Hard rolled-copper foil and method of manufacturing the hard rolled-copper foil

Abstract

A hard rolled-copper foil which, when heated and laminated on an insulating resin base material, can exhibit excellent bend-resistance characteristics without increasing a final reduction ratio, which, being not prone to develop rolling marks, can maintain a low surface coarseness and can therefore be preferably used in a flexible printed wiring board having excellent high-speed transmission characteristics, which is not prone to softening at room temperature, and which provides excellent operation efficiency and foil passing property when being processed into a flexible printed wiring board after having been stored. A hard rolled-copper foil in which a crystal orientation density in a copper orientation is not less than 10, and a crystal orientation density in a brass orientation is not less than 20.

Claims

1. A hard rolled-copper foil wherein a crystal orientation density in a copper orientation is 10 or more, and a crystal orientation density in a brass orientation is 20 or more.

2. The hard rolled-copper foil according to claim 1, wherein the crystal orientation density in the copper orientation is 25 or less, and the crystal orientation density in the brass orientation is 45 or less.

3. The hard rolled-copper foil according to claim 1, manufactured by rolling oxygen-free copper having a copper purity of 99.99% or more.

4. The hard rolled-copper foil according to claim 1, having a ten-point average roughness Rzjis94 of less than 1 m.

5. The hard rolled-copper foil according to claim 1, having a foil thickness of 12 m or less.

6. The hard rolled-copper foil according to claim 1, having a ten-point average roughness Rzjis94 is 0.5 m or less.

7. A printed wiring board comprising a laminate that includes the hard rolled-copper foil according to claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram showing a method of determining a recovery temperature range.

(2) FIG. 2 is a graph showing values of crystal orientation densities of hard rolled-copper foils of Examples and Comparative Examples.

(3) FIG. 3 is a view illustrating a method of a bending-resistance characteristic test.

(4) FIG. 4 is a view illustrating the method of a bending-resistance characteristic test.

(5) FIG. 5 is a view illustrating the method of a bending-resistance characteristic test.

DESCRIPTION OF EMBODIMENTS

(6) (Raw Material Copper Ingot)

(7) Copper used in the present invention is not particularly limited. Oxygen-free copper and tough pitch copper that are specified in JIS H0500 can also be used, and oxygen-free copper is preferred.

(8) The reason for this is as follows. In the case of oxygen-free copper, even when soft etching treatment is performed during the circuit formation, irregular shapes are unlikely to be formed on the surface compared with the case of tough pitch copper. Accordingly, the transmission loss can be reduced, which contributes to an improvement in the high-speed transmission characteristics.

(9) The copper purity of oxygen-free copper is not particularly limited but is preferably 99.99% or more. This is because the electrical conductivity improves.

(10) An example of oxygen-free copper having a copper purity of 99.99% or more is alloy number C1011 but is not limited to this.

(11) (Hot-Rolling Step)

(12) A hot-rolling step is a step of heating a copper ingot produced by casting to about 800 C. and rolling the copper ingot.

(13) (Repeating Step)

(14) The resulting copper plate subjected to hot rolling is further subjected to a heat treatment step as required, and subsequently rolled by a multi-stage cold rolling mill. A typical reduction ratio is about 50%, and heat treatment and cold rolling are repeated.

(15) (Final Rolled Copper Strip)

(16) After the hot-rolling step and the repeating step, a final rolled copper strip can be obtained.

(17) The reduction ratio immediately before obtaining the final rolled copper strip is preferably 70% or more. This is because sufficient -fibers need to be developed in the final rolled copper strip.

(18) Note that the final rolled copper strip preferably has a thickness such that the final reduction ratio of the hard rolled-copper foil which is the final product does not exceed 90%.

