JP2013167013A - Rolled copper foil for flexible printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rolled copper foil having excellent vibration resistance in addition to excellent flexibility.SOLUTION: A rolled copper foil has a cross-sectional occupancy at a (200) surface of 70% or more in a cross-section parallel to a rolling direction.

Description

  The present invention relates to a rolled copper foil for a flexible printed wiring board, and more particularly to a copper foil used for an in-vehicle flexible printed wiring board.

  A flexible printed wiring board (FPC) is obtained by bonding a metal as a conductive layer and a flexible insulating substrate typified by a resin film. In general, a copper foil is used for the conductive layer, and a rolled copper foil having excellent flexibility is used particularly for applications that require flexibility.

  A general FPC manufacturing process is as follows. First, the copper foil is bonded to the resin film. For joining, there are a method of imidizing by applying heat treatment to a varnish applied on a copper foil, and a method of laminating a resin film with an adhesive and a copper foil. The copper foil with a resin film joined by these steps is referred to as CCL (copper-clad laminate). Thereafter, wiring is formed by etching to complete the FPC.

Flexibility required for rolled copper foil for FPC has become strict as electronic devices become lighter, shorter, and more functional, and various improvements have been proposed for obtaining rolled copper foil with excellent flex resistance. Yes. As a means for improving the bending resistance of the rolled copper foil, a method of developing a cube texture (cube orientation) of the copper foil has been proposed. For example, JP-A-11-286760 (Patent Document 1), JP-A 2000-212661 (Patent Document 2), JP-A-2001-323354 (Patent Document 3), WO2008 / 050584 (Patent Document 4). JP-A-2009-292090 (Patent Document 5) and the like describe the strength (I) of 200 planes determined by X-ray diffraction of fine powdered copper having the strength (I) of 200 planes determined by X-ray diffraction of the rolled surface. ₀ )) to determine the ratio.

Japanese Patent Laid-Open No. 11-286760 JP 2000-212661 A JP 2001-323354 A International Publication No. 2008/050585 JP 2009-292090 A

  By developing the cube texture of the rolled surface, the bending resistance of the rolled copper foil is certainly improved. However, for example, in a vehicle-mounted FPC, vibration resistance is also required, and there is a demand for a rolled copper foil that is less likely to have a decrease in conductivity due to vibration. However, a conventional rolled copper foil does not have sufficient vibration resistance. .

  Then, this invention makes it one subject to provide the rolled copper foil which was excellent also in vibration resistance in addition to bending resistance. Moreover, this invention makes it another subject to provide FPC provided with such a rolled copper foil.

  The present inventor has intensively studied to solve the above-mentioned problems, and until now, there has been a problem that the cubic texture of the rolling surface, that is, only controlling the orientation of crystal grains on the outermost surface of the copper foil. I found out. In other words, even though the copper foil has a certain thickness, even if the crystal orientation of the surface is controlled, if the copper foil is not taken into consideration even in the orientation of crystal grains inside the copper foil, high vibration resistance Cannot be obtained. As a result of further investigation based on the above knowledge, the present inventor has made the (200) plane occupancy ratio 70% or more in the cross section parallel to the rolling direction of the copper foil, thereby providing bending resistance and vibration resistance. It has been found that a rolled copper foil excellent in both of the above can be obtained.

  Accordingly, in the first aspect, the present invention is a rolled copper foil having a (200) plane occupancy of 70% or more in a cross section parallel to the rolling direction.

  In the second aspect, the present invention is a rolled copper foil having a characteristic that the occupancy of the (200) plane is 70% or more in a cross section parallel to the rolling direction by heat treatment at 400 ° C. for 1 hour.

  In one embodiment of the rolled copper foil according to the first or second aspect of the present invention, the thickness of the copper foil is 50 to 300 μm.

  In one embodiment of the rolled copper foil according to the first aspect of the present invention, the occupation ratio of the (200) plane is 95% or more in the cross section parallel to the rolling direction.

  In one embodiment of the rolled copper foil according to the second aspect of the present invention, by performing heat treatment at 400 ° C. for 1 hour, the occupation ratio of the (200) plane is 95 in the cross-sectional structure parallel to the rolling direction. % Or more.

