JP5694094B2 - Copper foil for flexible printed wiring board, copper-clad laminate, flexible printed wiring board, and electronic device - Google Patents

Description

  The present invention relates to a copper foil for a flexible printed wiring board, a copper clad laminate, a flexible printed wiring board, and an electronic device.

Flexible printed wiring boards are soft printed wiring boards that can be bent, twisted, wound, and stacked, and can be mounted in narrow spaces, so mobile phones, computer-related products, audio-visual products, cameras, and automobiles. Used for wiring.
The characteristics required for a flexible printed wiring board include good bendability represented by MIT bendability and high cycle bendability represented by IPC bendability. Conventionally, copper foil having such characteristics And copper-resin substrate laminates have been developed (Patent Documents 1 to 3).

JP 2010-100877 A JP 2009-111203 A JP 2007-207812 A

  Flexible printed wiring boards are sometimes used by being folded to reduce space, but in recent years, the bending radius of such bending has become small, and it is used in such a harsh state that it cannot be evaluated by the MIT flexibility test. Has been. In particular, in a small device represented by a touch panel type smartphone, bending of a flexible printed wiring board connected to the touch panel and a flexible printed wiring board of an LED module is severe.

  After connecting a flexible printed wiring board that has been subjected to strict bending as described above to other parts, the bending process may be restored to the original state by redoing, etc. If the bending process is severe, the copper foil of the flexible printed wiring board may be broken only by repeating these several times. Moreover, in the MIT bendability test, a copper foil that does not break even if it is bent several hundreds or thousands of times may be broken only by repeating the above-mentioned severe bending process several times.

  Then, this invention makes it a subject to provide the copper foil for flexible printed wiring boards excellent in bending workability, the copper clad laminated board using the same, a flexible printed wiring board, and an electronic device.

  The present inventor has found that the bending workability of the copper foil is related to the ratio of the area in which the crystal orientation is in the range of 10 ° centered on the 001 orientation in the cross section of the copper foil. And based on such knowledge, by controlling the ratio of the area where the crystal orientation is in the range of 10 ° centered on the 001 orientation in the cross section of the copper foil, a copper foil for flexible printed wiring boards with excellent bending workability is provided. Found that you can.

The present invention completed on the basis of the above knowledge is, in one aspect, a copper foil, and when the cross section parallel to the thickness direction of the copper foil is observed, the cross section is 10 ° centered on the 001 orientation. the ratio of the area a of the portion having a crystal orientation in the range is der Ru full lexical Bull copper foil for printed wiring boards at least 10% of the viewing area of the cross section.

Another aspect of the present invention is a copper foil, and when heat treatment is performed at 200 to 350 ° C. for 30 minutes, a cross section parallel to the plate thickness direction of the copper foil is 10 ° centered on the 001 orientation. If the percentage of the area a of the portion having a crystal orientation in the range of observed the cross-section, a der Ru full lexical Bull copper foil for printed wiring boards at least 10% of the viewing area of the cross section.

  In one Embodiment of the copper foil for flexible printed wiring boards which concerns on this invention, the ratio of the said area A in the said cross section is 60% or more.

In another embodiment of the copper foil for a flexible printed wiring board according to the present invention, the substrate having a thickness of 4 to 50 μm is formed on a substrate having a thickness of 10 to 55 μm formed of a polyimide resin layer and a thermoplastic polyimide adhesive layer. A copper clad laminate formed by laminating copper foil and formed by thermocompression was subjected to 180 ° contact bending once to fix the bent portion of the copper foil, and obtained by cutting in a direction parallel to the bending direction. when observing the cross section of the bent portion of the copper foil, in the cross-section, 0 01 ratio of the area B of the portion having a crystal orientation in orientation in the range of center 10 ° for more than 10% of the observation area of the cross section It is.

  In still another embodiment of the copper foil for flexible printed wiring board according to the present invention, the ratio of the area B in the cross section of the bent portion of the copper foil is 60% or more.

  In still another embodiment of the copper foil for flexible printed wiring board according to the present invention, one or two selected from the group consisting of P, Fe, Zr, Mg, S, Ge and Ti as inevitable impurities The above is 20 ppm by mass or less in total.

  In still another embodiment of the copper foil for flexible printed wiring board according to the present invention, the total of one or more selected from the group consisting of Ag, In, Au, Pd and Sn is 20 to 500 ppm by mass. Including.

  In another aspect, the present invention is a copper clad laminate comprising the copper foil according to the present invention.

