KR102285062B1 - Copper foil for flexible printed circuit board, copper-clad laminate using the same, flexible printed circuit board, and electronic equipment - Google Patents

Abstract

[PROBLEMS] To provide a copper foil for flexible printed circuit boards having excellent flexibility after fine circuit formation, a copper clad laminate using the same, a flexible printed circuit board, and an electronic device.
[Solution] Using a copper foil containing 99.0 mass % or more of Cu and remaining unavoidable impurities, and using a two-layer single-sided CCL sample of 12.7 mm width and 200 mm length in which a circuit is formed from copper foil, 2000 with a radius of curvature R = 2.0 Surface roughness Ra of the circuit surface after performing IPC sliding bending|flexion of a meeting is 0.030 micrometer or more and 0.400 micrometer or less.

Description

Copper foil for flexible printed circuit boards, copper clad laminates using the same, flexible printed circuit boards and electronic devices

The present invention relates to a copper 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.

Since a flexible printed circuit board (a flexible wiring board, hereafter called "FPC") has flexibility, it is widely used for the bending part and movable part of an electronic circuit. For example, FPC is used for movable parts of disk-related devices such as HDDs, DVDs, and CD-ROMs, and for bending parts of foldable mobile phones.

In FPC, wiring is formed by etching Copper Clad Laminate (copper clad laminate, hereinafter referred to as CCL) in which copper foil and resin are laminated, and the above is covered with a resin layer called a coverlay. In the step before laminating the coverlay, as a part of the surface modification process for improving the adhesion between the copper foil and the coverlay, the surface of the copper foil is etched. Moreover, in order to reduce the thickness of copper foil and to improve a flexibility, thickness reduction etching may be performed.

By the way, the flexibility of FPC is further calculated|required with improvement of the compactness, thinness, and high performance of an electronic device. Then, the technique which improved the flexibility by regulating the average grain size and the largest grain size of copper foil is reported (patent document 1). Moreover, the technique which improved the MIT flexibility by prescribing|regulating the relationship between plate|board thickness and breaking elongation is reported (patent document 2).

Moreover, with the miniaturization, thinness, and high performance of an electronic device, refinement|miniaturization of the circuit width and space width of an FPC (for example, about 20-30 micrometers) is also calculated|required.

Japanese Patent Laid-Open No. 2016-188415 Japanese Patent Laid-Open No. 2018-131653

However, when the circuit of the FPC is miniaturized, when the FPC is bent, repeated deformation of low strain is applied to the circuit (copper foil), the surface roughness increases, stress is concentrated in the concave portion, and there is a problem that the flexibility is reduced.

That is, when the circuit width is sufficiently wide with respect to the thickness of the copper foil, deformation in the direction parallel to the bending direction is dominant, but in the case of a fine circuit, since the (thickness/width) value of the copper foil becomes large, the width perpendicular to the bending direction Changes in direction also need to be considered. Moreover, compared with the central part in the width direction of a circuit, generally, it is thought that the edge part vicinity has less restraint from the circumference|surroundings and it is thought that it is easy to deform|transform, but in a microcircuit, the ratio of the area|region which can be considered as the edge part vicinity which deform|transforms easily increases. For the above reason, it is thought that flexibility becomes stricter when circuit width becomes narrow.

This invention was made in order to solve the said subject, and aims at provision of the copper foil for flexible printed circuit boards excellent in the flexibility after fine circuit formation, a copper clad laminated body using the same, a flexible printed circuit board, and an electronic device.

As a result of various studies, the present inventors found that the increase in the surface roughness of the copper foil (circuit) due to repeated deformation that reduces the flexibility of the fine circuit of FPC is related to the deformation rate of the final pass in the final cold rolling. and the range of surface roughness which does not reduce flexibility was prescribed|regulated.

That is, the copper foil for flexible printed circuit boards of the present invention is a copper foil containing 99.0 mass% or more of Cu and residual unavoidable impurities, and a two-layer single-sided CCL sample having a width of 12.7 mm and a length of 200 mm in which a circuit is formed from the copper foil is used. Thus, the surface roughness Ra of the circuit surface after performing IPC sliding bending 2000 times with a radius of curvature R=2.0 is 0.030 µm or more and 0.400 µm or less. However, in the two-layer single-sided CCL sample, after performing copper roughening plating on one side of the copper foil, on both sides of a polyimide film having a thickness of 25 µm, each of the two copper foils is laminated toward the copper roughened plating side, 300 It is joined at 4 MPa by a hot press at °C x 30 minutes, and the copper foil on one side is completely removed by etch-out to produce a two-layer single-sided CCL. Then, on the copper foil side surface of the two-layer single-sided CCL sample, circuits extending along the rolling direction with a line width of 25 µm are etched to form eight circuits and a circuit interval of 125 µm.

