TWI717998B - Rolled copper foil for flexible printed circuit board, flexible copper clad laminate and flexible printed circuit board - Google Patents

Abstract

The present invention provides a rolled copper foil for a flexible printed circuit board and a flexible copper clad that can stably obtain flexibility regardless of the heating conditions when manufacturing a flexible copper clad laminate Laminated boards and flexible printed circuit boards.

45。 A rolled copper foil for flexible printed circuit boards, which contains 99.0% by mass or more of Cu, and the remainder is composed of inevitable impurities. It takes more than 5 seconds to heat from 25°C to 350°C and then at 350°C After heating in heating mode A for 30 minutes or heating mode B in heating mode B from 25°C to 350°C for 1 second, the intensity (I) of the (200) surface obtained by X-ray diffraction on the rolled surface is relative The intensity (I ₀ ) of the (200) plane obtained by X-ray diffraction in the fine powder copper is I/I ₀

45.

Description

Rolled copper foil for flexible printed circuit board, flexible copper clad laminate and flexible printed circuit board

The present invention relates to a rolled copper foil for a flexible printed circuit board, a flexible copper-clad laminate and a flexible printed circuit board that require flexibility.

The flexible printed circuit board (FPC: Flexible Printed Circuit) is formed by forming a circuit on a flexible copper clad laminate (FCCL: Flexible Cupper Clad Laminate). In addition, FCCL is formed by layering resin on one side or two areas of copper foil, and polyimide is often used in this resin. As FCCL, there are three-layer FCCL and two-layer FCCL according to its structure.

The three-layer FCCL has a structure in which a resin film such as polyimide and a copper foil used as a conductive material are bonded with an adhesive such as epoxy resin or acrylic resin. On the other hand, the double-layer FCCL has a structure in which a resin such as polyimide is directly joined to a copper foil as a conductive material. Compared with the three-layer FCCL, the two-layer FCCL is superior in heat resistance, dimensional stability, flexural resistance, etc. (Non-Patent Document 1).

High flexibility is required for copper foil used in FPC. As a method for imparting flexibility to copper foil, a technique for increasing the alignment of the crystal orientation of the (200) plane of the copper foil (Patent Document 1), and making the crystal penetrating in the thickness direction of the copper foil is known. The technology of increasing the ratio of particles (Patent Document 2) will be equivalent to that of copper foil A technique in which the surface roughness Ry (maximum height) of the groove depth is reduced to 2.0 μm or less (Patent Document 3).

The FPC used in the flexure part uses a double-layer FCCL manufactured by the following method: Coating a polyimide varnish on copper foil, heating it to dry and harden to make a laminated board called the casting method Method; or a method called laminating method in which a polyimide film and copper foil coated with a thermoplastic polyimide with adhesive in advance are overlapped and pressure-bonded by a heating roller or the like.

For example, a flexible copper-clad laminated board that obtains high flexibility by a casting method is known (Patent Document 4). The copper foil is recrystallized by the heat treatment in the FCCL manufacturing step.

In addition, in order to store the FPC in the narrow space of the casing of mobile phones, smart phones, tablet PCs, etc., the seams are bent after being crimped, or with a smaller curvature such as the read/write cable of a hard disk drive When the radius continuously flexes repeatedly, stricter flexibility is required.

Here, the so-called seam crimping refers to a state in which creases are provided for storage in a thinner casing, and the FPC is folded so that the upper surface side of the FPC is reversed 180 degrees to become the lower surface side. This situation is called "Seam Folding".

In addition, in order to cope with severe bending such as seam crimping, the technique described in Patent Document 1 mentioned above is to add a small amount of Ag or Sn to the copper foil to promote copper realized by annealing during the heat treatment of FCCL production. The foil is softened, and the crystalline cubes are located in a specific direction (200 planes) and the cubic assembly structure is developed.

As a result, when the stress at the time of bending is applied to the copper foil, the transfer and movement occurring in the crystal will not accumulate in the grain boundary, and by moving to the surface, the occurrence of cracks and the cause of the grain boundary are suppressed. The damage caused by the progress shows excellent flexural characteristics.

One of the important aspects of FPC for achieving high flexibility is to recrystallize the metal structure of the copper foil into a state with better flexibility during the heat treatment in the manufacture of FCCL. The metal structure with the best flexibility is a structure with a well-developed cube orientation and fewer grain boundaries, in other words, a larger grain structure. Here, the degree of development of the cube orientation can be the ratio of the X-ray diffraction intensity of 200 planes to I/I ₀ (I: the diffraction intensity of the 200 planes of copper foil, I ₀ : the diffraction intensity of the 200 planes of copper powder) The size indicates that the larger the value, the more developed the cube orientation.

