Antioxidant copper-based alloy foil strip and surface treatment method thereof

Abstract

The invention discloses an antioxidant copper-based alloy foil tape. The surface of the foil tape is provided with a composite protective film layer; the composite protective film layer comprises a transition bottom layer formed by plasma electrolytic oxidation and a nanocrystalline tin-indium alloy hole sealing surface layer formed by electro-deposition from inside to outside; the total thickness of the composite protective film layer is 15-30 [mu] m. According to the invention, a composite structure of a plasma electrolytic oxidation bottom layer and a nano tin-indium alloy surface layer is created for the first time, so that the foil tape has excellent oxidation resistance and corrosion resistance through the synergistic effect of multiple mechanisms such as physical isolation, chemical passivation and electrochemical protection. Meanwhile, the conductive function is mainly borne by the high-conductivity nano metal layer on the surface layer, the bottom layer is designed to be extremely thin, and the conductivity is optimized through element doping, so that the influence of the composite film layer on the intrinsic conductivity of the substrate is reduced to an extremely low level; and the core contradiction that the protection performance and the conductivity are mutually restricted in the traditional surface treatment technology is successfully solved.

Description

Technical Field

[0001] In the field of metal materials and surface engineering technology, this invention specifically relates to an anti-oxidation copper-based alloy foil strip with excellent comprehensive performance and its surface treatment method, which is particularly suitable for the manufacturing of high-end electronic components. Background Technology

[0002] Copper-based alloy foils are widely used in precision electronics fields such as flexible circuit boards, current collectors for new energy batteries, and high-end connectors due to their excellent electrical conductivity, thermal conductivity, and machinability. However, copper is extremely prone to oxidation in high-temperature, high-humidity, and oxygen-containing environments, forming cuprous oxide or copper oxide, which leads to a sharp increase in contact resistance and signal transmission loss, seriously affecting the long-term reliability and service life of devices.

[0003] To improve the oxidation resistance of copper alloys, surface treatment technology is commonly used in the industry. Common methods include chemical passivation and surface plating. However, these traditional methods have significant limitations: chemical passivation films are thin and have poor wear resistance, making them prone to failure in complex processing or harsh environments, and chromates are toxic and have poor environmental performance; the adhesion between a single metal plating layer and the copper substrate is limited, making it prone to peeling during subsequent bending, stamping, and other advanced processing, and thinning the plating layer to maintain conductivity sacrifices protective performance; in particular, existing technologies struggle to achieve a breakthrough balance between the contradictory performance indicators of "ultra-high oxidation resistance" and "ultra-high conductivity retention"; furthermore, as electronic devices develop towards miniaturization, high frequency, and high power density, almost stringent requirements are placed on the adhesion, flexibility, and environmental stability of foil surface treatment layers. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides an antioxidant copper-based alloy foil strip and its surface treatment method.

[0005] Antioxidant copper-based alloy foil strip, including a composite protective film layer on the surface of the foil strip; the composite protective film layer includes, from the inside out, a transitional underlayer formed by plasma electrolytic oxidation and a nanocrystalline tin-indium alloy sealing surface layer formed by electrodeposition; the total thickness of the composite protective film layer is 15-30 μm.

[0006] As a further technical solution of the present invention, in the nanocrystalline tin-indium alloy sealing surface layer, the indium content is 20%-50% by mass, and its average grain size is 20-80 nanometers.

[0007] As a further technical solution of the present invention, after being placed in an environment of 85℃ / 85% relative humidity for 1000 hours, the surface contact resistance increases by less than 10%, and its volume conductivity is not less than 97% of the conductivity of the substrate.

[0008] As a further technical solution of the present invention, the substrate of the copper-based alloy foil strip is C7025, C18150 or Klfe-1 copper alloy.

