JP6654613B2 - Conductive paste, electronic substrate and method of manufacturing the same - Google Patents

Description

  The present invention forms a conductive portion such as an electrode or a circuit on a ceramic substrate, and uses a conductive paste for manufacturing an electronic substrate such as a surface metalized substrate, a via-filled substrate, a through-hole wall metalized substrate, and the paste. The present invention relates to an obtained electronic substrate (ceramic substrate with a conductive portion) and a method for manufacturing the same.

  Conventionally, as a paste material for forming electrodes and circuits on the surface of a ceramic substrate, a 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 is generally used. Is 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 it at a temperature higher than the softening point of the glass component and lower than the melting point of the metal in the firing step. That is, in this paste, the glass component melted and softened by heating wets the ceramic substrate, and the paste and the substrate are joined together, and the metal powder is sintered to form a conductive portion. The conductive paste containing such 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 could not be denied that joining with a glass component was inferior in terms of joining strength as compared with other joining methods. In particular, with respect to ceramic substrates such as an aluminum nitride substrate and a silicon nitride substrate that are often used for the purpose of heat dissipation of high-power semiconductors, the glass component is hardly wet, and it has been difficult to obtain sufficient bonding strength. Therefore, in applications requiring high reliability, a thin film method by sputtering or a method of attaching a metal foil or a metal plate to a substrate using an active metal brazing is often used. However, these metallization methods are expensive, and there is still a strong demand for improving the bonding strength in a paste printing method that requires low cost.

  In JP-A-5-226515 (Patent Document 1), an aluminum nitride substrate is prepared by adding a compound of titanium (titanium hydride) as an active metal species to a conductive paste mainly containing an Ag-Cu alloy. A metallizing method for firmly joining a metallized layer is disclosed. According to this document, firing is performed in a non-oxidizing atmosphere, an inert atmosphere, or a vacuum atmosphere in order to prevent decomposition and oxidation of the Ag-Cu alloy and titanium hydride. It has been fired.

  In this method, the particles of the active metal or its compound are unlikely to react with the substrate surface when the active metal is used alone. Therefore, an appropriate molten component (often an Ag-Cu alloy) is used together. Therefore, it is easy to flow during firing, and it is difficult to form a pattern such as an electrode or a wiring, and is often used for applications such as bonding of metal plates. Furthermore, when firing in a vacuum, the substrate and the metallized layer are firmly joined to each other, and the pattern shape tends to be easily maintained. However, the Ag-Cu alloy melted during firing still shrinks and turns over, And the pattern tends to collapse due to being small and round. This tendency is particularly remarkable 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 a portion that is slightly in contact with the pattern is turned up. It is in a state of being barely joined to the substrate. It is presumed that firing in a vacuum in the embodiment of this document is due to such circumstances. Therefore, the paste of this document may be capable of firmly bonding a fine pattern shape such as electrodes and circuits to a substrate by vacuum firing, but the vacuum firing is a batch type and requires a very long time to raise or lower the temperature. Therefore, when nitrogen calcination is performed on a conveyor to improve productivity, the metallized layer shrinks, and it is difficult to maintain a fine pattern shape 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. According to this document, conventional titanium hydride is decomposed into hydrogen and titanium at about 400 to 500 ° C., and highly reactive titanium reacts with oxygen or carbon of a decomposition gas of an organic substance contained in the paste to form a ceramic. It is described that joining with a member was hindered.

  On the other hand, Patent Document 1 describes that titanium hydride is stable up to 700 ° C. However, in any case, since the firing temperature is as high as about 850 ° C., oxygen, carbon, nitrogen, etc. Exposure to this gas did not work well, and baking was usually performed in a vacuum without the gas.

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

  Therefore, an object of the present invention is to provide a conductive paste capable of firmly joining a conductive portion to a ceramic substrate, an electronic substrate obtained by using the paste, and a method of 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 non-oxidizing or inert atmosphere, an electronic substrate obtained by using this paste, and production thereof. It is to provide a method.

  The present inventors have conducted intensive studies to achieve the above object, and as a result, high melting point metal particles having a melting point higher than the sintering temperature, molten metal particles which are melted at the sintering temperature and have a melting point of 700 ° C. or less, The present inventors have found that when a conductive paste obtained by combining active metal particles containing a metal and an organic vehicle is applied or filled to a ceramic substrate and fired, the conductive portion can be firmly joined to the ceramic substrate, and the present invention has been completed.

