TWI402165B - Copper foil and the use of its copper clad laminate - Google Patents

Description

Copper foil and copper clad laminate using the same

The present invention relates to a copper foil used in, for example, a flexible printed wiring board (FPC), and a copper clad laminate in which the copper foil is laminated on at least one side of a resin layer.

As a circuit for driving an electronic device such as a digital camera or a mobile phone, a flexible printed wiring board (FPC) or a chip of flexible circuit (COF) is used. The FPC or COF is used for a copper-clad copper-clad laminate (CCL) on a single-sided or double-area layer of a resin layer, and a circuit pattern is formed on the copper foil.

Further, in order to reduce the size and function of such an electronic device, a method of folding and housing the FPC into a narrow space in the casing is employed. Moreover, in the case of using COF around the liquid crystal display, in order to make a bezel (so-called "frame") thin, the copper wiring of COF is folded back to the inside of a liquid crystal substrate.

However, when the FPC or the COF is folded, there is a problem in that the copper foil portion is subjected to a large deformation load and is liable to cause cracking.

For this reason, it has been disclosed that FPC is composed of an electrolytic copper foil containing columnar copper crystal grains and an elongation at 25 ° C of 5% or more, thereby obtaining an FPC in which the wiring pattern is not easily broken (Patent Document 1).

Patent Document 1: Japanese Laid-Open Patent Publication No. 2007-335541

In the past, it has been considered that the bendability of the copper foil of CCL is related to the elongation of the copper foil. Therefore, as disclosed in the above Patent Document 1, an electrolytic copper foil having a large elongation is used.

However, the inventors of the present invention have found that even when a rolled copper foil having a large elongation is used, there is a case where the bendability of CCL is not improved.

In other words, the present invention has been made to solve the problems described above, and an object of the invention is to provide a copper foil excellent in flexibility when used for a copper clad laminate and a copper clad laminate using the same.

The inventors of the present invention have found through various studies that it is not the elongation of the copper foil but the work hardening index (n value) as a factor for improving the flexibility of the CCL.

In order to achieve the above object, the copper foil of the present invention has a thickness of 5 to 30 μm, a surface roughness Ra of 0.1 μm in the parallel direction of rolling, and a work hardening index of 0.3 to 0.45 or less after annealing at 350 ° C for 0.5 hour.

The semi-softening temperature of the copper foil of the present invention is preferably 150 ° C or lower.

In addition, the copper foil of the present invention is preferably composed of oxygen-free copper or fine copper, or one or more of a group consisting of Ag and Sn in total of 500 ppm by mass or less in oxygen-free copper or refined copper.

When a sample having a single-layer resin layer of the copper foil and having a total thickness of 50 μm or less and a width of 3 mm or more and 5 mm or less is used, the exposed surface of the copper foil is 180 degrees tightly bent outside, The number of bendings until the copper foil is broken is preferably 4 or more.

Preferably, the total degree of processing of the final cold press delay is 85% or more, and the oil film equivalent of the last three passes in the last cold rolling is formed by the following conditions. In this case, the oil film equivalent of two passes before the last pass is set to 25,000 or less, the oil film equivalent of one pass before the last pass is set to 30,000 or less, and the oil film equivalent of the last pass is set to 35,000 or less. Here, after the ingot is hot rolled, when the copper foil is produced by cold rolling, cold rolling and annealing are alternately performed in cold rolling. Further, the cold rolling which is finally performed after the final annealing is referred to as "final cold rolling".

In the copper clad laminate of the present invention, the copper foil is laminated on at least one side of the resin layer.

According to the present invention, a copper foil excellent in flexibility when used for a copper clad laminate can be obtained.

Hereinafter, a copper foil according to an embodiment of the present invention will be described. Further, % in the present invention means % by mass unless otherwise specified.

The copper foil according to the embodiment of the present invention has a thickness of 5 to 30 μm, a surface roughness Ra of 0.1 μm in the parallel direction of rolling, and a work hardening index of 0.3 to 0.45 or less after annealing at 350 ° C for 0.5 hour.

