JP2019127603A - Copper foil for flexible printed circuit board, and copper clad laminate, flexible printed circuit board, and electronic apparatus including the same - Google Patents

Abstract

To provide a copper foil for flexible printed circuit boards having excellent etching properties, and a copper clad laminate, a flexible printed circuit board, and an electronic apparatus including the same.SOLUTION: A copper foil for flexible printed circuit boards contains 99.0 mass% or more of Cu, with the balance being inevitable impurities, and has an average crystal grain size of 0.5-4.0 μm, a degree of aggregation expressed by an X-ray diffraction intensity I(220)/I(220) on the copper foil surface of 1.3 or more and less than 7.0, and a conductivity of 80% or more.SELECTED DRAWING: Figure 1

Description

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

A flexible printed circuit board (flexible wiring board, hereinafter referred to as “FPC”) has flexibility, and is widely used in a bent portion and a movable portion of an electronic circuit. For example, FPCs are used for moving parts of disk-related devices such as HDDs, DVDs, and CD-ROMs, and bending parts of folding mobile phones.
The FPC is formed 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 then coating the wiring with a resin layer called a coverlay. Prior to laminating the coverlay, etching of the copper foil surface is performed as part of a surface modification process to improve the adhesion between the copper foil and the coverlay. Further, in order to improve the flexibility by reducing the thickness of the copper foil, thinning etching may be performed.

  By the way, with the miniaturization, thinning, and high performance of electronic devices, miniaturization of FPC circuit width and space width (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 are likely to deteriorate when the circuit is formed by etching (Patent Documents 1 and 2).

Patent Document 1: Japanese Patent Application Publication No. 2017-141501 Unexamined-Japanese-Patent No. 2017-179390

However, in the conventional technique, the average crystal grain size and the like are optimized as a measure for improving the etching property, but there is room for improvement in the etching property in forming a fine circuit.
The present invention has been made to solve the above-mentioned problems, and aims to provide a copper foil for a flexible printed circuit board excellent in etching property, a copper-clad laminate using the same, a flexible printed circuit board, and an electronic device. To do.

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

That is, the copper foil for flexible printed circuit boards according to the present invention is a rolled copper foil comprising 99.0% by mass or more of Cu and the balance inevitable impurities, and has an average crystal grain size of 0.5 to 4.0 μm, and X-rays on the copper foil surface The aggregation degree represented by the diffraction intensity I (220) / I 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 board of the present invention is preferably made of tough pitch copper standardized to JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020).
The copper foil for flexible printed circuit boards of the present invention further includes 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 in total. It is preferable to contain 0.7 mass% or less.
In the copper foil for a flexible printed circuit board of the present invention, the average crystal grain size is 0.5 to 4.0 μm, and the aggregation degree is 300 ° C. × 30 min annealing (where the temperature rising rate is 100 ° C./min to 300 ° C./min). It is preferable that the conductivity is 1.3 or more and less than 7.0 and the conductivity is 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 device of the present invention uses the flexible printed circuit board.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for flexible printed circuit boards excellent in etching property (especially soft etching property and an etching factor) is obtained.

It is a figure which shows the measuring method of etching factor EF. It is another figure which shows the measuring method of etching factor EF.

Hereinafter, embodiments of the 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 in etching property and the etching factor EF will be described.
The soft etching property is an index showing the accuracy of the circuit by etching due to the adhesion between the copper foil surface and the resist. The better the adhesion of the resist is, the more the resist follows the copper foil surface, the etchant penetrates between them. As a result, a defect that a part of the circuit is missing is suppressed, and a uniform circuit pattern can be obtained on the entire surface of the 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, 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.

Even if the soft etching property is good, if the etching factor EF is inferior, a uniform circuit pattern can be obtained on the entire surface of the copper foil to improve the yield, but when the circuit is miniaturized, the accuracy of the circuit pattern decreases.
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 miniaturized, but the etching solution tends to enter between the copper foil surface and the resist. Therefore, there is a problem that a part of the circuit is missing, 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 comprises 99.0% by mass or more of Cu and the balance of inevitable impurities.
In the embodiment of the present invention, by reducing the grain size of the copper foil before final cold rolling, accumulation of dislocations of the copper foil is promoted during cold rolling, and the recrystallized grains become fine during recrystallization. Become. Also, if the strain rate is made extremely high in the final pass of cold rolling, recrystallized grains are oriented in a specific orientation during recrystallization, that is, the {200} plane aggregation degree is suppressed, and the {220} plane aggregation degree Can be increased, and the etching property is improved.

