TWI396779B - Copper foil and its manufacturing method, and flexible printed circuit board - Google Patents

Description

Copper foil and its manufacturing method, and flexible printed circuit board

The present invention relates to a copper foil and a method of manufacturing the same, and a flexible printed circuit board, particularly a copper foil suitable for a flexible printed circuit board (hereinafter referred to as FPC), a method for producing the same, and an FPC using the copper foil.

The most recent FPCs are usually divided into two types. One of them is to attach a copper foil to an insulating film (polyimide, polyester, etc.) with an adhesive resin, and apply an etching treatment to the pattern. This form of FPC is generally referred to as a three-layer FPC. On the other hand, another form is an FPC in which a copper foil is directly laminated on an insulating film (polyimine, polyester, or the like) without using an adhesive. These are often referred to as two-layer FPCs. For example, the FPC is mainly used for internal wiring such as a flat panel display such as a liquid crystal display or a plasma display, a camera, an AV device, a personal computer, a computer terminal, an HDD, a mobile phone, and a vehicle electronic device. Since these wirings are attached to the machine by being bent or used in a place where the bending is repeated, it is an important characteristic that the bending property is excellent in the characteristics required for the copper foil for FPC.

The FPC copper foil can be used in two types. One of them is a rolled copper foil which is formed into a foil shape by subjecting an ingot of copper produced by a foundry to a rolling process. The other is electrolytic copper foil. In this case, as shown in FIG. 1, in the electrolytic cell provided with the anode 1, an electrolytic solution 3 containing copper sulfate as a main component is filled, and the copper is precipitated in a foil form by electroplating. Above the cathode (titanium drum) 2. Thereafter, the precipitated foil-like copper was continuously peeled off to produce an untreated copper foil 4, and the untreated copper foil was subjected to surface treatment to obtain an electrolytic copper foil.

Since copper foil for FPC is required to have excellent bendability, the ratio of using rolled copper foil has been high since the past. For this reason, since the rolled copper foil is heated in the step of bonding the copper foil and the polyimide during the production of the FPC, it is blunt and softened at a lower temperature of 120 ° C to 160 ° C. Bending and elongation are increased.

However, the rolled copper foil is more expensive than the electrolytic copper foil, and in particular, when the thickness is as thin as 12 μm or 9 μm, the cost is greatly increased. The reason for this is that when a thin object is formed, a thick copper foil is repeatedly rolled and manufactured.

Further, the width of the copper foil produced by rolling is generally as narrow as about 600 mm, which has the disadvantage of poor productivity in the production of FPC.

On the other hand, the electrodeposited copper foil is cheaper than the rolled copper foil, and generally has a width of 1000 mm or more. Therefore, it is advantageous in productivity at the time of FPC production. However, the electrolytic copper foil produced by the conventional manufacturing method is not blunt and softened even if heated to 200 ° C or higher, and has poor bendability. Therefore, in the case of the copper foil for FPC, only Used in limited use.

The applicant of the present invention solved the disadvantages of the conventional electrolytic copper foil as described above, and developed a copper foil having excellent flexibility (see Patent Document 1). The untreated copper foil shown in Patent Document 1 is characterized in that the surface roughness Rz of the rough surface (hereinafter referred to as M surface) is 2.1 μm or less, and the surface roughness of the shiny surface (hereinafter referred to as S surface). Rz is the same or smaller, and is made by electrolyzing a foil using a compound having a mercapto group, a chloride ion, a low molecular weight of 10,000 or less, and a polymer polysaccharide. (In addition, here, Untreated copper foil refers to the copper foil before the surface treatment, as described in the copper foil terminology used in the copper foil industry standard printed circuit board, CFIA 0001-1999.

This untreated electrolytic copper foil has the same degree of flexibility as the rolled copper foil.

On the other hand, in recent years, the technological innovation of electronic instruments has been remarkable, and the miniaturization of machines has been progressing. Therefore, in order to reduce the size of the machine, the FPC for these machines has rapidly progressed in pinning and fine pitching. Also, in order to meet these requirements while improving reliability, copper foil is required to have a longer bending life.

As described above, the FPC is on an insulating film (polyimine, polyester, liquid crystal polymer, etc.) on a copper clad laminate (hereinafter sometimes referred to as CCL) to which a copper foil is attached. A flexible printed circuit board that forms a circuit.

