Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1999-03-16
2002-01-22
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C156S153000, C156S308200, C156S309600, C156S330900, C428S214000, C428S332000, C428S337000, C428S458000, C428S473500
Reexamination Certificate
active
06340518
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for manufacturing a flexible metal foil laminate which is used in the field of electronic industries.
2. Description of the Prior Art
Polyimide metal foil laminates are mainly used as base materials for flexible printed-wiring boards having flexibility, and they are also used as thin-film heating elements, electromagnetic wave shielding materials, flat cables, wrapping materials and the like. In recent years, with the miniaturization and the density enhancement of electronic equipment using printed-wiring boards, there has been an increase in the utilization of the polyimide metal foil laminate sheets on which parts and elements can be practically mounted at a high density. However, the conventional flexible metal foil laminates have been manufactured by bonding a polyimide film to a metal foil by the use of an adhesive such as an epoxy resin. Therefore, their characteristics such as heat resistance, chemical resistance and electrical properties mainly depend on the properties of the adhesive to be used, so that the several excellent characteristics of a polyimide cannot be sufficiently utilized, and particularly, the heat resistance is not sufficient.
In order to improve these disadvantages of the conventional flexible metal foil laminate having an adhesive layer, it has been attempted that a polyimide or a polyamic acid varnish is directly cast onto a metal foil to obtain the flexible metal foil laminate without any conventional adhesive layer. Moreover, it has also been attempted that an adhesive polyimide is laminated on one surface or both the surfaces of a polyimide film, and then putting on a metal foil, or two metal foils thermally to obtain a similar flexible metal foil laminate having an insulating layer all comprising the polyimide.
However, when each of these methods is used selecting, for example, a copper foil as the metal foil, the adhesive strength between the copper foil having a smooth surface and the polyimide is low, so that any satisfactory product cannot be obtained. In order to overcome this drawback, the surface of the metal foil which contacts the polyimide is previously subjected to a surface treatment for roughing the surface to increase surface area.
However, with regard to the interrelation between the roughness on the treated surface of the metal foil and the thickness of the adhesive layer which comes in contact with this treated surface, sufficient discussion has not been made. That is to say, according to our investigation, it has been found that when the thickness of the adhesive layer is small considering the roughness on the treated surface, the recesses on the surface are not completely filled with the adhesive, which causes an adhesive failure. On the other hand, also when the thickness of the adhesive layer is very large considering the roughness on the treated surface, an adhesion cannot exceed a certain value, and the formation of the excessively thick adhesive layer causes the increase of the amount of the adhesive to be used and the extension of the time of an application step and a drying step, which leads to the increase of a manufacturing cost and requires an excessive thickness of the insulating layer.
The present invention intends to provide a method for manufacturing a flexible metal foil laminate in which a polyimide having excellent heat resistance, chemical resistance, electrical properties and the like is used as an insulator and a sufficient adhesion can be obtained between a metal foil and the polyimide.
SUMMARY OF THE INVENTION
The present inventors have intensively investigated, and as a result, it has been found that the thickness of an adhesive layer necessary to obtain a sufficient adhesion at a metal/insulator interface of a flexible metal foil laminate sheet is interrelated with the degree of the roughness on the surface of the metal foil which contacts the adhesive layer, and in consequence, the present invention has been completed.
That is to say, an object of the present invention is to provide a flexible metal foil laminate wherein a polyimide layer comprises a polyimide laminate having a three-layer structure in which thermoplastic polyimide layers are formed on both the surfaces of a polyimide film; metal foil layers are heated and pressed against both the sides of the polyimide laminate; and the thickness of the thermoplastic polyimide layer is 100% or more of an average roughness at 10 points on the surface of the metal foil which contacts the thermoplastic polyimide layer.
Another, object of the present invention is to provide a method for manufacturing a flexible metal foil laminate having a polyimide layer between two metal foil layers, wherein the polyimide layer comprises a polyimide laminate having a three-layer structure in which thermoplastic polyimide layers are formed on both the surfaces of a polyimide film; said method comprising the steps of putting the metal foil layers on both the sides of the polyimide laminate, respectively, and then heating and pressing them, the thickness of the thermoplastic polyimide layer being 100% or more of an average roughness at 10 points on the surface of the metal foil which contacts the thermoplastic polyimide layer.
Still another object of the present invention is to provide a method for manufacturing a flexible metal foil laminate having a polyimide layer between two metal foil layers; said method comprising the step of heating and pressing one metal foil and a polyimide/metal foil laminate including the other metal foil and a polyimide layer comprising a thermoplastic polyimide layer outermost to the other metal foil so that the thermoplastic polyimide layer is placed on the former metal foil, the thickness of the thermoplastic polyimide layer being 100% or more of an average roughness at 10 points on the surface of the metal foil which contacts the thermoplastic polyimide layer.
The present invention just described is characterized in that the metal foil is selected from metal foils comprising copper, iron, nickel, chromium, molybdenum, aluminum, or alloys including these metals.
According to the present invention, there can be manufactured a flexible metal foil laminate in which a necessary and sufficient adhesion is present in an interface between a metal foil and an insulating layer and which is excellent in heat resistance, chemical resistance, electrical properties and the like. In consequence, the thickness of a thermoplastic polyimide layer which is an adhesive layer can be decreased to a necessary and minimum level, which permits the reduction of manufacturing cost. In addition, the flexible metal foil laminate sheet in which the insulating layer is as thin as possible can be manufactured. Next, the present invention will be described in detail.
DETAILED DESCRIPTION OF THE INVENTION
No particular restriction is put on a kind of metal foil which can be used in the present invention, and examples of the usable metal foil include copper, copper alloys, iron, nickel, chromium, molybdenum, aluminum, stainless steels and beryllium-copper alloys. Furthermore, no particular restriction is put on the thickness of the metal foil which can be used in the present invention, but it is usually in the range of 5 to 175 &mgr;m, preferably 9 to 105 &mgr;m.
On the metal foil which can be used in the present invention, there can be formed an inorganic material such as a single metal or its oxide, or a coupling agent such as aminosilane, epoxysilane or mercaptosilane. On the surface of the metal foil, there can also be carried out a sandblast treatment, a honing treatment, a corona treatment, a plasma treatment or an etching treatment.
A polyimide layer as an insulating layer of the present invention is a polyimide laminate of a three-layer structure which can be formed by laminating a thermoplastic polyimide on both the surfaces of a polyimide film. As the polyimide film which can be used herein, a commercially available polyimide film may be used, or a polyimide film forme
Kayama Takashi
Kitahara Mikio
Mineta Naoshi
Mori Minehiro
Mitsui Chemicals Inc.
Nakarani D. S.
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