JP5235080B2 - Copper alloy foil and flexible printed circuit board using the same - Google Patents

Description

  The present invention relates to a rolled copper foil suitable for use in a wiring member such as a flexible printed circuit board and a flexible printed circuit board using the rolled copper foil.

A flexible printed circuit board (hereinafter referred to as “FPC”) has flexibility, and is therefore widely used for bent portions and movable portions of electronic circuits. 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. Recently, with the downsizing of electronic devices, FPCs are folded and mounted in narrow spaces such as around digital cameras, mobile phones, HDDs, printers, and liquid crystal panels.
For this reason, the FPC is required to have high durability against bending (bending resistance). Therefore, a rolled copper foil having higher bending resistance than that of an electrolytic copper foil, particularly a rolled copper foil of tough pitch copper or oxygen-free copper is used as a copper foil used as a conductive material for FPC.

In recent years, due to the demand for fine pitch of FPC, two-layer copper-clad laminates consisting of a base film and copper foil are increasing instead of the conventional three-layer substrate consisting of base film, adhesive and copper foil. There is a tendency. In this two-layer copper-clad laminate, adhesion of the base film to the copper foil is often performed at a higher temperature (about 350 ° C.) than before, and the thickness of the rolled copper foil used is 20 μm or less. Is also thinner.
By the way, when pure copper-type copper foil is heated for adhesion for a long time, there exists a problem of softening since heat resistance is low. Then, the rolled copper alloy foil containing a predetermined component is disclosed (refer patent documents 1 and 2).

JP 62-189738 A JP-A-64-12538

However, in the case of the conventional rolled copper alloy foil, it cannot be said that the bending resistance is sufficient.
That is, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide a copper alloy foil excellent in heat resistance, conductivity, and flexibility and a flexible printed board using the same.

  As a result of various studies, the present inventors have found that Sn, Mg, In, and Ag are additive elements that improve both heat resistance, conductivity, and flexibility, and two or more of these may be added. It was. In addition, we investigated the extent to which these elements improve heat resistance and conductivity (effectiveness), and succeeded in further improving heat resistance and conductivity by defining the addition ratio of each element. .

  That is, the copper alloy foil of the present invention contains at least two of 0.05 to 0.25% by mass of Sn, 0.03 to 0.1% by mass of Mg, 0.03 to 0.7% by mass of In and 0.02 to 0.1% by mass of Ag, The balance is a copper alloy foil having a thickness of 20 μm or less composed of Cu and unavoidable impurities, and formula 1: [mass% of Sn] + 1.9 × [mass% of Mg] + 1.5 × [mass% of In] +0 .9 × [mass% of Ag] ≧ 0.10 and Formula 2: 2.88 × [Atom% of Sn] + 0.65 × [Atom% of Mg] + 1.06 × [Atom% of In] + 0.14 × [Ag Of atoms%] ≦ 0.42.

  The semi-softening temperature when annealing time is 30 minutes is preferably 350 ° C. or higher, and the conductivity after annealing at 350 ° C. for 30 minutes is preferably 80% IACS or higher.

  It is preferable that recrystallized grains having an average crystal grain size of 2 μm or more and 7 μm or less are formed after annealing at 400 ° C. for 30 minutes, and the elongation is 15% or more.

The flexible printed board of the present invention uses a copper-clad laminate in which the copper alloy foil according to any one of claims 1 to 3 is laminated with a resin base material in an unrecrystallized state.
Moreover, the flexible printed circuit board of this invention uses the copper bonding laminated board laminated | stacked with the resin base material in the state which the said copper alloy foil recrystallized.

  According to the present invention, a copper alloy foil excellent in heat resistance, conductivity, and flexibility can be obtained.

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

(composition)
The copper alloy foil according to the present invention contains at least two of 0.05 to 0.25% by mass of Sn, 0.03 to 0.1% by mass of Mg, 0.03 to 0.7% by mass of In and 0.02 to 0.1% by mass of Ag, and the balance Consists of Cu and inevitable impurities.
First, the reason why Sn, Mg, In, and Ag are selected as additive elements will be described. Figure 1 shows that Cu, Sn, Mg, Ag, In, Fe, Cr, Zn, Ti, Be, and Cd, which are often used as additive elements for copper foil, are added to a predetermined amount of 99.96% or more of electrolytic copper and dissolved. FIG. 3 is a diagram showing a semi-softening temperature when the obtained ingot is hot rolled to a thickness of 10 mm, and then cold rolling and annealing are repeated to a thickness of 0.1 mm.
The semi-softening temperature is the Vickers hardness before annealing when the sample is annealed and the Vickers hardness is measured. ) Shows an annealing temperature indicating intermediate Vickers hardness when it is considered that the state in which no change occurs) is completely softened.

