Electrolytic copper foil for two-layer flexible copper-clad plate and surface treatment process of electrolytic copper foil

Abstract

The invention relates to the field of electrolytic copper foil processing and application, and discloses an electrolytic copper foil for a two-layer flexible copper-clad plate and a surface treatment process of the electrolytic copper foil, the Rz of the copper foil is smaller than 2.0 microns, the interface area expansion ratio Sdr is smaller than 30%, the number of times of bending after annealing is larger than 700, and the thickness of the copper foil is 9-18 microns. According to the preparation method of the flexible copper foil for the two-layer flexible copper-clad plate, the electrolytic copper foil with high bending resistance and low roughness can be prepared, and the defect that the requirements for improving the bending resistance and reducing the roughness of the conventional electrolytic copper foil cannot be compatible at the same time is overcome.

Description

Technical Field

[0001] The present invention relates to the field of electrolytic copper foil processing and applications, and particularly to an electrolytic copper foil for a two-layer flexible copper clad laminate and its surface treatment process. Background Art

[0002] Flexible copper clad laminates are divided into two-layer flexible copper clad laminates (2LFCCL) and three-layer flexible copper clad laminates (3L FCCL) according to whether there is an adhesive layer between the film and the copper foil. Compared with three-layer flexible copper clad laminates, two-layer flexible copper clad laminates have more excellent antioxidant properties, heat resistance, and dimensional stability, and are developing rapidly. They are mainly used in the manufacture of higher-end flexible boards, such as rigid-flex boards, COF, etc.

[0003] A two-layer flexible copper clad laminate usually consists of an insulating base film and a copper foil. Copper foils are divided into two categories: electrolytic copper foils and rolled copper foils. The advantage of electrolytic copper foils is that the copper foil is formed by electro-deposition using a copper sulfate electrolyte under the action of an externally applied direct current. The crystal structure arrangement of its copper particles is uniform, and the formed coating and the final surface after surface treatment are relatively flat. In addition, the copper particle structure is prone to form vertical line edges during the etching process, which is beneficial for the production of fine conductors.

[0004] The precipitation mechanism of electrolytic copper can be divided into a "nucleation process" that causes the precipitation of crystal nuclei and a "crystal growth process" in which the precipitated crystal nuclei grow. Adding specific additives will cause copper to grow under the condition that the nucleation rate is faster than the crystal growth rate, resulting in a copper foil with lower roughness. The lower the surface roughness of the copper foil, the lower the thickness of the adhesive layer required when manufacturing the FCCL, and the reduction of the total thickness is beneficial for improving the flexural performance. On the other hand, when the FCCL is bent and fractured, the copper foil always fractures at the grain boundary position. The copper foil with a larger surface roughness has a coarser crystal structure in the raw foil before treatment, and there are more obvious gaps at the peak and valley positions, making it more prone to fracture during repeated bending. However, if the content of the organic additive is too high, the nucleation process will be in an advantageous position, and then the crystal grain boundaries will contain impurities from the additive. After heat treatment, due to the influence of the impurities, a copper foil that can hardly be recrystallized will be formed. After lamination, the grain size of the copper foil is relatively small, which will cause a significant increase in the number of grain boundaries and dislocations in the crystal, thereby reducing the ability of the copper foil to resist fracture during repeated bending, which will seriously deteriorate the flexural performance of the copper foil. A two-layer flexible copper clad laminate is generally mainly composed of a PI film + TPI + copper foil laminated together. Copper foils with low roughness and low copper tooth size are of great value for protecting the TPI from being pierced.

[0005] Therefore, it is necessary to provide an electrolytic copper foil surface treatment process with low surface roughness of the treated surface, excellent flexural properties, and applicable to two-layer flexible copper clad laminates. Chinese Patent CN102618902B discloses a surface treatment process for copper foil suitable for flexible copper clad laminates. In the blackening step, a black ultra-fine coating layer that can improve the corrosion resistance and etching property of the copper foil is formed on the copper foil surface by adding a blackening agent. The surface roughness Rz of the prepared copper foil is ≤ 2.5 μm. This patent mainly focuses on improving the oxidation resistance of flexible copper foil and does not optimize and improve the roughness of the copper foil. Chinese Patent CN110093637A adds additives such as mercapto-containing nitrogen heterocyclic compounds and organic divalent sulfur compounds in the raw foil process to produce copper foil with a roughness Rz ≤ 2.0 μm. This patent mainly focuses on reducing the roughness of flexible copper foil and improving the tensile strength and elongation, and does not test the specific bending performance of the copper foil. Summary of the Invention