The work hardening index (n value) is represented by the index n when the relationship between the stress and the strain in the plastic deformation domain above the relief point is approximated by the following formula 1 (Hollomon formula).

[True stress]=[material constant]×[true strain]n (1)

The larger the work hardening index, the more difficult it is to cause local deformation, and the more difficult it is to break during deformation. Further, a material having a high work hardening index is excellent in stretch workability and is suitable for press working. Further, when a copper clad laminate is produced by laminating a copper foil on at least one side of the resin layer, and the bendability of the copper clad laminate is evaluated, it is considered that the copper foil having a work hardening index of 0.3 or more is less likely to be locally deformed. Further, since the entire curved portion is subjected to deformation, the copper foil is hard to be broken. However, a material having a work hardening index of more than 0.45 is less suitable for use as a copper clad laminate because of its low strength after annealing and deterioration in workability.

Here, the reason why the work hardening index after annealing at 350 ° C for 0.5 hour is defined is because the heating condition at the time of producing the copper clad laminate is such a degree. In addition, when the resin layer of the copper-clad laminate is applied by applying a resin composition to a copper foil and hardening (in the case where two layers of CCL of the adhesive layer are not interposed between the resin layer and the copper foil), The resin is hardened under the above heating conditions.

Further, as a factor for improving the flexibility of the copper foil, it is considered that the reason why the elongation of the copper foil is not the elongation of the work foil (n value) is as follows.

First, the work hardening index is one of the values indicating the work hardening behavior of the material, and the larger the value, the more easily the material has work hardening properties. Here, when the material is subjected to tensile deformation, the material locally shrinks and breaks. However, the material having a large work hardening coefficient hardens the portion where the shrinkage occurs, and the shrinkage portion is less likely to be deformed. Therefore, the other part replaces the shrinkable portion which is not easily deformed, and starts to deform. By repeating this step, the entire material is uniformly deformed. On the other hand, the elongation is a macroscopically grasped index without considering such a situation, so even if the elongation is large, the work hardening index is not necessarily large.

In the past, as an index of the ease of uniform deformation of the entire material, for example, in a drawing process of a material having a thickness, a work hardening index is used, whereas a material such as a copper foil is not subjected to a drawing process or the like, so There is no work hardening index as an indicator. Therefore, in the present invention, in consideration of an increase in the work hardening index of the copper foil, even if the CCL is tightly bent at 180 degrees, the entire curved portion is bent uniformly without being broken.

Further, the work hardening index after annealing at 200 ° C for 0.5 hour is also preferably 0.3 or more and 0.45 or less. This is because the lamination temperature at the time of producing a three-layer CCL in which a film is used as a resin layer and a film and a copper foil are laminated via an adhesive layer is about 200 ° C. Since the work hardening index increases due to recrystallization by heating, the work hardening index of 0.3 or more can be obtained at 350 ° C if the work hardening index at 200 ° C lower than 350 ° C is 0.3 or more. Further, in order to sufficiently obtain the recrystallized structure in the above annealing, the semi-softening temperature of the copper foil is preferably 150 ° C or lower.

The method of controlling the work hardening index of the copper foil after annealing at 350 ° C for 0.5 hours is 0.3 or more, and the total workability of the final cold press delay is 85% or more. Further, since it is necessary to obtain a recrystallized structure, it is preferred to control the half softening temperature of the copper foil to 150 ° C or lower. The recrystallization temperature is usually determined by the composition and processing degree of the copper foil. However, in order to make the work hardening index 0.3 or more, either method may be employed.

If the total processing degree of the final cold pressing delay is less than 85%, the degree of processing will decrease and the softening temperature of the copper foil will increase, so that the recrystallization of copper caused by the heating during the production of CCL becomes insufficient, and remains. The tendency to process strain and bendability is reduced.

In order to improve the flexibility when the copper foil is used for a copper clad laminate, in addition to the work hardening index described above, the influence of the surface roughness must also be considered. Here, the important factor for the size of the work hardening index is "to what extent the material can be hardened by machining." Therefore, in order to make the work hardening index a large value, the material in the initial stage must be in a state of being unprocessed and hardened, that is, a state in which the strain is removed. For the copper foil for CCL, the copper foil must be recrystallized by heat treatment in the CCL manufacturing step.