  In one embodiment of the rolled copper foil according to the first or second aspect of the present invention, the Cu concentration is 99.8% by mass or more, the oxygen concentration is 0.05% by mass or less, and Ag, Sn, B, The total concentration of Zr and Ti has a composition of 0.003 to 0.03% by mass.

  In one embodiment of the rolled copper foil according to the first or second aspect of the present invention, the Cu concentration is 99.9% by mass or more, the oxygen concentration is less than 0.01% by mass, and Ag, Sn, B, The total concentration of Zr and Ti has a composition of 0 to 0.03% by mass.

  In one Embodiment of the rolled copper foil which concerns on the 1st or 2nd side surface of this invention, it is used as a conductor material of a flexible printed wiring board.

  In one embodiment of the rolled copper foil according to the first or second aspect of the present invention, the flexible printed wiring board is for vehicle use.

  This invention is a flexible copper clad laminated board provided with the copper foil which concerns on this invention in the 3rd side surface.

  This invention is a flexible printed wiring board obtained by processing the flexible copper clad laminated board which concerns on this invention in the 4th side surface.

  According to the present invention, a rolled copper foil excellent in vibration resistance in addition to flex resistance is provided. The rolled copper foil according to the present invention is particularly useful as a conductor layer of, for example, an in-vehicle FPC.

It is a photograph which shows the attachment state of the loop-shaped test piece at the time of performing a vibration test.

  The copper foil base material used in the present invention is a rolled copper foil. The rolled copper foil is superior to the electrolytic copper foil in that it has high strength, can cope with an environment in which vibration continuously occurs, and has high bending resistance. In the present invention, “copper foil” includes copper alloy foil. There is no restriction | limiting in particular as a material of copper foil, What is necessary is just to select suitably according to a use or a required characteristic. The Cu concentration in the copper foil is preferably 99.8% by mass or more, more preferably 99.85% by mass or more, and more preferably 99.9% by mass or more for reasons of ensuring high conductivity. Is more preferable. However, even if the Cu concentration is too high, it leads to an increase in cost, so 99.999 mass% or less is preferable, and 99.995 mass% or less is more preferable. Since the oxygen concentration in the copper foil leads to an increase in cuprous oxide and leads to the suppression of the development of the cube orientation, it is preferably less than 0.01% by mass, preferably 0.005% by mass or less, For example, it can be 0.0001 mass% or more and less than 0.01 mass%. As a copper foil satisfying such conditions, for example, oxygen-free copper (OFC) standardized in JIS-H3510 or JIS-H3100 can be used.

  Also, copper alloys with addition of Sn, Ag, B, Zr, Ti, Fe, In, Te, Zn, etc., Cu—Ni—Si based copper alloys with addition of Ni, Si, etc. to oxygen-free copper, Cr Copper alloys such as Cu-Zr-based and Cu-Cr-Zr-based copper alloys to which Zr and the like are added can also be used. Among these, adding one or more elements selected from the group consisting of Ag, Sn, B, Zr, and Ti in total of 0.03 mass% or less can increase the (200) plane occupancy, the strength and elongation of the copper foil. From the viewpoint of If the total content of Ag, Sn, B, Zr, and Ti exceeds 0.03% by mass, the strength is further improved, but the elongation is lowered and the workability may be deteriorated. More preferably, the total content of Ag, Sn, B, Zr and Ti is 0.02% by mass or less. The lower limit of the total content of Ag, Sn, B, Zr and Ti is not particularly limited, but for example, 0.001% by mass can be set as the lower limit. If the total content of Ag, Sn, B, Zr and Ti is less than 0.001% by mass, the desired effect cannot be obtained, and the content is too small to control the content. There is a case. Preferably, the lower limit of the total amount of Ag, Sn, B, Zr and Ti is 0.003% by mass or more, more preferably 0.004% by mass or more, and most preferably 0.005% by mass or more.

