JP5055088B2 - Copper foil and flexible printed circuit board using the same - Google Patents

Description

  The present invention relates to a rolled copper foil suitable for use in a wiring member such as a flexible printed circuit board and a flexible printed circuit board using the rolled copper foil.

A flexible printed circuit board (hereinafter referred to as “FPC”) has flexibility, and is therefore widely used for bent portions and movable portions of electronic circuits. 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.
FPC is generally manufactured by laminating and heating a copper foil to be a circuit on a base film, and as copper foil, rolled copper foil of tough pitch copper or oxygen-free copper having superior flexibility than electrolytic copper foil is used. The In order to improve flexibility, the rolled copper foil is used for FPC in an annealed state.

In particular, the thinning of mobile phones and the like has progressed, and the bending radius of the FPC used for the movable part tends to be reduced accordingly, and higher flexibility is required. Therefore, the ratio of crystal grains penetrating in the thickness direction of the copper foil annealed after final rolling was increased (the crystal grain size was increased), and the deformation due to bending was changed to single crystal deformation to improve flexibility. A rolled copper foil has been reported (see Patent Document 1).
Also, after recrystallization annealing after the final cold rolling, the integral strength (I (200)) of 200 planes obtained by X-ray diffraction on the rolled surface is the integral of 200 planes obtained by X-ray diffraction of fine powder copper. A rolled copper foil in which I (200) / I ₀ (200) ≧ 40 with respect to the strength (I ₀ (200)) and a cubic texture is remarkably developed has been reported (see Patent Document 2).

JP 2006-117977 A JP 2001-323354 A

However, the techniques described in Patent Documents 1 and 2 have a problem that the strength is low and the film is too soft in order to improve the bending characteristics. For example, in the case of the technique described in Patent Document 2, the ratio of the (111) plane that contributes to the strength is extremely small.
On the other hand, the material strengthening method includes addition of a solid solution element and work hardening by strong processing. However, the former is limited to be applied to a copper foil for FPC because the conductivity decreases due to the addition of the solid solution element. There is. In addition, when work hardening is performed, the strength increases as the degree of processing increases. However, when heat treatment is performed by laminating a copper foil for FPC with a film, it is annealed to form coarse recrystallized grains. May decrease.
That is, the present invention has been made to solve the above-described problems, and aims to provide a copper foil having high strength while being excellent in heat resistance, conductivity, and flexibility, and a flexible printed board using the copper foil. To do.

  As a result of various investigations, the present inventors have obtained a copper foil that has no anisotropy and hardly generates coarse crystal grains by controlling the heat treatment during FPC processing so that the recrystallization texture does not develop and is not completely recrystallized. It was found that the strength and flexibility can be improved by managing the ratio of (tensile strength / Young's modulus) within a certain range. This copper foil is unlikely to be reduced in strength by heat treatment during FPC processing, the structure appropriately includes the (100) orientation and the (111) orientation, and the Young's modulus is a size reflecting the proportion of these orientations. Therefore, the Young's modulus is smaller than that of the rolled up material having the (111) orientation, that is, the ratio of (tensile strength / Young's modulus) can be higher than that of the conventional copper foil, so that the flexibility is excellent.

That is, the copper foil of the present invention satisfies 4.5 × 10 ⁻³ ≧ (tensile strength / Young's modulus) ≧ 3 × 10 ⁻³ after heat treatment at 300 ° C. for 30 minutes, and has a tensile strength of 250 MPa or more and an electrical conductivity. 80% IACS or more der is, selected Ti, or includes a total 1000~3000ppm one or more elements selected from the group consisting of Zr and Mg, or Ti, Zr, Mg, Cr, Sn, from the group of in and Ag It is characterized by containing a total of 1000 to 3000 ppm of two or more elements .

Moreover, the copper foil of the present invention satisfies 4.5 × 10 ⁻³ ≧ (tensile strength / Young's modulus) ≧ 3 × 10 ⁻³ after heat treatment at 300 ° C. for 30 minutes, and has a Young's modulus of 90 to 130 GPa and conductivity. selected Ri der but 80% IACS or more, Ti, or includes a total 1000~3000ppm one or more elements selected from the group consisting of Zr and Mg, or Ti, Zr, Mg, Cr, Sn, from the group of in and Ag It is characterized by containing a total of 1000 to 3000 ppm of two or more elements .

