Punched tin-plated copper strip and preparation method thereof

Abstract

The invention relates to the technical field of electronic materials, and discloses a punched tin-plated copper strip and a preparation method thereof.The punched tin-plated copper strip comprises a base material, a transition layer is arranged on the outer wall of the base material, a tin-plated layer is arranged on the outer wall of the transition layer, a passivation layer is arranged on the outer wall of the tin-plated layer, and punched holes are evenly distributed in the base material. The height of burrs on the edge of the punched hole does not exceed 5 micrometers, the thickness of the transition layer ranges from 0.2 micrometer to 0.5 micrometer, the thickness of the tin coating ranges from 1.5 micrometers to 3 micrometers, and the thickness of the passivation layer ranges from 0.1 micrometer to 0.3 micrometer. A multi-layer composite structure is adopted, the lattice constant of a transition layer is between the lattice constant of a copper base material and a pure tin layer, the mismatch degree is 2.8%, the bonding strength is larger than or equal to 15 MPa, the interface thermal stress is reduced by 30%-40%, the situation that a tin coating is stripped due to the difference of thermal expansion coefficients is avoided, the tin coating gives consideration to conductivity and corrosion resistance, and the salt mist corrosion resistance time is prolonged through a passivation layer; therefore, the effect of enhancing the corrosion resistance and the thermal shock resistance of the copper strip can be achieved.

Description

Technical Field

[0001] The invention relates to the technical field of electronic materials, in particular to a punched tinned copper strip and a preparation method thereof. Background Art

[0002] In the modern electronics industry, as electronic products develop towards miniaturization, lightweight and high performance, the requirements for electronic connection materials are becoming increasingly higher. Copper strip, as a commonly used conductive material, is widely used in circuit boards, electronic components and other fields. The tinning process can improve the weldability and oxidation resistance of copper strip to a certain extent.

[0003] The welding performance of existing copper strips needs to be improved during use, and their antioxidant ability is weak. The tinning process can improve the weldability and antioxidant properties of copper strips to a certain extent, but the current tinned copper strips are prone to plating peeling off under thermal shock and low corrosion resistance after punching. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention provides a punched tinned copper strip and a preparation method thereof, which solves the problem that the copper strip coating falls off under thermal shock and has low corrosion resistance due to the punching process of the tinned copper strip.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a punched tinned copper strip, comprising a substrate, an outer wall of the substrate is provided with a transition layer, an outer wall of the transition layer is provided with a tin-plated layer, an outer wall of the tin-plated layer is provided with a passivation layer, the substrate is provided with evenly distributed punchings, the burr height of the punching edges does not exceed 5μm, the thickness of the transition layer is 0.2-0.5μm, the thickness of the tin-plated layer is 1.5-3μm, and the thickness of the passivation layer is 0.1-0.3μm.

[0006] By adopting the above technical solution: a transition layer with a tin content of 15-25wt% is formed on the surface of the substrate through an electroplating pre-plating process. The lattice constant of the transition layer (a=1.102nm) is between that of copper and tin, which can reduce the interface thermal stress by 30%-40%, and the bonding strength is not less than 15MPa. The thickness of the transition layer is controlled in the range of 0.2-0.5μm, which can balance the interface bonding force and thermal shock resistance. When the thickness is less than 0.2μm, the bonding force will be reduced. When it exceeds 0.5μm, micro cracks will be generated due to increased brittleness. The optimal thickness of the tinned layer is 1.5-3μm. Within this range, good conductivity (resistance does not exceed 0.5mΩ / cm 2), while maintaining good corrosion resistance. If the tin plating layer thickness is less than 1.5μm, the porosity will increase and affect the corrosion resistance. If it exceeds 3μm, the surface roughness will increase, which is not conducive to the uniform coverage of the passivation layer. The thickness of the passivation layer is controlled between 0.1-0.3μm, and the film density is 1.2-1.5g / cm 3 , the impedance modulus reaches 1.2×10 5 Ω·cm 2 Ω·cm 2 When the thickness of the passivation layer is 0.2μm, the salt spray corrosion resistance can reach more than 120 hours, thereby achieving the effect of enhancing the corrosion resistance and thermal shock resistance of the copper strip.

[0007] Preferably, the diameter of the punching holes in the substrate is 0.5-2.0 mm, the spacing between the punching holes is 0.5-2.0 mm, and the arrangement is uniform distribution or staggered arrangement.

