TW201934767A - Copper foil for flexible printed substrate, copper clad laminate using the same, flexible printed substrate and electronic machine having an aggregation degree represented by the X-ray diffraction intensity of 1.3 or more and less than 7.0 - Google Patents

Abstract

This invention provides a copper foil for a flexible printed substrate with excellent etching property, a copper clad laminate using the same, a flexible printed substrate and an electronic machine. The copper foil for a flexible printed substrate of this invention is composed of 99.0% by mass or more of Cu and residual containing unavoidable impurities, with an average crystal grain diameter of 0.5 to 4.0 [mu]m, and an aggregation degree represented by the X-ray diffraction intensity I(220)/I0(220) on the surface of the copper foil is 1.3 or more and less than 7.0, and the electrical conductivity is 80% or more.

Description

Copper foil for flexible printed circuit board, copper-clad laminate using the same, flexible printed circuit board, and electronic device

The present invention relates to a copper foil that can be preferably used for wiring members such as flexible printed boards, a copper-clad laminate, a flexible wiring board, and an electronic device.

Flexible printed circuit boards (flexible wiring boards, hereinafter referred to as "FPCs") are widely used in bent or movable parts of electronic circuits because of their flexibility. For example, FPC is used for the movable part of HDD or DVD- and CD-ROM-related equipment, and the folding part of a folding mobile phone.

FPC is formed by etching Copper Clad Laminate (copper-clad laminate, hereinafter referred to as CCL) formed by laminating copper foil and resin, and is covered with a resin layer called a cover lay. Successor. In the stage before the overlaying layer, as a part of the surface modification step for improving the adhesion between the copper foil and the overlaying layer, the surface of the copper foil is etched. In addition, in order to reduce the thickness of the copper foil and improve the bendability, there may be a case where the thickness is etched.

Furthermore, with the miniaturization, thinness, and high performance of electronic devices, miniaturization of the circuit width and interval width of FPC is required (for example, about 20 to 30 μm). If the circuit of the FPC is miniaturized, there is a problem that when a circuit is formed by etching, an etching factor or circuit linearity is liable to deteriorate (Patent Documents 1 and 2).

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2017-141501

[Patent Document 2] Japanese Patent Laid-Open No. 2017-179390

However, in the conventional technology, optimization of the average crystal grain size and the like has been performed as a solution for improving the etching properties, but there is still room for improvement in the etching properties in the formation of fine circuits.

The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a copper foil for a flexible printed circuit board having excellent etching properties, a copper-clad laminated body using the same, a flexible printed circuit board, and an electronic device.

The present inventors have conducted various studies, and as a result, found that the etching rate in the <220> orientation is large. Especially in the etching using a copper chloride etchant, there is no difference in the etching speed due to orientation. Therefore, by increasing the number of grains in the <220> orientation, the etchability (especially soft etchability and etch factor) has been further improved.

That is, the copper foil for a flexible printed circuit board of the present invention is a rolled copper foil composed of 99.0% by mass or more of Cu and unavoidable impurities in the remainder, and has an average crystal grain size of 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 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 composed of refined copper of JIS-H3100 (C1100) standard or oxygen-free copper of JIS-H3100 (C1020).

The copper foil for a flexible printed circuit board of the present invention preferably further contains at least 1 selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb in a total amount of 0.7% by mass or less. One or two or more kinds are added as an additive element.

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

The copper-clad laminated system of the present invention is formed by laminating the copper foil for a flexible printed circuit board 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 formed using the flexible printed circuit board.

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

FIG. 1 is a diagram showing a method for measuring the etching factor EF.

FIG. 2 is another diagram showing a method for measuring the etching factor EF.

Hereinafter, embodiments of the copper foil of the present invention will be described. In addition, in this invention, unless otherwise stated,% means mass%.

First, the soft etchability and the etch factor EE in the etchability will be described.

