Thermosetting low-dielectric resin composition and use thereof

Stock material or miscellaneous articles – Layer or component removable to expose adhesive

Reexamination Certificate

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C428S447000, C428S448000, C428S450000, C428S473500, C428S606000, C523S202000, C523S209000, C523S210000, C523S212000, C523S213000, C526S258000, C526S262000, C526S263000

Reexamination Certificate

active

06713143

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermosetting low-dielectric resin composition for print circuit board and its use. More specifically, it relates to a thermosetting low-dielectric resin composition which has a low dielectric constant and a low dielectric tangent and which shows excellent adhesion to metals and scatters almost no resin during working and also relates to a laminated board, a metal-clad laminated board and a circuit laminate material to which the above resin composition is applied.
2. Description of Prior Art
In recent years, remarkable increases are found in signal speeds and operation frequency of electronic systems. For electronic systems for use in a high-frequency region, it is desired to use a resin for a laminated board which has excellent heat resistance, a low dielectric constant and a low dielectric tangent and a laminated board or a metal-clad laminate obtained from prepregs using a resin having the above properties. A laminated board or a metal-clad laminate using a low-dielectric material enables higher-speed processing of signals since it can increase the propagation rate of electric signals.
It has been also proposed to use a fluorine resin and a polyphenylene ether resin which have low dielectric constants. However, these have a problem that they are poor in workability and adhesion and less reliable. For improving, workability and adhesion, there has been proposed an epoxy-modified polyphenylene ether resin or a polyphenylene-ether-modified epoxy resin. Since, however, an epoxy resin has a high dielectric constant, satisfactory properties have not yet been obtained. There is known a curable resin composition prepared by mixing a polyphenylene ether resin, a polyfunctional cyanate ester resin and some other resin, adding a radical polymerization initiator and allowing the mixture to undergo a preliminary reaction (JP-A-57-185350), while the above resin composition is insufficient with regard to a decrease in dielectric constant.
Further, a polybutadiene resin containing a thermosetting 1,2-polybutadiene as a main component has a low dielectric constant, while it is poor in adhesion and is insufficient in heat resistance. There has been proposed a composition containing 100 parts by weight of a polyphenylene ether resin, 5 to 20 parts by weight of 1,2-polybutadiene resin, 5 to 10 parts by weight of a crosslinking monomer and a radical crosslinking agent (JP-A-61-83224). When 1,2-polybutadiene resin is used, however, sticking nature remains after a solvent is removed, and the practical problem is that a prepreg prepared by applying the above resin to a glass material or impregnating a glass material with it cannot maintain a tack-free state. When a 1,2-polybutadiene having a high molecular weight is used for removing the sticking nature, there is a problem that it has a low solubility in a solvent so that a solution has an increased viscosity and shows a decreased fluidity.
There has been proposed a low-dielectric laminated board or copper-clad laminate prepared by impregnating a fluorocarbon fiber fabric with a thermosetting resin (JP-B-2578097). In this case, however, it is required to surface-treat the fluorocarbon fiber for improving the adhesion between the fluorocarbon fiber and the thermosetting resin, and the laminated board or copper-clad laminate is very expensive since the fluorocarbon fiber is expensive, which results in difficulties in practical use.
A multi-layered printed circuit board for use in an electronic machine or device has an electric circuit on an inner layer as well. The multi-layered printed circuit board is fabricated by providing an inner circuit board on which a circuit is formed beforehand and copper foil(s) for outer-layer circuit(s), stacking the inner circuit board and the copper foil(s) through prepreg, shaping the resultant set under heat and pressure to prepare a multi-layered copper-clad laminate having an inner-layer circuit, and forming circuit(s) on outer layer(s). As the above prepreg, there is used a glass-cloth-substrate epoxy-resin prepreg. Since the signal speed and performance frequency of electronic machines and devices remarkably increase in recent years, thin circuit laminate materials having excellent heat resistance, a low dielectric constant and a low dielectric tangent are desired for micro-wiring in electronic machines and devices for use in a high-frequency region, particularly, electronic machines and devices which are required to be downsized and decreased in weight. With a thin circuit laminate material from a low-dielectric material, the propagation speed of electric signals can be increased, so that signals can be processed at a higher speed.
For a thin multi-layered printed circuit board, a thin glass-cloth-substrate epoxy-resin prepreg having a thickness of 30 to 100 &mgr;m is used at present. However, fiber lines are liable to appear, an uneven surface of an inner-layer circuit substrate cannot be absorbed within the prepreg, and an uneven surface is liable to be formed as a surface of an outer-layer, so that the smoothness of the surface is impaired, which is a bar against the formation of micro-wirings. There is therefore found a method in which the conventional glass-cloth-substrate epoxy-resin prepreg is replaced with a glass-cloth-free adhesive film as a prepreg, or a method in which a resin-applied copper foil prepared by stacking an adhesive layer on one surface of a copper foil for an outer-layer circuit beforehand is used as both a copper for an outer-layer circuit and a prepreg. The above adhesive film and the above resin-applied copper foil use a resin having film formability, and the resin that can be used is limited to those resin having film formability. When a resin having no film formability is used, the resin is liable to cause troubles such as breaking and chipping in the steps of transporting, cutting and laminating the adhesive film. Further, when the resin having no film formability is used as an insulating material for inter-layer connection of a multi-layered board, the inter-layer insulating layer is liable to extremely decreases in thickness in an inner-layer circuit presence portion during shaping of a multi-layered board under heat and pressure, or it is liable to cause troubles such as a decrease in inter-layer insulation resistance and a short circuit. As a resin having film formability, there have been proposed a thermoplastic polyimide adhesive film (U.S. Pat. No. 4,543,295), a high-molecular-weight epoxy resin (JP-A-4-120135), an acrylonitrile-butadiene copolymer/phenolic resin (JP-A-4-29393), a phenolic resin/butyral resin (JP-A-4-36366) and an acrylonitrile-butadiene copolymer/epoxy resin (JP-A-4-41581). However, these resin have a problem on dielectric constant properties, and they are not feasible for processing signals at a higher speed.
As a low-dielectric resin, there have been proposed a fluorine resin, a polyphenylene ether resin, a polybutadiene resin containing thermosetting 1,2-polybutadiene as a main component, and a composition containing 100 parts by weight of a polyphenylene ether resin, 5 to 20 parts by weight of 1,2-polybutadiene resin, 5 to 10 parts by weight of a crosslinking monomer and a radical crosslinking agent (JP-A-61-83224). However, these resin have difficulties in practical use since they are poor in heat resistance, workability and film formability.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermosetting resin composition which has a low dielectric constant and a low dielectric tangent for use in a printed circuit board and which has excellent adhesion to a metal and scatters almost no resin when a prepreg is prepared by punching or cutting.
It is another object of the present invention to provide a laminated board and a metal-clad laminate to which the above thermosetting resin composition is applied.
It is still another object of the present invention to provide an adhesive film of a thermosetting low-dielectric resin composition

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