KR101935129B1 - Copper foil for flexible printed wiring board, and copper-clad laminate, flexible printed wiring board and electronic device using the same - Google Patents

Abstract

[PROBLEMS] To provide a copper foil for a flexible printed circuit board excellent in bending property and etching property.
(Copolymer) A copper foil comprising 99.0 mass% or more of Cu and the remainder inevitable impurities, wherein the average grain size is 0.5 to 4.0 mu m and the tensile strength is 235 to 290 MPa.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a copper foil for a flexible printed circuit board, a copper clad laminate using the same, a flexible printed circuit board,

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

Flexible printed circuit boards (hereinafter referred to as " FPCs ") are widely used for folding or moving parts of electronic circuits because they have flexibility. For example, an FPC is used for a moving part of a disk-related device such as an HDD, a DVD and a CD-ROM, or a bent part of a folding mobile phone.

The FPC is formed by forming a wiring 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 the upper surface is covered with a resin layer called a coverlay. As a part of the surface modification step for improving the adhesion between the copper foil and the coverlay in the previous step of laminating the coverlay, etching of the copper foil surface is carried out. In addition, in order to reduce the thickness of the copper foil to improve the bending property, a thinning etching may be performed.

[0004] However, in order to implement a high-density mounting, it is necessary to fold the FPC inside the miniaturized device to bend it In other words, a high bending property is required.

On the other hand, a copper foil improved in flexural flexibility at high cycle, which is represented by IPC bending property, has been developed (Patent Documents 1 and 2).

Japanese Laid-Open Patent Publication No. 2010-100887 Japanese Laid-Open Patent Publication No. 2009-111203

However, in order to mount the FPC at a high density as described above, it is necessary to improve the bending property typified by the MIT bending resistance (folding endurance), and there is a problem that the conventional copper foil can not sufficiently improve the bending property .

In addition, with the miniaturization, thinness and high performance of electronic devices, the circuit width and space width of the FPC are reduced to about 20 to 30 mu m, and the etching factor and the circuit linearity are liable to be deteriorated when the circuit is formed by etching There is a problem, and this solution is also required.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a copper foil for a flexible printed circuit board excellent in bending property and etching property, a copper clad laminate using the same, a flexible printed board, and an electronic apparatus.

The inventors of the present invention have made various studies, and as a result, have found that the crystal grains after recrystallization of the copper foil can be finely refined to enhance the strength and improve the foldability. This is because as the crystal grains are made finer by the hole fetch rule, the strength becomes higher and the bending property becomes higher. However, if the crystal grains are excessively fine, the strength becomes excessively high, the bending rigidity becomes large, and the springback becomes large, which is not suitable for use in a flexible printed board. Therefore, the range of the crystal grain size is also specified.

In addition, by reducing the crystal grain size to about one-tenth of the circuit width of about 20 to 30 mu m of the recent FPC, the etching factor and circuit linearity when the circuit is formed by etching can also be improved.

That is, the copper foil for a flexible printed circuit board of the present invention is a copper foil comprising 99.0% by mass or more of Cu and the remainder inevitable impurities, and has an average crystal grain size of 0.5 to 4.0 μm and a tensile strength of 235 to 290 MPa.

In the copper foil for a flexible printed circuit board of the present invention, it is preferable that it is made of tough pitch copper standardized by JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1011).

Further, it is preferable that a total of 0.003 to 0.825 mass% of at least one additive element selected from the group of P, Ti, Sn, Ni, Be, Zn, In and Mg is contained.

It is preferable that the average crystal grain size after the heat treatment at 300 占 폚 for 30 minutes is 0.5 to 4.0 占 퐉 and the tensile strength is 235 to 290 MPa.

A copper clad laminate formed by laminating a polyimide resin film having a thickness of 25 占 퐉 on one surface of the copper foil was bent and bent 180 degrees so that the copper foil was outside at a bending radius of 0.05 mm, It is preferable that the crack is not visually observed when the copper foil is observed at a magnification of 200 times.