In order to improve the adhesion to the insulating film, the rolled copper foil and the electrolytic copper foil used in the present invention are subjected to a roughening treatment in which copper particles are adhered by plating at least on the surface of the copper foil adhered to the film. Further, on the other side, galvanizing treatment or chromic acid treatment for preventing rust or suppressing heat discoloration is applied.

Further, in the case of electrolytic copper foil, a roughening treatment is usually applied to the M surface, and a galvanizing treatment or a chromic acid treatment for preventing rust or suppressing heat discoloration is usually applied to the S surface without roughening treatment.

When the CCL is produced, the film is directly cast by heat-pressing the film through the adhesive resin on the roughened surface (three-layer FPC) or not by the adhesive resin, or the insulating film is laminated on the rough of the copper foil by hot pressing. Face (two-layer FPC) to make CCL.

Then, a circuit was formed by etching on the CCL fabricated in this manner, and a protective film of an insulating film was adhered to the circuit side to form an FPC.

The FPC produced in this manner is bent and mounted, or used in a place where it is repeatedly bent. Therefore, the bendability of the copper foil for FPC must be excellent.

Further, the test method for the bendability was carried out by a folding endurance test, a bending resistance test, or the like described in JIS C 5016-1994. In particular, the bending resistance test is considered to be close to the bending mode in which the FPC is actually used, and is generally used.

When the FPC bending test was carried out in accordance with the above-mentioned bending resistance test method, cracks occurred on the surface of the copper foil as the number of bending times increased, and the copper foil was broken at the end of the crack. When the process of cracking is observed carefully, in the case where the copper foil is an electrolytic copper foil, the crack does not come from the M surface side, and the entry from the S surface side is an overwhelming majority.

When the copper foil produced by the manufacturing method of the patent document 1 is analyzed, especially when the surface roughness of the S surface is large, it is easy to fracture.

The S surface of the electrolytic copper foil was observed by the naked eye and had a glossy surface. However, when observed by a SEM (Scanning Electron Microscope), the surface having many irregularities was observed.

As shown in Fig. 1, the electrolytic copper foil is obtained by depositing copper in a foil form into a rotating anode (titanium drum) 2 by an electrolytic solution 3 containing copper sulfate as a main component, and continuously peeling the copper by the same. The untreated copper foil 4 is opened. Since the S surface of the untreated copper foil after the foil formation is a surface that is in contact with the titanium drum, the surface is just copied to the surface of the titanium drum 2.

Since the titanium drum is periodically ground, the drum is relatively smooth after being ground, and the polishing stripe is shallow, but since the plating is performed using a strongly acidic electrolyte, the polishing strip will pass over time. deepen. This will be copied in the original state into the shape of the S surface of the electrolytic copper foil.

When the bending resistance test was performed on the electrolytic copper foil having the S surface on which the polishing streaks of the titanium drum were printed, it was found that the portion of the stripe which was copied on the S surface became the starting point of cracking of the copper foil.

In particular, in the case where the stripes are bent in parallel, it is relatively easy to break with respect to the case where the stripes are bent vertically.

[Patent Document 1] Japanese Patent No. 3,313,277 [Patent Document 2] Japanese Patent No. 3608840

The present invention has been completed for the purpose of making the bending life of the above-mentioned conventional electrolytic copper foil longer.

Accordingly, an object of the present invention is to provide an electrodeposited copper foil which is excellent in adhesion to an insulating film and excellent in bending resistance after adhesion to an insulating film.

In order to solve the above problems, the copper foil of the present invention is subjected to smooth plating on the shiny side of the untreated electrolytic copper foil, and the smooth plating is performed to form a granular crystal structure.

In the copper foil, it is preferable that the surface roughness Rz of the untreated electrodeposited copper foil on the rough surface side is 2.1 μm or less, and the surface roughness Rz on the gloss surface side is the same or smaller.

Among the above-mentioned copper foils, it is preferred that the untreated copper foil is formed by electrolytically forming a foil using a compound having a mercapto group, a chloride ion, and a low molecular weight gel having a molecular weight of 10,000 or less and a polymer polysaccharide.

Among the above-mentioned copper foils, a smooth plating which is applied to the shiny side of the untreated electrolytic copper foil is preferably a copper plating layer having an average crystal grain size of 2 μm or less.

Among the copper foils, a copper plating layer having a smooth plating weight of 18 ppm or less and a recrystallization temperature of 200 ° C or less is preferably applied to the shiny surface of the untreated electrolytic copper foil.