  In still another aspect, the present invention is a flexible printed wiring board made of the copper clad laminate according to the present invention.

  In still another aspect, the present invention is an electronic device including the flexible printed wiring board according to the present invention, and a first substrate and a second substrate electrically connected by the flexible printed wiring board.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for flexible printed wiring boards excellent in bending workability, the copper clad laminated board using the same, a flexible printed wiring board, and an electronic device can be provided.

It is a schematic diagram which shows the aspect of 180 degree contact | adherence bending. It is a schematic diagram which shows the bending direction of the copper clad laminated board of 180 degree adhesion | attachment bending.

(Configuration of copper foil for flexible printed wiring board)
As a material for the copper foil for a flexible printed wiring board, either a rolled copper foil or an electrolytic copper foil may be used, but it is preferable to use a rolled copper foil having good bending workability. As the rolled copper foil, tough pitch copper (JIS-H3100 C1100) or oxygen-free copper (JIS-H3100 C1020, JIS-H3510 C1011) can be used.
In this specification, “copper foil” includes copper alloy foil, and copper foil formed of “tough pitch copper” and “oxygen-free copper” includes copper alloy foil based on tough pitch copper and oxygen-free copper. It is. Specifically, the copper alloy foil based on tough pitch copper and oxygen-free copper contains 20 to 500 mass ppm in total of one or more selected from the group consisting of Ag, In, Au, Pd and Sn. This is preferable because the crystal orientation in the copper foil cross section described later has an effect of increasing the ratio of the area A in the range of 10 ° centered on the 001 orientation. If the total amount of the metals is less than 20 ppm by mass, the desired effect cannot be obtained, and if it exceeds 500 ppm by mass, the development in the range of 10 ° centering on the 001 orientation becomes small and the desired effect cannot be obtained.

  The copper foil which concerns on this invention is formed with the copper used industrially, and contains 99.9 mass% or 99.99 mass% copper and an unavoidable impurity. Among these, P, Fe, Zr, Mg, S, Ge and Ti as unavoidable impurities are easy to rotate in the crystal orientation by bending the copper foil even in the presence of a very small amount, and shear bands are also likely to enter. This is not preferable because bending workability is lowered. For this reason, the copper foil which concerns on this invention makes 1 mass or 2 types or more selected from the group which consists of P, Fe, Zr, Mg, S, Ge, and Ti as an unavoidable impurity to 20 mass ppm or less in total It is preferable to control.

  As thickness of the copper foil which concerns on this invention, 4-50 micrometers is preferable and 6-50 micrometers is more preferable. When the thickness of the copper foil is less than 4 μm, the handling of the copper foil is deteriorated, and when it is more than 50 μm, the flexibility is lowered. As for the thickness of copper foil, 12-35 micrometers is more preferable.

  The copper foil according to the present invention has a cross section in which the ratio of the area A in which the crystal orientation is in the range of 10 ° centered on the 001 orientation is 10% or more. The crystal orientation of the copper foil rotates when the bending is repeated several times. This rotation of crystal orientation causes cracking. If the 001 orientation of the crystal is in the cross section in the thickness direction of the copper foil and the direction parallel to the cross section is the bending direction, the crystal orientation becomes difficult to rotate, and the bending workability is improved. Moreover, it becomes difficult to enter a shear band which is one of the causes of cracks, and the bending workability is improved. Since the ratio of the area A in the range of 10 ° centering on the 001 orientation is 10% or more, the copper foil according to the present invention has good bending workability. The ratio of the area A in the cross section is more preferably 60% or more. The crystal orientation can be measured by an EBSD (Electron Back Scattering Diffraction) method.

The copper foil according to the present invention is a copper foil formed by laminating a copper foil having a thickness of 6 to 50 μm on a base material having a thickness of 10 to 55 μm formed of a polyimide resin layer and a thermoplastic polyimide adhesive layer, and thermocompression bonding. In the cross section of the bent portion of the copper foil obtained by fixing the bent portion of the copper foil by performing 180 ° contact bending once on the tension laminate, and cutting in a direction parallel to the bending direction, the crystal orientation is The ratio of the area B in the range of 10 ° around the 001 orientation may be 10% or more.
The aspect of the 180 ° contact bending is shown in FIG. First, as shown in state A, the copper-clad laminate is bent by a bending jig and bent so as to be folded back 180 ° as in state B. Subsequently, the copper clad laminate bent by 180 ° is opened using a return jig as shown in state C, and the bent part is returned to a straight line as shown in state D. This is defined as one 180 ° contact bending. By shifting this to the bending shown in state A again, the second and third times can be repeated.
The “bending direction” indicates a direction in which the copper clad laminate is bent as shown in FIG.
According to such a configuration, even after 180 ° contact bending is performed once, the ratio of the area B in which the crystal orientation is in the range of 10 ° centered on the 001 orientation is 10% or more. Has excellent bending workability. Further, the ratio of the area B in the cross section of the bent portion of the copper foil is more preferably 60% or more.

