Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-08-26
2002-12-31
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S517000, C428S519000, C428S516000, C525S241000, C525S315000, C525S323000, C525S324000, C525S240000
Reexamination Certificate
active
06500535
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Art Field
The present invention relates generally to a novel heat-resistant, low-dielectric polymeric material, and films, substrates, electronic parts and heat-resistant resin formed articles obtained by use of the same. Specifically, the present invention is concerned with a low-dielectric-constant polymeric material that has a low dielectric constant and a low dielectric loss tangent, is excellent in heat resistance in a high-temperature range and close contact with or adhesion to metals and metal foils as well, and is capable of injection molding, press molding, transfer molding and extrusion molding. More specifically, the present invention is directed to a substrate or the like that is prepared by thermal fusion and lamination of films obtainable from the low-dielectric-constant polymeric material itself.
2. Background Art
To meet recent sharp increases in the quantity of information communications, there are growing demands for size and weight reductions, and fast operation of communications equipment and, hence, low-dielectric electrical insulating materials capable of meeting such demands are now in urgent need. In particular, the frequencies of radio waves used for hand-portable mobile communications such as earphones and digital portable phones, and satellite communications are in high-frequency bands covering from the MHz to GHz bands. Size reductions, and high-density packing of housings, substrates and elements are attempted on account of the rapid progress of communications equipment used as these communications means. For achieving size and weight reductions of communications equipment used in the high-frequency band region covering from the MHz to GHz bands, it is now required to develop an electrical insulating material with excellent high-frequency transmission characteristics combined with suitable low dielectric characteristics. In other words, a device circuit undergoes energy losses in the transmission process, which are called dielectric losses. The energy losses are not preferable because they are consumed as thermal energy in the device circuit, and discharged in the form of heat. In a low-frequency region the energy losses occur due to a dipole field change caused by dielectric polarization, and in a high-frequency region they occur due to ionic polarization and electronic polarization. The ratio between the energy consumed in a dielectric material and the energy built up in the dielectric material per cycle of an alternating field is referred to as a dielectric loss tangent, represented by tan &dgr;. A dielectric loss is proportional to the product of a relative dielectric constant ∈ and the dielectric loss tangent of material. Consequently, tan &dgr; increases with increasing frequency in the high-frequency region. In addition, the quantity of heat generated per unit area increases due to the high-density packing of electronic elements. To reduce the dielectric loss of a dielectric material as much as possible, therefore, it is required to use a material having a small value for tan &dgr;. By use of a low-dielectric polymeric material having a reduced dielectric loss, the dielectric loss and the generation of heat due to electrical resistance are reduced so that the risk of signal malfunctions can be reduced. Materials having reduced transmission losses (energy losses) are thus strongly desired in the field of high-frequency communications. For materials electrically characterized by electrical insulation and a low-dielectric constant, it has been proposed so far in the art to use a diversity of materials such as thermoplastic resins, e.g., polyolefin, vinyl chloride resin and fluorine base resin, and thermosetting resins, e.g., unsaturated polyester resin, polyimide resin, epoxy resin, vinyltriazine resin (BT resin), crosslinkable polyphenylene oxide, and curable polyphenylene ether.
When materials having a low-dielectric constant are used as an electronic part (element) material, however, polyolefins such as polyethylene and polypropylene, like those set forth in JP-B 52-31272, have a grave disadvantage that their heat resistance is low although they have excellent insulation resistance as electrical properties. This is because they have a covalent bond such as a C—C bond, and are free of a large polar group. For this reason, their electrical properties (dielectric loss, dielectric constant, etc.) become worse when they are used at high temperatures. Thus, such polyolefins are not preferable for use as an insulating film (layer) for capacitors, etc. The polyethylene and polypropylene, once they have been formed into film, are coated and bonded onto a conductive material using an adhesive agent. However, this method does not only involve a complicated process but also offers some problems in view of coating, for instance, because it is very difficult to make the thickness of the film thin.
The vinyl chloride resin has high insulation resistance and excellent chemical resistance and fire retardance, but it has the demerits of lacking heat resistance as in the case of polyolefins, and having large dielectric losses as well.
Polymers containing a fluorine atom in their molecular chains, like vinylidene fluoride resin, trifluoroethylene resin, and perfluoroethylene resin, are excellent in terms of electrical properties (low dielectric constant, low-dielectric loss), heat resistance and chemical stability. However, one difficulty with such polymers is that, unlike thermoplastic resins, they cannot be heat-treated into formed articles or films due to their poor formability, and their poor ability to form coatings. Another disadvantage is that some added cost is needed for forming the polymers into devices. Yet another disadvantage is that the field to which the polymers are applicable is limited due to their low transparency. Such low-dielectric polymeric materials for general purpose use as mentioned above are all insufficient in terms of heat resistance because their allowable maximum temperature is below 130° C. and, hence, they are classified as an insulating material for electrical equipment into heat resistance class B or lower according to JIS-C4003.
On the other hand, the thermosetting resins such as epoxy resin, polyphenylene ether (PPE), unsaturated polyester resin, and phenolic resin are mentioned for resins having relatively good heat resistance. As disclosed in JP-A 6-192392, the epoxy resin conforms to performance requirements regarding insulation resistance, dielectric breakdown strength, and heat-resistant temperature. However, no satisfactory properties are obtained because of a relatively high dielectric constant of 3 or greater. The epoxy resin has another demerit of being poor in the ability to form thin films. In addition, a curable modified PPO resin composition is known, which composition is obtained by blending polyphenylene oxide resin (PPO) with polyfunctional cyanic acid ester resins and other resins, and adding a radical polymerization initiator to the blend for preliminary reactions. However, this resin, too, fail to reduce the dielectric constant to a satisfactory level.
With a view to improving the epoxy resin having poor heat resistance, combinations of the epoxy resin with, for instance, phenol-novolak resin, and vinyltriazine resin have been under investigation. However, a grave problem with these combinations is some significant drop of the dynamic properties of the resulting films.
For the purposes of solving the above problems while the electrical properties are maintained, and specifically introducing improvements in the processability on heating, and close contact with or adhesion to copper or other metal conductors (layers), proposals have been put forward for copolymers of branched cyclo-ring amorphous fluoropolymer, and perfluoroethylene monomer with other monomers. However, although these copolymers may satisfy electrical properties such as dielectric constant, and dielectric loss tangent, yet their heat resistance remains worse under the influence of a methylene chain prese
Asami Shigeru
Endou Kenji
Moriya Yasuo
Takahashi Takeshi
Yamada Michihisa
Tarazano D. Lawrence
TDK Corporation
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