阅读说明：本技术 硬质轧制铜箔及该硬质轧制铜箔的制造方法 (Hard rolled copper foil and method for producing the same ) 是由 森冈伸哲 笹井雄太 福田绘里 于 2017-11-29 设计创作，主要内容包括：本发明提供如下一种硬质轧制铜箔,即使不提高最终压下率,通过加热并层叠于绝缘性树脂基材上,呈现优异的耐弯折性能,并且,因为不容易产生轧痕,所以能够维持较低的表面粗糙度,因此适合用于高速传送特性优异的柔性印刷电路板,而且不容易发生常温软化,在保管后加工为柔性印刷电路板时的作业效率和通箔性优异。本发明的硬质轧制铜箔是一种铜型取向的晶体取向密度为10以上,且黄铜取向的晶体取向密度为20以上的硬质轧制铜箔。(The present invention provides a hard rolled copper foil which exhibits excellent bending resistance by being heated and laminated on an insulating resin base without increasing the final reduction ratio, is suitable for a flexible printed circuit board having excellent high-speed transfer characteristics because it is less likely to generate a rolling mark and can maintain a low surface roughness, is less likely to soften at room temperature, and is excellent in work efficiency and foil passing property when it is processed into a flexible printed circuit board after storage. The hard rolled copper foil of the present invention has a crystal orientation density of copper type orientation of 10 or more and a crystal orientation density of brass orientation of 20 or more.)

1. A hard rolled copper foil, wherein the crystal orientation density of the copper type orientation is 10 or more and the crystal orientation density of the brass orientation is 20 or more.

2. The hard rolled copper foil according to claim 1, wherein a crystal orientation density of copper type orientation is 25 or less and a crystal orientation density of brass orientation is 45 or less.

3. The hard rolled copper foil according to claim 1 or 2, which is rolled from oxygen-free copper having a copper purity of 99.99% or more.

4. The hard rolled copper foil according to any one of claims 1 to 3, wherein a final reduction is less than 90%.

5. The hard rolled copper foil according to any one of claims 1 to 4, wherein a ten-point average roughness Rzjis94 is less than 1 μm.

6. The hard rolled copper foil according to any one of claims 1 to 5, wherein the foil thickness is 12 μm or less.

7. A printed circuit board laminated with the hard rolled copper foil according to any one of claims 1 to 6.

8. a method for producing a hard rolled copper foil according to any one of claims 1 to 6, characterized in that the final cold rolling is performed after the heat treatment at a temperature in the recovery temperature range.

9. the method for producing a hard rolled copper foil according to claim 8, wherein the rolling is performed so that the final reduction ratio is 70% or more and less than 90%.

Technical Field

The present invention relates to a hard rolled copper foil suitable for a flexible printed circuit board. Specifically, the hard rolled copper foil exhibits excellent bending resistance when laminated on an insulating resin base material by heating without increasing the final reduction ratio, is less likely to cause rolling marks and can maintain low surface roughness without increasing the final reduction ratio, and therefore has excellent high-speed transfer characteristics, and is less likely to soften during storage at room temperature, and therefore has excellent work efficiency and foil passing properties when processed into a flexible printed wiring board.

Background

Portable electronic devices represented by smartphones are becoming increasingly smaller, thinner, and lighter, and are becoming increasingly functional.

Materials used for portable electronic devices need to be contained in a narrow housing, and also need to be high-frequency-compatible with digital signals.

Therefore, the conductor of the flexible printed circuit board needs to satisfy the requirements of bending performance and bending resistance that is not easily broken even by repeated bending, and also needs to satisfy the requirements of high-speed transmission characteristics.

Generally, a copper foil is used as a conductor of a flexible printed circuit board.