When the double-layer FCCL is manufactured by the casting method, the nucleation of recrystallization and the recrystallized crystal are generated in the copper foil through the process of increasing the temperature step by step during the lamination (when the resin material is applied to the copper foil) The growth of grains. In addition, when the copper foil is heated to 200°C for more than 4 seconds by the casting method, and then kept at 200°C for 30 minutes and then cooled to room temperature, the ratio of the X-ray diffraction intensity of the 200 faces is measured at room temperature If I/I ₀ is 40 or more, high flexibility can be obtained.

On the other hand, when the double-layer FCCL is manufactured by the lamination method, the polyimide film and the copper foil that have been coated with the adhesive and dried are pressure-bonded by a heating roller, but there is no need to evaporate the solvent, so it can be Instantly heat up to the temperature at which polyimide hardening reaction occurs. However, if the temperature rises at a faster rate, a multi-directional nucleus is generated and grows, and the development of the cubic azimuth is suppressed. Therefore, in the case of the lamination method, the flexibility tends to decrease compared with the casting method in which heating is performed relatively slowly during lamination (Patent Document 5).

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 3009383

[Patent Document 2] JP 2006-117977 A

[Patent Document 3] JP 2001-058203 A

[Patent Document 4] Japanese Patent Application Publication No. 2006-237048

[Patent Document 5] JP 2009-292090 A

[Non-Patent Literature]

[Non-Patent Document 1] Fujikura Technical Report, Fujikura Co., Ltd., No. 109 pp. 31-35 (2005)

As described above, as the manufacturing method of the double-layer FCCL, there are the casting method and the lamination method with different heating conditions, but there is a demand for a copper foil for FPC that can stably obtain flexibility without depending on the heating conditions.

In particular, there is a demand for a copper foil for FPC with stricter flexibility and excellent seam crimpability.

Therefore, the object of the present invention is to provide a rolled copper foil for a flexible printed circuit board that can stably obtain flexibility without depending on the heating conditions when manufacturing a flexible copper-clad laminate, and particularly has excellent seam crimpability. Flexible copper clad laminates and flexible printed circuit boards.

45的銅箔，則可不依據製造雙層FCCL時之加熱條件而穩定地獲得撓曲性。 The present inventors have made various studies and found the following situation: as long as the heating is by an analog processing of the FCCL manufacturing a double layer (200) plane become intensity I / I ₀

The 45 copper foil can stably obtain flexibility regardless of the heating conditions when manufacturing the double-layer FCCL.

45。 In order to achieve the above-mentioned object, the rolled copper foil for flexible printed circuit boards of the present invention contains 99.0 mass% or more of Cu, and the remainder is composed of inevitable impurities. It takes more than 5 seconds to heat from 25°C to 350°C , After heating mode A at 350℃ for 30 minutes, or heating mode B at 350℃ from 25℃ to 350℃ in 1 second, the rolling surface is calculated by X-ray diffraction. The intensity (I) relative to the intensity (I ₀ ) of the (200) plane obtained by X-ray diffraction of the fine powder copper is I/I ₀

45.

The rolled copper foil for flexible printed circuit boards of the present invention may contain 280 to 360 mass ppm of Ag relative to the oxygen-free copper specified in JIS-H0500 (C1011).

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

The flexible printed circuit board of this invention has the said flexible copper clad laminated board.

According to the present invention, it is possible to obtain a flexible printed circuit board and a rolled copper foil that can stably obtain flexibility regardless of the heating conditions when manufacturing the flexible copper-clad laminated board, especially the flexible printed circuit board with excellent seam foldability. Copper-clad laminates and flexible printed circuit boards.

[Fig. 1] is a diagram schematically showing the appearance of the FPC of the embodiment.

[Figure 2] is a diagram schematically showing the sequence of the seam creasing test.

Fig. 3 is a graph showing the relationship between the Ag concentration of the Examples and Comparative Examples and the working degree (true strain) η of the final cold rolling.

Fig. 4 is a diagram showing the I/I ₀ of copper foil after annealing corresponding to the casting method and the laminating method in the examples and comparative examples.

[Fig. 5] A graph showing the number of breaks in the joint creasing test of FPCs of Examples and Comparative Examples.

