TW201910524A - Copper foil for flexible printed circuit board, copper clad laminate using the same, flexible printed circuit board, and electronic equipment - Google Patents

Abstract

To provide a copper foil for a flexible printed circuit board (FPCB), which is excellent in both bendability and softening resistance, a copper-clad laminate using the same, a flexible printed circuit board and an electronic device. The copper foil for FPCB is a copper foil composed of 99.0% by mass or more of Cu and the remainder being unavoidable impurities, and each of the following elements is contained alone or in combination of two or more elements: 0.0005 mass% or more and 0.03 mass% or less of P, 0.0005 mass% or more and 0.05 mass% or less of Ag, 0.0005 mass% or more and 0.14 mass% or less of Sb, 0.0005 mass% or more and 0.163 mass% or less of Sn, 0.0005 mass% or more and 0.288 mass% or less of Ni, 0.0005 mass% or more and 0.058% by mass or less of Be, 0.0005 mass% or more and 0.812% by mass or less of Zn, 0.0005 mass% or more and 0.429 mass% or less of In, and 0.0005 mass% or more and 0.149 mass% or less of Mg; the semi-softening temperature of the copper foil is 160 to 300 DEG C, when the intensity of the (200) plane obtained by the X-ray diffraction of the rolling surface is I, and the intensity obtained by the X-ray diffraction of the fine powder copper is I0, then (I/I0) is 3.0 or less.

Description

   Copper foil for flexible printed circuit board, copper-clad laminate using the same, flexible printed circuit board, and electronic device   

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

Flexible printed circuit boards (flexible wiring boards, hereinafter referred to as "FPCs") are widely used in bending and moving parts of electronic circuits because of their flexibility. For example, FPCs are used in the movable parts of disk-related equipment such as HDDs, DVDs, and CD-ROMs, and in the bent parts of folding mobile phones.

FPC etches Copper Clad Laminate (copper-clad laminate, hereinafter referred to as CCL) laminated with copper foil and resin to form wiring, and covers a resin layer called a cover layer thereon. At the stage before laminating the cover layer, as a part of the surface modification step for improving the adhesion between the copper foil and the cover layer, the surface of the copper foil is etched. In addition, in order to reduce the thickness of the copper foil to improve the bendability, thinning etching may be performed.

However, with the miniaturization, thinness, and high performance of electronic devices, it is required to install FPCs inside these devices at high density. However, for high-density installation, FPCs need to be folded and housed inside miniaturized devices. That is, high bendability is required.

On the other hand, a copper foil with improved high cycle bendability typified by IPC bendability has been developed (Patent Document 1).

However, if the rolled coil is stored at room temperature for a long time, the plastic strain accumulated by the rolling may increase, and the semi-softening temperature may decrease, resulting in softening. If a softened copper foil is used to manufacture the FPC, problems such as deformation of the copper foil may occur, and the manufacturability of the FPC is significantly reduced. Therefore, a copper foil has been developed that improves the bendability of the rolled copper foil and increases the semi-softening temperature to suppress softening during storage (Patent Document 2).

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 3009383

[Patent Document 2] Japanese Patent Laid-Open No. 2000-192172

However, the semi-softening temperature of the copper foil described in Patent Document 2 is 120 to 150 ° C, and it may soften when stored in a high-temperature environment such as Southeast Asia.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a copper foil for a flexible printed circuit board having excellent bendability and softening resistance, a copper-clad laminate using the same, a flexible printed circuit board, and electronics. machine.

As a result of various studies, the present inventors have found that the copper foil contains specific additive elements and that the crystal grain size before the final cold rolling is made finer, so that the strains accumulated by rolling can be firmly entangled with each other. Therefore, the semi-softening temperature can be increased, the softening during storage can be suppressed, and the bendability of the copper foil can be improved.

