JPH0367282B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a conductive paste for forming an electric circuit, more specifically, a conductive paste containing silver as a main conductivity-imparting component suitable for constructing a thick film hybrid IC electric circuit board. Regarding. [Prior Art] Conventionally, an electric circuit pattern of a thick film hybrid IC is generally constructed by screen printing a conductive paste on an insulating substrate and then firing the paste. As this conductive paste, those containing silver as a conductivity-imparting component are often used. Furthermore, in order to prevent migration of electrical circuits formed by pastes containing silver as a conductivity imparting component, Ag-Pd based conductive pastes containing palladium are also frequently used. Conventional conductive pastes containing silver as a main conductivity-imparting component use silver powder as a silver source. More specifically, this silver powder and further palladium powder were dispersed in an organic vehicle together with glass frit as a binder during firing. Furthermore, since ethyl cellulose powder is used as the organic vehicle, an organic solvent is used to dissolve it. Therefore, conventional conductive pastes containing silver as the main conductivity-imparting component are compositions consisting of silver powder, lead borosilicate glass frit, an organic vehicle, and an organic solvent; The composition contained palladium powder. Instead of using palladium powder, silver powder plated with palladium was sometimes used. Such conductive paste is printed in a circuit pattern on the surface of an insulating substrate (alumina or enamel is often used) using a screen printer, then the organic solvent is evaporated and the organic vehicle is decomposed, and finally Since it is fired at a temperature above the melting point of glass, it is required to have various properties in addition to electrical properties. In other words, in addition to the required conductivity (specific resistivity value), adhesion strength to the board, solder dissolution resistance, solder wettability,
Film thickness leveling property, heat aging property, environmental resistance,
In addition to the various properties required for firing patterns such as resistance temperature characteristics and migration resistance, we also have appropriate viscosity as a paste, thixotropy, fine pattern properties, and the like required for screen printing.
It is required to have a wide variety of properties, such as powder dispersibility. [Problems to be Solved by the Invention] The present invention aims to solve the following two problems in particular in conventional conductive pastes containing silver powder as the main conductivity-imparting component while satisfying the various characteristics described above. That is. First of all, conventional conductive pastes contain silver powder as a conductivity-imparting component, palladium powder that provides migration resistance as well as conductivity-imparting component, and a binder when firing the conductive paste. Since a certain glass frit (fine powder with a glass composition) was used to disperse an organic dispersion medium (organic vehicle and its organic solvent), it was necessary to uniformly disperse it in the organic dispersion medium of these solid substances. For this purpose, sufficient mechanical mixing (usually using a roll mixer) had to be carried out. However, even if such powder is uniformly dispersed (dispersed in an organic dispersion medium) by mechanical mixing, the metal powder as a conductivity imparting component and the glass frit as a binder during firing are Since it is only a mixture of solids, there is no guarantee that the glass frit will completely cover the metal powder surface. Therefore, when such a conductive paste is fired, all of the added glass frit will not bond the metal powder. There is no guarantee that it will be used effectively. Therefore, the glass component, which is an insulator, is added in an amount greater than the minimum amount necessary for bonding the metal powder to ensure this bond and at the same time enhance bonding with the substrate.
As a result, other properties required of the conductive paste, such as electrical conductivity, were affected. The second problem is that conventional conductive pastes that use metal powder and glass frit cannot adequately meet the recent demands for thinner and finer electrical circuit patterns in thick-film hybrid ICs. From the standpoints of making electrical equipment lighter and smaller and reducing the amount of conductive paste that uses expensive metals,
In recent years, the film thickness has increased to around 10μm, and the line width has become approximately 100μm.