The copper clad laminate of the present invention is formed by laminating the copper foil for a flexible printed circuit 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 foil.

It is preferable that the L / S of the circuit is 40/40 to 15/15 (mu m / mu m). L / S (line and space) of a circuit is a ratio of the width (L: line) of the wiring constituting the circuit to the interval (S: space) of the adjacent wiring. L adopts the minimum value of L in the circuit, and S adopts the minimum value of S in the circuit.

Further, L and S may be in the range of 15 to 40 占 퐉, and they need not be the same value. For example, L / S = 20.5 / 35, 35/17 or the like may be taken.

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

According to the present invention, a copper foil for a flexible printed circuit board excellent in bending property and etching property is obtained.

1 is a view showing a test method for bending resistance of CCL.

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

<Composition>

The copper foil according to the present invention is composed of 99.0% by mass or more of Cu and the remainder inevitable impurities.

As described above, in the present invention, the crystal grains after the recrystallization of the copper foil are made finer, whereby the strength is increased to improve the foldability.

However, in the case of the above-mentioned composition of the pure copper system, it is difficult to make fine grains finer. Therefore, recrystallization annealing is performed only once at the beginning of cold rolling, and thereafter, recrystallization annealing is not performed, It is possible to realize dynamic recrystallization and miniaturization of crystal grains.

In order to increase the processing strain in the cold rolling, it is preferable that η = ln (final cold rolling before final cold rolling) is performed in the final cold rolling (finishing rolling performed after the final annealing in the entire process of repeating annealing and rolling) Plate thickness / plate thickness after final cold rolling) = 3.5 to 7.5 is preferable.

When? is less than 3.5, the accumulation of deformation during processing is small and the nuclei of the recrystallized grains are small, so that the recrystallized grains tend to become coarse. When? is larger than 7.5, deformation accumulates excessively to become a driving force of crystal growth, and crystal grains tend to become coarse. It is more preferable that? = 5.5 to 7.5.

When the total content of the additive elements selected from the group consisting of P, Ti, Sn, Ni, Be, Zn, In and Mg is 0.003 to 0.825 mass% , It is possible to more easily realize finer crystal grains. Since these added elements increase the dislocation density during cold rolling, the crystal grains can be more easily miniaturized. If the recrystallization annealing is carried out only once at the initial stage in the cold rolling and then the recrystallization annealing is not performed thereafter, a large amount of machining strain is introduced by cold rolling to cause dynamic recrystallization, have.

When the total content of the additional elements is less than 0.003 mass%, it becomes difficult to make the crystal grains finer. When the total content is more than 0.825 mass%, the conductivity may be lowered. Further, when the recrystallization temperature rises and is laminated with the resin, it is not recrystallized, and the strength is excessively increased, so that the bending property of the copper foil and CCL may deteriorate.

As a method for refining the crystal grains after the recrystallization of the copper foil, there are a method of performing the rolling of the polymer, a method of using pulse current when electrolytic deposition is carried out in the electrolytic copper foil, A method of adding an appropriate amount of urea or glue or the like may be mentioned.

The copper foil according to the present invention may be a composition comprising tough pitch copper (TPC) standardized by JIS-H3100 (C1100) or oxygen-free copper (OFC) of JIS-H3100 (C1011).

The TPC or OFC may be a composition containing the above-described additive element.

&Lt; Average crystal grain size &

The average grain size of the copper foil is 0.5 to 4.0 mu m. If the average crystal grain size is less than 0.5 占 퐉, the strength becomes too high, the bending rigidity becomes large, and the spring back becomes large, which is not suitable for use in a flexible printed board. If the average crystal grain size exceeds 4.0 占 퐉, grain refinement can not be realized, and it is difficult to improve the folding property by increasing the strength, and the etching factor and circuit linearity are deteriorated and the etching property is deteriorated.

In order to avoid an error, the average crystal grain size is measured by observing the surface of the foil in a field of 100 占 퐉 占 100 占 퐉 over three fields. The surface of the foil can be observed using a SIM (Scanning Ion Microscope) or an SEM (Scanning Electron Microscope), and the average crystal grain size can be determined based on JIS H 0501.