Soft etchability is an indicator of the accuracy of the circuit obtained by etching due to the adhesion between the surface of the copper foil and the resist. The better the adhesion of the resist and the more the resist follows the surface of the copper foil, the more Suppresses the defect that the etchant enters between the two parts and the circuit is missing, and obtains a uniform circuit on the entire surface of the copper foil Pattern, yield is improved.

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

Even if the soft etching property is good, but the etching factor EF is poor, 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 miniaturized, the accuracy of the circuit pattern is reduced.

Conversely, when the soft etching property is poor even though the etching factor EF is good, the circuit pattern accuracy is improved when the circuit is miniaturized, but (as the etching solution easily penetrates between the surface of the copper foil and the resist) As a result, a part of the circuit is lacking, and a uniform circuit pattern cannot be obtained on the entire surface of the copper foil, and the yield is reduced.

<Composition>

The copper foil of the present invention is composed of 99.0% by mass or more of Cu and inevitable impurities in the remaining portion.

In the embodiment of the present invention, by minimizing the crystal grain size before the final cold rolling of the copper foil, the accumulation of the differential rows of the copper foil during the cold rolling is promoted, and the recrystallized grains become fine during recrystallization. In addition, if the strain rate is extremely increased in the final pass of cold rolling, the recrystallized grains are aligned to a specific orientation during recrystallization, that is, the degree of {200} plane set is suppressed, and the {220} plane set can be increased Degree and improved etchability.

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

Specifically, the above-mentioned particle size can be controlled by adjusting the temperature of the final annealing and the workability of the cold rolling before the final annealing. Although the temperature of the final annealing varies depending on the manufacturing conditions of the copper foil, it is not limited, and may be set to, for example, 300 to 400 ° C. In addition, the workability of cold rolling before final annealing is also not limited. For example, the processing degree η may be set to 1.6 to 3.0.

The processing degree η is the thickness of the cold-rolled material immediately before the final annealing is set to A0, the thickness of the cold-rolled material immediately before the final annealing is set to A1, and η = ln (A0 / A1) Means.

When the crystal grain size before the final cold rolling exceeds 20 μm, the cross-intersection of the differential rows during processing becomes smaller, and the accumulation of strain becomes smaller. Therefore, after the recrystallization, the strain is not released and the grain size becomes finer. Inadequate tendency. In the case where the crystal grain size before the final cold rolling is less than 5 μm, the cross-intersection of the differential rows during processing occurs in approximately the entire area of the copper foil, and no more cross-intersection can occur. The effect of miniaturizing crystal grains is saturated. Therefore, the lower limit of the crystal grain size before the final cold rolling is set to 5 μm.

In addition, if it contains at least one kind or two or more kinds selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb with respect to the above composition in an amount of 0.7% by mass or less as an additive Element can make the recrystallized grains finer.

The above-mentioned added elements increase the frequency of intersecting differential rows during cold rolling, so recrystallized grains can be refined.

When the total content of the above-mentioned additional elements is more than 0.7% by mass, the conductivity is lowered and the copper foil for a flexible substrate may not be suitable. Therefore, the upper limit is set to 0.7% by mass. The lower limit of the content of the above-mentioned added elements is not particularly limited. However, for example, it is difficult to control each element industrially to less than 0.0005 mass%. Therefore, the lower limit of the content of each element may be set to 0.0005 mass%.

The copper foil of the present invention may be composed of fine copper (TPC) based on JIS-H3100 (C1100) or oxygen-free copper (OFC) based on JIS-H3100 (C1020).

The TPC or OFC may be a composition containing P.

<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, and the spring back becomes large, which is not suitable for a flexible printed circuit board. use. When the average crystal grain size exceeds 4.0 μm, soft etching properties are deteriorated.

The measurement of the average crystal grain size is performed in order to avoid errors by observing the surface of the foil in a viewing area of 100 μm × 100 μm for 3 or more viewing areas. Observation of the foil surface can be performed using SIM (Scanning Ion Microscope) or SEM (Scanning Electron Microscope), and the average crystal grain size can be determined based on JIS-H0501. However, the double crystal system was measured as a different crystal grain.

<Collection degree>

The aggregation degree 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.

