Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2001-11-30
2004-04-06
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S413000, C428S414000, C428S418000, C428S901000, C525S523000
Reexamination Certificate
active
06716530
ABSTRACT:
TECHNICAL FIELD
The present invention relates to resin applied-copper foil which is capable of manufacturing a printed wiring board without employing component materials of an insulating layer such as a prepreg, and to a copper-clad laminate and a printed wiring board which are excellent in flame retardancy.
BACKGROUND ART
A copper-clad laminate used for manufacturing a printed wiring board which is widely used in electric and electronic products is generally manufactured by employing the so-called prepreg, the prepreg being made by the impregnation of a glass cloth, kraft paper, a nonwoven glass fabric or the like with a thermosetting resin such as phenol resin or epoxy resin in order to make the resin in a semi-cured state, and by sticking and laminating the copper foil onto one side or both sides of the prepreg.
Further, in case of manufacturing a copper-clad laminate having three layers or more which is categorized as a multilayer printed wiring board, the copper-clad laminate is manufactured by once performing the conductive circuit formation on a surface of the copper-clad laminate to make an internal layer base material, and by sticking the copper foil onto the both sides of the internal layer base material via the prepreg, for example.
In recent years, with the downsizing and greater packaging density of the printed wiring board, it has become common to provide fine blind holes, i.e., via holes, on a surface of the printed wiring board. As a method for forming this via holes, laser beam machining or plasma machining, for example, may be used. At this time, in a state that inorganic components like glass fibers are contained as frame materials in an insulating layer of the copper-clad laminate (for example, this state corresponds to a case of an insulating layer being comprised of a glass-epoxy prepreg which is referred to as an FR-4 base material.), the inorganic components as framework materials will affect the processability despite the ease of sublimation and evaporation of the resin component which are caused by the laser beam or plasma. Consequently, in order to allow uniform perforating, the insulating layer is frequently fabricated only with the resin components without employing the framework materials, to be used. Also, nonexistence of the frame materials results in a capability of eliminating influences of unevenness or ridges formed at a surface of the frame materials on a flatness of the copper-clad laminate, so that an extremely flat surface can be obtained. For example, as for the above described FR-4 substrate, cloth grains of the glass cloth which is a framework material of the insulating layer develop on a surface of outer layer copper foil of the copper-clad laminate after being subjected to the hot press molding, so that in case of fabricating a thin resist layer such as a liquid resist, variations occur in a thickness of the resist layer, which consequently deteriorates a width precision of an etched circuit. Therefore, these problems can be resolved by eliminating the framework materials.
In case of fabricating an insulating layer of a copper-clad laminate without including framework materials, manufacture of a multilayer copper-clad laminate is performed by any one of the following methods: (1) a method characterized in that a liquid resin is coated on a surface of an internal layer substrate and copper foil is stuck onto the resin, (2) a method characterized in that a resin film being comprised of a thermosetting resin in a semi-cured state is sandwiched between an inner layer substrate and copper foil to be stuck thereto, in order to perform thermoforming, (3) a method wherein resin applied-copper foil, i.e., copper foil having a resin layer formed thereon, is directly stuck to a surface of an inner layer substrate, or the like. Then the resultant product undergoes formation of the so-called outer layer circuits or formation of via holes, to be processed into a printed wiring board.
The above described method (1) has some problems, that is, it is difficult to more precisely and uniformly coat the liquid resin on a surface of the inner layer substrate on which inner layer circuits are already formed and uneven configurations are also formed, and in case of performing interlayer conducting plating when forming through holes or the like, it takes much time for grinding and removing the resin content which is deposited on an inner wall of the perforation or hole portion. And the resin film used in the above described method (2) is manufactured by coating a resin composition on a plastic film, however, costly plastic films to be discarded after its usage become enormous and thus a large amount of wastes are generated, so that from the view point of the environmental protection, this method is unacceptable in the present society wherein the environmental protection is taken very seriously.
Therefore, considering from the various view points, we have reached a conclusion that it is most advantageous to use resin applied-copper foil, and the above described method (3) is becoming widely and commonly pervasive. As a resin content used for the resin applied-copper foil, epoxy resins are frequently used. As for this resin applied-copper foil, the inventors have already proposed various resin applied-copper foil which are favorable for manufacturing the copper-clad laminate used for the printed wiring boards as a result of our intensive studies, and have widely contributed to the manufacture of high density printed wiring boards because manufacturing the printed wiring boards with the use of this resin applied-copper foil allows easy forming of via holes or the like employing the laser processing method as well as forming of stable fine pitch circuits.
The copper-clad laminate manufactured by the use of such a resin applied-copper foil, when used for the printed wiring board, has practically satisfiable heat resistance, electric characteristics, and chemical resistant characteristics and has been widely supplied to the market.
As a resin used for the formation of resin layers of resin applied-copper foil which has conventionally been supplied to the market, epoxy halide resins or halogen based flame retarders are used in order to impart the flame retardancy. As for the demands for flame retardancy, it is required also from a viewpoint of the PL Standards or the like to meet a certain criterion such that the ignition will not occur for the purpose of safety in electronic and electric equipment at the time of their usage.
As the criteria for this flame retardancy, there are various quality standards for the printed wiring boards, and each of home electrical products manufacturers and industrial electronics manufacturers etc. may often adopt its original criterion. Among others, a criterion defined in section 18 of the UL 796 which is also commonly referred to as “the UL Standards”, defining whether an item can be designated as a subject matter of insurance by the U.S. insurance company, has become a de facto standard as a practical global standard, and this criterion is one of the very important quality standards for the printed wiring boards. An evaluation test of the flame retardancy is conducted for a substrate from which noncombustible copper foil is removed after a copper-clad laminate is manufactured. Therefore, a problem is not a flame retardancy required for the resin applied-copper foil itself, but a flame retardancy required for the copper-clad laminate from which the copper foil is removed, that is, the flame retardant characteristics of the resin layer of the resin applied-copper foil which remains on the substrate side becomes a problem.
However, halogen elements added to the resin used for formation of the resin layers of the resin applied-copper foil has been reported to have an opportunity to generate toxic compounds during the combustion treatment after being discarded, so that it has been required to develop resin compounds and resin applied-copper foil etc. which are free of halogen based flame retarders.
In order to try to solve this prob
Asai Tsutomu
Sato Tetsuro
Dawson Robert
Feely Michael J
Mitsui Mining & Smelting Co. Ltd.
Rothwell Figg Ernst & Manbeck
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