  That is, the conductive paste of the present invention has high melting point metal particles having a melting point higher than the firing temperature, molten metal particles having a melting point of 700 ° C. or lower, and active metal particles containing an active metal. And an organic vehicle, and does not include an alloy that is melted at a firing temperature and has a melting point of 400 ° C. or less. The molten metal particles may include at least one selected from Mg, Al, Zn, In, Sn, Bi, Pb, and Sb. 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 the metal. The mass ratio between the high melting point metal particles and the molten metal particles is approximately high melting point metal particles / molten metal particles = 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 high melting point metal particles and the molten metal particles. The central particle diameter of the molten metal particles is 0.01 to 30 μm. The central particle size of the active metal particles is about 0.1 to 15 μm. The central particle diameter of the refractory metal particles is about 0.01 to 15 μm.

  The present invention also includes a method of manufacturing an electronic substrate including a step of attaching the conductive paste to a ceramic substrate and a 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 non-oxidizing gas or an inert gas (particularly, nitrogen) atmosphere. In the firing step, the firing temperature is about 800 to 950 ° C.

  The present invention includes a ceramic substrate, a high-melting metal having a melting point equal to or higher than a firing temperature, a molten metal which is melted at a firing temperature and has a melting point of 700 ° C or lower, and a conductive portion including an active metal. Electronic substrates are also included. 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 metallized substrate.

  In the present invention, a combination of a high melting point metal particle having a melting point not lower than the firing temperature, a molten metal particle melted at the firing temperature and having a melting point of 700 ° C. or lower, an active metal particle containing an active metal, and an organic vehicle Therefore, the conductive portion can be firmly bonded to the ceramic substrate, and in particular, can be firmly bonded to the ceramic substrate without breaking a fine pattern shape even when baked in a non-oxidizing or inert atmosphere.

[Conductive paste]
The conductive paste of the present invention has high melting point metal particles having a melting point not lower than the firing temperature, molten metal particles having a melting point of 700 ° C. or lower, and active metal particles containing an active metal, Vehicle. The reason why the conductive portion can be firmly joined to the ceramic substrate by using the conductive paste of the present invention can be estimated as follows. In other words, the molten metal particles contained in the paste are melted at a low temperature and cover the surface of the active metal particles, so that even at a high temperature, the active metal or its compound is present in the surrounding gas (nitrogen and organic vehicle in the firing atmosphere gas are decomposed). Reacting with carbon and the like generated during the reaction). By such an action, the active metal can maintain its activity even at a high temperature even in a non-oxidizing or inert atmosphere (for example, a nitrogen atmosphere). It is presumed that it becomes possible to wet the ceramic substrate and react between the active metal and the ceramic substrate, thereby suppressing the metallized film from being turned up or shrunk. In addition, since the molten metal is literally liquefied and flows, the phenomenon that the pattern is turned up or shrinks round, or the phenomenon that the pattern spreads because it is too wet on the substrate, is completely controlled only by such an action. It can be estimated that it cannot be done. Therefore, in the present invention, the above-described shrinkage and spreading phenomena are suppressed by adding high melting point metal particles separately from the molten metal and the active metal compound. In other words, it can be assumed that the molten metal component also prevents excessive flow by wetting the surface of the high melting point metal particles. Depending on the type of the molten metal and the high melting point metal, it is also possible to suppress fluidization by utilizing the fact that the alloying proceeds between the molten metal and the high melting point metal during firing and the melting point of the molten metal increases. .

(High melting point metal particles)
The metal forming the high melting point metal particles is not particularly limited as long as it has a melting point higher than the firing temperature (for example, higher than 950 ° C. and 2500 ° C. or lower). 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 types of metal particles, and may be formed of an alloy combining two or more kinds as long as the melting point is equal to or higher than the firing temperature. Among these metals, at least one metal selected from the group consisting of Cu, Ag and Ni or an alloy containing this metal is preferable.

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

  Examples of the shape of the refractory metal particles include a spherical shape (true spherical shape or substantially spherical shape), an ellipsoidal shape (elliptical spherical shape), a polygonal shape (polygonal shape such as a polygonal pyramid, a square or a rectangular parallelepiped), and a plate shape. (A flat shape, a scale shape, a flake shape, etc.), a rod shape or a rod shape, a fiber shape, a tree needle shape, an irregular shape, and the like. The shape of the refractory metal particles is usually spherical, elliptical, polygonal, irregular, or the like.