However, the twin crystal is regarded as a separate crystal grain and is measured.

&Lt; Tensile Strength (TS) &gt;

The tensile strength of the copper foil is 235 to 290 MPa. As described above, the tensile strength is improved by making the crystal grains finer. If the tensile strength is less than 235 MPa, it is difficult to improve the folding performance by increasing the strength. If the tensile strength exceeds 290 MPa, the strength becomes excessively high, the flexural rigidity becomes large, and the spring back becomes large, which is not suitable for use in a flexible printed board.

The tensile strength was measured by a tensile test according to IPC-TM650 using a specimen having a width of 12.7 mm, a room temperature (15 to 35 캜), a tensile speed of 50.8 mm / min and a gauge length of 50 mm, And a tensile test was performed in a direction parallel to the test piece.

&Lt; Heat treatment at 300 占 폚 for 30 minutes>

The average grain size of the copper foil after heat treatment at 300 占 폚 for 30 minutes may be 0.5 to 4.0 占 퐉 and the tensile strength may be 235 to 290 MPa.

Since the copper foil according to the present invention is used in a flexible printed circuit board and CCL in which a copper foil and a resin are laminated is subjected to a heat treatment for curing the resin at 200 to 400 ° C, .

Therefore, before and after lamination with the resin, the average crystal grain size and tensile strength of the copper foil are changed. Thus, the copper foil for a flexible printed circuit according to claim 1 of the present application defines a copper foil in a state of being subjected to a curing heat treatment of a resin after being laminated with a resin to form a copper clad laminate.

On the other hand, the copper foil for a flexible printed circuit according to claim 4 of the present application defines a state in which the copper foil before lamination with the resin is subjected to the heat treatment. The heat treatment at 300 占 폚 for 30 minutes mimics the temperature condition in which the resin is subjected to a curing heat treatment at the time of CCL lamination.

The copper foil of the present invention can be produced, for example, as follows. First, the additive may be added to a copper ingot, followed by melting and casting, followed by hot rolling, cold rolling and annealing, and then performing the above-mentioned final cold rolling to produce a foil.

&Lt; Copper clad laminate and flexible printed board &gt;

(1) casting a resin precursor (for example, a polyimide precursor called varnish) and polymerizing it by applying heat; (2) using a thermoplastic adhesive of the same kind as the base film, By laminating the copper foil of the present invention, a copper clad laminate (CCL) composed of two layers of a copper foil and a resin substrate is obtained. In addition, a copper clad laminate (CCL) composed of three layers of a copper foil, a resin substrate, and an adhesive layer therebetween is obtained by laminating a base film on which an adhesive has arrived (applied) to the copper foil of the present invention. During the production of these CCLs, the copper foil is heat-treated and recrystallized.

A circuit is formed by using these photolithography techniques, a circuit is plated if necessary, and a coverlay film is laminated to obtain a flexible printed circuit board (flexible wiring board).

Therefore, the copper clad laminate of the present invention is formed by laminating a copper foil and a resin layer. The flexible printed 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). As the resin layer, these resin films may be used.

As a method of laminating the resin layer and the copper foil, a material to be a resin layer may be coated on the surface of the copper foil to be heated. Further, a resin film may be used as the resin layer, the following adhesive may be used between the resin film and the copper foil, or the resin film may be thermally pressed to the copper foil without using an adhesive. However, it is preferable to use an adhesive in order not to apply extra heat to the resin film.

When a film is used as the resin layer, the film may be laminated on the copper foil with the adhesive layer interposed therebetween. In this case, it is preferable to use an adhesive of 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 as the adhesive layer. In addition, the polyimide adhesive referred to herein refers to an adhesive containing an imide bond, and also includes a polyetherimide and the like.

The present invention is not limited to the above embodiment. The copper alloy in the above embodiment may contain other components as long as it exhibits the function and effect of the present invention.