That is, the copper foil for a flexible printed circuit board of the present invention is a copper foil consisting of 99.0% by mass or more of Cu and the remainder being unavoidable impurities. P is 0.0005 to 0.05% by mass of 0.0005% by mass to 0.03% by mass. Ag below 0.005% by mass, Sb below 0.0005% by mass and 0.14% by mass, Sn by 0.0005% by mass and 0.163% by mass, Ni by 0.0005% by mass and 0.288% by mass, Be by 0.0005% by mass and 0.058% by mass, Be, 0.0005 Zn above 0.812% by mass, Zn below 0.0005% by mass and 0.429% by mass, and Mg above 0.0005% by mass and 0.149% by mass are contained individually or in combination of two or more kinds. The semi-softening temperature is 160 ~ 300 ° C. When the intensity of the (200) plane obtained from the X-ray diffraction of the rolled surface is set to I, and the intensity calculated from the X-ray diffraction of the fine powder copper is set to I ₀ , (I / I ₀ ) is 3.0 or less.

In the copper foil for a flexible printed substrate of the present invention, when the intensity of the (200) plane obtained from the X-ray diffraction of the rolled surface after annealing at 320 ° C for 30 minutes is set to I, the X-rays of finely powdered copper are used. When the intensity obtained by the diffraction is set to I ₀ , (I / I ₀ ) is preferably 3.0 or less.

The copper-clad laminated system of the present invention is formed by laminating the above-mentioned copper foil for a flexible printed circuit board and a resin.

The flexible printed circuit board of the present invention is formed by forming a circuit from the copper foil in the copper-clad laminate.

The electronic device of the present invention is formed using the flexible printed circuit board.

According to the present invention, it is possible to obtain a copper foil for a flexible printed circuit board which is excellent in bending properties and softening resistance.

Hereinafter, embodiments of the copper foil of the present invention will be described. In the present invention, unless otherwise specified,% means mass%.

<Composition>

The copper foil of the present invention is composed of 99.0 mass% or more of Cu, and the remainder is unavoidable impurities. P is 0.0005 mass% or more and 0.03 mass% or less, P, 0.0005 to 0.05 mass% or less, Ag, 0.0005 mass% or more, and 0.14 mass. % Sb or less, 0.0005 mass% or more and 0.163 mass% or less Sn, 0.0005 mass% or more and 0.288 mass% or less Ni, 0.0005 mass% or more and 0.058 mass% or less Be, 0.0005 mass% or more and 0.812 mass% or less Zn, 0.0005 Each of In is 0.4 mass% or more and 0.429 mass% or less, and Mg of 0.0005 mass% or more and 0.149 mass% or less is contained alone or in two or more kinds.

P, Ag, Sb, Sn, Ni, Be, Zn, In, and Mg (hereinafter referred to as additive elements) will increase the frequency of differential intertwining during cold rolling, so it can not only easily increase the stretch after recrystallization Strength, and can increase the recrystallization temperature of copper foil and increase the semi-softening temperature.

If P exceeds 0.03% by mass, Ag exceeds 0.05% by mass, Sb exceeds 0.14% by mass, Sn exceeds 0.163% by mass, Ni exceeds 0.288% by mass, Be exceeds 0.058% by mass, Zn exceeds 0.812% by mass, and In exceeds 0.429% by mass or Mg When it exceeds 0.149% by mass, the electrical conductivity is decreased, which is not suitable as a copper foil for a flexible substrate.

When the content of P, Sb, Sn, Ni, Be, Zn, In, and Mg is less than 0.0005 mass% for each element, it is industrially difficult to increase the semi-softening temperature, so the lower limit of the content of each element is set to 0.0005 mass%.

In addition, if recrystallization annealing is performed only once at the beginning of cold rolling, and then recrystallization annealing is not performed (for example, in the order of cold rolling, recrystallization annealing, scale removal, and cold rolling), cold rolling is used. The intertwining of the differential rows can be increased, and a large amount of processing strain is introduced, so that the softening temperature is increased, and the (I / I ₀ ) of the 200 orientation is reduced, so that the bendability can be further improved.