Moreover, the heat treatment conditions in the CCL manufacturing step depend on the nature of the resin, so the recrystallization temperature of the copper foil must conform to the heat treatment conditions. The recrystallization temperature of the copper foil is affected by the composition and the degree of workability, and the softening temperature becomes too high for a large amount of the composition containing the added element. Further, even if the composition of the copper foil is appropriate, if the degree of processing is too high, softening at room temperature occurs, and if the degree of processing is too low, the softening temperature becomes too high.

In addition to such factors, the surface roughness is affected by the difference in work hardening index. When the surface roughness is large and there is a notch-like unevenness on the surface of the material of the copper foil, the stress concentrates on the tip end of the notch when bending, and causes cracking.

In this case, the surface roughness Ra of the copper foil of the embodiment of the present invention in the parallel direction of rolling is 0.1 μm or less. The reason for this is that when the surface roughness Ra exceeds 0.1 μm, when the copper foil is bent, cracking (fracture) is likely to occur from the unevenness of the surface. The depression called the oil pit formed on the surface of the copper foil by rolling is formed into an elongated groove shape in the direction perpendicular to the rolling direction, so that the surface roughness is measured in the parallel direction of the rolling. Ra is an arithmetic mean roughness measured in accordance with JIS (Japanese Industrial Standards) - B0601.

As a method of adjusting the surface roughness Ra of the rolling direction of the copper foil in the parallel direction to 0.1 μm or less, the oil film equivalent in the last three passes of the final cold rolling may be adjusted. Specifically, the oil film equivalent of two passes before the last pass of the final cold rolling is set to 25,000 or less, the oil film equivalent of one pass before the last pass is set to 30,000 or less, and the oil film equivalent of the last pass is set to 35000. the following.

Further, if the thickness of the material is thinned, the oil film equivalent tends to increase, so that the value of the oil film equivalent of the last three passes gradually increases. Therefore, for the last 3 passes of different thicknesses, an appropriate oil film equivalent must be set.

In the final cold rolling, if the rolling oil viscosity and the material lodging stress are equal in all passes, the oil film equivalent is proportional to (calendering speed) / (biting angle). When the thickness of the material is thinned, the bite angle becomes small, so that the oil film equivalent tends to increase as it approaches the last pass. Further, in order to ensure productivity, it is more necessary to increase the rolling speed as the final pass of the material length is longer, and thus the oil film equivalent tends to increase as it approaches the last pass.

Further, if the surface roughness of the material in the middle pass of the final cold rolling is high, the surface of the material cannot be sufficiently smoothed even if the oil film equivalent is suppressed to a low level in the last pass. Based on this, the oil film equivalent of the last three passes of the final cold rolling is managed.

On the other hand, in the last three passes of the final cold rolling, if not all of the oil film equivalents of 2 passes before the last pass are 25000 or less, and the oil film equivalent of 1 pass before the last pass is 30,000 or less, the last pass The oil film equivalent is 35,000 or less (if the oil film equivalent exceeds the above value in any of the last 3 passes), the surface of the copper foil becomes rough and the surface roughness Ra in the parallel direction of rolling exceeds 0.1 μm, resulting in the following Bad condition.

In order to reduce the oil film equivalent, the final pass rolling degree is 25%. Just go up.

Further, the above oil film equivalent is represented by the following formula.

(oil film equivalent) = {(calendering oil viscosity, dynamic viscosity at 40 ° C; cSt) × (calendering speed; m / min)} / {(material lodging stress = kg / mm ² ) × (roll bite angle; rad )}

The rolling oil viscosity can be set to about 4.0 to 8.0 cSt, the rolling speed is 200 to 600 m/min, and the bite angle of the roller is preferably 0.001 to 0.04 rad.

In the copper foil according to the embodiment of the present invention, when the copper foil is subjected to atmospheric annealing at 350 ° C for 0.5 hours, and the X-ray diffraction of the rolled surface is performed, the integral values of the respective (220) planes and (200) planes are integrated ( The ratio I(220) / I(200) of I) is preferably 0.11 or less. In this case, the ratio of the (220) surface in the copper foil is increased, and recrystallization of the copper foil is performed at 350 ° C × 0.5 hour annealing, and the processing strain is reduced to improve the flexibility.

