KR20190089732A - Copper foil for flexible printed circuit, and copper clad laminate, flexible printed circuit and electronic device using copper foil - Google Patents

Abstract

Provided are a copper foil for a flexible printed circuit board with excellent in etching property, a copper clad laminated body using the same, a flexible printed circuit board, and an electronic device. The present invention relates to the copper foil for the flexible printed circuit board wherein the copper foil is composed of 99.0 mass% or more of Cu and the remaining balance consisting of unavoidable impurities, an average crystal grain size is 0.5-4.0 μm, an X-ray diffraction intensity I(220)/I_0(220) of the copper foil surface is greater than or equal to 1.3 and less than or equal to 7.0, and a conductivity is greater than or equal to 80%.

Description

Technical Field [0001] 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.

BACKGROUND ART A flexible printed circuit board (hereinafter referred to as " FPC ") is widely used for folding and moving parts of electronic circuits because of its flexibility. For example, an FPC is used in a moving part of a disk-related device such as an HDD, a DVD and a CD-ROM, or a bending 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. The surface of the copper foil is etched 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. Further, in order to reduce the thickness of the copper foil to improve the bending property, a thickness reduction etching may be performed.

[0004] Meanwhile, miniaturization (for example, about 20 to 30 [micro] m) of the circuit width and space width of the FPC has been demanded with the miniaturization, thinness and high performance of electronic devices. When the circuit of the FPC is made finer, there is a problem that the etching factor and the circuit linearity are liable to deteriorate when the circuit is formed by etching (Patent Documents 1 and 2).

Japanese Laid-Open Patent Publication No. 2017-141501 Japanese Laid-Open Patent Publication No. 2017-179390

However, in the conventional technique, as a measure for improving the etching property, the average crystal grain size and the like are optimized, but there is room for improvement in the etching property in the formation of a fine circuit.

An object of the present invention is to provide a copper foil for a flexible printed circuit board excellent in etching property, a copper clad laminate using the copper foil, a flexible printed board, and an electronic apparatus.

The inventors of the present invention have studied variously and found that the etching rate in the <220> orientation is large. In particular, it has been considered that there is no difference in etching rate due to azimuth in the etching with a cupric chloride etchant. Thus, by increasing the crystal grain orientation in the <220> orientation, the inventors succeeded in further improving the etchability (in particular, the soft etchability and the etching factor).

That is, the copper foil for a flexible printed wiring board of the present invention is a rolled copper foil comprising 99.0% by mass or more of Cu and the remainder inevitable impurities. The copper foil has an average crystal grain size of 0.5 to 4.0 占 퐉 and an X- ₀ (220) is 1.3 or more and less than 7.0, and the conductivity is 80% or more.

The copper foil for a flexible printed circuit board of the present invention is preferably made of tough pitch copper specified by JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020).

The copper foil for a flexible printed circuit board according to the present invention may further comprise at least one or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb as a total of 0.7 By mass or less.

In the copper foil for a flexible printed circuit board according to the present invention, the average crystal grain size is 0.5 to 4.0 占 퐉 and the aggregation degree is 1.3 or more after annealing at 300 占 폚 for 30 min (at a heating rate of 100 占 폚 / min to 300 占 폚 / min) 7.0, and the conductivity is preferably 80% or more.

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 forming a circuit on the copper foil in the copper clad laminate.

The electronic apparatus 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 excellent in etching property (in particular, soft etching property and etching factor).

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

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

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

The soft etchability is an index showing the accuracy of the circuit by etching caused by the adhesion of the copper foil surface and the resist. The etching solution penetrates between the resist and the copper foil surface as the resist follows the surface of the copper foil. The problem is suppressed and a uniform circuit pattern is obtained on the entire surface of the copper foil, thereby improving the yield.

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

If the etching factor EF is inferior even though the soft etching property is good, a uniform circuit pattern can be obtained on the entire surface of the copper foil and the yield is improved. However, when the circuit is made finer, the precision of the circuit pattern is lowered.

On the other hand, when the etch factor EF is good but the soft etchability is inferior, the precision of the circuit pattern is improved when the circuit is miniaturized. However, since the etchant is likely to invade between the copper foil surface and the resist, So that a uniform circuit pattern can not be obtained on the entire surface of the copper foil and the yield is lowered.

<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.