Further, the copper foil of the present invention, after heat treatment at 300 ° C. for 30 minutes, the ratio of the integrated intensity I (200) of (200) orientation and the integrated intensity I (111) of (111) orientation by X-ray diffraction is 15 ≧ I (200) / I ( 111) ≧ 1.5 der Rukoto are preferred.

It is preferable that the final rolling degree is 80 to 96%, and the crystal grain size immediately before the final rolling is 5 to 10 μm.
The copper foil not subjected to the heat treatment preferably has a semi-softening temperature of 300 ° C. or higher when the annealing time is 30 minutes .

  The flexible printed circuit board of the present invention uses the copper foil.

  According to the present invention, it is possible to obtain a copper foil having high strength while being excellent in heat resistance, conductivity and flexibility.

Hereinafter, the copper foil which concerns on embodiment of this invention is demonstrated. In the present invention, “%” means “% by mass” unless otherwise specified.
Moreover, since the copper foil which concerns on embodiment of this invention is requested | required of electroconductivity, such as FPC, electrical conductivity is 80% IACS or more. The copper foil of the present invention includes a copper alloy foil.

[Σ / E (tensile strength / Young's modulus) ratio]
The copper foil according to the embodiment of the present invention satisfies 4.5 × 10 ⁻³ ≧ (tensile strength / Young's modulus) ≧ 3 × 10 ⁻³ .
Conventionally, the relationship between the bending life of a material and the magnitude of strain applied to the surface of the material is known as Baskin's equation (Equation 1).
log (2N) ∝ {c− (1 / b) log (σ / E)} + (1 / b) · log (Δε _T / 2) (1)
N: Bending life, b: Negative constant specific to material, σ: Breaking strength, E: Young's modulus, Δε _T : Strain magnitude From Equation 1, the larger σ / E (tensile strength / Young's modulus), the greater the strain The bending life with respect to is increased, and the flexibility is improved. In order to increase σ / E, the strength may be increased or the Young's modulus may be decreased.

To lower the Young's modulus, it is better to develop a recrystallized texture. However, if annealing is performed to develop a recrystallized texture, annealing softening occurs, the strength decreases, and σ / E does not increase.
Therefore, by controlling the heat treatment during FPC processing so that the recrystallized texture does not develop and is not completely recrystallized, a copper foil that has no anisotropy and is difficult to produce coarse crystal grains can be obtained (tensile strength / Young's modulus). ) Ratio can be managed within a certain range to improve strength and flexibility. This copper foil is unlikely to be reduced in strength by heat treatment during FPC processing, the structure appropriately includes the (100) orientation and the (111) orientation, and the Young's modulus is a size reflecting the proportion of these orientations. Therefore, the Young's modulus is smaller than that of the rolled up material having the (111) orientation, that is, the ratio of (tensile strength / Young's modulus) can be higher than that of the conventional copper foil, so that the flexibility is excellent.

In order to suppress the development of the recrystallized texture, it is preferable that the degree of rolling work is not increased so much that the crystal grain size before rolling is not too small. This is because the higher the degree of rolling and the smaller the grain size before rolling, the easier the recrystallized texture develops.
As a preferable range of the rolling degree and the crystal grain size before rolling, the final rolling degree is 80 to 96%, and the crystal grain size immediately before the final rolling is 5 to 10 μm.

When σ / E <3 × 10 ⁻³ , the strength is lowered, and particularly the strength is significantly lowered by heat treatment during FPC processing. On the other hand, the higher σ / E, the better, but the upper limit is 4.5 × 10 ^-3 for heat treatment during FPC processing (30 minutes at 300 ° C). To obtain a higher σ / E, the heat treatment temperature is 300 ° C. The FPC cannot be manufactured.

[Young's modulus]
The lower the Young's modulus, the larger the σ / E can be. However, if the Young's modulus is less than 90 GPa, the foil becomes too soft and loses its waist, and the deformation of the FPC (foil) follows the sliding radius during bending. In some cases, hip breaks may occur. When the hip break occurs, the deformation load concentrates on the hip break and breaks. On the other hand, the maximum Young's modulus of copper foil is about 130 Gpa.
From the above, the copper foil according to one embodiment of the present invention is defined to have a Young's modulus of 90 to 130 Gpa.

