JP2009194163A - Copper foil for circuit board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a copper foil for a circuit board which has outstanding bending characteristics. <P>SOLUTION: A coat 3 is formed on a surface of a rolled copper foil 2 with metals or an alloy thereof, thereby phenomenon from the formation of an adherence slip band to a first stage crack is relaxed, and thereby the copper foil for a circuit board improved in bending characteristics or having high bending lifetime in another word used for a flexible printed-wiring board or the like is provided. For example, in a metal like Fe which includes a body-centered cubic structure, when a cyclic load is added, two or more slip systems work, moreover intersection slide also tends to occur. Therefore, the coat 3 of a material like Fe is formed on a surface of the rolled copper foil 2, the load is distributed into two or more slip systems, the concentration of a local slip band to the rolled copper foil 2 is relaxed, the formation of the first stage crack is made to hardly arise in the copper foil and coat 3, thereby the bending lifetime of rolled copper foil (a copper foil for a circuit board) can be prolonged. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a copper foil for a circuit board, and more particularly to a copper foil for a circuit board that is used in a flexible printed circuit board (FPC) and the like and has excellent bending characteristics.

  A material for a flexible printed circuit board (hereinafter referred to as FPC) is formed by cladding a copper foil and an insulating resin film such as polyimide. The cladding method includes a method of laminating via an epoxy adhesive or the like, a method of directly thermocompression bonding, a method of applying a polyimide varnish to a copper foil, and the like. The FPC is manufactured as a wiring material by forming a fine circuit on a copper foil of a clad substrate by etching.

  The FPC is mainly used for a movable part such as a printer head or a hinge part of a mobile phone, and therefore, it is required to have excellent flexibility. From this point, as the copper foil, a rolled copper foil that is more flexible than the electrolytic copper foil is mainly used.

  The recrystallized material is superior in the flexibility of the rolled copper foil to the hard material after rolling. However, in the process in which the rolled copper foil and the resin film are clad, it is more convenient and convenient for the rolled copper foil to be a hard material. Therefore, the rolled copper foil is designed to be recrystallized in the final heat treatment to be clad. From this, for FPC, such as tough pitch copper and oxygen-free copper so as to soften at 120 ° C to 250 ° C. Pure copper rolled copper foil is used.

Further, it has been found that the flexural properties of the recrystallized material show better properties as the cubic texture formed in the material develops. Therefore, in the manufacturing process of the rolled copper foil, a device for making the cold rolling work degree after the final annealing as high as possible is made, and cold rolling is usually performed at a work degree of 90% or more. Here, the rolling degree, the plate thickness before rolling t _0, when the plate thickness after rolling was t, is a number expressed as a percentage of _{(t 0 -t) / t 0} .

  Thus, as a conventional technique, there is known a method for producing a rolled copper foil in which a cubic texture is developed by increasing the degree of final cold rolling (for example, 90% or more) (for example, see Patent Document 1).

The method for producing this rolled copper foil consists of hot rolling a tough pitch copper or oxygen-free copper ingot, then repeating cold rolling and annealing, and finally finishing the thickness to 0.050 mm or less by cold rolling. Specifically, (1) cold rolling with a workability of 90% or more, (2) recrystallization annealing at a furnace temperature of 150 ° C. to 250 ° C. for 1 to 10 hours, or 500 ° C. to 800 ° C. By performing recrystallization annealing in the order of 5 to 60 seconds at a furnace temperature of (3) cold rolling at a workability of 5 to 40%, a cube assembly structure is formed in the rolled copper foil. Since it develops, it is possible to produce a rolled copper foil having excellent bending characteristics.
JP 2001-262296 A

  However, according to the conventional rolled copper foil manufacturing method, the higher the final cold rolling degree, the more difficult it is to roll by work hardening, and the closer to the final thickness, the lower the rolling reduction per pass. (Processing degree) is reduced, and the number of rolling passes is increased correspondingly, so that there is a problem that manufacturing efficiency is lowered.

  In recent years, with the progress of downsizing, high integration (high density mounting), high performance, and the like of electronic devices, FPCs have been increasingly demanded for higher bending characteristics than before. Since the bending characteristics of the FPC are substantially determined by the rolled copper foil, it is essential to further improve the bending characteristics of the rolled copper foil in order to satisfy the requirements.

  Accordingly, an object of the present invention is to provide a copper foil for circuit boards having high production efficiency and excellent bending characteristics.