[0008] Preferably, the transition layer is a copper-tin alloy layer, and the passivation layer is a bismuth-based alloy passivation film.

[0009] A method for preparing a punched tinned copper strip comprises the following steps:

[0010] S1. Raw material preparation: Select copper strips with a purity of not less than 99.95%, and perform surface cleaning and pretreatment;

[0011] S2. Punching: Use high-speed CNC punching machine and high-precision mold for punching, the punch speed is controlled at 5-15mm / s, and the punching pressure is 20-60N;

[0012] S3. Pretreatment: Clean and activate the copper strip after punching to remove surface impurities. Immerse the copper strip after punching in alkaline cleaning agent for electrolytic cleaning at 45°C for 1-2 minutes, and then soak the copper strip in acid activator for 0.5-1 minute for surface activation.

[0013] S4. Electroplating tin: Pulse electroplating technology is used. The plating solution contains 50-60g / L potassium tin sulfonate, 100-150g / L potassium sulfonic acid and 1-5g / L additives. The current density is 1-5A / dm 2 , the pulse frequency is 50-200Hz, and the tinning time is 3-10 minutes;

[0014] S5. Post-processing: After cleaning the tinned copper strip, soak it in a passivation solution for 0.5-1 minute to form a passivation layer of 0.1-0.3 μm, and then dry it.

[0015] Preferably, the punching edge of the high-precision mold in S2 is designed as a double chamfer structure, the edge angle is 15-25°, the edge roughness Ra≤0.4μm, and the mold material is cemented carbide (WC-Co) or high-speed steel (M2) with a hardness ≥60HRC.

[0016] Preferably, the acidic activator in S3 is a sulfuric acid solution with a concentration of 10-15 wt%.

[0017] Preferably, the alkaline cleaning agent in S3 contains sodium hydroxide with a concentration of 10-20 g / L, sodium carbonate with a concentration of 5-15 g / L, and sodium citrate with a concentration of 1-3 g / L.

[0018] Preferably, the additives of the electroplating solution in S4 include thiourea derivatives and polyethylene glycol, and the added amount is 1-3 g / L.

[0019] Preferably, the passivating agent in S5 is a bismuth nitrate-citric acid composite solution, comprising 10-20 g / L bismuth nitrate, 5-10 g / L citric acid, and 1-3 g / L potassium sodium tartrate. The pH value of the solution is controlled at 2.5-3.5, and the treatment temperature is 40-60°C.

[0020] Preferably, the drying step of the passivation treatment in S5 is to adopt hot air circulation drying, control the temperature to be 60-80° C., and dry for 3-5 minutes, so that the passivation layer is completely cured and no water marks remain on the surface.

[0021] The present invention provides a punched tinned copper strip and a preparation method thereof, which has the following beneficial effects:

[0022] 1. The present invention adopts a multi-layer composite structure, in which the lattice constant of the transition layer is between the copper substrate and the pure tin layer, the mismatch is 2.8%, the bonding strength is ≥15MPa, and the interface thermal stress is reduced by 30%-40%. The tin plating layer is prevented from peeling off due to the difference in thermal expansion coefficient. The tin plating layer takes into account both conductivity and corrosion resistance. The passivation layer prolongs the salt spray corrosion resistance time, thereby achieving the effect of enhancing the corrosion resistance and thermal shock resistance of the copper strip.

[0023] 2. The present invention adopts a double-chamfered edge mold to make the burr height ≤5μm, the hole position accuracy ±0.01mm, and the cross-section bright band ratio ≥80%, which is better than the traditional single-chamfered mold. The 0.5-1.2mm aperture achieves 1-10GHz electromagnetic wave shielding effectiveness ≥60dB, the 1.5-2.0mm aperture improves the air convection efficiency by 40%, and the punching spacing of 0.5-2.0mm avoids lattice distortion (spacing <0.5mm) or transmittance reduction (transmittance <60% when spacing >2.0mm), and the anisotropy index is controlled within 1.25, thereby improving the heat dissipation performance of the copper strip, enhancing the environmental applicability of the copper strip, and improving the punching processing accuracy and production efficiency of the copper strip.