[0009] A surface treatment method for anti-oxidation copper-based alloy foil strips includes the following steps: S1 performs degreasing, acid pickling activation and micro-etching pretreatment on copper-based alloy foil strips; S2 plasma electrolytic oxidation treatment: The pretreated foil strip is used as the anode and placed in an electrolyte containing silicates, phosphates, organic complexing agents and molybdates and / or tungstates. A high-frequency pulsed current is applied to perform oxidation treatment to form the transition underlayer. S3 Nano-tin-indium alloy electroplating: The foil strip treated in step S2 is used as the cathode and placed in a plating solution of methanesulfonate system. The nanocrystalline tin-indium alloy sealing surface layer is deposited using pulse electrodeposition technology.

[0010] As a further technical solution of the present invention, in step S2, the electrolyte comprises: sodium silicate 10-30 g / L, phosphate 5-15 g / L, organic carboxylic acid complexing agent 5-15 g / L, molybdate and / or tungstate 1-5 g / L; the pH value of the electrolyte is 9-11.

[0011] As a further technical solution of the present invention, in step S2, the parameters of the high-frequency pulse current are: current density 2-10 A / dm². 2 The pulse frequency is 500-2000Hz, the positive pulse duty cycle is 20-40%, and the processing time is 30-180 seconds.

[0012] As a further technical solution of the present invention, in step S3, the methanesulfonate system plating solution includes: Sn provided by stannous methanesulfonate. 2 ⁺20-50g / L, Indium methanesulfonate provides In 3 ⁺5-20g / L, methanesulfonic acid 80-200g / L, as well as grain refiners and brighteners.

[0013] As a further technical solution of the present invention, in step S3, the parameters of the pulse electrodeposition are: forward pulse current density 0.5-3.0 A / dm². 2 The process employs bidirectional pulses or periodic commutation pulses, with an electroplating time of 30-120 seconds and a plating solution temperature of 20-40℃.

[0014] A flexible circuit board, lithium-ion battery current collector, or high-frequency connector uses an antioxidant copper-based alloy foil strip.

[0015] In summary, the present invention has at least one of the following beneficial technical effects: 1. The pioneering composite structure of "plasma electrolytic oxidation underlayer + nano-tin-indium alloy surface layer" achieves excellent oxidation and corrosion resistance through the synergistic effect of multiple mechanisms, including physical isolation, chemical passivation, and electrochemical protection. Meanwhile, the conductivity is primarily provided by the highly conductive nano-metal layer on the surface. The underlayer is designed to be extremely thin and its conductivity is optimized through elemental doping, thus minimizing the impact of the composite film on the intrinsic conductivity of the substrate. This successfully resolves the core contradiction between protective and conductive properties in traditional surface treatment technologies. 2. The plasma electrolytic oxidation process enables the transition layer to form a strong metallurgical bond with the copper substrate, with a bonding force far exceeding that of physical adsorption or ordinary electrodeposition layers; the nanocrystalline tin-indium surface layer has excellent density and moderate plasticity; this "rigid-flexible" composite structure allows the overall film layer to withstand severe bending, stamping, stretching and other subsequent deep processing without cracking, peeling or flaking, showing extremely high process adaptability and long-term reliability. 3. This composite film structure provides long-term and stable protection for the substrate; under harsh environmental conditions such as high temperature, high humidity, and salt spray, the film can effectively block the penetration and erosion of corrosive media, maintain an extremely low contact resistance growth rate and a stable surface state, and significantly extend the service life and reliability of electronic components using this foil. 4. The entire process avoids the use of toxic and harmful substances such as chromates, and the electrolyte and plating solution system used is more environmentally friendly; the process flow is simple and controllable, suitable for continuous or roll-to-roll production, and has good prospects for industrial application and economic benefits. Detailed Implementation

[0016] The present application will be further described in detail below with reference to the embodiments.

