JP2016188415A - Copper alloy foil for flexible printed circuit board, and copper cladding laminate, flexible printed circuit board and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper alloy foil for a flexible printed circuit board excellent in conductivity and flexibility even after heat treatment at a low temperature for a short time in the FPC(CCL) production step.SOLUTION: There is provided a copper alloy foil which comprises 96.30 mass% or more of Cu, one or more elements selected from the group consisting of P, Si, Al, Ge, Ga, Zn, Ni and Sb and a balance of inevitable impurities, wherein when the surface is observed with a view of 100 μm×100 μm, and the rolled parallel section is observed in the range of a 100 μm wide, in both cases, the recrystallized part has an average crystal grain diameter of 0.1 to 3.0 μm and a maximum crystal grain size of 6 μm or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper alloy foil suitable for use in a wiring member such as a flexible printed circuit board, a copper-clad laminate using the same, a flexible wiring board, and an electronic device.

A flexible printed circuit board (flexible wiring board, hereinafter referred to as “FPC”) has flexibility, and is widely used in a bent portion and a movable portion of an electronic circuit. For example, FPCs are used for movable parts of disk-related devices such as HDDs, DVDs, and CD-ROMs, and for folding parts of foldable mobile phones.
The FPC is formed by etching a copper clad laminate (copper-clad laminate, hereinafter referred to as CCL) in which a copper foil and a resin are laminated, and then coating the wiring with a resin layer called a coverlay. The copper foil surface is etched as part of the surface modification step for improving the adhesion between the copper foil and the coverlay before the coverlay is laminated. Further, in order to improve the flexibility by reducing the thickness of the copper foil, thinning etching may be performed.
In any case, a sulfuric acid-hydrogen peroxide type or an ammonium persulfate type is generally used as an etching solution.

  On the other hand, in a copper foil for bending, if there is unevenness on the surface of the copper foil, breakage occurs due to stress concentration in the recesses and the flexibility is lowered, so that surface smoothness is required. Further, if the surface roughness of the copper foil is large, the circuit formability is lowered and a fine circuit cannot be formed. In particular, in recent years, since signals in a high frequency band have been used, smoothing of the copper foil surface is required in order to suppress transmission loss.

As a copper foil for high-frequency circuits that reduces conductor loss in high-frequency applications, it consists of a granular crystal structure with an average particle size of 0.3 μm or more at a depth of 4 μm from the surface, and the surface is roughened by electrolytic etching. Is disclosed (see Patent Document 1).
In addition, as an optimal rolled copper foil for copper-clad laminates subjected to extremely fine pitch processing, oxygen-free copper contains 0.07 to 0.5% Ag by mass, O is 10 ppm or less, and S is 10 There is disclosed one having a ppm or less and a total concentration of Bi, Pb, Sb, Se, As, Fe, Te and Sn being 10 ppm or less (see Patent Document 2).

In addition, when thinning etching or the like is performed on the rolled copper foil, there is a problem that the surface roughness after etching becomes rougher than before etching. Moreover, in the copper foil in which the crystal grains are coarsened in order to improve the flexibility, a basin-shaped depression is formed after the etching due to the difference in the etching rate due to the crystal orientation.
Therefore, the present applicant adds one or more of Sn, Mg, In, and Ag to the copper foil, thereby reducing the average crystal grain size to 5 μm or less after the heat treatment in the FPC manufacturing process, and etching the copper foil A technology capable of reducing the surface roughness was developed (see Patent Document 3).

JP 2006-351677 JP 2003-96526 A Japanese Patent No. 5356714 (Claim 1)

By the way, the technique described in Patent Document 3 assumes a high-temperature and long-time treatment at 300 ° C. for 15 minutes as a heat treatment in the FPC (CCL) manufacturing process. Is stipulated.
However, in recent FPC (CCL) manufacturing processes, heat treatment at a lower temperature (about 200 ° C.) or in a shorter time (5 minutes or less) is required. It was found that it was difficult to refine the crystals with the additive elements (Sn, Mg, In and Ag). In addition to etching properties, excellent flexibility is also required.
The present invention has been made to solve the above problems, and is a copper alloy foil for a flexible printed circuit board that is excellent in conductivity and flexibility even in heat treatment at a low temperature of about 200 ° C. or in a short time of 5 minutes or less. An object of the present invention is to provide a copper clad laminate, a flexible printed circuit board, and an electronic device using the same.

