Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2001-08-20
2003-09-23
Berhane, Adolf D. (Department: 2836)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
Reexamination Certificate
active
06625032
ABSTRACT:
FIELD OF THE ART
The invention concerns an aqueous dispersion forming conductive layer, a conductive layer formed from the aqueous dispersion, an electronic part equipped with the conductive layer, a circuit board, equipped with a conductive layer formed with the abovementioned aqueous dispersion forming conductive layer, and a method of manufacturing the circuit board, and a multilayer wiring board and a method of manufacturing the multilayer wiring board.
BACKGROUND ART
Since priorly, the metal plating method has been used to form a conductive layer, which is to serve as an electrode, wiring pattern and the like on a substrate. Another method of forming the conductive layer is the method of dispersing a conductive powder in a liquid thermosetting resin material to form a conductive paste and applying the conductive paste onto a substrate by coating, printing, or other method, and thereafter thermosetting the resin. Also, Japanese Unexamined Patent Publication No. Hei-9-134891 discloses a thin film forming method, wherein an ultrafine metal particle dispersive solution, prepared by uniformly dispersing ultrafine particles of a metal in an organic dispersion medium, is coated onto a semiconductor substrate and then the organic solvent is eliminated and the ultrafine metal particles are fused by heat.
Also in recent years, in accompaniment with demands for advanced functions and compact size in electronic equipment, electronic parts of high degrees of integration and large numbers of electrodes are coming to be used and the mounting of such electronic parts at high density is being required. Thus in place of single-sided printed wiring boards, with which a wiring layer is formed on just one surface of an insulating substrate, and double-sided printed wiring boards, with which wiring layers are formed on both surfaces of a substrate, multilayer printed wiring boards, with which insulating layers and wiring layers are layered in an alternating manner on one surface or both surfaces of a substrate, are coming to be used as wiring boards for electronic parts and wiring boards for mounting electronic parts.
Conventionally, the mainstream method of manufacturing a multilayer printed circuit board was the method of laminating a plurality of core wiring substrates, each of which is arranged by forming wiring layers that are electrically connected to each other on both surfaces of an insulating layer, and thermosetting resin prepreg sheets in an alternating manner and performing heat pressing to integrally laminate the plurality of core wiring boards with insulating layers interposed (this method shall be referred to hereinafter as the “lamination press method”).
However, with this lamination press method, interlayer shorting parts (buried vias and blind vias), which extend in the thickness direction through just an insulating layer that exists between wiring layers of adjacent core wiring substrates, cannot be formed for electrical connection between the wiring layers, and since interlayer shorting parts (through holes) that extend in the thickness direction through the entire multilayer wiring board must thus be formed, the forming of high-density wiring layers was difficult.
For this reason, the build-up method, with which an insulating layer and a wiring layer are formed successively one layer at a time on a core wiring substrate, has come to be noted recently as a method of manufacturing multilayer printed wiring boards with high-density wiring layers. With the build-up method, high-density wiring layers can be formed since the electrical connection between respective wiring layers can be realized through shorting parts that extend in the thickness direction through just an insulating layer that exists between the wiring layers.
To be more specific, with the build-up method, an insulating layer, having through holes that correspond to the interlayer shorting parts (vias) that are to be formed, is formed on the surface of a core wiring substrate, and thereafter, conductors, which comprise the interlayer shorting parts, are formed inside the through holes in the insulating layer, a wiring layer is formed on the surface of the insulating layer, and the process is repeated a prescribed number of times to obtain the desired multilayer wiring board.
Known methods of forming the insulating layer with through holes on the surface of a core wiring substrate in the above-described process include the method of coating a liquid radiation-curing resin material on the surface of the core wiring substrate and thereafter performing an exposure treatment and a development treatment on the coated film to form an insulating layer with through holes corresponding to the desired shorting parts (via holes), and the method of coating a liquid thermosetting resin material or setting a sheet-like thermosetting resin material on the surface of the core substrate, performing heat treatment to form the insulating layer, and then illuminating laser light on the insulating layer to form through holes corresponding to the desired interlayer shorting parts.
Further known methods of forming conductors inside the through holes of an insulating layer include the method of forming metal thin films by deposition of metal on the inner surfaces of the through holes of the insulating layer by electroless deposition and then performing electroplating, using the metal thin films as electrodes, to deposit metal and thereby form conductors comprised of metal layers of the required thickness, the method of depositing metal on the inner surfaces of the through holes of the insulating layer by electroless deposition to form conductors comprised of metal layers of the required thickness, the method of filling the interiors of the through holes of the insulating layer with an abovementioned conductive paste, for example, by screen printing or other printing method and then curing the conductive paste to form conductors, with which conductive powder is dispersed within a thermosetting resin, and the like.
However, with the above-described plating methods, since the rate at which a plated film grows from the metal ions is slow, a considerable amount of time is required to form a metal layer of the required thickness in cases where a rather thick conductive film (for example, with a film thickness of 10 &mgr;m or more), a conductive layer that fills the abovementioned through hole, via hole, an abovementioned interlayer shorting part, or the like is to be formed. A high productivity therefore cannot be achieved. Especially with the above-described build-up method, since the interlayer shorting parts, which pass through an insulating layer in its thickness direction, must be formed each time the insulating layer is formed, the slowness of the rate of deposition of metal by plating has a large influence on the productivity.
Also, with methods of forming a conductive layer by coating, printing and the like using a conductive paste or ultrafine metal particle dispersive solution, it is difficult to perform precise control of the thickness of the conductive layer that is obtained, the formation position of the conductive layer and the like. In particular, since a conductive paste that is comprised of resin and conductive powder is relatively high in viscosity (for example, approximately 100 Pa·s at 25° C.) in general, it is difficult to form conductive layers that are high in the precision of formation position, shape and the like. Also in the case where the diameter of the through holes of the insulating layer is small (for example, less than 100 &mgr;m in diameter), the interiors of the through holes cannot be filled readily with a conductive paste of such high viscosity, and thus a multilayer wiring board of high connection reliability cannot be obtained.
Also, with the method described in Japanese Unexamined Patent Publication No. Hei-9-134891, though the viscosity of the ultrafine metal particle dispersive solution can be made low, since the dispersion does not contain a resin component, the conductive layer becomes cracked in cas
Ito Nobuyuki
Koyama Ken-ichi
Berhane Adolf D.
JSR Corporation
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