[0017] This application designs an anti-oxidation copper-based alloy foil strip, the surface of which has a composite protective film layer; the composite protective film layer includes, from the inside out, a transitional underlayer formed by plasma electrolytic oxidation and a nanocrystalline tin-indium alloy sealing surface layer formed by electrodeposition; the total thickness of the composite protective film layer is 15-30 μm; in the nanocrystalline tin-indium alloy sealing surface layer, the indium mass percentage content is 20%-50%, and its average grain size is 20-80 nanometers; after being placed in an environment of 85℃ / 85% relative humidity for 1000 hours, the surface contact resistance increase rate is less than 10%, and its volume conductivity is not less than 97% of the substrate conductivity; the substrate of the copper-based alloy foil strip is C7025, C18150 or Klfe-1 copper alloy.

[0018] A surface treatment method for anti-oxidation copper-based alloy foil strips includes the following steps: S1. Pre-treatment of copper-based alloy foil strips by degreasing, pickling activation and micro-etching; S2. Plasma electrolytic oxidation treatment: The pretreated foil strip is used as the anode and placed in an electrolyte containing silicates, phosphates, organic complexing agents and molybdates and / or tungstates. A high-frequency pulsed current is applied to perform oxidation treatment to form the transition underlayer. S3. Electroplating of nano-tin-indium alloy: The foil strip treated in step S2 is used as the cathode and placed in a plating solution of methanesulfonate system. The nanocrystalline tin-indium alloy sealing surface layer is deposited using pulse electrodeposition technology. In step S2, the electrolyte comprises: sodium silicate 10-30 g / L, phosphate 5-15 g / L, organic carboxylic acid complexing agent 5-15 g / L, molybdate and / or tungstate 1-5 g / L; the pH value of the electrolyte is 9-11; in step S2, the parameters of the high-frequency pulse current are: current density 2-10 A / dm³. 2 The pulse frequency is 500-2000Hz, the positive pulse duty cycle is 20-40%, and the processing time is 30-180 seconds; in step S3, the methanesulfonate system plating solution contains: Sn provided by stannous methanesulfonate. 2 ⁺20-50g / L, Indium methanesulfonate provides In 3 The additives include ⁺5-20 g / L, methanesulfonic acid 80-200 g / L, grain refiner, and brightener; in step S3, the parameters for pulse electrodeposition are: forward pulse current density 0.5-3.0 A / dm³. 2 The process employs bidirectional pulses or periodic commutation pulses, with an electroplating time of 30-120 seconds and a plating solution temperature of 20-40℃.

[0019] Example 1 Substrate C7025 (Cu-Ni-Si) copper alloy foil strip with a thickness of 0.1mm.

