste. The firing temperature (maximum temperature reached) may be 500 ° C. or higher, for example, 750 to 1000 ° C. (eg 780 to 980 ° C.), preferably 800 to 950 ° C., more preferably 850 to 930 ° C. (especially 880 to 920 ° C.). ) Firing time (firing time at the highest temperature reached) is, for example, 1 minute to 3 hours, preferably 3 minutes to 1 hour, and more preferably about 5 to 30 minutes. If the firing temperature is too low, the reaction does not proceed sufficiently and the bonding strength with the substrate may be weakened. On the other hand, if the firing temperature is too high, the fluidity of the melted component increases, and there is a risk that patterning will be deteriorated due to the occurrence of creaking, shrinkage, or bleeding.

  The firing atmosphere can be selected according to the type of metal particles, and is not particularly limited. The firing atmosphere can be any of air, inert gas (eg, nitrogen gas, argon gas, helium gas) atmosphere, and vacuum atmosphere. However, it is preferably in an inert gas atmosphere because an electronic substrate can be manufactured with high productivity. In particular, in the present invention, a nitrogen atmosphere is particularly preferable because the pattern can be firmly bonded to the substrate even in a nitrogen gas atmosphere.

  Firing (especially in a nitrogen atmosphere) may be performed using a batch furnace or a belt-conveying tunnel furnace.

  The conductive part (metallized film or via filling part) obtained by baking may have its surface physically or chemically polished. Examples of the physical polishing method include buff polishing, lapping polishing, polishing polishing, and the like. Examples of the chemical polishing method (surface treatment method) include a method of soft-etching the outermost surface with an aqueous sodium persulfate solution.

  After physically or chemically polishing, the metallized film or via filling surface may be plated. As a plating method, various plating methods can be used regardless of electrolysis or electroless. Furthermore, the metal species of the plating layer can be selected widely. For example, nickel gold plating, nickel palladium gold plating, tin plating, solder plating may be used to improve solder bondability, wire bondability, bump bondability, etc. In order to increase the reflectivity, silver plating may be used.

  Further, a general-purpose conductive paste such as a copper paste or a silver paste may be stacked on the metallized film or via filling portion to increase the film thickness.

  Furthermore, when the electronic substrate is a via-filled substrate or a through-hole wall-surface metallized substrate, the via-filled portion and the wall-surface metallized film are provided for the purpose of improving the conductivity between the front and back of the substrate and the thermal conductivity. The wiring pattern may be the conductive paste of the present invention, but may be a general-purpose conductive paste. For example, in the via-filled substrate, only the via-filled portion may be formed with the conductive paste of the present invention, and the surface electrode and the wiring may be formed by sputtering or plating.

[Electronic substrate]
An electronic substrate of the present invention is obtained by the above manufacturing method, and includes a ceramic substrate, a high melting point metal having a melting point equal to or higher than a firing temperature, a molten alloy having a melting point of 400 ° C. or less, and a conductive part including an active metal. I have.

  The material of the ceramic substrate may be any ceramic that can react with active metals, such as metal oxides (quartz, alumina or aluminum oxide, zirconia, sapphire, ferrite, zinc oxide, niobium oxide, mullite, beryllia, etc.), oxidation Silicon (such as silicon dioxide), metal nitride (such as aluminum nitride and titanium nitride), silicon nitride, boron nitride, carbon nitride, metal carbide (such as titanium carbide and tungsten carbide), silicon carbide, boron carbide, metal double oxide [ Metal titanate (barium titanate, strontium titanate, lead titanate, niobium titanate, calcium titanate, magnesium titanate, etc.), metal zirconate (barium zirconate, calcium zirconate, lead zirconate, etc.), etc. ] Etc. are mentioned. These ceramics can be used alone or in combination of two or more.

  Of these ceramic substrates, an alumina substrate, an alumina-zirconia substrate, an aluminum nitride substrate, a silicon nitride substrate, and a silicon carbide substrate are preferable from the viewpoint of high reliability in the electric and electronic field, and further have high heat resistance, Cu particles, Ag An alumina substrate, an aluminum nitride substrate, and a silicon nitride substrate are particularly preferable because the effect of improving the bonding force with a refractory metal such as particles is great.