Furthermore, the single-layer resin layer of the copper foil of the embodiment of the present invention has a total thickness of 50 μm or less and a width of 3 mm or more and 5 mm or less, and the exposed surface of the copper foil is 180 degrees outside. In the case of tight bending, the number of times of bending until the copper foil is broken is preferably 4 or more.

In the single-layer resin layer of the copper foil, the sample having a total thickness of 50 μm or less is a simulated copper-clad laminate, and the degree of bending of the 180-degree close bending is used to evaluate the bendability of the copper-clad laminate.

The resin layer may be a thermoplastic resin such as a polyimide, a polyethylene terephthalate (PET), a thermosetting resin such as an epoxy resin or a phenol resin, or a saturated polyester resin, but is not limited thereto. Wait. Further, a varnish obtained by dissolving the resin layer components in a solvent (for example, a polyamidamine solution which is a polyimide precursor) may be applied to one surface of the copper foil and heated to remove the solvent. The reaction (for example, hydrazine imidization reaction) is allowed to proceed to harden it.

The 180 degree close bending system folds back the sample in such a manner that the crease is parallel to the width direction of the crease, and is repeatedly pressed and flattened by a hand press. Further, the copper foil portion of the cross section of the curved portion was observed by an optical microscope for the presence or absence of breakage. If there is no break, the sample after the close bending is opened, and after being stretched flat by using a hand press, it is folded back again at the same portion and flattened by a hand press. Thus, the number of times of bending until the copper foil was broken was obtained.

The composition of the copper foil according to the embodiment of the present invention is preferably composed of oxygen-free copper or refined copper (all defined by JIS-H3100). In addition, one or more of a group consisting of Ag and Sn in total of 500 ppm by mass or less may be contained in the oxygen-free copper or the refined copper. In the copper foil of the embodiment of the present invention, when one or more of the group of Ag and Sn are added in an amount exceeding 500 ppm by mass in total, the recrystallization temperature is excessively increased, and recrystallization does not occur in the heat treatment in the CCL production step. Sufficient situation.

In the copper clad laminate of the present invention, the copper foil is laminated on at least one side of the resin layer. Since the copper foil of the embodiment of the present invention is excellent in flexibility, the copper clad laminate using the same is also excellent in flexibility. For example, the copper clad laminate of the present invention can be suitably used for a purpose of bending 90 to 180 degrees with a radius of 5 mm or less.

Example

Oxygen-free copper or refined copper (JIS H3100) was melted, and if necessary, Ag and Sn were added in an amount shown in Table 1 to carry out casting, thereby producing an ingot. After the ingot is subjected to hot rolling, cold rolling and annealing are appropriately repeated to prepare a copper foil. In order to adjust the softening temperature, the total working degree of the final cold pressing delay is 85% or more, and in order to reduce the surface roughness, the final cold rolling is performed using a roll having a smooth surface (Ra ≦ 0.1 μm in the roll direction) to produce a copper foil. . Adjusting the viscosity of the oil in the range of 4.0 to 8.0 cSt, the rolling speed of 200 to 600 m/min, and the bite angle of the roller from 0.003 to 0.03 rad, so that the oil film equivalent of the last 3 passes of the final cold rolling is One is less than 35,000.

<Process Hardening Index>

The copper foil obtained was subjected to atmospheric annealing at 200 ° C for 0.5 hours and 350 ° C for 0.5 hours, and then subjected to a tensile test (in accordance with JIS-Z2241) to obtain a work hardening index. Furthermore, it is necessary to use a uniform elongation and stress after the material has been lowered to determine the work hardening index, so the value from the elongation of 2% to the maximum stress point is used. Further, the true logarithm of the true strain and the true stress obtained from the measured elongation and stress are approximated by a least square method, and the work hardening index is obtained from the slope of the curve. The true strain and the true stress are obtained by the following equation.

