JP2018154888A - Copper foil for flexible printed circuit board, and copper clad laminate, flexible printed circuit board, and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil for flexible printed circuit boards having excellent bendability.SOLUTION: A copper foil for flexible printed circuit board contains, in the tough pitch copper specified in JIS-H3100 (C1100) or the oxygen-free copper specified in JIS-H3100 (C1020), Ag of 0.001-0.05 mass%; contains P of 0.03 mass% or less, Sb of 0.14 mass% or less, Sn of 0.163 mass% or less, Ni of 0.288 mass% or less, Be of 0.058 mass% or less, Zn of 0.812 mass% or less, In of 0.429 mass% or less, and Mg of 0.149 mass% or less, respectively alone or in combination of two or more kinds; and when its plate thickness is x[μm], the breaking elongation y[%] is formula 1: [y=-0.0365x+2.1352x-5.7219] or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a copper foil suitable for a wiring member such as a flexible printed circuit board, a copper clad laminate using the copper foil, a flexible wiring board, and an electronic device.

A flexible printed circuit board (flexible wiring board, hereinafter referred to as “FPC”) has flexibility, and is widely used in a bent portion and a movable portion of an electronic circuit. For example, FPCs are used for movable parts of disk-related devices such as HDDs, DVDs, and CD-ROMs, and for folding parts of foldable mobile phones.
The FPC is formed by etching a copper clad laminate (copper-clad laminate, hereinafter referred to as CCL) in which a copper foil and a resin are laminated, and then coating the wiring with a resin layer called a coverlay. The copper foil surface is etched as part of the surface modification step for improving the adhesion between the copper foil and the coverlay before the coverlay is laminated. Further, in order to improve the flexibility by reducing the thickness of the copper foil, thinning etching may be performed.

By the way, along with the downsizing, thinning, and high performance of electronic devices, it is required to mount FPCs in these devices at a high density. The FPC needs to be folded and accommodated, that is, high bendability is required.
On the other hand, copper foils with improved high-cycle flexibility represented by IPC flexibility have been developed (Patent Documents 1 and 2).

JP 2010-100877 A JP 2009-111203 A

However, in order to mount the FPC at a high density as described above, it is necessary to improve the bendability represented by MIT fold resistance, and the conventional copper foil cannot be said to have sufficient improvement in bendability. There's a problem.
The present invention has been made to solve the above-mentioned problems, and aims to provide a copper foil for a flexible printed circuit board excellent in bendability, a copper-clad laminate using the same, a flexible printed circuit board, and an electronic device. To do.

  As a result of various studies, the present inventors have found that by reducing the crystal grain size before the final cold rolling of the copper foil, the elongation at break after recrystallization can be increased and the bendability can be improved. This is because as the elongation at break is increased according to the coffin-manson rule, the number of bendings until the break increases.

That is, the copper foil for flexible printed circuit boards of the present invention contains 0.001 to 0.05 mass% of Ag with respect to tough pitch copper standardized to JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020); P 0.03% by mass, Sb 0.14% by mass, Sn 0.163% by mass, Ni 0.288% by mass, Be 0.058% by mass, Zn 0.812% by mass, In 0.429% by mass and Mg Is 0.149% by mass or less, each containing one or more of them; when the plate thickness is x [μm], the elongation at break y [%] is expressed by the formula 1: [y = −0.0365x ² + 2.1352x− 5.7219] or more.

  It is preferable that the copper foil is a rolled copper foil, and the elongation at break y [%] after annealing at 300 ° C. for 30 minutes (however, the rate of temperature increase is 100 to 300 ° C./min) is equal to or greater than Formula 1.

  The copper clad laminate of the present invention is formed by laminating the flexible printed circuit board copper foil and a resin layer.

  The flexible printed board of the present invention is formed by forming a circuit on the copper foil in the copper clad laminate.

  The electronic device of the present invention uses the flexible printed circuit board.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for flexible printed circuit boards excellent in the bendability is obtained.

It is a figure which shows the relationship between the copper foil thickness of an Example and a comparative example, and breaking elongation.

  Hereinafter, embodiments of the copper foil according to the present invention will be described. In the present invention, “%” means “% by mass” unless otherwise specified.