For example, the surface of the copper foil may be subjected to surface treatment by roughening treatment, rust-preventive treatment, heat-resistant treatment, or a combination thereof.

Example

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited thereto. Elements shown in Table 1 were added to an electric copper having a purity of 99.9% or more, and cast in an Ar atmosphere to obtain an ingot. The oxygen content of the ingot was less than 15 ppm. The ingot was subjected to homogenization annealing at 900 DEG C, hot rolled to a thickness of 30 mm, cold rolled to 14 mm, annealed once, and then the surface was subjected to machining to obtain a final cold Rolled to obtain a foil having a final thickness of 17 mu m. The resulting foil was subjected to a heat treatment at 300 ° C for 30 minutes to obtain a copper foil sample.

<A. Evaluation of Copper Samples>

1. Conductivity

The conductivity (% IACS) at 25 ° C was measured for each copper foil sample after the heat treatment by the four-terminal method based on JIS H 0505.

When the conductivity is 75% IACS or more, the conductivity is good.

2. Particle Size

The sample surface of each copper foil after the heat treatment was observed using an SEM (Scanning Electron Microscope), and the average particle size was determined based on JIS H 0501. However, the twin crystal was regarded as a separate crystal grain and measurement was performed. The measurement area was 100 mu m x 100 mu m on the surface.

3. Insulation resistance of copper foil (MIT bending resistance)

For each copper foil sample subjected to the heat treatment, the number of times of MIT breakage (the number of reciprocating bending) was measured based on JIS P 8115. However, R of the bending clamp was 0.38 and the load was 500 g.

If the number of times of MIT insertion is more than 75 times, the bending property of the copper foil is good.

4. Tensile strength of copper foil

The tensile strength of each copper foil sample after the heat treatment was measured under the above conditions by a tensile test according to IPC-TM650.

<B. Evaluation of CCL>

5. CCL's folding

After the final cold rolling, copper plating was performed on one side of the copper foil sample (copper foil before heat treatment) not subjected to the heat treatment. The copper plating bath is electroplated with a composition of Cu: 10-25 g / l and sulfuric acid: 20-100 g / l for 1-5 seconds at a bath temperature of 20-40 ° C and a current density of 30-70 A / dm 2, The amount of copper adhered was 20 g / dm &lt; 2 &gt;.

A polyimide film (product name: &quot; Yufilex VT &quot;, product of Ube Kosan Co., Ltd., thickness: 25 占 퐉) was laminated on the roughened surface of the copper foil sample and subjected to a heat treatment at 300 占 폚 for 30 minutes in a hot press (4 MPa) , And a CCL sample was obtained. The dimensions of the CCL sample used in the bending test were 50 mm in the rolling direction (longitudinal direction) and 12.7 mm in the width direction.

As shown in Fig. 1, the CCL sample 30 was sandwiched by a 0.1 mm thick plate 20 (a titanium copper plate standardized by JIS-H3130 (C1990)) so that the copper foil faced the outside, And placed between the lower mold 10a and the upper mold 10b of the compression tester 10 (product name "Autograph AGS" manufactured by Shimadzu Corporation).

In this state, the upper mold 10b was lowered and folded so as to come into close contact with the plate 20 at a portion where the CCL sample 30 was folded in two (Fig. 1 (a)). The CCL sample 30 is immediately taken out of the compression tester 10 and the bending tip portion 30s of the "transverse V-shaped" portion of the two folded portions is placed on a microscope (product name: "one shot 3D measurement microscope VR- 3000 "was used to visually confirm whether or not the copper foil surface was cracked at a magnification of 200. The bent tip end 30s corresponds to a 180-degree close bending with a bending radius of 0.05 mm.

In the case where cracks were confirmed, the test was ended, and the number of times of compression in Fig. 1 (a) was determined as the number of times of CCL bending.

The CCL sample 30 is inserted into the lower mold 10a and the upper mold 10b of the compression tester 10 so that the bent tip 30s is upward as shown in Fig. 1 (b) And in this state, the upper die 10b is lowered to open the bent leading end 30s.