[true strain]=ln(1+[strain])

[True stress]=(1+[true strain])×[stress]

<Semi-softening temperature>

The copper foil obtained was subjected to atmospheric annealing at 100 to 400 ° C for 0.5 hours, and then subjected to a tensile test to determine the strength (tensile strength) corresponding to the heat treatment conditions. The annealing temperature after the annealing TSH is the average of the strength TSasroll at the completion of calendering (before annealing) and the strength of the fully softened state TSanneal is set to a semi-softening temperature.

<Number of bends of copper clad laminates>

Next, on one side of the obtained copper foil, a polyimine layer having a thickness of about 20 μm was formed by a cast film method to produce a single-sided CCL. Specifically, the single side of the obtained copper foil was subjected to chemical treatment (electroplating), and the surface of the copper foil was coated with a polyimide varnish (U-varnished by Ube Industries) in a thickness of 20 μm. A). Thereafter, it was dried in a hot air circulating high temperature bath set at 130 ° C for 30 minutes, and gradually heated to 350 ° C for 2,000 seconds to be hardened (yttrium imidized) to form a resin layer (polyimine layer). To make a single-sided CCL.

The 180 degree close bending system was carried out in the following order. First, the one-side CCL was cut out as a test piece with a width of 3.2 mm and a length of 30 mm and the longitudinal direction of the test piece was parallel to the rolling direction, and the resin layer was inside and made into a ring shape, and the hand was The press is flattened and then bent at 180 degrees. Then, the copper foil portion of the cross section of the bent portion was observed by an optical microscope for the presence or absence of breakage. If there is no break, the sample after the close bending is opened, and after being stretched flat by using a hand press, it is folded back again at the same portion and flattened by a hand press. Thus, the number of times of bending until the copper foil was broken was obtained.

<The number of sliding bends of copper foil>

Next, the obtained copper foil was cut out to have a width of 12.7 mm and a length of 200 mm, and the longitudinal direction of the test piece was parallel to the rolling direction, and was used as a test piece, and heated at 200 ° C for 30 minutes to be recrystallized. The number of IPC sliding bends was measured by the IPC (The Institute of Printed Circuits) sliding bending device shown in FIG. This apparatus is a structure in which the vibration transmitting member 3 is coupled to the oscillation driving body 4, and the test piece 1 is fixed to the apparatus at a total of four points of the portion of the screw 2 indicated by the arrow and the front end portion of the third portion. When the vibrating portion 3 is driven up and down, the intermediate portion of the test piece 1 is bent into a hairpin shape with a predetermined radius of curvature r. In this test, the number of times until the fracture was repeated under the following conditions was determined.

The test was carried out under the conditions of a radius of curvature r: 2.5 mm, a vibration stroke: 25 mm, and a vibration speed: 1500 beats/min.

<I(220)/I(200)>

After the obtained copper foil was subjected to atmospheric annealing at 350 ° C for 0.5 hours, X-ray diffraction of the rolled surface was performed, and integral values (I) of the diffraction peak intensities of the (220) plane and the (200) plane were obtained.

Table 1 shows the results obtained. Further, in the composition of Table 1, OFC and TPC respectively represent oxygen-free copper and refined copper (JIS H3100), and Ag100 ppm TPC means that 100 mass ppm of Ag is added to the refined copper.

According to Table 1, it is clear that the semi-softening temperature is 150 ° C or less, and the surface roughness Ra ≦ 0.1 μm in the parallel direction is rolled, and the work hardening index after annealing at 350 ° C for 0.5 hour is 0.3 or more. In the case of the case, the number of times of bending when the 180-degree adhesion is performed is four or more times, and the bending property is excellent.

On the other hand, in the case of Comparative Examples 3, 6, 7, and 8 in which the total processing degree of the final cold pressing delay is less than 85%, the work hardening index after annealing at 350 ° C for 0.5 hours is less than 0.3, and 180 degree dense is performed. When the bending is performed, the number of bending is less than four times, and the bending property is deteriorated. Further, in the case of Comparative Example 1, since the addition amount of Sn in the copper foil exceeded 500 ppm by mass, the semi-softening temperature exceeded 150 ° C, and the work hardening index was less than 0.3.