In general, a copper foil is subjected to roughening treatment for forming fine metal particles called roughening particles on the surface thereof, and various surface treatments for imparting heat resistance, chemical resistance, and adhesiveness, and then the treated copper foil is laminated on an insulating resin substrate by a process of laminating the copper foil on the insulating resin substrate in a pressure form using a heating roller, or a process of applying an insulating resin substrate and then drying or treating the resin substrate at a high temperature, and finally the copper foil is partially etched to form a circuit, thereby manufacturing a flexible printed wiring board.

As the copper foil used as the conductor, either a rolled copper foil or an electrolytic copper foil can be used, and in the case of using a rolled copper foil, a hard rolled copper foil is generally used.

Generally, a hard rolled copper foil is manufactured by hot rolling a copper ingot, repeating cold rolling and heat treatment to reduce the thickness thereof in order, and finally cold rolling to a desired thickness.

The reason why the cold rolling is used is that the precision of the foil thickness is more excellent than that of the hot rolling.

In the cold rolling process, since the rolled copper is solidified by working, heat treatment is performed to make it soft again and to make it easy to work.

The heat treatment, also referred to as annealing, is generally carried out at 200 ℃ for 1 hour under an inert atmosphere or vacuum.

It is known that rolled copper is sequentially softened through a process called "recovery" → "recrystallization" → "grain growth", depending on the progress of the heat treatment.

Since the heat treatment is performed for the purpose of softening the rolled copper and making it into a state of easy working, it is usually heated to a state of "grain growth".

After heating to a state of "grain growth", the copper foil is repeatedly cold rolled to form a hard rolled copper foil having a desired thickness.

In this rolling process, the final cold rolling to be worked to a desired thickness is referred to as final cold rolling, the reduction ratio in the final cold rolling is referred to as final reduction ratio, the heat treatment immediately before the final cold rolling is referred to as final heat treatment, and the state before the final heat treatment is referred to as a final rolled copper bar.

By the final cold rolling, the individual crystal grains of the final rolled copper strip are deformed and rotated with them, respectively, to be oriented in a certain stable orientation. Such a certain crystal orientation distribution state of the polycrystal is referred to as a texture, and a texture produced by rolling is referred to as a rolling texture. The texture resulting from "grain growth" by heat treatment after rolling is referred to as a recrystallized texture.

The rolled texture is also known as β -fiber and is oriented in an orientation cluster that continuously links three orientations called Copper (Copper) orientation {112} < 111 >, S-orientation {123} < 634 >, and Brass (Brass) orientation {110} < 112 >.

In addition, { hkl } represents the miller index of a crystal plane parallel to the sample surface when a certain crystal is concerned, and < uvw > represents the miller index of the orientation parallel to the rolling direction.

As a method for improving the bending property and bending resistance of a hard rolled copper foil, a method of developing a cubic orientation consisting of a cubic (Cube) orientation {100} < 010 > in a recrystallized texture is known.

As a method for developing the cubic orientation, there is a method comprising: hard rolled copper foil having a high final reduction ratio is laminated on an insulating resin substrate, and the cubic orientation is developed by heat at the time of lamination.

However, a hard rolled copper foil having a high final reduction ratio has accumulated strain and a reduced softening temperature, and if stored at room temperature, the copper foil softens during storage (hereinafter referred to as room-temperature softening).

In the case where the copper foil is softened, there are problems as follows: in the step of laminating the copper foil on the insulating resin base material, the foil passing property is deteriorated due to breakage of the copper foil or generation of a ripple, and therefore, the work efficiency is lowered and the product yield is lowered.

In addition, there are also problems as follows: the hard rolled copper foil having a high final reduction ratio has a high surface roughness because of the rolling mark (streak) left on the surface of the copper foil, but if the copper foil having a high surface roughness is a conductor, the transmission loss of the printed wiring board becomes large and the high-speed transmission characteristics are degraded because the higher the current is, the more easily the high-frequency signal flows near the surface of the copper foil as a conductor (skin effect).