Copper foil for flexible printed circuit boards of this invention WHEREIN: It is preferable that surface roughness Ra of the said circuit surface before performing the said IPC sliding bending is 0.010 micrometer or more and 0.200 micrometer or less.

It is preferable that the copper foil for flexible printed circuit boards of this invention contains the tough-pitch copper standardized by JIS-H3100 (C1100), or the oxygen-free copper of JIS-H3100 (C1020).

The copper foil for flexible printed circuit boards of this invention is 0.7 mass % in total of at least 1 type, or 2 or more types selected from the group which consists of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb as an additive element further. It is preferable to contain the following.

The copper clad laminate of this invention laminates|stacks the said copper foil for flexible printed circuit boards, and a resin layer.

The flexible printed circuit board of this invention forms a circuit in the said copper foil in the said copper clad laminated body.

The electronic device of this invention is made|formed using the said flexible printed circuit board.

ADVANTAGE OF THE INVENTION According to this invention, the copper foil for flexible printed circuit boards excellent in the flexibility after microcircuit formation is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the bending test method.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of the copper foil which concerns on this invention is described. In addition, in this invention, unless otherwise indicated, % shall represent mass %.

First, the evaluation of flexibility after formation of a fine circuit will be described.

As described above, in the case of a microcircuit, since the (thickness/width) value of the copper foil increases, the deformation in the width direction perpendicular to the bending direction increases, and the ratio of the end region of the circuit that is easily deformed increases. As a result, when repeated deformation of low strain is applied to the circuit (copper foil), the surface roughness increases, stress is concentrated in the concave portion, and the flexibility decreases.

Then, a microcircuit was simulated, and the surface roughness of the circuit (copper foil) before and after performing a predetermined bending test was measured, and Ra after bending was prescribed|regulated to 0.030 micrometer or more and 0.400 micrometer or less.

By managing Ra after bending in the said range, the stress applied to the surface can be disperse|distributed uniformly, and the outstanding flexibility is expressed.

When Ra after bending is less than 0.030 µm, the surface is too smooth, stress is concentrated on small undulations (oil pits, etc.) existing before deformation, and the flexibility is rather reduced. When Ra after bending exceeds 0.400 µm, the surface roughness becomes large, stress is concentrated in the concave portion, and the flexibility decreases.

Moreover, it is preferable that Ra before bending is 0.010 micrometer or more and 0.200 micrometer or less.

When the Ra before bending is less than 0.010 µm, the Ra after bending tends to be less than 0.030 µm, and when Ra before bending exceeds 0.200 µm, the Ra after bending also easily exceeds 0.400 µm.

A simulated microcircuit is produced as follows. First, copper roughening plating is performed on one side of the copper foil after final cold rolling, and laminating on both sides of a polyimide film (25 µm in thickness) on the roughened plating side of the copper foil, respectively, bonding by hot press (4 MPa), three-layer double-sided copper foil Obtain a CCL sample. In addition, heat treatment for 300°C x 30 minutes is applied at the time of lamination of the film. Moreover, among the double-sided copper foil CCL samples of three layers, copper foil of one side is completely removed by etch-out, and two-layer single-sided CCL is produced.

The copper foil which concerns on this invention is used for a flexible printed circuit board, CCL which laminated|stacked copper foil and resin in that case performs the heat processing for hardening resin at 200-400 degreeC. This heat treatment was assumed, and it was set as 300 degreeC x 30 minutes.

On the copper foil side surface of the two-layer single-sided CCL sample, circuits extending along the rolling direction with a line width of 25 µm were etched to form eight circuits and a circuit interval of 125 µm. The etching factor EF of the circuit is set to 4.0 or more.

In addition, as for rough plating, if peeling of copper foil and resin can be prevented during a bending test, although plating conditions in particular are not limited, For example, the following are illustrated as what is generally used in FPC use, for example. Plating bath composition: Cu 15g/L, Co 8.5g/L, Ni 8.6g/L, plating solution pH: 2.5, plating temperature: 38°C, current density: 20A/dm2, plating time: 2.0 seconds

The etching liquid may be, for example, CuCl ₂ -2H ₂ O: 3 mol/L, HCl: 4 mol/L, and the etching temperature may be adjusted, for example, at 50° C. and the etching time so that the circuit width is 25 µm.

And with respect to the CCL in which this circuit was formed, after performing sliding bending 2000 times with the IPC (American Printed Circuit Manufacturers Association) bending test apparatus shown in FIG. 1, using a laser microscope, the surface roughness of the direction parallel to the circuit direction Measure Ra.

This device has a structure in which the vibration transmitting member 3 is coupled to the oscillation driving body 4 , and the FPC 1 is a total of a screw 2 indicated by an arrow and a tip of the vibration transmitting member 3 . It is fixed to the device at 4 points. When the vibration transmitting member 3 is driven up and down, the middle portion of the FPC 1 is bent in a hairpin shape with a predetermined radius of curvature r. In this test, bending is repeated under the following conditions.