<Composition>
The copper foil according to the present invention contains 0.001 to 0.05 mass% of Ag with respect to tough pitch copper specified in JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020); and 0.03 mass% or less of P. , Sb 0.14 mass% or less, Sn 0.163 mass% or less, Ni 0.288 mass% or less, Be 0.058 mass% or less, Zn 0.80.8 mass% or less, In 0.429 mass% or less, and Mg 0.149 mass% or less. Singly or in combination of two or more.
As described above, by refining the crystal grain size of the copper foil before the final cold rolling, the elongation at break after recrystallization can be increased and the bendability can be improved.
However, in the case of the above-described pure copper-based composition, it is difficult to increase the elongation at break after recrystallization of the copper foil, so the initial stage during cold rolling (at the time of initial cold rolling when annealing and cold rolling are repeated) ), It is possible to introduce a large amount of processing strain by cold rolling and to increase the elongation at break after recrystallization.

Also, in order to increase the elongation at break after recrystallization of the copper foil, the crystal grain size before final cold rolling (before the final rolling performed after final annealing in the entire process of repeating annealing and rolling) is set to 20 to 15 μm. It is preferable.
When the crystal grain size before the final cold rolling is larger than 20 μm, the frequency of dislocation entanglement during processing decreases and the accumulation of strain decreases, so that the elongation at break after recrystallization tends to decrease. When the crystal grain size before the final cold rolling is smaller than 15 μm, the effect of increasing the elongation at break is saturated only by the entanglement of dislocations during processing being saturated and the rolling load being increased. Therefore, the lower limit of the crystal grain size before the final cold rolling is set to 15 μm.

Moreover, 0.001-0.05 mass% Ag is contained as an additional element which refines | miniaturizes a crystal grain.
Ag makes the recrystallized grain size less sensitive to recrystallization annealing conditions. That is, as will be described later, heat treatment for curing the resin is performed at the time of CCL lamination. Actually, the temperature and time of the heat treatment vary, and the rate of temperature rise varies depending on the manufacturing apparatus, manufacturer, and the like. For this reason, there exists a possibility that the particle size of the recrystallized grain of copper foil may become large depending on heat processing. Thus, by containing Ag, the crystal grains can be stably refined even if the heat treatment conditions during CCL lamination change.

Furthermore, P is 0.0005 mass% to 0.03 mass%, Sb is 0.0005 mass% to 0.14 mass%, Sn is 0.0005 mass% to 0.163 mass%, Ni is 0.0005 mass% to 0.288 mass%, and Be is 0.0005 mass% % Containing 0.055 mass% or more, Zn containing 0.0005 mass% or more and 0.812 mass% or less, In containing 0.0005 mass% or more and 0.429 mass% or less, and Mg containing 0.0005 mass% or more and 0.149 mass% or less, each alone or in combination. The elongation at break can be increased after recrystallization.
P, Sb, Sn, Ni, Be, Zn, In, and Mg increase the frequency of dislocation entanglement during cold rolling, so that the elongation at break can be more easily increased after recrystallization. In addition, if recrystallization annealing is performed only once in the initial stage of cold rolling and no subsequent recrystallization annealing is performed, a large amount of processing strain is introduced by increasing the entanglement of dislocations by cold rolling. Thus, the elongation at break can be easily increased after recrystallization.

Since it is industrially difficult to control the Ag content to be smaller than 0.001% by mass, the lower limit of the Ag content is set to 0.001% by mass. Further, if the Ag content exceeds 0.05% by mass, the recrystallization temperature rises and does not recrystallize when laminated with the resin, and the strength becomes too high and the bending properties of the copper foil and CCL may deteriorate. .
P exceeds 0.03 mass%, Sb exceeds 0.14 mass%, Sn exceeds 0.163 mass%, Ni exceeds 0.288 mass%, Be exceeds 0.058 mass%, Zn exceeds 0.812 mass%, In If the content exceeds 0.429% by mass or Mg exceeds 0.149% by mass, the electrical conductivity is lowered and may not be suitable as a copper foil for flexible substrates. Therefore, the above range is set as the upper limit.
The lower limit of the content of P, Sb, Sn, Ni, Be, Zn, In, and Mg is not particularly limited. For example, it is industrially difficult to control less than 0.0005% by mass for each element. The lower limit of the amount is preferably 0.0005% by mass.