[0020] Surface treatment process Pretreatment: alkaline degreasing (60℃, 5min) → 10% sulfuric acid activation (30s) → ammonium persulfate micro-etching (50g / L, 45s) → thorough water rinsing between each step; PEO treatment Electrolyte: Sodium silicate 20g / L, sodium dihydrogen phosphate 10g / L, trisodium citrate 8g / L, ammonium molybdate 3g / L, pH=10.5; Parameters: Current density 3A / dm 2 The pulse frequency is 1000Hz, the duty cycle is 25%, the processing time is 90s, and the temperature is 25℃. A dense gray-black substrate with a thickness of approximately 10 μm was obtained; Nano Sn-In electroplating Plating solution: Sn 2 ⁺(from MSAtin) 40g / L, In3 ⁺ (from MSAindium) 15g / L, methanesulfonic acid 180g / L, grain refiner 1.5g / L, pH=1.5; Parameters: Pulse electroplating, forward current density 2.0A / dm³ 2 (Ton=2.0ms), reverse current density -0.5A / dm 2 (Toff=0.5ms), time 70s, temperature 30℃; A nanocrystalline coating with a thickness of approximately 12 μm and a bright silver-white color was obtained (average grain size ~50 nm, In content ~30 at.%). Final product A copper alloy foil strip with a composite film layer on the surface with a total thickness of approximately 22 μm; Example 2 The difference from Example 1 is that the PEO treatment time was adjusted to 60s (bottom layer ~8μm), and the Sn-In electroplating time was adjusted to 90s (top layer ~16μm); the total film thickness is approximately 24μm. Comparative Example 1 (Conventional Chromate Passivation) The substrate is the same as in Example 1. After pretreatment, it is treated in a standard chromate passivation solution (containing CrO3) at 40°C for 2 minutes, then washed with water and dried to form a colored passivation film (thickness <1μm). Comparative Example 2 (Single Chemical Nickel Plating) The substrate is the same as in Example 1; after pretreatment, it is plated in a commercial electroless nickel plating solution at 85°C for 15 minutes to obtain a nickel-phosphorus alloy coating with a thickness of about 5 μm. Comparative Example 3 (PEO treatment only) The substrate is the same as in Example 1; only the pretreatment and PEO steps of Example 1 are performed, without Sn-In electroplating; a single PEO oxide layer (approximately 10 μm thick) is obtained. Comparative Example 4 (Sn-In plating only on bare copper) The substrate is the same as in Example 1; after pretreatment, the Sn-In electroplating step of Example 1 is performed directly on the bare copper surface; a Sn-In plating layer with a thickness of about 12 μm is obtained; Performance Testing and Comparison The key performance tests were performed on the above samples, and the results are summarized in the table below: Test Project Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Untreated substrate Conductivity (%IACS) 63.5 63.3 58.5 15.0 32.0 63.8 65.0 (Retention rate) (97.7%) (97.4%) (90.0%) (23.1%) (49.2%) (98.2%) (100%) <![CDATA[Weight gain (mg / cm) after oxidation at 180°C for 100 h 2 )]]> 0.21 0.23 0.78 0.15 0.95 0.35 2.35 Time to red rust appear in neutral salt spray (h) >500 >500 72 >500 48 240 8 Contact resistance increase at 85℃ / 85%RH for 1000 hours <8% <9% ~45% >200% >150% ~25% Failure Film state after 180° bending 10 times intact intact Localized peeling Cracks at the bend Powdering and peeling peeling - Test results show that the samples of the present invention maintain extremely high conductivity (>97%), while exhibiting significantly better oxidation resistance, corrosion resistance, environmental stability, and flexibility than the other pairs. In particular, the overall performance is superior, demonstrating the synergistic advantages of the composite structure design of the present invention.

[0021] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

[0022] Working principle 1. Plasma electrolytic oxidation (PEO) substrate: Constructing a strong "molecular anchor" and "intrinsic diffusion barrier" This is the primary innovation of the present invention, namely, successfully adapting the PEO technology, which is usually used for valve metals such as aluminum and magnesium, to copper substrates and overcoming the traditional problems of poor conductivity and weak bonding of copper oxides. In-situ metallurgical bonding mechanism: Under a high-voltage pulsed electric field, micro-region plasma discharge occurs on the surface of the copper alloy, generating instantaneous high temperature and pressure (locally reaching thousands of degrees Celsius); under these extreme conditions, copper atoms on the substrate surface are ionized and react with oxygen anions (O3) that migrate to the interface from the electrolyte. 2 ⁻), Silicate (SiO3) 2 ⁻), Phosphate (PO4) 3 Violent electrochemical-plasma chemical reactions occur; the generated oxides (such as CuO, Cu2O, and composite silicates and phosphates) are not simply adhered, but under the "micro-forging" effect of the discharge micro-region, they are sintered and interdiffused with the copper substrate in situ, forming a transition layer mainly composed of chemical bonds and micro-metallurgical bonding; this bonding method fundamentally solves the adhesion bottleneck between the film layer and the soft copper foil; Densification and Functional Element Doping Mechanism: By employing a "soft" plasma oxidation mode characterized by "high frequency, short duty cycle, and moderate current density," the micro-arc discharge is made small, uniform, and brief, preventing the molten oxide from being violently ejected by gas and forming a porous structure. This results in a dense amorphous / nanocrystalline composite structure with low porosity (<5%). This structure lacks continuous grain boundaries, effectively hindering ion diffusion paths. Crucially, molybdate or tungstate ions introduced in the electrolyte are reduced or doped into the oxide layer during the discharge process. 6 ⁺ / W 6 High-valence ions such as ⁺ can occupy lattice sites or interstitial sites in copper oxides, significantly reducing the concentration and mobility of oxygen vacancies in the lattice. This thermodynamically and kinetically inhibits the rate of outward diffusion of copper ions and inward diffusion of oxygen ions, thus constructing a strong intrinsic antioxidant "wall".