In addition, the test conditions are as follows: specimen width: 12.7 mm, specimen length: 200 mm, specimen collection direction: sampled so that the longitudinal direction of the specimen is parallel to the rolling direction, radius of curvature r: 2 mm, vibration stroke: 20 mm, vibration speed : 100 times/min, bending direction: FPC (1) with copper foil inside.

Surface roughness (arithmetic mean roughness) Ra is a centerline average roughness computed according to JIS B0601-1994 from the uneven profile of the surface of copper foil.

For the measurement of surface roughness Ra, a shape analysis laser microscope VK-X1050 manufactured by Keyence Corporation can be used. As the measurement conditions, 10 line roughness analyzes are performed parallel to the circuit direction under the conditions of objective lens: 50 times and intermediate lens: 24 times, and the average value is adopted as the surface roughness Ra. The interval of line analysis is adjusted at equal intervals so that the interval between the 1st and 10th lines becomes 80% or more of the width of the circuit surface.

<Composition>

The copper foil which concerns on this invention contains 99.0 mass % or more of Cu, and remainder unavoidable impurities.

In addition, as an additive element, 0.7 mass % or less of at least one or two or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb in total with respect to the composition is contained. , it is possible to suppress the increase in surface roughness due to repeated deformation by refining the recrystallized grains.

Since the said additive element increases the frequency of entanglement of dislocations at the time of cold rolling, it can refine|miniaturize a recrystallized grain.

When the said additive element is contained exceeding 0.7 mass % in total, electrical conductivity will fall and since it may not be suitable as copper foil for flexible substrates, 0.7 mass % was made into the upper limit. The lower limit of the content of the additional element is not particularly limited. For example, since it is industrially difficult to control the content of each element to be smaller than 0.0005 mass%, the lower limit of the content of each element may be set to 0.0005 mass%.

The copper foil according to the present invention may have a composition containing tough pitch copper (TPC) standardized in JIS-H3100 (C1100) or oxygen-free copper (OFC) of JIS-H3100 (C1020).

Moreover, it is good also as a composition formed by containing P with respect to the said TPC or OFC.

The copper foil of this invention can be manufactured as follows, for example. First, after melt|dissolving and casting a copper ingot, foil can be manufactured by performing hot rolling, performing cold rolling and annealing, and performing final cold rolling.

Here, if the deformation rate of the last pass in final cold rolling is raised, increase in the surface roughness of the circuit (copper foil) by repeated deformation can be suppressed. For this reason, when a deformation rate is enlarged, compared with the inside of copper foil, large deformation|transformation will concentrate and accumulate|store on the rolling surface of copper foil. As a result, at the time of recrystallization of the copper foil, fine grains are arranged in a random orientation on the rolling surface, and the deformation due to repeated deformation does not concentrate on local areas, thereby suppressing roughness of the surface and maintaining smoothness. The deformation rate of the final pass in the final cold rolling ^{is preferably 7.4×10 3} (1/s) or more. However, if the strain rate is too large, the copper foil may break during rolling and there is a risk of lowering the manufacturability. Therefore, 9.5×10 ³ (1/s) may be set as the upper limit of the final pass strain rate.

<Copper-clad laminate and flexible printed circuit board>

In addition, (1) casting a resin precursor (for example, a polyimide precursor called varnish) to the copper foil of the present invention and applying heat to polymerize it, (2) using a thermoplastic adhesive of the same type as the base film By laminating to the copper foil of , the copper clad laminate (CCL) which consists of two layers of copper foil and a resin base material is obtained. Furthermore, by laminating the base film to which the adhesive agent was applied to the copper foil of this invention, the copper clad laminated body (CCL) which consists of three layers of copper foil, a resin base material, and the adhesive layer in between is obtained. In manufacturing these CCLs, copper foil is heat-treated and recrystallized.

A flexible printed circuit board (flexible wiring board) is obtained by forming a circuit in these using a photolithography technique, plating a circuit as needed, and laminating a coverlay film.

Therefore, the copper clad laminate of this invention laminates|stacks 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 lamination method of a resin layer and copper foil, you may apply|coat the material used as a resin layer on the surface of copper foil, and may heat-form it into a film. In addition, using a resin film as a resin layer, the following adhesive agents may be used between a resin film and copper foil, and a resin film may be thermocompression-bonded to copper foil without using an adhesive agent. However, it is preferable to use an adhesive agent from the point of not applying excess heat|fever to a resin film.

When a film is used as a resin layer, what is necessary is just to laminate|stack this film on copper foil through an adhesive bond layer. In this case, it is preferable to use an adhesive of the same component as the film. For example, when using a polyimide film as a resin layer, it is preferable to use a polyimide-type adhesive agent also for an adhesive bond layer. In addition, the polyimide adhesive used here refers to the adhesive agent containing an imide bond, and polyetherimide etc. are included.