  In addition to the copper foil composition of the present invention described above as a method for increasing the elongation at break after recrystallization after recrystallization of copper foil, a method of polymerization rolling, a pulse when electrodepositing on electrolytic copper foil Examples thereof include a method using an electric current or a method of adding an appropriate amount of thiourea, glue or the like to the electrolytic solution using an electrolytic copper foil.

<Elongation at break>
When the plate thickness is x [μm], the breaking elongation y [%] is equal to or greater than Formula 1: [y = −0.0365x ² + 2.1352x−5.7219].
The elongation of the copper foil varies depending on the thickness, and the greater the thickness, the greater the elongation. Therefore, the bendability depends on the elongation corresponding to the thickness of the copper foil. For this reason, in order to improve the bendability, it is necessary to define not only the absolute value of the elongation of the copper foil but also the relationship between the elongation and the thickness. The present invention thus focuses on the relationship between elongation and thickness.
FIG. 1 shows the relationship between the thickness and breaking elongation of Examples 1 to 15 and Comparative Examples described later. As shown in FIG. 1, even when the groups of Examples 7 to 11 have the same thickness, the breaking elongation is smaller than the groups of Examples 1 to 6. Further, when viewed at the same thickness, the breaking elongation of all Examples 1 to 15 is larger than the breaking elongation of the group of Comparative Examples (Comparative Examples 1 to 7).

From this, if it is a region where the elongation at break is larger than that of the comparative example, it is considered that the bending property (the number of MIT foldings) is excellent, and the minimum value (lower limit) at which the elongation at break becomes larger than the comparative example, An approximate quadratic curve passing through each plot of the groups of Examples 7 to 11 having a smaller elongation at break than the groups of Examples 1 to 6 was obtained by the method of least squares. As a result, Formula 1: [y = −0.0365x ² + 2.1352x−5.7219] indicated by a broken line in FIG. 1 was obtained. In addition, since Example 5 and 6 overlap, the number of plots of Examples 1-6 became five instead of six.
From the above, if the elongation at break y [%] is the region S (see FIG. 1) equal to or greater than Formula 1, the bendability is excellent.
For example, when the copper foil thickness is 12 μm, the elongation at break (%) and the bendability (times) are Example 3 (: 35%: 347 times), Example 9 (: 15%: 247 times), and Comparative Example, respectively. 4 (: 12%: 188 times), both Examples 3 and 9 are superior to Comparative Example 4 in bendability, and Example 4 is most excellent.

Formula 2: [y = −0.0762x ² + 4.4090x-7.5054] is an approximation that passes through the plots of Examples 1 to 6, which are groups having the same thickness and larger elongation at break than those of Examples 7 to 11. It is the result of having calculated | required the quadratic curve by the least squares method.
Of course, if the elongation at break is higher, it is preferable to have a higher elongation. Therefore, it goes without saying that those exceeding the value of Formula 2 are also included in the scope of the present invention, but there is a limit to improving the elongation at break even with the same copper foil thickness. As an example of the limit, Equation 2 was obtained. Accordingly, the range S1 (see FIG. 1) of the formula 1 or more and the formula 2 or less can be set as a range for realizing the present invention more reliably, but the present invention is limited to the range of the formula 2 or less. It is not a thing.

If the elongation at break is less than [y = -0.0365x ² + 2.1352x-5.7219], the copper foil cannot follow the elongation of the resin when the flexible printed circuit board is bent, and the bendability is poor. Not suitable for.
The breaking elongation y [%] after annealing the copper foil at 300 ° C. for 30 minutes (temperature increase rate: 100 to 300 ° C./min) is also preferably within the above range.

<Tensile strength (TS), elongation at break>
Tensile strength and elongation at break were determined by a tensile test in accordance with IPC-TM650, with a test piece width of 12.7 mm, room temperature (15 to 35 ° C.), a tensile speed of 50.8 mm / min, and a gauge length of 50 mm. Tensile tests were performed in parallel directions.