(19) The reduction ratio (R) can be expressed by the following formula 1 where Ti represents a foil thickness before rolling, and Tf represents a foil thickness after rolling.
Reduction ratio R={(TiTf)/Ti}100<Formula 1>
(Final Heat Treatment Step)

(20) The final rolled copper strip prepared as described above is subjected to final heat treatment at a temperature of the state of recovery in the degree of progress of heat treatment, and then subjected to final cold rolling, thus providing a hard rolled-copper foil in which not only the brass orientation but also the copper orientation of the rolling texture is developed.

(21) When the final rolled copper strip is maintained in the state of recovery, the crystal orientation of some of -fibers in the rolling texture of the final rolled copper strip is replaced with a specific crystal orientation. Thus, the copper orientation is considered to be developed by the final cold rolling.

(22) If the final heat treatment is performed at a temperature of the state of grain growth, bending-resistance characteristics are not exhibited as long as the final reduction ratio is less than 90%.

(23) (Determination of Final Heat Treatment Temperature)

(24) Temperatures at which the final rolled copper strip is in the state of recovery can be determined by the following method.

(25) As shown in Table 1, a tensile strength (N/mm.sup.2) is measured when a final rolled copper strip is subjected to heat treatment for a certain period of time at various temperatures.

(26) TABLE-US-00001 TABLE 1 Temper- ature [ C.] 25 80 100 110 120 130 140 150 160 180 200 250 300 Tensile 480 477 476 476 471 453 410 321 256 221 215 205 205 strength [N/mm.sup.2]

(27) Subsequently, as illustrated in FIG. 1, a curve is drawn by plotting the values of the tensile strength on a graph where the X-axis represents the temperature and the Y-axis represents the tensile strength. Subsequently, a temperature at an inflection point 1 at which the tensile strength rapidly decreases is defined as a recrystallization start temperature, and a temperature at a point of intersection (intersection point 2) between a tangent 5 of the inflection point and a baseline 6 of the curve on the low-temperature side is defined as a minimum heating temperature. A temperature between the minimum heating temperature and the recrystallization start temperature is a final heat treatment temperature.

(28) Herein, the state up to the recrystallization start temperature (inflection point 1) is defined as recovery, and, with a further increase in the temperature exceeding the recrystallization start temperature, the process passes from recrystallization to grain growth. Thus, herein, a temperature range between the minimum heating temperature and the recrystallization start temperature is defined as a recovery temperature range.

(29) The determination of the recovery temperature range is preferably performed in an inert atmosphere or under vacuum for a holding time of 30 minutes to 1 hour.

(30) In Table 1, the holding time at each temperature is 30 minutes, and a tensile/compression tester IM-20 (manufactured by INTESCO Co., Ltd.) is used to measure the tensile strength.

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

(32) (Final Cold Rolling Step)

(33) After the final heat treatment is performed, the resulting rolled copper strip is rolled by final cold rolling to have a desired foil thickness. Thus, a hard rolled-copper foil can be produced.

(34) A well-known cold rolling method can be employed in the final cold rolling.

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

(36) The reason for this is as follows. If the final reduction ratio is 90% or more, rolling marks appear significantly, and the surface roughness increases. In addition, strains accumulate in the hard rolled-copper foil in a large amount, and the softening temperature decreases, which may cause room temperature softening.

(37) In addition, the reason is that the growth of the copper orientation is suppressed at a final reduction ratio of 90% or more.

(38) (Crystal Orientation Density)

(39) Crystal orientation densities of the hard rolled-copper foil can be calculated by evaluating the rolling texture by a pole figure measurement using X-ray diffraction.

(40) (Surface Roughness)

(41) The ten-point average roughness Rzjis94 of a surface of the hard rolled-copper foil according to the present invention is preferably less than 1 m, more preferably 0.5 m or less.

(42) This is because the transmission loss of the resulting printed wiring board is reduced.

(43) (Foil Thickness)

(44) The hard rolled-copper foil preferably has a foil thickness of 12 m or less in terms of the nominal thickness specified in JIS C6515.