  FIG. 1 shows that the semi-softening temperature varies depending on the additive element. Since the semi-softening temperature of pure copper is 160 ° C., the amount (ΔT) of the increase in the semi-softening temperature of each element from 160 ° C. was obtained and compared with Table 1 based on this temperature.

Sn is known to be effective as an element for improving heat resistance. In the present invention, Sn is used as a reference when selecting an additive element. Therefore, from Table 1, when ΔTSn of Sn is 1, the ratio of ΔT (ΔT / ΔTSn) of each element (at the time of adding 0.05%) was obtained. This ratio indicates the degree (effectiveness) that each element improves the heat resistance with respect to Sn. From this ratio, elements equivalent to Sn (the above ratio is 0.7 or more) are Mg, Ag, In, Cr, Ti, and Cd.
Table 1 also shows Δρi (contribution ratio of component I to specific resistance: μΩcm / at.%) In the Maeehiessen rule. According to Matthesen's rule, the resistivity ρ of a copper alloy is represented by the sum of the resistivity ρCu of a pure substance (pure Cu) and the resistivity of an additive element. The specific resistance of the additive element is represented by Δρi × Ni (concentration of component I in alloy: at.%).
That is, the Matthewsen rule is expressed by ρ = ρCu + ΣΔρi × Ni.
Therefore, Δρi indicates the degree (effectiveness) at which each element reduces the conductivity.
Δρi was based on literature values (authors: Yotaro Murakami and Kiyoshi Kamei, “Asakura Metal Engineering Series Nonferrous Metal Materials Science”, first edition, first edition, Asakura Shoten, published in April 1978, p13).

Comparing Δρi, among the elements selected from the viewpoint of heat resistance, elements whose Δρi is smaller than Sn (= it is difficult to reduce the conductivity) are Mg, Ag, In, and Cd, but Cd is toxic. When excluded, Mg, Ag, and In are selected.
From the above, Sn, Mg, In, and Ag are selected as elements that improve heat resistance and conductivity.
In addition, in the examples described later, as a result of detailed investigation of which element among Sn, Mg, In, and Ag improves not only heat resistance and conductivity but also flexibility, Sn, Mg, In, It was found that the effect was produced only when two or more of Ag were added. Therefore, in the present invention, it is defined that at least two of Sn, Mg, In and Ag are contained.

The heat resistance improves as the amount of the additive element added increases, but the conductivity tends to decrease. Therefore, it is necessary to define the optimum amount of Sn, Mg, In, and Ag. As described above, Sn, Mg, In, and Ag have different effects on heat resistance and conductivity. Therefore, when determining the amount of addition, it is necessary to reflect the heat resistance and conductivity of the element.
However, as described above, increasing the amount of the additive element increases the heat resistance, but the conductivity decreases. Therefore, the addition amount for optimizing the heat resistance and the addition amount for optimizing the conductivity are specified. Is not compatible. Therefore, in the present invention, the range for optimizing the heat resistance and the range for optimizing the conductivity are defined by different relational expressions, and the portion satisfying both of these relational expressions is defined as the optimum addition amount of the additive element. Stipulate.

First, as the regulation of the amount of addition to optimize heat resistance, Table 1 is weighted by the coefficient (ΔT / ΔTSn) as the effect of heat resistance of each element on the amount of addition of Sn, Mg, In, and Ag. 1 is specified.
Where Equation 1 is
[Mass% of Sn] + 1.9 × [mass% of Mg] + 1.5 × [mass% of In] + 0.9 × [mass% of Ag] ≧ 0.10
And the addition amount on the left side needs to be 0.10 or more. According to the examples described later, a lot of data was taken on the relationship between the value on the left side of Equation 1 and the semi-softening temperature when the addition amount of Sn, Mg, In, and Ag was changed, and this was plotted in FIG. Then, when the semi-softening temperature is about 400 ° C. or less, there is a substantially linear relationship between the left side of Equation 1 and the semi-softening temperature, and when the semi-softening temperature becomes 350 ° C. from the slope of the straight line obtained by the least square method. It turned out that the value of the left side of Formula 1 of 0.10 is 0.10. Therefore, heat resistance improves by making the value of the left side of Formula 1 into 0.10 or more.
In addition, when prescribing Formula 1, the reason why the semi-softening temperature is 350 ° C. or higher is that the general heat treatment temperature in the process of manufacturing a two-layer copper-clad laminate comprising a base film and a copper foil is 300 to 350 ° C. Because.