  The center particle diameter or the 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 of maintaining both the pattern shape retention and the adhesion to the ceramic substrate. It is preferably about 0.05 to 10 μm (for example, 0.1 to 7 μm), and more preferably about 0.3 to 1 μm (particularly 0.4 to 0.8 μm). Further, the center particle size of the high melting point 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, and the adhesion to the ceramic substrate may be reduced. For important applications, it may for example be of the order of 0.2 to 10 μm (particularly 0.3 to 8 μm). If the particle size is too small, the economic efficiency may decrease, and the dispersibility in the paste may also decrease. If the particle size is too large, the printability and uniformity of dispersion of the paste may decrease.

  In the present description and the appended claims, the central particle size means an average particle size (based on volume) measured using a laser diffraction / scattering type particle size distribution analyzer.

  The melting point of the high melting point metal particles may be any melting point not lower than the firing temperature, and may be, for example, higher than 950 ° C and not higher than 2500 ° C, preferably 955-2000 ° C, more preferably 960-1500 ° C (particularly 980 ° C). 〜1200 ° C.). If the melting point is too low, it may be difficult to form a pattern having a fine shape.

  The high melting point metal particles can be produced by a conventional method, for example, by various production methods such as a wet reduction method, an electrolytic method, an atomizing method, and a water atomizing method.

(Molten metal particles)
The molten metal particles are particles that melt at the firing temperature and have a melting point of 700 ° C. or less, and melt at the firing temperature. The bondability with the ceramic substrate can be improved.

  The metal forming the molten metal particles is not particularly limited as long as the metal is at a firing temperature or lower and has a melting point of 700 ° C. or lower. Specifically, examples of the metal include Mg, Al, Zn, In, Sn, Bi, Pb, and Sb. These metals can be used alone or in combination of two or more. The metal particles may be a combination of different types of metal particles, and may be formed of an alloy combining two or more kinds as long as the melting point is equal to or lower than the firing temperature and equal to or lower than 700 ° C. Among these metals, at least one metal selected from the group consisting of In, Sn, and Bi or an alloy containing this metal (particularly, a single metal) is preferable.

  The melting point of the molten metal particles may be not higher than the firing temperature and not higher than 700 ° C., preferably not higher than 400 ° C., for example, 60 to 700 ° C., preferably 80 to 600 ° C. (eg, 100 to 500 ° C.), and Preferably it is about 120 to 400 ° C (particularly 200 to 250 ° C).

  The molten metal particles having a melting point of 700 ° C. or less (first molten metal particles) include, for example, Mg particles (melting point 651 ° C.), Al particles (melting point 660 ° C.), Zn particles (melting point 419 ° C.), In particles (melting point 419 ° C.) 156 ° C.), Sn particles (melting point 232 ° C.), Bi particles (melting point 271 ° C.), Pb particles (melting point 528 ° C.), Sb particles (630 ° C.), and the like. Further, the first molten metal particles may be alloy particles such as Al-Si-Fe-Cu alloy particles and Ag-Cu-Zn-Sn alloy particles. Such a molten metal particle (alloy particle) may be a solder powder used for a solder paste or the like, for example, Al-12Si-0.8Fe-0.3Cu (melting point 580 ° C), 58Ag-22Cu- 17Zn-5Sn (melting point 650 ° C.). These first molten metal particles can be used alone or in combination of two or more.

  Among these first molten metal particles, In particles, Sn particles, and Bi particles are preferable in terms of fluidity and the like, and Sn particles are particularly preferable in that a fine pattern can be firmly bonded to a substrate.

  The molten metal particles further include, in addition to the first molten metal particles, metal particles having a melting point of more than 700 ° C. and equal to or lower than the firing temperature (second molten metal particles) within a range not impairing the effects of the present invention. You may go out. By combining with the second molten metal particles, the fluidity of the first molten metal particles can be adjusted, and the bonding between the substrate and the conductive portion and the fine pattern shape can be compatible.

  The melting point of the second molten metal particles is, for example, more than 700 ° C and 880 ° C or less, preferably 730 to 850 ° C, and more preferably about 750 to 800 ° C.

  The second molten metal particles are not particularly limited as long as they have such a melting point, and may be metal particles such as Ba (melting point 717 ° C.) and Ce (melting point 785 ° C.). The alloy particles containing the metal contained in the first molten metal particles are preferable because the affinity with the molten metal particles can be improved, and the high melting point metal particles are formed because the wettability with the high melting point metal particles can be improved. Alloy particles containing a metal (Cu, Ag, etc.) are also preferred. Among them, it is particularly preferable that both the first and second molten metal particles are formed of an alloy containing a metal (Cu, Ag, or the like) that forms the high melting point metal particles. Preferred second molten metal particles are alloys containing Cu and / or Ag (for example, Ag-Cu alloys), such as silver brazing material 72Ag-28Cu (melting point about 780 ° C.) widely used as brazing material paste. Is mentioned.