Moreover, in order to refine crystal grains after recrystallization of copper foil, when the crystal grain size before final cold rolling performed after final annealing is 5 μm or more and 20 μm or less in the entire process of repeating annealing and rolling. preferable.
Specifically, the grain size can be controlled by adjusting the temperature of final annealing and the degree of cold rolling before final annealing. Although the temperature of final annealing changes also with the manufacturing conditions of copper foil, it is not limited, For example, what is necessary is just to be 300-400 degreeC. Moreover, although the working degree of the cold rolling before final annealing is not limited, either, for example, the working degree η may be set to 1.6 to 3.0.
The processing degree η is represented by η = ln (A0 / A1), where A0 denotes the thickness of the material immediately before cold rolling before final annealing and A1 denotes the thickness of the material immediately after cold rolling before final annealing.

  If the crystal grain size before final cold rolling exceeds 20 μm, the entanglement of dislocations during processing will be small and the accumulation of strain will be reduced, so the strain will not be released after recrystallization and the crystal grains will be insufficiently refined. Tend to be. If the crystal grain size before final cold rolling is less than 5 μm, dislocation entanglement during processing occurs in almost the entire area of the copper foil and further entanglement can not be made, and recrystallized grains are generated during recrystallization of the copper foil. The effect of miniaturization is saturated. Therefore, the lower limit of the crystal grain size before the final cold rolling is set to 5 μm.

Further, as an additive element, a total of at least one or more selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn and Sb is 0.7% by mass or less based on the above composition. When contained, recrystallized grains can be refined.
The above-described additive elements increase the frequency of dislocation entanglement during cold rolling, so that recrystallized grains can be refined.
If the total amount of the additive elements exceeds 0.7% by mass, the electrical conductivity is lowered and may not be suitable as a copper foil for a flexible substrate, so 0.7% by mass was made 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 smaller than 0.0005% by mass, the lower limit of the content of each element may be 0.0005% by mass.

The copper foil according to the present invention may be composed of tough pitch copper (TPC) standardized to 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 crystal grain size>
The average crystal grain size of the copper foil is 0.5 to 4.0 μm. If the average crystal grain size is less than 0.5 μm, the strength becomes too high, the bending rigidity becomes large, the spring back becomes large, and it is not suitable for flexible printed circuit board applications. When the average crystal grain size exceeds 4.0 μm, the soft etching property deteriorates.
In order to avoid an error, the average grain size is measured by observing three or more fields of view on the foil surface with a field of view of 100 μm × 100 μm. For observation of the foil surface, the average crystal grain size can be determined based on JIS-H0501 using SIM (Scanning Ion Microscope) or SEM (Scanning Electron Microscope). However, twins are measured as being considered as separate crystal grains.

<Degree of assembly>
The degree of aggregation represented by the X-ray diffraction intensity I (220) / I ₀ (220) on the copper foil surface 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 is reduced, and the etching factor of the copper foil described later is lowered. In the case of a strain rate at which the degree of aggregation is 7.0 or more, the etching factor is good, but the shape of the rolled copper foil is deteriorated and it may be difficult to use as a copper foil for FPC.

The degree of assembly is measured as follows. First, the X-ray diffraction intensity of the {220} plane of the rolled surface of the copper foil is measured and set to I (220).
In addition, X-ray diffraction intensity of {220} plane was measured for pure copper powder (325 mesh (JIS Z 8801, purity 99.5%), used after heating at 300 ° C. for 1 hour in a hydrogen stream under the same conditions) And I ₀ (220).

And standardize as follows.
* Degree of {220} plane assembly: 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,
・ Divergent slit: 1 degree
・ Scatter slit: 1 degree
・ Light receiving slit: 0.3 mm,
・ Divergent longitudinal restriction slit: 10 mm,
・ Monochrome light receiving slit 0.8mm