[0006] The main object of the present invention is to solve the technical problem that the requirements of improving the bend resistance performance and reducing the roughness of conventional electrolytic copper foil in the prior art cannot be compatible at the same time. The technical solution adopted by the present invention is: an electrolytic copper foil for two-layer flexible copper clad laminates, characterized in that the copper foil has Rz < 2.0 μm, an interface area expansion ratio Sdr < 30%, the number of bendable times after annealing (180 °C for 1 hour) > 700 times, and the thickness of the copper foil is 9 - 18 μm.

[0007] The present invention also relates to an electrolytic copper foil surface treatment process for two-layer flexible copper clad laminates, including the following steps:

[0008] Step 1, removing the oxide layer on the surface of the electrolytic copper foil raw foil to be surface-treated through a pickling tank;

[0009] Step 2, performing roughening electroplating in an electroplating solution containing roughening additives to promote the growth of copper nodules on the surface of the raw foil. The roughening additive composition consists of two components, sodium phosphotungstate and sodium gluconate, wherein the concentration of sodium phosphotungstate is: 3 - 20 mg / L, and the concentration of sodium gluconate is: 3 - 30 mg / L;

[0010] Step 3, performing a curing treatment to firmly bond the roughened copper nodules to the raw foil substrate; Steps 2 and 3 are repeated 2 - 3 times;

[0011] Step 4, performing blackening nickel plating, ashing zinc plating, and passivation chromium plating;

[0012] Step 5: Double-sided coating with silane coupling agent and drying. The silane coupling agent is selected from one or a combination of two of epoxy group, amino group, acrylic group, vinyl group, and mercapto group. The concentration of the configured silane coupling agent is 0.1-1.5 wt%, the hydrolysis time is 1-5 hours, the hydrolysis temperature is 20-50 °C, the hydrolysis solvent is one or a mixture of water / ethanol, and the ethanol concentration is 0.1-1.5 wt%.

[0013] In the said Step 1, the thickness of the electrolytic copper foil raw foil is 9-18 μm, and Rz ≤ 1.5 μm.

[0014] The composition of the electroplating solution containing roughening additive in the said Step 2 is Cu 2+ : 10-20 g / L, H2SO4: 100-200 g / L; the current density is 20 A-80 A / dm 2 .

[0015] In the said Step 2, an anode curtain is added to the anode plate during roughening electroplating.

[0016] The composition of the electroplating solution used for curing treatment in the said Step 3 is Cu 2+ : 40-60 g / L, H2SO4: 100-200 g / L; the current density for curing treatment is 15 A-70 A / dm 2 .

[0017] The current density for blackening nickel plating in the said Step 4 is 0.3-1.0 A / dm 2 , and the electroplating time is 6-15 S.

[0018] The current density for ashing zinc plating in the said Step 4 is 0.3-1.0 A / dm 2 , and the electroplating time is 6-15 S.

[0019] The current density for passivation chromium plating in the said Step 4 is 0.3-1.0 A / dm 2 , and the electroplating time is 6-15 S.

[0020] Other processes in the said Steps 1 to 5 are processed with reference to the conventional copper foil surface treatment process.

[0021] Beneficial effects:

[0022] The mixing ratio of sodium phosphotungstate and sodium gluconate in the present invention can most significantly inhibit the growth of copper crystal nuclei. The inhibitory effects of the two additives combined with the double-sided silane coating play an important role in the grain stability after annealing. By controlling the concentrations of the special additives for coarsening 1 and the three ions of zinc, nickel, and cobalt in the non-copper metal coating, as well as optimizing the silane coating process, the flexural performance and antioxidant performance of the flexible copper foil are significantly improved simultaneously. For the 12-μm copper foil, Rz < 2.0 μm, and the interfacial area expansion ratio Sdr < 30%. After annealing (180 °C for 1 hour), the number of bendable times > 700 times. It solves the problem that the requirements for improving the bend resistance performance and reducing the roughness of conventional electrolytic copper foils cannot be compatible at the same time. Brief Description of the Drawings

[0023] Figure 1 Schematic diagram of the surface of the copper foil treated in Example 1;

[0024] Figure 2 SEM image of the copper foil treated in Comparative Example 1;

[0025] Figure 3 Electron microscope of the copper foil section treated in Example 1;

[0026] Figure 4 IPF diagram of the cross-section EBSD of the copper foil treated in Example 1. Detailed Description of the Invention

[0027] The terms "first", "second", "third", "fourth", etc. (if any) in the specification, claims and above-mentioned drawings of the present invention are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence. In addition, the terms "comprising" or "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device that includes a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0028] Example 1

[0029] Use a raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 and perform the following steps according to the surface treatment method described in the present invention.

