JP5185066B2 - Copper foil excellent in flexibility, manufacturing method thereof, and flexible copper-clad laminate - Google Patents

Description

  The present invention relates to a copper foil used for a flexible printed circuit (FPC) that is suitably used for a bent portion of an electric circuit, and a flexible copper-clad laminate using the copper foil.

Currently, FPCs used for bent parts of mobile phones, etc. are coated with a polyimide varnish on copper foil, dried and cured by heating, and a method called the cast method, which is bonded in advance. It is manufactured by a method called a laminating method in which a polyimide film coated with a strong thermoplastic polyimide and a copper foil are stacked and pressure-bonded through a heating roll or the like. The flexible copper-clad laminate obtained by these methods is called a two-layer flexible copper-clad laminate.
A three-layer flexible copper-clad laminate in which a copper foil and a polyimide film are bonded with an epoxy-based adhesive is also known.
As these FPC copper foils, a technique is known in which the I / I0 of the 200 plane that gives reflex annealing and gives flexibility is 40 or more (Patent Documents 1 and 2).

JP 2001-323354 A (paragraph 0014) JP 11-286760

However, although the copper foils described in the above-mentioned Patent Documents 1 and 2 increase the degree of orientation in the (200) orientation and improve the flexibility, the recrystallized copper foil is very soft, so Wrinkles are likely to occur, and if recrystallization annealing is performed before lamination with a resin, there is a problem that it becomes difficult to handle the copper foil when laminated on the flexible copper-clad laminate. Therefore, a method of recrystallizing a copper foil using a heat treatment for curing a polyimide varnish or a thermoplastic polyimide after laminating with a resin is common.
However, the CCL produced by the laminating method has a problem that the degree of orientation of the copper foil in the (200) direction is not high and the flexibility is lowered. As a result of various studies, the inventors have found that the degree of orientation of the copper foil in the (200) direction decreases as the rate of temperature increase in the recrystallization annealing of the copper foil increases. In other words, the difference in the degree of orientation due to the CCL manufacturing method is considered to be due to the difference in the heating rate in the recrystallization annealing of the copper foil in the CCL manufacturing process.
For example, in the case of the casting method described above, the varnish is dried and cured, so that the copper foil is heated relatively slowly in a heating furnace, and a recrystallized texture that is sufficiently oriented in the (200) direction is obtained, and the flexibility is also high. improves. However, in the case of the laminating method described above, the film and the copper foil are pressure-bonded with a heat roll, so the copper foil is rapidly heated with the heat roll, and the degree of orientation in the (200) direction does not increase.

  Here, the reason why the degree of (200) orientation of the copper foil differs depending on the rate of temperature rise is estimated as follows. First, when the rate of temperature rise is slow, the copper foil is exposed to a low temperature for a long time, so that only crystal orientations with low recrystallization nucleation energy are recrystallized, and recrystallization nuclei in other orientations are not generated. And as the heating temperature rises, the recrystallized nuclei with the preferred orientation are grown, and the entire copper foil is occupied with crystal grains with the preferred orientation. On the other hand, if the heating rate is high, the copper foil becomes hot in a short period of time, so nucleation occurs even in crystal orientations where recrystallization nuclei are difficult to form, and a recrystallized structure with random orientation is generated. The

  Therefore, the objective of this invention is providing the copper foil which was excellent in the flexibility, and ensured intensity | strength, and the flexible copper-clad laminated board using the same.

The inventors of the present invention have made a preferred orientation in (200) even if the temperature rise rate when laminating the flexible copper-clad laminate is rapid by making recrystallized nuclei in the preferred orientation in the copper foil. It has been found that it is possible to grow crystal grains.
That is, the copper foil of the present invention comprises tough pitch copper, oxygen-free copper, or a composition in which one or more selected from the group of Ag, Sn, and In is added to 0.05 mass% or less in total to tough pitch copper or oxygen-free copper. A rolled copper foil having a thickness of 20 μm or less, a tensile strength of 400 MPa or more, an X-ray diffraction intensity ratio I / I0 (200) of (200) plane of 15 or less, and an X-ray diffraction measurement (200 ) X-ray diffraction intensity ratio I of the (200) plane when the peak half-value width is 0.15 or less and the temperature is increased to 300 ° C. at a temperature increase rate exceeding 50 ° C./second and heat treatment is held for 5 seconds. / I0 (200) is 40 or more.

