METHOD FOR MANUFACTURING COPPER FOIL FOR HIGH FREQUENCY CIRCUIT

Abstract

A method of manufacturing a copper foil for a high frequency circuit includes sequentially forming a fine roughness copper nodule layer on a surface of an electroplated copper layer, the fine roughness copper nodule layer being consisted essentially of copper particles or copper alloy particles with a particle size of 100 nm to 200 nm; then, performing electroplating with a ZnNi co-electroplating formula for 3 seconds or more to form a ZnNi plating layer on the fine roughness copper nodule layer, the ZnNi plating layer including 90-150 g/dm.sup.2 of zinc and 75-120 g/dm.sup.2 of nickel; forming a rust-proof layer on the ZnNi plating layer, the rust-proof layer including 20-40 g/dm.sup.2 of chromium; and next, forming a hydrophobic layer on the rust-proof layer, the hydrophobic layer having a water contact angle of 80 to 150 degrees.

Claims

1. A method of manufacturing a copper foil for a high frequency circuit, comprising: forming a fine roughness copper nodule layer on a surface of an electroplated copper layer, the fine roughness copper nodule layer being consisted essentially of copper particles or copper alloy particles with a particle size of 100 nm to 200 nm; performing electroplating with a ZnNi co-electroplating formula for 3 seconds or more to form a ZnNi plating layer on the fine roughness copper nodule layer, the ZnNi plating layer comprising 90-150 g/dm.sup.2 of zinc and 75-120 g/dm.sup.2 of nickel; forming a rust-proof layer on the ZnNi plating layer, the rust-proof layer comprising 20-40 g/dm.sup.2 of chromium; and forming a hydrophobic layer on the rust-proof layer, the hydrophobic layer having a water contact angle of 80 to 150 degrees.

2. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein the ZnNi co-electroplating formula comprises zinc, nickel, and potassium pyrophosphate.

3. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein a duration of the electroplating for forming the ZnNi plating layer is 3 to 5 seconds.

4. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein an organosilane solution for forming the hydrophobic layer comprises vinyl silane, epoxy silane, or amino silane.

5. The method of manufacturing a copper foil for a high frequency circuit according to claim 4, wherein the amino silane comprises: (3-trimethoxysilylpropyl)ethylenediamine, (3-triethoxysilylpropyl)ethylenediamine, (3-aminopropyl)trimethoxysilane, or (3-aminopropyl)triethoxysilane.

6. The method of manufacturing a copper foil for a high frequency circuit according to claim 4, wherein the vinyl silane comprises: vinyltrimethoxysilane or vinyltriethoxysilane.

7. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein the copper alloy particles are formed of copper and elements selected from a group consisting of Fe, and Mo.

8. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein a step of forming the fine roughness copper nodule layer comprises treating the surface of the electroplated copper layer by an ultra-fine surface roughening process.

9. The method of manufacturing a copper foil for a high frequency circuit according to claim 8, wherein a solution used in the ultra-fine surface roughening process comprises a copper sulfate-based solution with Fe and Mo added as inhibitors in the ultra-fine surface roughening process.

10. The method of manufacturing a copper foil for a high frequency circuit according to claim 8, wherein the ultra-fine surface roughening process comprises performing an nucleation electroplating and then performing a covering electroplating.

11. The method of manufacturing a copper foil for a high frequency circuit according to claim 10, further comprising performing a bonding electroplating after cycling twice of the nucleation electroplating and the covering electroplating.

12. The method of manufacturing a copper foil for a high frequency circuit according to claim 1, wherein a step of forming the rust-proof layer comprises impregnating the ZnNi plating layer in a chromic acid solution.

13. The method of manufacturing a copper foil for a high frequency circuit according to claim 12, wherein a duration of the impregnating for forming the rust-proof layer is 10 to 15 seconds.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The FIGURE is a schematic diagram illustrating a copper foil for a high frequency circuit according to an embodiment of the disclosure.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0010] Referring to the embodiments below and the accompanied drawings for a detailed description of the disclosure. However, the provided embodiments are not meant to limit the scope covered by the disclosure. Moreover, the drawings are merely illustrative and are not drafted according to the actual dimensions. Different layers may be enlarged or reduced to be presented in the same drawing.

[0011] The FIGURE is a schematic diagram illustrating a copper foil for a high frequency circuit according to an embodiment of the disclosure.

[0012] Referring to The FIGURE, a copper foil 100 for a high frequency circuit of the present embodiment has a roughness sRq of 0.1 m to 0.5 m, and the copper foil 100 for a high frequency circuit includes an electroplated copper layer 102, a fine roughness copper nodule layer 104 located on a surface 102a of the electroplated copper layer 102, a ZnNi plating layer 106 located on the fine roughness copper nodule layer 104, a rust-proof layer 108 located on the ZnNi plating layer 106, and a hydrophobic layer 110 located on the rust-proof layer 108.