<Heat treatment at 300 ° C for 30 minutes>
The copper foil which concerns on this invention is used for a flexible printed circuit board, In that case, since CCL which laminated | stacked copper foil and resin performs the heat processing for hardening resin at 200-400 degreeC, a crystal grain is formed by recrystallization. There is a possibility of coarsening.
Accordingly, the tensile strength and breaking elongation of the copper foil change before and after lamination with the resin. Then, the copper foil for flexible printed circuit boards concerning Claim 1 of this application has prescribed | regulated the copper foil of the state which received the hardening heat processing of resin after it became a copper clad laminated body laminated | stacked with resin.
On the other hand, the copper foil for flexible printed circuit boards according to claim 3 of the present application defines a state when the above heat treatment is performed on the copper foil before being laminated with the resin. This heat treatment at 300 ° C. for 30 minutes simulates the temperature condition for curing and heat-treating the resin during CCL lamination. In addition, the temperature increase rate should just be between 100-300 degreeC / min.

  The copper foil of this invention can be manufactured as follows, for example. First, P is added to a copper ingot to be melted and cast, and then hot rolled, cold rolled and annealed, recrystallized annealed at the initial stage of cold rolling, and the above-mentioned final cold rolling is performed. By doing so, a foil can be produced.

<Copper-clad laminate and flexible printed circuit board>
Also, (1) a resin precursor (for example, a polyimide precursor called varnish) is cast on the copper foil of the present invention and polymerized by applying heat, and (2) a thermoplastic adhesive of the same type as the base film is used. By laminating the base film on the copper foil of the present invention, a copper clad laminate (CCL) composed of two layers of the copper foil and the resin base material is obtained. Further, by laminating a base film obtained by applying an adhesive to the copper foil of the present invention, a copper clad laminate (CCL) comprising three layers of a copper foil, a resin base material, and an adhesive layer therebetween is obtained. During the production of these CCLs, the copper foil is heat-treated and recrystallized.
A circuit is formed on these using a photolithographic technique, a circuit is plated as needed, and a cover-lay film is laminated, and a flexible printed circuit board (flexible wiring board) is obtained.

Therefore, the copper clad laminate of the present invention is formed by laminating a copper foil and a resin layer. Moreover, the flexible printed circuit board of this invention forms a circuit in the copper foil of a copper clad laminated body.
Examples of the resin layer include, but are not limited to, PET (polyethylene terephthalate), PI (polyimide), LCP (liquid crystal polymer), and PEN (polyethylene naphthalate). Moreover, you may use these resin films as a resin layer.
As a method of laminating the resin layer and the copper foil, a material for forming the resin layer may be applied to the surface of the copper foil and heated to form a film. Further, a resin film may be used as the resin layer, and the following adhesive may be used between the resin film and the copper foil, or the resin film may be thermocompression bonded to the copper foil without using the adhesive. However, it is preferable to use an adhesive from the viewpoint of not applying excessive heat to the resin film.

  When a film is used as the resin layer, this film may be laminated on the copper foil via an adhesive layer. In this case, it is preferable to use an adhesive having the same component as the film. For example, when a polyimide film is used as the resin layer, it is preferable to use a polyimide-based adhesive for the adhesive layer. In addition, the polyimide adhesive here refers to the adhesive agent containing an imide bond, and polyether imide etc. are also included.

In addition, this invention is not limited to the said embodiment. Moreover, as long as there exists an effect of this invention, the copper alloy in the said embodiment may contain another component.
For example, the surface of the copper foil may be subjected to a surface treatment by roughening treatment, rust prevention treatment, heat resistance treatment, or a combination thereof.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these. Each element shown in Table 1 was added to electrolytic copper standardized to JIS-H3100 (C1100), and cast in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. This ingot is homogenized and annealed at 900 ° C, then hot-rolled and then cold-rolled, and the annealing conditions are optimized so that recrystallization occurs even at a low annealing temperature. The diameter was adjusted. Thereafter, the oxide scale generated on the surface was removed, and final cold rolling was performed at a working degree η shown in Table 1 to obtain a foil having a desired final thickness. A heat treatment at 300 ° C. for 30 minutes was added to the obtained foil to obtain a copper foil sample.
Next, although a comparative example is given and this invention is demonstrated further in detail, a comparative example is not limited to these. Each element shown in Table 1 was added to electrolytic copper standardized to JIS-H3100 (C1100), and cast in an Ar atmosphere to obtain an ingot. The oxygen content in the ingot was less than 15 ppm. When this ingot is homogenized and annealed at 900 ° C, it is hot rolled and then cold rolled, and if it is annealed once at a high temperature, it will recrystallize even when the crystal grain size is larger than 20μm and the annealing temperature is low. In addition, when the annealing conditions were optimized and single annealing was performed, a crystal grain size of 20 μm was obtained. Thereafter, the oxide scale generated on the surface was removed, and final cold rolling was performed at a working degree η shown in Table 1 to obtain a foil having a desired final thickness. A heat treatment at 300 ° C. for 30 minutes was added to the obtained foil to obtain a copper foil sample.