The method for producing a copper foil of the present invention comprises a composition in which one or more selected from the group of Ag, Sn, and In are added to a total of 0.05% by mass or less to tough pitch copper, oxygen free copper, or tough pitch copper or oxygen free copper. When an ingot is manufactured by repeating hot rolling and cold rolling and annealing, and after the final cold rolling, an annealing temperature T (° C.) and an annealing time t (h) are obtained, Equation 1; P = ( P obtained by (T + 273) × (14 + log (t)) is 0.96P _h ≦ P ≦ P _{h with} respect to P _h obtained by the above formula 1 with respect to the semi-softening temperature T _h at an annealing time of 0.5 _h. annealed in the range of, and preliminary annealing exposing for more than three seconds to a temperature range where the 0.4T _h ~1.2T _h relative half-softening temperature T _h in the temperature rising process of the annealing.

  The flexible copper-clad laminate of the present invention is formed by laminating the copper foil and a base resin.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil which was excellent in the flexibility and ensured intensity | strength, and a flexible copper-clad laminated board using the same can be obtained.

An important point for obtaining a flexible copper-clad laminate exhibiting high flexibility is to recrystallize the metal structure of the copper foil into a state favorable for flexibility when it becomes a laminate. The most preferable metal structure for flexibility is a structure in which the cubic orientation is very developed and the crystal grain boundary is small, in other words, the crystal grain is large. Here, the degree of development of the cube orientation is expressed by the magnitude of the 200 plane X-ray diffraction intensity ratio I / I0 (I: 200 plane diffraction intensity of copper foil, I0: 200 plane diffraction intensity of copper powder). The larger this value, the more the cube orientation is developed.
On the other hand, the copper foil material before being laminated on the flexible copper-clad laminate can be sufficiently annealed in advance in a temperature range suitable for recrystallization in the (200) orientation to increase the degree of orientation in the (200) orientation. Flexibility is improved, but the recrystallized copper foil is very soft, so it tends to cause creases and wrinkles during handling. Therefore, a certain level of strength is required for the copper foil before lamination. As a measure of this strength, 400 MPa, which is the strength of a general rolled tough pitch copper foil, corresponds.

In other words, if it is annealed in a temperature range suitable for recrystallization in the (200) orientation to the extent that it does not become a complete recrystallized structure, while maintaining a predetermined strength, by heating at the time of lamination to the flexible copper-clad laminate, ( It is possible to impart flexibility by improving the degree of orientation in the (200) direction.
FIG. 1 is a conceptual diagram showing heat treatment for producing a copper foil according to an embodiment of the present invention. In a preferred embodiment of the present invention, the copper foil base material is annealed under predetermined conditions to be described later, so that the (200) orientation is appropriately developed, and the heating during the subsequent lamination (or imitating this) The (200) orientation is increased by a heat treatment in which the temperature is increased to 300 ° C. at a temperature increase rate exceeding 50 ° C./second and held for 5 seconds. In addition, since the annealing is not excessive, the strength of the copper foil is maintained, and the strength is sufficient to maintain the handleability during lamination.