(Configuration of flexible printed wiring board)
A flexible printed wiring board according to the present invention includes an insulating substrate and a wiring pattern formed on the surface of the insulating substrate. The insulating substrate is not particularly limited as long as it has good bendability and bendability that can be applied to a flexible printed wiring board. For example, polyimide film, liquid crystal polymer film, polyethylene naphthalate, etc. should be used. Can do. The thickness of the insulating substrate is preferably 12 to 50 μm. When the thickness is less than 12 μm, the handling becomes worse, and when it exceeds 50 μm, the flexibility is lowered. The wiring pattern is formed using the above-mentioned rolled copper foil for flexible printed wiring boards. The shape of the wiring pattern is not particularly limited, and any shape may be used.

(Manufacturing method of copper foil for flexible printed wiring boards)
When the copper foil for flexible printed wiring boards is a rolled copper foil, it can be produced by the following production method.
First, high-purity electrolytic copper with a low content of P, Fe, Zr, Mg, S, Ge, and Ti is used as a copper raw material. One or two or more selected from the group consisting of P, Fe, Zr, Mg, S, Ge, and Ti as inevitable impurities are added in a total of 20 ppm by mass so that P, Zr, and Mg are not mixed. An ingot is produced under the following control. At this time, an ingot may be produced by adding subcomponents so that one or two or more selected from the group consisting of Ag, In, Au, Pd and Sn may be 20 to 500 mass ppm in total. .
Next, after this ingot is hot-rolled, the oxide is removed by surface grinding, and cold rolling, annealing, and pickling are repeated and processed to a predetermined thickness, whereby a rolled copper foil for a flexible printed wiring board is obtained. Make it. In the rolling process, in order to control the ratio in the range of 10 ° centered on the 001 orientation which is the crystal orientation to 10% or more with respect to the cross section in the thickness direction, the rolling tension of 0.1 mm or less is set to 100 MPa or less. The degree of processing for one pass is 20% or less. Further, the kinematic viscosity of the rolling oil is 1 to 5 mm ² / s, and the rolling strain rate is 30 to 800 / s.

(Production method of flexible printed wiring board)
A flexible printed wiring board can be manufactured using the copper foil. Below, the manufacture example of a flexible printed wiring board is shown.
First, a copper-clad laminate is manufactured by laminating a copper foil and an insulating substrate such as a polyimide film or a liquid crystal polymer film having good bendability and foldability. The copper foil may be subjected to a predetermined surface treatment in advance.

  In the case of a polyimide film, the bonding is performed by applying a thermoplastic polyimide adhesive to a thermosetting polyimide film, drying it, laminating it with a copper foil, and thermocompression bonding. As a pressure bonding method, there are a method of vacuum hot pressing and a method of laminating with a heat roll. Moreover, in the case of a polyimide film, a copper-clad laminate is produced by coating, drying and curing a polyimide precursor on a copper foil.

  A method well-known to those skilled in the art may be used for the process of producing a flexible printed wiring board from a copper clad laminated board. For example, an etching resist is applied only to a necessary portion as a wiring pattern on a copper foil surface of a copper clad laminate, and unnecessary copper foil is removed by spraying an etching solution onto the copper foil surface to form a circuit pattern. Next, a flexible printed wiring board is produced by peeling and removing the etching resist to expose the wiring pattern.

  Various electronic devices can be manufactured by providing this flexible printed wiring board between two electronic substrates and electrically connecting them. The electronic device is not particularly limited, and examples thereof include a liquid crystal display, a car navigation system, a mobile phone, a game machine, a CD player, a digital camera, a TV, a DVD player, an electronic notebook, an electronic dictionary, a calculator, a video camera, a printer, and the like. It is done.

  EXAMPLES Examples of the present invention will be described below, but these are provided for better understanding of the present invention and are not intended to limit the present invention.