  The thickness of the ceramic substrate may be appropriately selected depending on the application, and is, for example, about 0.001 to 10 mm, preferably 0.01 to 5 mm, more preferably 0.05 to 3 mm (particularly 0.1 to 1 mm). May be.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In the following examples, the materials used in the examples, the pattern of the substrate for evaluation, and the evaluation method of the obtained electronic substrate are shown below.

[Materials used]
(High melting point metal particles)
Cu particles A: copper particles having a center particle diameter of 0.1 μm, melting point 1085 ° C.
Cu particles B: copper particles having a center particle size of 0.5 μm, melting point 1085 ° C.
Cu particles C: copper particles having a center particle diameter of 3 μm, melting point 1085 ° C.
Cu particle D: Copper particle having a center particle diameter of 7 μm, melting point of 1085 ° C.
Cu particles E: copper particles having a center particle diameter of 15 μm, melting point 1085 ° C.
Ag particles: silver particles with a center particle size of 0.5 μm, melting point 962 ° C.
Ni particles: nickel particles having a central particle diameter of 0.7 μm, melting point 1455 ° C.

(Molten alloy particles)
SnAgCu particles: Sn-Ag-Cu alloy particles having a center particle size of 5 μm, melting point 220 ° C.
SnBi particles: Sn-Bi alloy particles having a center particle diameter of 5 μm, melting point 140 ° C.
AuSn particles: Au-Sn alloy particles having a center particle diameter of 5 μm, melting point 280 ° C.
AgCu particles: Ag—Cu alloy particles having a center particle diameter of 5 μm, melting point 780 ° C.

(Active metal particles)
Titanium hydride (TiH ₂ ) particles: Titanium hydride particles with a center particle size of 6 μm Titanium boride (TiB ₂ ) particles: Titanium boride particles with a center particle size of 3 μm Zirconium hydride (ZrH ₂ ) particles: with a center particle size of 5 μm Zirconium hydride particles.

(Organic vehicle)
Organic binder: Polybutylmethacrylate Organic solvent: Terpineol.

[Pattern for evaluation substrate]
A sample in which square patterns of 2 mm × 2 mm size were arranged vertically and horizontally on the surface of a ceramic substrate of 50.8 mm × 50.8 mm was used as an evaluation substrate. The patterns were connected by a thin line so that electroplating was possible.

[Evaluation of electronic board]
(Pattern shape)
The appearance (2 mm × 2 mm square pattern) of the electronic board after firing was observed visually and with a magnifying glass (15 times), and the pattern held without deformation was further image-measured, and the following criteria It was evaluated with.

× (Edge turning): The edge of the pattern is turned up × (Shrink): The edge of the pattern is not turned up, but the square is broken and the edge is rounded, or the size is down ○ (Good) ): The shape of the 2 mm × 2 mm pattern is held without being deformed, but is not in the range of 1.97 mm × 1.97 mm to 2.03 mm × 2.03 mm when the image is further measured. The shape of the 2 mm x 2 mm pattern is held without deformation, and the size of the 2 mm x 2 mm pattern is hardly changed in the image measurement, and the range of 1.97 mm x 1.97 mm to 2.03 mm x 2.03 mm is maintained. is there.

(Peel strength test and fracture condition)
A peel strength test was performed on an electronic substrate having a good pattern shape. After soldering a tin-plated copper wire (peel wire) along the top surface of a 2 mm x 2 mm square pattern (through the center of the square and parallel to the side), peel the peel wire outside the 2 mm pattern The film was peeled off by bending 90 degrees and pulled vertically upward with respect to the substrate surface, and the peel strength was measured. The highest strength at break was recorded as the peel strength. Moreover, the destruction place after a test was observed and the destruction state was evaluated according to the following criteria.

◎ (Substrate destruction): The substrate is destroyed so that it can be punched, and the peel strength is 4 kg or more. ○ (Substrate failure): The substrate is destroyed so that it can be punched, and the peel strength is 2 kg or more and less than 4 kg. ): Fracture at the interface between the substrate and the metallized film, and peel strength of 2 kg or more x (Interfacial failure): Fracture at the interface between the substrate and the metallized film, and peel strength of less than 2 kg x (In-film failure): Metallization The film is broken inside and broken inside the film, and the peel strength is less than 2 kg.