  As a result of various studies, the present inventors have found that heat treatment in the FPC manufacturing process is performed at a lower temperature (about 200 ° C.) by using an additive element selected from the group of P, Si, Al, Ge, Ga, Zn, Ni, and Sb. ) And even shorter time (5 minutes or less), it was found that the crystal grains can be made finer and the flexibility can be improved. That is, by using the additive element as an element contributing to the refinement of crystal grains and adjusting the degree of cold rolling, the crystal grains can be obtained even after low-temperature or short-time heat treatment in the FPC manufacturing process. Becomes finer.

  That is, the copper alloy foil for a flexible printed circuit board according to the present invention includes 96.30% by mass or more of Cu and one or more elements selected from the group of P, Si, Al, Ge, Ga, Zn, Ni, and Sb as additive elements. Re-crystallized in both cases when the surface is observed in a 100 μm × 100 μm field of view, and when the rolled parallel cross section is observed in a range of 100 μm in width. The average crystal grain size of the part is 0.1 to 3.0 μm and the maximum crystal grain size is 6 μm or less.

  Moreover, the copper alloy foil for flexible printed circuit boards of this invention is 96.30 mass% or more of Cu, and 1 or more types of elements chosen from the group of P, Si, Al, Ge, Ga, Zn, Ni, and Sb as an additional element. Copper alloy foil containing the remaining inevitable impurities and having a surface after heat treatment of 320 ° C. or more and 10 minutes or less for a short time, or 240 ° C. or less and 20 minutes or more for a low temperature and long time 100 μm When observed in a field of × 100 μm and when the rolled parallel cross section was observed in the range of 100 μm in width, the average crystal grain size of the recrystallized part was 0.1 to 3.0 μm and the maximum crystal grain size was 6 μm or less in any case. is there.

In the copper alloy foil for a flexible printed circuit board of the present invention, P is 0.0066 to 0.0837% by mass, Si is 0.0102 to 0.1289% by mass, Al is 0.0308 to 0.3925% by mass, Ge is 0.0274 to 0.3466% by mass, and Ga is 0.0701 to 0.888% by mass. %, Zn is contained in the range of 0.2920 to 3.6940 mass%, Ni is contained in the range of 0.0670 to 0.8500 mass%, and Sb is preferably contained in the range of 0.0322 to 0.4070 mass%.
It is preferable that the average crystal grain size is 0.1 to 2.5 μm and the maximum crystal grain size is 5 μm or less.
Furthermore, it is preferable to contain Sn 0.01-0.1 mass%.

  The copper clad laminate of the present invention is formed by laminating the copper alloy foil for flexible printed circuit boards and a resin layer.

  The flexible printed board of the present invention is formed by using the copper-clad laminate and forming a circuit on the copper alloy foil.

  The electronic device of the present invention uses the flexible printed circuit board.

  According to the present invention, a copper alloy foil for a flexible printed circuit board having excellent conductivity and flexibility can be obtained even after heat treatment at a low temperature or in a short time in the FPC (CCL) manufacturing process.

It is a figure which shows a bending test method.

  Hereinafter, embodiments of the copper alloy foil according to the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

<Composition>
The copper alloy foil according to the present invention contains 96.30% by mass or more of Cu and one or more elements selected from the group of P, Si, Al, Ge, Ga, Zn, Ni, and Sb as additive elements, The balance consists of inevitable impurities.
In the technique described in Patent Document 3 described above, Sn, Mg, In, and Ag were selected as additive elements by paying attention to the fact that the crystal grains become finer as the semi-softening temperature of the copper alloy is higher. However, when the semi-softening temperature of the copper alloy increases, the recrystallization temperature also increases. Therefore, when heat treatment is performed at a low temperature of about 200 ° C. or for a short time of 5 minutes or less, recrystallization may be insufficient. Therefore, the present inventors have found the above additive element as an element that can be recrystallized even by heat treatment at a low temperature or in a short time. It has also been found that the copper alloy foil recrystallized using the above additive elements has improved flexibility.