Therefore, the copper foil of the present invention has a tensile strength of 400 MPa or more and an (200) plane X-ray diffraction intensity ratio I / I0 (200) of 15 or less, and X-ray diffraction measurement ( (200) X-ray diffraction intensity ratio of (200) plane when the half-value width of the peak is 0.15 or less and the temperature is increased to 300 ° C at a temperature increase rate exceeding 50 ° C / second and heat treatment is held for 5 seconds. I / I0 (200) is 40 or more.
The reason why the tensile strength is 400 MPa or more is that the strength of a general rolled tough pitch copper foil is 400 MPa, and if the strength is higher than this, handling at the time of stacking on a flexible copper-clad laminate is not difficult.
Here, the copper foil of the present invention has the characteristic that the ratio I / I0 is 40 or more, but in the sense that a copper-clad laminate is produced by laminating the above-mentioned heat-treated copper foil. In other words, when the copper foil of the present invention is taken out before lamination and subjected to the above-described heat treatment, the ratio I / I0 becomes 40 or more.

  In addition, the reason for the heat treatment condition that the temperature is increased to 300 ° C. at a temperature increase rate exceeding 50 ° C./second is that when the flexible copper-clad laminate is produced by the laminating method, the polyimide film and the copper foil are used. This is because it approximates the heating conditions (foil passing speed of about 3 m / min) for repeated pressure bonding with a heating roll. In a general laminating method, the roll temperature is 250 to 300 ° C., and the contact time between the roll and the copper foil is several seconds. That is, the temperature rising rate of the copper foil is estimated to be about 70 to 150 ° C./second. In addition, if I / I0 (200) is 40 or more in the heat treatment that is heated to 300 ° C at a heating rate exceeding 50 ° C / second and held for 5 seconds, the heating rate can be reduced by another method that is slower than the laminating method. Even when a flexible copper-clad laminate is manufactured, I / I0 (200) is certainly 40 or more. When I / I0 (200) is 40 or more at the time of becoming a laminate, the flexibility of the copper foil is excellent. Since the copper foil is laminated with the base resin after becoming a laminated plate, there is no problem even if the strength of the copper foil itself is reduced to less than 400 MPa.

The tensile strength of the copper foil is 400 MPa or more, the (200) plane X-ray diffraction intensity ratio I / I0 (200) is 15 or less, and the (200) peak half-value width by X-ray diffraction measurement is 0.15 or less. Yes, the X-ray diffraction intensity ratio I / I0 (200) of the (200) plane when heated to 300 ° C at a heating rate exceeding 50 ° C / second and maintained for 5 seconds is 40 or more As a method for imparting such characteristics to the copper foil, it is possible to anneal the copper foil base material to such an extent that the copper foil base material is not excessively annealed, and to keep the strength moderately.
Specifically, for example, when the annealing temperature T (° C.) and the annealing time t (h) are set, the formula 1;
P obtained by P = (T + 273) × (14 + log (t)) is 0.96P _h ≦ P with respect to P _h obtained by the above formula 1 with respect to the semi-softening temperature T _h at an annealing time of 0.5 _h . ≦ P _h is annealed in the range of, and the copper foil to a temperature range where the 0.4T _h ~1.2T _h relative half-softening temperature T _h in the course of temperature elevation該焼blunt is exposed beyond 3 seconds Is preferred. By annealing under these conditions, a copper foil having the above-described strength and orientation can be produced. Here, the reason that the copper foil base material needs to be exposed to the temperature range of 0.4 T _{h to} 1.2 Th _h for more than 3 seconds is the exposure time (holding time) of the copper foil base material to the above temperature range In the case of rapid annealing, such as 3 seconds or less, even if the copper foil base material is exposed (held) for a sufficient time at the maximum annealing temperature that exceeds this temperature range, the copper foil becomes hot within a short time Because. In such rapid annealing, nucleation occurs even in crystal orientations where recrystallization nuclei are difficult to form, and recrystallized structures with random orientations are generated, and recrystallized texture does not develop. is there.
In order to perform the annealing under the above-described conditions, it is desirable to use a hot air circulation type or a radiant heat type annealing furnace. Although the heating rate can be controlled by a method of sequentially contacting a large number of heating rolls having different temperatures from low temperature to high temperature, it is not practical because the equipment becomes complicated.