If the degree of aggregation is less than 1.3, the etching rate in the thickness direction will decrease, and the etching factor described later in the copper foil will decrease. When the aggregation degree is a strain rate of 7.0 or more, although the etching factor is good, the shape of the rolled copper foil is deteriorated and it is difficult to use it as a copper foil for FPC.

The degree of aggregation is measured as follows. First, about the rolled surface of the copper foil, the X-ray diffraction intensity of the {220} plane was measured, and it was set to I (220).

Also, under the same conditions, for pure copper powder (325mesh (JIS Z8801, purity 99.5%), used after heating at 300 ° C for 1 hour in a hydrogen gas stream), the X-ray diffraction intensity on the {220} plane was measured and set to I ₀ (220).

Furthermore, it standardized as follows.

． {220} Face collection degree: I (220) / I ₀ (220)

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

． Incident X-ray source: Co ,. Accelerating voltage: 25kV,. Tube current: 20mA,. Divergent slit: 1 degree,. Scattering slit: 1 degree, ． Light receiving slit: 0.3mm,. Divergence longitudinal limit slit: 10mm,. Monochromatic light receiving slit: 0.8mm

<Heat treatment at 300 ° C for 30 minutes>

The copper foil of the present invention is used for a flexible printed circuit board. At this time, the CCL formed by laminating the copper foil and the resin is heat-treated at 200 to 400 ° C to harden the resin. Therefore, the average crystal grain size, and I ( 220) / I ₀ (220) changes in the degree of aggregation.

Therefore, before and after lamination with the resin, the average crystal grain size and the degree of aggregation change. Therefore, the copper foil for a flexible printed circuit board of claim 1 of the present case specifies a copper foil in a state where it is subjected to a heat treatment when it becomes a copper-clad laminate formed by being laminated with a resin. That is, the copper foil has been subjected to heat treatment, and thus is not in a state of being subjected to a new heat treatment.

On the other hand, the copper foil for flexible printed circuit board of claim 4 of the present case specifies the state when the above-mentioned heat treatment is performed on the copper foil before being laminated with the resin (for example, the copper foil coil before the heat treatment is incorporated into the CCL manufacturing plant Heated state when laminated in CCL). The heat treatment at 300 ° C for 30 minutes is a temperature condition that simulates the hardening heat treatment of the resin when the CCL is laminated. Furthermore, in order to prevent oxidation of the copper foil surface caused by heat treatment, the heat treatment environment is preferably a reducing or non-oxidizing environment. For example, as long as it is set to a vacuum environment or made of argon, nitrogen, hydrogen, carbon monoxide gas, or The environment constituted by these mixed gases is sufficient. 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, hot rolling, cold rolling, and annealing are performed. Preferably, recrystallization annealing is performed at the initial stage of cold rolling, and final recrystallization annealing and final cold rolling are performed, thereby manufacturing a foil.

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

When the total processing degree η is set to 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 strain rate of the final pass before the final cold rolling is set to 1000 (/ sec) or more, the degree of aggregation can be increased more reliably.

<Copper-clad laminate and flexible printed circuit board>

In addition, (1) a resin precursor (for example, a polyimide precursor called varnish) is cast on the copper foil of the present invention and is polymerized by applying heat, and (2) a base film is used. The same kind of thermoplastic adhesive is used to laminate a base film on the copper foil of the present invention, thereby obtaining a copper-clad laminate (CCL) composed of two layers of a copper foil and a resin substrate. Furthermore, by laminating a base film coated with an adhesive on the copper foil of the present invention, a copper-clad laminate composed of three layers of a copper foil, a resin substrate, and an adhesive layer therebetween ( CCL). When these CCLs are manufactured, the copper foil is heat-treated and recrystallized.

A circuit is formed on the substrate using photolithography, and the circuit is plated as necessary, and a cover lay film is laminated to obtain a flexible printed circuit board (flexible wiring board).

Therefore, the copper-clad laminated system of the present invention is formed by laminating a copper foil and a resin layer. 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 it is not limited thereto. . As the resin layer, such a resin film can be used.