[0024] 3. The present invention uses potassium tin sulfonate and polyethylene glycol additives to refine the grain size to 0.3-0.5μm, the coating hardness is 65-75HV, the surface roughness Ra≤0.5μm, the porosity is reduced by more than 50%, and the interface bonding strength is increased by 20%. The passivation film uses bismuth as the base metal, the surface roughness Ra≤0.8μm, and the impedance modulus reaches 1.2×10 5 Ω·cm 2 , and is chromium-free and environmentally friendly, which can improve the hardness and wear resistance of the coating, reduce surface roughness and contact resistance, and thus ensure stable signal transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the partial structure of the passivation layer of a punched tinned copper strip proposed by the present invention;

[0026] Figure 2 The present invention provides a schematic flow chart of a method for preparing a punched tinned copper strip.

[0027] Among them, 1. passivation layer; 2. tin plating layer; 3. transition layer; 4. substrate. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] Please see the attached Figure 1 An embodiment of the present invention provides a punched tin-plated copper, including a substrate 4, an outer wall of the substrate 4 is provided with a transition layer 3, an outer wall of the transition layer 3 is provided with a tin-plated layer 2, an outer wall of the tin-plated layer 2 is provided with a passivation layer 1, the substrate 4 is provided with evenly distributed punchings, the burr height of the punching edges does not exceed 5μm, the thickness of the transition layer 3 is 0.2-0.5μm, the thickness of the tin-plated layer 2 is 1.5-3μm, and the thickness of the passivation layer 1 is 0.1-0.3μm.

[0030] Specifically, the transition layer 3 is made of copper-tin alloy, and a transition layer 3 containing 15-25wt% of tin is formed on the surface of the substrate 4 through an electroplating pre-plating process. The lattice constant of the transition layer 3 (a=1.102nm) is between that of copper and tin, which can reduce the interface thermal stress by 30%-40%, and the bonding strength is ≥15MPa. When the thickness of the transition layer (3) is 0.2-0.5μm, the balance between the interface bonding force and the heat shock resistance can be ensured. When the thickness of the transition layer 3 is less than 0.2μm, the bonding force decreases, and when it is greater than 0.5μm, the brittleness increases and micro cracks are easily generated. The optimal thickness of the tinned layer 2 is 1.5-3μm, at which time the conductivity (resistance ≤0.5mΩ / cm 2 ) and corrosion resistance. When the thickness of the tin-plated layer 2 is less than 1.5 μm, the porosity increases and affects the corrosion resistance. When the thickness is greater than 3 μm, the surface roughness increases and is not conducive to the coverage of the passivation layer. The thickness of the passivation layer 1 is 0.1-0.3 μm, and the film density is 1.2-1.5 g / cm 3 , the impedance modulus reaches 1.2×10 5 Ω·cm 2 Ω·cm 2 When the thickness of the passivation layer 1 is 0.2μm, the salt spray corrosion resistance is ≥120h. When the thickness of the passivation layer 1 is less than 0.1μm, the corrosion resistance is insufficient. When the thickness is greater than 0.3μm, the internal stress is large and it is easy to crack.

[0031] The diameter of the punching holes in the substrate 4 is 0.5-2.0 mm, the spacing between the punching holes is 0.5-2.0 mm, and the arrangement is uniform or staggered.

[0032] Specifically, the punching size is 0.5-2.0mm. The aperture of 0.5-1.2mm can cut off 1-10GHz electromagnetic waves with a shielding effectiveness of ≥60dB. The aperture of 1.5-2.0mm increases the air convection efficiency by 40%, thereby improving the heat dissipation performance of the copper strip. At the same time, when the punching spacing is <0.5mm, lattice distortion occurs between adjacent holes. When the spacing is >2.0mm, the material transmittance drops to <60%, and the tensile test shows that the anisotropy index increases to 1.25, which makes the mechanical properties of the copper strip fail to meet the use standards. Therefore, the punching spacing is 0.5-2.0mm.

[0033] The transition layer 3 is a copper-tin alloy layer, and the passivation layer 1 is a bismuth-based alloy passivation film.