  Here, P is a Larson mirror parameter used in the stress relaxation test, and is a value including both the heat treatment time and the heat treatment temperature as shown in Equation 1. Since both stress relaxation and recovery recrystallization by heat treatment are phenomena due to dislocations and movement of grain boundaries, it is considered that the Larson Miller parameter is generally suitable for evaluating the degree of recovery. Moreover, P reproduced well the experimental results conducted by the present inventors.

Also, determine the P _h by the formula 1 for half-softening temperature T _h at the annealing time 0.5h for the following reason. In other words, different for copper alloys of various compositions softening behavior due to represent the degree of softening for the heat treatment conditions half-softening temperature T _h is preferred to obtain the P _h at T _h from the equation 1, this P _h This is because it is effective to manage P of the copper foil on the basis of the above.
Note that Th is an annealing temperature at which the strength when the annealing temperature is 0.5 _h is ½ of the sum of the strength before annealing and the strength in the completely annealed state.
A heat treatment exceeding Ph develops a recrystallized structure, but it becomes too soft and the strength is reduced to less than 400 MPa, so that the handleability of the copper foil may be lowered. Further, in the heat treatment at less than 0.96Ph, the dislocation does not move sufficiently, so that the effect of developing the (200) orientation by heat treatment may not be obtained.

There is no problem as long as the specific annealing temperature and annealing time of the copper foil are within the range of P defined by the above formula 1. For example, if the annealing temperature is 100 ° C., the annealing time is about 5 hours, and if the annealing temperature is 250 ° C., the annealing time is about 10 seconds.
From the above, preferable annealing conditions for batch annealing, continuous line, etc. are in the range of annealing temperature of 100 to 200 ° C. and annealing time of 10 seconds to 5 hours, more preferably annealing temperature of 100 to 140 ° C. and annealing time of 5 It is in the range of minutes to 5 hours.
In the present invention, the “annealing temperature” is the highest temperature reached within a predetermined annealing time. Moreover, annealing may be performed at the time of manufacture of copper foil, and may be performed after performing a roughening process to copper foil.

  Note that the value 14 in the above equation 1 is a material constant C inherent to the material reflecting the ease of stress relaxation (atomic diffusion and ease of dislocation movement). Usually, the characteristic (strength) with respect to the annealing condition is measured and obtained by the least square method, but in the present invention, 14 generally used in pure copper-based copper alloys is adopted as a value.

With the annealing described above, (200) recrystallization nuclei with a preferential orientation can be preferentially generated in the copper foil material. Therefore, even if the rate of temperature rise when laminating the flexible copper-clad laminate is rapid, crystal grains having a preferred orientation in (200) can be grown.
Moreover, since the annealing does not become excessive, the strength of the copper foil can be maintained.

The X-ray diffraction intensity ratio I / I0 (200) of the (200) plane of the copper foil is 15 or less, and the half width of the (200) peak by X-ray diffraction measurement is 0.15 or less for the following reason. .
Usually, copper foil used in high bending applications has a copper foil I / I0 (200) of 40 or more when annealed until it is completely recrystallized. When it is 15 or less, it means that it is not completely recrystallized. That is, I / I0 (200) of 15 or less is an indicator that annealing is not excessive. On the other hand, if I / I0 (200) exceeds 15 and I / I0 (200) does not exceed 40, then I / I0 (200) will not exceed 40 even if heating is performed in the laminating process. Absent.

In addition, the half width of the (200) peak in X-ray diffraction reflects the degree of strain of the crystal, and the more the crystal is distorted, the wider the peak width is because the local interatomic distance varies. Become. That is, the full width at half maximum is large in an as-rolled copper foil.
Therefore, a half width of 0.15 or less indicates a state in which the copper foil has been subjected to a heat treatment and the processing strain during rolling is released, and the copper foil that has not been annealed after rolling is excluded. Even if there is a copper foil that is still rolled and has a tensile strength of 400 MPa or more, the copper foil that has not been annealed after rolling in this way is up to 300 ° C at a temperature rising rate exceeding 50 ° C / second. This is because I / I0 (200) does not increase to 40 or more even when heat treatment is held for 5 seconds after the temperature is raised.