As a method of laminating a resin layer and a copper foil, the surface of the copper foil can be coated with a material that becomes a resin layer and heated to form a film. In addition, a resin film is used as the resin layer, and the following adhesion can be used between the resin film and the copper foil It is also possible to thermocompression-bond a resin film to a copper foil without using an adhesive. However, it is preferable to use an adhesive from the point which does not apply excess heat to a resin film.

When a film is used as the resin layer, the film may be laminated on a copper foil via an adhesive. In this case, it is preferable to use an adhesive having the same composition as the film. For example, in the case where a polyimide film is used as the resin layer, it is preferable to use a polyimide-based adhesive in the adhesive layer. Here, the polyfluorene imine adhesive refers to an adhesive containing a fluorene imine bond, and also includes polyether fluorene imine and the like.

The present invention is not limited to the embodiments described above. Moreover, as long as the effect of this invention is exhibited, the copper alloy of the said embodiment may contain other components. Moreover, it may be electrolytic copper foil.

For example, the surface of the copper foil may be subjected to a roughening treatment, an anti-rust treatment, a heat-resistant treatment, or a combination of these.

[Example]

Next, the present invention will be described in more detail with examples, but the present invention is not limited to these. The elements shown in Table 1 were added to the electrolytic copper to have the composition shown in Table 1, and casting was performed in an Ar environment to obtain an ingot. The oxygen content in the ingot did not reach 15 ppm. The ingot was homogenized and annealed at 900 ° C, and then hot-rolled, followed by repeated cold rolling and recrystallization annealing, and then final recrystallization annealing and final cold rolling to obtain a rolled copper foil.

The obtained rolled copper foil was heat-treated at 300 ° C for 30 minutes under an argon atmosphere to obtain a copper foil sample. The heat-treated copper foil simulates the state of being subjected to heat treatment when the CCL is laminated.

<Evaluation of copper foil samples>

Electrical conductivity

For each copper foil sample after the heat treatment, the electrical conductivity (% IACS) at 25 ° C was measured by the 4-terminal method based on JIS H 0505.

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

2. Degree of collection

For each copper foil sample after the heat treatment, the degree of aggregation was measured by the above method using an X-ray diffraction device (RINT-2500: manufactured by Rigaku Electric). In addition, the X-ray diffraction intensity of the {200} plane was measured in the same manner except for the degree of aggregation represented by I (220) / I ₀ (220), and I (200) / I ₀ (200) was also determined.

3. Etching factor EF

The copper foil was bonded to the resin, and then a dry film resist was laminated on the surface of the copper foil to form a short strip (L / S = 25/25) circuit pattern on the resist. The etching is performed by changing the etching time by spray etching of a copper chloride etchant.

There are various methods for measuring EF. In the present invention, the most common method for obtaining the etching factor EF is to evaluate the etching factor in the depth direction with respect to the width direction. In the present invention, the measurement is performed as shown in FIGS. 1 and 2. In addition, the following formula (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, EF is obtained from the etching rate in the width direction and the depth direction of the cross section of a circuit by the following formula (1).

EF = etch rate in depth direction / etch rate in width direction (1)

However, since the measurement of the etching rate itself is difficult, the width and depth of the circuit when the etching time is changed are measured separately. Next, as shown in FIG. 2, the horizontal axis is set to the width of the circuit, and the vertical axis is set to the depth of the circuit. Each data is plotted and approximated by the following formula (2). That is, the slope of the graph of FIG. 2 is obtained as the EF from an approximate formula using the least square method.

EF ≒ Time change in depth / (Time change in width / 2) = 2 × Time change in depth / Time change in width (2)

Here, the coefficient “2” of the formula (2) is performed on the left and right sides of FIG. 1 due to the etching in the width direction. It must be halved.

Then, the following index was evaluated based on the value of EF. When the evaluation was ◎ or ○, it was 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 etching

The surface of each copper foil sample after the heat treatment was soft-etched under the following conditions. As an index for evaluating soft etchability, the arithmetic average roughness Ra of the copper foil surface after soft etch based on JIS-B0601 (2001) was measured.