[0013] The fine roughness copper nodule layer 104 is consisted essentially of copper particles or copper alloy particles with a particle size of 100 nm to 200 nm, and the copper alloy is formed of copper and elements selected from a group consisting of cobalt (Co), nickel (Ni), iron (Fe), and molybdenum (Mo), such as CuFeMo and CuCoNi. From the perspective of inhibiting growth of the copper alloy particles, the material of the copper alloy particles may include molybdenum. Since the particle size of the fine roughness copper nodule layer 104 is merely 100 nm or so, bonding between the copper foil 100 for a high frequency circuit and a high frequency resin substrate material (not illustrated) is significantly enhanced, which further reduces a content of non-copper elements plated in a subsequent process and also ensures electrical performance. The ZnNi plating layer 106 includes 90-150 g/dm.sup.2 of zinc and 75-120 g/dm.sup.2 of nickel. In an embodiment, the ZnNi plating layer 106 includes 90-130 g/dm.sup.2 of zinc and 75-105 g/dm.sup.2 of nickel. The rust-proof layer 108 includes 20-40 g/dm.sup.2 of chromium. The hydrophobic layer 110 has a water contact angle of 80 to 150 degrees. In an embodiment, the hydrophobic layer 110 is selected from a group consisting of materials derived from organosilane, such as vinyl silane, epoxy silane, and amino silane. In an embodiment, the vinyl silane is (but is not limited to) vinyltrimethoxysilane or vinyltriethoxysilane, for example. The epoxy silane is (but is not limited to) epoxy functional methoxysilane, for example. The amino silane is selected from (but is not limited to) (3-trimethoxysilylpropyl)ethylenediamine, (3-triethoxysilylpropyl)ethylenediamine, (3-aminopropyl)trimethoxysilane, or (3-aminopropyl)triethoxysilane, for example.

[0014] Moreover, since thicknesses of each layer are extremely small, content ranges of each component are obtained by analyzing a surface composition. In other words, the foregoing element content ranges and ratios of each layer are obtained by analyzing the surface composition. In an embodiment, a weight ratio of nickel of the ZnNi plating layer 106 to silicon of the hydrophobic layer 110 (i.e., a Ni/Si weight ratio) is 1.8 to 4.5. A weight ratio of zinc of the ZnNi plating layer 106 to silicon of the hydrophobic layer 110 (i.e., a Zn/Si weight ratio) is 2.2 to 5.5. If the Zn/Si value is 5.5 or smaller, heat resistance is not only enhanced, but acid resistance of the copper foil is also maintained; if the Zn/Si value is 2.2 or greater, heat resistance is exhibited. If the Ni/Si value is 4.5 or smaller, a surface resistance is not increased, and it is favorable to perform an etching process; if the Ni/Si value is 1.8 or greater, acid resistance and heat resistance are exhibited. If the Cr/Si value is 1.6 or smaller, an increase in the surface resistance is small while surface oxidation resistance is increased, and it is favorable for high frequency transmission; if the Cr/Si value is 0.5 or greater, oxidation resistance is exhibited.

[0015] In the text below, experimental examples are provided to verify the effect of the embodiments of the disclosure, but the disclosure is not limited to the description below.

Experimental Example 1

[0016] A raw foil (electroplated copper layer) with Rz<1.5 m was provided, and a surface of the raw foil was treated by an ultra-fine surface roughening process to form a fine roughness copper nodule layer. The ultra-fine surface roughening process was based on a low-copper content copper sulfate-based solution, to which Fe and Mo were added as inhibitors in the ultra-fine surface roughening process (a formula of the fine roughness solution was Cu: 2 g/L, sulfuric acid: 90 g/L, Fe: 100 ppm, Mo: 400 ppm), such that a size of particles formed on the surface was uniform and thin. Moreover, electroplating conditions were controlled to bond the formed particles to the surface of the electroplated copper layer. The electroplating conditions are: nucleation current density: 6 A/dm.sup.2, covering current density: 1.2 A/dm.sup.2, bonding electroplating condition: 0.5 A/dm.sup.2. The electroplating process is: performing nucleation electroplating for 3 seconds, and then performing covering electroplating for 5 seconds. After this process was cycled twice, bonding electroplating was performed for 10 seconds, and the fine roughness copper nodule layer having a surface covered by copper nodules with a particle size of 100 nm to 200 nm was obtained.

[0017] Next, electroplating was performed on the fine roughness copper nodule layer with a ZnNi co-electroplating formula for 4 seconds (the co-electroplating formula is Zn: 2 g/L, Ni: 0.75 g/L, potassium pyrophosphate: 60 g/L), then the electroplated fine roughness copper nodule layer was impregnated in a chromic acid solution for about 10 to 15 seconds, and finally a N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (KBM-603) solution was sprayed thereto, wherein the organosilane solution concentration was 0.5 vol %. After spraying, the product was completed after being oven-dried at 105 C. for 5 minutes.