(Example 1: Examples 1 to 22)
Ingots were prepared by adding the elements shown in Table 1 to high-purity electrolytic copper. At this time, P, Fe, and Zr as inevitable impurities are prevented by not mixing impurities from the crucible, the mold, and the refractory and further preventing P, Zr, and Mg from being mixed in the deoxidation treatment. , Mg, S, Ge and Ti were controlled so that one or more selected from the group consisting of Mg, S, Ge and Ti would be 20 ppm by mass or less in total.
Subsequently, this ingot was processed into a 7 mm thick plate by hot rolling, oxide was removed by surface grinding, and then cold rolling, annealing, and pickling were repeated, and 0.1 mm rolling was performed in all passes. The tension was 100 MPa or less and the processing degree was 20% or less. Examples 3 and 10 have a strain rate of 60 / s, the kinematic viscosity of the rolling oil is 1.5 mm ² / s, Examples ² , 4, 9, and 12 have a strain rate of 800 / s and a kinematic viscosity of 1.5 mm ² / s In this example, rolling was performed at a strain rate of 60 / s and a kinematic viscosity of 5 mm ² / s.
Then, the roughening process of Cu-Ni plating was performed to the copper foil single side | surface, and Cr immersion plating was performed after that. The reverse side was chromated.
Subsequently, a 27 μm-thick resin layer formed by applying 2 μm of the thermoplastic PI adhesive to Kapton EN (registered trademark) and drying is laminated on the copper foil and vacuum hot pressed (heated at 200 to 350 ° C. for 30 minutes). A copper-clad laminate was prepared.

(Example 2: Comparative Examples 1-2)
In Comparative Examples 1 and 2, a commercially available special electrolytic copper foil having a thickness of 18 μm was used, and a 27 μm-thick resin layer formed by applying 2 μm of a thermoplastic PI adhesive to Kapton EN (registered trademark) and drying the copper foil A copper-clad laminate was prepared by vacuum hot pressing (heating at 200 to 350 ° C. for 30 minutes).

(Example 3: Comparative Examples 3-4)
In Comparative Examples 3 to 4, oxygen-free copper (JIS-H3100 C1020) ingots to which the elements shown in Table 1 were added were prepared. At this time, inevitable impurities are not suppressed, and one or two or more selected from the group consisting of P, Fe, Zr, Mg, S, Ge, and Ti become more than 20 mass ppm in total. It was.
Subsequently, this ingot was processed into a plate having a thickness of 7 mm by hot rolling, the oxide was removed by surface grinding, and then cold rolling, annealing, and pickling were repeated and processed to the thickness shown in Table 1. . At this time, in rolling with a thickness of 0.1 mm or less, a pass with a tension exceeding 100 MPa was performed at least once. Rolling was performed at a kinematic viscosity of 6 m ² / s and a strain rate of 900 / s.
Subsequently, a 27 μm-thick resin layer formed by applying 2 μm of the thermoplastic PI adhesive to Kapton EN (registered trademark) and drying is laminated on the copper foil and vacuum hot pressed (heated at 200 to 350 ° C. for 30 minutes). A copper-clad laminate was prepared.

The specimens of Examples 1 to 22 and Comparative Examples 1 to 4 thus produced were cut in the thickness direction using the CP method (cross session polisher method) to obtain a copper foil cross section. Then, immediately using the electron microscope JEOL FE-SEM in the area of “copper foil thickness described in Table 1” × “300 μm width”, the KAM value was calculated by taking EBSP using analysis software manufactured by TSL, The ratio of the area A in which the crystal orientation is in the range of 10 ° centered on the 001 orientation was calculated.
As a result, in each of the examples, as shown in Table 1, there was a cross section in which the ratio of the area A in the range of 10 ° centered on the 001 orientation was 10% or more. A circuit of (line) / S (space) = 300 μm / 300 μm was formed to obtain a flexible printed wiring board.
On the other hand, since all of the comparative examples had no cross section in which the ratio of the area A in the range of 10 ° centered on the 001 orientation was 10% or more as shown in Table 1, it was parallel to the MD (machine direction). Thus, a circuit of L (line) / S (space) = 300 μm / 300 μm was formed to obtain a flexible printed wiring board.
Next, 180 ° contact bending is performed once on the flexible printed wiring boards according to the example and the comparative example, and the flexible printed wiring board is bent and fixed with resin, and the CP method (cross method) is used in parallel with the circuit. Session polisher method) was used to obtain a copper foil cross section of the bent portion. After that, in order to prevent the formation of an oxide film, the EBSD immediately in an area of “copper foil thickness described in Table 1” × “total width of 100 μm (see FIG. 2) of 50 μm width on both sides centering on the bending vertex of the copper foil”. Ten cross sections were measured, and the ratio of the area B in the range of 10 ° centered on the 001 orientation in the total area was calculated.
Moreover, it was observed whether or not the copper foil was broken during bending.
Here, the occurrence of breakage was determined as follows. That is, a constant current (0.01 to 0.1 mA) is passed through the copper foil circuit of the flexible printed wiring board, a voltage value necessary to pass the current is measured, and the copper of the flexible printed wiring board is measured from the measured voltage value. The resistance value of the foil circuit was calculated. When the calculated resistance value was 500% or more of the initial value (resistance value before bending), it was determined that a fracture occurred.
The measurement results are shown in Table 1.

