KR101280486B1 - Copper foil and method for manufacturing the same, and flexible printed circuit board - Google Patents

Abstract

The present invention is to provide an electrolytic copper foil which is excellent in adhesiveness for bonding with an insulating film, and excellent in bending resistance after bonding with an insulating film, and provides an FPC excellent in bending resistance.

Smooth plating is performed on the gloss surface of an untreated electrolytic copper foil. Moreover, this smooth plating is formed by copper plating which is a grain-shaped crystal structure and whose average crystal grain diameter is 2 micrometers or less. Moreover, this smooth plating is formed at 18 ppm or less of carbon amount and 200 degrees C or less of recrystallization temperature.

Copper foil, flexible printed wiring board, smooth plating, insulation film, untreated electrolytic copper foil

Description

Copper foil and method for manufacturing the same, and flexible printed circuit board

1 is an explanatory diagram showing a structure of an electrolytic metal foil production apparatus.

<Explanation of symbols for the main parts of the drawings>

1: Anode (DSA) of electrolytic metal foil manufacturing apparatus

2: cathode (titanium drum) of electrolytic metal foil manufacturing apparatus

3: electrolyte

4: untreated copper foil

BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a copper foil, a method for producing the same, and a flexible printed wiring board, and more particularly, to a copper foil suitable for a flexible printed wiring board (hereinafter referred to as 'FPC'), a method for producing the same, and an FPC using the copper foil.

Recent FPCs are usually divided into two types. One is to apply copper foil to an insulating film (polyimide, polyester, etc.) with an adhesive resin, and to perform a pattern by etching. This type of FPC is commonly referred to as 'three layer FPC'. On the other hand, another type is FPC which laminated | stacked the copper foil directly with the insulation film (polyimide, liquid crystal polymer, etc.), without using an adhesive agent. This is commonly referred to as 'two layer FPC'. Such FPC is mainly used for internal wiring of flat panel displays such as liquid crystal displays and plasma displays, cameras, AV devices, personal computers, computer terminal devices, HDDs, mobile phones, car electronic devices, and the like. Since these wirings are used in places that are bent to the equipment or are repeatedly bent, one of the important characteristics is excellent flexibility as a characteristic required for the copper foil for FPC.

There are two types of this copper foil for FPC. One is the rolled copper foil which performed the rolling process to the copper ingot manufactured by casting, and made it into metal foil shape. Another is electrolytic copper foil. In this case, as shown in FIG. 1, the electrolytic solution in which the anode 1 was provided is filled with the electrolyte solution 3 which contains copper sulfate as a main component, and the cathode (rotating drum made from electrolytic plating method) is rotated by the electroplating method; 2) Copper is deposited on the metal foil shape. Then, this precipitated copper foil-like copper is continuously peeled off, the untreated copper foil 4 is manufactured, and surface treatment is performed on this untreated copper foil 4, and an electrolytic copper foil is obtained.

Since excellent flexibility is required as the copper foil for FPC, the ratio of using a rolled copper foil was high conventionally. This is because the rolled copper foil is annealed at a relatively low temperature of 120 to 160 ° C. and softened when heated in the step of bonding the copper foil and polyimide during FPC production, resulting in increased flexibility and elongation.

However, a rolled copper foil is expensive compared with an electrolytic copper foil, and especially costly increases as it is thin like 12 micrometers and 9 micrometers. This is because, when making a thin one, a thick copper foil is repeatedly rolled several times.

Moreover, the width | variety of the copper foil manufactured by rolling is narrow normally about 600 mm, and there existed a fault that productivity in FPC manufacture falls.

On the other hand, electrolytic copper foil is inexpensive compared with rolled copper foil, and since it can usually manufacture by width 1,000 or more, there exists an advantage that the productivity at the time of FPC manufacture is excellent. However, since the electrolytic copper foil manufactured by the conventional manufacturing method does not anneal and soften even if it heats more than 200 degreeC compared with a rolled copper foil, since it is inferior in flexibility, it was used only for the limited use as copper foil for FPC.