Next, as the definition of the addition amount for optimizing the conductivity, Formula 2 is defined by weighting the addition amount of Sn, Mg, In, and Ag with the degree of conductivity of each element as a coefficient. Each coefficient adopts Δρi as it is.
Where Equation 2 is
2.88 x [Sn atom%] + 0.65 x [Mg atom%] + 1.06 x [In atom%] + 0.14 x [Ag atom%] ≤ 0.42
It is necessary that the amount of addition on the left side be 0.42 or less. The reason for this is that, according to the Matthesen rule, the resistivity of the additive element needs to be 0.42 or less in order to make the conductivity of the entire copper alloy 80% IACS or more. In other words, in Matthewsen's law
2.16 (value of conductivity 80% in terms of specific resistance) = 1.73 (specific resistance of pure Cu) + ΣΔρi × Ni
From this, the specific resistance (ΣΔρi × Ni) of the additive element is 0.43, but the upper limit is 0.42 in consideration of errors.
The reason why the conductivity is 80% is that the conductivity required for the two-layer copper-clad laminate is 80% IACS or more.

  The addition amount of each element of Sn, Mg, In, and Ag is Sn: 0.05 to 0.25%, Mg: 0.03 to 0.1%, In: 0.03 to 0.1%, and Ag: 0.02 to 0.1%. When the addition amount of each element is less than the lower limit of each range, heat resistance and flexibility are not improved, and when the upper limit of each range is exceeded, the conductivity is less than 80%.

  Moreover, the copper alloy foil of this invention can form the copper bonding laminated board laminated | stacked with the following resin base materials etc. also in the non-recrystallized state or the recrystallized state. In this case, the strength after forming the copper-clad laminate is improved by using an amorphous copper alloy foil. However, if the following conditions are satisfied, even if it is a recrystallized copper-clad laminate, it is highly flexible. Is obtained.

Usually, when the crystal grain size at the time of recrystallization is large, there may be no crystal grain boundary in the thickness direction of the copper foil, or there may be fewer crystal grain boundaries per circuit unit length. In such a case, the strengthening effect due to the grain boundaries cannot be obtained, and the resistance to tensile and compressive stress on the copper foil surface caused by bending is low. Therefore, it is necessary to strengthen by increasing the crystal grain boundary by reducing the crystal grain size, and not to lower the flexibility.
The inventors of the present invention examined the crystal grain size necessary for preventing the flexibility from being lowered, and found that when the crystal grain size after recrystallization exceeds 7 μm, the flexibility is significantly reduced. On the other hand, reducing the crystal grain size after recrystallization to less than 2 μm is not industrial because fine temperature control is required, and if it becomes a mixed grain structure of unrecrystallized grains and recrystallized grains, it is microscopically mechanical. The difference in the mechanical properties becomes large, and the flexibility when the circuit is made fine decreases. Therefore, the preferable average crystal grain size at the time of recrystallization is specified to be 2 μm or more and 7 μm or less.

An example of a method for adjusting the grain size of the recrystallized grains to the above-described range is to heat-treat the non-recrystallized copper alloy foil at 400 ° C. for 30 minutes. This temperature condition is suitable for heat during processing of a practical copper-clad laminate and a flexible printed circuit board, and is easy to manufacture.
Even if the grain size of the recrystallized grains is reduced, the strength is lower than that of the copper foil that has not been recrystallized, and plastic deformation occurs with a small stress. On the other hand, it is thought that by imparting a large ductility to the copper foil, the flexibility can be extended even if plastic deformation occurs. And, when the present inventors experimented, the recrystallized grains described above In the case of flexible printed circuit boards having an average crystal grain size of 2 μm to 7 μm, the ones with good flexibility have an elongation of 15% or more, so the copper alloy foil of the present invention is used in a recrystallized state. In this case, the preferred elongation is specified to be 15% or more.
Thus, in the copper alloy foil of the present invention, the elongation after annealing at 400 ° C. for 30 minutes is preferably 15% or more. In addition, in the copper alloy foil of the present invention, when processed into a flexible printed circuit board, an elongation of 15% or more is obtained when the raw foil (copper alloy foil) is heat treated at 400 ° C. for 30 minutes for 15%. It corresponds to the one with the above growth.