As the soft etching conditions, the soft etching used to provide the adhesion between the copper foil and the resist was simulated, and the copper foil was placed in an aqueous solution (liquid temperature 25 ° C) of 100 g / L sodium sulfate concentration and 35 g / L hydrogen peroxide concentration. Dip for 420 seconds. A case where the arithmetic average roughness Ra is 0.2 μm or less is regarded as good soft etchability (○), and a case where the arithmetic average roughness Ra exceeds 0.2 μm is regarded as poor soft etchability (×).

When the resist follows the surface of the copper foil well after the soft etching, the adhesion is excellent, the accuracy of the circuit pattern is improved, and the soft etching is good. When Ra exceeds 0.2 μm, it is difficult for the resist to follow the surface of the copper foil, and a gap is easily generated between the resist and the surface of the copper foil. In addition, the accuracy of the circuit pattern is reduced due to the etching solution entering the gap.

5. Crystal size

About each copper foil sample after the said heat processing, the rolled surface was observed using SEM (Scanning Electron Microscope), and the average particle diameter was calculated | required based on JIS H 0501. However, the double crystal system was measured as a different crystal grain. The measurement area is 400 μm × 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, when 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, Both the etching factor and soft etchability are excellent. As a result, a uniform circuit pattern can be obtained on the entire surface of the copper foil, and the yield is improved, thereby further improving the accuracy of the circuit pattern when the circuit is miniaturized.

In the case of Comparative Examples 1 to 4 in which the strain rate in the final pass of the final cold rolling did not reach 1000 (s-1), the degree of aggregation did not reach 1.3, and although the soft etching property was good, the etching factor decreased. Therefore, when the circuit is miniaturized, the accuracy of the circuit pattern is reduced.

In the case of Comparative Example 5 where the average crystal grain size before the final cold rolling and after the final recrystallization annealing exceeds 20 μm, the average crystal grain size of the product exceeds 4.0 μm. Although the etching factor is good, the soft etchability is poor. Therefore, a uniform circuit pattern cannot be obtained on the entire surface of the copper foil, and the yield is reduced.

In the case of Comparative Example 6 in which the total processing degree did not reach 6.10, the aggregation degree did not reach 1.3, and the etching factor decreased.

In the case of Comparative Example 7 where the total content of the added elements exceeds 0.7% by mass, the electrical conductivity is less than 80%, and the electrical conductivity is poor.

Claims (8)

A copper foil for a flexible printed circuit board, which is a copper foil composed of 99.0% by mass of Cu or more and unavoidable impurities, and has an average crystal grain size of 0.5 to 4.0 μm. The aggregation degree represented by the X-ray 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 circuit board as described in claim 1 is composed of JIS-H3100 (C1100) standard copper or JIS-H3100 (C1020) oxygen-free copper. The copper foil for a flexible printed circuit board according to claim 1, which further contains 0.7% by mass or less of a group selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb. At least one or two or more of them are added as an additive element. The copper foil for a flexible printed circuit board according to claim 2, which further contains 0.7% by mass or less of a group selected from the group consisting of P, Ag, Si, Ge, Al, Ga, Zn, Sn, and Sb. At least one or two or more of them are added as an additive element. The copper foil for a flexible printed circuit board according to any one of claims 1 to 4, wherein after the annealing is performed at 300 ° C for 30 minutes (wherein the heating rate is 100 ° C / min to 300 ° C / min), the average The crystal grain size is 0.5 to 4.0 μm, the degree of aggregation is 1.3 or more and less than 7.0, and the electrical conductivity is 80% or more. A copper-clad laminate comprising a copper foil for a flexible printed circuit board according to any one of claims 1 to 5 and a resin layer. A flexible printed circuit board is formed by forming a circuit on the copper foil in the copper-clad laminate according to claim 6. An electronic device using the flexible printed circuit board according to claim 7.