The crystal grains become finer as the additive element is added, but the conductivity tends to decrease. For this reason, a preferable range of the content of each additive element is defined.
That is, P is 0.0066 to 0.0837% by mass, Si is 0.0102 to 0.1289% by mass, Al is 0.0308 to 0.3925% by mass, Ge is 0.0274 to 0.3466% by mass, Ga is 0.0701 to 0.8880% by mass, Zn is 0.2920 to 3.6940% by mass, Ni is preferably contained in the range of 0.0670 to 0.8500% by mass and Sb in the range of 0.0322 to 0.4070% by mass.
If the content of each additive element is less than each of the above lower limits, the effect of crystal grain refinement cannot be sufficiently obtained, and if each upper limit is exceeded, the crystal grains become finer, but the conductivity is less than 60%. May decrease. In the case of P, when the upper limit is exceeded, the recrystallization temperature rises, and the above heat treatment does not cause recrystallization.

<Recrystallized grains>
The surface of the copper alloy foil in a state where it has undergone a curing heat treatment of the resin after becoming a copper clad laminate; or a high temperature short time of 320 ° C. or more and 10 minutes or less, or a low temperature length of 240 ° C. or less and 20 minutes or more When observing the surface after heat treatment for 100 hours with a field of view of 100 μm × 100 μm, and when observing the rolled parallel section in a range of 100 μm in width, the average crystal grain size of the recrystallized part is 0.1 to 3.0 μm and The maximum crystal grain size is 6 μm or less.
As described above, the copper alloy foil according to the present invention is used for a flexible printed circuit board. In this case, the CCL in which the copper alloy foil and the resin are laminated performs a heat treatment for curing the resin at 200 to 400 ° C. The crystal grains may be coarsened by recrystallization. When the average crystal grain size of the recrystallized portion exceeds 3.0 μm, dislocation cells are formed at the time of bending, so that the flexibility is lowered.
Note that the smaller the average crystal grain size of the recrystallized portion, the better. However, it is difficult to manufacture the average crystal grain size of less than 0.1 μm. The average crystal grain size of the recrystallized part is preferably 0.1 to 2.5 μm.

Therefore, the average crystal grain size of the recrystallized part is specified to be 0.1 to 3.0 μm. The reason why the average grain size of the copper alloy foil is defined for the surface after the above heat treatment is that the resin is cured by heat treatment at a low temperature of about 200 ° C. or a short time of 5 minutes or less as described above. Therefore, this temperature condition is reproduced. The heat treatment conditions are defined for the copper alloy foil before being laminated with the resin. An example of heat treatment conditions for a short time at high temperature is 350 ° C. for 5 minutes. As an example of the heat treatment conditions for a long time at low temperature, 30 minutes at 200 ° C. can be mentioned. Further, the upper temperature limit of the heat treatment for high temperature and short time is, for example, 400 ° C., and the lower limit of the time is, for example, 1 minute. For example, the lower temperature limit for the low-temperature long-time heat treatment is 160 ° C., and the upper time limit is 60 minutes, for example.
And the copper alloy foil for flexible printed circuit boards which concerns on Claim 1 of this application has prescribed | regulated the copper alloy foil of the state which received the hardening heat processing of resin after becoming a copper clad laminated body after resin and lamination | stacking . Moreover, the copper alloy foil for flexible printed circuit boards concerning Claim 2 of this application has prescribed | regulated the state when the said heat processing is performed to the copper alloy foil before laminating | stacking with resin.
The average crystal grain size is measured by observing at least 3 fields of view on the surface of the foil in a 100 μm × 100 μm field in order to avoid errors. For observation of the foil surface, the average crystal grain size can be determined based on JIS H 0501 using a SIM (Scanning Ion Microscope) or SEM (Scanning Electron Microscope).

Further, the maximum crystal grain size of the recrystallized portion is 6 μm or less.
The reason for setting the maximum crystal grain size of the recrystallized part to 6 μm or less is that even if the average crystal grain size of the recrystallized part is 3.0 μm or less, if there are very large grains exceeding the maximum crystal grain size of 6 μm, This is because sometimes dislocation cells are formed and flexibility is lowered. The maximum crystal grain size of the recrystallized portion is preferably 5 μm or less.