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

  The molten metal particles can be produced by a so-called atomizing method or the like in which a gas, air, water, or the like is sprayed on the alloy in a molten state to instantaneously perform pulverization and cooling and solidification to form a powder. Among these methods, particles produced by a water atomizing method in which water is sprayed may be used because alloy particles having a micron order close to a perfect sphere can be produced.

  Examples of the shape of the molten metal particles include a spherical shape (true spherical shape or substantially spherical shape), an ellipsoidal shape (elliptical spherical shape), a polygonal shape (polygonal shape such as a polygonal pyramid, a square or a rectangular parallelepiped), and a plate shape ( Flat, scale-like or flake-like), rod-like or rod-like, fibrous, irregular-shaped and the like. The shape of the molten metal particles is usually spherical, elliptical, polygonal, irregular, or the like.

  The central particle diameter (D50) of the molten metal particles is, for example, about 0.01 to 30 μm, preferably about 0.1 to 25 μm, and more preferably about 0.5 to 20 μm (particularly about 1 to 10 μm). If the particle size is too small, the yield in the production of the particles may be significantly reduced, and the cost may be significantly increased. Conversely, if the particle size is too large, the ratio of one particle size at the time of forming a fine pattern becomes high, and the uniformity in the pattern decreases, and defects such as chipping of a pattern, voids, and non-uniform bonding with a substrate are caused. This may occur. Further, when printing with a mesh screen, there is a possibility that mesh clogging may be caused.

  The mass ratio of the high melting point metal particles to the molten metal particles can be selected, for example, from the range of high melting point metal particles / molten metal particles = about 99/1 to 10/90, for example, 95/5 to 30/70 (for example, 90/5). / 10 to 40/60), preferably about 85/15 to 45/55, more preferably about 80/20 to 50/50 (particularly about 75/25 to 60/40). If the ratio of the molten metal particles is too large, the fluidity of the molten alloy cannot be sufficiently suppressed, and the edge of the pattern is likely to be turned up due to shrinkage during firing and to seep out of the pattern. On the other hand, if the ratio of the molten metal particles is too small, the solid-liquid contact interface serving as a reaction field between the ceramic substrate and the active metal component is reduced, so that good bonding may not be obtained.

(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. Among these active metals, Ti and / or Zr are preferable, and Ti is particularly preferable, since they have excellent activity in the firing step and can improve the bonding strength between the ceramic substrate and the conductive portion.

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

The compound containing the active metal is not particularly limited. For example, a titanium compound [eg, 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. And hafnium compounds [for example, hafnium boride (HfB ₂ ), hafnium hydride (HfH ₂ ), hafnium sulfide (HfS ₂ ), hafnium tetrachloride (HfCl ₄ ), and the like. Among these, titanium hydride (TiH ₂ ), titanium boride (TiB ₂ ), and zirconium hydride (ZrH ₂ ) are preferable from the viewpoint of excellent activity in the firing step.

  These active metal particles containing an active metal 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 preferable.

  Examples of the shape of the active metal particles include a spherical shape (true spherical shape or substantially spherical shape), an ellipsoidal shape (elliptical spherical shape), a polygonal shape (polygonal shape such as a polygonal pyramid, a square or a rectangular parallelepiped), and a plate shape ( Flat, scale-like or flake-like), rod-like or rod-like, fibrous, irregular-shaped and the like. The shape of the active metal particles is usually spherical, elliptical, polygonal, irregular, or the like.

  The central particle diameter (D50) of the active metal particles is, for example, about 0.1 to 15 μm (eg, 1 to 15 μm), preferably about 0.5 to 10 μm, and more preferably about 1 to 7 μm (particularly about 3 to 6 μm). The smaller the particle size, the better in terms of paste uniformity. However, if the particle size is too small, the yield in the preparation of the particles may be significantly reduced, and the economic efficiency may be reduced. On the other hand, if the particle diameter is too large, the ratio of one particle size in the formation of a fine pattern increases, and the uniformity in the pattern decreases, so that defects such as chipping of a pattern, voids, and non-uniform bonding with a substrate are caused. Easy to occur. In addition, when printing with a mesh screen, mesh clogging may occur.

