KR20200141427A - Copper foil for flexible printed circuit, and copper clad laminate, flexible printed circuit and electronic device using copper foil - Google Patents

Abstract

The present invention provides a copper foil for a flexible printed circuit with an excellent etching property and a copper foil laminate, a flexible printed circuit, and an electronic device using the copper foil. The copper foil comprises: at least 99.0 wt% of Cu; and a remaining of inevitable impurities. The copper foil has 0.5-4.0 μm of an average crystal grain size, an X-ray diffraction intensity of a surface of the copper foil indicated as I (220)/I_0 (220), 1.3-7.0 of an aggregation degree, and at least 80% of conductivity.

Description

Copper foil for a flexible printed circuit board, a copper clad laminate using the same, a flexible printed circuit board, and an electronic device TECHNICAL FIELD TECHNICAL FIELD [0002] TECHNICAL FIELD [0002]

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

Flexible printed circuit boards (flexible wiring boards, hereinafter referred to as "FPC") are widely used in bent portions and movable portions of electronic circuits because they have flexibility. For example, FPCs are used for moving parts of disk-related devices such as HDD, DVD, and CD-ROM, and bending parts of foldable mobile phones.

In the 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 top is covered with a resin layer called coverlay. In the previous step of laminating the coverlay, etching of the surface of the copper foil is performed as part of a surface modification process for improving the adhesion between the copper foil and the coverlay. Further, in order to reduce the thickness of the copper foil and improve the flexibility, thickness reduction etching is sometimes performed.

By the way, as electronic devices become smaller, thinner, and higher in performance, miniaturization of the circuit width and space width of the FPC (for example, about 20 to 30 μm) is required. If the circuit of the FPC is miniaturized, there is a problem that the etching factor and circuit linearity tend to deteriorate when a circuit is formed by etching (Patent Documents 1 and 2).

Japanese Patent Application Publication No. 2017-141501 Japanese Patent Application Publication No. 2017-179390

However, in the prior art, while optimizing the average crystal grain size and the like as a measure to improve the etching property, there is room for improvement in the etching property in the formation of a fine circuit.

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 having excellent etching properties, a copper clad laminate using the same, a flexible printed circuit board, and an electronic device.

As a result of various investigations by the present inventors, it was found that the etching rate in the <220> orientation was large. In particular, it has been considered that there is no difference in the etching rate depending on the orientation in the etching with the cupric chloride etchant. Therefore, it succeeded in further improving the etching property (especially soft etching property and etching factor) by increasing the number of crystal grains in the <220> orientation.

That is, the copper foil for a flexible printed circuit of the present invention is a rolled copper foil composed of 99.0% by mass or more of Cu and the remainder of inevitable impurities, and has an average crystal grain size of 0.5 to 4.0 µm, and the X-ray diffraction intensity I(220)/I on the surface of the copper foil _The degree of aggregation represented by ₀ (220) is 1.3 or more and less than 7.0, and the electrical conductivity is 80% or more.

The copper foil for flexible printed circuit boards of the present invention is preferably made of tough pitch copper standardized in JIS-H3100 (C1100) or oxygen-free copper made in JIS-H3100 (C1020).

The copper foil for a flexible printed circuit of the present invention further contains at least one or two or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb as an additive element in total of 0.7 It is preferable to contain it by mass% or less.

In the copper foil for a flexible printed circuit of the present invention, after annealing at 300° C. x 30 min (however, after annealing at a heating rate of 100° C./min to 300° C./min), the average crystal grain size is 0.5 to 4.0 μm, and the aggregate degree is 1.3 or more. It is preferable that it is less than 7.0 and the said electrical conductivity is 80% or more.

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

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

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

According to the present invention, a copper foil for a flexible printed circuit board excellent in etching properties (especially soft etching properties and etching factor) can be obtained.

1 is a diagram showing a method of measuring an etching factor EF.
2 is another diagram showing a method of measuring an etching factor EF.

Hereinafter, an embodiment of the copper foil according to the present invention will be described. In addition, in the present invention,% is assumed to represent mass% unless otherwise specified.

First, the soft etching property in the etching property and the etching factor EF will be described.