  As the copper foil of the present invention, not only tough pitch copper itself and oxygen-free copper itself, but also copper alloy foil or the like obtained by adding a trace amount of elements to tough pitch copper or oxygen-free copper can be used. Further, as the copper foil of the present invention, one having a chemical treatment (copper-based rough plating) on one side can be usually used. The degree of processing and thickness of the copper foil are not limited, but those having a thickness of 20 μm or less are preferable. In particular, a rolled copper foil with a thickness of 20 μm or less is preferred, comprising a composition in which one or more selected from the group of Ag, Sn, and In is added in total to 0.05% by mass or less to tough pitch copper or oxygen-free copper.

The flexible copper-clad laminate of the present invention only needs to be a laminate of a copper foil and a base resin. In particular, a two-layer flexible copper-clad laminate in which a copper foil and a base resin are laminated without using an epoxy-based adhesive is preferred. As a two-layer flexible copper-clad laminate, for example, a polyimide varnish is applied to a copper foil, dried and cured by applying heat, and a method called a cast method to form a laminate, or a thermoplastic polyimide with adhesive in advance is applied In general, the polyimide film and the copper foil are manufactured by a method called a laminating method in which the polyimide film and the copper foil are stacked and pressure-bonded through a heating roll or the like.
For example, polyimide is used as the base resin, but in the case of the laminate method, it is a film before lamination, and in the case of the cast method, it is a liquid (uncured) polyimide before lamination, which is applied to a copper foil. When heated, it hardens and becomes a base resin (layer).

In the following examples, a two-layer flexible copper-clad laminate was produced by a laminating method.
<Copper foil>
Copper foil for two-layer flexible copper-clad laminates is manufactured by manufacturing a rectangular parallelepiped ingot with a thickness of about 200 mm by melt casting, processing to around 10 mm by hot rolling, and repeating cold rolling and annealing. After the cold rolling, those subjected to (preliminary) annealing shown in the following tables were used. The composition of the copper foil is as shown in each table. The copper foil was rolled to a final working degree of 99% to a thickness of 12 μm. One surface of the annealed foil was subjected to chemical treatment (copper-based roughening plating) and subjected to lamination.
In addition, about tough pitch copper, the final rolling work degree was changed according to each Example and the comparative example.
At room temperature, the X-ray diffraction intensity ratio I / I0 and tensile strength of 200 surfaces of the copper foil were measured. The full width at half maximum is obtained based on JIS K0131 and is a peak width at a value half the peak height of the X-ray diffraction intensity.

<Lamination method>
As a polyimide film for producing a two-layer flexible copper-clad laminate by a laminating method, a 25 μm-thick film (Upilex VT manufactured by Ube Industries Co., Ltd.) coated with thermoplastic polyimide on both sides was used. The thermoplastic polyimide adhesive on the surface is not a resin different from the polyimide film of the core part, but after being laminated with a copper foil, it becomes a base resin as a whole and becomes a two-layer flexible copper-clad laminate.
As shown in FIG. 2, two copper foils (reference numeral 2) are stacked on both sides of the polyimide film 4 having the adhesive 4a on both sides so that the above-described chemically treated surfaces face each other. The foil was sandwiched and laminated, and heated with a heating roll of about 300 ° C. at a foil passing speed of 3 m / min.

<Evaluation of flexibility>
Of the two-layer flexible copper-clad laminate obtained by the laminating method, one copper foil was removed by etching with a ferric chloride aqueous solution. After this, using a known photolithographic technique, a wiring with a circuit width of 200 μm is formed on the remaining copper foil, and a polyimide film coated with an epoxy adhesive is thermocompression-bonded as a coverlay for FPC for bending tests Was made.
Using an IPC sliding bending tester, 100 times per minute repeated sliding with a bending radius of 1 mm was applied to the FPC piece, and the end point was the number of bendings where the electrical resistance of the wiring increased by 10% from the initial stage. The case where the number of bendings exceeded 100,000 was judged as good (◯), and the number of bendings less than 100,000 was judged as bad (×).