  The ratio of the active metal particles can be selected from a range of about 0.1 to 50 parts by mass relative to a total of 100 parts by mass of the high melting point metal particles and the molten metal particles, for example, 0.3 to 40 parts by mass (for example, 0.5 to 0.5 parts by mass). To 30 parts by mass), preferably 1 to 20 parts by mass (for example, 1.5 to 4 parts by mass), and more preferably about 2 to 10 parts by mass (particularly 2.5 to 5 parts by mass). If the ratio of the active metal particles is too small, there is a possibility that the bondability with the ceramic substrate is reduced. Conversely, if the amount is too large, the metallized film and the filled via may be fragile.

(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 (a solution of the organic binder in the organic solvent).

The organic binder is not particularly limited, and includes, for example, a thermoplastic resin (olefin resin, vinyl resin, acrylic resin, styrene resin, polyether resin, polyester resin, polyamide resin, cellulose derivative, etc.), Thermosetting resins (thermosetting acrylic resins, epoxy resins, phenolic resins, unsaturated polyester resins, polyurethane resins, etc.) and the like can be mentioned. These organic binders can be used alone or in combination of two or more. Among these organic binders, resins that are easily burned off during the firing process and have low ash content, for example, acrylic resins (polymethyl methacrylate, polybutyl methacrylate, etc.), cellulose derivatives (nitrocellulose, ethyl cellulose, butyl cellulose, cellulose acetate) ), Polyether resins (such as polyoxymethylene), and rubbers (such as polybutadiene and polyisoprene) are widely used, and from the viewpoint of thermal decomposability, polymethyl (meth) acrylate and poly (meth) acrylic acid are used. Poly (meth) acrylic acid C _1-10 alkyl esters such as butyl are preferred.

The organic solvent is not particularly limited, and may be any organic compound that imparts an appropriate viscosity to the paste and can be easily volatilized by a drying treatment after the paste is applied to a substrate, and may be a high-boiling organic solvent. Good. Such organic solvents include, for example, aromatic hydrocarbons (such as para-xylene), esters (such as ethyl lactate), ketones (such as isophorone), amides (such as dimethylformamide), and aliphatic alcohols (octanol and decanol). , Diacetone alcohol, etc.), cellosolves (methyl cellosolve, ethyl cellosolve, etc.), cellosolve acetates (ethyl cellosolve acetate, butyl cellosolve acetate, etc.), carbitols (carbitol, methyl carbitol, ethyl carbitol, etc.), carbitol Acetates (ethyl carbitol acetate, butyl carbitol acetate, etc.), aliphatic polyhydric alcohols (ethylene glycol, diethylene glycol, dipropylene glycol, butanediol, triethylene) Glycols, glycerin, etc.), alicyclic alcohols [eg, cycloalkanols such as cyclohexanol; terpeneols, terpene alcohols such as dihydroterpineol (such as monoterpene alcohol)], aromatic alcohols (such as metacresol), Examples thereof include aromatic carboxylic acid esters (such as dibutyl phthalate and dioctyl phthalate) and nitrogen-containing heterocyclic compounds (such as dimethylimidazole and dimethylimidazolidinone). These organic solvents can be used alone or in combination of two or more. Among these organic solvents, alicyclic alcohols such as terpineol and _C1-4 alkyl carbitol acetates such as butyl carbitol acetate are preferable from the viewpoint of paste fluidity and the like.

  When combining an organic binder and an organic solvent, the ratio of the organic binder is, for example, 1 to 200 parts by mass, preferably 10 to 100 parts by mass, and more preferably about 30 to 80 parts by mass with respect to 100 parts by mass of the organic solvent. Yes, it is 5 to 80% by mass, preferably 10 to 50% by mass, and more preferably about 15 to 40% by mass based on 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, based on the whole 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, and more preferably 100 parts by mass of the conductive component (the total amount of the high melting point metal particles, the molten metal particles and the active metal particles). It is 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 (eg, glass frit), curing agents (eg, acrylic resin curing agents), colorants (eg, dyes and pigments), hue improvers, dye fixing agents, gloss-imparting agents, and metals. Corrosion inhibitors, stabilizers (antioxidants, ultraviolet absorbers, etc.), surfactants or dispersants (anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, etc.), dispersion Examples include stabilizers, viscosity modifiers or rheology modifiers, humectants, thixotropic agents, leveling agents, defoamers, bactericides, fillers and the like. These other components can be used alone or in combination of two or more. The proportion of the other components can be selected according to the type of the components, and is usually about 10% by mass or less (for example, 0.01 to 10% by mass) based on the entire conductive paste. Further, the conductive paste of the present invention may not include an inorganic binder such as a glass frit.