In the embodiment of the present invention, accumulation of the dislocations of the copper foil during cold rolling is promoted by making the crystal grain size before the final cold rolling of the copper foil finer, and the recrystallized phase is refined at the time of recrystallization. When the deformation speed is extremely increased in the final pass of the cold rolling, the recrystallized grains are oriented in a specific orientation at the time of recrystallization, that is, the {200} aggregation degree can be suppressed and the {220} The etching property is improved.

In order to miniaturize the crystal grains after the recrystallization of the copper foil, it is preferable to set the crystal grain size before the final cold rolling to be 5 占 퐉 or more and 20 占 퐉 or less after the final annealing in the entire process of repeating the annealing and rolling.

Specifically, the particle diameter can be controlled by adjusting the temperature of the final annealing and the degree of processing of the cold rolling before the final annealing. The temperature of the final annealing varies depending on the manufacturing conditions of the copper foil. For example, it may be 300 to 400 캜. The degree of cold rolling before final annealing is also not limited, but may be, for example, from 1.6 to 3.0.

The machinability? Is represented by? = Ln (A0 / A1), where A0 is the thickness of the material immediately before cold rolling before final annealing, and A1 is the thickness of the material immediately after cold rolling before final annealing.

If the crystal grain size before final cold rolling is more than 20 占 퐉, the dislocation of the dislocations at the time of processing becomes small and the accumulation of deformation becomes small, so that the deformation is not released after recrystallization and the grain refinement tends to become insufficient. If the crystal grain size before final cold rolling is less than 5 占 퐉, the dislocation of the dislocations at the time of processing occurs in almost the entire region of the copper foil, no further tangling occurs, and the effect of refining the recrystallized copper foil at the time of recrystallization of the copper foil is saturated. Therefore, the lower limit of the crystal grain size before final cold rolling was set to 5 탆.

When the total content of the additive element is 0.7% by mass or less in total of at least one or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb, The sizing can be miniaturized.

Since the added element increases the frequency of entanglement during cold rolling, the recrystallized grains can be made finer.

When the total of the above-mentioned additional elements is contained in excess of 0.7 mass%, the conductivity is lowered and it may not be suitable as a copper foil for a flexible substrate, so that the upper limit is set to 0.7 mass%. The lower limit of the content of the added element is not particularly limited. For example, it is industrially difficult to control the content of the added element to less than 0.0005% by mass, so that 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 comprising tough pitch copper (TPC) specified by JIS-H3100 (C1100) or oxygen free copper (OFC) of JIS-H3100 (C1020).

The TPC or OFC may be a composition containing P.

&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 springback becomes large, which is not suitable for use in a flexible printed board. If the average crystal grain size exceeds 4.0 占 퐉, soft etchability deteriorates.

In order to avoid an error, the average crystal grain size is measured by observing the surface of the foil with a field of view of 100 占 퐉 占 100 占 퐉 or more over three fields. The surface of the foil can be observed using an SIM (Scanning Ion Microscope) or an SEM (Scanning Electron Microscope), and the average crystal grain size can be determined based on JIS-H0501. However, twin crystals are regarded as different crystal grains and are measured.

<Set diagram>

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

If the degree of aggregation is less than 1.3, the etching rate in the thickness direction becomes smaller, and the etching factor, which will be described later, of the copper foil decreases. In the case of a deformation rate at which the degree of aggregation is 7.0 or more, although the etching factor is satisfactory, the shape of the rolled copper foil becomes poor and it may be difficult to use the copper foil for FPC.

The degree of aggregation is measured as follows. First, the X-ray diffraction intensity of the {220} plane is measured on the rolled surface of the copper foil to obtain 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 (220).

Then, standardize as follows.

(220) plane aggregation degree: I (220) / I ₀ (220)

The X-ray diffraction measurement conditions are as follows.

· Incident X source: Co,

· Acceleration voltage: 25 kV,

· Tube current: 20 mA,

· Divergent slit: 1 degree,

Scattering slit: 1 degree,

Receiving slit: 0.3 mm,

· Divergent vertical limit slit: 10 mm,

· Monochrome receiving slit 0.8 mm

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

Since the copper foil according to the present invention is used in a flexible printed circuit board and the CCL obtained by laminating the copper foil and the resin at this time is subjected to a heat treatment for curing the resin at 200 to 400 ° C, / I ₀ (220) is changed.