Soft etchability is an index indicating the accuracy of the circuit by etching due to the adhesion between the surface of the copper foil and the resist. The better the adhesion of the resist is, the more the resist follows the surface of the copper foil, the more the etchant enters between the two and part of the circuit is damaged. The problem is suppressed, a uniform circuit pattern is obtained over the entire copper foil, and the yield is improved.

The etching factor EF is an index of the cross-sectional shape of the circuit formed by etching, and the higher the EF is, the sharper the cross section of the circuit formed by etching becomes, and thus the accuracy of the circuit pattern is improved when the circuit is miniaturized.

Even if the soft etching property is good, when the etching factor EF is inferior, a uniform circuit pattern is obtained on the entire surface of the copper foil and the yield is improved, but when the circuit is refined, the accuracy of the circuit pattern is lowered.

Conversely, even if the etching factor EF is good, if the soft etching property is inferior, the accuracy of the circuit pattern is improved when the circuit is refined, but a part of the circuit is damaged (because the etching liquid easily penetrates between the copper foil surface and the resist). Occurs, and a uniform circuit pattern cannot be obtained on the entire surface of the copper foil, resulting in a decrease in yield.

<Composition>

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

In the embodiment of the present invention, by miniaturizing the crystal grain size before the final cold rolling of the copper foil, the accumulation of dislocations of the copper foil during cold rolling is promoted, and the recrystallized grains become fine during recrystallization. In addition, if the deformation rate is extremely high in the final pass of cold rolling, the recrystallized grains are oriented in a specific orientation at the time of recrystallization, that is, the "200" plane aggregation degree is suppressed, and the "220" plane aggregation degree can be increased. Etchability is improved.

In addition, in order to refine the crystal grains after recrystallization of the copper foil, it is preferable to set the crystal grain size before the final cold rolling performed after the final annealing into 5 µm or more and 20 µm or less in the entire process of repeating annealing and rolling.

Specifically, the particle diameter can be controlled by adjusting the temperature of the final annealing and the degree of workability of cold rolling before the final annealing. The temperature of the final annealing also varies depending on the production conditions of the copper foil, and is not limited, but may be, for example, 300 to 400°C. In addition, the working degree of cold rolling before final annealing is also not limited, but, for example, the working degree η may be 1.6 to 3.0.

In the workability η, the thickness of the material immediately before cold rolling before the final annealing is A0, the thickness of the material immediately after cold rolling before the final annealing is A1, and is represented by η = ln (A0/A1).

When the crystal grain size before the final cold rolling is more than 20 µm, the entanglement of dislocations at the time of processing becomes small, and the accumulation of strain decreases, so that after recrystallization, the strain is not released and the refinement of the crystal grains tends to be insufficient. When the crystal grain size before the final cold rolling is less than 5 µm, entanglement of dislocations during processing occurs in almost the entire region of the copper foil, no further entanglement occurs, and the effect of recrystallization of recrystallized grains at the time of recrystallization of the copper foil is saturated. Therefore, the lower limit of the grain size before the final cold rolling was set to 5 µm.

In addition, as an additive element, if at least one or two or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb are contained in a total of 0.7% by mass or less with respect to the above composition, recrystallization The sizing can be refined.

The additive element increases the frequency of entanglement of dislocations during cold rolling, so that recrystallized grains can be refined.

When the total amount of the additional elements exceeds 0.7% by mass, the electrical conductivity is lowered, which may not be suitable as a copper foil for flexible substrates. Therefore, 0.7% by mass was used as the upper limit. The lower limit of the content of the additional element is not particularly limited, but it is industrially difficult to control the content of each element to be less than 0.0005% by mass. Therefore, the lower limit of the content of each element may be set to 0.0005% by mass.

The copper foil according to the present invention may be a composition made of 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 which contains P with respect to said TPC or OFC.

<Average grain size>

The average crystal grain size of the copper foil is 0.5 to 4.0 µm. If the average grain size is less than 0.5 µm, the strength becomes too high, the bending stiffness becomes large, and the spring back becomes large, which is not suitable for the use of a flexible printed circuit board. When the average grain size exceeds 4.0 µm, soft etching property deteriorates.