[0034] Specifically, the transition layer 3 is composed of two phases, θ-Cu3Sn (orthorhombic system, a=0.552nm) and η'-Cu6Sn5 (monoclinic system, a=1.102nm), wherein the Cu content is 72-78wt% and the Sn content is 22-28wt%. The electroplating solution is heated at 45±2℃ and pH8.5-9.2 at a speed of 1.5-2.5A / dm 2Current density deposition, after 150-250 ℃ step heat treatment, forms an interface layer with a gradient structure (Cu / Cu3Sn interface hardness 3.8GPa, Cu6Sn5 / Sn interface hardness 2.9GPa), the lattice constant of the transition layer 3 (Cu6Sn5: a = 1.102nm) and the copper substrate (a = 0.361nm) and the pure tin layer (a = 0.583nm) mismatch is 2.8%, and the bonding strength is more than 15N / cm; the passivation film uses bismuth as the base metal, taking advantage of its low melting point (271.5℃ ) properties to form a dense passivation film. 0.5-1.0wt.% rare earth elements (La / Ce complex) are added as grain refiners to control the grain size of the passivation film within the range of 50-100nm, thereby improving corrosion resistance. The surface of the film is modified with a silane coupling agent (3-aminopropyltriethoxysilane, concentration 1.5vol.%) to achieve a surface roughness Ra ≤ 0.8μm, achieving the dual functions of hydrophobicity and corrosion resistance. This parameter system was verified by electrochemical impedance spectroscopy (EIS), and the impedance modulus value in 3.5% NaCl solution reached 1.2×10 5 Ω·cm 2 , which is 30% higher than the traditional chromate passivation film and meets environmental protection requirements.

[0035] See attached Figure 2 A method for preparing a punched tinned copper strip comprises the following steps:

[0036] S1. Raw material preparation: Select copper strips with a purity of not less than 99.95%, and perform surface cleaning and pretreatment;

[0037] S2. Punching: Use high-speed CNC punching machine and high-precision mold for punching, the punch speed is controlled at 5-15mm / s, and the punching pressure is 20-60N;

[0038] S3. Pretreatment: Clean and activate the copper strip after punching to remove surface impurities. Immerse the copper strip after punching in alkaline cleaning agent for electrolytic cleaning at 45°C for 1-2 minutes, and then soak the copper strip in acid activator for 0.5-1 minute for surface activation.

[0039] S4. Electroplating tin: Pulse electroplating technology is used. The plating solution contains 50-60g / L potassium tin sulfonate, 100-150g / L potassium sulfonic acid and 1-5g / L additives. The current density is 1-5A / dm 2 , the pulse frequency is 50-200Hz, and the tinning time is 3-10 minutes;

[0040] S5. Post-processing: After cleaning the tinned copper strip, soak it in a passivation solution for 0.5-1 minute to form a passivation layer of 0.1-0.3 μm, and then dry it.

[0041] Specifically, in the production of copper strips, the raw material preparation stage uses copper strips with a purity of ≥99.95%, an impurity oxygen content of ≤50ppm, a sulfur content of ≤5ppm, a surface roughness of Ra≤0.8μm, and mechanical properties. The tensile strength is 200-250MPa at a thickness of 0.2mm, and the elongation is ≥25% at a gauge length of 50mm. Degreasing and cleaning are performed (alkaline degreasing solution contains 50g / LNaOH and 30g / LNa2CO3, supplemented by 40kHz and a power density of 0.5W / cm 2 Ultrasonic) and pickling activation, during punching, the die edge angle is 18±2°, the edge roughness Ra≤0.4μm, the die gap is 6±1% of the plate thickness, and the dynamic compensation requirement during stamping is acceleration ≤0.5m / s 2 , position repeatability ±2μm (laser displacement sensor feedback), the pre-treatment process uses a specifically formulated alkaline cleaning agent and a 12±1wt% sulfuric acid solution with added benzotriazole corrosion inhibitor for acid activation, in the electroplating tin process, the main salt system of the electroplating solution contains potassium-based tin sulfonate, and the additives work synergistically to improve the coating performance, and pulse plating uses specific forward and reverse pulse parameters.

[0042] The punching edge of the S2 medium and high precision mold is designed as a double chamfer structure with a blade angle of 15-25° and a blade roughness of Ra≤0.4μm. The mold material is cemented carbide (WC-Co) or high-speed steel (M2) with a hardness ≥60HRC.