Therefore, before and after lamination with the resin, the average crystal grain size and the degree of aggregation change. Thus, the copper foil for a flexible printed circuit according to claim 1 of the present application defines a copper foil that has undergone a heat treatment when the copper foil is laminated with a resin. In short, it is a copper foil in a state in which a new heat treatment is not performed because it has already been subjected to a heat treatment.

On the other hand, in the copper foil for a flexible printed circuit according to claim 4 of the present application, when the copper foil before lamination with the resin is subjected to the heat treatment (for example, the copper foil before the heat treatment is delivered to the CCL manufacturing plant, (I.e., a heated state at the time when it is heated). The heat treatment at 300 DEG C for 30 minutes is based on a temperature condition in which the resin is subjected to a curing heat treatment at the time of CCL lamination. In order to prevent oxidation of the surface of the copper foil by the heat treatment, the atmosphere of the heat treatment is preferably a reducing or non-oxidizing atmosphere. For example, a vacuum atmosphere or a mixed gas of argon, nitrogen, hydrogen, carbon monoxide, And the like. The temperature raising rate may be between 100 and 300 캜 / min.

The copper foil of the present invention can be produced, for example, as follows. First, the ingot of copper is melted and cast, then hot-rolled, cold-rolled and annealed, preferably subjected to recrystallization annealing at the beginning of cold-rolling, and finally subjected to final recrystallization annealing and final cold rolling Foil can be produced.

The average grain size and the degree of aggregation can be controlled by adjusting the total machinability? Of the cold rolling, the average crystal 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.

When the total process degree eta is set to 6.10 or more, the degree of aggregation represented by I (220) / I ₀ (220) can be more reliably increased.

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

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

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

(1) casting a resin precursor (for example, a polyimide precursor called a varnish) to polymerize by heating; (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, by laminating a base film coated with an adhesive on a copper foil of the present invention, a copper clad laminate (CCL) composed of three layers of a copper foil, a resin base material and an adhesive layer therebetween is obtained. The copper foil is heat-treated and recrystallized during the production of CCL.

A circuit is formed on these by a photolithography technique, 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. Further, 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). These resin films may be used as the resin layer.

As a method for laminating the resin layer and the copper foil, a material for forming a resin layer may be coated on the surface of the copper foil to form a film by heating. 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 having the same composition 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. The polyimide adhesive referred to herein refers to an adhesive containing an imide bond, and includes 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 the effect of the present invention is exerted. It may also be an electrolytic copper foil.

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

(Example)

Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. The elements shown in Table 1 were added to the electric copper, respectively, and the composition shown in Table 1 was obtained. The ingot was cast in an Ar atmosphere to obtain an ingot. The oxygen content of the ingot was less than 15 ppm. The ingot was homogenized at 900 DEG C, hot rolled, cold rolled and recrystallized annealed, and further subjected to final recrystallization annealing and final cold rolling to obtain a rolled copper foil.

The obtained rolled copper foil was subjected to a heat treatment at 300 캜 for 30 minutes in an argon atmosphere to obtain a copper foil sample. The copper foil after the heat treatment shows a state in which heat treatment is performed at the time of laminating the CCL.

<Evaluation of Copper Samples>

1. Conductivity

For each of the copper foil samples subjected to the heat treatment, the conductivity (% IACS) at 25 캜 was measured by the four-terminal method based on JIS H 0505.

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

2. Assembly Chart

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

3. Etching factor EF

The copper foil and the resin were stuck together, and then a dry film resist was laminated on the surface of the copper foil to form a circuit pattern of short strips (L / S = 25/25) on the resist. Etching was performed by changing the etching time by spraying a cupric chloride etchant.

Although there are various methods of measuring EF, in the present invention, evaluation is made by the etching rate in the depth direction with respect to the width direction, which is the most common method for obtaining the etching factor EF. In the present invention, measurement is carried out as shown in Fig. 1 and Fig. In the following equation (1), attention is paid only to the etching rate in the depth direction and the width direction, and the etching rate in the oblique direction is not considered.

EF is obtained from the etching rate in the width direction and the depth direction of one cross section of the circuit by the following equation (1), as shown in Fig.

