TW201920700A - Copper foil for flexible printed circuit and copper clad laminate and flexible printed circuit and electronic device using the same - Google Patents

Abstract

The present invention provides a copper foil for a flexible printed circuit board excellent in bending properties. The rolled copper foil is a copper foil for a flexible printed circuit board, which comprises: 99 mass% or more of copper; and the remaining inevitable impurities. The highest degree of aggregation is less than 5 among four degrees of aggregation of I (111)/I0 (111), I (200)/I0 (200), I (220)/I0 (220), and I (311)/I0 (311), and the conductivity is 75% or greater.

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 suitable for a wiring member such as a flexible printed circuit board, a copper-clad laminated body using the same, 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 in the movable part of HDD or DVD- and CD-ROM-related equipment, or the folding part of a folding mobile phone.

FPC is formed by etching a copper clad laminate (hereinafter referred to as CCL) formed by laminating a copper foil and a resin, and coating the wiring with a resin layer called a cover layer. to make. At the stage before laminating the cover layer, as a part of the surface modification step to improve the adhesion between the copper foil and the cover 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, thinning etching may be performed.

However, with the miniaturization, thinness, and high performance of electronic devices, it is required to construct FPCs inside these devices at a high density. However, in order to perform high-density installations, FPCs must be folded and housed in miniaturized devices. Inside the machine, that is, higher bending properties are required.

On the other hand, the following copper foils have been developed which have improved high cycle bendability typified by IPC bendability (Patent Documents 1 and 2).

[Prior technical literature]

[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2010-100887

[Patent Document 2] Japanese Patent Laid-Open No. 2009-111203

However, in order to construct FPCs with a high density as described above, it is necessary to improve the bending property represented by the MIT folding resistance. The conventional copper foil has a problem that the improvement of the bending property is insufficient.

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 bendability, a copper-clad laminate using the same, a flexible printed circuit board, and an electronic device.

The present inventors have conducted various studies, and as a result, it has been found that by reducing the crystal grain size before the final cold rolling of the copper foil, the accumulation of the differential rows in the entire area of the copper foil becomes cold during rolling. If it is equal, strain is released in the entire area during recrystallization, and recrystallized grains are not formed in a specific direction, so it is expected to improve bendability.

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 the remaining inevitable impurities, and the surface of the copper foil is I (111) / I ₀ ( 111), I (200) / I ₀ (200), I (220) / I ₀ (220), and I (311) / I ₀ (311) Below 5, the electrical conductivity of the copper foil for a flexible printed circuit board is 75% or more.

In the copper foil for a flexible printed circuit board of the present invention, the above-mentioned copper foil for a flexible printed circuit board was used to prepare a short-sign-shaped test piece having a length of 150 mm on the long side and a length of 12.7 mm on the short side, and measured based on JIS P 8115 When the number of times of MIT bending resistance (where R of the bending jig is 0.38mm, the load is 250 g) The ratio of the number of times of MIT folding resistance when the longitudinal direction of the test piece is parallel to the rolling direction, the ratio of the number of times of MIT folding resistance when the longitudinal direction of the test piece and the parallel direction of rolling is 45 °, And the ratio of the MIT folding resistance times when the long side direction of the test piece is the right angle direction of rolling is preferably 0.7 to 1.3, respectively.

The copper foil for a flexible printed circuit board of the present invention is preferably composed of refined copper specified in JIS-H3100 (C1100) or oxygen-free copper specified in JIS-H3100 (C1020).

The copper foil for a flexible printed circuit board of the present invention is preferably as follows: it further contains 0.5% by mass or less of a total selected from the group consisting of P, Ag, Sb, Sn, Ni, Be, Zn, In, and Mg At least one kind 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, after annealing at 300 ° C. for 30 minutes (wherein, the temperature rise rate is 100 ° C./min to 300 ° C./min), the maximum degree of aggregation is preferably 5 or less.

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

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 bendability can be obtained.

Hereinafter, embodiments of the copper foil of the present invention will be described. Furthermore, in the present invention In the case of%, unless otherwise specified, it means mass%.

<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.