Further, in the case of Comparative Examples 1, 7, and 8 in which the semi-softening temperature exceeds 150 ° C, the work hardening index after annealing at 350 ° C for 0.5 hours is less than 0.3, and the number of bends at 180 degree close bending is less than 4 The bending property is deteriorated.

As the oil film equivalent of the last 3 passes of the final cold rolling, the oil film equivalent of 2 passes before the last pass exceeds 25000, the oil film equivalent of 1 pass before the last pass exceeds 30,000, and the last pass of the oil film equivalent exceeds 35000. In the case of Comparative Example 2, the surface roughness Ra in the rolling parallel direction exceeded 0.1 μm, and the number of bendings when the 180-degree adhesion was performed was less than four times, and the bendability was deteriorated.

In the case of the oil film equivalent of the last three passes of the final cold rolling, in the case of Comparative Example 4 in which the oil film equivalent of one pass before the last pass exceeds 30,000, the surface roughness Ra of the rolling parallel direction exceeds 0.1 μm, and 180 is performed. When the degree of tightness is bent, the number of bending is less than four times, and the bendability is deteriorated.

In the case of the oil film equivalent of the last three passes of the final cold rolling, in the case of Comparative Example 5 in which the oil film equivalent of 2 passes before the last pass exceeds 25,000, the surface roughness Ra of the rolling parallel direction is more than 0.1 μm. When the 180 degree close bending is performed, the number of bending is less than four times, and the bendability is deteriorated.

Further, it can be seen that in the case of Comparative Examples 1 to 8, the evaluation of the previous bending property, that is, the number of IPC sliding bending was also the same as in the respective examples, and the bendability of the copper clad laminate could not be evaluated in the sliding bending test.

1. . . Test piece

2. . . Screw

3. . . Vibration transmitting member

4. . . Oscillating drive

r. . . Radius of curvature

Fig. 1 is a view showing a sliding bending method using an IPC sliding bending device.

1. . . Test piece

2. . . Screw

3. . . Vibration transmitting member

4. . . Oscillating drive

r. . . Radius of curvature

Claims (8)

A copper foil having a thickness of 5 to 30 μm, a surface roughness Ra ≦ 0.1 μm in a rolling parallel direction, and a work hardening index after annealing at 350 ° C for 0.5 hours is 0.3 or more and 0.45 or less. The copper foil of the first aspect of the patent application has a semi-softening temperature of 150 ° C or less. The copper foil of the first aspect of the patent application, which is composed of oxygen-free copper or refined copper, or one of a group consisting of Ag and Sn in total of 500 ppm by mass or less in oxygen-free copper or refined copper. the above. The copper foil of claim 2, which is composed of oxygen-free copper or refined copper, or one of a group consisting of Ag and Sn in total of 500 ppm by mass or less in oxygen-free copper or refined copper. the above. The copper foil according to any one of claims 1 to 4, wherein a sample having a single-layer resin layer of the copper foil and having a total thickness of 50 μm or less and a width of 3 mm or more and 5 mm or less is used. When the exposed surface of the copper foil is bent outward at 180 degrees, the number of times of bending until the copper foil is broken is four or more. The copper foil according to any one of claims 1 to 4, wherein the total cold working delay is 85% or more, and the oil film equivalent of the last 3 passes of the final cold rolling is set to the following. The condition is calendered; wherein the oil film equivalent of 2 passes before the last pass is 25000 or less; the oil film equivalent of 1 pass before the last pass is 30,000 or less; the last pass oil film equivalent is 35000 or less. For example, the copper foil of the fifth aspect of the patent application has a total working degree of the final cold pressing delay of 85% or more, and the oil film equivalent of the last three passes of the final cold rolling is subjected to the following conditions for calendering; Among them, the oil film equivalent of 2 passes before the last pass is 25000 or less; the oil film equivalent of 1 pass before the last pass is 30,000 or less; the oil film equivalent of the last pass is 35000 or less. A copper-clad laminate in which a copper foil according to any one of claims 1 to 7 is laminated on at least one side of a resin layer.