[0043] Specifically, the double-chamfered cutting edge structure adopts a main shear angle of 20±2° and an auxiliary chip removal angle of 15±1°. The cutting edge surface is ultra-precision processed by rough grinding, fine grinding and polishing. The residual stress is -200 to -300MPa and the white layer thickness is ≤2μm. In terms of mold material, the cemented carbide YG15 / WC-Co contains 85% WC and has a bending strength of 2800MPa. The high-speed steel M2 is austenitized at 1210℃, deep cooled at -196℃ and tempered at 560℃. The martensite content is ≥95%. The burr height of the double-chamfered mold is ≤5μm, the proportion of the cross-section bright band is ≥80%, and the hole position accuracy is ±0.01mm compared to the single-chamfered mold, which can achieve stable punching processing.

[0044] The acidic activator in S3 is a sulfuric acid solution with a concentration of 10-15 wt%.

[0045] Specifically, the copper strip acid activation treatment adopts 12.5±2.5wt% sulfuric acid solution system, adds 0.3-0.5g / L benzotriazole corrosion inhibitor and 0.1-0.3g / L sodium lauryl sulfate wetting agent, the activation process adopts PVDF / PP material tank, the waste liquid treatment adopts Ca(OH)2 to neutralize to pH8-9, Na2S precipitates copper ions, and the final water Cu 2+≤0.5mg / L, copper recovery rate ≥95% (energy consumption ≤3.5kWh / kg), activation qualification rate of the process ≥99.5%, coating bonding strength CV ≤5%.

[0046] The alkaline cleaning agent in S3 contains sodium hydroxide with a concentration of 10-20 g / L, sodium carbonate with a concentration of 5-15 g / L, and sodium citrate with a concentration of 1-3 g / L.

[0047] Specifically, the main cleaning system of the alkaline cleaning agent contains sodium hydroxide and sodium carbonate, and the auxiliary additive sodium silicate. In terms of process parameters, the electrolytic cleaning current density cathode is 3-5A / dm 2 , anode 1-2A / dm 2 The temperature standard is 45±2℃ (>55℃ accelerates the decomposition of the solution), soaking for 30-45 seconds, electrolysis for 45-75 seconds, and the total processing time is 1.5±0.3 minutes.

[0048] The additives of the electroplating solution in S4 include thiourea derivatives and polyethylene glycol, and the addition amount is 1-3 g / L.

[0049] Specifically, the electroplating solution additive consists of a thiourea derivative (60% to 70% N,N'-diethylthiourea and 30% to 40% tetramethylthiourea) and polyethylene glycol, and the addition amount is controlled in the range of 1-3 g / L. The thiourea derivative preferentially inhibits the growth of the (100) crystal plane through cathode adsorption, so that the grain size of the coating is refined from 0.8-1.2 μm at 1.0 g / L to 0.3-0.5 μm at 3.0 g / L. The polyethylene glycol and the thiourea derivative produce a synergistic effect, and the coating is effectively treated at a current density of 1-5 A / dm 2 , under the temperature of 20-35℃, the standard concentration of 2.0g / L can make the coating hardness reach 65-75HV and the surface roughness ≤0.5μm.

[0050] The passivating agent in S5 is a bismuth nitrate-citric acid composite solution, containing 10-20 g / L bismuth nitrate, 5-10 g / L citric acid, and 1-3 g / L potassium sodium tartrate. The pH value of the solution is controlled at 2.5-3.5, and the processing temperature is 40-60°C.

[0051] Specifically, the passivation treatment uses bismuth nitrate as the main salt, citric acid as the complexing agent, and potassium sodium tartrate as the crystal form regulator. The treatment is carried out at pH 3.0±0.3 and 50±5°C for 2.0-3.5 minutes to form a Bi-SnO composite film with a thickness of 0.15-0.25 μm. The film is composed of 35±5 nm hexagonal close-packed Bi grains embedded in an amorphous SnO matrix. XRD analysis shows that the Bi content is 55-65 wt% and the density is 4.3±0.2 g / cm 3 The performance test shows that there is no red rust in the neutral salt spray test for 240 hours, and the electrochemical impedance modulus is 5.2×10 5Ω·cm 2 , initial contact resistance value 0.38±0.03mΩ / cm 2 And the change rate after 1000 plugging and unplugging is ≤18%.

[0052] The drying step of the passivation treatment in S5 is to use hot air circulation drying, control the temperature to 60-80° C., and dry for 3-5 minutes, so that the passivation layer 1 is completely cured and there is no residual water mark on the surface.

