1. Field of the Invention
The present invention relates to a method for forming a conductive pattern by use of a photosensitive conductive paste and to a method for producing a ceramic multi-layer substrate.
2. Description of the Related Art
Recently, high-frequency electronic components used in mobile communication devices, satellite broadcasting receiving devices, computers and the like having small size and high performance have been demanded. Concurrently, wiring patterns of high-frequency electronic components are required to have increased density and signal speed. In order to increase density and signal speed in the wiring pattern, conductive patterns such as wiring and electrodes must be made finer and yet form a thicker film.
A conventional method for forming a conductive pattern of a high-frequency electronic component involves first forming a pattern on an insulating substrate by use of a conductive paste comprising powder of a multivalent metal such as copper and an organic vehicle containing an organic binder and an organic solvent. Subsequently, the resultant pattern is dried and fired. In this method, a conductive pattern is generally formed through screen printing, and the lower limit of the width and pitch of the thus-formed conductive pattern is approximately 50 xcexcm.
Japanese Patent Application Laid-Open (kokai) No. 99596/1988 discloses a transferring method wherein conductive patterns are formed on a plurality of supports and the patterns are transferred onto green sheets. By means of the transferring method, bleeding and blurring can be suppressed and a fine conductive pattern can be formed with high accuracy, as compared with a conductive pattern formed on a green sheet through screen printing. In the transferring method, however, conductive patterns are formed on supports through screen printing and thus, the lower limit of the width and pitch of the conductive pattern is approximately 50 xcexcm as in the described conventional method.
In addition, Japanese Patent Application Laid-Open (kokai) Nos. 75039/1998, 200260/1998, and 209334/1998 disclose a method employing the above-described transferring method wherein a conductive pattern is formed on a support through photolithography by use of a photosensitive conductive paste, and the resultant pattern is transferred onto a ceramic green sheet. By means of this method, bleeding and blurring of a conductive pattern can be suppressed and a very fine pattern having a width and a pitch of 50 xcexcm or less can be formed.
Recently, in consideration of the environment, it is demanded that photolithography development be carried out by use of water or alkali. Therefore, the photosensitive organic binder contains an acidic functional group such as a carboxyl group, which group has a property to release a proton.
In the case of employment of such a photosensitive organic binder in the above-described transferring method, particularly when powder of a multivalent metal such as copper is used as a conductive material, ions of the multivalent metal may react with anions of the organic binder, which anions are formed after protons are released, to thereby form a three-dimensional network by ionic cross-linking. In addition, the photosensitive conductive paste may become a gel.
When a photosensitive conductive paste becomes a gel, the paste has high viscosity and application of the paste to a support becomes difficult. Even if the paste is applied to the support before occurrence of gelation, unexposed portions of the paste may fail to dissolve in a developer during exposure and development. In addition, ability to transfer onto a ceramic green sheet is reduced.
In order to prevent gelation of a photosensitive conductive paste, Japanese Patent Application Laid-Open (kokai) No. 218509/1997 discloses a method wherein a phosphorous-containing compound such as phosphoric acid is incorporated into the paste, and Japanese Patent Application Laid-Open (kokali) Nos. 218508/1997 and 209334/1998 disclose a method wherein a compound having an azole structure such as benzotriazole is incorporated into the paste. However, these methods in practice enable only slight retardation of gelation of the paste, and formation of a fine conductive pattern is difficult through the above-described transferring method.
In addition, in order to prevent gelation of a photosensitive paste effectively, Japanese Patent Application Laid-Open (kokai) No. 171107/1998 discloses a method wherein 3-methyl-3-methoxybutanol is added into the paste. However, 3-methyl-3-methoxybutanol has a boiling point as low as 174xc2x0 C., and thus, when a film formed on a support is dried, the 3-methyl-3-methoxybutanol may vaporize from the film and the effect of preventing gelation may be considerably reduced. As is described above, when coating film after drying becomes gel, unexposed portions of the film may not dissolve into the developer and transferability onto a ceramic green sheet may be reduced.
To overcome the above described problems, preferred embodiments of the present invention provide a method for forming a conductive pattern, which method enables sufficient suppression of gelation of a photosensitive conductive paste and of a dried film, and enables formation of a fine conductive pattern with high accuracy.
Further, preferred embodiments of the present invention provide a ceramic multi-layer substrate having sufficiently increased signal speed and wiring density by the formation of a fine conductive pattern on a ceramic green sheet with high accuracy.
Accordingly, the present invention provides a method for forming a conductive pattern, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder and mono-ol compound having a boiling point of about 178xc2x0 C. or more;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste; and
transferring the conductive pattern formed on the support onto a substrate. Hereinafter, this method will be referred to as the first method for forming a conductive pattern of the present invention.
The prevent invention also provides a method for forming a conductive pattern, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder, and an anion-adsorbing substance having ability to adsorb the anion of the organic binder;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste; and
transferring the conductive pattern formed on the support onto a substrate. Hereinafter, this method will be referred to as the second method for forming a conductive pattern of the present invention.
The present invention also provides a method for forming a conductive pattern, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder, and a thixotropic agent;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste; and
transferring the conductive pattern formed on the support onto a substrate. Hereinafter, this method will be referred to as the third method for forming a conductive pattern of the present invention.