[0030] Step A Pickling pretreatment: Remove the oxide layer on the surface of the electrolytic copper foil raw foil to be treated through a pickling tank. The process parameters are as follows:

[0031] Cu 2+ = 10 g / L

[0032] H2SO4 = 140 g / L

[0033] Temperature: 28°C

[0034] Flow rate: 10m 3 / h

[0035] Pretreatment time: 8S;

[0036] Step B Roughening treatment: The electrolytic copper foil passes through the roughening treatment tank to promote the growth of copper nodules on the surface of the electrolytic copper foil and increase the contact area with the substrate. The key performance indicators are as follows:

[0037] Cu 2+ = 12g / L

[0038] H2SO4 = 140g / L

[0039] Electrolysis current density: 60A / dm 2

[0040] Additive formula: Sodium phosphotungstate, Sodium gluconate;

[0041] Additive concentration: Sodium phosphotungstate 10mg / L, Sodium gluconate 13mg / L;

[0042] Roughening solution flow rate: 10m 3 / h

[0043] Roughening solution temperature: 28°C

[0044] Electroplating time: 7S

[0045] Step C Curing electroplating: The copper foil after step B is subjected to curing treatment to make the copper nodules grown by roughening bond more firmly with the copper foil substrate. The key performance indicators are as follows:

[0046] Cu 2+ = 50g / L

[0047] Electrolysis current density: 70A / dm 2

[0048] Curing solution flow rate: 10m 3 / h

[0049] Curing solution temperature: 50°C

[0050] Electroplating time: 7S

[0051] Step D: Repeat steps B and C 2 times to increase the number and size of the copper nodules after treatment;

[0052] Step E Blackening treatment: Deposit a layer of Ni with a content of 5mg / ㎡ on the surface of the foil after rough curing to provide better chemical corrosion resistance for the copper foil. The process parameters are as follows:

[0053] K4P2O7 = 85 g / L

[0054] NiSO4·6H2O = 4.5 g / L

[0055] Electric current density during energization: 0.5 A / dm 2

[0056] Blackening solution flow rate: 7 m 3 / h

[0057] Blackening solution temperature: 40 °C

[0058] pH of blackening solution = 8.5

[0059] Electroplating time: 7 S

[0060] Step F, ashing treatment: The copper foil after blackening treatment is electroplated in a complex solution system of potassium pyrophosphate and zinc sulfate. A layer of Zn with a content of 35 mg / ㎡ is electroplated on both the smooth side and the matte side of the copper foil to provide high-temperature oxidation resistance. The process parameters are as follows:

[0061] K4P2O7 = 85 g / L

[0062] ZnSO4·6H2O = 5.5 g / L

[0063] Electric current density during energization: 1.0 A / dm 2

[0064] Ashing solution flow rate: 7 m 3 / h

[0065] Ashing solution temperature: 40 °C

[0066] pH of ashing solution = 8.5

[0067] Electroplating time: 7 S

[0068] Step G, passivation treatment: The copper foil after blackening treatment is electroplated in a passivation solution containing chromic anhydride. A layer of Cr with a trace amount of about 10 mg / ㎡ is electroplated on both the smooth side and the matte side of the copper foil to provide normal-temperature oxidation resistance. The process parameters are as follows:

[0069] Cr 6+ = 1.5 g / L

[0070] Electric current density during energization: 0.3 A / dm 2

[0071] Passivation solution flow rate: 7 m 3 / h

[0072] Passivation solution temperature: 35 °C

[0073] pH of passivation solution = 11

[0074] Electroplating time: 7S

[0075] Step H, coating of silane: By combining spraying and roller coating, a layer of silane coupling agent is coated on both the treated surface and the non-treated surface of the copper foil to enhance the chemical bonding force between the copper foil and the substrate and the crystal structure stability after high-temperature annealing. The process parameters are as follows:

[0076] Type of silane: epoxy silane

[0077] Si content = 1200mg / L

[0078] The silane solution is clear and transparent;

[0079] Silane coating method: double-sided coating;

[0080] Step I, drying: Remove the residual moisture on the foil surface and further promote the coupling reaction between the silane coupling agent and the hydroxyl groups on the copper foil surface.