In addition, in order to increase the softening temperature of the copper foil and improve the bendability, it is preferable to crystallize the grains before the final cold rolling (in the entire process of repeating annealing and rolling, and before the finishing rolling after the final annealing). The diameter is set to 5 to 30 μm.

When the crystal grain size before the final cold rolling is larger than 30 μm, the frequency of the differential rows intertwined during processing becomes smaller, and the accumulation of strain becomes smaller, so the softening temperature decreases, and the (I / I ₀ ) of the 200 orientation changes. Large and tend to decrease the bendability. In the case where the crystal grain size before the final cold rolling is less than 5 μm, only the intertwining of the differential rows during processing will be saturated, the rolling load becomes high, and the effect of reducing the softening temperature is saturated. Therefore, the lower limit of the crystal grain size before the last cold rolling is set to 5 μm.

As mentioned above, by making the copper foil contain the above-mentioned additive elements and miniaturizing the crystal grain size before the last cold rolling, the frequency of the differential rows intertwined during cold rolling can be increased, the softening temperature can be increased, and the 200% of the orientation (I / I ₀ ) after crystallization improves the bendability. Here, in the case of increasing the intertwining of the differential rows in cold rolling and introducing a large amount of processing strain, it is not easy to cause the preferential growth of the 200 orientation, and the I / I _{0 of the} 200 orientation becomes small. The smaller the I / I ₀ of the 200 orientation, the less likely it is that cracks caused by the difference in plastic deformation behavior between the 200 orientation and other orientations are bent, so the bendability is improved.

Therefore, in the present invention, when the intensity of the (200) plane obtained from the X-ray diffraction of the rolled surface is set to I, and the intensity obtained from the X-ray diffraction of the fine powder copper is set to I ₀ , ( I / I ₀ ) is specified to be 3.0 or less.

The copper foil of the present invention can be obtained by containing, for example, refined copper (TPC) according to JIS-H3100 (C1100) standard or oxygen-free copper (OFC) of JIS-H3100 (C1020) containing the above-mentioned additive element.

<Semi-softening temperature>

The semi-softening temperature of copper foil is 160 ~ 300 ℃. If the semi-softening temperature does not reach 160 ° C, there is a possibility that softening may occur during storage in a high-temperature environment. If the semi-softening temperature exceeds 300 ° C, recrystallization will not occur in the manufacturing steps of FPC, so the bendability will be deteriorated.

The measurement of the semi-softening temperature is performed by subjecting a copper foil to annealing at a specific temperature for 30 minutes in a non-oxidizing environment, and then performing a tensile test to determine the strength (tensile strength) relative to the heat treatment conditions. The annealing temperature is set to a semi-softening temperature which is an intermediate value between the strength after the rolling is completed (before annealing) and the strength after being completely softened (annealed at 400 ° C. for 30 minutes). If the semi-softening temperature is in the range of 160 to 300 ° C, it is judged that it has appropriate softening characteristics.

<I / I ₀ >

When the intensity of the (200) plane obtained from the X-ray diffraction of the rolled surface is set to I and the intensity obtained from the X-ray diffraction of the fine powder copper is set to I ₀ , (I / I ₀ ) is 3.0 or less .

As described above, the smaller the (I / I ₀ ) of the 200 orientation after recrystallization, the more the bendability can be improved. Therefore, (I / I ₀ ) is set to 3.0 or less.

<Heat treatment at 320 ° C for 30 minutes>

The copper foil in claim 1 of the present case stipulates "a copper foil in a state of being a copper-clad laminate after being laminated with a resin, and being subjected to a hardening heat treatment of the resin". Therefore, even if the copper foil is not heat-treated at 320 ° C. for 30 minutes, it shows the 200-direction (I / I ₀ ) after the heat treatment of the equivalent resin.