The present applicant solved the drawback of such a conventional electrolytic copper foil, and developed the copper foil excellent in bendability (refer Japanese Unexamined-Japanese-Patent No. 3313277 (following patent document 1)). The untreated copper foil shown in Patent Literature 1 has a surface roughness Rz on the rough surface (hereinafter referred to as the 'M surface') of 2.1 µm or less and a surface roughness Rz of the glossy surface (hereinafter referred to as the 'S surface'). An untreated electrolytic copper foil characterized by being equal to or less than that, an untreated copper foil prepared electrolytically using an electrolyte solution containing a mercapto group, a chloride ion, and a low molecular weight glue and a high molecular weight polysaccharide having a molecular weight of 10,000 or less (also Here, an untreated copper foil shows copper foil before surface treatment, as described in the copper foil industry association standard and the copper foil term CFIA 0001-1999 for a printed wiring board).

The flexibility of this untreated electrolytic copper foil has the same level of flexibility as that of the rolled copper foil.

On the other hand, the technological innovation of the electronic device has recently been made remarkably, and the miniaturization of the device is in progress. For this reason, in the FPC used for these devices, in order to cope with the miniaturization of devices, multipinning and fine pitching are rapidly progressing. And in order to satisfy such a request and to improve the reliability, the copper foil with a longer bending life is calculated | required.

As mentioned above, FPC is a flexible printed wiring board which formed the circuit in the copper clad laminated board (Hereinafter, it may abbreviate as CCL) which stuck copper foil on the insulation film (polyimide, polyester, liquid crystal polymer, etc.).

Both the rolled copper foil and the electrolytic copper foil used for this apply the roughening process which adhered the particle | grains by plating to the surface which adhere | attaches at least the film of copper foil in order to improve the adhesive force with an insulating film. On the other side, zinc plating, chromate treatment, and the like are performed for the purpose of suppressing rust prevention or heat discoloration.

In the case of the electrolytic copper foil, a roughening treatment is usually performed on the M surface, and a roughening treatment is not performed on the S surface, and galvanizing treatment or chromate treatment is performed for the purpose of suppressing rust prevention or heat discoloration.

In manufacturing CCL, the roughened surface is thermally pressed with a film through an adhesive resin (3 layers FPC), or an insulating film is laminated by direct casting or thermocompression bonding to a copper foil rough surface without an adhesive resin (2 layers FPC). To create a CCL.

Then, a circuit is formed on the CCL thus produced by the etching method, and the coverlay of the insulating film is adhered to the circuit side to form FPC.

The FPC created in this way is used for a place which is bent and mounted or repeatedly bent. Therefore, the copper foil for FPC should be excellent in flexibility.

In addition, as an evaluation test method of bendability, the fracture resistance test, the bend resistance test, etc. which are described in JIS C 5016-1994 are performed. In particular, the flex resistance test is generally used because it is said to be close to the elastic mode when FPC is actually used.

When the bending test of the FPC is performed by the bending resistance test method as described above, as the number of bending increases, a crack occurs on the surface of the copper foil, and finally, the copper foil breaks from the crack. When the process of a crack is observed in detail, when a copper foil is an electrolytic copper foil, the crack occurs predominantly from S surface side instead of M surface side.

As a result of analyzing this phenomenon, it turned out that the copper foil created by the manufacturing method of patent document 1 tends to be broken when a bending resistance test is performed especially when the surface roughness of S surface is coarse.

The S surface of the electrolytic copper foil is a glossy surface when viewed with the naked eye, but when observed with a SEM (Scanning Electron Microscope), it has a surface shape with many stem-shaped irregularities.

