Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2002-02-28
2003-12-16
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S216000, C428S323000, C428S422800, C428S462000, C428S515000, C428S901000, C174S250000, C174S251000, C174S257000, C174S258000
Reexamination Certificate
active
06663946
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multi-layer wiring substrates for use in electronic instruments such as various types of AV instruments, home electric appliances, communication instruments, computers and peripheral instruments thereof and, particularly, to a multi-layer wiring substrate in which a liquid crystal polymer layer is used as a portion of a dielectric layer.
2. Description of Related Art
Heretofore, a multi-layer wiring substrate for forming a mixed integrated circuit in which a predetermined electronic circuit is constructed by mounting thereon a multiple of active components such as a semiconductor element and the like, and passive components such as a capacitor element, a resistor element and the like have been formed by forming a vertical through-hole by means of a drill on a dielectric layer made up by impregnating an epoxy resin in glass cloth, forming a plurality of wiring conductors on an inside of the thus-formed through-hole and on a surface of the dielectric layer to form a wiring substrate and, then, laminating a multiple of the thus-formed wiring substrate.
Ordinarily, a present-day electronic instrument, as is represented by a mobile communication instrument, is requested to be small in size, thin, and light in weight, to have a high performance, high functionality, a high quality and high reliability. For this reason, electronic components such as a mixed integrated circuit and the like to be mounted on such electronic instrument has come to be requested to be small in size and of a high-density package. In order to meet such a requirement for the high-density package, minuteness of the wiring conductor, thinness of the dielectric layer and minuteness of the through-hole have come to be required also for the multi-layer wiring substrate which constitutes the electronic component. For this reason, in recent years, in order to allow the through-hole to be minute, laser processing which enables minute processing than drill processing has come to be employed.
However, in the dielectric layer made up of impregnating the epoxy resin in the glass cloth, there is a difficulty in providing a hole in the glass cloth by a laser whereby there is a limitation on minuteness of the through-hole and, further, there is a problem that it is difficult to form the through-hole having a uniform pore diameter due to the fact that a thickness of the glass cloth is not uniform.
In order to solve these problems, it has been proposed that the multi-layer wiring substrate in which an insulating backing material made up of either impregnating the epoxy resin in a non-woven fabric made of aramid resin fibers or coating an epoxy-type adhesive on a polyimide film was used for the dielectric layer.
However, the insulating backing material using the aramid non-woven fabric or the polyimide film is highly hygroscopic whereupon there is a problem that, when the insulating backing material which has absorbed moisture is subjected to a soldering reflow, the moisture absorbed therein is vaporized to generate a gas thereby causing a separation of the dielectric layer or other unfavorable phenomena. Further, the epoxy-type adhesive is high in a dielectric constant whereupon there is another problem that transmission characteristics thereof in a high frequency region are deteriorated.
In order to solve these problems, it has been studied to use a liquid crystal polymer as a material for the dielectric layer of the multi-layer wiring substrate. Since a layer comprising the liquid crystal polymer is constituted by rigid molecules whereupon these molecules have a structure such that they are orderly aligned to some extent and an attraction force between the molecules is strong, the layer exhibits high thermal resistance, a high Young's modulus, high dimensional stability and a low hygroscopic property to have characteristics that there is no need of using a reinforcing material such as glass cloth therein and, further, it is excellent in a microfabrication property. Further, the layer has characteristics that, even in a high frequency region, it has a low dielectric constant and a low dielectric tangent and, also, an excellent high frequency property.
While making use of such characteristics of the liquid crystal polymer, Japanese Unexamined Patent Publication JP-A 8-97565 (1996) has proposed a multi-layer printed circuit substrate in which a plurality of circuit layers contain a first liquid crystal polymer and allow an adhesive layer which contains a second liquid crystal polymer having a lower melting point than that of the first liquid crystal polymer to be inserted therebetween. Further, Japanese Unexamined Patent Publication JP-A 2000-269616 (2000) has proposed a high-frequency circuit substrate in which a thermoplastic liquid crystal polymer film and a metallic foil were adhered with each other by the epoxy-type adhesive to form a liquid crystal polymer film which is then used as an electric dielectric layer.
However, in the multi-layer printed circuit substrate proposed by JP-A 8-97565, when the adhesive layer containing the liquid crystal polymer is inserted between a plurality of circuit layers and adhered them with one another by means of thermal compression bonding, due to the fact that the liquid crystal polymer is rigid to be incapable of moving into a fine dent formed on a surface of the circuit layer, there is a problem that it can not exert a sufficient anchor effect whereupon adhesiveness between the circuit layer and the adhesive layer is inferior to exhibit an insulation failure by a high temperature bias test.
Further, in the high-frequency circuit substrate proposed by JP-A 2000-269616, since a dielectric constant of the epoxy-type adhesive is different from that of the liquid crystal polymer to a great extent, by a small variation of thickness to be caused by a pressure to be applied at the time of lamination, there appears a problem that the transmission characteristics are deteriorated in the high frequency region, particularly, in a frequency region of 100 MHz or more. Further, since a film in which an orientation property of liquid crystal polymer molecules is corrupted is used, an attraction force between the liquid crystal polymer molecules becomes weak whereby coefficient of thermal expansion of liquid crystal polymer film is increased and, as a result, when the multi-layer wiring substrate is constituted by these substrates, there is a problem that a wiring failure is generated at a joint between a through-hole conductor and a wiring conductor therein by a temperature cycle test. Further, in accordance with a weak attraction force between the molecules, flexural strength becomes weak whereupon there is a problem that, when the wiring substrate is brought to be thinner than before by decreasing a thickness of the electric dielectric layer, a camber will be generated therein.
SUMMARY OF THE INVENTION
The invention has been attained to solve these problems of the prior art and has an object of providing a multi-layer wiring substrate having a high-density wiring and being excellent in soldering thermal resistance, insulating property, and high-frequency transmission characteristics.
The invention provides a multi-layer wiring substrate comprising:
a lamination of a plurality of dielectric layers which each comprise an organic material and are each provided with a wiring conductor of a metallic foil on at least one surface of upper and bottom surfaces of the respective dielectric layers, the wiring conductors between which the dielectric layer is disposed being electrically connected with each other via a through conductor formed in the dielectric layer, wherein the dielectric layers each individually are composed of a liquid crystal polymer layer and cladding layers comprising a polyphenyleneether-type organic substance, formed on upper and bottom surfaces of the liquid crystal polymer layer.
According to the invention, since the dielectric layer comprises the cladding layer which comprising the polyphenyle
Hayashi Katsura
Kume Kenji
Matsunaga Takahiro
Miyatani Isao
Nagasawa Tadashi
Hogan & Hartson
Jones Deborah
Kyocera Corporation
Xu Ling
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