Hereinafter, the rolled copper foil for a flexible printed circuit board according to an embodiment of the present invention will be described. Furthermore, in the present invention, the so-called% system means mass% unless otherwise specified.

(composition)

The composition of the rolled copper foil for flexible printed circuit boards contains 99.0% by mass or more of Cu, and the remainder is composed of unavoidable impurities.

In particular, it is preferably a composition containing 280 to 360 mass ppm of Ag relative to the oxygen-free copper specified in JIS-H0500 (C1011).

45。特別是，於相當於在積層時銅箔急速加熱之層壓法之情形時，立方體集合組織進一步變得難以生長。 If the content of Ag is less than 280 ppm by mass, there are situations where the amount of strain introduced into the material by rolling becomes less, and the growth of the cube assembly structure becomes insufficient to achieve the I/I described below. ₀

45. In particular, in the case of a lamination method equivalent to a copper foil rapidly heating during lamination, the cubic aggregate structure becomes more difficult to grow.

If the Ag content exceeds 360 mass ppm, the recrystallization temperature of the copper foil becomes high, and even if the heating is used to manufacture the double-layer FCCL, the recrystallization is insufficient and many unrecrystallized crystal grains remain in the copper foil. , The seam crimpability of the obtained FPC is obviously poor.

More preferably, it contains 290~340 mass ppm of Ag with respect to oxygen-free copper.

The thickness of the rolled copper foil is not particularly limited, as long as it is appropriately selected according to the required characteristics, and it can be set to, for example, 1 to 100 μm. In particular, in order to improve the seam foldability or the formation of microcircuits, the thickness is preferably thinner, preferably 6 to 35 μm, more preferably 9 to 18 μm.

[Collection Organization]

45。 In the rolled copper foil for a flexible printed circuit board according to the embodiment of the present invention, it takes 5 seconds or more to heat from room temperature (25°C) to 350°C, and then hold at 350°C for 30 minutes in heating mode A, Or it takes 1 second to heat from normal temperature (25°C) to 350°C in heating mode B. After heating in the atmosphere, the intensity (I) of the (200) surface obtained by X-ray diffraction of the rolled surface is relative to the fine powder copper ( 325mesh, heated at 300°C for 1 hour in a hydrogen gas stream. The intensity (I ₀ ) of the (200) plane obtained by X-ray diffraction is 1/I ₀

45.

Heating at 350°C for 30 minutes simulates the heating conditions when the double-layer FCCL is manufactured by the casting method, which means that the copper foil is slowly heated from room temperature (25°C) to 350°C.

In addition, heating at 350°C for 1 second simulates the heating conditions when the double-layer FCCL is manufactured by the lamination method, which means the rapid heating to the highest temperature (350°C) by the lamination method (1 second from room temperature) (25°C) up to 350°C).

In addition, the intensity (I) and (I ₀ ) are measured at room temperature (25°C). In addition, the copper foil heated to the maximum temperature of 350°C by the above heating modes A and B is cooled to room temperature by natural cooling. However, even if the cooling rate at this time is not specifically defined, the structure of the copper foil no effect.

45而成為如下之銅箔：撓曲性優異之立方體方位非常發達，可不依據製造可撓性覆銅積層板時之加熱條件而穩定地獲得撓曲性，特別是接縫壓折性優異。 As mentioned above, by specifying as I/I ₀

45 and become the copper foil as follows: the cubic orientation with excellent flexibility is very developed, and the flexibility can be stably obtained regardless of the heating conditions when manufacturing the flexible copper-clad laminate, especially the seam crimpability.

The upper limit of I/I ₀ is 100, for example.

(manufacture)

The rolled copper foil for a flexible printed circuit board according to the embodiment of the present invention can usually be manufactured in the order of repeatedly performing hot rolling, cold rolling, and annealing on an ingot.

It is sufficient to set the rolling processing degree of the final cold rolling to 92.0-99.8% (the true strain η is 2.53 to 6.21).

Here, the relationship between the Ag concentration and the true strain η of the Examples and Comparative Examples described below is shown in FIG. 3.

45。另一方面，呈如下傾向：若使η變得過高，則於壓延銅箔中較多地導入阻礙立方體集合組織生長之剪切帶，同樣變得難以實現I/I₀

45。 As shown in Figure 3, the tendency is as follows: the higher the Ag concentration in rolled copper foil, the more difficult it is to introduce the strain that is the driving force for recrystallization if the rolling process (true strain) η of the final cold rolling is not increased. , It becomes difficult to achieve I/I ₀

45. On the other hand, there is a tendency that if η becomes too high, more shear bands that inhibit the growth of the cubic aggregate structure are introduced into the rolled copper foil, and it also becomes difficult to achieve I/I ₀

45.