[0081] The product is tested by electron microscopy, and the results are as Figure 1 , it can be seen that the copper nodules are evenly distributed, and the growth inhibition effect at the top of the copper nodules is obvious. For the copper tooth height of the product, the results are as Figure 3 , it can be seen that the copper tooth size < 2.0 μm and is evenly distributed. The cross-section of the product after ion milling is analyzed by EBSD, and the results are as Figure 4 , it can be seen that after the surface treatment of the product, the crystal structure is mainly columnar crystals, and the smooth surface mainly grows small blocky crystals.

[0082] Example 2

[0083] Use a raw foil with a thickness of 12μm and a basis weight of 97g / m 2 for treatment. The key process parameters are as follows:

[0084] Step B:

[0085] Additive formula: sodium phosphotungstate

[0086] Additive concentration: sodium phosphotungstate 10mg / L

[0087] All other process parameters and steps are the same as in Example 1.

[0088] Example 3

[0089] Use a raw foil with a thickness of 12μm and a basis weight of 97g / m 2 for treatment. The key process parameters are as follows:

[0090] Step B:

[0091] Additive formula: sodium gluconate

[0092] Additive concentration: Sodium gluconate 10 mg / L

[0093] All other process parameters and steps are the same as those in Example 1.

[0094] Example 4

[0095] Using raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 The key process parameters are as follows:

[0096] Step H: The coating method of silane is single-sided coating (only coating the treated surface of the copper foil);

[0097] All other process parameters and steps are the same as those in Example 1.

[0098] Example 5

[0099] Using raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 for treatment, the key process parameters are as follows:

[0100] Step B:

[0101] Additive formula: Sodium phosphotungstate, sodium gluconate;

[0102] Additive concentration: Sodium phosphotungstate 5 mg / L, sodium gluconate 20 mg / L;

[0103] All other steps are the same as those in Example 1.

[0104] Example 6

[0105] Using raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 for treatment, the key process parameters are as follows:

[0106] Step B:

[0107] Additive formula: Sodium phosphotungstate, sodium gluconate;

[0108] Additive concentration: Sodium phosphotungstate 10 mg / L, sodium gluconate 40 mg / L;

[0109] All other steps are the same as those in Example 1.

[0110] Comparative Example 1

[0111] Using raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 for treatment,

[0112] Step B:

[0113] Additive formula: No additive is added

[0114] All other process parameters and steps are the same as those in Example 1.

[0115] Comparative Example 2 (Changing the Silane Coating Method)

[0116] Treat the raw foil with a thickness of 12 μm and a basis weight of 97 g / m 2 ;

[0117] Step B:

[0118] Additive formula: No additives are added

[0119] Step H: The silane coating method is single-sided coating (only the treated surface of the copper foil is coated);

[0120] All other process parameters and steps are the same as those in Example 1.

[0121] All other steps are the same as those in Example 1.

[0122] To more intuitively understand the process parameters of the embodiments and comparative examples of the present invention, the differences between each embodiment and the comparative example are given in Table 1.

[0123] Table 1 Differences in Process Parameters between Embodiments and Comparative Examples

[0124]

[0125] The specific data of the embodiments and control examples are shown in Table 1. Relevant physical property tests were carried out on the copper foils prepared in the above Examples 1-6 and Comparative Examples 1-2. The roughness test (Rz) was carried out according to the test method IPC-TM-650, and the Rz value of the rough surface of the copper foil was measured using a Mitutoyo portable roughness meter SJ-210 made in Japan. The tensile strength and elongation tests were carried out according to the test method IPC-TM-650, and the test results were obtained using an AGS-X type tensile testing machine manufactured by SHIMADZU CORPORATION. The bending resistance performance test was obtained using an SG-ICP01 PCB bending resistance performance tester prepared by Jin Ge Testing Instruments. The relevant physical property test results of the 12 μm copper foils prepared in Examples 1-6 and Comparative Examples 1-2 are shown in Table 2.