The measurement of the average crystal grain size is performed by observing three or more fields of view on the surface of the foil in a field of view of 100 µm × 100 µm in order to avoid errors. Observation of the foil surface can use a SIM (Scanning Ion Microscope) or SEM (Scanning Electron Microscope), and obtain an average crystal grain size based on JIS-H0501. However, twin crystals are measured by considering them as different crystal grains.

＜Community chart＞

The degree of aggregation represented by the X-ray diffraction intensity I(220)/I ₀ (220) on the surface of the copper foil is 1.3 or more and less than 7.0.

When the degree of aggregation is less than 1.3, the etching rate in the thickness direction decreases, and the etching factor to be described later of the copper foil decreases. In the case of the strain rate at which the degree of aggregation is 7.0 or more, although the etching factor is good, the shape of the rolled copper foil deteriorates, and it may become difficult to use as a copper foil for FPC.

The degree of aggregation is measured as follows. First, the X-ray diffraction intensity of the "220" plane with respect to the rolled surface of the copper foil is measured to be I(220).

In addition, under the same conditions, the net copper powder (325 mesh (JIS Z8801, purity: 99.5%), after 1 hours heating at 300 ℃ in a hydrogen gas stream using) I ₀ by measuring the X-ray diffraction intensity of the {220} for Let it be (220).

And, it is standardized as follows.

·Attachment drawing on page 220: I(220)/I ₀ (220)

The measurement conditions for X-ray diffraction are as follows.

· Incident X-ray source: Co,

· Acceleration voltage: 25 kV,

Tube current: 20 mA,

· Divergence slit: 1 degree,

· Scattering slit: 1 degree,

· Receiving slit: 0.3 mm,

· Divergence length limiting slit: 10 mm,

・Monochrome light receiving slit 0.8 mm

<Heat treatment at 300°C for 30 minutes>

The copper foil according to the present invention is used for a flexible printed circuit board, and in that case, the CCL obtained by laminating the copper foil and the resin is subjected to heat treatment for curing the resin at 200 to 400°C, so the average crystal grain size and I(220) /I ₀ (220) changes the aggregation.

Therefore, before and after lamination with the resin, the average grain size and degree of aggregation are changed. Therefore, the copper foil for flexible printed circuit boards according to claim 1 of the present application stipulates a copper foil in a state that has undergone heat treatment when it becomes a copper clad laminate after lamination with resin. In short, since it has already undergone heat treatment, it is a copper foil in a state in which no new heat treatment is performed.

On the other hand, the copper foil for a flexible printed circuit according to claim 4 of the present application is in a state when the above-described heat treatment is performed on the copper foil before lamination with resin (for example, a copper foil coil before heat treatment is delivered to a CCL manufacturing plant and laminated on CCL. When heated) is specified. This heat treatment at 300° C. for 30 minutes mimics the temperature conditions for curing the resin at the time of lamination of CCL. In addition, in order to prevent oxidation of the copper foil surface due to heat treatment, the atmosphere of the heat treatment is preferably a reducing or non-oxidizing atmosphere, for example, a vacuum atmosphere, or argon, nitrogen, hydrogen, carbon monoxide, etc., or a mixed gas thereof What is necessary is just to set it as an atmosphere made up of. The rate of temperature increase may be between 100 and 300°C/min.

The copper foil of this invention can be manufactured as follows, for example. First, after melting and casting the copper ingot, hot rolling, cold rolling and annealing, preferably recrystallization annealing at the beginning of cold rolling, and final recrystallization annealing and final cold rolling. You can make a gourd.

By adjusting the total workability η of cold rolling, the average grain size before the final cold rolling and after the final recrystallization annealing, and the deformation rate of the final pass before the final cold rolling, the average grain size and the degree of aggregation can be controlled.

If the total machining degree η is 6.10 or more, the degree of aggregation represented by I(220)/I ₀ (220) can be increased more reliably.

If the average crystal grain size before the final cold rolling and after the final recrystallization annealing is 5 to 20 µm, the average crystal grain size of the product can be reliably set to 0.5 to 4.0 µm.

If the deformation rate of the final pass before the final cold rolling is 1000 (/sec) or more, the degree of aggregation can be increased more reliably.

