Metal treatment – Stock – Copper base
Reexamination Certificate
2001-03-14
2003-08-05
Ip, Sikyin (Department: 1742)
Metal treatment
Stock
Copper base
Reexamination Certificate
active
06602362
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a copper-alloy foil having high strength and high conductivity, more particularly to a copper-alloy foil which can be used for the conductors on the suspension member of a hard disc drive and can transmit signals at high speed there through.
PRIOR ART
A hard-disc drive is used in a memory device of a computer. The hard-disc drive comprises a magnetic head for reading the information recorded on a magnetic disc, and an arm member for supporting the magnetic head on the front end of such member. The arm member is made of stainless sheets and suspended at its rear end rotatably around a shaft, and is hereinafter referred to as the suspension member. The suspension member is rotated around the shaft and is displaced toward a predetermined point, when reading the information on a magnetic disc and writing the information with the magnetic head. Input and output of the signal are thus performed. Recently, a hard disc is required to have enhanced information capacity and transmission speed of signals, to miniaturize and to increase reliability. Consequently, the system including the suspension member and the magnetic head is required to increase the arrangement density of conductors, positional accuracy, electric conductivity, and the like. The tracking width of the hard-disc is at present 2 &mgr;m and the positional accuracy of a magnetic head is 0.2 &mgr;m or less at present.
Referring to
FIG. 1
, a plane view at the front end of the suspension member of a hard-disc drive is illustrated. Conventionally, wires are used for the conductors, which are aligned on the suspension member for supporting the magnetic head of a hard-disc drive. However, copper-alloy foils
1
can attain high dimensional accuracy, and the connection of conductors and the handling are easy. Furthermore, production cost is low as compared with the wires. Therefore, recent conductors, which are more frequently used than the conventional wires are the 18 &mgr;m thick copper-alloy foils
1
, bonded on the suspension member
2
via resin
3
such as polyimide.
The suspension member is produced by the following process. First, a copper foil and a substrate such as an approximately 0.020 mm thick stainless-steel sheet (SUS 304 and the like) are thermally bonded via polyimide to form a three-layer laminate structure. The laminate structure is then subjected to etching so as to remove specific portions of the copper foil, the stainless-steel substrate or the like and the polyimide. As a result, a suspension member having a predetermined shape and conductors is provided. The etching is carried out from both sides of the copper-alloy foil and the stainless-steel substrate. A two-layer laminate of the copper-foil and polyimide free of the stainless-steel substrate removed by etching, another two-layer laminate of polyimide resin and the stainless-steel substrate free of the copper-alloy foil removed by etching, and a three-layer laminate of the copper-alloy foil, the polyimide and the stainless steel substrate, are co-present in the post-etched member.
The following properties are required for the copper-alloy foil used for the conductors. First, high strength is required such that the foil does not deform or break during the production process of the laminated sheets and the assembling process of a magnetic head. The copper-alloy foil thermally expands and shrinks during the thermal bonding and laminating of the sheets in the production process of the laminate. If such thermal expansion and shrinkage do not match with the dimensional change of the polyimide and the stainless-steel sheet, copper-alloy foil deflects during the laminating process of the sheets or after the subsequent etching process. In this case, the dimensional accuracy of the suspension member of the hard-disc drive is detrimentally impaired.
It is known to use a Cu—Ni—Si alloy for the electric and electronic parts. The production process of the Cu—Ni—Si alloy to be used for the electric and electronic parts proposed in Japanese Patent No. 2,651,122 is related to a production of copper alloy, which contains from 4.1 to 10 wt % of Ni, from 1.0 to 1.5 wt % of Si, 0.2 wt % or less of Mn, and 1.0 wt % or less of Zn, the S content being 15 ppm or less, the balance being Cu and unavoidable impurities. The alloy is solution-heat treated by holding at 950 to 1000° C. for 1 minute or more, followed by cooling at a cooling speed of 10° C./second or more maintained at least in a region of from 300 to 600° C. Cold rolling is then carried out at 50% or more of the working degree. Heat treatment is carried out at a temperature of 450 to 550° C. for 1 to 30 minutes. The cold rolling is then carried out at 30-80% of working degree. The heat treatment is then carried out at 380 to 440° C. for 5 to 180 minutes. The two-stage heat treatment is carried out in this process. That is, the preceding heat treatment at 450 to 550° C. and the succeeding heat treatment at 380 to 440° C. are carried out for the following reasons. Precipitation is promoted and recrystallization is induced in the preceding heat treatment. Fine precipitates are formed so as to enhance the strength and electric conductivity in the succeeding heat treatment. The cold working is carried out before each heat treatment for the following reasons. The cold working before the first heat treatment aims to promote the recrystallization in the first heat treatment. The cold working before the second heat treatment aims to induce the work hardening and to promote the recrystallization in the second heat treatment. The properties described in Japanese Patent No. 2,651,122 are tensile strength, elongation and electric conductivity. Neither the coefficient of thermal expansion nor thermal expansion and shrinkage are described in such Japanese patent.
Problems to be Solved by Invention
The present inventors carried out researches to determine how the copper-alloy foil, the stainless-steel substrate and polyimide expand or shrink due to heat treatment. As a result, it was discovered that thermal expansion and shrinkage of the copper-alloy foil and the stainless-steel substrate are irreversible. That is, when these materials are subjected to the heating and cooling cycle, and are reverted to the initial temperature, the dimension of these materials is not reverted to those before the heating cycle. These materials may, therefore, occasionally expand and occasionally shrink, as compared with the original dimensions. As a result of further research, it was discovered that the irreversible dimensional change of the copper alloy is related to a diminishing process of the lattice defects introduced due to the rolling. That is, while the lattice defects diminish due to heating, the dimensional change occurs.
Ideally, the constituent members of the suspension member, i.e., the copper-alloy foil, the stainless-steel substrate and polyimide should have identical thermal expanding and shrinking characteristics. No deflection then occurs. Practically, the thermal expanding and shrinking characteristics of these materials are different from one another. Therefore, if the strains of these materials are balanced in the three-layer laminate structure, there is no deflection. Even if the strains of these materials are balanced under this state, when the three-layer laminate is etched, the strains become unbalanced so that a longitudinal deflection occurs. In the case of a recent suspension member of the hard disc drive, even a small deflection results in failure of the tracking performance because high dimensional accuracy is required for the recent magnetic head. Therefore, in order to attain high dimensional accuracy, the thermal expansion and shrinkage of the copper-alloy foil must be strictly controlled to match those of the stainless steel and polyimide.
In most cases, the longitudinal direction of the suspension members is set perpendicular to the rolling direction in the light of productivity. It is, therefore, occasionally unsatisfactory to control the dimensional change only in
Era Naohiko
Maki Tetsuo
Tomioka Yasuo
Ip Sikyin
Nippon Mining and Metals Co., Ltd.
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