As described above, if the grain size of the copper foil is refined before the final cold rolling, and the accumulation of the differential rows in each area of the copper foil is made equal during cold rolling, it will be at any time during recrystallization. The release of strain occurs in all regions, and the recrystallized grains are not formed in a specific direction, so the bendability is improved.

However, when the pure copper-based composition of Cu 99.0 mass% or more is described above, it is difficult to suppress the recrystallization particles from being gathered in a specific direction during the recrystallization of the copper foil. At the time of cold rolling, in the early stage of cold rolling), recrystallization annealing is performed, and a large amount of processing strain can be introduced by cold rolling, so that recrystallized grains can be prevented from being gathered in a specific orientation.

In addition, in order to prevent the copper foil from being gathered in a specific orientation after recrystallization, in all the steps of repeated annealing and rolling, the crystal grain size before the final cold rolling after the final annealing should be 5 μm or more and less than 10 μm .

Specifically, if the temperature of the final annealing and the workability of the cold rolling before the final annealing are adjusted, the above-mentioned particle size can be controlled. The temperature of the final annealing also varies depending on the manufacturing conditions of the copper foil, but it is not limited. For example, it may be set to 300 to 400 ° C. The workability of cold rolling before final annealing is also not limited, and for example, the workability η can be set to 0.91 to 1.61.

The processing degree η refers to the thickness of the material before the final annealing and about to be cold-rolled to A0, and the thickness of the material before the final annealing and just after cold-rolling to A1, which is expressed by η = ln (A0 / A1).

In the case where the crystal grain size before the final cold rolling is 10 μm or more, the combined interaction of the differential rows during processing is locally reduced, and the accumulation of strain is reduced, so there is a set of specific directions without releasing the strain after recrystallization The tendency to become higher. When the crystal grain size before the final cold rolling is less than 5 μm, the merge interaction of the time difference during processing almost occurs on the entire copper foil, and no more merge interaction can be formed. When the foil is recrystallized, the effect of inhibiting the recrystallized grains from gathering in a specific direction cannot be improved. 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, Sb, Sn, Ni, Be, Zn, In, and Mg with respect to the above composition in an amount of 0.5% by mass or less in total Element, it can further inhibit the recrystallized grains from gathering in a specific direction.

The above-mentioned added elements increase the frequency of the merged interactions of the differential rows during cold rolling, so that the recrystallized grains can be further suppressed from gathering in a specific direction. In addition, if the recrystallization annealing is performed only once in the initial stage of cold rolling, and then the recrystallization annealing is not performed, the combined interaction of differential rows is increased by cold rolling, and a large amount of processing strain is introduced, which can be used for copper foil. At the time of recrystallization, it is further suppressed that the recrystallized particles gather in a specific direction.

When the total content of the above-mentioned additional elements is more than 0.5% by mass, the electrical conductivity is lowered and the copper foil for flexible substrates is not suitable. Therefore, the upper limit is set to 0.5% by mass. The lower limit of the content of the above-mentioned added elements is not particularly limited. For example, it is difficult to achieve less than 0.0005 mass% for each element in the industry. Therefore, the lower limit of the content of each element may be set to 0.0005 mass%.

The copper foil composition of the present invention may be made of fine copper (TPC) specified in JIS-H3100 (C1100) or oxygen-free copper (OFC) of JIS-H3100 (C1020).

Moreover, it may be set as the composition which contains P with respect to the said TPC or OFC.

<Collection degree>

I (111) / I ₀ (111), I (200) / I ₀ (200), I (220) / I ₀ (220), and 4 of I (311) / I ₀ (311) on the surface of copper foil The maximum degree of aggregation that reaches the highest value among the five degrees of aggregation is 5 or less.

The {111} plane, {200} plane, {220} plane, and {311} plane are the main diffraction surfaces of copper and copper alloys. If hot rolling, cold rolling, and annealing accompanied by recrystallization, there are four Any particular one of the degree of aggregation will have a very high value, and it may become an aggregate organization aligned in a specific crystalline direction. At this time, by taking these The maximum value of the four aggregation degrees (maximum aggregation degree) can indicate the degree to which the specific aggregation degree becomes extremely high.

