SURFACE-TREATED COPPER FOIL WITH HEAT RESISTANCE, AND COPPER CLAD LAMINATE AND PRINTED WIRING BOARD INCLUDING THE SAME

Abstract

Disclosed is a surface-treated copper foil having long-term high-temperature reliability and being suitable for use in high-frequency circuits due to a low transmission loss, wherein the surface-treated copper foil has a surface treatment layer, the surface treatment layer including: a primary particle layer containing Cu or Cu alloy particles formed on at least one surface of an original copper foil; and a secondary particle layer containing Zn particles formed on the primary particle layer, the secondary particle layer being composed of particle clusters formed by clustering of a plurality of Zn particles.

Claims

1. A surface-treated copper foil having a surface treatment layer, the surface treatment layer comprising: a primary particle layer containing Cu or Cu alloy particles formed on at least one surface of an original copper foil; and a secondary particle layer containing Zn particles formed on the primary particle layer, wherein the secondary particle layer is composed of particle clusters formed by clustering a plurality of Zn particles.

2. The surface-treated copper foil of claim 1, wherein the particle clusters are discontinuously distributed on the primary particle layer.

3. The surface-treated copper foil of claim 1, wherein the surface treatment layer of the surface-treated copper foil has a surface roughness (Rz) of 1.0 m or less.

4. The surface-treated copper foil of claim 1, wherein, on average, at least two particle clusters are distributed in an area of 5 m5 m of the surface-treated copper foil.

5. The surface-treated copper foil of claim 1, wherein at most 15 particle clusters are distributed in an area of 5 m5 m of the surface-treated copper foil

6. The surface-treated copper foil of claim 1, wherein the particle size of the secondary particle layer is larger than that of the primary particle layer.

7. The surface-treated copper foil of claim 6, wherein the average particle size of the primary particle layer is less than 100 nm, and the average size of the particle clusters of the secondary particle layer is 0.5-2.0 m.

8. The surface-treated copper foil of claim 1, wherein the Zn concentration of the surface-treated layer is 2000 g/dm2 or more.

9. The surface-treated copper foil of claim 1, wherein the Zn concentration of the surface-treated layer is 3500 g/dm2 or less.

10. The surface-treated copper foil of claim 1, further comprising an anti-rust layer on the secondary particle layer.

11. The surface-treated copper foil of claim 1, wherein the anti-rust layer contains chromium.

12. The surface-treated copper foil of claim 1, wherein the original copper foil is an electrolytic copper foil.

13. A copper clad laminate comprising the surface-treated copper foil of claim 1 laminated on a resin substrate.

14. The copper clad laminate of claim 13, wherein the resin substrate is a PTFE substrate.

15. The copper clad laminate of claim 13, wherein the high-temperature deterioration rate in adhesive strength of the copper clad laminate is less than 10%.

16. A printed wiring board manufactured using the copper clad laminate of claim 13.

Description

DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is an electron microscopic image obtained by photographing a cross-section of a surface-treated copper foil according to an embodiment of the present disclosure.

[0022] FIG. 2 is an electron microscopic image obtained by photographing a surface of a surface-treated copper foil according to an embodiment of the present disclosure.

[0023] FIGS. 3A and 3B are electron microscopic images obtained by observing surfaces of surface-treated copper foils prepared in an example and a comparative example, respectively.

BEST MODE

[0024] The features described in exemplary embodiments and shown in drawings in the present specification are for merely illustrating one of the most preferable exemplary embodiments, but are not intended to represent the technical spirit of the present disclosure, and thus the present disclosure may cover various equivalents and modifications which can substitute for the exemplary embodiments at the time of filing the present application. Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings.

[0025] A surface-treated copper foil of the present disclosure includes an original foil, a primary particle layer on at least one surface of the original foil, and a secondary particle layer on the primary particle layer. Additionally, the surface-treated copper foil of the present disclosure may further include an anti-rust layer on the secondary particle layer.

[0026] FIGS. 1 and 2 are electron microscopic images obtained by photographing a cross-sectional structure and a surface structure of a surface-treated copper foil according to an embodiment of the present disclosure, respectively.

[0027] Referring to FIG. 1, a multi-layered surface treatment layer composed of a primary particle layer 20 and a secondary particle layer 30 is formed on one surface of an original foil 10. It can be seen from the picture of FIG. 1 that the primary particle layer 20 covers substantial all the regions of the surface of the original foil but the secondary particle layer 30 is discontinuously distributed on the primary particle layer 20.