(Evaluation)
In Examples 1 to 22, any one or two or more selected from the group consisting of P, Fe, Zr, Mg, S, Ge, and Ti as inevitable impurities are 20 ppm by mass or less in total. As a result of measuring the ratio of area A before 180 ° contact bending and the ratio of area B in a state where the bending was performed once and fixed, both were 10% or more, and 180 ° contact bending was performed four times or The copper foil was not broken even after repeated 8 times.
In Comparative Examples 1 to 4, one or two or more selected from the group consisting of P, Fe, Zr, Mg, S, Ge and Ti as inevitable impurities are in total more than 20 mass ppm, As a result of measuring the ratio of area A before 180 ° contact bending and the ratio of area B in a state where the bending was performed once and fixed, both were less than 10%, and 180 ° contact bending was performed twice. A rupture occurred in the copper foil immediately.
In addition, the copper foil used for Examples 1, 3, 14, 15, 19, 20, 21, and 22 was heated at 200 to 350 ° C. for 30 minutes without being laminated on the resin layer. Then, the ratio (%) of the area A of the copper foil was measured. As a result, the ratio (%) of the area A of the copper foil is the ratio of the area A before 180 ° adhesion bending of Examples 1, 3, 14, 15, 19, 20, 21, and 22 shown in Table 1, respectively. (%) And the same value.

Claims (11)

Copper foil,
When a cross section parallel to the plate thickness direction of the copper foil is observed , the ratio of the area A of the portion having a crystal orientation in the range of 10 ° centered on the 001 orientation in the cross section is 10 of the observation area of the cross section. der Ru full lexical Bull copper foil for printed wiring boards or%. Copper foil,
When the heat treatment is performed at 200 to 350 ° C. for 30 minutes, the ratio of the area A of the portion having the crystal orientation in the range of 10 ° centered on the 001 orientation in the cross section parallel to the plate thickness direction of the copper foil is when observing the cross-section, Ru der least 10% of the viewing area of the cross-section off lexical Bull copper foil for printed wiring boards.   The copper foil for flexible printed wiring boards according to claim 1 or 2, wherein a ratio of the area A in the cross section is 60% or more. With respect to a copper clad laminate formed by thermocompression bonding by laminating the copper foil having a thickness of 4 to 50 μm on a substrate having a thickness of 10 to 55 μm formed of a polyimide resin layer and a thermoplastic polyimide adhesive layer. ° adhesion bending was performed once to fix the bent portions of the copper foil, when the bent portion of the cross section of the bending direction and the copper foil obtained by cutting in a direction parallel to the observation, in the cross section, 0 The copper for flexible printed wiring boards according to any one of claims 1 to 3, wherein a ratio of an area B of a portion having a crystal orientation in a range of 10 ° centered on a 01 orientation is 10% or more of an observation area of the cross section. Foil.   The copper foil for flexible printed wiring boards according to claim 4, wherein a ratio of the area B in a cross section of a bent portion of the copper foil is 60% or more.   The total amount of one or more selected from the group consisting of P, Fe, Zr, Mg, S, Ge, and Ti as inevitable impurities is 20 mass ppm or less. Copper foil for flexible printed wiring boards.   The copper foil for flexible printed wiring boards in any one of Claims 1-6 which contain 20-500 mass ppm in total of the 1 type (s) or 2 or more types selected from the group which consists of Ag, In, Au, Pd, and Sn.   The copper clad laminated board provided with the copper foil in any one of Claims 1-7.   A flexible printed wiring board made of the copper clad laminate according to claim 8.   An electronic device comprising: the flexible printed wiring board according to claim 9; and a first substrate and a second substrate electrically connected by the flexible printed wiring board. An electronic device using the flexible printed wiring board according to claim 9.

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