  Similarly, when the above copper alloy is used for the copper foil according to the invention of the present application, the oxygen concentration in the copper foil is preferably less than 0.01% by mass, and preferably 0.005% by mass or less. More preferably, when a copper alloy is used, it is acceptable that the oxygen concentration in the copper foil is somewhat high. Specifically, the oxygen concentration is allowed to be 0.05% by mass or less, and typically 0.01 to 0.03% by mass. For this reason, the tough pitch copper prescribed | regulated to JIS-H3100, for example can also be used as a copper raw material.

  There is no restriction | limiting in particular in the thickness of copper foil, What is necessary is just to select suitably according to a required characteristic. Generally, it is 1 to 300 μm, but when used as a conductor layer of a flexible printed wiring board, it is possible to obtain higher flexibility and vibration resistance when the copper foil is thinned. From such a viewpoint, the thickness of the copper foil is generally 2 to 50 μm, typically about 5 to 20 μm. However, for applications such as in-vehicle use where large current flows and heat generation due to energization is particularly disliked, copper foil is used from the viewpoint of reliably transmitting electrical signals without disconnection while ensuring conductivity and heat dissipation. Since it should be relatively thick, in such a case, the thickness is preferably 50 μm or more, and more preferably 70 μm or more. However, if the thickness is excessively large, it may be difficult to remove the conductor layer by etching. Therefore, the thickness is preferably 300 μm or less, and more preferably 150 μm or less.

  The copper foil which concerns on this invention is prescribed | regulated by the occupation rate of the (200) plane in the cross section parallel to a rolling direction in one side. A higher occupancy ratio is advantageous in bending resistance and vibration resistance. In one embodiment of the rolled copper foil according to the present invention, the occupancy ratio of the (200) plane in the cross section parallel to the rolling direction is 70%. Or more, preferably 80% or more, more preferably 90% or more, and even more preferably 95% or more, for example, 80 to 99%.

  In this invention, the point which has prescribed | regulated about the occupation rate of the (200) plane in a copper foil cross section differs from the conventional rolled copper foil which prescribed | regulated the crystal orientation of the rolling surface. According to the present invention, since the orientation of the crystal in the entire thickness of the copper foil is controlled, particularly in the case of a copper foil having a large thickness, the characteristics when compared with the rolled copper foil that defines the crystal orientation of the surface The difference of Therefore, the rolled copper foil according to the present invention uses a relatively large thickness copper foil, and is required to have vibration resistance, especially for in-vehicle use (particularly FPC used around transmissions and engines) and automatic machine control (automatic conveyance). It is particularly suitable as a conductor material used for FPC for control of equipment moving on rails such as lines.

  The occupancy ratio of the (200) plane in the cross section parallel to the rolling direction is determined by EBSP (electron backscattering analysis image method) after exposing the FPC cross section with FIB (focused ion beam) or CP (cross-section polisher). ) To calculate the area ratio of the (200) plane per unit area.

  The copper foil which concerns on this invention can be manufactured as follows, for example. First, a copper raw material such as electrolytic copper, oxygen-free copper, tough pitch copper or the like is melted, and an alloy element is added as necessary, and then the molten metal is cast to produce an ingot having a thickness of about 100 to 300 mm. Adjustment of the oxygen concentration in the melting step can be performed by techniques known to those skilled in the art, such as carbon sealing of the molten metal and release to the atmosphere. Then, after performing hot rolling, annealing and cold rolling are repeated, and the copper foil base material after final cold rolling is obtained. The higher the rolling reduction here, the easier the (200) plane develops by the subsequent annealing. Therefore, the degree of reduction in the final cold rolling is 85% or more, more preferably 90% or more, and still more preferably 95% or more. When manufacturing a copper foil having a large thickness, it tends to be impossible to ensure a large reduction ratio in the final cold rolling (because it is difficult to perform annealing in a state where the plate thickness is thick). Therefore, in the case of a copper foil having a thickness of 35 μm or more after the final cold rolling, considering the ease of actual production, the reduction ratio of the final cold rolling is preferably 96% or less, and 95% or less. Is more preferable, and it is further more preferable to set it as 93% or less.