The present invention further provides a method for producing a ceramic multi-layer substrate, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder and mono-ol compound having a boiling point of about 178xc2x0 C. or more;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste;
transferring the conductive pattern formed on the support onto a ceramic green sheet; and
stacking a plurality of the ceramic green sheets having the conductive pattern and firing the resultant laminate. Hereinafter, this method will be referred to as the first method for producing a ceramic multi-layer substrate of the present invention.
The present invention also provides a method for producing a ceramic multi-layer substrate, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder and an anion-adsorbing substance having ability to adsorb the anion of the organic binder;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste;
transferring the conductive pattern formed on the support onto a ceramic green sheet; and
stacking a plurality of the ceramic green sheets having the conductive pattern and firing the resultant laminate. Hereinafter, this method will be referred to as the second method for producing a ceramic multi-layer substrate of the present invention.
The present invention also provides a method for producing a ceramic multi-layer substrate, comprising the steps of:
applying a photosensitive conductive paste to a support, the photosensitive conductive paste containing an organic binder having an acidic functional group, a photosensitive organic component, a multivalent metallic powder and a thixotropic agent;
forming a predetermined conductive pattern by exposure and development of the photosensitive conductive paste;
transferring the conductive pattern formed on the support onto a ceramic green sheet; and
stacking a plurality of the ceramic green sheets having the conductive pattern and firing the resultant laminate. Hereinafter, the method will be referred to as the third method for producing a ceramic multi-layer substrate of the present invention.
In the first method for forming a conductive pattern of the present invention, a photosensitive conductive paste contains one or more mono-ol compounds having a boiling point of about 178xc2x0 C. or more, and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed at high accuracy.
In the first method for producing a ceramic multi-layer substrate of the present invention, a photosensitive conductive paste contains the mono-ol compound having a boiling point of about 178xc2x0 C. or more, and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed on a ceramic green sheet with high accuracy. As a result, a ceramic multi-layer substrate having sufficiently increased signal speed and wiring density can be produced.
The hydroxyl group in a mono-ol compound has very high ability to bind to a multivalent metallic ion as compared with an acidic functional group of an organic binder (particularly a carboxylic group). Therefore, the reaction between the mono-ol compound and the multivalent metallic ion precedes the reaction between the organic binder and the ion, and ionic cross-linking between the organic binder and the multivalent metallic ion and formation of a three-dimensional network are hindered. Since the mono-ol compound has only one hydroxyl group, when it bonds to the multivalent metallic ion, no three-dimensional network is formed by ionic cross-linking. In addition, the compound has a boiling point of about 178xc2x0 C. or more, and thus, even after a photosensitive conductive paste is applied and dried, the mono-ol compound significantly remains in the dried composition and exhibits sufficient ability to prevent gelation. As a result, consistent development can be carried out.
In the second method for forming a conductive pattern of the present invention, the photosensitive conductive paste contains one or more anion-adsorbing substances such as hydroxyapatite, and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed at high accuracy.
In the second method for producing a ceramic multi-layer substrate of the present invention, the photosensitive conductive paste contains the anion-adsorbing substance such as hydroxyapatite, and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed on a ceramic green sheet with high accuracy. As a result, a ceramic multi-layer substrate having sufficiently increased signal speed and wiring density can be produced.
The reason why the fine conductive pattern can be formed is that when an anion-adsorbing substance having the property to adsorb an anion is mixed with an organic binder containing an acidic functional group, such as a carboxyl group, which group has a property to free a proton, the anion-adsorbing substance adsorbs the anion of the organic binder which is generated after the proton is freed to thereby form a micro-structure such as a micro-phase-separated substance in the resultant mixture. As a result, the mixture becomes uniform macroscopically although not uniform microscopically, and a three-dimensional network is difficult to form by ionic cross-linking.
In the third method for forming a conductive pattern of the present invention, a photosensitive conductive paste contains one or more thixotropic agents (thixotropy adjusting agent) and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed at high accuracy.
In the third method for producing a ceramic multi-layer substrate of the present invention, the photosensitive conductive paste contains the thixotropic agent, and therefore gelation of the paste and a dried film can be sufficiently suppressed and a fine conductive pattern can be formed on a ceramic green sheet with high accuracy. As a result, a ceramic multi-layer substrate having sufficiently increased signal speed and wiring density can be produced.
The reason why the fine conductive pattern can be formed is that when a thixotropic agent is incorporated into a photosensitive conductive paste containing a photosensitive organic binder, the thixotropic agent is entangled with a polymer chain of the organic binder to thereby form a so-called network structure. Gelation of the photosensitive conductive paste and the film proceeds by ionic bonding between the anion of the organic binder and a multivalent metallic ion. However, the anion and the metallic ion must be sufficiently close such that Coulomb forces of these ions act on each other in order to form the ionic bond. In addition, when the network structure is formed by incorporation of the thixotropic agent, additional energy is required in order to break the structure and to form the ionic bond. Therefore, a three-dimensional network formed of the multivalent metal is difficult to form by ionic cross-linking and gelation of the photosensitive conductive paste and the film can be suppressed.