[0028] Referring to FIG. 2, the secondary particle layer 30 is composed of particle clusters with an average size of 0.5-2 m appearing relatively bright and the primary particle layer 20 is composed of fine particles with less than 0.1 m appearing dark, the primary particle layer forming the background of the secondary particle layer. The primary particle layer is formed of Cu particles and the secondary particle layer is formed of Zn particles.

[0029] The individual particles in the particle clusters of the secondary particle layer have a size of less than 0.5 m, but coarse Zn particles that are 2 to 5 times larger compared with the primary particle layer are clustered as a bundle of grapes. It can be also seen that some of the Zn particles constituting the secondary particle layer are in the form of single particles, but most of the particles form a particle cluster by aggregation of two or more particles. It can be seen that these particle clusters have a size of 0.5-2 m on average. In the present disclosure, the particle clusters are formed in local regions, and some of the particle clusters are isolated from each other.

[0030] Hereinafter, the original foil, the primary particle layer, the secondary particle layer, and the anti-rust layer, and manufacturing methods therefor of the present disclosure will be described in detail.

A. Original Foil

[0031] In the present disclosure, an original copper foil refers to a copper foil that has not been subjected to surface treatment or anti-rust treatment. A known copper foil may be used without limitation as an original copper foil. According to an embodiment, an untreated copper foil may be an electrolytic copper foil or a rolled copper foil.

[0032] In the present disclosure, the thickness of the original copper foil is not particularly limited, but when the surface-treated copper foil is used for a printed wiring board, the thickness of the original foil may be, for example, 6 to 35 m, and preferably 7 to 17 m.

[0033] In the present disclosure, the original foil preferably has a tensile strength of 35 kgf/mm.sup.2 to 60 kgf/mm.sup.2, 35 kgf/mm.sup.2 to 50 kgf/mm.sup.2, or 35 kgf/mm.sup.2 to 45 kgf/mm.sup.2.

[0034] In the present disclosure, the mechanical properties of the original foil are preferably maintained uniform before and after hot pressing during the binding with a prepreg for molding a copper clad laminate or a printed wiring board. In the present disclosure, the original foil has a very small change in crystal grains before and after pressing.

[0035] For example, the change rate of the tensile strength value of the original foil after thermal treatment for a predetermined time at a pressure of 4.9 Mpa and a temperature of 220 C. relative to the tensile strength value at room temperature may be less than 5% or less than 3%. In addition, the change rate of elongation of the original foil after thermal treatment for a predetermined time at a pressure of 4.9 Mpa and a temperature of 220 C. relative to the elongation at room temperature may be less than 5% or less than 3%.

B. Primary Particle Layer (Nodular Layer)

[0036] In the present disclosure, the primary particle layer may be formed on one surface or both surfaces of the original foil. A surface treatment method for forming the surface treatment layer of the present disclosure is not particularly limited, but the surface treatment layer may be formed by, for example, electroplating of the original foil. As an electrolyte, an aqueous solution containing 5 to a 60 g/L copper salt and 50 to 200 g/L ethylenediaminetetraacetic acid disodium (EDTA-2Na) and adjusted to, for example, pH 1 to 8 (e.g., 6 to 7) may be used. Examples of the copper salt may include copper sulfate (CuSO.sub.4), copper nitrate (Cu(NO.sub.3).sub.2), copper chloride (CuCl.sub.2), copper acetate (Cu(CH.sub.3COO).sub.2), and the like, and as an additive, at least one selected from the group consisting of citric acid (C.sub.6H.sub.8O.sub.7), ethylene diamine tetraacetic acid (C.sub.10H.sub.16N.sub.2O.sub.8), nitrilotriacetic acid (C.sub.6H.sub.9NO.sub.6), sodium citrate (C.sub.6H.sub.5Na.sub.3O.sub.7), and tartaric acid (C.sub.4H.sub.6O.sub.6) may be used, but is not limited thereto. For example, electroplating may be performed by immersing an insoluble electrode as a positive electrode and an untreated original foil as a negative electrode in an electrolyte and conducting electrolysis at a liquid temperature of 25 to 45 C. and a current density of 0.5 to 10 A/dm.sup.2 for, for example, 5 to 20 seconds, but is not limited thereto.