  Next, this copper foil base material is annealed at 400 to 500 ° C. for 1 hour or longer. Annealing is preferably performed in an inert gas atmosphere such as nitrogen or Ar for the reason of preventing oxidation. It is also possible to anneal in a vacuum. By annealing at 400 ° C. or higher for 1 hour or longer, it is possible to control the crystal orientation in the copper foil. In the case of a copper foil having a large thickness, it is difficult to control the crystal orientation inside, and thus such high temperature and long time annealing is particularly necessary. Even if the annealing temperature is too high, it is inconvenient, and the effect of improving the azimuth occupancy can be obtained by setting it to 450 ° C. or less. A longer annealing time is advantageous for the development of the (200) plane, and it is preferable to anneal for 1 hour or longer. However, it is not necessary to anneal excessively, and the production efficiency is also lowered, so that it is preferably 2 hours or less, and more preferably 1.5 hours or less.

  In other words, the rolled copper foil according to the present invention is in a state after final cold rolling on one side surface, and is (200) plane in a cross section parallel to the rolling direction by heat treatment at 400 ° C. for 1 hour. It is also said that the copper foil has a characteristic that the occupancy ratio can be 70% or more, preferably 80% or more, more preferably 90% or more, still more preferably 95% or more, for example, 80 to 99%. it can.

  A flexible copper-clad laminate (FCCL) can be manufactured by laminating and bonding the rolled copper foil after annealing on one or both sides of a flexible insulating substrate made of polyester, polyimide, or the like. As an adhesion method, an adhesive made of a thermosetting resin such as epoxy is used, and a copper foil and a polyimide resin film are bonded to each other and heat treatment is performed, or a varnish containing polyamic acid which is a precursor of a polyimide resin Is coated on a copper foil and cured by heating to form a polyimide film on the copper foil. When laminating copper foil on both sides, after forming a single-sided copper clad laminate, there are a method of crimping the copper foil layer by hot pressing, and a method of sandwiching a polyimide film between two copper foil layers and crimping by hot pressing. is there. These heat treatments are generally carried out at 100 to 250 ° C. for 30 to 150 minutes. There is also a method of laminating a copper foil and a resin with an adhesive without going through a heat treatment step.

  As described above, in the FCCL manufacturing process, heat treatment is often performed for bonding the insulating substrate and the copper foil. Therefore, the annealing process after the final cold rolling described above can be used as the heat treatment. However, since it is difficult to sufficiently control the crystal orientation inside the copper foil under the general heat treatment conditions at the time of bonding described above, the heat treatment at the time of bonding is changed to the above conditions at 400 to 500 ° C. for 1 hour or more. By doing so, it is possible to simultaneously fabricate the copper foil having the characteristics according to the present invention and adhere it to the insulating substrate.

  It is possible to manufacture a flexible printed wiring board (FPC) by forming wiring according to a known procedure using the FCCL according to the present invention as a material. For example, apply an etching resist to the copper foil surface of the FCCL only on the necessary part as the conductor pattern, spray the etching solution onto the copper foil surface to remove the unnecessary copper foil, form the conductor pattern, and then peel off the etching resist -The method of removing and exposing a conductor pattern is mentioned. After forming the conductor pattern, it is common to apply a protective coverlay film. Such FPCs are FPCs used for movable parts in hard disks, hinge parts and slide sliding parts of mobile phones, printer head parts, optical pickup parts, movable parts of notebook PCs, etc. in electronic and electrical equipment. To do. In particular, the FPC according to the present invention is suitable as a vehicle-mounted or automatic machine control FPC that uses a relatively large thickness of copper foil and also requires vibration resistance.

  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.