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, the width and depth of the circuit when the etching time is changed are measured. 2, each data is plotted with the horizontal axis as the width of the circuit and the vertical axis as the circuit depth, and is approximated by the following equation (2). In short, the slope of the graph of Fig. 2 is obtained from the approximate equation of the first order by the least squares method to obtain EF.

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

Here, the coefficient &quot; 2 &quot; in the equation (2) is required to be halved because the etching in the width direction proceeds to both right and left sides in Fig.

Then, according to the value of EF, the following indexes were evaluated. If the evaluation is ⊚ and ◯, it is good.

◎: EF of 1.4 or higher

○: EF of 1.1 or more and less than 1.4

X: 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 for evaluating the soft etchability, the arithmetic average roughness Ra of the surface of the copper foil after soft-etching based on JIS-B0601 (2001) was measured.

As soft etching conditions, a soft etching for imparting adhesion between a copper foil and a resist was simulated, and a copper foil was immersed in an aqueous solution (liquid temperature 25 ° C) of a sodium persulfate concentration of 100 g / L and a hydrogen peroxide concentration of 35 g / . When the arithmetic average roughness Ra is 0.2 탆 or less, the soft etchability is good (∘), and when the arithmetic mean roughness Ra is more than 0.2 탆, the soft etchability is poor (x).

When the resist follows the surface of the copper foil after the soft etching, the adhesion is excellent, the precision of the circuit pattern is improved, and the soft etchability is improved. If Ra exceeds 0.2 占 퐉, the resist hardly follows the surface of the copper foil, and a clearance between the resist and the surface of the copper foil tends to occur. Then, the penetration of the etchant into the gap lowers the precision in forming the circuit pattern.

5. Crystal grain size

For each copper foil sample subjected to the heat treatment, the rolled surface was observed using a scanning electron microscope (SEM), and the average grain size was determined based on JIS H 0501. However, the twin crystals were regarded as different crystal grains and measurement was carried out. The measurement area was 400 μm × 400 μm in 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 each of the embodiments in which the crystal grain size is 0.5 to 4.0 탆 and the degree of aggregation represented by I (220) / I ₀ (220) is 1.3 to less than 7.0, The factor and the soft etchability were excellent. Thus, a uniform circuit pattern can be obtained on the entire surface of the copper foil, the yield is improved, and the precision of the circuit pattern is improved when the circuit is further miniaturized.

In the case of Comparative Examples 1 to 4 in which the strain 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 etch factor was lowered although the soft etchability was good. Therefore, when the circuit is miniaturized, the precision of the circuit pattern is lowered.

In the case of Comparative Example 5 in which the average crystal grain size after final cold rolling and after the final recrystallization annealing exceeded 20 탆, the average crystal grain size of the product exceeded 4.0 탆 and the etch factor was satisfactory, but the soft etchability was inferior . Therefore, a uniform circuit pattern can not be obtained on the entire surface of the copper foil, and the yield is lowered.

In the case of Comparative Example 6 in which the total degree of processing 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 became less than 80% and the conductivity was inferior.

Claims (7)

Cu of at least 99.0% by mass, and a remainder inevitable impurities,
An average crystal grain size of 0.5 to 4.0 占 퐉 and a degree of aggregation expressed by X-ray diffraction intensity I (220) / I ₀ (220) of the surface of the copper foil is 1.3 or more and less than 7.0,
A copper foil for a flexible printed circuit board having a conductivity of 80% or more. The method according to claim 1,
A copper foil for a flexible printed circuit board comprising a tough pitch copper specified in JIS-H3100 (C1100) or an oxygen free copper of JIS-H3100 (C1020). The method according to claim 1,
In addition, for a flexible printed circuit board comprising a total of 0.7 mass% or less of at least one or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Copper foil. The method according to claim 1,
Wherein the average crystal grain size is 0.5 to 4.0 mu m, the aggregation degree is 1.3 or more and less than 7.0, and the electrical conductivity is 80% or more after annealing at a temperature of 300 DEG C for 30 minutes (at a heating rate of 100 DEG C / min to 300 DEG C / min) Copper foil for substrates. A copper clad laminate obtained by laminating a copper foil for a flexible printed circuit according to any one of claims 1 to 4 and a resin layer. A flexible printed circuit board comprising a copper clad laminate according to claim 5 and a circuit formed on the copper clad. An electronic device using the flexible printed circuit board according to claim 6.

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