[0037] In the present disclosure, the primary particle layer is preferably configured of fine copper particles with an average particle diameter of 100 nm or less. For example, the fine copper particles of the primary particle layer may have an average particle diameter of 10 to 100 nm, 20 to 100 nm, or 50 to 100 nm. In the present disclosure, the average particle diameter of the copper particles can be calculated by obtaining a scanning electron microscope (SEM) image and measuring the particle diameter of copper particles through image analysis. The average particle diameter can be calculated by averaging the measurement values of a total of 100 particles. When the average particle diameter of the fine copper particles of the primary particle layer is within such a range, the copper foil has excellent adhesive strength with a resin substrate and is suitable as a high-frequency foil due to a small transmission loss.

C. Secondary Particle Layer

[0038] The secondary particle layer may be formed by electroplating the surface-treated foil with the primary particle layer. The electroplating may be performed by using an aqueous solution containing 1-5 g/L zinc and 1-5 g/L phosphoric acid as an electrolyte, immersing the surface-treated foil as a negative electrode in the electrolyte, and conducting electrolysis at a liquid temperature of 25 to 45 C. and a current density of 1 to 3 A/dm.sup.2 for, for example, 5 to 10 seconds, but is not limited thereto.

D. Anti-Rust Layer

[0039] In the present disclosure, an anti-rust layer may be formed on the secondary particle layer. The anti-rust layer may contain chromium (Cr). The anti-rust layer may contain a metal, such as nickel (Ni), zinc (Zn), cobalt (Co), titanium (Ti), or tin (Sn), instead of or together with chromium.

[0040] In the present disclosure, chromate anti-rust treatment may be performed by using an electrolyte of 1-5 g/l chromium and conducting plating at a liquid temperature of 25-35 C. and a current density of 0.5 A/dm.sup.2 for 1-5 seconds, followed by washing with water.

[0041] In the present disclosure, the surface-treated copper foil may be bound with a low-dielectric resin, a polyimide, or a hydrocarbon or polytetrafluoroethylene film to manufacture a copper clad laminate.

[0042] In the present disclosure, the surface roughness (Rz) of the surface-treated copper foil is preferably less than 1.0 m, and more preferably, the surface roughness of the surface-treated copper foil is in the range of 0.85-0.95. In the present disclosure, the 3D roughness (Sa) of the surface-treated copper foil is preferably 0.3 or more, and more preferably 0.3-0.35.

[0043] The above-described surface-treated copper foil laminated on a resin substrate may be used as a copper clad laminate, and such a copper clad laminate may be used to manufacture a printed wiring board.

[0044] In the present disclosure, the surface-treated copper foil shows high adhesive strength with a resin substrate, such as a low-dielectric resin, a polyimide, or hydrocarbon or polytetrafluoroethylene, and the surface-treated copper foil, even when exposed to a high temperature for a long time, has a very low possibility of deterioration in adhesive strength.

[0045] The surface-treated copper foil of the present disclosure may have an adhesive strength with a PTFE resin of 2.0 kgf/cm or more, 2.5 kgf/cm or more, 2.7 kgf/cm or more, or 2.8 kgf/cm or more. The adhesive strength may be measured based on the JIS C6481 standard.

[0046] The surface-treated copper foil of the present disclosure is made into a copper clad laminate by binding with a resin substrate, such as a PTEF resin, and then the deterioration rate (%) of adhesive strength, corresponding to the change rate of the adhesive strength at a temperature of 177 C. after 10 days relative to the adhesive strength value after 1 day, is preferably 10% or less, 9% or less, 8% or less, 7% or less, 6% or less, or 5% or less.

MODE FOR INVENTION

[0047] Hereinafter, the present disclosure will be described in detail with reference to examples. However, these examples are shown by way of illustration and should not be construed as limiting the present disclosure in any way.

EXAMPLES

Example 1

[0048] An original foil (electrolytic copper foil) with a thickness of 12 m was immersed in an aqueous solution containing 10-20 g/L copper and 100-200 g/L EDTA-2Na and subjected to plating for 4 seconds under the conditions of a liquid temperature of 25 C., pH 7, and a current density 8 A/dm.sup.2, thereby forming a primary particle layer (nodular layer).

[0049] Then, the copper foil with the primary particle layer was immersed in an aqueous solution of zinc sulfate (a zinc concentration of 1-5 g/L) and 1-5 g/L phosphoric acid and treated twice for 6 seconds under the conditions of 3.5 A/dm.sup.2, thereby forming a secondary particle layer. Thereafter, the surface-treated copper foil was immersed in an aqueous solution of 2 g/L chromium for 3 seconds and washed with water, thereby forming an anti-rust layer. Then, the anti-rust-treated copper foil was immersed in a solution of a silane coupling agent at 1-10 g/L for 3 seconds and then dried with hot air at a temperature of 100 C., thereby preparing a surface-treated copper foil.