[Crystal orientation]
The Young's modulus has a correlation with the crystal orientation. In the face-centered cubic lattice containing copper, the Young's modulus is the lowest in the (100) direction, and the Young's modulus in other orientations is higher than the Young's modulus in the (100) direction. Therefore, the Young's modulus in the rolling parallel direction can be lowered by developing the recrystallized texture so that the (100) orientation is aligned in the rolling direction. The degree of assembly in the (100) direction is the ratio of the integrated intensity I (200) in the (200) direction by X-ray diffraction and the integrated intensity I (111) in the (111) direction, I (200) / I ( It can be evaluated by the value of 111).
If I (200) / I (111) <1.5, the (100) orientation that reduces the Young's modulus decreases, and σ / E decreases, and the flexibility may not be improved. On the other hand, if I (200) / I (111)> 15, the Young's modulus is lowered, but the strength is greatly lowered, and the foil becomes too soft and the waist is lost and the waist may be broken.
From the above, the copper foil according to one embodiment of the present invention is defined in the range of 15 ≧ I (200) / I (111) ≧ 1.5.

[composition]
In general, since the heat treatment temperature in the process of processing copper foil into FPC is about 250 to 350 ° C. (in the case of a two-layer material of foil and film), pure copper containing no additive element is completely recrystallized. . Therefore, in order to suppress recrystallization at the time of processing, the copper foil according to the embodiment of the present invention contains an element within a range where the electrical conductivity does not decrease.
The rolled copper foil according to the embodiment of the present invention contains one or more elements selected from the group consisting of Ti, Zr and Mg in total of 1000 to 3000 ppm, or Ti, Zr, Mg, Cr, Sn, In and Ag. It is preferable to contain a total of 1000 to 3000 ppm of one or more elements selected from the group.
The above elements are effective elements for improving heat resistance. This is because the element that improves the heat resistance can suppress the coarsening of crystal grains due to recrystallization of the copper foil in the FPC processing step. However, if the additive element is contained in a large amount, the electrical conductivity is lowered, which is not preferable as a copper foil for FPC.

Therefore, an element that has little influence on conductivity and is effective in improving heat resistance even in a small amount is selected.
Fig. 1 shows that Cu, Sn, Mg, Ag, In, Fe, Cr, Zn, Ti, Be, Cd, and Zr, which are often used as additive elements for copper foil, are added to copper with a purity of 99.96% or more respectively. The semi-softening temperature is shown when the ingot obtained is melted and hot rolled to a thickness of 10 mm, and then cold rolling and annealing are repeated to a thickness of 0.1 mm.
The semi-softening temperature is the Vickers hardness before annealing when the sample is annealed and the Vickers hardness is measured, and when fully softened (even if the annealing temperature is further increased after 30-minute annealing, the strength (Vickers hardness ) Shows an annealing temperature indicating intermediate Vickers hardness when it is considered that the state in which no change occurs) is completely softened.

  FIG. 1 shows that the semi-softening temperature varies depending on the additive element. Since the semi-softening temperature of pure copper is 160 ° C., the amount (ΔT) of the increase in the semi-softening temperature of each element from 160 ° C. was obtained and compared with Table 1 based on this temperature.

Sn is known to be effective as an element for improving heat resistance. In the present invention, Sn is used as a reference when selecting an additive element. Therefore, from Table 1, when ΔTSn of Sn is 1, the ratio of ΔT (ΔT / ΔTSn) of each element (at the time of adding 0.05%) was obtained. This ratio indicates the degree (effectiveness) that each element improves the heat resistance with respect to Sn. From this ratio, elements equivalent to Sn (the above ratio is 0.7 or more) are Mg, Ag, In, Cr, Ti, Cd, and Zr. However, Cd is not suitable as an additive element.
When the total addition amount of these elements is less than 1000 ppm (0.1% by mass), it is not effective for improving the heat resistance, and when the total addition amount exceeds 3000 ppm, the conductivity tends to decrease.
It should be noted that the electrical conductivity of the alloy can be calculated by the Matthiessen equation. If Δρi of the above elements is substituted into this equation, the electrical conductivity becomes less than 80 IACS when the total addition amount exceeds 3000 ppm. Δρi is based on literature values (author: Yotaro Murakami and Kiyoshi Kamei, “Asakura Metal Engineering Series Nonferrous Metallology”, first edition, first edition, Asakura Shoten, published in April 1978, p13).