  The obtained results are shown in Tables 1 and 2.

As is clear from Table 1, in each example, the tensile strength of the copper foil before lamination was 400 MPa or more, and the temperature was increased to 300 ° C. at a temperature increase rate of 70 ° C./sec. However, the X-ray diffraction intensity ratio (I / I0) of 200 surfaces after heat treatment held for 5 seconds is 40 or more, and the strength (handling property) of copper foil when pre-annealed and the flexibility after lamination with copper Was also good. In the case of the embodiment, in the preliminary annealing after cold rolling, the copper foil was exposed for more than three seconds to a temperature range where the 0.4T _h ~1.2T _h.

On the other hand, in Comparative Examples 1, 3, 4, 9, 10, 11, 14, 16, and 17 in which P / Ph during pre-annealing exceeded 1, the tensile strength of the copper foil decreased to less than 400 MPa. This is thought to be because the pre-annealing was excessive and the copper foil was too slack.
In the case of Comparative Examples 12 and 15 where pre-annealing was not performed, and Comparative Examples 2, 7, 8, 13 and 18 where P / Ph during pre-annealing was less than 0.96, the temperature rise imitating heating during lamination The X-ray diffraction intensity ratio (I / I0) of the 200 surface after heat treatment was raised to 300 ° C. at a rate of 70 ° C./second and held for 5 seconds decreased to less than 40, and the flexibility after copper lamination was inferior . This is presumably because the effect of pre-annealing was insufficient and the crystal grains having the preferred orientation at (200) could not be sufficiently introduced into the copper foil.

Comparative Examples 5, 6, and 11 in which the rate of temperature increase during pre-annealing after cold rolling was high, and the time during which the copper foil was exposed to the temperature range of 0.4 T _{h to} 1.2 T _{h in} the temperature increasing process was 3 seconds or less. In the case of, the flexibility after copper lamination was inferior.
In the case of Comparative Example 5, since the pre-annealing temperature was 200 ° C., P / Ph was a value between 0.96 and 1.0. However, in Comparative Example 6, the pre-annealing temperature was as high as 300 ° C. / Ph exceeded 1.

It is a conceptual diagram which shows the heat processing for manufacturing the copper foil which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the two-layer flexible copper bonding laminated board which concerns on embodiment of this invention.

Explanation of symbols

2 Copper foil 4 Base resin (polyimide film)
4a Adhesive

Claims (3)

Made of tough pitch copper, oxygen-free copper, or tough pitch copper or oxygen-free copper, a composition in which one or more selected from the group of Ag, Sn, and In is added in a total amount of 0.05% by mass or less. The tensile strength is 400 MPa or more, the (200) plane X-ray diffraction intensity ratio I / I0 (200) is 15 or less, and the (200) peak half-value width by X-ray diffraction measurement is 0.15 or less. Yes, the X-ray diffraction intensity ratio I / I0 (200) of the (200) plane is 40 or more when heat treatment is performed at a rate of temperature exceeding 50 ° C / sec. A certain copper foil.   An ingot composed of tough pitch copper, oxygen-free copper, or tough pitch copper or oxygen-free copper added with one or more selected from the group of Ag, Sn and In, in total of 0.05% by mass or less, hot-rolled and cooled Hot rolling and annealing are repeated and after the final cold rolling,
  When the annealing temperature T (° C.) and the annealing time t (h) are set, Formula 1;
  P calculated by P = (T + 273) × (14 + log (t)) is semi-softening temperature T at annealing time 0.5h. _h P obtained from Equation 1 above _h Against 0.96P _h ≦ P ≦ P _h And a semi-softening temperature T in the temperature raising process of the annealing. _h 0.4T against _h ~ 1.2T _h A method for producing a copper foil, in which pre-annealing is performed by exposing to a temperature range exceeding 3 seconds. A flexible copper-clad laminate obtained by laminating the copper foil according to claim 1 and a base resin.

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