  The copper alloy foil of the present invention can be produced, for example, as follows. First, after adding the said additive to a copper ingot, melt | dissolving and casting, it can hot-roll and can manufacture foil by performing cold rolling and annealing. Also, (1) a resin precursor (for example, a polyimide precursor called varnish) is cast and polymerized by applying heat to the copper alloy foil of the present invention, and (2) the same kind of thermoplastic adhesive as the base film is used. By laminating the base film on the copper alloy foil of the present invention, a copper-clad laminate composed of two layers of the copper alloy foil and the resin base material is obtained. Further, by laminating a base film obtained by applying an adhesive to the copper alloy foil of the present invention, a copper-clad laminate composed of three layers of a copper alloy foil, a resin base material, and an adhesive layer therebetween can be obtained. A flexible printed circuit board is obtained by forming a circuit on these using a photolithography technique, plating the circuit as necessary, and laminating a coverlay film.

  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.

EXAMPLES Next, although an Example is given and this invention is demonstrated further in detail, this invention is not limited to these.
The elements shown in Tables 2 and 3 were respectively added to electrolytic copper having a purity of 99.96% or more to obtain ingots. The ingot was hot rolled to a thickness of 10 mm, then the surface was chamfered, and cold rolling and annealing were repeated to obtain a plate sample having a final thickness of 0.1 mm.
The semisoftening temperature was measured for each plate-like sample. The semi-softening temperature was obtained by annealing the plate-like sample, obtaining the Vickers hardness before annealing and the Vickers hardness when completely softened, and setting the annealing temperature at the intermediate Vickers hardness.

The ingot was hot rolled to a thickness of 10 mm, then the surface was chamfered, and cold rolling and annealing were repeated to obtain a foil having a final thickness of 0.02 mm (20 μm). Copper roughening plating was performed on one side of the obtained foil, polyimide (thickness 30 μm) and foil were laminated by a cast method, and then etching was performed to form a circuit with a predetermined pattern. FPC sample (long 12.7 mm in width) A circuit width of 1 mm) was obtained.
For each FPC sample, the conductivity at 25 ° C. was measured by the 4-terminal method. Moreover, the bending test was done by the following method.
The bending test was performed by bending the FPC sample into a U shape in the longitudinal direction, fixing one end to the movable plate, fixing the other end to the fixed plate, and reciprocatingly vibrating the movable plate in the long side direction of the FPC sample. The test conditions were a U-shaped radius of curvature of 1.3 mm, a vibration stroke of 5 mm, and a vibration frequency of 1200 times / minute. In addition, the electrical resistance of the sample during the bending test was measured, and the number of bendings until the resistance increased by 10% from the initial resistance was determined.

In addition, the foil was annealed at 350 ° C. for 15 minutes as a heat treatment equivalent to the thermal history in FPC processing, and then the tensile strength was measured according to JIS-Z2241, and 0.2% yield strength (YS: yield strength) Asked. The sample was produced according to JIS Z 2241.
Furthermore, a polyimide (thickness 30 μm) and a foil were laminated on the copper alloy foil (non-recrystallized) of the present invention, followed by etching to form a circuit with a predetermined pattern, and an FPC sample (width 12.7 mm long) A circuit width of 1 mm) was obtained. This was heat-treated at 400 ° C. for 30 minutes, and then subjected to 0.2% proof stress and bending test in the same manner as described above, and the average particle diameter (JIS H 0501) and elongation (JIS Z 2241) were measured. did.
The obtained results are shown in Tables 2 to 4.

  As is clear from Tables 2 to 4, in each Example including at least two of Sn, Mg, In and Ag and satisfying the relationship of Formula 1 and Formula 2, the semi-softening temperature is 350 ° C. or higher. In addition, the electrical conductivity was 80% or more, and the number of bendings was 100,000 or more. In addition, when heat treatment was performed at 400 ° C. for 30 minutes, the elongation was 15% or more and the number of bendings was 100,000 or more.