[0126] Table 2

[0127]

[0128]

[0129] By comparing and analyzing the test results in Table 1, it can be seen that the additive combination and the silane coating process of the present invention can balance the two key parameters of roughness and flexural performance simultaneously compared with the conventional electrolytic copper foil production process. The number of bending resistance times of the prepared 12μm flexible raw foil after high-temperature annealing is greater than 700 times. Preferably, in the best embodiment, the roughness can reach 1.8μm and the number of bending resistance times can reach 768 times. At the same time, the copper foil can still maintain good tensile strength and elongation. In the best embodiment, the mixing ratio of sodium phosphotungstate and sodium gluconate can most significantly inhibit the growth of copper crystal nuclei. The inhibitory effects of the two additives combined with the double-sided silane coating play an important role in the grain stability after annealing, and the best effect is obtained in this embodiment. The method for preparing a flexible copper foil for a two-layer flexible copper clad laminate provided by the present invention can prepare an electrolytic copper foil with high bending resistance performance and low roughness, and solves the problem that the requirements of improving the bending resistance performance and reducing the roughness of the conventional electrolytic copper foil cannot be compatible at the same time.

[0130] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An electrolytic copper foil for a two-layer flexible copper clad laminate, characterized in that, The copper foil has Rz < 2.0 μm, an interfacial area expansion ratio Sdr < 30%, the number of bendable times after annealing > 700 times, and the thickness of the copper foil is 9 - 18 μm.

2. A surface treatment process for electrolytic copper foil used in two-layer flexible copper clad laminates, characterized in that, It includes the following steps: Step 1, removing the oxide layer on the surface of the electrolytic copper foil raw foil to be surface-treated; Step 2, performing roughening electroplating in an electroplating solution containing a roughening additive to promote the growth of copper nodules on the surface of the raw foil. The roughening additive consists of 3 - 20 mg / L of sodium phosphotungstate and 3 - 30 mg / L of sodium gluconate; Step 3, curing treatment, adding a curing additive to firmly bond the roughened copper nodules to the raw foil substrate; Steps 2 and 3 are repeated 2 - 3 times; Step 4, performing blackening nickel plating treatment, ashing zinc plating treatment, and passivation chromium plating treatment; Step 5, through the combination of spraying and roller coating, a layer of silane coupling agent is coated on both the treated surface and the non-treated surface of the copper foil. After the silane coupling agent is hydrolyzed, it is dried to obtain the treated copper foil; The treated copper foil has Rz < 2.0 μm, an interfacial area expansion ratio Sdr < 30%, the number of bendable times after annealing > 700 times, and the thickness of the copper foil is 9 - 18 μm.

3. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, The silane coupling agent is selected from one or more of epoxy group silane coupling agents, amino group silane coupling agents, acrylic group silane coupling agents, vinyl group silane coupling agents, and mercapto group silane coupling agents; the concentration of the silane coupling agent is 0.1 - 1.5 wt%, the hydrolysis time is 1 - 5 hours, the hydrolysis temperature is 20 - 50 °C, the hydrolysis solvent is one or a mixed solution of water / ethanol, and the ethanol has a concentration of 0.1 - 1.5 wt%.

4. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, In Step 1, the thickness of the electrolytic copper foil raw foil is 9 - 18 μm, and Rz ≤ 1.5 μm.

5. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, The composition of the electroplating solution containing the roughening additive in the second step is Cu 2+ : 10 - 20 g / L, H2SO4: 100 - 200 g / L; the current density is 20 - 80 A / dm 2 .

6. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, wherein, When performing roughening electroplating in Step 2, an anode curtain is added to the anode plate.

7. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, The composition of the electroplating solution used for the curing treatment in the third step is Cu 2+ : 40 - 60 g / L, H2SO4: 100 - 200 g / L; the current density for the curing treatment is 15 - 70 A / dm 2 .

8. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, In the fourth step, the current density of black nickel plating is 0.3 - 1.0 A / dm 2 , and the electroplating time is 6 - 15 s.

9. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, In the fourth step, the current density for ashing galvanization is 0.3 - 1.0 A / dm 2 , and the electroplating time is 6 - 15 s.

10. The surface treatment process of the electrolytic copper foil for a two-layer flexible copper clad laminate according to claim 2, characterized in that, The current density of passivation chromium plating in the fourth step is 0.3 - 1.0 A / dm 2 , and the electroplating time is 6 - 15 s.

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