The average crystal grain size is measured using the cutting method defined in JIS H0501. The maximum crystal grain size is measured by analyzing the SIM image using image analysis software (for example, LUZEX-F manufactured by Niraco). Since image analysis software used at this time is general, there is no problem even if any software is used.
Further, observing a rolled parallel section in a range of 100 μm in width means observing a section in the thickness direction at a length of 100 μm along the rolling direction.

In addition, even if it adds the said additional element, it may not refine | miniaturize, if the workability at the time of cold rolling is not controlled. In particular, as the degree of processing in final cold rolling (finish rolling performed after the last annealing in the entire process of annealing and rolling), η = ln (plate thickness after final cold rolling / before final cold rolling) Plate thickness) = 3.5 to 7.5.
When η is less than 3.5, the accumulation of strain during processing is small and the nuclei of the recrystallized grains are reduced, so that the recrystallized grains tend to be coarse. When η is greater than 7.5, excessive strain is accumulated to serve as a driving force for crystal grain growth, and the crystal grains tend to be coarse. More preferably, η = 5.5 to 7.5.

  The copper alloy foil of the present invention can be produced, for example, as follows. First, after adding the said additive to a copper ingot and melt | dissolving and casting, it hot-rolls, performs cold rolling and annealing, and can manufacture foil by performing the above-mentioned final cold rolling.

<Copper-clad laminate and flexible printed circuit board>
Also, (1) a resin precursor (for example, a polyimide precursor called varnish) is cast and polymerized by applying heat to the copper alloy foil of the present invention, and (2) the same kind of thermoplastic adhesive as the base film is used. By laminating the base film on the copper alloy foil of the present invention, a copper clad laminate (CCL) comprising two layers of the copper alloy foil and the resin base material is obtained. Further, by laminating a base film obtained by applying an adhesive to the copper alloy foil of the present invention, a copper clad laminate (CCL) composed of three layers of a copper alloy foil, a resin base material, and an adhesive layer therebetween can be obtained. . During the production of these CCLs, the copper alloy foil is heat-treated and recrystallized.
A circuit is formed on these using a photolithographic technique, a circuit is plated as needed, and a cover-lay film is laminated, and a flexible printed circuit board (flexible wiring board) is obtained.

Therefore, the copper clad laminate of the present invention is formed by laminating a copper foil and a resin layer. Moreover, the flexible printed circuit board of this invention forms a circuit in the copper foil of a copper clad laminated body.
Examples of the resin layer include, but are not limited to, PET (polyethylene terephthalate), PI (polyimide), LCP (liquid crystal polymer), and PEN (polyethylene naphthalate). Moreover, you may use these resin films as a resin layer.
As a method of laminating the resin layer and the copper foil, a material for forming the resin layer may be applied to the surface of the copper foil and heated to form a film. Further, a resin film may be used as the resin layer, and the following adhesive may be used between the resin film and the copper foil, or the resin film may be thermocompression bonded to the copper foil without using the adhesive. However, it is preferable to use an adhesive from the viewpoint of not applying excessive heat to the resin film.
When a film is used as the resin layer, this film may be laminated on the copper foil via an adhesive layer. In this case, it is preferable to use an adhesive having the same component as the film. For example, when a polyimide film is used as the resin layer, it is preferable to use a polyimide-based adhesive for the adhesive layer. In addition, the polyimide adhesive here refers to the adhesive agent containing an imide bond, and polyether imide etc. are also included.

In addition, this invention is not limited to the said embodiment. Moreover, as long as there exists an effect of this invention, the copper alloy in the said embodiment may contain another component.
For example, the surface of the copper foil may be subjected to a surface treatment by roughening treatment, rust prevention treatment, heat resistance treatment, or a combination thereof.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.
The elements shown in Table 1 were added to electrolytic copper with a purity of 99.96% or more, respectively, and cast in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. This ingot is homogenized and annealed at 900 ° C., hot-rolled to a thickness of 60 mm, then the surface is chamfered, cold rolling and annealing are repeated, and the final cold is applied at a working degree η shown in Table 1. Rolling was performed to obtain a foil having a final thickness of 33 μm. The obtained foil was subjected to heat treatment at 200 ° C. for 30 minutes or 300 ° C. for 5 minutes to obtain a copper foil sample.