Therefore, there has been a demand for a hard rolled copper foil which exhibits excellent bending resistance by being heated and laminated on an insulating resin base material without increasing the final reduction ratio, has high-speed conveyance characteristics, does not soften at room temperature during storage, is excellent in working efficiency and foil passing property when laminated on an insulating resin base material, and improves the product yield.

Disclosure of Invention

Problems to be solved by the invention

Patent document 1 discloses one of the following techniques: since the crystal grains having the {220} crystal plane of brass orientation are changed to the crystal grains having the {200} crystal plane of cubic orientation by recrystallization among the plurality of crystal planes, the brass orientation of β -fiber in the rolled texture of the hard rolled copper foil is developed by increasing the final reduction ratio, the cubic texture oriented vertically by heat at the time of lamination with the insulating resin substrate is developed and the bending property is exhibited, and the development of the cubic texture of cubic orientation and the height of the final reduction ratio have a positive correlation.

However, there are problems as follows: since the final reduction ratio is high, the surface roughness is increased by the rolling mark and the high-speed conveyance characteristic is lowered, and the softening temperature is lowered by the accumulation of strain, so that the room-temperature softening occurs.

Patent document 2 discloses one of the following techniques: a copper foil for printed wiring boards having excellent bending properties can be produced by heating a copper foil having a final reduction of 90% or more in final cold rolling at a temperature of 100 ℃ or more to form a cubic orientation.

However, there are problems as follows: since the final reduction ratio is as high as 90% or more, the surface roughness is increased, the high-speed conveyance characteristic is lowered, and the room-temperature softening occurs.

Patent document 3 discloses one of the following techniques: in order to solve the problem of softening at room temperature caused by a high final reduction ratio, a slight amount of Ag is added to form a solid solution in order to appropriately raise the softening temperature of the copper foil.

However, there are problems as follows: the electric conductivity is lowered compared to pure copper due to the Ag content, and since the final reduction ratio is high, the surface roughness becomes high due to the rolling mark, so that the high-speed transfer characteristic is lowered.

The present inventors have found that an important finding is achieved by repeatedly searching and conducting a large number of trials and experiments to solve the above-mentioned problems, that is, not only in the brass orientation of β -fiber of the rolled texture of the hard rolled copper foil, and there is a strong positive correlation between Orientation distribution Function (hereinafter abbreviated as "ODF") and bending resistance in the copper type Orientation, and the hard rolled copper foil having a crystal orientation density of copper type orientation of 10 or more and a crystal orientation density of brass orientation of 20 or more even if the final reduction ratio is not high, also, when the laminate is heat-laminated with an insulating resin base material, excellent bending resistance is exhibited, and since the final reduction ratio is not high, therefore, the surface roughness is not increased, the high-speed transfer characteristic is excellent, and the room-temperature softening is not generated, thereby solving the technical problems.

Means for solving the problems

As described below, the present invention can solve the above-described technical problems.

The invention provides a hard rolled copper foil having a crystal orientation density of copper type orientation of 10 or more and a crystal orientation density of brass orientation of 20 or more.

The present invention is the hard rolled copper foil described above, wherein the crystal orientation density of the copper type orientation is 25 or less and the crystal orientation density of the brass orientation is 45 or less.

The hard rolled copper foil is rolled from oxygen-free copper having a copper purity of 99.99% or more.

Also, the present invention is the hard rolled copper foil having a final reduction of less than 90%.

Also, the present invention is the hard rolled copper foil having a ten-point average roughness Rzjis94 of less than 1 μm.

The hard rolled copper foil of the present invention has a foil thickness of 12 μm or less.

The present invention also provides a printed wiring board in which the hard rolled copper foil is laminated.

The present invention also provides a method for producing the hard rolled copper foil, which is characterized by performing a heat treatment at a temperature in the recovery temperature range and then performing a final cold rolling.

The present invention also provides a method for producing the hard rolled copper foil, characterized in that the copper foil is rolled so that the final reduction ratio is 70% or more and less than 90%.