η

(0.04C_Ag-7.3)。 Therefore, in order to perform final cold rolling in the area between the two upper right straight lines BC and AD that were experimentally determined to distinguish the embodiment of FIG. 3 and the comparative example, the Ag in the rolled copper foil When the concentration is set to C _Ag (mass ppm), set it to (0.04×C _Ag -9.3)

η

(0.04C _Ag -7.3).

The straight line AD is represented by η=(0.04×C _Ag -9.3), and the straight line BC is represented by η=(0.04×C _Ag -7.3). In addition, the straight line AB represents the lower limit of the Ag concentration in the rolled copper foil, namely C _Ag = 280 mass ppm, and the line CD represents the upper limit of the Ag concentration in the rolled copper foil, namely C _Ag = 360 mass ppm.

Furthermore, the true strain η is defined by the following formula.

η=In{(the cross-sectional area of the material before the final cold rolling)/the cross-sectional area of the material just after the final cold rolling)}

[Example]

Hereinafter, examples of the present invention are shown, but these examples are provided for a better understanding of the present invention, and are not intended to limit the present invention.

[Manufacture of rolled copper foil]

Cast the ingot with the copper alloy of the composition listed in Table 1 as the raw material, and perform hot rolling at 800°C or higher Until the thickness is 10mm, the scale on the surface is face-cut, then cold-rolled and annealed repeatedly, and finally finished to a thickness of 0.009~0.018mm by cold rolling. The oxygen-free copper system described in Table 1 is JIS-H0500 (C1011) standard.

η

(0.04C_Ag-7.3)之範圍。 The rolling degree of final cold rolling is set to 85~99.9% (true strain η is 1.9~6.6). The rolling degree of final cold rolling (true strain η) of the embodiment is based on the Ag concentration of the sample (280~360ppm) ) Within the range shown in Figure 3, adjust to the above (0.04×C _Ag -9.3)

η

(0.04C _Ag -7.3) range.

Each rolled copper foil sample obtained in this way was evaluated for I/I ₀ and seam crush resistance.

(1) Cube collection organization (I/I ₀ )

After heating the copper foil samples in the heating modes A and B, respectively, the integrated value (I) of the (200) surface intensity of the rolled surface obtained by X-ray diffraction was obtained at 25°C. This value is divided by the pre-measured integrated value (I ₀ ) of the (200) surface strength of finely powdered copper (325 mesh, heated in a hydrogen gas stream at 300° C. for 1 hour) to calculate the I/I ₀ value.

(2) Seam crush resistance

After heating the copper foil sample by the above heating modes A and B to recrystallize it, apply a 2μm thermoplastic polyimide adhesive on one side of the polyimide film (the side to be bonded to the copper foil) It was then dried to form a resin layer with a thickness of 27 μm. A copper foil was layered on the adhesive area of the resin layer and vacuum hot pressed to produce FCCL. After that, the circuit is formed by etching to produce the FPC shown in FIG. 1.

As shown in Figure 2, while confirming the continuity of the FPC with a tester, the FPC was repeatedly squeezed and bent by a load of 100N to investigate the seam buckling resistance of the FPC.

Specifically, the FPC gently bent into a ring is mounted on a stainless steel workbench as shown in Figure 2(1), and the same stainless steel pressing member is lowered at a speed of 6mm/min, as shown in Figure 2(2) ) Is generally 100 The load of N performs seam creasing on the FPC. After applying a load of 100N for 5 seconds, the pressing member is raised at a speed of 1,000mm/min as shown in Figure 2(3) to expand the FPC that has been folded by the seam. After that, apply a load of 100N to the FPC for 5 seconds as shown in Figure 2(4) to make the FPC bend back, and again raise the pressing member at a speed of 1,000mm/min as shown in Figure 2(5) to gently bend the FPC into ring.

Set Figure 2(1)~(5) as 1 cycle, and investigate the cycle at which the FPC circuit breaks and cannot be turned on (=FPC circuit breaks).

It was judged that the number of times of seam creasing to break was 7 times or less as poor (×), 8 times or more and 14 times or less as normal (△), and 15 times or more as good (○). As long as the evaluation is △ or ○, there is no practical problem.