[1] In order to achieve the above object, the present invention provides a copper foil for circuit boards, characterized in that a film made of a metal having a body-centered cubic structure is formed on the surface of the rolled copper foil.

[2] In order to achieve the above object, the present invention provides the copper foil for a circuit board according to [1], wherein the coating is made of Mo, Fe, or an alloy thereof.

[3] The present invention provides the copper foil for a circuit board according to [1] or [2], wherein the film has a thickness of 50 nm to 500 nm in order to achieve the above object. .

  According to the above-described configuration, the manufacturing efficiency is high and excellent bending characteristics can be obtained.

  According to such a configuration, manufacturing efficiency is high and excellent bending characteristics can be obtained.

  Embodiments of a copper foil for circuit boards according to the present invention will be described below in detail with reference to the drawings.

[Embodiment]
First, a mechanism for improving the bending characteristics of a rolled copper foil (a copper foil for a circuit board) used for manufacturing an FPC according to an embodiment of the present invention will be described. When stress is applied to the metal crystal, dislocations easily move along the slip plane of the crystal, but the crystal grain boundary is generally an obstacle to the movement of dislocations. In a rolled copper foil that is a polycrystalline body, when dislocations accumulate at a grain boundary or the like due to a bending motion, cracks are likely to occur at the accumulation location, and so-called metal fatigue is considered to occur. In other words, if the dislocations can be prevented from accumulating in the polycrystalline body, it is expected that the bending property is improved. In other words, in the conventional rolled copper foil, as described above, in the manufacturing process, the final cold working degree is increased to develop the cubic structure after recrystallization, and the sliding surface peculiar to the face-centered cubic structure of the copper crystal. Bending characteristics have been improved by controlling the arrangement of certain {111} planes to make it difficult for dislocations to accumulate at grain boundaries.

  However, even with a rolled copper foil that has been considered in this way, when a repeated load is applied, slip concentrates on the {111} plane, forming a slip band that persists from the occurrence of the slip band, and causing an initial crack on the rolled copper foil surface. It is generated and gradually progresses to a large crack.

  Therefore, in this embodiment, by forming a film with a metal or an alloy thereof, which will be described later, on the surface of the rolled copper foil, the bending property is improved by relaxing the phenomenon from the formation of the sticking slip band to the initial crack. In other words, the present invention provides a rolled copper foil having a high bending life. As a result of intensive studies by the present inventors on this point, it is clear that the bending property is improved by forming a metal film having a body-centered cubic structure on the surface of the rolled copper foil, and in particular, the bending life is extended. became. The reason can be considered as follows, for example.

  A metal such as Fe (αFe; ferrite) having a body-centered cubic structure, when a repeated load is applied, has a plurality of slip systems, and cross slip easily occurs. Therefore, by forming a coating of a material such as Fe on the surface of Cu (rolled copper foil), the load is dispersed in a plurality of slip systems, so the concentration of local slip bands on Cu is alleviated and initial cracks are reduced. Is difficult to form on Cu and Fe.

  Therefore, Cr, Nb, Ta, W, Mo, Fe, or an alloy thereof having a body-centered cubic structure is suitable as the metal to be coated. Of these, Mo and Fe are preferable. If the thickness is too thick, flexibility is lost due to the hardness of the formed film, which becomes an obstacle when etching is performed in the FPC manufacturing process. Moreover, since an effect cannot be expected if it is too thin, at least about 50 nm is the limit.

(FPC1 manufacturing process)
FIG. 1A to FIG. 1D are diagrams showing manufacturing steps of an FPC according to an embodiment of the present invention.
(1) First, as shown to Fig.1 (a), cold rolling and annealing are repeated as a base material of the copper foil for circuit boards, and the rolled copper foil 2 is produced.
(2) As shown in FIG. 1 (b), a metal such as Fe having the above-described body-centered cubic structure is coated on the rolled copper foil 2 using a method such as electroplating or ion plating, A coating 3 is formed.
(3) As shown in FIG. 1C, a method of laminating the copper foil on which the coating 3 is formed and the insulating resin film 4 via an epoxy adhesive or directly thermocompression bonding. Or, clad using a method of applying a polyimide varnish to a copper foil.
(4) As shown in FIG.1 (d), it etches with respect to the copper foil in which the film 3 was formed based on the predetermined | prescribed fine circuit, and FPC1 is manufactured.

  Hereinafter, the present invention will be described in more detail based on examples.