<Heat treatment at 300 ° C for 30 minutes>
The copper foil according to the present invention is used for a flexible printed board, and in that case, the CCL in which the copper foil and the resin are laminated is subjected to a heat treatment for curing the resin at 200 to 400 ° C. The degree of aggregation displayed by I (220) / I ₀ (220) changes.
Therefore, the average crystal grain size and the degree of aggregation change before and after lamination with the resin. Then, the copper foil for flexible printed circuit boards concerning Claim 1 of this application prescribes | regulates the copper foil of the state which received the heat processing at the time of becoming a copper clad laminated body after resin and lamination | stacking. In other words, the copper foil is in a state where it has not been subjected to a new heat treatment since it has already undergone a heat treatment.
On the other hand, the copper foil for a flexible printed circuit board according to claim 4 of the present application is in a state (for example, a copper foil coil before heat treatment is delivered to a manufacturing plant of CCL) The heated state when being stacked on the CCL). The heat treatment at 300 ° C. for 30 minutes simulates the temperature conditions under which the resin is cured and heat treated during lamination of CCL. In order to prevent oxidation of the surface of the copper foil by heat treatment, the atmosphere for heat treatment is preferably a reducing or non-oxidizing atmosphere, for example, a vacuum atmosphere, or argon, nitrogen, hydrogen, carbon monoxide, etc. An atmosphere made of a mixed gas may be used. The heating rate 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 a copper ingot, it is hot-rolled, cold-rolled and annealed, and preferably recrystallization annealing is performed at the initial stage of cold-rolling, final recrystallization annealing and final cold rolling By doing so, a foil can be produced.
Average grain size by adjusting the total working degree η of cold rolling, the average grain size before final cold rolling and after final recrystallization annealing, and the strain rate of the final pass before final cold rolling, and The degree of assembly can be controlled.

If the total processing degree η is 6.10 or more, the aggregation degree represented by I (220) / I ₀ (220) can be more reliably increased.
When 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 surely set to 0.5 to 4.0 μm.
If the strain rate of the final pass before final cold rolling is set to 1000 (/ second) or more, the degree of assembly can be more reliably increased.

<Copper-clad laminate and flexible printed circuit board>
In addition, (1) casting a resin precursor (for example, a polyimide precursor called varnish) onto the copper foil of the present invention and polymerizing by heat, (2) using a thermoplastic adhesive of the same type as the base film By laminating the base film on the copper foil of the present invention, a copper clad laminate (CCL) composed of two layers of the copper foil and the resin base material is obtained. Further, by laminating a base film obtained by applying an adhesive to the copper foil of the present invention, a copper clad laminate (CCL) comprising three layers of a copper foil, a resin base material, and an adhesive layer therebetween is obtained. During the production of these CCLs, the copper foil is heat-treated and recrystallized.
A circuit is formed on these using a photolithographic technique, a circuit is plated as needed, and a cover-lay film is laminated, and a flexible printed circuit board (flexible wiring board) is obtained.

Therefore, the copper clad laminate of the present invention is formed by laminating a 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 method of laminating the resin layer and the copper foil, a material to be the 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, and the following adhesive may be used between the resin film and the copper foil, or the resin film may be thermocompression bonded to the copper foil without using the adhesive. However, it is preferable to use an adhesive from the viewpoint of not applying excessive heat to the resin film.

  When a film is used as the resin layer, this film may be laminated on the copper foil via an adhesive layer. 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 for the adhesive layer. The polyimide adhesive as used herein refers to an adhesive containing an imide bond, and also includes polyetherimide and the like.

In addition, this invention is not limited to the said embodiment. Moreover, as long as there exists an effect of this invention, the copper alloy in the said embodiment may contain another component. Moreover, an electrolytic copper foil may be used.
For example, the surface of the copper foil may be subjected to a surface treatment by roughening treatment, rust prevention treatment, heat resistance treatment, or a combination thereof.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. The elements shown in Table 1 were added to electric copper, respectively, to obtain compositions shown in Table 1, and casting was performed in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. After this ingot was homogenized and annealed at 900 ° C., after hot rolling, cold rolling and recrystallization annealing were repeated, and final recrystallization annealing and final cold rolling were performed to obtain a rolled copper foil.
The obtained rolled copper foil was heat-treated at 300 ° C. for 30 minutes in an argon atmosphere to obtain a copper foil sample. The copper foil after the heat treatment imitates a state where the heat treatment is performed during the lamination of the CCL.

<Evaluation of copper foil sample>
1. Electrical conductivity The electrical conductivity (% IACS) at 25 ° C. was measured for each copper foil sample after the heat treatment by a four-terminal method based on JIS H 0505.
If the conductivity is greater than 80% IACS, the conductivity is good.
2. Assembly degree About each copper foil sample after the said heat processing, the assembly degree was measured by the above-mentioned method using the X-ray-diffraction apparatus (RINT-2500: Rigaku Corporation make). In addition to the degree of aggregation represented by I (220) / I ₀ (220), the X-ray diffraction intensity of the {200} plane was measured in the same manner to obtain I (200) / I ₀ (200).

3. Etching factor EF
A copper foil and a resin were laminated, and then a dry film resist was laminated on the surface of the copper foil to form a strip-like (L / S = 25/25) circuit pattern on the resist. Etching was performed by changing the etching time by spray etching of cupric chloride etchant.