Example 2

[0050] An original foil with a thickness of 12 m was immersed in an aqueous solution containing 10-20 g/L copper and 100-200 g/L EDTA-2Na and subjected to plating for 4 seconds under the conditions of a liquid temperature of 25 C., pH 7, and a current density 8 A/dm.sup.2, thereby forming a primary particle layer (nodular layer).

[0051] Then, the copper foil with the primary particle layer was immersed in an aqueous solution of 1-5 g/L zinc and 1-5 g/L phosphoric acid and treated twice for 6 seconds under the conditions of 2.5 A/dm.sup.2, thereby forming a secondary particle layer. Thereafter, the surface-treated copper foil was immersed in an aqueous solution of 2 g/L chromium for 3 seconds and washed with water, thereby forming an anti-rust layer. Then, the anti-rust-treated copper foil was immersed in a solution of a silane coupling agent at 1-10 g/L for 3 seconds and then dried with hot air at a temperature of 100 C., thereby preparing a surface-treated copper foil.

Comparative Example 1

[0052] An original foil with a thickness of 12 m was immersed in an aqueous solution containing 10-20 g/L copper and 100-200 g/L EDTA-2Na and subjected to plating for 4 seconds under the conditions of a liquid temperature of 25 C., pH 7, and a current density 8 A/dm.sup.2, thereby forming a primary particle layer (nodular layer).

[0053] Then, the copper foil with the primary particle layer was immersed in an aqueous solution of 1-5 g/L zinc and 1-5 g/L phosphoric acid and treated twice for 6 seconds under the conditions of 2.0 A/dm.sup.2, thereby forming a secondary particle layer. Thereafter, the surface-treated copper foil was immersed in an aqueous solution of 2 g/L chromium for 3 seconds and washed with water, thereby forming an anti-rust layer. Then, the anti-rust-treated copper foil was immersed in a solution of a silane coupling agent at 1-10 g/L for 3 seconds and then dried with hot air at a temperature of 100 C., thereby preparing a surface-treated copper foil.

Comparative Example 2

[0054] An original foil with a thickness of 12 m was immersed in an aqueous solution containing 10-20 g/L copper and 100-200 g/L EDTA-2Na and subjected to plating for 4 seconds under the conditions of a liquid temperature of 25 C., pH 7, and a current density 8 A/dm.sup.2, thereby forming a primary particle layer (nodular layer).

[0055] Then, the copper foil with the primary particle layer was immersed in an aqueous solution of 1-5 g/L zinc and 1-5 g/L phosphoric acid and treated twice for 40 seconds under the conditions of 0.5 A/dm.sup.2, thereby forming a secondary particle layer. Thereafter, the surface-treated copper foil was immersed in an aqueous solution of 2 g/L chromium for 3 seconds and washed with water, thereby forming an anti-rust layer. Then, the anti-rust-treated copper foil was immersed in a solution of a silane coupling agent at 1-10 g/L for 3 seconds and then dried with hot air at a temperature of 100 C., thereby preparing a surface-treated copper foil.

Comparative Example 3

[0056] An original foil with a thickness of 12 m was immersed in an aqueous solution containing 10-20 g/L copper and 100-200 g/L EDTA-2Na and subjected to plating for 4 seconds under the conditions of a liquid temperature of 25 C., pH 7, and a current density 8 A/dm.sup.2, thereby forming a primary particle layer (nodular layer). Then, covering plating for preventing nodular detachment was performed for 3 seconds under conditions of 60-70 g/L, sulfuric acid 120 g/L, and 15 A/dm.sup.2.

[0057] Then, the covering-plated copper foil was immersed in an aqueous solution of 1-5 g/L zinc and 1-5 g/L phosphoric acid and treated twice for 6 seconds under the conditions of 0.3 A/dm.sup.2, thereby forming a secondary particle layer. Thereafter, the surface-treated copper foil was immersed in an aqueous solution of 2 g/L chromium for 3 seconds and washed with water, thereby forming an anti-rust layer. Then, the anti-rust-treated copper foil was immersed in a solution of a silane coupling agent at 1-10 g/L for 3 seconds and then dried with hot air at a temperature of 100 C., thereby preparing a surface-treated copper foil.