<Evaluation>
1. Conductivity For each copper foil sample, the conductivity (% IACS) at 25 ° C. was measured by the 4-terminal method based on JIS H 0505.
2. Particle size The surface of each copper foil sample was observed using a SIM (Scanning Ion Microscope), and the average particle size was determined based on JIS H 0501. The maximum particle size and area ratio of the surface were calculated by analyzing the SIM image with image analysis software (LUZEX-F manufactured by Niraco). The measurement area was 100 μm × 100 μm on the surface. Also, FIB (focused ion beam) was used, the copper foil sample was cut and processed in parallel with rolling, and the cross section was observed using SIM (Scanning Ion Microscope). Based on this, the average particle size was determined. The maximum particle size and area ratio of the cross section were calculated by analyzing the SIM image with image analysis software (LUZEX-F manufactured by Niraco). The measurement area was 100 μm long along the rolling direction.
3. Presence / absence of recrystallization The copper foil sample (copper foil after heat treatment) has a tensile strength of 50% or less of the copper foil after the final cold rolling (copper foil before heat treatment) and the elongation percentage of the copper foil sample is the final cold. The case of 1.7 times or more of the copper foil after hot rolling was judged to be recrystallized after the heat treatment. The other cases were considered “unrecrystallized”. Tensile strength and elongation were measured at 25 ° C. based on JIS C 6515.

4). Flexibility Copper roughening plating is performed on one side of a 33μm-thick copper foil (copper foil before heat treatment) after final cold rolling, a polyimide film (thickness 27μm) and a foil are laminated, and then bonded with a hot press (4MPa) In combination, a CCL sample was obtained. In addition, the heat processing at 200 degreeC * 30 minutes or 300 degreeC * 5 minutes was added at the time of lamination | stacking of a film. Therefore, “300 ° C. × 5 minutes” in Table 2 is a heat treatment with a copper foil alone or a heat treatment during CCL lamination in each copper foil sample. A predetermined circuit having a line width of 300 μm was formed on the copper foil portion of the CCL sample to obtain an FPC. The bending fatigue life was measured by an IPC (American Printed Circuit Industry Association) bending test apparatus shown in FIG. This apparatus has a structure in which a vibration transmission member 3 is coupled to an oscillation driver 4. The FPC 1 is fixed to the apparatus at a total of four points, that is, a screw 2 portion indicated by an arrow and a tip portion of the vibration transmission member 3. The When the vibration transmitting member 3 is driven up and down, the intermediate portion of the FPC 1 is bent into a hairpin shape with a predetermined curvature radius r. In this test, the number of times until breakage when bending was repeated under the following conditions was determined.
The test conditions are as follows: Specimen width: 12.7 mm, Specimen length: 200 mm, Specimen sampling direction: Collected so that the length direction of the specimen is parallel to the rolling direction, curvature radius r : 2 mm, vibration stroke: 20 mm, vibration speed: 1500 times / minute, bending fatigue life: at a time when the initial electric resistance value is higher than 10%.
In addition, when the bending fatigue life was 100,000 times or more, it was considered that the film had excellent flexibility, and when the bending fatigue life was less than 100,000 times, the bending property was evaluated as inferior.

  The obtained results are shown in Tables 1 and 2.

  As is apparent from Tables 1 and 2, it contains one or more elements selected from the group consisting of P, Si, Al, Ge, Ga, Zn, Ni, and Sb, and at 350 ° C. for 5 minutes or 200 ° C. In each example in which the average crystal grain size of the recrystallized portion of the surface after 30 minutes of heat treatment is 3 μm or less and the maximum crystal grain size is 6 μm or less, the conductivity is 60% or more and excellent flexibility It was.