Effects of the invention

The present invention is a hard rolled copper foil which can be produced by performing final cold rolling after performing final heat treatment at a temperature at which a "recovery" state, which is a state before a "recrystallization" state in the progress of heat treatment, is maintained, and which is a hard rolled copper foil having a copper type oriented crystal orientation density of 10 or more and a brass oriented crystal orientation density of 20 or more, and therefore exhibits excellent bending resistance by softening to a stage of "grain growth" by heat at the time of lamination with an insulating resin base without increasing the final reduction ratio.

Further, since the final reduction ratio is not high, the occurrence of rolling marks is not likely to occur, and the surface roughness can be maintained low, so that even a high-frequency signal is used as a conductor, the transmission loss due to the skin effect can be suppressed, and a conductor having excellent high-speed transmission characteristics can be obtained.

Further, since the final reduction ratio is not high, strain accumulated in the hard rolled copper foil is small, and the softening temperature is not lowered, so that ordinary temperature softening is not likely to occur.

Since softening at room temperature does not easily occur, even a hard rolled copper foil stored therein is excellent in workability and foil passing property when it is laminated on an insulating resin base material, and therefore, a high product yield can be obtained.

Further, by using oxygen-free copper having a copper purity of 99.99% or more as the raw material, it is possible to form a conductor having more excellent high-speed transfer characteristics because unevenness is not easily generated on the surface even by soft etching when forming a circuit in addition to high electrical conductivity.

Further, since the final heat treatment is performed at a temperature in the recovery temperature range, even if the rolling is performed so that the final reduction ratio is 70% or more and less than 90%, the hard rolled copper foil having excellent bending resistance when laminated on the insulating resin base material is obtained.

Drawings

FIG. 1 is a diagram showing a method for determining a recovery temperature range;

FIG. 2 is a graph showing the values of crystal orientation density of the hard rolled copper foils of examples and comparative examples;

FIG. 3 is a view showing a method of a bending resistance test;

FIG. 4 is a view showing a method of a bending resistance test;

FIG. 5 is a view showing a method of a bending resistance test.

Detailed Description

(copper ingot of raw Material)

The copper used in the present invention is not particularly limited, and oxygen-free copper and tough pitch copper specified in JIS HO500 can be used, and oxygen-free copper is preferable.

This is because: in the case of using oxygen-free copper, the surface is less likely to have irregularities even if soft etching treatment is performed in forming a circuit, as compared with tough pitch copper, and therefore, transmission loss can be suppressed, which is advantageous for improving high-speed transmission characteristics.

The copper purity of the oxygen-free copper is not particularly limited, and is preferably 99.99% or more. This is because the electrical conductivity can be improved.

As oxygen-free copper having a copper purity of 99.99% or more, alloy No. C1011 can be exemplified, but it is not limited thereto.

(Hot Rolling Process)

In the hot rolling step, the copper ingot having passed through the ingot is heated to about 800 ℃ and rolled.

(repeating step)

The hot-rolled copper plate is subjected to a heat treatment process as appropriate, and then is rolled by a multi-stage cold rolling mill. Generally, the rolling reduction is about 50%, and the heat treatment and the cold rolling are repeated.

(Final Rolling copper strip)

After the hot rolling step and the repeating step, a final rolled copper bar can be obtained.

The reduction rate before the final rolled copper bar is obtained is preferably 70% or more. This is because β -fiber is required to develop the final rolled copper bar sufficiently.

In addition, the thickness of the final rolled copper strip is preferably a thickness at which the final reduction of the hard rolled copper foil as a final product is not more than 90%.

When the foil thickness before rolling is Ti and the foil thickness after rolling is Tf, the reduction ratio (R) can be expressed by the following formula 1.

