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.
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 (xcexcm). 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 xcexcm lead width has ranged from about 15 to 35 xcexcm in correspondence to the width of the wiring pattern, the thickness of metal foil employed in the formation of ten-odd micron (xcexcm) 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 xe2x80x9cshiny sidexe2x80x9d, and the surface at which copper deposition is completed is referred to as xe2x80x9cmatte sidexe2x80x9d. 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 xcexcm, 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 xcexcm. In the conventional electrodeposited copper foil of about 35 xcexcm 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 (xcexcm) 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 xcexcm pitch, of an electrodeposited copper foil whose 1-2 xcexcm 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 xcexcm. 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 xcexcm (1 ounce), or 17.5 xcexcm (xc2xd 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 xcexcm.
However, the non-treated copper foil whose average surface roughness (Rz) falls within the range of 0.01 to 1 xcexcm, 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 xcexcm to less than 60 xcexcm 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 xcexcm while the surface roughness (Rz) after nodulating treatment on the matte side is in the range of 1.5 to 2.0 xcexcm. 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 xcexcm 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 xcexcm.
However, the buffing of electrodeposited copper foil at a stretch as described in this publication may cause streaks on the buffed surface. These streaks result from polishing made deeper than predetermined. Some streaks have not posed any problem when use is made of the conventional thick electrodeposited copper foils. However, these streak portions are formed by excess polishing of copper, so that, when use is made of thin copper foils, the depth of streak portions is extremely large. Thus, these are likely to become the cause of defective occurrence, for example, high possibility of open circuit at such portions in a wiring pattern or the like. Furthermore, in the execution of such buffing, stress is exerted on protrudent parts of the copper foil surface along the direction of buff rotation, so that protrudent parts of the copper foil surface are likely to deform along the direction of buff rotation. It is difficult to effect uniform roughening treatment on the buffed copper foil having thus deformed protrudent parts. Nonuniform roughening treatment would invite problems such that the adherence to insulating films, etching uniformity, bonding reliability, etc. are deteriorated. These problems are likely to occur especially when thin electrodeposited copper foils are mechanically polished.
As apparent from the above, all the mechanical polishing, chemical polishing and electrolytic polishing methods, conventionally employed in the polishing of the matte side of the electrodeposited copper foil, have been highly useful for the polishing of electrodeposited copper foil for forming wiring patterns of 100 xcexcm or more pitch. However, the single employment of the above conventional polishing methods in the polishing of the matte side of the electrodeposited copper foil used to produce a printed wiring board whose pitch is becoming tens of microns or less involves the highly probable danger of causing the formed wiring pattern to be brittle and hence tends to render it difficult to supply printed wiring boards having reliable properties.
An object of the present invention is to provide an electrodeposited copper foil which is especially suitable for producing a printed wiring board of fine pitch and to provide a process for producing such an electrodeposited copper foil.
Another object of the present invention is to provide an electrodeposited copper foil with its matte side surface prepared, the preparing performed by a plurality of different polishing operations under extremely mild conditions in place of a single polishing operation to thereby realize a matte side surface prepared with high uniformity, and to provide a process for producing such an electrodeposited copper foil.
Further objects of the present invention are to provide a printed wiring board of stable quality produced with the use of the above electrodeposited copper foil with its surface prepared with high uniformity and to provide a multilayer laminate printed wiring board consisting of a laminate of such printed wiring boards.
The process for producing an electrodeposited copper foil with its surface prepared according to the present invention comprises the steps of:
subjecting an electrodeposited copper foil having a shiny side and a matte side whose average surface roughness (Rz) is in the range of 2.5 to 10 xcexcm to at least one mechanical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 1.5 to 3.0 xcexcm, and
subjecting the matte side having undergone the mechanical polishing to a selective chemical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 0.8 to 2.5 xcexcm.
The electrodeposited copper foil with its surface prepared according to the present invention is one having a shiny side and a prepared matte side whose average surface roughness (Rz) is in the range of 0.8 to 2.5 xcexcm, the above prepared matte side obtained through the steps of subjecting a matte side of electrodeposited copper foil whose average surface roughness (Rz) is in the range of 2.5 to 10 xcexcm to at least one mechanical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 1.5 to 3.0 xcexcm, and subjecting the matte side having undergone the mechanical polishing to a selective chemical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 0.8 to 2.5 xcexcm.
The prepared matte side surface of the electrodeposited copper foil with its surface prepared according to the present invention is preferably furnished with a roughened layer. A corrosion preventive layer is preferably disposed on the surface of the roughened layer, and a silane coupling agent layer is preferably disposed on the surface of the corrosion preventive layer.