Then, the bending of Fig. 1 (a) was carried out again, and the presence or absence of cracking of the bent tip portion 30s was visually confirmed. 1 (a) to 1 (b) were repeated in the same manner, and the number of times of bending was determined.

If the bending number of the CCL is 3 or more, the bending property of the CCL is good.

6. Etchability

A circuit of a desk having L / S (line / space) = 40/40 탆, 35/35 탆, 25/25 탆, 20/20 탆 and 15/15 탆 was formed on the copper foil portion of the CCL sample. As a comparison, a circuit was formed in the same manner as a commercially available rolled copper foil (tough pitch copper foil). Then, the linearity of the circuit and the linearity of the circuit (the ratio represented by the etching depth / upper and lower average etching widths) of the circuit and the linearity of the circuit were visually determined by a microscope and evaluated by the following criteria. The evaluation is OK.

?: Good etching property and circuit linearity as compared with commercial rolled copper foil

?: The etching property and the linearity of the circuit are equal to those of a commercial rolled copper foil

X: Inferior in linearity of etch factor and circuit compared to commercially available rolled copper foil

The obtained results are shown in Table 1.

As is apparent from Table 1, in each of the examples in which the mean grain size of the copper foil was 0.5 to 4.0 mu m and the tensile strength was 235 to 290 MPa, the bending property and the etching property were excellent. Further, in Example 1, the rolling was performed in the last pass of the final cold rolling.

On the other hand, in the case of Comparative Examples 1 and 4 in which the working degree? In the final cold rolling was less than 3.5, the average crystal grain size of the copper foil exceeded 4.0 占 퐉 and the tensile strength became less than 235 MPa, Respectively. In addition, in the case of Comparative Example 4, the average crystal grain size of the copper foil was 4.5 탆, which was slightly larger than 4.0 탆.

In the case of Comparative Example 3 in which the total content of the added elements is less than the lower limit value, refinement of the recrystallized grains by the additive element is insufficient and the average crystal grain size of the copper foil is considerably exceeded to 4.0 탆, and the tensile strength is less than 235 MPa So that the copper foil and the CCL were inferior in bending property and etching property. In the case of Comparative Example 2 in which the total content of the added elements exceeded the upper limit value, the conductivity was inferior.

In the case of Comparative Example 5 in which the total content of the added elements exceeded the upper limit value, the recrystallization temperature became high and the recrystallization was not performed in the heat treatment at 300 캜, and the conductivity decreased and the tensile strength increased to more than 290 MPa. Therefore, the bending properties of the copper foil and the CCL were considerably deteriorated.

Claims (9)

Cu of at least 99.0% by mass, and a remainder inevitable impurities,
An average crystal grain size of 0.5 to 4.0 mu m and a tensile strength of 235 to 290 MPa. The method according to claim 1,
A copper foil for a flexible printed circuit board made of tough pitch copper standardized by JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1011). The method according to claim 1,
Further comprising 0.003 to 0.825 mass% of a total of one or more additional elements selected from the group consisting of P, Ti, Sn, Ni, Be, Zn, In and Mg. The method according to claim 1,
The average crystal grain size after the heat treatment at 300 占 폚 for 30 minutes is 0.5 to 4.0 占 퐉 and the tensile strength is 235 to 290 ㎫. 5. The method according to any one of claims 1 to 4,
A copper clad laminate formed by laminating a polyimide resin film having a thickness of 25 占 퐉 on one surface of the copper foil was bent and bent 180 degrees so that the copper foil was outside at a bending radius of 0.05 mm, Is repeated three times and the copper foil is observed at a magnification of 200, so that no crack is visible. A copper clad laminate obtained by laminating a copper foil for a flexible printed circuit board and a resin layer according to any one of claims 1 to 4. A flexible printed board comprising the copper clad laminate according to claim 6 and a circuit formed on the copper foil. 8. The method of claim 7,
Wherein the circuit has an L / S of 40/40 to 15/15 (mu m / mu m). An electronic device using the flexible printed circuit board according to claim 7.

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