< equation 1 > reduction ratio R { (Ti-Tf)/Ti }. times.100

(Final Heat treatment Process)

The obtained final rolled copper strip is subjected to final heat treatment at a temperature of "recovery" state in the progress of the heat treatment, and then to final cold rolling, whereby a hard rolled copper foil having a rolling texture in which not only brass orientation but also copper type orientation is developed can be formed.

It is understood that by maintaining the "recovered" state, a part of β -fi ber is substituted with a specific crystal orientation in the rolling texture of the final rolled copper bar, and thus the copper type orientation is developed by the final cold rolling.

If the final heat treatment is performed at a temperature of "grain growth" state, it is difficult to exhibit bending resistance unless the final reduction is 90% or more.

(determination of Final Heat treatment temperature)

The temperature at which the final rolled copper strip is brought into the "recovered" state can be determined by the following method.

Each tensile strength (N/mm2) was measured by changing the temperature of the finally rolled copper strip and performing heat treatment for a predetermined period of time as shown in Table 1.

[ Table 1]

Next, as shown in fig. 1, a curve is plotted on a graph in which the temperature is represented by the X axis and the tensile strength is represented by the Y axis, the temperature of the inflection point 1 at which the tensile strength is rapidly decreased is represented by the recrystallization start temperature, the temperature of the intersection (intersection 2) between the tangent 5 of the inflection point and the base line 6 of the low-temperature side curve is represented by the minimum heating temperature, and the temperature between the minimum heating temperature and the recrystallization start temperature may be defined as the final heat treatment temperature.

In the present specification, a state up to the recrystallization start temperature (inflection point 1) is set as "recovery", and a temperature between the lowest heating temperature and the recrystallization start temperature is set as a recovery temperature range on the assumption that the recrystallization start temperature is exceeded and a process of "recrystallization" and "crystal grain growth" is passed as becoming higher temperature.

The recovery temperature range is preferably determined by holding the temperature for 30 minutes to 1 hour under an inert atmosphere or vacuum.

The holding time at each temperature in Table 1 was 30 minutes, and a tensile compression tester IM-20 (manufactured by INTESCO, Japan) was used for measuring the tensile strength.

The final heat treatment is performed by holding the final rolled copper bar at a temperature within a predetermined recovery temperature range for 30 minutes to 1 hour under an inert atmosphere or vacuum.

(Final Cold Rolling Process)

After the final heat treatment, the foil is finally cold rolled to a desired foil thickness, whereby a hard rolled copper foil can be obtained.

As the final cold rolling, a known cold rolling method can be employed.

The reduction ratio (final reduction ratio) of the final cold rolling is preferably 70% or more and less than 90%, and more preferably 75% or more and less than 90%.

This is because: if the final reduction ratio is 90% or more, a strong rolling mark is generated and the surface roughness is increased, and the hard rolled copper foil accumulates a large amount of strain and the softening temperature is lowered, and thus room temperature softening occurs.

Further, the reason is that if the final reduction ratio is 90% or more, the growth of the copper type orientation is suppressed.

(Crystal orientation Density)

The crystal orientation density of the hard rolled copper foil can be calculated by evaluating the rolled texture by pole figure measurement using X-ray diffraction.

(surface roughness)

The ten-point average roughness Rzjis94 of the hard rolled copper foil surface of the present invention is preferably less than 1 μm, and more preferably 0.5 μm or less.

This is because the transmission loss of the printed circuit board is suppressed.

(thickness of foil)

The foil thickness of the hard rolled copper foil is preferably 12 μm or less in a nominal thickness specified in JIS C6515.

This is because: as the foil thickness becomes thinner, the stress applied to the copper foil becomes smaller, which is advantageous in improving the bending resistance, and is also advantageous in downsizing, thinning, and lightening of portable equipment.

(insulating resin base)

The insulating resin substrate on which the hard rolled copper foil according to the present invention is laminated is not particularly limited, and examples thereof include polyimide resins, polyester resins, liquid crystal polymer resins, and substrates obtained by applying an adhesive such as epoxy resins or polyimide resins to these resins.