[Method of manufacturing electronic substrate]
The electronic substrate (ceramic substrate with a conductive part) of the present invention includes a bonding step of bonding the conductive paste to a ceramic substrate, and a firing step of firing the conductive paste bonded to the ceramic substrate to form a conductive part. can get.

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

  Examples of the method of applying and filling the conductive paste include printing methods such as a screen printing method, an inkjet printing method, an intaglio printing method (for example, a gravure printing method), a lithographic printing method, an offset printing method, a flexographic printing method, and the like. , A direct coating method such as a spin coating method, a dip method, a roll pressing method, a sugege pressing method, a press pressing method, and the like. Among these methods, a screen printing method or the like is preferable.

  The paste attached to the substrate may be naturally dried before the baking treatment, 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 5 minutes to 2 hours, and more preferably about 10 minutes to 1 hour.

  In the firing step, the firing temperature may be at least the sintering temperature of the high melting point metal particles in the conductive paste. The firing temperature (maximum temperature) may be 500 ° C or higher, for example, 750 to 1000 ° C (for example, 780 to 980 ° C), preferably 800 to 950 ° C, more preferably 850 to 930 ° C (especially 880 to 920 ° C). ). The firing time (the firing time at the highest temperature) is, for example, about 1 minute to 3 hours, preferably about 3 minutes to 1 hour, and more preferably about 5 to 30 minutes. If the firing temperature is too low, the reaction may 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 molten component is increased, and the pattern may be deteriorated due to the rise, shrinkage, or bleeding of the melt.

  The firing atmosphere can be selected according to the type of the metal particles, and is not particularly limited. In the air, a non-oxidizing gas (for example, nitrogen gas or the like), or an inert gas (for example, argon gas or helium gas). The atmosphere may be either an atmosphere or a vacuum atmosphere, but is preferably a non-oxidizing gas atmosphere or an inert gas atmosphere because an electronic substrate can be manufactured with high productivity. In particular, in the present invention, even in a nitrogen gas atmosphere, a nitrogen atmosphere is particularly preferable because the pattern can be firmly bonded to the substrate.

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

  The conductive portion (metalized film or via-filled portion) obtained by firing may have its surface physically or chemically polished. Examples of the physical polishing method include buff polishing, lap 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 or the like.

  After being physically or chemically polished, the surface of the metallized film or via filling portion may be plated. As the plating method, various plating methods can be used irrespective of electrolysis or electroless. Further, a wide variety of metal species for the plating layer can be selected. For example, nickel gold plating, nickel palladium gold plating, tin plating, or solder plating may be used to improve solder bonding properties, wire bonding properties, bump bonding properties, and the like. Or silver plating to increase the reflectance.

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

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

[Electronic substrate]
The electronic substrate of the present invention is obtained by the above manufacturing method, and comprises a ceramic substrate, a high melting point metal having a melting point higher than a firing temperature, a molten metal which is melted at a firing temperature and has a melting point of 700 ° C. or lower, and an active metal. And a conductive portion including:

  The material of the ceramic substrate may be any ceramic capable of reacting with an active metal, such as metal oxide (quartz, alumina or aluminum oxide, zirconia, sapphire, ferrite, zinc oxide, niobium oxide, mullite, beryllia), oxide 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, and metal double oxide [ Metal titanates (barium titanate, strontium titanate, lead titanate, niobium titanate, calcium titanate, magnesium titanate, etc.) and metal zirconates (barium zirconate, calcium zirconate, lead zirconate, etc.) And the like. These ceramics can be used alone or in combination of two or more.

  Among 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 field of electric and electronic devices, and further have high heat resistance, Cu particles and Ag. An alumina substrate, an aluminum nitride substrate, and a silicon nitride substrate are particularly preferable because the effect of improving the bonding strength with a high melting point metal such as particles is great.

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

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples. In the following examples, the materials used in the examples, the patterns of the evaluation substrates, and the evaluation methods of the obtained electronic substrates are shown below.

[Material used]
(High melting point metal particles)
Cu particles: copper particles having a central particle size of 0.5 μm, melting point 1085 ° C.
Ag particles: silver particles having a central particle size of 0.5 μm, melting point 962 ° C.
Ni particles: nickel particles having a center particle diameter of 0.7 μm, melting point 1455 ° C.