(Comprehensive judgment)
The evaluation result of the pattern shape and the evaluation result of the peel strength test were comprehensively evaluated according to the following criteria.

◎: Both pattern shape and peel strength are judged as “◎”
○: Both the pattern shape and peel strength are judged as “○”, or one is “◎” and the other is “○”.
X: Either the pattern shape or the peel strength determination is “x”.

Example 1
The paste 1 prepared with the composition shown in Table 1 was printed on the evaluation pattern by screen printing, and then fired in a tunnel furnace substituted with nitrogen. An aluminum nitride substrate was used as the ceramic substrate. Firing was performed at a maximum temperature of 900 ° C., this temperature was maintained for 10 minutes, and the time from charging to collection including temperature rise and fall was about 60 minutes. When the metallized film on the substrate after firing coming out of the furnace was observed, it was in a good shape. After baking the surface of the metallized film after baking, electrolytic nickel gold plating was applied to the surface. When subjected to a peel strength test of the obtained electronic substrate, the failure mode was substrate failure, and the substrate and the metallized film were bonded at a strength higher than the substrate strength, indicating sufficient bondability.

Examples 2-3
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 2 and 3 shown in Table 1 were used instead of the paste 1 and the molten alloy particles in the paste were changed. The obtained electronic substrate was good in both the pattern shape and peel test. However, in relative evaluation with Example 1, the pattern shape of Example 2 slightly decreased, and the peel strength of Example 3 slightly decreased.

Examples 4-5
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 4 and 5 shown in Table 1 were used instead of the paste 1 and the active metal particles in the paste were changed. The obtained electronic substrate was good in both the pattern shape and peel test. However, in any relative evaluation with Example 1, the peel strength slightly decreased.

Examples 6-7
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 6 and 7 shown in Table 1 were used instead of the paste 1 and the refractory metal particles in the paste were changed. The obtained electronic substrate had the same good results as in Example 1 both in the pattern shape and peel test.

Examples 8-9
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 8 and 9 shown in Table 1 were used instead of the paste 1 and the ratio of the refractory metal particles and the molten alloy particles in the paste was changed. The obtained electronic substrate was good in both the pattern shape and peel test. However, in the relative evaluation with Example 1, the peel strength of Example 8 slightly decreased, and the pattern shape of Example 9 slightly decreased.

Examples 10-11
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 10 and 11 shown in Table 1 were used instead of the paste 1 and the ratio of the active metal particles in the paste was changed. The obtained electronic substrate was good in both the pattern shape and peel test. However, in the relative evaluation with Example 1, both the pattern shape and the peel strength in Example 10 were slightly decreased, and the peel strength in Example 11 was slightly decreased.

Examples 12-14
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 12 to 14 shown in Table 1 were used instead of the paste 1 and the molten alloy particles in the paste were replaced with the two types of molten alloy particles shown in Table 1. . The obtained electronic substrate was good in both the pattern shape and peel test. Specifically, in Example 12, the pattern shape and the peel test were the same results as in Example 1. In Example 13, whether the fluidity was adjusted to an appropriate range by combining molten alloy particles having a melting point exceeding 400 ° C. with molten alloy particles having a melting point of 400 ° C. or less. Compared to the pattern shape. Furthermore, in Example 14, the pattern shape and the peel test were the same results as in Example 3.

Examples 15-18
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 15 to 18 shown in Table 1 were used instead of the paste 1 and the particle diameter of the refractory metal particles in the paste was changed. The obtained electronic substrate was good in both the pattern shape and peel test. However, in relative evaluation with Example 1, the peel strength of Example 15 is slightly reduced, the pattern shape of Examples 16 to 17 is slightly reduced, and the pattern shape and peel strength of Example 18 are slightly reduced. did.

Examples 19-20
An electronic substrate was obtained in the same manner as in Example 1 except that the paste was not changed and the type of the ceramic substrate was changed to alumina or silicon nitride. The obtained electronic substrate had the same good results as in Example 1 both in the pattern shape and peel test.