As shown in FIG. 1, the electrolytic copper foil is untreated copper foil 4 by depositing copper in a metal foil shape on a rotating cathode (titanium drum) 2 from an electrolytic solution 3 containing copper sulfate as a main component and continuously peeling it. To prepare. Since the S surface of this manufactured untreated copper foil 4 was the surface which contacted the titanium drum, the surface becomes a surface to which the state of the titanium drum 2 surface was transferred.

Since the titanium drum is periodically polished, the polishing stem is relatively smooth immediately after the drum is polished and the depth of the polishing stem is shallow. However, since the electroplating is performed using a strongly acidic electrolyte, the polishing stem becomes deeper with time. Lose. This leads to the shape of the S surface of an electrolytic copper foil as it is.

When the bending resistance test was performed with respect to the electrolytic copper foil which has the S surface with which the grinding | polishing stem of such a titanium drum was transferred, it turned out that the stem part transferred to the S surface originated and a crack generate | occur | produced in copper foil.

In particular, when it is bent in parallel with the stem compared to the case where it is bent in a direction perpendicular to the stem, it is more likely to break.

The present invention has been completed as a result of research for the purpose of further extending the bending life of the conventional electrolytic copper foil.

Therefore, an object of this invention is to provide the electrolytic copper foil which was excellent in the adhesiveness which adhere | attaches with an insulating film, and excellent in the bending resistance after adhesion with an insulating film.

In order to solve the said subject, the copper foil of this invention is copper foil which performed the smooth plating on the gloss surface of the untreated electrolytic copper foil, and is formed so that the said smooth plating may become a grain-shaped crystal structure.

In the said copper foil, it is preferable that the said untreated electrolytic copper foil has the surface roughness Rz of 2.1 micrometers or less, and is equal to or less than the surface roughness Rz of the gloss surface.

In the said copper foil, it is preferable that the said unprocessed electrolytic copper foil is formed by electrolytic manufacture using the compound which has a mercapto group, chloride ion, and the electrolyte solution which added the low molecular weight glue and high molecular weight polysaccharide of 10,000 or less molecular weight.

In the said copper foil, it is preferable that the smooth plating performed on the gloss surface of an untreated electrolytic copper foil is copper plating whose average crystal grain diameter of the said crystal structure is 2 micrometers or less.

In the said copper foil, it is preferable that the smooth plating performed on the gloss surface of an untreated electrolytic copper foil is copper plating whose carbon amount is 18 ppm or less and recrystallization temperature is 200 degrees C or less.

Moreover, it is a flexible printed wiring board produced using the said copper foil for flexible printed wiring boards.

(Embodiments)

In the embodiment according to the present invention, the untreated electrolytic copper foil is produced electrolytically using an electrolyte solution to which a compound having a mercapto group, a chloride ion, and a low molecular weight glue and a polymer polysaccharide having a molecular weight of 10,000 or less is added. The roughness is surface roughness Rz of 2.1 µm or less and is equal to or smaller than the surface roughness Rz on the gloss surface side. Here, surface roughness Rz is 10-point average roughness Rz, and is shown by JIS B0601-1994.

In the Example which concerns on this invention, the reason for performing smooth plating on the gloss surface of an untreated electrolytic copper foil is to fill and smooth the stem of S surface which transferred the grinding | polishing stem of the said drum when manufacturing copper foil. By filling the stem of S surface, a crack does not easily arise in copper foil with respect to elasticity.

On the other hand, the smooth plating performed on the gloss surface of an untreated electrolytic copper foil is formed so that it may become a grain-shaped crystal structure, and the average crystal grain diameter is copper plating with 2 micrometers or less.

The crystal structure of copper formed by this plating may become columnar crystal structure by the plating liquid composition. However, as plating performed on the S surface of an untreated electrolytic copper foil, plating of columnar structure is not suitable when high flex resistance is needed.

This is because when elastic stress is applied to the copper foil, in the case of columnar crystal structure, there is a high probability of cracking along the columnar grain boundary and rather fragility.