Furthermore, by controlling the maximum degree of aggregation to 5 or less, any of the four degrees of aggregation does not become extremely high, and it is possible to suppress the recrystallization particles from being gathered in a specific direction (the increase in the anisotropy of the structure).

When the maximum degree of aggregation exceeds 5, the anisotropy of the structure of the copper foil becomes large, and when used as a flexible printed circuit board, the anisotropy of the bendability becomes large, and the bendability decreases.

In principle, there is no case where the maximum degree of aggregation does not reach 1. The maximum degree of aggregation is preferably 1 to 5.

The degree of aggregation is measured as follows. First, the X-ray diffraction intensity was measured for the {111} plane, {200} plane, {220} plane, and {311} plane of the rolled surface of copper foil, which were respectively set to I (111), I (200), I (220) and I (311).

Also, under the same conditions, for pure copper powder (325mesh (JIS Z8801, purity 99.5%), heated at 300 ° C for 1 hour in a hydrogen stream and used), the {111} plane, {200} plane, {220 The X-ray diffraction intensity of the} plane and the {311} plane are set to I ₀ (111), I ₀ (200), I ₀ (220), and I ₀ (311), respectively.

Then, it is standardized as follows.

‧ {111} surface aggregation: I (111) / I ₀ (111)

‧ {200} surface aggregation: I (200) / I ₀ (200)

‧ {220} surface aggregation: I (220) / I ₀ (220)

‧ {311} surface aggregation: I (311) / I ₀ (311)

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

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

<Tensile strength (TS), elongation at break>

The tensile strength and elongation at break are based on the tensile test according to IPC-TM650. The test piece width is 12.7mm, room temperature (15 ~ 35 ° C), tensile speed is 50.8mm / min, and the length of the scale is 50mm. A tensile test was performed in a direction in which the rolling direction of the copper foil was parallel.

<300 ° C for 30 minutes heat treatment>

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 subjected to a heat treatment for hardening the resin at 200 to 400 ° C, so that grains are caused by recrystallization. The possibility of coarsening.

Therefore, before and after lamination with the resin, the tensile strength and elongation at break of the copper foil will change. Therefore, the copper foil for a flexible printed circuit board of claim 1 of the present case is defined as a copper foil which is a state of being cured and heat-treated by a resin after being laminated with a copper-clad laminate. That is, since the heat treatment has been performed, the copper foil is in a state where no new heat treatment is performed.

On the other hand, the copper foil for flexible printed circuit board of claim 3 of the present case is defined as a state when the above-mentioned heat treatment is performed on the copper foil before being laminated with the resin. The heat treatment at 300 ° C for 30 minutes is a temperature condition that simulates the heat treatment for curing the resin when the CCL is laminated. Furthermore, in order to prevent oxidation of the surface of the copper foil caused by heat treatment, the environment of the heat treatment is preferably a reducing or non-oxidizing environment. For example, as long as it is a vacuum environment or argon, nitrogen, hydrogen, carbon monoxide, or the like The environment including the mixed gas and the like may be sufficient. The heating rate may be between 100 and 300 ° C / min.

Examples of the copper foil of the present invention can be produced in the following manner. First, after melting and casting a copper ingot, hot rolling, cold rolling, and annealing are performed. It is preferable to perform recrystallization annealing at the initial stage of cold rolling and perform the above-mentioned final cold rolling, thereby manufacturing a foil.

Here, if the crystal grain size before final cold rolling (meaning cold rolling after final annealing throughout the entire process of repeating cold rolling and annealing) is refined to 5 μm or more and less than 10 μm, recrystallization can be suppressed. The particles are aggregated in a specific direction, and the maximum degree of aggregation is controlled to be 5 or less.

<Copper-clad laminate and flexible printed circuit board>

Furthermore, the copper foil of the present invention (1) is coated with a resin precursor (for example, a polyimide precursor called varnish) and heat is applied to polymerize it, and (2) a thermoplastic adhesive of the same kind as the base film is used. The base film is laminated to the copper foil of the present invention to obtain a copper-clad laminate (CCL) composed of two layers of a copper foil and a resin substrate. In addition, by laminating and laminating the copper foil of the present invention with an adhesive base film, a copper-clad laminate (CCL) composed of a copper foil, a resin substrate, and an adhesive layer therebetween can be obtained. During the production of these CCLs, copper foils are heat-treated to recrystallize them.

