Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
2000-08-30
2002-10-15
Cuneo, Kamand (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S261000, C174S262000, C174S264000, C361S792000, C029S830000
Reexamination Certificate
active
06465742
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-262328, filed Sep. 16, 1999, the entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
The present invention relates to a photonic crystal used in a light functional element, a multi-layer wiring board and a steric wiring board indispensable for a high density mounting in a portable equipment, and a method of manufacturing the same.
A three dimensional structure having a structure of several &mgr;m to hundreds of &mgr;m can be applied to a photonic crystal used in a light functional element such as a branching filter, an optical waveguide, a light delay element or a laser and to a steric wiring used in, for example, a built-up wiring board. In the photonic crystal, a regular periodic structure is required to be formed of substances differing from each other in the refractive index.
A photonic crystal is greatly featured in its optical characteristics. For example, it is possible to produce a wavelength region called photonic band gap, in which the light is not transmitted in any direction (E. Yablonovitch, Phys. Rev. Lett. 58 (20), 2059 (1987)). Also, the photonic crystal exhibits very large optical anisotropy or dispersibility. Therefore, an optical waveguide, a polarizer and a branching filter, which permit controlling the natural light emission and have a very small radius of curvature of a curved corner, have been proposed to date, and it is highly expected for these apparatuses to be put to a practical use.
A three dimensional structure having a distribution of refractive index such as a photonic crystal can be prepared by, for example, a method of laminating beads of silica or a polymer, a method using a self-organized structure such as a polymer, a self-Croning process utilizing a CVD process, a method of three dimensionally dry-etching a semiconductor in three directions, a method of laminating wafers, a method of laminating polycrystalline silicon (polysilicon) layers, a method of forming a distribution of composition of photosensitive agent photopolymerizing a medium consisting of two kinds of photosensitive agents, and a light-shaping process for three dimensionally photo-setting a polymerizable monomer. In each of these methods, the shape that can be formed is limited. For example, in the method of laminating beads or in the method of using a self-organized structure such as a polymer, the three dimensional structure that can be formed is limited. In the case of the self-Croning process, the dry etching method, the wafer fusing method or the polysilicon layer laminating method, a relatively costly semiconductor process is required. In addition, the width of the material selection is narrow. In the method of forming a composition distribution, it is difficult to obtain a large refractive index ratio among regions differing from each other in the refractive index, with the result that the materials used are limited to polymer materials. Similarly, the materials used are limited to polymer materials in the light-shaping process. Also, it is impossible to form isolated regions such as detached territories, making it necessary to form all the regions continuously.
On the other hand, the steric wiring is indispensable to a high density mounting, and various methods are proposed for formation of the steric wiring. In general, these steric wirings are multi-layered structure such as a built-up wiring board prepared by laminating two dimensional printed wiring boards and a multi-layered wiring board. It is difficult to form a steric wiring having a free three dimensional shape. The built-up wiring board or the multi-layered wiring board has a structure that adjacent wiring layers are connected to each other by a conductive column called via. The via is formed by processing a coated insulating layer by a photolithography process using a photosensitive polyimide or resist. For forming a via by such a method, it is necessary to repeat a plurality of times the steps of resist coating, light exposure and etching, making the via formation highly laborious. In addition, it is difficult to improve the yield.
It is also possible to form the via by forming a through-hole (via hole) of a predetermined size in an insulating substrate constituting a printed wiring board by using a drill or a CO
2
laser, followed by applying plating to the via hole or by filling the via hole with a conductive paste. In these methods, however, it is difficult to form freely a fine via having a size of scores of microns or less at a desired position.
As a method of forming a conductive column without forming a via hole in an insulating substrate, proposed is an anisotropic conductive film prepared by forming a conductive column by an electroless plating in a thickness direction of a three dimensional porous film such as PTFE as disclosed in, for example, Japanese Patent Disclosure (Kokai) No. 55-161306, Japanese Patent Disclosure No. 7-207450, U.S. Pat. No. 5,498,467 and Japanese Patent Disclosure No. 11-25755. In this method, it is possible to form a conductive column extending in the thickness direction of the film without forming a via hole in a predetermined position.
Where the anisotropic conductive film having a conductive column formed therein is used in the via layer of a multi-layered wiring board, not as a single layer anisotropic conductive film, it is necessary to ensure a good electrical and mechanical bonding properties between the via end face and a pat of the wiring, good bonding properties with the wiring layer, in which a wiring is formed, in the insulating layer portion, a high mechanical strength of the insulating layer, and good electrical insulating properties. However, since an open pore is formed within the film, the decrease in the insulating properties caused by the surface conduction on the inner wall of the pore, which is derived from the moisture absorption, is brought about as a problem in the case of using the film in the via layer (i.e., an insulating substrate having a via formed therein) of the multi-layered wiring substrate. Also, it is impossible to ensure a sufficiently high mechanical strength. In the conventional technology pointed out above, the porous film is impregnated after the via formation with, for example, a thermosetting resin to make the porous portion solid so as to ensure the required adhesivity. However, if the resin is impregnated after the via formation, the end face of the via is covered with the thermosetting resin, leading to a poor connection and an increased contact resistance. For removing the resin layer covering the end face of the via, a troublesome extra step is required.
Also proposed is a method of forming an anisotropic conductive sheet in which the via portion alone is porous and the portion other than the via portion is in the form of a solid film. In this method, a predetermined region of a polysilane sheet is exposed so as to bring about photo-oxidation and, thus, to convert the exposed portion into polysiloxane, thereby making the sheet porous. Then, the porous portion is loaded with a conductive substance by, for example, a plating technology so as to form a conductive column. In this technology, the insulating material used is limited to polysilane. It should be noted that polysilane tends to be deteriorated by an acidic substance, by an oxidizing reaction, etc. Also, polysilane does not exhibit an adhesivity in general. Therefore, in the case of using an anisotropic conductive sheet formed of polysilane as a via layer of a multi-layered board, an adhesive layer for bonding adjacent layers is newly required. What should be noted is that the end face of the via tends to be covered with the new adhesive layer.
A porous film prepared by elongating a uniform film such as PTFE is used as a three dimensional porous film in which a wiring or a via is formed. Particularly, where the film is made porous by elongation, an irregular three dimensional s
Asakawa Koji
Hiraoka Toshiro
Hotta Yasuyuki
Cuneo Kamand
Kabushiki Kaisha Toshiba
Patel I B
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