(45) This is because, with a decrease in the foil thickness, the stress applied to the copper foil decreases, which contributes to an improvement in the bending-resistance characteristics and also contributes to a reduction in the size, a reduction in the thickness, and a reduction in the weight of portable devices.

(46) (Insulating Resin Base Material)

(47) Examples of the insulating resin base material laminated with the hard rolled-copper foil according to the present invention include, but are not particularly limited to, base materials made of a polyimide resin, a polyester resin, or a liquid crystal polymer resin, and base materials made of any of these resins to which an adhesive such as an epoxy or polyimide adhesive is applied.

EXAMPLES

(48) Examples and Comparative Examples of the present invention will be described. However, the present invention is not limited thereto.

(49) In Examples 1 and 2 and Comparative Examples 1 to 3, a final rolled copper strip (trade name: OFC strip sheet, manufactured by Mitsubishi Shindoh Co., Ltd.) having a copper purity of 99.99% or more was used. The recrystallization start temperature and the minimum heating temperature of the final rolled copper strip were 145 C. and 132 C., respectively, as calculated in accordance with the method of determining the final heat treatment temperature. Accordingly, the recovery temperature range was set to 132 C. to 145 C.

(50) In Comparative Example 4, tough pitch copper (trade name: TC strip sheet, manufactured by Mitsubishi Shindoh Co., Ltd.) having a copper purity of 99.97% was used. The recrystallization start temperature and the minimum heating temperature were 125 C. and 110 C., respectively, as calculated in accordance with the method of determining the final heat treatment temperature. Accordingly, the recovery temperature range was set to 110 C. to 125 C.

Example 1

(51) A final rolled copper strip having a foil thickness of 100 m was held at 140 C., which was a temperature in the recovery temperature range, for 30 minutes in a reduced nitrogen atmosphere to perform final heat treatment.

(52) After the final heat treatment, final cold rolling was performed to produce a hard rolled-copper foil having a foil thickness of 11 m.

Example 2

(53) A hard rolled-copper foil of Example 2 was produced as in Example 1 except that a final rolled copper strip having a foil thickness of 50 m was used.

Comparative Example 1

(54) A hard rolled-copper foil of Comparative Example 1 was produced as in Example 1 except that the final heat treatment was performed by holding the final rolled copper strip at 200 C., which was equal or higher than the recrystallization start temperature, for 30 minutes.

Comparative Example 2

(55) A hard rolled-copper foil of Comparative Example 2 was produced as in Example 2 except that the final heat treatment was performed by holding the final rolled copper strip at 200 C. for 30 minutes.

Comparative Example 3

(56) A hard rolled-copper foil of Comparative Example 3 was produced as in Example 1 except that a final rolled copper strip having a foil thickness of 800 m was used and held at 200 C. for 30 minutes.

Comparative Example 4

(57) A hard rolled-copper foil of Comparative Example 4 was produced as in Example 1 except that a final rolled copper strip having a foil thickness of 500 m was held at 120 C., which was a temperature in the recovery temperature range, for 30 minutes.

(58) (Crystal Orientation Density)

(59) Crystal orientation densities of the hard rolled-copper foils produced in Examples and Comparative Examples were calculated.

(60) A horizontal sample-type multipurpose X-ray diffraction system Ultima IV (manufactured by Rigaku Corporation) and an attachment ML4 for multipurpose measurement were used for the measurement.

(61) Other conditions are as follows. X-ray tube: sealed copper tube Tube voltage: 40 kV Tube current: 30 mA Detector: scintillation counter

(62) First, with regard to {111}, {200}, and {220} planes of each of the hard rolled-copper foils of Examples and Comparative Examples, 2/ scanning was performed under the conditions for a focusing method to determine 2 at a peak position.