In the copper foil according to the embodiment of the present invention, it is preferable that the maximum height Ry of the surface in the rolling parallel direction is 0.5 μm or less and the thickness is 20 μm or less.
This is because the thinner the copper foil, the smaller the amount of deformation applied to the copper foil during bending, and the bending life becomes longer when compared with the same bending radius.
On the other hand, in order to reduce the thickness of the copper foil, it is necessary to increase the degree of final rolling. However, if the strong processing is performed, an oil pit is formed on the surface of the copper foil and the surface becomes rough. And as Rz increases, the tensile strength (TS) decreases. This is because the effective thickness of the copper foil is reduced at the oil pit portion, and the load is concentrated on that portion. On the other hand, since the Young's modulus does not depend on the surface roughness, if Rz is large, the value of σ / E decreases and the flexibility tends to decrease.
For these reasons, Ry is preferably 0.5 μm or less. An example of a method for setting Ry to 0.5 μm or less is to set rolling conditions such as rolling oil viscosity and roll roughness and to set an upper limit on the final rolling degree.

The flexible printed circuit board (FPC) of this invention uses the said copper foil.
In addition, if it is heated excessively in the FPC processing process, recrystallization proceeds and a texture develops. Therefore, the heat treatment temperature in the FPC processing step is preferably set to the semi-softening temperature of the copper foil + 50 ° C. or less.

  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.

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 Tables 2 and 3 were respectively added to electrolytic copper having a purity of 99.96% or more to obtain ingots. The ingot was hot rolled to a thickness of 10 mm, then the surface was chamfered, and cold rolling and annealing were repeated to obtain a plate sample having a final thickness of 0.1 mm.
The semisoftening temperature was measured for each plate-like sample. The semi-softening temperature was obtained by annealing the plate-like sample, obtaining the Vickers hardness before annealing and the Vickers hardness when completely softened, and setting the annealing temperature at the intermediate Vickers hardness.
For each plate sample, the maximum surface height Ry was measured according to JIS-B0601 (stylus roughness measurement), and the crystal grain size before final rolling was measured according to JIS-H0501 (cutting method).
For each plate-like sample, the tensile strength (TS) after final rolling is measured according to JIS-Z2241, and the Young's modulus (E) is measured by Young's modulus measuring instrument (TE-RT (Non-contact electrostatic drive system manufactured by Nippon Techno Plus Co., Ltd. Measured using a cantilevered natural vibration method Young's modulus measuring device) The sample dimensions for measuring Young's modulus were 15 mm long × 3.2 mm wide.
Each plate-like sample was also measured for tensile strength and Young's modulus after annealing at 300 ° C. for 30 minutes as a heat treatment equivalent to the thermal history in FPC processing.

  The ingot was hot-rolled to a thickness of 10 mm, then the surface was chamfered, and cold rolling and annealing were repeated to obtain foils having final thicknesses shown in Tables 2 and 3. Copper roughening plating is performed on one side of the obtained foil, and a polyimide (thickness 20 μm) and foil are laminated by a cast method, followed by etching to form a circuit with a predetermined pattern, and an FPC sample (long with a width of 12.7 mm) A circuit width of 1 mm) was obtained.

For each FPC sample, the conductivity at 25 ° C. was measured by the 4-terminal method.
Moreover, the bending test was done by the following method.
The bending test (ICP) is performed by bending the FPC sample into a U shape in the longitudinal direction, fixing one end to the movable plate, fixing the other end to the fixed plate, and reciprocally vibrating the movable plate in the long side direction of the FPC sample. It was. The test conditions were a U-shaped radius of curvature of 1 mm, a vibration stroke of 5 mm, and a vibration frequency of 1200 times / minute. In addition, the electrical resistance of the sample during the bending test was measured, and the number of bendings until the resistance increased by 10% from the initial resistance was determined. ◎ if the number of flexing required for the electrical resistance of the sample to increase by 10% of the initial resistance is 100,000 times or more, ○ if it is 50,000 times or more and less than 100,000 times, △ if it is 10,000 times or more and less than 50,000 times △ X less than 10,000 times. If the evaluation is ◎ or ○, there is no practical problem.
The sliding bending test apparatus was the same as that described in FIG. 1 of JP-A-2001-323354.
The obtained results are shown in Tables 2 and 3. In addition, the ratio (subscript of a composition) of the additional element of Table 2 and Table 3 is the mass%.

As is clear from Table 2, in each Example satisfying 4.5 × 10 ⁻³ ≧ σ / E ≧ 3 × 10 ⁻³ , the flexibility was excellent.

