Radiation imagery chemistry: process – composition – or product th – Visible imaging including step of firing or sintering
Reexamination Certificate
2001-11-30
2003-03-11
Schilling, Richard L. (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Visible imaging including step of firing or sintering
C430S015000, C430S016000, C430S169000, C430S192000, C430S195000, C430S258000, C430S260000, C430S270100, C430S280100, C430S281100, C430S311000, C430S327000, C430S330000, C430S910000
Reexamination Certificate
active
06531257
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photosensitive copper paste used for forming a desired electrode pattern on a substrate surface or each of the substrates which constitute a multilayer substrate in manufacturing a circuit board or a multilayer substrate, or the like, and a method of forming a copper pattern using the photosensitive copper paste.
2. Description of the Related Art
Radio-frequency electronic parts used for mobile communication equipment, satellite receivers, computers, etc. have been increasingly miniaturized in recent years and concurrently undergone an increase in performance with miniaturization of these apparatuses. Also, wiring patterns of the radio-frequency electronic parts have strongly been required to support an increase in density and signal transmission speed.
In order to achieve increases in the density and the signal transmission speed of the wiring patterns of the radio-frequency electronic parts, the wiring patterns must be made fine while increasing their thickness (thickening).
A wiring pattern of a radio-frequency electronic part is conventionally formed by a method comprising forming a pattern on an insulating substrate by using a conductor paste containing a conductive metal powder composed of a polyvalent metal such as copper, and an organic vehicle comprising an organic binder and an organic solvent, and then drying the pattern and baking the pattern to form a predetermined wiring pattern.
Although a screen printing method is generally used for forming the wiring pattern, this method makes it difficult to decrease the wiring width and the wiring pitch of the wiring pattern to 50 &mgr;m or less in order to obtain a fine wiring pattern. It is generally recognized that a wiring width and wiring pitch of about 50 &mgr;m or less each are the refining limit of the screen printing method.
On the other hand, a photolithography method of forming fine and thick wiring by using a photosensitive conductor paste is proposed in Japanese Unexamined Patent Application Publication Nos. 5-287221 and 8-227153. This method comprises coating, on an insulating substrate, a photosensitive conductor paste comprising a conductive metal powder, an acrylic copolymer having carboxyl groups and ethylenic unsaturated groups in the side chains thereof, a photoreactive compound and a photopolymerization initiator, drying the coating, and then patterning the coating by photolithography.
Also, a photolithography method of forming fine and thick wiring by using a photosensitive conductor paste containing a glass powder is proposed in Japanese Unexamined Patent Application Publication Nos. 6-224538 and 8-335757. In this method, the glass powder is contained in the photosensitive conductor paste to improve adhesion between the conductor pattern and the ceramic substrate.
In consideration of the environment, the photolithography method using a photosensitive conductor paste has recently been desired to be developed with water or an alkali aqueous solution. Therefore, an acid functional group having the property of liberating protons, such as a carboxyl group or the like, is introduced into the organic binder. However, when a polyvalent metal, particularly copper, is selected as a conductor for the photosensitive conductor paste, the copper ions elute and react with the organic binder anions produced after release of protons to form a three-dimensional network due to ion crosslinkage, thereby causing gelation. The gelation of the photosensitive copper paste causes the problems of difficulties in coating and destabilizing development even if coating can be performed.
As a method of preventing gelation, for example, Japanese Unexamined Patent Application Publication No. 9-218509 discloses a photosensitive conductor paste containing, as a gelation inhibitor, a phosphorus-containing compound such as phosphoric acid; Japanese Unexamined Patent Application Publication No. 9-218508 discloses a photosensitive conductor paste containing a compound having an azole structure, such as benzotriazole; Japanese Unexamined Patent Application Publication No. 9-222723 discloses a photosensitive conductor paste containing an organic compound having a carboxyl group, such as acetic acid. However, the methods of using the gelation inhibitor can only slightly lengthen the time to gelation of the photosensitive copper paste, but difficulties in use of the photosensitive copper paste remain under the present conditions.
Also, in Japanese Unexamined Patent Application Publication No. 10-171107, 3-methyl-3-methoxybutanol is used as an organic solvent for preventing gelation. However, a phenomenon similar to gelation, i.e., a phenomenon in which a three-dimensional network is formed by ion crosslinkage to increase the substantial molecular weight, occurs in the dry paste, thereby causing the problem of failing to elute an unexposed portion with a developer.
SUMMARY OF THE INVENTION
The present invention has been achieved for solving the above problems, and an object of the present invention is to provide a photosensitive copper paste causing less gelation, and exhibiting excellent storage stability and permitting the formation of a fine and thick copper pattern having high adhesion to a substrate. Another object of the present invention is to provide a method of forming a copper pattern, a circuit board and a ceramic multilayer substrate using the photosensitive copper paste.
As a result of various experiments and research performed for achieving the above objects, the inventor found that by using a copper powder having a surface coating of a copper oxide in a system containing an organic binder having an acid functional group and the copper powder, gelation can effectively be inhibited.
Further experiment and examination led to the achievement of the present invention.
A photosensitive copper paste of the present invention comprises a mixture of an organic binder having an acid functional group, a copper powder and a photosensitive organic component, wherein the copper powder comprises a copper oxide coating on the surface thereof, and at least the surface layer having a thickness of about 0.1 &mgr;m from the surface being composed of CuO as a main component.
The photosensitive copper paste of the present invention comprises the copper powder having the surface coating of copper oxide in which at least the surface layer having a thickness of about 0.1 &mgr;m from the surface is composed of CuO as a main component. Therefore, the occurrence of gelation can be sufficiently suppressed either in the paste state before coating or in the coated state after coating and drying. Therefore, the photosensitive copper paste can be coated, patterned by exposure and developed, and then baked to efficiently form a fine and thick copper pattern.
In the photosensitive copper paste of the present invention, the organic binder having an acid functional group is a wide concept representing an organic binder comprising a material having a functional group having the property of releasing protons, such as a: carboxyl group, a hydroxyl group, a sulfonic group or the like, or an organic binder containing a material having the functional group. The type of the acid function group is not limited.
The photosensitive copper paste of the present invention comprises the copper powder having the surface coating composed of CuO as a main component at least in the surface layer having a thickness of about 0.1 &mgr;m from the surface thereof. This is because with the surface layer composed of CuO as a main component and having a thickness of about 0.1 &mgr;m or less, a region (inner layer) composed of Cu
2
O as a main component readily occurs in the outermost layer of the copper powder during kneading in the process for producing the photosensitive copper paste.
In the present invention, “composed of CuO as a main component” is a concept representing that the molar ratio of CuO exceeds about 50%. The copper powder preferably has an average particle diameter of about 1 to 10 &mgr;m,
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd
Schilling Richard L.
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