[0023] 2. Nanocrystalline Tin-In (Sn-In) Alloy Surface Layer: Constructing an Intelligent "Conductive Sealing Layer" and "Dynamic Sacrificial Protection Layer" The second core innovation of this invention is that a functional metal coating with nanostructure and specific components is integrated on the PEO base layer, realizing the functional zoning and synergy of protection and conductivity. Nanocrystalline Physical Sealing and High Conductivity Mechanism: Using pulsed electrodeposition technology, Sn-In alloy layers with grain sizes of 20-80 nanometers were obtained under precisely controlled plating bath composition and process parameters. The nanocrystalline structure means an extremely large number of grain boundaries and an exceptionally dense grain arrangement, like a non-porous wall built of "nano-bricks," which can perfectly seal any possible micro-cracks or pores in the underlying PEO layer, achieving the ultimate barrier of physical isolation. At the same time, Sn and In are excellent conductors. Although the nanocrystalline structure increases grain boundaries, the electron scattering effect is optimized due to the extremely small grain size, and the overall coating is continuous and uniform, providing an excellent electron conduction path. More importantly, this metal surface layer forms a low-resistance ohmic contact with external interfaces (such as solder joints), ensuring interfacial conductivity efficiency. Sacrificial anode and dynamic self-protection mechanism: By controlling the indium (In) content in the coating (20-50wt%), the electrode potential of the Sn-In alloy is optimized, making it more negative relative to the copper substrate, thus becoming an anodic coating for copper. When the composite film is locally damaged under extreme mechanical or chemical action, the exposed Sn-In alloy will preferentially undergo oxidation corrosion as a sacrificial anode. Its corrosion products can temporarily cover and seal the damage points, thereby actively protecting the copper substrate, which acts as the cathode, from corrosion. This "self-sacrificing" electrochemical protection provides the film with a dynamic and active second layer of protection.

[0024] 3. Synergistic effect mechanism of "PEO bottom layer / Sn-In surface layer" This is the fundamental reason why the present invention achieves a performance leap of "1+1>2", which reflects a systematic design concept; Synergistic mechanical properties: The inner layer is a high-hardness, high-modulus ceramic-based PEO layer, providing support and scratch resistance; the outer layer is a nano-metal layer with certain plasticity and toughness, which can buffer stress; the combination of the two forms a mechanical gradient structure of "hard core and soft shell", so that when the composite film layer is subjected to deformation such as bending and wrinkling, it will not crack brittlely like a pure ceramic layer, nor will it be easily scratched like a pure metal coating. Synergistic protective functions: The PEO layer, as a long-lasting and static intrinsic diffusion barrier, slows down the oxidation and corrosion process from the inside of the material; the Sn-In layer, as an immediate and dynamic physical isolation and electrochemical protection layer, provides immediate protection from the external environment and damage response; the two together form a multi-dimensional and three-dimensional defense system in the time and space dimensions. Synergistic Electrical Functions: This invention innovatively employs a functional partitioning design of "inner insulating / semiconductor (PEO) layer and outer good conductor (Sn-In) layer"; the conductivity task is mainly undertaken by the thick outer good conductor metal layer, and its performance is not dominated by the properties of the thin inner layer; while the thin and dense inner PEO layer focuses on providing bonding and basic protection, and its contribution to the overall resistance is minimized by precisely controlling the thickness and element doping; this design philosophy cleverly resolves the direct conflict between protection and conductivity in traditional single film layers; In summary, this invention is not simply a combination of two processes, but rather a result of a deep understanding of the formation mechanism and functional characteristics of each layer, and a meticulous design of the structure and composition. Ultimately, it achieves the orderly integration and synergistic effect of multiple protection mechanisms and conductive pathways at the microscale, thereby constructing an intelligent composite defense line on the surface of the copper-based alloy foil strip that is both "unbreakable" and "unobstructed".