Evaluation of Properties

[0058] Each of the surface-treated copper foil samples prepared in the examples and comparative examples were measured for properties. Property evaluation items and measurement methods are as follows.

a. Roughness

[0059] As for the surface of each of the surface-treated copper foils prepared in the examples and comparative examples, the 10-point average roughness Rz for each of before and after surface treatment of the copper foil was measured using the SURFCOM 1400D (TSK, Tokyo Precision) surface roughness measurement instrument according to the JIS B0601 standards.

b. Three-Dimensional Roughness

[0060] As for the surface of each of the surface-treated copper foils prepared in the examples and comparative examples, three-dimensional roughness was determined by measuring the shape of minute stepped portions of an object in a non-contact manner through a 3D Profiler, NV-2200, by Nanosystems.

c. Average Particle Diameter of Primary Particle Layer

[0061] The primary particle layer was formed on the surface of the original foil in each of the examples and comparative examples, and then immediately, an FE-SEM image of the surface was photographed using a scanning electron microscope. The particle diameters of 100 copper particles in an area of 5 m5 m were measured and averaged.

d. Average Particle Diameter of Secondary Particle Layer

[0062] The secondary particle layer was formed in each of the examples and comparative examples, and then immediately, an FE-SEM image of the surface was photographed using a scanning electron microscope. The particle diameters of 50 secondary particles in an area of 5 m5 m were measured and averaged, thereby obtaining an average particle diameter.

e. Adhesive Strength (Unit: kgf/cm)

[0063] A copper foil specimen was prepared with a width of 10 mm and pressed on Teflon resin at 380 C., thereby preparing a sample. The adhesive strength was investigated by the 90 peel method according to JIS C 6471 8.1. A Teflon product with a thickness of 50 m, which was the product name EA-2000 by AGC, was used as an insulator.

f. Particle Amount of Secondary Particle Layer

[0064] A 1010 cm sample of surface-treated copper foil was prepared, immersed in a hydrochloric acid solution to melt the surface with a thickness of 1 m, and then the crude solution was measured by ICP analysis to measure the particle amount of the secondary particle layer (Zn).

g. High-Temperature Deterioration Rate in Adhesive Strength

[0065] The sample, which had been hot-pressed on Teflon resin and checked for adhesive strength, was measured for adhesive strength by the above method, and the measurement value was then set as a reference value. Thereafter, the corresponding sample was kept in an oven at a temperature of 177 C. for 10 days, and then measured for adhesive strength. The change rate on the basis of the reference value was calculated as a high-temperature deterioration rate (%) in adhesive strength.

[0066] Table 1 below shows measured property values.

TABLE-US-00001 TABLE 1 Particle Adhesive amount of strength 3D Size of Size of secondary Adhesive (177 C., Deterioration Roughness roughness primary secondary particles strength after rate Classification (Rz) (Sa) particles particles (g/dm.sup.2) (1 day) 10 days) (%) Example 1 0.9 0.32 <100 nm >100 nm 2790 3.0 2.97 1% Example 2 0.9 0.31 <100 nm >100 nm 2450 3.0 2.79 7% Comparative 1.0 0.29 <100 nm >100 nm 1990 3.0 1.49 49% Example 1 Comparative 1.0 0.22 <100 nm 3000 3.0 0.12 >90% Example 2 Comparative 1.5 0.83 >500 nm 300 3.0 0.13 >90% Example 3

[0067] FIGS. 3A and 3B are electron microscopic images obtained by observing the surfaces of the surface-treated copper foils prepared in Example 1 and Comparative Example 2, respectively.

[0068] Referring to FIG. 3, in Example 1, a particle cluster-structured secondary particle layer composed of coarser particles than the primary particle layer of the background on the surface was formed. However, in Comparative Example 2, no particle cluster structure was developed. It seems that Zn supplied as a secondary particle source was evenly deposited on the particle surface of the primary particle layer rather than forming a separate layer. This was also observed in Comparative Example 3, indicating a very low value of deterioration rate.

[0069] In Comparative Example 1, a particle cluster structure was formed, but the particle amount of the secondary particle layer was lower than those in Examples 1 and 2, and this cause was considered to cause a rapid increase in the deterioration rate.

[0070] Although the present disclosure has been described through a certain embodiment, it shall be appreciated that various permutations and modifications of the described embodiment are possible by those skilled in the art to which the present disclosure pertains without departing from the scope of the present disclosure. Therefore, the scope of the present disclosure shall not be defined by the described embodiment but shall be defined by the appended claims and their equivalents.

INDUSTRIAL APPLICABILITY

[0071] The present disclosure is applicable to electrolytic copper foils, COPPER CLAD LAMINATE AND PRINTED WIRING BOARD.