The copper foil of claim 2 of the present case provides "the state of the copper foil before lamination with resin". In addition, the heat treatment at 320 ° C for 30 minutes is a simulation of the temperature conditions of the hardening heat treatment of the resin when the CCL is laminated. Therefore, in claim 2, the "I / I _{0 of} the 200 orientation of the copper foil after heat treatment at 320 ° C for 30 minutes in a non-oxidizing environment" was specified to reproduce "the coating after being laminated with the resin A copper foil in the state after the copper laminate is cured and heat-treated with resin. " Moreover, the heating rate of the heat treatment may be between 100 and 300 ° C / min.

The copper foil of this invention can be manufactured as follows, for example. First, a specific element is added to a copper ingot, and after melting and casting, hot rolling, cold rolling, and annealing are performed, recrystallization annealing is performed at the initial stage of cold rolling, and the last cold rolling is performed. Foil.

<Copper-clad laminate and flexible printed circuit board>

The copper foil of the present invention (1) is cast with a resin precursor (for example, a polyimide precursor called varnish) and heated to polymerize it. (2) a thermoplastic adhesive of the same kind as the base film is used The base film is laminated on the copper foil of the present invention, whereby a copper-clad laminate (CCL) composed of two layers of a copper foil and a resin substrate can be obtained. Furthermore, a base film coated with an adhesive is laminated on the copper foil of the present invention, whereby a copper-clad laminate (CCL) composed of three layers of a copper foil, a resin substrate, and an adhesive layer therebetween can be obtained. When these CCLs are manufactured, the copper foil is heat-treated and recrystallized.

A photolithography technique is used to form a circuit in these, and the circuit is plated as necessary, and a cover film is laminated to obtain a flexible printed circuit board (flexible wiring board).

Therefore, the copper-clad laminated system of the present invention is formed by laminating copper foil and resin. The flexible printed circuit board of the present invention is formed by forming a circuit on a copper foil of a copper-clad laminate.

Examples of the resin layer include PET (polyethylene terephthalate), PI (polyimide), LCP (liquid crystal polymer), and PEN (polyethylene naphthalate). Limited to this. As the resin layer, such a resin film may be used.

As a method for laminating a resin layer and a copper foil, the surface of the copper foil may be coated with a material as a resin layer 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 thermally compression-bonded to the copper foil without using an adhesive. However, it is preferable to use an adhesive from the point that unnecessary heat is not applied to the resin film.

When using a film as a resin layer, this film can be laminated | stacked on a copper foil through an adhesive layer. In this case, it is preferable to use an adhesive having the same composition as the film. For example, in the case where a polyimide film is used as the resin layer, it is preferable to use a polyimide-based adhesive in the adhesive layer. The polyfluorene imine adhesive here refers to an adhesive containing a fluorene imine bond, and also includes polyether fluorene imine and the like.

The present invention is not limited to the embodiments described above. In addition, as long as the effect of the present invention is achieved, the copper alloy of the above embodiment may contain other components. Moreover, it may be electrolytic copper foil.

For example, the surface of the copper foil may be subjected to roughening treatment, rust prevention treatment, heat treatment, or a combination of these.

[Example]

Next, the present invention will be described in more detail with examples, but the present invention is not limited to these examples. Adding the additional elements shown in Tables 1 and 2 to electrolytic copper with a purity of 99.0% or more, and casting in an Ar environment to obtain an ingot. The oxygen content in the ingot did not reach 15 ppm. This ingot was homogenized and annealed at 900 ° C, followed by hot rolling, cold rolling, and then recrystallization annealing. The recrystallization annealing conditions are adjusted in advance so that the crystal grain size before final cold rolling becomes 5 to 30 μm. Then, the oxidized scale on the surface was removed, and the final cold-rolling was performed at the processing degree η shown in Tables 1 and 2 to obtain a copper foil having a target final thickness. The obtained copper foil was heat-treated at 320 ° C for 30 minutes in a non-oxidizing environment to obtain a copper foil sample.