On the other hand, in the case of Comparative Example 1 containing no additive element and in the case of Comparative Example 2 containing only Sn less than 0.05% by mass, the value of Formula 1 is less than 0.10, the semisoftening temperature is less than 350 ° C., and bending The number of times became less than 100,000 times. In addition, when heat treatment was performed at 400 ° C. for 30 minutes, the elongation was less than 15% and the number of bendings was less than 100,000.
In the case of Comparative Example 3 in which the value of Formula 2 exceeded 0.42, the conductivity was less than 80%.
In Comparative Example 3 in which only Sn was added in excess of 0.25%, the value of Formula 2 exceeded 0.42 and the conductivity was less than 80%.
In the case of Comparative Examples 4 and 5 in which only Ag is added within the range of the specified amount of the present invention, the value of Formula 1 is less than 0.10, the semisoftening temperature is less than 350 ° C., and the number of bendings is less than 100,000. became. In addition, when heat treatment was performed at 400 ° C. for 30 minutes, the elongation was less than 15% and the number of bendings was less than 100,000.

In the case of Comparative Example 6 in which Sn, Mg, and Ag were added below the specified lower limit, the value of Formula 1 was less than 0.10, the semisoftening temperature was less than 350 ° C., and the number of flexing was less than 100,000. In addition, when heat treatment was performed at 400 ° C. for 30 minutes, the elongation was less than 15% and the number of bendings was less than 100,000.
In the case of Comparative Example 7 in which Sn, Mg, and Ag were added in excess of the upper limit of the specified amount, the value of Formula 2 exceeded 0.42 and the conductivity was less than 80%.
In the case of Comparative Example 6 in which Sn, Mg and In were added in less than the lower limit of the specified amount, the value of Formula 1 was less than 0.10, the semisoftening temperature was less than 350 ° C., and the number of flexing was less than 100,000. In addition, when heat treatment was performed at 400 ° C. for 30 minutes, the elongation was less than 15% and the number of bendings was less than 100,000.

From Table 2 to Table 4, in the case of Comparative Example 9 in which only Sn was added out of Sn, Mg and Ag and Fe was further added, the semi-softening temperature was less than 350 ° C. and the conductivity was less than 80%.
In the case of Comparative Example 10 in which only Sn of Sn, Mg and Ag was added and Cr was further added, the conductivity was less than 80%.
In the case of Comparative Example 11 in which only Sn was added out of Sn, Mg and Ag and Zn was further added, the semisoftening temperature was less than 350 ° C.
In the case of Comparative Example 12 in which none of Sn, Mg and Ag was added and Fe and Zn were added instead, the semi-softening temperature was less than 350 ° C. and the conductivity was less than 80%.
In the case of Comparative Example 12 in which none of Sn, Mg and Ag was added and Cr and Zn were added instead, the semi-softening temperature was less than 350 ° C.

  In addition, the relationship of the semi-softening temperature with respect to the value of Formula 1 of each Example and Table 4 of Tables 2 to 4 and the relationship of the conductivity with respect to the value of Formula 2 are shown in FIGS.

It is a figure which shows the semi-softening temperature of copper which added the additive element. It is a figure which shows the relationship between the value of Formula 1 when changing the addition amount of Sn, Mg, In, and Ag, and a semi-softening temperature. FIG. 4 is a diagram showing the relationship of conductivity with respect to the value of Equation 2.

Claims (6)

It contains at least two of 0.05 to 0.25% by mass of Sn, 0.03 to 0.1% by mass of Mg, 0.03 to 0.1% by mass of In, and 0.02 to 0.1% by mass of Ag, with the balance being Cu and inevitable impurities. A copper alloy foil having a thickness of 20 μm or less,
Formula 1: [mass% of Sn] + 1.9 × [mass% of Mg] + 1.5 × [mass% of In] + 0.9 × [mass% of Ag] ≧ 0.10, and formula 2: 2.88 × [Sn Copper atom foil satisfying the relationship of [Atom%] + 0.65 × [Mg Atom%] + 1.06 × [In Atom%] + 0.14 × [Ag Atom%] ≦ 0.42. The copper alloy foil according to claim 1, wherein the semi-softening temperature is 350 ° C. or higher when the annealing time is 30 minutes. The copper alloy foil according to claim 1 or 2, wherein the electrical conductivity after annealing at 350 ° C for 30 minutes is 80% IACS or more. The copper alloy foil according to any one of claims 1 to 3, wherein recrystallized grains having an average crystal grain size of 2 µm or more and 7 µm or less are formed after annealing at 400 ° C for 30 minutes, and elongation is 15% or more. A flexible printed board using a copper-clad laminate in which the copper alloy foil according to claim 1 is laminated with a resin base material in an unrecrystallized state. The flexible printed circuit board using the copper bonding laminated board laminated | stacked with the resin base material in the state which the copper alloy foil in any one of Claims 1-4 recrystallized.