(63) The conditions for the focusing method are as follows. Divergent height limiting slit (DHL): 10 mm Divergent slit (DS): 2/3 Schultz slit: not used 2 Scan range: 40.00 to 46.00, 47.43 to 53.43, and 71.13 to 77.13 2 Step angle: 0.01 Scan speed: 4.0/sec. Scattering slit (SS): 2 Receiving slit (RS): 0.15 mm

(64) Next, with regard to the three planes, a pole figure measurement was performed under the conditions for a Schultz reflection method.

(65) The conditions for the Schultz reflection method are as follows. Divergent height limiting slit (DHL): 2 mm Divergent slit (DS): open Schultz slit: used Inclination angle () scan range: 15 to 90 Rotation angle () scan speed: 720/min. Step angle of and : 5 -Oscillation width: 10 mm Scattering slit (SS): 2 Receiving slit (RS): 0.15 mm

(66) An incomplete pole figure obtained from the pole figure measurement was converted onto an Euler angle space represented by an orthogonal coordinate system of g=(1, , 2) by using the Bunge notation to obtain the ODF.

(67) Furthermore, a crystal orientation density function f (gCopper) of the copper orientation and a crystal orientation density function f (gBrass) of the brass orientation were obtained from the ODF, and crystal orientation densities in the copper orientation and the brass orientation were calculated.

(68) For data processing of the incomplete pole figure, ODFPole FIG. 2 (manufactured by HelperTex Office) was used.

(69) For the conversion from the incomplete pole figure to a complete pole figure and the conversion from the incomplete pole figure to the ODF, LaboTex (Symmetrization: Triclinic to orthorhombic/manufactured by LaboSoft s.c.) was used.

(70) For extraction of the crystal orientation distribution functions of the copper orientation and the brass orientation, ODFDisplay2 (Smoothing: off, FCC -skeleton5/manufactured by HelperTex Office) was used.

(71) Analysis conditions are as follows.

(72) ODFPoleFigure2 data pre-processing Background removal: executed Absorption correction: executed Defocus correction: executed Smoothing: twice at a weighting of 4 Normalization: executed
<Defocus Correction>

(73) As a random sample, a copper powder Cu-HWQ 3 m-grade (manufactured by Fukuda Metal Foil & Powder Co., Ltd.) that had been subjected to reduction heat treatment at 200 C. for 30 minutes in a stream of hydrogen and nitrogen at a mixing ratio of hydrogen:nitrogen=3:1 was measured and used for the correction.

(74) The copper orientation and the brass orientation each appear on the Euler angle space at a plurality of positions. Accordingly, in the present invention, gCopper=(90, 35, 45) and gBrass=(35, 45, 90) were adopted as the Euler angles of the crystal orientation density functions f (gCopper) and f (gBrass), respectively.

(75) FIG. 2 shows crystal orientation densities in respective orientations of Examples and Comparative Examples.

(76) (Room-Temperature Softening Characteristics)

(77) Room-temperature softening characteristics were evaluated by a softening rate.

(78) The softening rate RS was calculated by the following <Formula 2> where TSi represents a tensile strength (N/mm.sup.2) within two weeks after the manufacturing of the hard rolled-copper foil, and TSf represents a tensile strength after heat treatment at 100 C. for 10 minutes.

(79) In the evaluation, a copper foil having a softening rate RS of less than 30% was evaluated as good, and a copper foil having a softening rate RS of more than 30% was evaluated as not good.
Softening Rate RS={(TSiTSf)/TSi}100<Formula 2>
(Surface Roughness)

(80) For a surface of each hard rolled-copper foil, a surface roughness was evaluated in accordance with JISB0601:1994 standard in terms of ten-point average roughness Rz (that is, Rzjis94 in JISB0601:2013 standard).

(81) A surface roughness measuring instrument SURFCORDER SE1700 (manufactured by Kosaka Laboratory Ltd.) was used for the measurement of the surface roughness.

(82) (Bending-Resistance Characteristics)

(83) Bending-resistance characteristics were evaluated by a bending test.