Although the goal is to construct thin and fine conductor circuits with internal and external connections, a conductive paste that can satisfy these requirements has not yet been found. In order to make the film thinner and finer,
The metal powder itself needs to be ultra-fine, but there is a limit to how fine a silver powder can be. Requires sufficient glass frit formulation to cover. In order to form a fine conductor, it is necessary to create a conductor free from migration (shoots caused by Ag ionization), and in order to prevent this, the amount of palladium added is increased. Palladium is more expensive than silver, and in order to obtain the anti-migration effect of palladium, the finer the silver powder, the higher the amount of palladium must be added. In addition, the amount of inorganic glass frit used as a binder during firing must exceed the minimum required for bonding the metal powder. Therefore, from this point of view,
Conventional conductive pastes that use powder as the conductivity-imparting component and bonding component have not been able to adequately meet the demands for thinner and finer conductor circuits. The present invention attempts to solve these problems. [Means for Solving the Problems] The present invention solves the above problems by using a glass-forming organic compound instead of the conventional glass frit as a binder for binding metal powders during firing. Furthermore, when part or all of the silver powder is replaced with a silver organic compound and palladium is added, the above-mentioned solution can be solved by replacing part or all of this palladium powder with a palladium organic compound. This is an attempt to solve the problem of. That is, the present invention is characterized in that (1) a conductive paste containing silver as a main conductivity-imparting component and dispersed in an organic dispersion medium contains a glass-forming organic compound as a binder during firing of the conductive paste; (2) A conductive paste containing silver as the main conductivity-imparting component and dispersed in an organic dispersion medium, in which a glass-forming organic compound is blended as a binder during firing of the conductive paste, and A conductive paste characterized in that part or all of silver as a conductivity-imparting component is blended as a silver organic compound, and (3) silver and palladium are dispersed in an organic dispersion medium as conductivity-imparting components. In the conductive paste, a glass-forming organic compound is blended as a binder during firing of the conductive paste, some or all of the silver as a conductivity imparting component is blended as a silver organic compound, and some or all of the palladium is blended. The present invention provides a conductive paste characterized in that it is formulated as a palladium organic compound. The glass-forming organic compound that can be used in the present invention is an organic compound that thermally decomposes when heated to form a glassy substance, such as silicon alkoxide, polydimethyl Examples include siloxanes, lead alkoxides or soaps, boron-based organic compounds such as boric acid esters, tin alkoxides or soaps, cadmium alkoxides or soaps, sodium alkoxides or soaps, potassium alkoxides or soaps, and the like. these are,
They can be used by mixing in a predetermined ratio. The silver powder that can be used in the present invention has, for example, an average particle size (value averaged by number based on the maximum diameter of one particle in electron microscopy observation) of 2 μm or less,
Examples include those with a maximum particle diameter of 5 μm or less. When the average particle size exceeds 2 μm, not only is it difficult to form a thin film and fine pattern in screen printing, but also sintering between particles is difficult to proceed.
Furthermore, when the maximum particle size exceeds 5 μm, the uniformity of the thickness of the conductive layer decreases, and the effect of reducing the thickness of the conductive layer decreases. Further, as the palladium powder to be added to increase the migration resistance of silver, it is preferable to use one finer than silver powder. A mixed powder in which the weight ratio of palladium to silver is 5 to 30% is preferred. Examples of the silver organic compound according to the present invention which is blended from a part of silver to the whole silver include complex salts such as silver-acetylacetate, fatty acid silver such as silver 2-ethylhexanoate, silver rosinate, polymerized silver rosinate, etc. Examples include silver resinate, silver naphthenate, and the like. Examples of the palladium organic compound according to the present invention to be blended as part or all of palladium include complex salts such as palladium-acetylacetonate, fatty acid palladium such as palladium 2-ethylhexanoate, palladium rosin acid, polymerized palladium rosin acid, etc. Examples include palladium resinate, palladium naphthenate, and mercapto. Further, in the present invention, an organic solvent,
Organic vehicles are used, and organic solvents that can be used in the present invention include, for example, pine oil, terpineol, terpene oil, xylene, toluene,
Examples include ethyl acetate, mineral turpentine, etc.
Examples of organic vehicles include polyethers such as polyethylene glycol and polypropylene glycol; celluloses such as methylcellulose, ethylcellulose, and nitrocellulose; acrylic resins and oligomers such as butyl polyacrylate; and synthetic resin oligomers such as acrylic-styrene oligomers. Rosins such as rosin acid, polymerized rosin acid, and rosin acid esters; Waxes such as polyethylene wax and carbana wax. As a result, the conductive paste of the present invention constructed in this manner is a composition containing silver powder, a silver organic compound, a palladium powder, a palladium organic compound, a glass-forming organic compound, an organic solvent, an organic vehicle, etc. be. Regarding the quantitative ratio of the components of this composition, the type of organic solvent and organic vehicle used, the amount of silver powder replaced by the silver organic compound,
It varies depending on the amount of palladium powder substituted with the palladium organic compound, and such variation is allowed as long as it satisfies the various characteristics required for conductive paste as stated at the beginning. Therefore, although it is not possible to discuss this matter, as far as the present inventors have confirmed, the glass-forming organic compound can be blended in an amount of 1 to 20 parts by weight per 100 parts by weight of the paste.