Examples 21-23
The electronic substrate was obtained in the same manner as in Example 1 except that the paste was not changed and the firing temperature was changed. The obtained electronic substrate was good in both the pattern shape and peel test. The obtained electronic substrate was the same as Example 1 in both the pattern shape and peel test in Example 22 where the firing temperature was 850 ° C., but in Example 21 where the firing temperature was 800 ° C. In Example 23 in which the strength was slightly lower than in Example 1 and the firing temperature was 950 ° C., the pattern shape was slightly lower than in Example 1.

Comparative Examples 1-3
Example except that pastes 19 to 21 shown in Table 2 were used instead of paste 1, and the alloy was changed using only Ag—Cu alloy particles having a melting point of 780 ° C. without using an alloy having a melting point of 400 ° C. or less as the molten alloy particles. In the same manner as in Example 1, an electronic substrate was obtained. In Comparative Example 1, the pattern shape was good, but the peel strength was low, and sufficient bonding could not be obtained. As the proportion of the Ag—Cu alloy particles was increased, the pattern shape was lowered, and edge turning and shrinkage occurred. From these results, an electronic substrate having a good pattern shape and excellent bondability with the substrate could not be obtained only with a melting component having a high melting point.

  Table 2 shows the evaluation results of the electronic substrates obtained in the examples and comparative examples.

  The conductive paste of the present invention can be used for a circuit board, an electronic component, a semiconductor package substrate, and the like, and can be particularly effectively used as a paste for forming a conductive portion of an electronic substrate.

Claims (17)

  A high-melting-point metal particle having a melting point exceeding the firing temperature, a molten alloy particle containing an alloy that melts at the firing temperature and has a melting point of 400 ° C. or less, an active metal particle that contains an active metal, and a conductive material that includes an organic vehicle Sex paste.   The conductive paste according to claim 1, wherein the molten alloy particles contain Sn.   The conductive paste according to claim 2, wherein the molten alloy particles include at least one selected from the group consisting of Sn—Ag—Cu alloy particles, Sn—Bi alloy particles, and Au—Sn alloy particles.   The conductive paste according to claim 1, wherein the active metal is Ti and / or Zr.   The conductive paste according to claim 4, wherein the active metal particles are at least one selected from the group consisting of titanium hydride particles, titanium boride particles, and zirconium hydride particles.   The conductive paste according to any one of claims 1 to 5, wherein the refractory metal particles are formed of at least one metal selected from the group consisting of Cu, Ag, and Ni or an alloy containing the metal.   7. The conductive paste according to claim 1, wherein a mass ratio of the refractory metal particles and the molten alloy particles is refractory metal particles / molten alloy particles = 90/10 to 40/60.   The conductive paste according to any one of claims 1 to 7, wherein the ratio of the active metal particles is 0.5 to 30 parts by mass with respect to 100 parts by mass in total of the refractory metal particles and the molten alloy particles.   The conductive paste according to any one of claims 1 to 8, wherein the molten alloy particles have a center particle size of 0.1 to 15 µm.   The conductive paste according to claim 1, wherein the active metal particles have a center particle size of 1 to 15 μm.   The conductive paste according to claim 1, wherein the refractory metal particles have a center particle size of 0.01 to 10 μm.   An electronic substrate comprising: an attaching step of attaching the conductive paste according to claim 1 to a ceramic substrate; and a firing step of firing the conductive paste attached to the ceramic substrate to form a conductive portion. Production method.   The manufacturing method of Claim 12 which bakes an electrically conductive paste in nitrogen atmosphere in a baking process.   The method according to claim 12 or 13, wherein in the firing step, the firing temperature is 800 to 950 ° C.   An electronic substrate comprising a ceramic substrate, a high melting point metal having a melting point equal to or higher than a firing temperature, a molten alloy having a melting point of 400 ° C. or lower, and a conductive part including an active metal.   The electronic substrate according to claim 15, wherein the ceramic substrate is an alumina substrate, an alumina-zirconia substrate, an aluminum nitride substrate, a silicon nitride substrate, or a silicon carbide substrate.   The electronic substrate according to claim 15 or 16, which is a surface metallized substrate, a via-filled substrate, or a through-hole wall surface metallized substrate.