(84) The bending test was performed as follows. For each of the hard rolled-copper foils of Examples and Comparative Examples, a rectangular sample having a width of 12.7 mm and a length of 40 mm was cut out such that the longitudinal direction was parallel to the rolling direction. The sample was then subjected to heat treatment at 200 C. for 30 minutes in air. Thus, a heat-softened copper foil in the state of grain growth was prepared.

(85) As illustrated in FIG. 3, in the bending test, a heat-softened copper foil 10 was disposed on a flat base 12. A spacer 11 was placed on the heat-softened copper foil 10. Subsequently, a cycle including operations 1 and 2 described below is defined as one cycle, and this cycle was repeated.

(86) 1. The spacer 11 having a thickness of 50 m was disposed on the specimen 10, and the specimen 10 was folded by 180 so as to sandwich the spacer 11. In this state, a load of 50 kgf was applied from a planar tool 13 to the specimen by an air pressure (FIG. 4).
2. The folded specimen was extended by 180 so as to return to the original shape. In this state, a load of 50 kgf was similarly applied (FIG. 5).

(87) The folded position was one position near the center in the longitudinal direction, and the specimen was folded at the same position for the second time and thereafter.

(88) The test was continued until the specimen was broken. The number of times immediately before the breakage was recorded.

(89) The test was performed by using five specimens (n=5) for each of the hard rolled-copper foils of Examples and Comparative Examples. The average was defined as the value of the bending-resistance characteristics (the maximum number of times of bending).

(90) In this bending test, a maximum number of times of bending of more than 20 is evaluated as good, and a maximum number of times of bending of less than 20 is evaluated as not good.

(91) Table 2 shows evaluations of the hard rolled-copper foils of Examples and Comparative Examples.

(92) TABLE-US-00002 TABLE 2 Thickness of final Hard-rolled copper Maximum Heat rolled foil Surface Crystal number treatment copper Final roughness orientation of times Room temperature strip Thickness reduction Rzjis94 density of temperature C. m m ratio % m Copper Brass bending softening Example 1 140 100 11 89.0 0.8 18.5 37.1 22 Good (Recovery) Example 2 140 50 11 78.0 0.7 12.9 36.9 21 Good (Recovery) Comparative 200 100 11 89.0 0.8 11.7 16.1 14 Good Example 1 (or higher) Comparative 200 50 11 78.0 0.7 11.7 13.8 12 Good Example 2 (or higher) Comparative 200 800 11 98.6 1.1 6.4 26.9 19 Not good Example 3 (or higher) Comparative 120 500 11 97.8 1.1 8.5 32.9 20 Not good Example 4 (Recovery) *In the column of heat treatment temperature, Recovery represents the recovery temperature range, and or higher represents the recrystallization start temperature or higher.

(93) As shown in Table 2, it was proved that the hard rolled-copper foils according to the present invention in which not only the brass orientation but also the copper orientation was developed were hard rolled-copper foils which exhibited excellent bending-resistance characteristics even at a final reduction ratio of 90% or less, had a low surface roughness, and were unlikely to be softened at room temperature.

INDUSTRIAL APPLICABILITY

(94) The hard rolled-copper foil according to the present invention is a hard rolled-copper foil which, when heated and laminated with an insulating resin base material, exhibits excellent bending-resistance characteristics without highly increasing a final reduction ratio, which can maintain a low surface roughness and has excellent high-speed transmission characteristics because the final reduction ratio is not increased, and thus can be suitably used in a flexible printed wiring board, and which is unlikely to be subjected to room temperature softening and therefore provides excellent operation efficiency and foil passing property when processed into a flexible printed wiring board after storage.

(95) Accordingly, the present invention is an invention having high industrial applicability.

REFERENCE SIGNS LIST

(96) 1 inflection point 2 intersection point 5 tangent of inflection point 6 baseline 10 heat-softened copper foil 11 spacer 12 base 13 planar tool