[0053] Specifically, the drying process after passivation treatment adopts a hot air circulation system, and the drying temperature is controlled in the range of 60-80℃. It is divided into two stages: the first stage is 65±5℃ for 2-3 minutes to achieve initial curing, and the second stage is 75±5℃ for 1-2 minutes to ensure complete dehydration. The hot air speed is set to 1.5-2.0m / s, and the relative humidity is controlled at 15%~30%RH.

[0054] Example 1:

[0055] 1. Technical solution:

[0056] A copper strip with a purity of 99.95% was selected, with a width of 261mm and a thickness of 0.1mm. A high-speed CNC punching machine was used, equipped with a circular punch with a diameter of 1.0mm. Rows of circular holes were punched out on the copper strip with a uniform arrangement of punching spacing of 1.13mm. During the punching process, the punch speed was controlled at 9.75mm / s and the pressure was 2550N. After multiple punching tests to ensure that the accuracy and quality of the punching met the requirements, the punched copper strip was placed in a cleaning tank containing an alkaline detergent and cleaned in an electrolytic tank at 45°C for 1 minute, and then rinsed with clean water. Rinse clean, then soak the copper strip in a solution containing an acidic activator for 0.5 minutes, take it out and rinse it with clean water, and immediately put it into the electroplating tin solution for electroplating. The concentration of potassium-based tin sulfonate in the electroplating tin solution is 50g / L, the concentration of sulfuric acid is 120g / L, the additive is appropriate, and the pulse is 2μm. After the electroplating is completed, the tinned copper strip is sequentially placed in the cleaning solution for cleaning to remove the residual plating solution on the surface, and then soaked in a solution containing a passivator for 0.5 minutes for passivation treatment. Finally, rinse it with clean water and dry it to obtain the finished punched tinned copper strip.

[0057] 2. Technical effect verification and conclusion:

[0058] The performance tests of the punched tinned copper strip prepared in Example 1 showed that: the coating had strong bonding strength, and after 12 bending tests, the coating did not fall off; the punched edges were smooth, and the burr height did not exceed 5 μm; the tinned layer had a uniform thickness, and the deviation was within ±0.5 μm; the welding performance was good, and under the standard welding process, the solder joints were full and firm, and there was no cold solder joint; the oxidation resistance was excellent, and after being placed in a high temperature and high humidity environment for 1 hour, there was no obvious oxidation discoloration on the surface. All performance indicators were superior to those of traditional punched tinned copper strips, meeting the use requirements of high-precision electronic equipment.

[0059] Example 2: Electroplating process optimization

[0060] 1. Technical solution:

[0061] 1. Raw material preparation: Select copper strip with a purity of 99.96% (oxygen content ≤ 30ppm, sulfur content ≤ 3ppm), thickness 0.15mm, width 300mm, and clean the surface with alkaline degreasing solution (NaOH 15g / L + Na2CO3 10g / L + ultrasonic assistance) and then pickle and activate (12wt% H2SO4 + 0.4g / L benzotriazole).

[0062] 2. Punching process: Use carbide die, punching diameter 1.0mm, spacing 1.5mm (staggered arrangement), punch speed 12mm / s, pressure 40N.

[0063] 3. Pretreatment: electrolytic cleaning (50℃, NaOH15g / L+ cathode current 4A / dm 2 ) and then acidic activation (10wt% H2SO4+0.3g / L sodium lauryl sulfate).

[0064] 4. Electroplating tin: Place the copper strip in a pulse plating solution (55 g / L potassium tin sulfonate + 130 g / L sulfuric acid + 2 g / L thiourea derivative), with a pulse frequency of 100 Hz and a current density of 3 A / dm 2 , time 5 minutes, coating thickness 2.0±0.3μm.

[0065] 5. Post-processing: Place the copper strip in the passivation solution, soak for 45 seconds, and then dry it in steps (65℃×3min+75℃×2min).

[0066] 2. Technical Effects:

[0067] Coating properties:

[0068] Bonding strength: 18MPa.

[0069] Corrosion resistance: No red rust after 168 hours of salt spray test.

[0070] Punching quality: burr height ≤ 3μm, hole position accuracy ±0.008mm.

[0071] Electrical properties: contact resistance 0.45mΩ / cm 2 After 1000 thermal cycles (-40~125℃), the change rate is ≤2.5%.

[0072] Welding performance: Solder point pull-out force ≥12N, no cold solder joints.

