Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
2001-07-02
2003-10-07
Young, Christopher G. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S017000, C430S270100, C430S322000
Reexamination Certificate
active
06630287
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods for forming thick film patterns and to photosensitive pastes used for forming thick film patterns.
2. Description of the Related Art
Concomitant with the movement toward higher integration and higher processing of high-frequency electronic apparatuses, wiring conductors constituting high-frequency circuits provided in these electronic apparatuses are increasingly required to have a finer design, a larger thickness and a rectangular cross-section.
Heretofore, a thick conductor film forming a wiring conductor on a substrate is formed by the steps of preparing a conductive paste formed of an organic binder mixed with a powdered conductor, applying the conductive paste to the substrate by screen printing so as to form a desired pattern, and firing the desired pattern in order to remove the organic binder and to sinter the conductive component in the conductive paste.
However, the pattern mask accuracy used for screen printing is not always satisfactory, and for example, it has been difficult to form a fine pattern having a line width of about 100 &mgr;m or less. Accordingly, proposed as a method for forming a fine pattern which cannot be obtained by screen printing, as disclosed in Japanese Unexamined Patent Application Publication Nos. 54-121967, 54-13591 and 59-143149, is a method of forming a fine pattern on a substrate by the steps of preparing a photosensitive paste formed of a photosensitive resin composition mixed with a powdered conductor, and applying the photosensitive paste to the substrate by a photolithographic technique so as to form the fine pattern on the substrate.
As the photosensitive resin composition for forming the photosensitive paste described above, a known photopolymerizable compound, a photo-modification compound or the like may be used, and for example, (1) a mixture of a monomer or an oligomer having reactive functional groups such as unsaturated groups and a photopolymerization initiator such as an aromatic carbonyl compound, (2) a so-called diazo resin such as a condensation product of an aromatic bis-azide and formaldehyde, (3) a mixture of an addition-polymerizable compound such as an epoxy compound and a photo-acid generator such as a diallyliodonium salt and (4) a naphthoquinone diazide compound may be used.
Among these materials described above, the mixture of the monomer having reactive functional groups such as unsaturated groups and the photopolymerization initiator such as an aromatic carbonyl compound (1) is particularly preferable.
When a conductor layer having a high electrical conductivity is formed, it is necessary to avoid defects such as wire breakage or crack generation which occurs while the conductor layer shrinks during firing, and as a result, it is necessary to increase the content of powdered conductor which is mixed with a photosensitive resin composition. However, when the content of the powdered conductor is increased, the optical transmittance of the photosensitive paste is decreased, resulting in insufficient curing in the paste, i.e., resulting in insufficient curing of the photosensitive resin composition contained in the paste. Accordingly, pattern formation becomes difficult to perform, and even when pattern formation is performed, a pattern having an inversed trapezoidial cross-section or having a so-called edge curl may be formed, significantly decreasing the transmission characteristics at a high frequency band.
The problems described above occur not only in a photosensitive paste containing a powdered conductor as a powdered inorganic material but also occur in a photosensitive paste containing a powdered insulator as a powdered inorganic material.
SUMMARY OF THE INVENTION
Accordingly, in order to solve the problems described above, an object of the present invention is to provide a method for forming a thick film pattern having superior high-frequency transmission characteristics, in which even when a photosensitive paste having a high content of a powdered conductor and thereby having a low optical transmittance is used, a desired pattern having a rectangular cross-section can be easily formed, and is to provide a photosensitive paste used for forming the thick film pattern.
Through intensive research by the inventor of the present invention in order to solve the problems described above, it was discovered that a thick film pattern having a rectangular cross-section and superior high-frequency transmission characteristics could be obtained by measuring the photocurable depth of a photosensitive paste film beforehand and subsequently determining the thickness thereof in consideration of the photocurable depth described above. After further experiments and studies were performed, the present invention was finally made.
The method for forming a thick film pattern of the present invention comprises the steps of measuring a photocurable depth d of a photosensitive paste beforehand; coating with the photosensitive paste in consideration of the photocurable depth d so as to form a photosensitive paste film having a predetermined thickness t; exposing the photosensitive paste film; and developing the exposed photosensitive paste film so as to form a thick film pattern having a predetermined shape.
Since the shape (the cross-section) of the thick film pattern to be formed can be estimated to some extent from the photocurable depth d of the photosensitive paste and the film thickness t of the photosensitive paste film, a thick film pattern having a desired cross-section can be efficiently formed by measuring the photocurable depth d of the photosensitive paste beforehand and by determining the thickness t of the photosensitive paste film in consideration of the photocurable depth d. Consequently, a thick film pattern having superior adhesiveness to an object (typically, a substrate) on which the thick film pattern is formed and having a high shape accuracy can be formed.
When the thickness of the photosensitive paste film is larger than the photocurable depth to some degree, the thickness pattern to be formed tends to have a cross-section in an inversed trapezoidial shape to some extent; when the thick film pattern to be formed is not required to have a high shape accuracy, a thickness larger than the photocurable depth to some degree may be employed as the thickness of the photosensitive paste film.
In the present invention, the photosensitive paste means a paste containing a powdered inorganic material and a photosensitive resin component, and when necessary, the photosensitive paste may contain a storage stabilizer such as a solvent or a polymerization inhibitor, an anti-oxidant, a dye, a pigment, a defoaming agent, a surfactant, or the like. The type and the composition of the photosensitive paste are not specifically limited, and as long as the advantages of the present invention can be fully obtained, photosensitive pastes having various compositions may be used.
In the present invention, the photosensitive paste film means a film in a dry state which is formed by applying the photosensitive paste to a base body, such as a ceramic substrate or a PET film, by a known technique, such as screen printing or spin coating, and by drying the photosensitive paste on the base body. The thickness of the photosensitive paste film means the thickness of the film in a dry state.
In addition, the photocurable depth d of the photosensitive paste film means the depth from the surface of the film toward the inside thereof at which the energy of radiated light such as ultraviolet light is reduced to less than the minimum energy required for curing the resin component of the film either by being consumed by curing the resin component or being attenuated due to the absorption therein while the light is passing through the paste film.
As a method for evaluating (measuring) the photocurable depth described above, the following method may be mentioned by way of example.
(1) First, the photosensitive paste film is formed on a substrate such as a
Dickstein Shapiro Morin & Oshinsky LLP.
Murata Manufacturing Co. Ltd.
Young Christopher G.
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