Experimental Example 2

[0018] The same preparation method as Experimental Example 1 was adopted, but the organosilane used was replaced with 3-aminopropyltriethoxysilane (KBE-903).

Experimental Example 3

[0019] The same preparation method as Experimental Example 1 was adopted, but the organosilane used was replaced with vinyltrimethoxysilane (KBM-1003).

Comparative Example 1

[0020] The same preparation method as Experimental Example 1 was adopted, but the organosilane spraying step was omitted, and the product was directly oven-dried at 105 C. for 5 minutes.

[0021] The copper foil products of Experimental Examples 1 to 3 and Comparative Example 1 respectively underwent a measurement of water contact angle and a peel strength test which the copper foils mentioned above were boned with the same type of high frequency prepregs. The results are presented in Table 1 below. Specifically, the peel strength was measured after hot pressing process. Moreover, the roughness sRq of the copper foil products of Experimental Examples 1 to 3 and Comparative Example 1 were measured by a white light interferometry (in accordance with the ISO25178 standard), and the results are presented in Table 1 below.

TABLE-US-00001 TABLE 1 Experimental Experimental Experimental Comparative Example 1 Example 2 Example 3 Example 1 Water 82.7 93.1 145 11.2 contact angle (degree) Peel strength 0.38 0.67 0.66 0.3 (kg/cm) sRq (m) 0.22 0.22 0.22 0.22

[0022] According to Table 1, the organosilane-treated surfaces (having a hydrophobic layer) had water contact angles greater than that of the surface without the organosilane treatment and exhibited more desirable peel strengths.

Experimental Example 4

[0023] The same method as Experimental Example 2 was adopted, but electroplating was performed with the ZnNi co-electroplating formula for 3 seconds.

Experimental Example 5

[0024] The same method as Experimental Example 2 was adopted, but electroplating was performed with the ZnNi co-electroplating formula for 5 seconds.

[0025] Surface compositions of the copper foil products of Experimental Example 2 and Experimental Examples 4 to 5 were respectively analyzed, and the results are presented in Table 2 below.

TABLE-US-00002 TABLE 2 Experimental Experimental Experimental Component Example 4 Example 2 Example 5 (g/dm.sup.2) (3 seconds) (4 seconds) (5 seconds) Zn 90-100 120-130 140-150 Ni 75-90 95-105 110-120 Mo 18-25 18-25 18-25 Cr 20-40 20-40 20-40 Si 30-40 30-40 30-40

[0026] According to Table 2, content ranges of components in the cases of electroplating for 3 to 5 seconds were, for example, 90-150 g/dm.sup.2 of zinc, 75-120 g/dm.sup.2 of nickel, and 20-40 g/dm.sup.2 of chromium.

Experimental Example 6

[0027] The same method as Experimental Example 2 was adopted, but the ZnNi co-electroplating time was altered, and the subsequent chromic acid and organosilane treatments were both identical (0.5 vol % of KBE-903). Peel strength variations after tests of acid resistance (impregnated in 18% HCl for 1 hour) and boiling water resistance (impregnated in boiling water for 2 hours) are presented in Table 3.

TABLE-US-00003 TABLE 3 0 2 3 5 seconds seconds seconds seconds As-received peel strength (kg/cm) 0.6 0.63 0.67 0.67 Peel strength after acid resistance 0.4 0.5 0.67 0.67 test (kg/cm) Peel strength after boiling 0.35 0.45 0.67 0.67 water resistance test (kg/cm)

[0028] According to Table 3, the copper foils undergoing the ultra-fine surface roughening process and the ZnNi co-electroplating for 3 seconds or more (namely, the copper foil surface included 90-150 g/dm.sup.2 of zinc, 75-120 g/dm.sup.2 of nickel, and 20-40 g/dm.sup.2 of chromium) all passed the acid resistance and boiling water resistance tests. The copper foils of which the surface zinc content was less than 90 g/dm.sup.2, the nickel content was less than 75 g/dm.sup.2, and the chromium content was less than 20 g/dm.sup.2 had peel strengths reduced to 0.6 kg/cm or less after the acid resistance and boiling water resistance tests due to insufficient acid resistance and heat resistance.

[0029] In summary of the above, in the embodiments of the disclosure, the fine roughness copper nodule layer with a small particle size is manufactured on the copper foil surface by using the ultra-fine surface roughening technique. The fine roughness copper nodule layer along with the specific ZnNi plating layer, rust-proof layer, and hydrophobic layer together form the copper foil for a high frequency circuit having a small surface roughness and a low surface alloying element content, which exhibits excellent bonding with the high frequency substrate material and is favorable for high frequency transmission.

[0030] Although the embodiments are already disclosed as above, these embodiments should not be construed as limitations on the scope of the disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations provided that they fall within the scope of the following claims and their equivalents.