Further, it is a flexible printed circuit board produced by using the above-described copper foil for a flexible printed circuit board.

The present invention can provide a copper foil which is excellent in bending life, excellent in adhesion to an insulating film, and excellent in bending resistance after adhesion to an insulating film, and a method for producing the same. Further, the present invention can provide an FPC excellent in bending resistance.

In the embodiment of the present invention, the untreated electrolytic copper foil is formed by electrolyzing a foil using a compound having a mercapto group, a chloride ion, and a low molecular weight gel having a molecular weight of 10,000 or less and a polymer polysaccharide. The surface roughness Rz of the surface side is 2.1 μm or less, and the surface roughness Rz of the glossy surface side is the same or smaller. Here, the surface roughness Rz is a ten-point average roughness (Rz) and is shown in JIS B 0601-1994.

In the embodiment of the present invention, the reason why the glossy surface of the untreated electrolytic copper foil is subjected to smooth plating is to smooth the polishing fringe that is copied onto the drum when the copper foil is foiled. By filling the stripe on the S surface, the copper foil is not easily cracked when it is bent.

On the other hand, the smooth plating applied to the shiny surface of the untreated electrolytic copper foil forms a granular crystal structure and is a copper plating layer having an average crystal grain size of 2 μm or less.

The crystal structure of copper formed by the plating may become a columnar crystal structure depending on the composition of the plating solution. However, in the plating of the S surface of the untreated electrolytic copper foil, the plating of the columnar structure is not suitable for the case where high bending resistance is required.

The reason for this is that when a bending stress is applied to the copper foil, if it is a columnar crystal structure, the columnar crystal grain boundary is cracked, and the possibility of being easily broken is high.

Further, in order to fill the S surface, it is preferred that the average crystal grain size is 2 μm or less, and if the average crystal grain size exceeds 2 μm, the effect of filling the S surface stripe is low, and the copper foil is increased. The number of bends until the crack becomes difficult.

Further, in the average particle diameter referred to in the present invention, the surface on which the crystal grains are formed is first photographed by a transmission microscope, and after actually measuring the area of the crystal grains in the photograph by 10 or more, the diameter of the area is calculated as a perfect circle. Calculated.

Further, in the present invention, the smooth plating applied to the shiny surface (S surface) of the untreated electrolytic copper foil is a copper plating layer having a carbon amount of 18 ppm or less and a recrystallization temperature of 200 ° C or lower. In this case, for example, the copper plating solution described in Patent Document 2 (Japanese Patent No. 3608840) is preferably used.

In order to make the amount of carbon 18 ppm or less, it is necessary to make the organic additive added to the plating solution extremely small or not added at all. The copper plating layer formed of the copper plating solution is a columnar crystal structure immediately after plating. However, since the amount of the organic additive present at the boundary of the crystal grain is small (the amount of the organic additive can be quantified by measuring the amount of carbon in the copper), it is recrystallized at a lower temperature of 200 ° C to be converted into a granular crystal structure. That is, in order to recrystallize at a temperature of 200 ° C or lower, it is necessary to make the amount of carbon in the copper foil 18 ppm or less.

The copper plating layer formed in this manner is recrystallized by heating to about 150 ° C when the three-layer copper-clad laminate is produced, and is changed into a granular crystal structure.

This is the same situation as manufacturing a two-layer copper-clad laminate. Further, when a two-layer copper-clad laminate is produced, a temperature of 300 ° C or higher is usually used. Therefore, similarly to the three-layer copper-clad laminate, the copper plating layer is recrystallized and converted into a granular crystal structure.

In this manner, the copper plating layer which is recrystallized and converted into a granular crystal structure can prevent the copper foil from being cracked even when the bending stress is applied to the FPC, and the number of times of bending until the bending fracture of the copper foil can be increased.

Further, in the case of performing the plating, plating conditions such as composition of the plating solution, temperature, and current density conditions are selected so as to fill the stripes of the S surface.

The thickness of the smooth plating is preferably from 0.05 μm to the same range as the thickness of the original foil (untreated electrolytic copper foil). That is to say, when the original foil thickness is 9 μm, plating is applied to a thickness of 0.05 μm to 9 μm. The reason for this is that even if plating of less than 0.05 μm is performed, there is no effect of filling the S surface.

Further, when smooth plating is applied to the S surface of the untreated electrolytic copper foil, it is preferable to apply smooth plating to the M surface. Further, when the copper plating solution used for the production of the original foil is the same as the copper plating solution for smooth plating of the S surface, it is not necessary to perform smooth plating on the M surface.