(Molten metal particles)
Sn particles: tin particles having a central particle diameter of 8 μm, melting point: 232 ° C.
Bi particles: bismuth particles having a central particle diameter of 16 μm, melting point 271 ° C.
In particles: Indium particles having a central particle size of 25 μm, melting point 156 ° C.
Zn particles: zinc particles having a central particle diameter of 7 μm, melting point of 419 ° C.
Al particles: aluminum particles having a central particle diameter of 7 μm, melting point 660 ° C.
AgCuZnSn particles: 58Ag-22Cu-17Zn-5Sn alloy particles having a center particle diameter of 5 μm, melting point 650 ° C.
AgCu particles: 72 Ag-28Cu alloy particles having a central particle size of 5 μm, melting point 780 ° C.

(Active metal particles)
Titanium hydride (TiH ₂ ) particles: Titanium hydride particles having a center particle diameter of 6 μm Zirconium hydride (ZrH ₂ ) particles: Zirconium hydride particles having a center particle diameter of 5 μm.

(Organic vehicle)
Organic binder: polybutyl methacrylate Organic solvent: terpineol.

[Evaluation board pattern]
A sample in which 2 mm × 2 mm square patterns were arranged vertically and horizontally on a surface of a 50.8 mm × 50.8 mm ceramic substrate was used as an evaluation substrate. The patterns were connected with thin wires so that electroplating could be performed.

[Evaluation of electronic substrates]
(Pattern shape)
The appearance (square pattern of 2 mm × 2 mm size) of the electronic substrate after firing was visually observed and observed with a loupe (× 15), and a pattern whose shape was maintained without being deformed was further subjected to image measurement. Was evaluated.

X (edge turning): the edge of the pattern is turned up. X (shrinkage): the edge of the pattern is not turned up, but the square is collapsed and the edge is rounded or the size is reduced. ): The shape of the 2 mm × 2 mm pattern is held without being deformed, but when the image is further measured, it is not in the range of 1.97 mm × 1.97 mm to 2.03 mm × 2.03 mm. ◎ (particularly good): 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 hardly changes in the image measurement, and is within the range of 1.97 mm x 1.97 mm to 2.03 mm x 2.03 mm. is there.

(Peel strength test and broken state)
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 upper surface of the 2 mm × 2 mm square pattern (passing through the center of the square and parallel to the sides), the peel wire is placed outside the 2 mm pattern. The film was bent 90 degrees, pulled up perpendicularly to the substrate surface, peeled off the film, and measured for peel strength. The highest strength at break was recorded as the peel strength. In addition, the fracture site after the test was observed, and the fracture state was evaluated according to the following criteria.

◎ (Substrate destruction): The substrate is broken to be peeled, and the peel strength is 4 kg or more. ○ (Substrate destruction): The substrate is broken to be peeled, and the peel strength is 2 kg to less than 4 kg. ): Destruction occurs at the interface between the substrate and the metallized film, and the peel strength is 2 kg or more. X (Interfacial fracture): Destruction occurs at the interface between the substrate and the metallized film, and the peel strength is less than 2 kg. The film breaks loose inside the film, and the peel strength is less than 2 kg.

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

◎: Both the pattern shape and the determination of peel strength were “「 ”
：: Judgment of both pattern shape and peel strength was “○”, or one was “◎” and the other was “○”
×: Either of the determination of the pattern shape and the peel strength is “×”.

Example 1
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 purged with nitrogen. An aluminum nitride substrate was used as the ceramic substrate. The firing was performed at a maximum temperature of 900 ° C., and this temperature was maintained for 10 minutes, and the time from charging to the furnace, including raising and lowering the temperature, to recovery was about 60 minutes. Observation of the metallized film on the fired substrate out of the furnace revealed a good shape. After baking the surface of the fired metallized film, the surface was plated with electrolytic nickel gold. When the obtained electronic substrate was subjected to a peel strength test, the destruction mode was substrate destruction, and the substrate and the metallized film were bonded at a strength higher than the substrate strength, indicating sufficient bonding properties.

Examples 2-3
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 good results in both the pattern shape and the peel test. In particular, the electronic substrate obtained in Example 3 using the ceramic substrate formed of silicon nitride had the same good results as Example 1 in both the pattern shape and the peel test. However, in the evaluation relative to Example 1, the peel strength of Example 2 was slightly reduced.

Examples 4 to 8
An electronic substrate was obtained in the same manner as in Example 1 except that pastes 2 to 6 shown in Table 1 were used instead of paste 1 and the molten metal particles in the paste were changed. The obtained electronic substrate had good results in both the pattern shape and the peel test. However, in the evaluation relative to Example 1, in Examples 4, 6 to 8, the peel strength was slightly reduced, and in Example 5, the pattern shape was slightly reduced.