In addition, this invention is not limited to the said embodiment. In addition, as long as the effect of this invention is exhibited, the copper alloy in the said embodiment may contain another component. Moreover, an electrolytic copper foil may be sufficient.

For example, you may give the surface of copper foil surface treatment by a roughening process, a rust prevention process, a heat-resistant process, or these combination.

<Example>

Next, although an Example demonstrates this invention further in detail, this invention is not limited to these. Each of the elements shown in Table 1 was added to the copper to give the composition shown in Table 1, and cast in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. This ingot was subjected to homogenization annealing at 900°C and hot rolling, followed by repeating cold rolling and recrystallization annealing, and further performing final recrystallization annealing and final cold rolling to obtain a rolled copper foil.

CCL was produced in the same manner as described above for the obtained rolled copper foil.

<Surface roughness of copper foil (circuit) before and after bending test>

Measurement was carried out as described above.

<Bending fatigue life>

With respect to the sample produced in the same way as the CCL (two-layer single-sided CCL) having completed the circuit for the bending test described above, in the IPC sliding bending test, the initial electrical resistance value flowing through both ends of the circuit increased by more than 10% was taken as the flex fatigue life. The measurement conditions for determining the flexural fatigue life are as follows: specimen width: 12.7 mm, specimen length: 200 mm, specimen collection direction: specimen so that the longitudinal direction of the specimen is parallel to the rolling direction, radius of curvature r: 5 mm, vibration stroke : 20 mm, vibration speed: 1500 times/min, bending direction: FPC (two-layer single-sided CCL) (1) with copper foil inside.

In addition, when the flexural fatigue life is 80,000 or more, it is said to have excellent flexibility, and when the flexural fatigue life is less than 80,000 times, the flexibility is evaluated as inferior.

The obtained results are shown in Table 1.

As is clear from Table 1, in the case of each Example in which the surface roughness Ra of the circuit surface after a bending test is 0.030 micrometer or more and 0.400 micrometer or less, it became the thing excellent in bending fatigue life.

In the case of Comparative Example 1 in which Ra was less than 0.030 μm, the flexural fatigue life was deteriorated. This is thought to be because the surface was too smooth, and stress concentrated on small undulations (oil pits, etc.) that existed before deformation.

In the case of Comparative Examples 2 to 6 in which Ra exceeded 0.400 μm, the flexural fatigue life was deteriorated. Moreover, in the case of Comparative Examples 2-6, the deformation rate of the last pass in the final cold rolling was lower than that of Example, and it is thought that deformation|transformation was not fully accumulated in the rolling surface.

Claims (8)

It is copper foil containing 99.0 mass % or more of Cu, remainder unavoidable impurities,
Using a two-layer single-sided CCL sample having a width of 12.7 mm and a length of 200 mm in which a circuit is formed from the copper foil, the surface roughness Ra of the circuit surface after performing IPC sliding bending 2000 times with a radius of curvature R=2.0 is 0.030 µm or more The copper foil for flexible printed circuit boards which is 0.400 micrometer or less.
However, in the two-layer single-sided CCL sample, after performing copper roughening plating on one side of the copper foil, on both sides of a polyimide film having a thickness of 25 µm, each of the two copper foils is laminated toward the copper roughened plating side, 300 It is joined at 4 MPa by a hot press at °C x 30 minutes, and the copper foil on one side is completely removed by etch-out to produce a two-layer single-sided CCL. Then, on the copper foil side surface of the two-layer single-sided CCL sample, circuits extending along the rolling direction with a line width of 25 µm are etched to form eight circuits and a circuit interval of 125 µm. The copper foil for flexible printed circuit boards of Claim 1 whose surface roughness Ra of the said circuit surface before performing the said IPC sliding bending is 0.010 micrometer or more and 0.200 micrometer or less. The copper foil for flexible printed circuit boards of Claim 1 containing the tough pitch copper standardized by JIS-H3100 (C1100), or the oxygen-free copper of JIS-H3100 (C1020). The additive element according to claim 1 or 2, wherein at least one or two or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb is 0.7 in total. The copper foil for flexible printed circuit boards which contains not more than mass %. The copper clad laminate formed by laminating|stacking the copper foil for flexible printed circuit boards in any one of Claims 1-3, and a resin layer. The flexible printed circuit board which forms a circuit in the said copper foil in the copper clad laminated body of Claim 5. The electronic device using the flexible printed circuit board of Claim 6. The strain rate of the final pass in the final cold rolling of the copper foil is 7.4×10 ³ (1/s) or more and 9.5×10 ³ (1/s) or less. , copper foil for flexible printed circuit boards.

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