<Evaluation>

1. Crystal grain size before final cold rolling

Each sample was observed with a SEM (Scanning Electron Microscope) before the heat treatment and before the last cold rolling (after the last annealing), and the average particle diameter was determined based on JIS H 0501. Among them, twin crystals are regarded as different crystal grains for measurement. The measurement area was 400 μm × 400 μm in a cross section parallel to the rolling direction.

2.Semi-softening temperature

The measurement of the semi-softening temperature is performed as described above.

3.200 I / I ₀

For each copper foil sample after the heat treatment, an integrated value (I) of the (200) plane strength obtained from the X-ray diffraction of the rolled surface was obtained. Divide this value by the integral value (I ₀ ) of the (200) plane strength of the finely powdered copper measured in advance to calculate the value of I / I ₀ .

4.Conductivity

For each copper foil sample after the heat treatment described above, the electrical conductivity (% IACS) at 25 ° C. was measured by the 4-terminal method based on JIS H 0505.

When the electrical conductivity is greater than 75% IACS, the electrical conductivity is good.

5.Bendability of copper foil (MIT resistance)

For each copper foil sample after the heat treatment, the number of times of MIT resistance (number of round trips) was measured based on JIS P 8115. Among them, the bending fixture has an R of 0.38 mm and a load of 250 g.

If the MIT folding resistance number is 75 or more, the bendability of the copper foil is good.

The obtained results are shown in Tables 1 and 2.

As is clear from Tables 1 and 2, when each specific example contains specific additive elements in a specific amount range and is recrystallized and annealed so that the crystal grain size before final cold rolling becomes 5 to 30 μm, The semi-softening temperature is high, and the I / I ₀ at the 200 orientation of 320 ° C × 30min after the heat treatment is 3 or less, and the bendability is excellent.

Furthermore, in each of the examples, the higher the recrystallization annealing temperature, the larger the crystal grain size before the final cold rolling.

On the other hand, in the case of Comparative Example 1 not containing an additive element, the semi-softening temperature did not reach 160 ° C, and the softening resistance was poor.

Also, in the case of Comparative Example 2 after recrystallization annealing was performed once with a crystal grain size of more than 30 μm before the final cold rolling, the semi-softening temperature did not reach 160 ° C. and the I / I ₀ at the 200 orientation was greater than 3, Therefore, the bending property is poor.

In addition, in the case of Comparative Example 3 in which the amount of P added exceeds 0.03%, the conductivity is poor.

Claims (5)

A copper foil for a flexible printed circuit board is composed of 99.0% by mass or more of Cu, and the remainder is unavoidable impurities. P is 0.0005% by mass or more and 0.03% by mass or less, Ag is 0.0005 to 0.05% by mass, or 0.0005. Sb above 0.14% by mass, Sn above 0.0005% by mass and 0.163% by mass, Ni above 0.0005% by mass and 0.288% by mass, Be at 0.0005% by mass and 0.058% by mass, Be above 0.0005% by mass and 0.812 ^{% by} mass The following Zn, 0.0005 mass% to 0.429 mass%, In, and 0.0005 mass% to 0.149 mass%, Mg are contained separately or two or more kinds, and the semi-softening temperature is 160 to 300 ° C. When the intensity of the (200) plane obtained by the diffraction is set to I, and when the intensity obtained from the X-ray diffraction of the fine powder copper is set to I ₀ , (I / I ₀ ) is 3.0 or less. The copper foil for a flexible printed circuit board according to claim 1, wherein when the strength of the (200) plane obtained from X-ray diffraction of the rolled surface after annealing at 320 ° C for 30 minutes is set to I, When the intensity obtained by X-ray diffraction of powder copper is set to I ₀ , (I / I ₀ ) is 3.0 or less.     A copper-clad laminate comprising a copper foil for flexible printed circuit board and a resin as described in claim 1 or 2.         A flexible printed circuit board is formed by forming a circuit from the copper foil in the copper-clad laminate according to claim 3.         An electronic device using the flexible printed circuit board according to claim 4.