Example 9
An electronic substrate was obtained in the same manner as in Example 1 except that the paste 7 shown in Table 1 was used instead of the paste 1 and the molten metal particles in the paste were replaced with the two types of molten metal particles shown in Table 1. The obtained electronic substrate had good results in both the pattern shape and the peel test. In the evaluation relative to Example 1, the peel strength of Example 9 was slightly reduced, but the same result as that of Example 4 was obtained.

Examples 10 to 11
An electronic substrate was obtained in the same manner as in Example 1 except that pastes 8 and 9 shown in Table 1 were used instead of paste 1, except that the high melting point metal particles in the paste were changed. The obtained electronic substrate had the same good results as in Example 1 in both the pattern shape and the peel test.

Example 12
An electronic substrate was obtained in the same manner as in Example 1 except that paste 10 shown in Table 1 was used instead of paste 1 and active metal particles in the paste were changed. The obtained electronic substrate had good results in both the pattern shape and the peel test. However, in the evaluation relative to Example 1, the peel strength was slightly reduced.

Examples 13 and 14
An electronic substrate was obtained in the same manner as in Example 1 except that the pastes 11 and 12 shown in Table 1 were used instead of the paste 1, and the ratio of the high melting point metal particles to the molten metal particles in the paste was changed. The obtained electronic substrate had good results in both the pattern shape and the peel test. However, in the evaluation relative to Example 1, in Example 13, the peel strength was slightly reduced, and in Example 14, the pattern shape was slightly reduced.

Examples 15 to 16
In the same manner as in Example 1 except that the pastes 13 and 14 shown in Table 1 were used instead of the paste 1, and the ratio of the active metal particles to the total amount of the high melting point metal particles and the molten metal particles in the paste was changed. A substrate was obtained. The obtained electronic substrate had good results in both the pattern shape and the peel test. However, in the evaluation relative to Example 1, the peel strength was slightly reduced.

Comparative Examples 1-3
Example 1 was repeated except that pastes 15 to 17 shown in Table 1 were used instead of paste 1 and that only the Ag-Cu alloy particles having a melting point of 780 ° C. were used as the molten metal particles without using a metal having a melting point of 700 ° C. or less. An electronic substrate was obtained in the same manner as in Example 1. In Comparative Example 1, the pattern shape was good, but the peel strength was low and sufficient bonding was not obtained. As the ratio of the Ag-Cu alloy particles was increased, the pattern shape was reduced, and edge turning and shrinkage occurred. From these results, it was not possible to obtain an electronic substrate having a good pattern shape and an excellent bondability with the substrate only by a molten component having a high melting point.

  Table 2 shows the evaluation results of the electronic substrates obtained in Examples and Comparative Examples.

  INDUSTRIAL APPLICABILITY The conductive paste of the present invention can be used for circuit boards, electronic components, substrates of semiconductor packages, and the like, and can be particularly effectively used as a paste for forming a conductive portion of an electronic board.

Claims (11)

  High melting point metal particles having a melting point higher than the firing temperature, melted at the firing temperature, and molten metal particles having a melting point of 700 ° C. or less, titanium hydride particles, and an organic vehicle, comprising the titanium hydride particles The ratio is 0.1 to 10 parts by mass with respect to the total of 100 parts by mass of the high melting point metal particles and the molten metal particles, and does not include an alloy that is melted at a firing temperature and has a melting point of 400 ° C. or less. Conductive paste.   The conductive paste according to claim 1, wherein the molten metal particles include at least one selected from Mg, Al, Zn, In, Sn, Bi, Pb, and Sb.   3. The conductive paste according to claim 1, 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.   The conductive paste according to any one of claims 1 to 3, wherein the mass ratio of the high melting point metal particles to the molten metal particles is high melting point metal particles / molten metal particles = 90/10 to 40/60.   The conductive paste according to any one of claims 1 to 4, wherein the central particle size of the molten metal particles is 0.01 to 30 m.   The conductive paste according to any one of claims 1 to 5, wherein a center particle diameter of the titanium hydride particles is 0.1 to 15 µm.   The conductive paste according to any one of claims 1 to 6, wherein the high melting point metal particles have a center particle size of 0.01 to 15 µm.   An electronic board 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.   9. The method according to claim 8, wherein in the firing step, the conductive paste is fired in a non-oxidizing gas or inert gas atmosphere.   The method according to claim 8, wherein in the firing step, the conductive paste is fired in a nitrogen atmosphere.   The method according to any one of claims 8 to 10, wherein in the firing step, the firing temperature is 800 to 950 ° C.