<A. Evaluation of copper foil sample>
1. Electrical conductivity The electrical conductivity (% IACS) at 25 ° C. was measured for each copper foil sample after the heat treatment by a four-terminal method based on JIS H 0505.
If the conductivity is greater than 75% IACS, the conductivity is good.
2. Tensile strength and elongation at break Each copper foil sample after the above heat treatment was subjected to a tensile test in accordance with IPC-TM650, with a test piece width of 12.7 mm, room temperature (15 to 35 ° C.), tensile speed of 50.8 mm / min, and gauge length of 50 mm. The tensile strength and elongation at break were measured by conducting a tensile test in a direction parallel to the rolling direction of the copper foil.

3. Copper foil bendability (MIT folding resistance)
About each copper foil sample after the said heat processing, the MIT folding endurance (number of reciprocal bending) was measured based on JISP8115. However, the bending clamp R was 0.38 mm and the load was 250 g.
If the MIT folding endurance number is larger than that of the comparative example having the same thickness, the copper foil has good bendability.
4). Crystal grain size The surface of each copper foil sample before the heat treatment and before the final cold rolling (after the final annealing) was observed using a SEM (Scanning Electron Microscope), and the average grain size was determined based on JIS H 0501. . However, the twins were measured as if they were separate crystal grains. The measurement region was 400 μm × 400 μm in a cross section parallel to the rolling direction.

  The obtained results are shown in Table 1.

As is clear from Table 1, each grain size before final cold rolling is 15 to 20 μm, and elongation at break y [%] is equal to or greater than Formula 1: [y = -0.0365x ² + 2.1352x-5.7219] In the case of the example, the MIT flexibility was superior to the comparative example having the same thickness.

  On the other hand, in the case of Comparative Examples 1 to 6 in which the crystal grain size before the final cold rolling exceeded 20 μm, the breaking elongation y [%] was smaller than that of Formula 1, and the MIT flexibility was inferior to each of the Examples having the same thickness. .

In the case of Comparative Example 7 in which only 0.01% by mass of Ag was added, the elongation at break y [%] was less than Formula 1: [y = −0.0365x ² + 2.1352x−5.7219]. MIT flexibility was inferior to 9, 12, 13, 14 and 15.
In the case of Comparative Example 8 in which the addition amount of P exceeded 0.03% by mass, the conductivity was 75% or less and the conductivity was inferior.

Claims (5)

For tough pitch copper standardized to JIS-H3100 (C1100) or oxygen-free copper of JIS-H3100 (C1020),
Containing 0.001 to 0.05 mass% of Ag;
P is 0.03 mass% or less, Sb is 0.14 mass% or less, Sn is 0.163 mass% or less, Ni is 0.288 mass% or less, Be is 0.058 mass% or less, Zn is 0.812 mass% or less, In is 0.429 mass% or less, and Mg contains 0.149% by mass or less, each containing one or more kinds;
A copper foil for a flexible printed circuit board having a breaking elongation y [%] of formula 1: [y = -0.0365x ² + 2.1352x-5.7219] or more when the plate thickness is x [μm]. The copper foil is a rolled copper foil,
2. The copper foil for a flexible printed circuit board according to claim 1, wherein the elongation at break y [%] after annealing at 300 ° C. for 30 minutes (however, the temperature rising rate is 100 ° C./min to 300 ° C./min) is equal to or greater than the formula 1.   The copper clad laminated body formed by laminating | stacking the copper foil for flexible printed circuit boards of Claim 1 or 2, and a resin layer.   The flexible printed board formed by forming a circuit in the said copper foil in the copper clad laminated body of Claim 3.   An electronic device using the flexible printed circuit board according to claim 4.

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