In order to fill the S surface, the average crystal grain size is preferably 2 µm or less. When the average crystal grain diameter exceeds 2 µm, the effect of filling the stem of the S surface is less effective. This is because it becomes difficult to stretch.

In addition, the average particle diameter referred to in this invention first takes the photograph of the surface in which the crystal grain is formed with the transmission microscope, and after measuring 10 or more areas of the crystal grain in the photograph, it rounds off the area. It calculates by calculating the diameter at the time of ().

In addition, in this invention, the smooth plating performed on the gloss surface (S surface) of an untreated electrolytic copper foil is copper plating in which carbon amount is 18 ppm or less and recrystallization temperature is 200 degrees C or less. In this case, it is suitable to use the copper plating liquid of Unexamined-Japanese-Patent No. 3608840 as a plating liquid to be used, for example.

In order to make carbon amount 18 ppm or less, the organic additive added in plating liquid should be made into the trace amount, or should not be added at all. In the copper plating formed from such a copper plating solution, the state immediately after plating becomes a columnar crystal structure. However, since there are few organic additive components present at the grain boundaries (the amount of organic additive can be quantified by measuring the amount of carbon in copper), the crystal grain structure is changed to recrystallized at a relatively low temperature of 200 ° C. or less. That is, in order to recrystallize at 200 degrees C or less, the amount of carbon in copper foil needs to be 18 ppm or less.

The copper plating layer thus formed is heated to around 150 ° C. when the three-layer copper clad laminate is manufactured to be recrystallized to change into a particulate crystal structure.

This also applies to the case of manufacturing a copper clad laminated board of two layers. In addition, when manufacturing a copper clad laminated board of two layers, since temperature is normally 300 degreeC or more, like a three-layer copper clad laminated board, a copper plating layer recrystallizes and changes into a grain-shaped crystal structure.

In this manner, the copper plating layer which is recrystallized and changed into a grainy crystal structure prevents cracking of the copper foil even when the FPC is subjected to elastic stress, thereby increasing the number of bends leading to the bending fracture of the copper foil.

In addition, when performing this plating, the composition, temperature, and current density conditions of a plating liquid are selected, and plating conditions are selected so that the stem of S surface may be filled up.

The thickness of the smooth plating is suitably up to the same thickness as the thickness of the foil used as 0.05 µm to one foil (untreated electrolytic copper foil). That is, when the thickness of the copper foil used as a raw foil is 9 micrometers, what is necessary is just to perform plating so that it may become thickness of 0.05 micrometer-9 micrometers. This is because even if plating of less than 0.05 mu m is not effective to fill the stem of the S surface.

In addition, it may be suitable to perform smooth plating on the S surface of the untreated electrolytic copper foil and to perform smooth plating on the M surface. In addition, when the copper plating liquid used when manufacturing the raw foil and the copper plating liquid used when performing the smooth plating on the S surface are not the same, it is not necessary to perform the smooth plating further on the M surface.

However, when the copper plating liquid used when manufacturing the raw foil and the copper plating liquid used when performing the smooth plating on the S surface are different from each other, the smoothness plating may also be improved on the M surface.

The reason why smooth plating is also performed on the M surface is that the performance value (tensile strength, elongation, etc.) of the copper electrolytically deposited from the copper plating solution used for plating the S surface is significantly different from the performance value (tensile strength, elongation, etc.) of the raw foil. In some cases, when the above plating is performed only on the S surface, the balance between the S surface and the M surface may not be balanced, which may cause a problem. In such a case, it is necessary to apply plating to the M surface at the same time as the S surface to balance the S surface and the M surface.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment which concerns on this invention is described in detail by an Example.