Although there are various methods for measuring EF, in the present invention, evaluation is performed 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 performed as shown in FIGS. The following equation (1) focuses only on the etching rate in the depth direction and the width direction, and does not consider the etching rate in the oblique direction.
As shown in FIG. 1, the EF is obtained from the etching rate in the width direction and the depth direction of the cross section of one circuit by the following equation (1).
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. Then, as shown in FIG. 2, each data is plotted with the horizontal axis as the circuit width and the vertical axis as the circuit depth, and is approximately obtained by the following equation (2). That is, the slope of the graph of FIG. 2 is obtained from a first-order approximation formula using the least square method and is defined 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 “2” in Expression (2) is because etching in the width direction proceeds to both the left and right sides in FIG.

And it evaluated with the following parameter | index according to the value of EF. If evaluation is (double-circle) and (circle), it is favorable.
:: 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 etching property About each copper foil sample after the said heat processing, the surface was soft-etched on condition of the following. As an index for evaluating the soft etching property, arithmetic average roughness Ra based on JIS-B0601 (2001) on the surface of the copper foil after the soft etching was measured.
As soft etching conditions, we simulated soft etching to give adhesion between copper foil and resist and put it into an aqueous solution (solution temperature 25 ° C) with sodium persulfate concentration of 100 g / L and hydrogen peroxide concentration of 35 g / L. The second copper foil was immersed. When the arithmetic average roughness Ra is 0.2 μm or less, the soft etching property is good (◯), and when the arithmetic average roughness Ra exceeds 0.2 μm, the soft etching property is poor (×).

  If the resist follows the surface of the copper foil well after soft etching, the adhesion is excellent, the accuracy of the circuit pattern is improved, and the soft etching property is good. When Ra exceeds 0.2 μm, the resist hardly follows the surface of the copper foil, and a gap is likely to be generated between the resist and the copper foil surface. Then, when the etching solution enters the gap, the accuracy in forming the circuit pattern is lowered.

5. Crystal grain size About each copper foil sample after the said heat processing, the rolling surface was observed using SEM (Scanning Electron Microscope), and the average particle diameter was calculated | required based on JISH0501. However, the twins were measured as if they were separate crystal grains. The measurement region was 400 μm × 400 μm in a cross section parallel to the rolling direction.

  The obtained results are shown in Tables 1 and 2.

As is clear from Tables 1 and 2, 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. In each of the examples, both the etching factor and the soft etching property were excellent. As a result, a uniform circuit pattern is obtained on the entire surface of the copper foil, yield is improved, and the accuracy 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 etching factor decreased although the soft etching property was good. Therefore, the accuracy of the circuit pattern is reduced when the circuit is miniaturized.
In the case of Comparative Example 5 in which the average crystal grain size before final cold rolling and after final recrystallization annealing exceeds 20 μm, the average crystal grain size of the product exceeds 4.0 μm and the etching factor is 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 degree of processing was less than 6.10, the degree of assembly was less than 1.3, and the etching factor was reduced.
In the case of Comparative Example 7 in which the total content of the additive elements exceeded 0.7% by mass, the conductivity was less than 80%, and the conductivity was inferior.

Claims (7)

Copper foil consisting of 99.0% by mass or more of Cu and the balance inevitable impurities,
The average grain size is 0.5 to 4.0 μm, and the copper foil surface has an aggregation degree of 1.3 or more and less than 7.0, which is represented by the X-ray diffraction intensity I (220) / I ₀ (220)
Copper foil for flexible printed circuit boards having an electrical conductivity of 80% or more.   The copper foil for flexible printed circuit boards of Claim 1 which consists of a tough pitch copper specified to JIS-H3100 (C1100) or an oxygen free copper of JIS-H3100 (C1020).   Furthermore, it comprises at least 0.7 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. Item 3. The copper foil for a flexible printed board according to Item 1 or 2.   After annealing at 300 ° C. for 30 minutes (however, the heating rate is 100 ° C./min to 300 ° C./min), the average crystal grain size is 0.5 to 4.0 μm, the aggregation degree is 1.3 or more and less than 7.0, the conductivity The copper foil for flexible printed circuit boards as described in any one of Claims 1-3 whose rate is 80% or more.   The copper clad laminated body formed by laminating | stacking the copper foil for flexible printed boards as described in any one of Claims 1-4, and a resin layer.   The flexible printed circuit board formed by forming a circuit in the said copper foil in the copper clad laminated body of Claim 5.   An electronic apparatus using the flexible printed circuit board according to claim 6.

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