  After melting a tough pitch copper ingot for the copper foil for circuit boards, a material having a thickness of 12 mm was obtained by hot rolling. Next, this material was subjected to cold rolling and annealing to obtain a dough material having a thickness of 0.1 mm before final rolling. This was subjected to final annealing and cold rolling to produce a rolled copper foil having a thickness of 0.016 mm.

  The rolled copper foil was subjected to the film forming treatment according to the present invention, and samples shown in Table 1 were produced. The conditions for each film formation treatment are as follows.

<Fe-Ni coating>
Fe-Ni is prepared by building a plating solution of 300 g / L of ferrous chloride, 50 g / L of nickel chloride and 150 g / L of calcium chloride, and electroplating at pH 3.0, bath temperature 60 ° C., current density 2 A / dm 2. A film was formed. The coating composition (Mol%) is Fe (95) and Ni (5), and the thickness of the coating is 400 nm on one side.

<Fe-Mo coating>
Fe-Mo coating was formed by a general ion plating method. The coating composition (Mol%) is Fe (70) and Mo (30), and the thickness of the coating is 400 nm on one side.

<Mo coating>
Mo film formation was performed by the general method of ion plating. The coating composition (Mol%) is Mo (100), and the thickness of the coating is 400 nm on one side.

<Fe-Ni coating>
An Fe—Ni coating was formed based on the same method as in Example 1. The coating composition is the same as in Example 1, but the film thickness is 60 nm on one side.

(Comparative Example 1)
<Fe-Ni coating>
An Fe—Ni coating was formed based on the same method as in Example 1. The coating composition is the same as in Example 1, but the film thickness is 30 nm on one side.

(Comparative Example 2)
An Fe—Ni coating was formed based on the same method as in Example 1. The coating composition is the same as in Example 1, but the film thickness is 700 nm on one side.

(Comparative Example 3)
Comparative Example 3 represents a case where no film is formed on the rolled copper foil.

  Next, the evaluation of the bending characteristics of these test materials was carried out by heating each test material at 180 ° C. for 60 minutes to recrystallize the rolled copper foil, and then measuring each of the widths of 12.5 mm and 200 mm. A sample was taken and measured. The measurement was carried out by the same method as the FPC bending resistance test defined by the IPC standard (TM-650-2.4.2.1), and the radius of curvature was 2.5 mm with the coating-formed surface of the specimen facing outside. The number of bendings at the time of sample breakage when the stroke was set to 10 mm and the bending speed was set to 1500 times / minute was defined as the bending life. Moreover, the average shown in Table 2 represents that the bending life was averaged by the number (n = 10) of the measured specimens of the same type.

  According to the measurement results of the bending life shown in Table 2, it can be seen that Examples 1 to 4 subjected to the film formation treatment have a significantly increased bending life compared to Comparative Example 3 where the film formation treatment was not performed. .

  Comparative Example 1 has the same coating composition as Example 1, but the film thickness is 30 nm, which is thinner than Example 1. From this result, it can be seen that the bending life cannot be extended when the film thickness is thin. Moreover, since the film of Comparative Example 2 is as thick as 700 nm, the flexibility is lowered, and the flexibility that is equal to or higher than that of Examples 1-4 cannot be exhibited.

(effect)
According to the above-described embodiment, the bending characteristics of the rolled copper foil are greatly improved. Moreover, when it is going to acquire the bending characteristic comparable as the conventional rolled copper foil, in the manufacturing process of a rolled copper foil, the final rolling work degree can be restrained low. Therefore, an increase in the number of rolling passes can be avoided, and the production efficiency can be greatly improved.

(Modification)
The copper foil for circuit boards is laminated with a polyimide film or the like. Therefore, various treatments such as roughening treatment and corrosion resistance treatment are performed to improve the adhesion. Also in the rolled copper foil in this Embodiment mentioned above, such a various process can be performed after performing a film formation process to the rolled copper foil surface.

  The present invention is not limited to the above-described embodiments and modifications, and various modifications can be made without departing from or changing the technical idea of the present invention.

(A)-(d) is a figure which shows the manufacturing process of FPC which concerns on embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... FPC, 2 ... Rolled copper foil, 3 ... Coating, 4 ... Insulating resin film

Claims (3)

  A copper foil for circuit boards, wherein a film made of a metal having a body-centered cubic structure is formed on the surface of the rolled copper foil.   The copper foil for circuit boards according to claim 1, wherein the coating is made of Mo, Fe, or an alloy thereof. The copper foil for circuit boards according to claim 1 or 2, wherein the film has a thickness of 50 nm or more and 500 nm or less.

Images