(Example 1)

In this embodiment, as shown in Fig. 1, an electrolytic solution 3 is provided in an electrolytic cell of a device in which a rotating drum-shaped cathode (made of titanium) 2 and a cathode (made of DSA) concentrically arranged with respect to the cathode (cathode) thereof are arranged. ) Was charged, and a current was passed between the anodes to prepare an untreated electrolytic copper foil 4. The copper plating liquid used here was the following composition 1, and the untreated electrolytic copper foil 4 was formed so that thickness might be set to 35 micrometers. Then, using the plating liquid of the composition 1, copper plating of 0.07 micrometer thickness was formed in S surface by the smooth plating. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

Plating solution composition 1:

 Plating bath: Cu: 70 ~ 130g / L

H ₂ SO ₄ : 80 ~ 140g / L

         3-mercapto 1-propanesulfonic acid sodium: 0.5 to 5 ppm

         Hydroxyethylcellulose: 1 ~ 10ppm

         Low molecular weight glue (molecular weight 3,000): 1-10 ppm

         Chloride Ion: 5 ~ 50ppm

Current density: 10 to 100 A / dm ²

  Bath temperature: 40 ~ 60 ℃

(Example 2)

On the S surface of the untreated electrolytic copper foil 4 manufactured so that thickness might be 34 micrometers on the conditions of Example 1, copper plating with a thickness of 1 micrometer was formed by smooth plating similarly to Example 1. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Example 3)

On the S surface of the untreated electrolytic copper foil 4 manufactured so that thickness might be 32 micrometers on the conditions of Example 1, copper plating with a thickness of 3 micrometers was formed by smooth plating similarly to Example 1. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Example 4)

On the S surface of the untreated electrolytic copper foil 4 manufactured so that thickness might be set to 17.5 micrometers on the conditions of Example 1, copper plating with a thickness of 17.5 micrometers was formed by smooth plating similarly to Example 1. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Example 5)

On the S surface of the untreated electrolytic copper foil 4 manufactured so that thickness might be 34 micrometers on the conditions of Example 1, 1 micrometer-thick copper plating was formed by smooth plating using the plating liquid of composition 2. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

Plating Composition 2:

 Plating bath: Cu: 70 ~ 130g / L

H ₂ SO ₄ : 80 ~ 140g / L

Current Density: 10 ~ 100A / dm ²

 Bath temperature: 40 ~ 60 ℃

In the copper foil to which smooth copper plating was performed by the said plating liquid composition 2, when the carbon amount with respect to the smooth copper plating was measured, it was C = 6.0 ppm.

In addition, the carbon amount was measured by EMIA-U 511 of Horiba, Japan.

The measurement was converted to a degreased copper foil as the carbon amount measured by the infrared absorption with respect to the CO ₂ gas produced by firing in an electric furnace of an oxygen atmosphere.

Standard sample name: JSS 200-11

Standard value: 56.00 ppm

Auxiliaries (measured): None-During calibration-Sn 0.5g

Combustion Condition: 1250 ℃

(Example 6)

On the S surface of the untreated electrolytic copper foil 4 manufactured so that thickness might be 32 micrometers on the conditions of Example 1, the copper plating of thickness 3 micrometers was formed using the plating liquid of plating liquid composition 2. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Example 7)

Under the conditions of Example 1, the copper plating of thickness 3micrometer was formed on the S surface of the untreated electrolytic copper foil 4 manufactured so that it might be set to 29 micrometers, and the thickness might also be 3 on the M surface. Copper plating was formed which was μm. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Comparative Example 1)

The untreated electrolytic copper foil 4 whose thickness is 35 micrometers on the conditions of Example 1 was created. Then, the roughening process and the rust prevention process for adhesive improvement were performed through the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

(Comparative Example 2)

On the conditions of Example 1, copper foil with a thickness of 34 micrometers was created, and copper plating with a thickness of 1 micrometer was formed on the S surface using the plating liquid of plating liquid composition 3. Then, the roughening process and the rust prevention process for adhesiveness improvement were performed using the surface treatment apparatus, and the copper foil of 35 micrometers in thickness was obtained.