However, if the copper plating solution used for the production of the original foil is different from the copper plating solution for smooth plating of the S surface, the smooth plating of the M surface may improve the bendability.

The reason why the M surface is also subjected to smooth plating in this manner is the characteristic value (tensile strength, elongation, etc.) of the copper which is electrolyzed by the copper plating solution used for the plating of the S surface, and the characteristic value of the original foil ( The tensile strength, the elongation, and the like may be large. Therefore, when the plating is applied only to the S surface, the S surface and the M surface may not be balanced, which may cause a problem. In this case, it is necessary to apply electroplating simultaneously to the M surface and the S surface to obtain a balance between the S surface and the M surface.

Hereinafter, embodiments of the present invention will be described in further detail by way of examples.

[Example 1]

In the present embodiment, as shown in Fig. 1, the following devices are disposed: a rotating drum-shaped cathode (made of titanium) 2 and an electrolytic cell having a concentric shape (manufactured by DSA) 1 with respect to the cathode. The electrolytic solution 3 is filled, and then an electric current is passed between the two electrodes to produce an untreated electrolytic copper foil 4. Here, the copper plating solution used was the following composition 1, and the untreated electrolytic copper foil 4 was formed so as to have a foil thickness of 35 μm. Thereafter, a plating solution of composition 1 was used to form a copper plating layer having a thickness of 0.07 μm on the S surface as smooth plating. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

Electroplating solution composition 1: Electroplating bath: Cu 70~130g/LH ₂ SO ₄ 80~140g/L 3-mercapto-1-propane sulfonate 0.5~5ppm hydroxyethyl cellulose 1~10ppm low molecular weight glue (molecular weight 3000) 1~10ppm chloride ion 5~50ppm current density: 10~100A/dm ² bath temperature: 40~60°C

[Embodiment 2]

Under the conditions of Example 1, a copper plating layer having a thickness of 1 μm as a smooth plating was formed in the same manner as in Example 1 on the S surface of the untreated electrolytic copper foil 4 having a thickness of 34 μm. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Example 3]

Under the conditions of Example 1, a copper plating layer having a thickness of 3 μm as a smooth plating was formed in the same manner as in Example 1 on the S surface of the untreated electrolytic copper foil 4 having a thickness of 32 μm. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Example 4]

Under the conditions of Example 1, a copper plating layer having a thickness of 17.5 μm as a smooth plating was formed in the same manner as in Example 1 on the S surface of the untreated electrolytic copper foil 4 having a thickness of 17.5 μm. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Example 5]

Under the conditions of Example 1, a copper plating layer having a thickness of 1 μm as a smooth plating was formed on the S surface of the untreated electrolytic copper foil 4 manufactured to have a thickness of 34 μm using the plating liquid of composition 2. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

Electroplating solution composition 2: Electroplating bath: Cu 70~130g/LH ₂ SO ₄ 80~140g/L Current density: 10~100A/dm ² Bath temperature: 40~60°C

In the copper foil to which the smooth plating copper plating layer was applied with the plating liquid composition 2 described above, the amount of carbon of the smooth copper plating layer was measured, and as a result, C = 6.0 ppm.

Further, the amount of carbon was measured by EMIA-U511, a market maker.

This measurement is performed by measuring the infrared absorption of the CO ₂ gas generated by burning the degreased copper foil in an electric furnace in an oxygen atmosphere, and converting it into carbon.

Standard sample name: JSS200-11 Standard value: 56.00ppm Combustion agent: None at the time of measurement, when calibrated: Sn 0.5g Burning condition: 1250 °C

[Embodiment 6]

Under the conditions of Example 1, a plating solution having a plating liquid composition 2 was used on the S surface of the untreated electrolytic copper foil 4 having a thickness of 32 μm to form a copper plating layer having a thickness of 3 μm. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Embodiment 7]

Under the conditions of Example 1, a plating solution of a plating solution composition 2 was used on the S surface of the untreated electrolytic copper foil 4 having a thickness of 29 μm to form a copper plating layer having a thickness of 3 μm, and at the same time, The M side also forms a copper plating layer having a thickness of 3 μm. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Comparative Example 1]

Under the conditions of Example 1, an untreated electrolytic copper foil 4 having a thickness of 35 μm was produced. Thereafter, a roughening treatment for improving the adhesion and a rustproof treatment were carried out using a surface treatment apparatus to obtain a copper foil having a thickness of 35 μm.