A flexible printed circuit board (flexible wiring board) can be obtained by forming a circuit using a photolithography technique, plating the circuit as needed, and laminating a cover film.

Therefore, the copper-clad laminated system of the present invention is formed by laminating a copper foil and a resin. 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, but are not limited to, PET (polyethylene terephthalate), PI (polyimide), LCP (liquid crystal polymer), and PEN (polyethylene naphthalate). . As the resin layer, such a resin film may be used.

As a method for laminating a resin layer and a copper foil, a material for forming a resin layer may be coated on the surface of the copper foil and heated to form a film. 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 thermally bonded to the copper foil without using an adhesive. However, in terms of not applying excessive heat to the resin film, it is preferable to use an adhesive.

When a film is used as the resin layer, the film may be laminated on a copper foil via an adhesive layer. 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 that a polyimide-based adhesive is also used as the adhesive layer. Moreover, what is called here The polyfluorene imine adhesive refers to an adhesive containing a fluorene imine bond, and also includes polyether fluorene.

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 in 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 roughening treatment, rust prevention treatment, heat treatment, or a combination of these.

[Example 1]

Next, the present invention will be described in more detail with examples, but the present invention is not limited to these examples. Each of the elements shown in Table 1 was added to electrolytic copper to have the composition shown in Table 1, and casting was performed in an argon (Ar) atmosphere to obtain an ingot. The oxygen content in the ingot did not reach 15 ppm. This ingot was homogenized and annealed at 900 ° C, then hot-rolled, then cold-rolled at a workability η = 1.26, and finally annealed at 300 ° C to adjust the crystal grain size to 5 μm or more and less than 10 μm.

Thereafter, the scale oxidized scale generated on the surface was removed, and final cold rolling was performed at the processing degree η shown in Table 1 to obtain a target final thickness foil. The obtained foil was heat-treated at 300 ° C for 30 minutes under an argon atmosphere to obtain a copper foil sample. The copper foil after heat treatment is simulated in the state of being subjected to heat treatment when the CCL is laminated.

<A. Evaluation of copper foil samples>

Electrical conductivity

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

When the electrical conductivity is greater than 75% IACS, the electrical conductivity is good.

2. Degree of collection

For each sample after the above heat treatment, an X-ray diffraction device (RINT-2500: Rigaku Denki) was used, and the degree of aggregation was measured by the above method.

3.Tensile strength and elongation at break

For the copper foil samples after the above heat treatment, through the tensile test according to IPC-TM650, the test piece width is 12.7mm, room temperature (15 ~ 35 ° C), tensile speed is 50.8mm / min, and the length of the scale is 50mm. A tensile test was performed in a direction parallel to the rolling direction of the copper foil, thereby measuring the tensile strength and elongation at break.

4. Bending of copper foil (MIT resistance)

With respect to each of the copper foil samples after the heat treatment, the number of times of MIT bending resistance (the number of round-trip bending) was measured based on JIS P 8115. The test piece is a short-tab-like shape with a length of 150 mm on the long side and a length of 12.7 mm on the short side. The R of the bending splint is set to 0.38 mm, and the load is set to 250 g.

If the number of times of MIT resistance is larger than that of the comparative example having the same thickness, the bending property of the copper foil is good.

In the table, "rolling direction" is defined as the longitudinal direction of the test piece is the rolling parallel direction. "45 ° with the rolling direction" is defined as that the longitudinal direction of the test piece is 45 ° parallel to the rolling direction. "Rolling right angle direction" is defined as the longitudinal direction of the test piece is the rolling right angle direction (= the direction perpendicular to the rolling parallel direction).