Silver powder or mixed powder of silver powder and palladium powder is 40 to 70 parts by weight, silver organic compound and palladium organic compound have a net silver content, palladium content of 40 by itself or in total with metal powder. ~
It seems best to mix it so that it is 70 parts by weight. Note that the remainder becomes an organic solvent and an organic vehicle. When producing an electrical circuit pattern for a thick film hybrid IC using the conductive paste of the present invention,
After printing a pattern on a substrate by screen printing, the pattern is dried at a temperature of, for example, 200°C or less, and the dried film is fired at a desired temperature to produce a thick film electrical circuit with desired characteristics. It can be done. This required firing temperature is the temperature necessary for the glass-forming organic compound to decompose, as well as for the organic substances such as the organic vehicle and the silver organic compound to decompose (varies depending on the material used), and This is the temperature required to melt the decomposed glass components and sinter the silver. This firing may be performed in one stage, or may be performed in two or more stages. [Effect] The conductive paste of the present invention can be used for thick film hybrid
The film thickness can be reduced without impairing the various characteristics required for the electric circuit of an IC, and a conductive circuit with a fine pattern with narrow line width can be constructed. Further, compared to the conventional method using glass frit as a sintering agent, sintering strength can be achieved with a smaller amount of glass, and a highly conductive circuit can therefore be formed. When an organic silver compound or a palladium organic compound is used, an electric circuit with a thinner and finer pattern can be constructed, and the conductivity is also improved.
In addition, by using a silver organic compound, it is possible to maintain the various properties necessary for the conductive paste even if the amount of silver blended is reduced, and when using a palladium organic compound, the amount of palladium used can be reduced. It becomes possible to maintain sufficient migration resistance even when [Example] Silver powder, palladium powder, glass-forming organic compound, silver organic compound, palladium organic compound, organic solvent, and organic vehicle were blended in the formulation shown in Table 1 (parts and percentages are based on weight). , this is 3
After kneading into a paste using this roll mill, a suitable pattern is printed on a 96% pure alumina ceramic board using a 325 mesh stainless steel screen, and this printed pattern is
After drying at 150°C for 10 minutes, it was fired at 800°C. The surface sheet resistance value, film thickness, fine pattern property, and migration property of the obtained circuit were evaluated, and the results are shown in Table 2. The surface sheet resistance value was measured using a digital multimeter, and the film thickness was determined by using a surface roughness meter to determine the difference between the film thickness and the glass plate. Regarding fine pattern properties, circuits were printed by changing the spacing between the mesh of a stainless steel screen and the resist applied to the screen, and by electron microscopic observation after firing, defects such as blisters, pinholes, and line edge defects were detected. The line with the smallest line width was quantified. Regarding migration properties, we applied a voltage of 6V between circuits printed at 0.5 mm intervals, poured pure water between these intervals, and after how many seconds the resin was formed.
We measured whether Ag was precipitated.

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Claims (1)

[Scope of Claims] 1 A conductive paste comprising silver as a main conductivity imparting component and dispersed in an organic dispersion medium, characterized in that a glass-forming organic compound is blended as a binder during firing of the conductive paste. conductive paste. 2. In a conductive paste containing silver as the main conductivity-imparting component and dispersed in an organic dispersion medium, a glass-forming organic compound is blended as a binder during firing of this conductive paste, and silver as the conductivity-imparting component is mixed. A conductive paste characterized by containing a part or all of silver as an organic compound. 3 In a conductive paste in which silver and palladium are dispersed in an organic dispersion medium as conductivity-imparting components, a glass-forming organic compound is blended as a binder during firing of this conductive paste, and silver and palladium as conductivity-imparting components are mixed. A conductive paste characterized in that part or all of silver is blended as an organic compound, and part or all of palladium is blended as a palladium organic compound.