[Comparative Example 2]

Under the conditions of Example 1, a copper foil having a thickness of 34 μm was formed, and on the S surface, a plating solution of a plating liquid composition of 3 was used to form a copper plating layer having a thickness of 1 μm, and then a surface treatment apparatus was used. A roughening treatment for roughening and rust-preventing treatment is carried out to obtain a copper foil having a thickness of 35 μm.

Electroplating solution composition 3: Electroplating bath: Cu 70~130g/LH ₂ SO ₄ 80~140g/L glue 1~10ppm chloride ion 5~50ppm Current density: 10~100A/dm ² Bath temperature: 40~60°C

(Production of Bending Resistance Evaluation Test Piece) The copper foils shown in Examples 1 to 6 and Comparative Examples 1 and 2 were manufactured by Nikkan Industrial Co., Ltd., and the Nikes Rex CISV-2525 (polyimine film). 25 μ m, adhesive thickness 25 μm), laminated at 150 ° C, 40 kg/cm ² , 55 minutes, and prepared as line/space = 1.5 mm/JIS C 5016-1994 1.0 mm bending resistance specimen. Thereafter, Nikki Rex CISV-2525 was laminated as a protective film.

Bending resistance test The above-mentioned bending resistance evaluation test piece (FPC) was attached to an FPC high-speed bending tester SEK-31B2S manufactured by Shin-Etsu Engineering Co., Ltd., and had a curvature radius of 1.5 mm, a stroke length of 20.0 mm, and bending. The bending resistance was measured under the conditions of 2000 times/min. In this measurement, the circuit resistance was measured over time, and the number of times until the break was counted. The test results are shown in Table 1.

As a result of the tests of Examples 1 to 7 shown in Table 1, it was found that the smooth plating of the granular crystal on the S surface was more frequent than the comparative example 1 to which the smooth plating was not applied.

Further, in the case where the smooth plating applied to the S surface of Comparative Example 2 was a columnar crystal, the number of cycles of the fracture was smaller than that of Comparative Example 1. These are caused by cracks in the crystal grain boundaries of the columnar crystals when the circuit is bent, and are easily broken.

Moreover, the number of times of reaching the fracture in the bendability test was increased in accordance with the thickness of the smooth plating, and was improved. For example, in the case where the thickness of the smooth plating is 0.03 μm, although it is not greatly improved, as shown in the first embodiment, the case of 0.07 μm is greatly improved.

As described above, the electrodeposited copper foil of the present invention is excellent in bending resistance and has the same performance as or better than that of the rolled copper foil. Further, compared with the rolled copper foil, it is relatively inexpensive, and a wide foil can be produced, so that productivity can be improved.

1. . . Electrolytic foil device anode (DSA)

2. . . Cathode of electrolytic foil-making device (titanium drum)

3. . . Electrolyte

4. . . Untreated copper foil

Fig. 1 is a view showing the configuration of an electrolytic foil-making apparatus.

1. . . Electrolytic foil device anode (DSA)

2. . . Cathode of electrolytic foil-making device (titanium drum)

3. . . Electrolyte

4. . . Untreated copper foil

Claims (6)

A copper foil which is subjected to smooth plating on a glossy surface of an untreated electrolytic copper foil, wherein the smooth plating is a copper plating layer having a carbon content of 18 ppm or less and a recrystallization temperature of 200 ° C or less, and the smooth plating is granular Crystal structure. The copper foil of the first aspect of the invention, wherein the surface roughness Rz of the rough surface side of the untreated electrolytic copper foil is 2.1 μm or less, and the surface roughness Rz on the glossy surface side is the same or smaller. The copper foil according to claim 2, wherein the untreated electrolytic copper foil is obtained by adding an electrolyte having a mercapto group, a chloride ion, a low molecular weight gel having a molecular weight of 10,000 or less, and a polymer polysaccharide. Electrolytic foil is formed. The copper foil according to claim 3, wherein the smooth plating is a copper plating layer having an average crystal grain size of the crystal structure of 2 μm or less. A method for producing a copper foil produced by smooth plating on a glossy surface of an untreated electrolytic copper foil, wherein the smooth plating is copper formed to have a carbon content of 18 ppm or less and a recrystallization temperature of 200 ° C or lower. The granular crystal structure of the plating layer is formed. A flexible printed circuit board produced by using a copper foil according to any one of claims 1 to 4.