Stock material or miscellaneous articles – All metal or with adjacent metals – Foil or filament smaller than 6 mils
Reexamination Certificate
2000-09-05
2002-11-05
Zimmerman, John J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Foil or filament smaller than 6 mils
C428S607000, C428S626000, C428S612000, C428S675000, C428S687000, C205S222000, C174S256000, C451S057000
Reexamination Certificate
active
06475638
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to an electrodeposited copper foil with its surface prepared wherein a matte side, namely a surface at which copper deposition is completed, is mechanically polished at least once and the thus mechanically polished matte side is subjected to a selective chemical polishing so as to attain preparing thereof, and relates to a process for producing the same and a use of the electrodeposited copper foil with its surface prepared in, for example, a printed wiring board.
BACKGROUND OF THE INVENTION
In recent years, both the size and weight of electronic equipment such as a notebook-sized personal computer are being reduced to increasing extents. Accordingly, IC wiring is also becoming finer.
With respect to the wiring pattern formed on a substrate used in such an electronic equipment, the lead width is now as small as ten-odd microns (&mgr;m). In accordance therewith, the metal foil constituting the wiring pattern is becoming thinner. Specifically, while the designated thickness of metal foil for use in the formation of the conventional wiring pattern of about 100 &mgr;m lead width has ranged from about 15 to 35 &mgr;m in correspondence to the width of the wiring pattern, the thickness of metal foil employed in the formation of ten-odd micron (&mgr;m) wiring pattern must be reduced in correspondence thereto.
For example, an aluminum foil or a copper foil is used as the metal foil for constituting the above wiring pattern. It is preferred to employ a copper foil, especially an electrodeposited copper foil, as the metal foil.
The electrodeposited copper foil employed for forming the above wiring pattern is produced by electrodepositing copper on a drum surface. With respect to the thus produced electrodeposited copper foil, the surface at which copper deposition is initiated, namely the surface at which formation of copper deposits brought into contact with the drum is initiated, is referred to as “shiny side”, and the surface at which copper deposition is completed is referred to as “matte side”. The surface condition of the shiny side is substantially the same as that of the drum. That is, the 10-point average surface roughness (Rz) in ISO 4287 of the drum is about from 1.2 to 2.5 &mgr;m, to which the 10-point average surface roughness (Rz) of the shiny side is nearly equal. On the other hand, with respect to the matte side, its surface roughness is greater than the surface roughness of the shiny side, and the 10-point average surface roughness of the matte side, although varied depending on the deposition condition of copper and the thickness thereof, is generally in the range of about 2.5 to 10 &mgr;m. In the conventional electrodeposited copper foil of about 35 &mgr;m nominal thickness, it has been rare that the surface roughness of the matte side poses a problem. However, in the electrodeposited copper foil of ten-odd micron (&mgr;m) thickness, the surface roughness of the matte side is equivalent to tens of percents of the thickness of the whole electrodeposited copper foil, and the condition of the matte side exerts marked influence on the electrical properties of formed wiring pattern and board per se. It is known that, for example, mechanical polishing, chemical polishing and electrolytic polishing are available as the means for preparing the state of surface of the copper foil. The mechanical polishing is a method of smoothing the surface of the copper fail with the use of, for example, a buff. When use is made of a thin copper foil, the copper foil may be broken by mechanical stress exerted on the copper foil. Thus, the mechanical polishing is suitable for the preparing of the surface of relatively thick copper foils. On the other hand, no mechanical stress is exerted on the copper foil in the chemical polishing and electrolytic polishing, as different from the mechanical polishing, so that even thin copper foils would not be broken by the chemical polishing and electrolytic polishing. Thus, it has been believed that the chemical polishing and electrolytic polishing are suitable for the preparing of the surface of relatively thin copper foils.
For example, Japanese Patent Unexamined Publication No. Hei 5-160208 discloses a tape carrier having a lead pattern formed from an electrodeposited copper foil wherein the overall surface of matte side obtained by electrodeposition has been polished. This publication discloses the use, in the formation of a lead pattern of 60 to 80 &mgr;m pitch, of an electrodeposited copper foil whose 1-2 &mgr;m of matte side surface profile has been chemically polished to thereby attain preparing of the matte side. The thickness of the there employed electrodeposited copper foil after the preparing is in the range of 18 to 30 &mgr;m. It is disclosed that a highly reliable carrier tape with desired lead strength can be provided by the use of the copper foil whose matte side overall surface has been chemically polished.
However, the preparing of copper foil by chemical polishing as described in the above publication, although protrudent parts of the matte side are leached with relatively high selectivity to thereby effect preparing thereof, also invites leaching of the copper constituting the depressed parts of the matte side. Therefore, in this chemical polishing, the whole copper foil tends to become thin. Accordingly, when the thin electrodeposited copper foil employed in conformity with the recent trend toward fine pitch, for example, the electrodeposited copper foil having a thickness of 35 &mgr;m (1 ounce), or 17.5 &mgr;m (½ ounce), or less is chemically polished to such an extent that a desired state of surface is attained, the whole electrodeposited copper foil is thinned to such an extent that the mechanical strength of wiring pattern or lead becomes poor. Further, this chemical surface polishing poses a problem such that it is difficult to control reaction conditions for chemical polishing so as to have the matte side uniformly treated. These problems of chemical polishing also occur in the electrolytic polishing involving leaching of copper.
In this connection, Japanese Patent Application Publication (Unexamined) No. Hei 3-296238 discloses a method of producing a TAB tape having a wiring pattern formed from a non-treated copper foil. The average surface roughness of the non-treated copper foil is described as falling within the range of 0.01 to 1 &mgr;m.
However, the non-treated copper foil whose average surface roughness (Rz) falls within the range of 0.01 to 1 &mgr;m, disclosed in this publication, is a rolled copper foil. The surface roughness of this non-treated rolled copper foil is too low to ensure satisfactory peel strength (bonding strength). Accordingly, it is needed to preheat the copper foil or increase the diameter of the roller so as to form a covering thin film of cuprous oxide on the surface of the rolled copper foil. This poses a problem such that the process becomes laborious. Further, the use of this rolled copper foil renders it difficult to form a wiring pattern of extremely fine pitch such as one of from 30 &mgr;m to less than 60 &mgr;m pitch width.
Still further, Japanese Patent Unexamined Publication No. Hei 9-195096 discloses an invention directed to an electrodeposited copper foil for printed wiring board wherein the surface roughness (Rz) of the matte side of electrodeposited copper foil prior to nodulating treatment is not greater than 1.5 &mgr;m while the surface roughness (Rz) after nodulating treatment on the matte side is in the range of 1.5 to 2.0 &mgr;m. This electrodeposited copper foil is described as being producible by a method comprising buffing the matte side of an electrodeposited copper foil so as to cause the surface roughness (Rz) prior to roughening treatment to become in the range of 1.5 &mgr;m or less and subsequently effecting a roughening treatment on the matte side so as to cause the surface roughness (Rz) to become in the range of 1.5 to 2 &mgr;m.
However, the buffing of electrodeposited copper foil at a stretch as descr
Kurabe Hitoshi
Mashiko Yasuaki
Mitsuhashi Masakazu
Mitsui Mining & Smelting Co. Ltd.
Webb Ziesenheim & Logsdon Orkin & Hanson, P.C.
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