<Manufacture of rolled copper foil>
Ingots having respective compositions shown in Table 1 in which predetermined elements were added to tough pitch copper (TPC) or oxygen-free copper (OFC) were melt cast.
After this was hot-rolled, annealing and cold rolling were repeated, and the final cold rolling was performed at the rolling reduction shown in Table 1 and adjusted to the thickness shown in Table 1. Finally, annealing was performed in an Ar atmosphere under annealing conditions of 200 ° C. × 1 hour, 300 × 1 hour, or 400 ° C. × 1 hour to obtain each rolled copper foil.
In Comparative Example 4, a special electrolytic copper foil (EDC) having a thickness of 35 μm was used, and annealing was performed in an Ar atmosphere at 200 ° C. × 1 hour, 300 × 1 hour, or 400 ° C. × 1 hour. Got. Moreover, about Example 10, annealing was also performed on condition of 400 degreeC x 0.5 hour by Ar atmosphere.

<Manufacture of FPC>
After performing roughening treatment with electrodeposited copper particles at a thickness of 50 μm on the front and back of each obtained rolled copper foil, a polyimide film with a thickness of 50 μm is laminated on the front and back under lamination conditions of hot pressing at a temperature of 180 ° C. for 2 hours, A double-sided FCCL was made. Thereafter, eight circuit etchings of 120 mm in length and line and space of 0.3 mm × 0.3 mm were formed, and finally a polyimide coverlay film having a thickness of 50 μm was hot-pressed on both sides at a temperature of 180 ° C. for 1 hour. By laminating, each test piece of FPC having a length of 150 mm and a width of 15 mm was produced.

<200 share (%)>
The occupancy ratio of the (200) plane in the cross section parallel to the rolling direction (“200 occupancy ratio (%)”) was measured by the procedure described above. That is, after exposing a cross-sectional structure parallel to the rolling direction of FPC, orientation analysis is performed in EBSP (JEOL Ltd. model JXA8500F), and (200) plane occupies per unit area (thickness of copper foil × 150 μm width) The area ratio of the region within 10 ° from the angle was calculated as the occupation ratio of the (200) plane. The measurement was performed twice, and the average value was taken as the measured value.

<Vibration resistance time (h)>
About each obtained FPC test piece, the vibration test was implemented based on the JIS-D1601 sweep vibration endurance test. The above-mentioned test piece is looped with a loop dimension L = 20 mm, and both ends are fixed, and a vibration test is performed at a frequency of 5 to 170 Hz / 5 min, an amplitude width of 0.6 mm, a vibration acceleration of 45 m / s ² , and a test temperature of 35 to 115 ° C. The resistance increase rate of the test piece when a constant current (1.0 mA) was applied to the test piece was recorded, and the time until the resistance increase rate of the test piece reached 20% was measured. The test temperature was maintained at room temperature (20 ° C.) for 10 minutes, then gradually decreased to −30 ° C. over 1.5 hours, held at −30 ° C. for 10 minutes, and then increased to 115 ° C. over 1.5 hours. The cycle of holding at 115 ° C. for 10 minutes and then lowering to room temperature (20 ° C.) over 1 hour was repeated. The test apparatus used F-400BM-E04 fully automatic vibration test apparatus by Shin-Nippon Sokki Co., Ltd. and temperature-humidity test apparatus VC-500DAR (33) M3C3R by Emic Co., Ltd.
In addition, as shown in FIG. 1, a loop dimension refers to the distance from the fixed location of a test piece to the front-end | tip of a test piece.

<Electric heat generation>
Each FPC test piece using a copper foil annealed at 400 ° C. for 1 hour was energized, the surface heat generation temperature was measured with a contact thermometer, and the heat generation characteristics were examined. Specifically, the surface temperature of the test piece when energized at 30 A for 30 minutes at room temperature was measured and evaluated according to the following criteria.
× = 40 ° C. or more Δ = 35 ° C. to less than 40 ° C. ○ = 30 ° C. to less than 35 ° C. ◎ = less than 30 ° C.