Plating solution composition 3:

 Plating bath: Cu: 70 ~ 130g / L

H ₂ SO ₄ : 80 ~ 140g / L

         Glue: 1 ~ 10ppm

         Chloride Ion: 5 ~ 50ppm

Current Density: 10 ~ 100A / dm ²

  Bath temperature: 40 ~ 60 ℃

Preparation of flex resistance evaluation test piece

The conditions of 150 degreeC, 40 kg / cm <2>, 55 minutes to Nikaflex CISV-2525 (polyimide film 25 micrometers, adhesive thickness 25 micrometers) by the Nikkan Industries Co., Ltd. were used for the copper foil shown in Examples 1-6 and Comparative Examples 1-2. After lamination, the bending resistance sample of line / space = 1.5 mm / 1.0 mm described in JIS C 5016-1994 was prepared. Thereafter, Nikaplex CISV-2525 was laminated as a coverlay.

Flex resistance test

The said bending resistance evaluation test piece (FPC) was set in the FPC high speed bending test machine SEK-31B2S made from Shin-Etsu Engineering Co., Ltd., and measurement of bending resistance on condition of bending radius 1.5 mm, stroke length 20.0 mm, and bending number 2000 times / min. Was performed. In this measurement, the circuit resistance was measured over time, and the number of times until break was counted.

The test results are shown in Table 1.

As can be seen from the test results of Examples 1 to 7 shown in Table 1 above, the smooth plating of the particulate crystals on the S surface is more frequent until fracture than in Comparative Example 1 without the smooth plating. It is obvious.

In addition, when the smooth plating performed on the S surface as in the case of Comparative Example 2 is a columnar crystal, the breaking cycle is smaller than that of Comparative Example 1. This is because when the circuit is bent, cracks are generated from the grain boundaries of the columnar crystals and are more likely to break.

In addition, the number of times until fracture due to the bendability test increases with the thickness of the smooth plating to be improved. For example, when the thickness of smooth plating is 0.03 micrometer, it does not improve significantly, but when it is 0.07 micrometer like Example 1, it improves significantly.

Thus, the electrolytic copper foil which concerns on this invention is excellent in bending resistance, and has the performance equivalent to or more than rolled copper foil. Moreover, since a foil which is cheaper and wider than a rolled copper foil can be manufactured, productivity can also be improved.

The present invention can provide a copper foil having a long bending life, excellent adhesiveness for adhering to an insulating film, and excellent bending resistance after adhesion with an insulating film, and a method for producing the same. In addition, the present invention can provide an FPC excellent in flex resistance.

Claims (7)

As copper foil which smooth-plated the gloss surface of S surface of the untreated electrolytic copper foil formed in the electrolytic cell which has the cathode of a rotating drum shape, Said smooth plating is a grain crystalline structure whose average particle diameter is 2 micrometers or less, Copper foil characterized by the above-mentioned. The method according to claim 1, The untreated electrolytic copper foil has a surface roughness (Rz) of 2.1 µm or less at the same time as the surface roughness (Rz) and a surface roughness (Rz) at or less than the glossy surface side. The method according to claim 2, The said untreated electrolytic copper foil is formed by electrolytic manufacture using the electrolyte solution which added the compound which has a mercapto group, Copper foil characterized by the above-mentioned. The method of claim 3, The said smooth plating layer is formed using the said electrolytic cell using the electrolyte solution which added the compound which has a mercapto-group compound, The copper foil for flexible printed wiring boards characterized by the above-mentioned. The method according to claim 1, The said smooth plating is carbon amount 18 ppm or less, and copper foil formed by recrystallization temperature 200 degrees C or less. An untreated electrolytic copper foil formed in an electrolytic cell having a rotating drum-shaped cathode is formed, and on the S surface of the untreated electrolytic copper foil, a smooth plating having a grain-like crystal structure having an average particle diameter of 2 µm or less is formed. Manufacturing method. It was produced using the copper foil of any one of Claims 1-5, The flexible printed wiring board characterized by the above-mentioned.

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