On the other hand, in the case of Comparative Example 1 which was strongly processed during rolling (98%), the tensile strength immediately after rolling was high, but the strength decreased after heat treatment, and σ / E <3 × 10 ⁻³ , so the flexibility deteriorated. did. This is thought to be due to the introduction of shear bands by strong processing.
In the case of Comparative Example 2 in which annealing (450 ° C. for 30 minutes) was added after the final rolling, the Young's modulus decreased, but the strength decreased significantly, and σ / E <3 × 10 ⁻³ . Deteriorated.
In the case of Comparative Example 3, the strength was remarkably reduced after the heat treatment and σ / E <3 × 10 ⁻³ , so that the flexibility deteriorated. This is probably because the grain size before rolling was large (exceeding 10 nm), making it difficult to strengthen the work by rolling.

In the case of Comparative Example 4 in which the heat treatment was performed at 200 ° C. for 30 minutes, σ / E exceeded 4.5 × 10 ⁻³ , but in the first place, FPC cannot be produced at this heat treatment temperature, which is inappropriate.
In Comparative Examples 5 and 7 in which the amount of the additive element was less than 1000 ppm, the strength was remarkably lowered after the heat treatment, and σ / E <3 × 10 ⁻³ . This is presumably because recrystallization during heat treatment could not be suppressed due to the small amount of added elements. In particular, in the case of Comparative Example 7, the strength decreased most because the (200) azimuth increased extremely, and since the material did not have a waist, folding occurred during the bending test.
In Comparative Examples 6 and 8 in which the amount of additive element exceeded 3000 ppm, the conductivity was less than 80% IACS.

From Table 3, in the case of Reference Examples 1 and 2 using known tough pitch copper, the strength was remarkably lowered after the heat treatment, and σ / E <3 × 10 ⁻³ .
In the case of Reference Examples 3 to 5 in which 0.019% by mass of Ag is added to a known tough pitch copper, the strength is remarkably lowered after heat treatment in the cases of Reference Examples 6 and 7 in which 0.012% by mass of Sn is added to a known oxygen-free copper, Since σ / E <3 × 10 ⁻³ , the flexibility deteriorated. Reference Examples 3 to 7 are known copper materials described in JP 2001-323354 A (paragraph 0011).
In Reference Examples 8 and 9 using known 7/3 brass, σ / E was 3 × 10 ⁻³ or more and excellent flexibility, but the conductivity was less than 80% IACS.

It is a figure which shows the semi-softening temperature of copper which added the additive element.

Claims (6)

After heat treatment for 30 minutes at 300 ° C., satisfies the 4.5 × 10 ^-3 ≧ (tensile strength / Young's modulus) ≧ 3 × 10 ^-3, and a tensile strength Ri der conductivity 80% IACS or more than 250 MPa, Ti One or more elements selected from the group of Zr and Mg are included in a total of 1000 to 3000 ppm, or two or more elements selected from the group of Ti, Zr, Mg, Cr, Sn, In and Ag are combined in a total of 1000 to Copper foil characterized by containing 3000ppm. 30 minutes after the heat treatment at 300 ℃, 4.5 × 10 ^-3 ≧ met (tensile strength / Young's modulus) ≧ 3 × 10 ^-3, and the Young's modulus Ri der conductivity 80% IACS or more 90～130GPa, Contains a total of 1000 to 3000 ppm of one or more elements selected from the group of Ti, Zr, and Mg, or a total of 1000 of two or more elements selected from the group of Ti, Zr, Mg, Cr, Sn, In, and Ag Copper foil characterized by containing ~ 3000ppm . After a heat treatment at 300 ° C. for 30 minutes, the ratio of the integrated intensity I (200) in the (200) direction to the integrated intensity I (111) in the (111) direction by X-ray diffraction is 15 ≧ I (200) / I (111 ) copper foil according to claim 1 or 2, characterized in that Ru ≧ 1.5 der. The copper foil according to any one of claims 1 to 3, wherein the final rolling degree is 80 to 96%, and the crystal grain size immediately before the final rolling is 5 to 10 µm. The copper foil according to any one of claims 1 to 4, wherein the copper foil not subjected to the heat treatment has a semi-softening temperature of 300 ° C or higher when the annealing time is 30 minutes. The flexible printed circuit board using the copper foil in any one of Claims 1-5 .

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