On the other hand, in Comparative Examples 1 and 2 in which Mg or Sn was added as an additive element, recrystallization did not occur in heat treatment at 350 ° C. for 5 minutes or 200 ° C. for 30 minutes, and the flexibility was poor. This is presumably because coarse crystal grains before rolling remained because recrystallization did not occur and dislocation cells were formed during bending.
In the case of Comparative Example 3 made of pure copper containing no additive element and in the case of Comparative Example 6 in which the content of P as an additive element is less than the lower limit, the suppression of coarsening during recrystallization by the additive element is not sufficient. The average crystal grain size of the recrystallized portion of the surface exceeded 3.0 μm, and the maximum crystal grain size exceeded 6 μm. As a result, the flexibility was poor.
In the case of Comparative Example 4 in which the workability η in the final cold rolling exceeded 7.5, the average crystal grain size of the recrystallized portion on the surface exceeded 3.0 μm, and the maximum crystal grain size exceeded 6 μm. As a result, the flexibility was poor. This is presumably because the crystal grains became coarse due to strong processing and dislocation cells were formed during bending.
In Comparative Examples 5 and 8 in which the degree of work η in the final cold rolling was less than 3.5, the maximum crystal grain size of the recrystallized portion on the surface exceeded 6 μm, and the flexibility was poor. This is presumably because coarse crystal grains before rolling remained due to the low degree of processing, and dislocation cells were formed during bending.

In the case of Comparative Example 7 in which the Ge content exceeded the preferable upper limit (0.3466% by mass), the flexibility was excellent, but the conductivity decreased to less than 60%.
In the case of Comparative Example 9 in which the P content exceeded the preferable upper limit (0.0837% by mass), it was not recrystallized by heat treatment at 350 ° C. for 5 minutes or 200 ° C. for 30 minutes, and the conductivity was reduced to less than 60%. Declined. Since Comparative Example 9 was not recrystallized, the flexibility was not evaluated.

Claims (8)

A copper alloy foil containing at least 96.30% by mass of Cu and one or more elements selected from the group of P, Si, Al, Ge, Ga, Zn, Ni and Sb as additive elements, and the balance being inevitable impurities There,
When observing the surface with a field of view of 100 μm × 100 μm, and when observing the rolled parallel cross section in the range of 100 μm in width, the average crystal grain size of the recrystallized part is 0.1 to 3.0 μm and the maximum crystal grain size is Copper alloy foil for flexible printed circuit boards that is 6μm or less. A copper alloy foil containing at least 96.30% by mass of Cu and one or more elements selected from the group of P, Si, Al, Ge, Ga, Zn, Ni and Sb as additive elements, and the balance being inevitable impurities There,
When the surface after heat treatment at 320 ° C or more and 10 minutes or less for a short time, or 240 ° C or less and a low temperature and long time of 20 minutes or more is observed in a 100 μm × 100 μm field of view, and the rolling parallel section is 100 μm in width The copper alloy foil for flexible printed circuit boards in which the average crystal grain size of the recrystallized part is 0.1 to 3.0 μm and the maximum crystal grain size is 6 μm or less in any case.   0.0066-0.0837 mass% for P, 0.0102-0.1289 mass% for Si, 0.0308-0.3925 mass% for Al, 0.0274-0.3466 mass% for Ge, 0.0701-0.888 mass% for Ga, 0.2920-3.6940 mass% for Zn, Ni The copper alloy foil for flexible printed circuit boards according to claim 1 or 2, comprising 0.0670 to 0.8500 mass% and Sb in the range of 0.0322 to 0.4070 mass%.   The copper alloy foil for flexible printed circuit boards according to any one of claims 1 to 3, wherein the average crystal grain size is 0.1 to 2.5 µm and the maximum crystal grain size is 5 µm or less. Furthermore, the copper alloy foil for flexible printed circuit boards as described in any one of Claims 1-4 which contains 0.01-0.1 mass% of Sn.   The copper clad laminated body formed by laminating | stacking the copper alloy foil for flexible printed circuit boards as described in any one of Claims 1-5, and a resin layer.   The flexible printed circuit board formed by forming a circuit in the said copper alloy foil using the copper clad laminated body of Claim 6.   An electronic apparatus using the flexible printed circuit board according to claim 7.