The printed wiring board of the present invention comprises an insulating substrate having its surface furnished with a wiring pattern formed from an electrodeposited copper foil with its surface prepared, this electrodeposited copper foil with its surface prepared having a shiny side and a prepared matte side whose average surface roughness (Rz) is in the range of 0.8 to 2.5 xcexcm, the prepared matte side obtained through the steps of subjecting a matte side of electrodeposited copper foil whose average surface roughness (Rz) in the range of 2.5 to 10 xcexcm to at least one mechanical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 1.5 to 3.0 xcexcm, and subjecting the matte side having undergone the mechanical polishing to a chemical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 0.8 to 2.5 xcexcm.
The multilayer printed wiring board of the present invention comprises a laminate of a plurality of boards of given thickness, the above boards capable of being electrically connected to each other in the direction of the thickness of the laminate, each of the boards having its surface furnished with a wiring pattern formed from an electrodeposited copper foil with its surface prepared, this electrodeposited copper foil with its surface prepared having a shiny side and a prepared matte side whose average surface roughness (Rz) is in the range of 0.8 to 2.5 xcexcm, the prepared matte side obtained through the steps of subjecting a matte side of electrodeposited copper foil whose average surface roughness (Rz) is in the range of 2.5 to 10 xcexcm to at least one mechanical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 1.5 to 3.0 xcexcm, and subjecting the matte side having undergone the mechanical polishing to a chemical polishing so that the average surface roughness (Rz) of the matte side becomes in the range of 0.8 to 2.5 xcexcm.
In the present invention, it is preferable for the electrodeposited copper foil with its surface prepared that the sharp edges of the matte side have been substantially eliminated by the chemical polishing after at least one mechanical polishing.
The electrodeposited copper foil with its surface prepared, employed for forming the printed wiring board or the multilayer printed wiring board, preferably has its chemically polished matte side treated for roughening.
In the present invention, a copper-clad laminate comprises a substrate and the electrodeposited copper foil with is surface prepared which is laminated on the substrate.
There is a vast plurality of unevenness on the surface of the matte side of the electrodeposited copper foil, wherein, for example, protrudent part heights and depressed part depths are not fixed. The surface condition of the matte side is often expressed by the average surface roughness (Rz). As described later, the average surface roughness (Rz) is an average of depths of depressed parts and heights of protrudent parts constituting the surface of the matte side. Thus, on the matte side having a given average surface roughness (Rz), there is a multiplicity of protrudent parts whose roughness (Rmax) is greater than the average surface roughness (Rz). In the first step of the process for producing an electrodeposited copper foil with its surface prepared according to the present invention, mainly apex portions of the protrudent parts are mechanically removed by the mechanical polishing. Thus, the matte side is freed mainly of apex portions of the protrudent parts. In this mechanical polishing, stress is applied to portions to be polished so that, referring to, for example, FIG. 4(a), apex portions of the protrudent parts 112 are removed. Accordingly, there inevitably occurs a directionality along which mechanical polishing stress is applied. For example, referring to FIG. 4, when apex portions of the protrudent parts are polished by a rotary buff, stress is applied to the apex portions of the protrudent parts 112 in the same direction as the direction of buff rotation with the result that, as shown in FIG. 4(b), the protrudent part portion first brought into contact with the rotary buff is polished more easily than the side later brought into contact with the rotary buff. Furthermore, apex portions of the protrudent parts 112 are ground while being slightly deformed along the direction of stress application, so that polished upper portions of the protrudent parts may suffer from deformation corresponding to the stress exerted by the rotary buff or the like. For example, referring to FIG. 4(b), it has been found that the protrudent parts may be deformed along the direction of buff rotation with the result that shelf-shape deformations 111 are formed downstream in the direction of stress application.
As apparent from the above, stress is produced during the mechanical polishing, so that the mechanical polishing is inevitably accompanied by a directionality. Further, in the process of the present invention, it is intended to mainly polish and remove apex portions of the protrudent parts of the matte side by the mechanical polishing, but not to polish the whole surface of the matte side so as to render the surface specular. Rather, from the viewpoint of attaining stable bonding to the surface of an insulating substrate, it is preferred that the matte side surface be not completely smooth. Therefore, in the present invention, apex portions of the protrudent parts are mainly mechanically polished. However, referring to FIG. 4(b), this mechanical polishing forms boundary 120 between polished portion and portion not polished. When the matte side is directly subjected to the subsequent treatment for roughening, the states of being roughened may be different between the polished portion and the portion not polished.
Therefore, in the present invention, referring to FIG. 4(c), the matte side having undergone the above mechanical polishing is further chemically polished to thereby remove discontinuous polishing boundary 120 and instead create round curved surface 121. Moreover, performing the chemical polishing after the mechanical polishing can also correct the directionality of polished surface due to stress, generated during the mechanical polishing.