5. Crystal size

Using SEM (Scanning Electron Microscope), each sample was observed before the heat treatment and before the final cold rolling (after the final annealing), and the average particle diameter was determined based on JIS H 0501. However, the double crystal system was measured as a different crystal grain. The measurement area was set to 400 μm × 400 μm in a cross section parallel to the rolling direction.

The obtained results are shown in Tables 1 and 2.

Tables 1 and 2 show that the MIT bendability is excellent in each example where the maximum degree of aggregation is 5 or less.

In Table 2, the value obtained by dividing the number of times of MIT folding resistance in a direction of 45 ° from the direction of rolling is divided by the number of times of MIT folding resistance in the rolling direction as an index of anisotropy. Similarly, the rolling method is used. The value obtained by dividing the number of times of MIT folding resistance in the line direction by the number of times of MIT folding resistance in the rolling direction is used as an index of anisotropy. At this time, in the case of each embodiment, the anisotropy of the number of times of MIT folding resistance is in the range of 0.7 to 1.3, and the anisotropy of bendability is also reduced. If the bending anisotropy is low, the number of times of MIT folding resistance in any direction is increased, and there is an advantage that the degree of freedom in designing the wiring of the flexible printed circuit board is increased. In addition, even if the direction of the wiring is not properly designed with respect to the rolling direction of the copper foil, the bendability in a specific direction is not easily reduced, and flexible printing is possible. The reliability of the wiring of the substrate is improved.

On the other hand, in Comparative Example 1 in which the final annealing temperature was greater than 400 ° C. and the crystal grain size before the final cold rolling reached 10 μm or more, the maximum degree of aggregation exceeded 5, and the anisotropy of the number of times of MIT resistance exceeded 0.7 ~ 1.3, the anisotropy of bending becomes larger. Specifically, in the case of Comparative Example 1, in a flexible printed circuit board, it is necessary to avoid designing wiring along a direction of 45 ° with respect to the rolling direction and at right angles to the rolling direction, so that the degree of freedom in wiring design is poor.

Moreover, in the case of Comparative Example 2 where the amount of P added exceeds 0.03%, the conductivity is not good because the conductivity is less than 75%.

Claims (8)

A copper foil for a flexible printed circuit board, which is a rolled copper foil composed of 99.0% by mass or more of Cu and inevitable impurities remaining, and the surface of the copper foil is I (111) / I ₀ (111) Among the four sets of I, 200, I (200) / I ₀ (200), I (220) / I ₀ (220), and I (311) / I ₀ (311), the maximum set degree is 5 or less The electrical conductivity of the copper foil for a flexible printed circuit board is 75% or more. The copper foil for a flexible printed circuit board as described in claim 1, wherein the short copper-shaped test piece having a length of 150 mm and a length of 12.7 mm on the short side is produced using the above-mentioned copper foil for flexible printed substrates, and is based on When JIS P 8115 measures the number of times of MIT folding resistance (where R of the bending jig is 0.38 mm and the load is 250 g), the number of times of MIT folding resistance when the longitudinal direction of the test piece is parallel to the rolling direction. The ratio of the number of times of MIT folding resistance when the longitudinal direction of the sheet is parallel to the rolling direction at 45 °, and the ratio of the number of times of MIT folding resistance when the longitudinal direction of the test piece is parallel to the rolling direction It is 0.7 ~ 1.3. The copper foil for a flexible printed circuit board as described in claim 1 is composed of the fine copper specified in JIS-H3100 (C1100) or the oxygen-free copper of JIS-H3100 (C1020). The copper foil for a flexible printed circuit board according to claim 1 or 2, further comprising a total of 0.5% by mass or less selected from the group consisting of P, Ag, Sb, Sn, Ni, Be, Zn, In, and Mg At least one or two or more of these groups are added as an additive element. The copper foil for flexible printed substrates according to any one of claims 1 to 3, wherein the above-mentioned maximum degree of aggregation after 300 ° C × 30min annealing (wherein, the heating rate is 100 ° C / min to 300 ° C / min) It is 5 or less. A copper-clad laminate, which is a flexible printed product according to any one of claims 1 to 4. A copper foil for a brush substrate is laminated with a resin. A flexible printed circuit board is formed by forming a circuit from 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.