<Copper clad laminate and flexible printed circuit board>

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

A flexible printed circuit board (flexible wiring board) is obtained by forming a circuit on them using a photolithography technique, plating the circuit as necessary, and laminating a coverlay film.

Therefore, the copper clad laminate of the present invention is formed by laminating a copper foil and a resin layer. Further, 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), but are not limited thereto. Moreover, you may use these resin films as a resin layer.

As a lamination method of a resin layer and a copper foil, you may apply a material which becomes a resin layer to the surface of a copper foil, and you may heat-form. Moreover, a resin film may be used as a resin layer, the following adhesive may be used between a resin film and a copper foil, and a resin film may be thermocompressed to copper foil without using an adhesive. However, it is preferable to use an adhesive from the point that extra heat is not applied to the resin film.

When a film is used as the resin layer, this film may be laminated to copper foil through an adhesive layer. In this case, it is preferable to use an adhesive of the same component as a film. For example, when using a polyimide film as a resin layer, it is preferable to use a polyimide type adhesive also for an adhesive layer. In addition, the polyimide adhesive mentioned here refers to an adhesive containing an imide bond, and polyetherimide etc. are also contained.

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

For example, the surface of the copper foil may be subjected to roughening treatment, rust prevention treatment, heat resistance 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. Each element shown in Table 1 was added to the electrical copper, and it was set as the composition shown in Table 1, and it cast in Ar atmosphere, and obtained the ingot. The oxygen content in the ingot was less than 15 ppm. After homogenizing annealing this ingot at 900°C, hot rolling, cold rolling and recrystallization annealing were repeated, and final recrystallization annealing and final cold rolling were further performed to obtain a rolled copper foil.

The obtained rolled copper foil was subjected to heat treatment at 300°C for 30 minutes in an argon atmosphere to obtain a copper foil sample. The copper foil after heat treatment is modeled after being subjected to heat treatment at the time of lamination of CCL.

<Evaluation of copper foil sample>

1. Conductivity

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

If the conductivity is greater than 80% IACS, the conductivity is good.

2. Assembly diagram

For each copper foil sample after the heat treatment, the degree of aggregation was measured by the method described above using an X-ray diffraction apparatus (RINT-2500: manufactured by Rigaku Electric Corporation). In addition to the aggregate diagram represented by I(220)/I ₀ (220), I(200)/I ₀ (200) was also obtained by measuring the X-ray diffraction intensity of the plane {200} in the same manner.

3. Etch Factor EF

Copper foil and resin were bonded together, and a dry film resist was laminated on the copper foil surface after that, and the circuit pattern of strip shape (L/S=25/25) was formed on the resist. Etching was performed by changing the etching time by spray etching of cupric chloride etchant.

Although there are various methods of measuring EF, in the present invention, the etching rate in the depth direction relative to the width direction is evaluated as the most common method for obtaining the etching factor EF. In the present invention, measurement is performed as shown in FIGS. 1 and 2. In addition, the following equation (1) pays attention only to the etching rate in the depth direction and the width direction, and does not take into account the etching rate in the oblique direction.

As shown in FIG. 1, EF is calculated|required by following formula (1) from the width direction and the depth direction etching rate of the cross section of one circuit.

EF = etching rate in the depth direction / etching rate in the width direction (1)

However, since it is difficult to measure the etching rate itself, measure the width and depth of the circuit when the etching time is changed, respectively. And, as shown in Fig. 2, each data is plotted with the horizontal axis as the width of the circuit and the vertical axis as the depth of the circuit, and approximated by the following equation (2). In short, the slope of the graph in Fig. 2 is obtained from the approximation of the first order by the least squares method, and is set as EF.

EF ≒ time change of depth / (time change of width / 2) = 2 × time change of depth / time change of width (2)

Here, the coefficient &quot;2&quot; of the formula (2) is because the etching in the width direction proceeds to both the left and right sides of Fig. 1, so it is necessary to be halved.

And, according to the value of EF, it evaluated with the following index. If the evaluation is ◎ or ○, it is good.