The results obtained are shown in Table 1. The comprehensive judgment is as follows. As long as it is comprehensively judged as ◎, ○, and △, even if the FCCL is produced by either the casting method or the lamination method, high seam crush resistance is found.

◎: After annealing equivalent to casting method and after annealing equivalent to lamination method, the judgment of the joint creasing test is ○

○: In the judgment of the joint compression test after annealing equivalent to the casting method and after annealing equivalent to the lamination method, one is ○ and the other is △

△: The judgment of the joint compression test after annealing equivalent to casting method and after annealing equivalent to lamination method are both △

×: At least one of the judgments of the joint compression test after annealing equivalent to the casting method and the joint compression test after annealing equivalent to the lamination method is ×

45。因此，使用相當於澆鑄法、相當於層壓法中之任一者之退火後之銅箔製作的FPC亦表現出高耐接縫壓折性。 According to Table 1, it is clear that in the case of each embodiment, the copper foil satisfies I/I ₀ after annealing equivalent to either the casting method or the lamination method.

45. Therefore, the FPC produced using the copper foil after annealing which is equivalent to either the casting method or the lamination method also exhibits high seam crush resistance.

In the case of Comparative Examples 1, 4, and 5, the processing degree η is lower than the straight line A-D in FIG. 3, which means that the processing degree is insufficient with respect to the Ag concentration. Therefore, the cumulative amount of strain that is the driving force for recrystallization is small, and the recrystallization temperature of the copper foil becomes higher. As a result, the copper foil is not sufficiently recrystallized by annealing corresponding to at least one of the casting method or the laminating method, and the seam crush resistance is poor. In addition, it is thought that unrecrystallized crystal grains that may become the starting point of cracks that tend to accumulate strain remain.

45。因此，耐接縫壓折性較差。 In the case of Comparative Example 2 where the Ag concentration is less than 280 ppm, the amount of strain introduced into the material by rolling is reduced, and the growth of the cubic aggregate structure becomes insufficient by the annealing equivalent to the lamination method, thereby not satisfying I/ I ₀

45. Therefore, the seam crush resistance is poor.

45之原因在於：澆鑄法於積層時緩慢地加熱銅箔，因此立方體集合組織易於生長。 Furthermore, in Comparative Example 2, the cubic aggregate structure was sufficiently grown by annealing equivalent to the casting method to satisfy I/I ₀

The reason for 45 is that the casting method slowly heats the copper foil during lamination, so the cubic aggregate structure is easy to grow.

In the case of Comparative Example 3 where the Ag concentration exceeds 360 ppm, the recrystallization temperature becomes high. Therefore, the copper foil is insufficiently recrystallized by annealing corresponding to at least one of the casting method or the laminating method, and resistance to bonding The seam foldability is poor. In addition, it is considered that unrecrystallized crystal grains that can become the starting point of cracks that tend to accumulate strain remain.

In the case of Comparative Examples 6 and 7, the processing degree η is higher than the straight line BC in FIG. 3, which means that the processing degree η is too high relative to the Ag concentration. Therefore, it becomes I/I ₀ <45 by annealing equivalent to at least one of the casting method or the laminating method, and the seam crush resistance is poor.

It is thought that this is because the degree of processing η is too high and many shear bands are introduced into the copper foil. As a result, the development of the cubic aggregate structure is hindered, and crystal grains with other directions grow. That is, it is considered that when the cube aggregate structure grows, the crystal grains of the cube aggregate structure grow while merging the surrounding crystal grains with other orientations. However, if there is a shear zone, the growth of the cube aggregate structure is hindered, leaving behind the crystal grains with other orientations. The grains grow.

Claims (3)

A rolled copper foil for flexible printed circuit boards, which contains 99.0% by mass or more of Cu, and the remainder is composed of inevitable impurities. It takes more than 5 seconds to heat from 25°C to 350°C and then at 350°C After heating in heating mode A for 30 minutes or heating mode B in heating mode B from 25°C to 350°C for 1 second, the intensity (I) of the (200) surface obtained by X-ray diffraction on the rolled surface is relative The intensity (I ₀ ) of the (200) plane obtained by X-ray diffraction in the fine powder copper is I/I ₀

45, and contains 280~360 mass ppm Ag relative to the oxygen-free copper specified in JIS-H0500 (C1011). A flexible copper-clad laminated board, which is formed by laminating the flexible printed circuit board of claim 1 with rolled copper foil and resin. A flexible printed circuit board having the flexible copper-clad laminated board of claim 2.

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