Claims

1. An anti-oxidation copper-based alloy foil strip, characterized in that, The foil strip has a composite protective film layer on its surface; the composite protective film layer includes, from the inside out, a transitional underlayer formed by plasma electrolytic oxidation and a nanocrystalline tin-indium alloy sealing surface layer formed by electrodeposition; the total thickness of the composite protective film layer is 15-30 μm.

2. The antioxidant copper-based alloy foil strip according to claim 1, characterized in that: In the nanocrystalline tin-indium alloy sealing surface layer, the indium content is 20%-50% by mass, and its average grain size is 20-80 nanometers.

3. The surface treatment method for the anti-oxidation copper-based alloy foil strip according to claim 1 or 2, characterized in that, Includes the following steps: S1 performs degreasing, acid pickling activation and micro-etching pretreatment on copper-based alloy foil strips; S2 plasma electrolytic oxidation treatment: The pretreated foil strip is used as the anode and placed in an electrolyte containing silicates, phosphates, organic complexing agents and molybdates and / or tungstates. A high-frequency pulsed current is applied to perform oxidation treatment to form the transition underlayer. S3 Nano-tin-indium alloy electroplating: The foil strip treated in step S2 is used as the cathode and placed in a plating solution of methanesulfonate system. The nanocrystalline tin-indium alloy sealing surface layer is deposited using pulse electrodeposition technology.

4. The surface treatment method for the anti-oxidation copper-based alloy foil strip according to claim 3, characterized in that: In step S2, the electrolyte comprises: sodium silicate 10-30 g / L, phosphate 5-15 g / L, organic carboxylic acid complexing agent 5-15 g / L, molybdate and / or tungstate 1-5 g / L; the pH value of the electrolyte is 9-11.

5. The surface treatment method for the anti-oxidation copper-based alloy foil strip according to claim 3 or 4, characterized in that: In step S2, the parameters of the high-frequency pulse current are: current density 2-10 A / dm³. 2 The pulse frequency is 500-2000Hz, the positive pulse duty cycle is 20-40%, and the processing time is 30-180 seconds.

6. The surface treatment method for the antioxidant copper-based alloy foil strip according to claim 3, characterized in that: In step S3, the methanesulfonate system plating solution contains: Sn provided by stannous methanesulfonate. 2 ⁺20-50g / L, Indium methanesulfonate provides In 3 ⁺5-20g / L, methanesulfonic acid 80-200g / L, as well as grain refiners and brighteners.

7. The surface treatment method for the anti-oxidation copper-based alloy foil strip according to claim 3 or 6, characterized in that: In step S3, the parameters for pulse electrodeposition are: forward pulse current density 0.5-3.0 A / dm³. 2 The process employs bidirectional pulses or periodic commutation pulses, with an electroplating time of 30-120 seconds and a plating solution temperature of 20-40℃.

8. The antioxidant copper-based alloy foil strip according to claim 1 or 2, characterized in that, After being placed in an environment of 85℃ / 85% relative humidity for 1000 hours, the surface contact resistance increases by less than 10%, and its volume conductivity is not less than 97% of the conductivity of the substrate.

9. The antioxidant copper-based alloy foil strip according to claim 1 or 2, characterized in that, The substrate of the copper-based alloy foil strip is C7025, C18150 or Klfe-1 copper alloy.

10. A flexible circuit board, lithium-ion battery current collector, or high-frequency connector, characterized in that, It uses the antioxidant copper-based alloy foil strip as described in any one of claims 1, 2, 8 or 9.