<MIT flex test>
About each FPC test piece using the copper foil annealed at 400 degreeC for 1 hour, it implemented based on the JIS-P8115MIT testing machine method. The above-mentioned test piece is set in the MIT test apparatus. When the foil thickness is 50 μm or less, the load (tension) is 250 g. When the foil thickness is 70 μm or more, the load (tension) is 500 g. The test was conducted at 135 degrees. The test apparatus used was a model D manufactured by Toyo Seiki Seisakusho.
Flexibility was evaluated according to the following criteria.
○ = Number of flexing times to break 5000 times or more × = Number of flexing times to break less than 5000 times

  The results are shown in Table 1. In Examples 1 to 18, since the occupation ratio (%) of the (200) plane was 70% or more, it was possible to obtain a long vibration resistance time as compared with the comparative example having the same foil thickness. And it can be understood that the higher the (200) plane occupancy (%), the longer the anti-vibration time tends to be. It can also be understood that a test piece having a larger foil thickness suppresses energization heat generation. Furthermore, in Examples 1-18, the high flexibility was shown. In addition, when the above-mentioned evaluation was performed on the copper foil when heated at 400 ° C. for 0.5 hour in Example 10, the (200) plane occupancy (%) was 68%, and the vibration resistance time was 13 hours. Met.

In Comparative Example 1, tough pitch copper was used as the material, but the composition was inappropriate, and the rolling texture was not developed, so the (200) plane occupancy (%) did not rise sufficiently. . Since the final rolling reduction was small, the flexibility was poor due to insufficient development of the recrystallized structure after heat treatment.
In Comparative Example 2, the final reduction ratio was large and the flexibility was excellent, but the occupancy ratio of the (200) plane was not sufficiently increased.
In Comparative Example 3 having a large foil thickness, although the reduction ratio during the final cold rolling was further increased as compared with Comparative Example 2, the composition was inappropriate, and therefore the (200) plane occupation ratio was 400 ° C. after heating for 1 hour. There was little rise. Flexibility was also poor due to inappropriate development of recrystallized structure after heat treatment.
In Comparative Example 4, a special electrolytic copper foil was used as the material, but the 200 occupancy (%) did not rise sufficiently due to the development of the (111) plane, which is an electrodeposited texture. Flexibility was also poor due to inappropriate development of recrystallized structure after heat treatment.
In Comparative Example 5, a material obtained by adding 400 mass ppm of Sn to oxygen-free copper was used. However, since the amount of Sn added was large, stacking faults increased, and the occupancy rate (%) did not increase sufficiently. Flexibility was also poor due to inappropriate development of recrystallized structure after heat treatment.
In Comparative Example 6, a material obtained by adding 400 mass ppm of Ag to tough pitch copper was used. However, since the amount of Ag added was large, stacking faults increased, and the occupancy rate (%) did not increase sufficiently. Flexibility was also poor due to inappropriate development of recrystallized structure after heat treatment.

Claims (11)

  A rolled copper foil having a (200) plane occupancy of 70% or more in a cross section parallel to the rolling direction.   A rolled copper foil having a characteristic that the occupancy of the (200) plane is 70% or more in a cross section parallel to the rolling direction by heat treatment at 400 ° C. for 1 hour.   The rolled copper foil according to claim 1 or 2, wherein the copper foil has a thickness of 50 to 300 µm.   The rolled copper foil according to claim 1 or 3, wherein an occupancy ratio of the (200) plane is 95% or more in a cross section parallel to the rolling direction.   The rolled copper foil according to claim 2 or 3, which has a characteristic that the occupancy of the (200) plane is 95% or more in a cross-sectional structure parallel to the rolling direction by performing a heat treatment at 400 ° C for 1 hour.   The Cu concentration is 99.8% by mass or more, the oxygen concentration is 0.05% by mass or less, and the total concentration of Ag, Sn, B, Zr and Ti is 0.003 to 0.03% by mass. The rolled copper foil as described in any one of 1-5.   The Cu concentration is 99.9 mass% or more, the oxygen concentration is less than 0.01 mass%, and the total concentration of Ag, Sn, B, Zr and Ti has a composition of 0 to 0.03 mass%. The rolled copper foil as described in any one of 5.   The rolled copper foil as described in any one of Claims 1-7 used as a conductor material of a flexible printed wiring board.   The rolled copper foil according to claim 8, wherein the flexible printed wiring board is for vehicle use.   The flexible copper clad laminated board provided with the rolled copper foil as described in any one of Claims 1-9.   The flexible printed wiring board obtained by processing the flexible copper clad laminated board of Claim 10.