◎: EF is 1.4 or more

○: EF is 1.1 or more and less than 1.4

×: EF is less than 1.1

4. Soft Etchability

For each copper foil sample after the heat treatment, the surface was soft etched under the following conditions. As an index to evaluate the soft etching property, the arithmetic average roughness Ra based on JIS-B0601 (2001) of the copper foil surface after soft etching was measured.

As the soft etching conditions, soft etching to impart adhesion between the copper foil and the resist was simulated, and the copper foil was immersed for 420 seconds in an aqueous solution (liquid temperature of 25°C) with a sodium persulfate concentration of 100 g/L and a hydrogen peroxide concentration of 35 g/L. I decided to do it. When the arithmetic mean roughness Ra was 0.2 µm or less, the soft etchability was good ((circle)), and when the arithmetic average roughness Ra exceeded 0.2 µm, the soft etchability was poor (x).

If the resist follows the copper foil surface well after soft etching, adhesion is excellent, the accuracy of the circuit pattern is improved, and the soft etching property is improved. When Ra exceeds 0.2 µm, it is difficult for the resist to follow the copper foil surface, and a gap is liable to occur between the resist and the copper foil surface. And, by invading the etchant into the gap, the precision at the time of forming the circuit pattern is lowered.

5. Crystal grain size

For each copper foil sample after the heat treatment, the rolled surface was observed using a SEM (Scanning Electron Microscope), and the average particle diameter was calculated based on JIS H 0501. However, the twin crystals were respectively regarded as different crystal grains and measured. The measurement area was set to 400 µm x 400 µm in a cross section parallel to the rolling direction.

The obtained results are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, in the case of each example in which the crystal grain size is 0.5 to 4.0 µm, and the degree of aggregation represented by I(220)/I ₀ (220) is 1.3 or more and less than 7.0, etching The factor and soft etchability were both excellent. Thereby, a uniform circuit pattern is obtained over the entire copper foil, the yield is improved, and when the circuit is further refined, the accuracy of the circuit pattern is improved.

In the case of Comparative Examples 1 to 4 in which the deformation rate of the final pass of the final cold rolling was less than 1000 (s ⁻¹ ), the degree of aggregation was less than 1.3, and the soft etching property was good, but the etching factor was lowered. Therefore, when the circuit is miniaturized, the accuracy of the circuit pattern is lowered.

In the case of Comparative Example 5 in which the average crystal grain diameter before the final cold rolling and after the final recrystallization annealing exceeded 20 µm, the average crystal grain size of the product exceeded 4.0 µm and the etching factor was good, but the soft etching property was inferior. . Therefore, a uniform circuit pattern cannot be obtained on the entire surface of the copper foil, and the yield decreases.

In the case of Comparative Example 6 in which the total working degree was less than 6.10, the degree of aggregation was less than 1.3, and the etching factor was lowered.

In the case of Comparative Example 7, in which the total content of the additional elements exceeded 0.7% by mass, the conductivity was less than 80%, and the conductivity was inferior.

Claims (7)

A copper foil composed of 99.0% by mass or more of Cu and the remainder of inevitable impurities,
The average crystal grain size is 0.5 to 4.0 μm, the degree of aggregation represented by the X-ray diffraction intensity I(220)/I ₀ (220) on the surface of the copper foil is 1.3 or more and less than 7.0,
Copper foil for flexible printed circuit boards having a conductivity of 80% or more. The method of claim 1,
Copper foil for flexible printed circuit boards made of tough pitch copper according to JIS-H3100 (C1100) or oxygen-free copper according to JIS-H3100 (C1020). The method of claim 1,
In addition, for flexible printed circuit boards containing 0.7% by mass or less in total of at least one or two or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb as additive elements Copper foil. The method of claim 1,
A flexible print having the average crystal grain size of 0.5 to 4.0 µm, the aggregation degree of 1.3 to less than 7.0, and the conductivity of 80% or more after annealing at 300°C x 30 min (however, a heating rate of 100°C/min to 300°C/min) Copper foil for substrate. A copper clad laminate obtained by laminating the copper foil for flexible printed circuit boards according to any one of claims 1 to 4 and a resin layer. A flexible printed circuit board formed by forming a circuit on the copper foil in the copper clad laminate according to claim 5. An electronic device using the flexible printed circuit board according to claim 6.

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