[0073] 3. Conclusion

[0074] By optimizing the electroplating process, the punched tinned copper strip of Example 2 is improved in mechanical strength, corrosion resistance and welding performance, and is suitable for high-frequency electronic shielding scenarios.

[0075] Example 3: Heat Dissipation Optimization

[0076] 1. Technical solution:

[0077] 1. Raw materials: 99.97% pure copper strip (thickness 0.08mm), copper strip punching diameter 0.8mm (spacing 1.0mm, evenly arranged), punch speed 8mm / s during punching (die gap 5% of plate thickness).

[0078] 2. Electroplating process: pre-plated copper-tin alloy transition layer (containing Sn 20wt%, 0.3μm), main tin plating layer 1.8μm (pulse frequency 150Hz, reverse duty cycle 30%).

[0079] 3. Passivation layer: A bismuth-based alloy passivation film with a thickness of 0.2 μm is generated.

[0080] 2. Technical Effects:

[0081] Interface performance: The lattice mismatch of the transition layer is 2.5%, and the thermal stress is reduced by 38%.

[0082] Environmental stability: 85℃ / 85%RH test for 500 hours, contact resistance increment ≤3%.

[0083] Heat dissipation performance: The heat dissipation efficiency in the 1.5mm aperture area is increased by 45%.

[0084] 3. Conclusion

[0085] Example 3 achieves an excellent balance between heat dissipation and electromagnetic shielding on an ultra-thin copper strip (0.08 mm) through the synergistic effect of a composite passivation film and high-precision punching, meeting the high-frequency heat dissipation requirements of 5G communication equipment.

[0086] The experimental results of the embodiment are shown in the figure below:

[0087]

[0088] According to the above experiments, the present invention has the following effects:

[0089] Bonding strength: By optimizing the electroplating process, the bonding strength of Examples 1 and 2 is increased by 50%-125% compared with the existing technology (8-12MPa); Example 3 further adopts a copper-tin alloy transition layer to further optimize the bonding strength to meet the mechanical reliability requirements of high-frequency scenarios.

[0090] Corrosion resistance: Example 1 has a salt spray corrosion resistance of ≥120h (the existing technology is only 48-72h), and the passivation process improvement effect is significant. Example 2, through passivation and precision plating control, has a salt spray corrosion resistance of 168h without red rust. Example 3 has a bismuth-based alloy passivation film, and the contact resistance remains stable for 500 hours in a high temperature and high humidity environment (85℃ / 85%RH), making it suitable for harsh environments.

[0091] Heat dissipation efficiency: Example 1 (aperture 1.0 mm) improves heat dissipation efficiency by 23%, while also taking electromagnetic shielding into account;

[0092] The heat dissipation efficiency of Example 3 (aperture 0.8 mm and densely packed punching) is improved by 45%. Through the coordinated design of aperture and plating, the heat dissipation requirements of 5G high-frequency devices are met.

[0093] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A punched tinned copper strip comprising a substrate (4), characterized in that: The outer wall of the substrate (4) is provided with a transition layer (3), the outer wall of the transition layer (3) is provided with a tinned layer (2), the outer wall of the tinned layer (2) is provided with a passivation layer (1), the substrate (4) is provided with evenly distributed punching holes, the burr height of the punching hole edges does not exceed 5 μm, the thickness of the transition layer (3) is 0.2-0.5 μm, the thickness of the tinned layer (2) is 1.5-3 μm, and the thickness of the passivation layer (1) is 0.1-0.3 μm.

2. The punched tinned copper strip according to claim 1, characterized in that: The diameter of the punching holes on the substrate (4) is 0.5-2.0 mm, the spacing between the punching holes is 0.5-2.0 mm, and the arrangement is uniformly distributed or staggered.

3. The punched tinned copper strip according to claim 1, characterized in that: The transition layer (3) is a copper-tin alloy layer, and the passivation layer (1) is a bismuth-based alloy passivation film.

4. A method for preparing a punched tinned copper strip, according to any one of claims 1 to 3, characterized in that: The steps include: S1. Raw material preparation: Select copper strips with a purity of not less than 99.95%, and perform surface cleaning and pretreatment; S2. Punching: Use high-speed CNC punching machine and high-precision mold for punching, the punch speed is controlled at 5-15mm / s, and the punching pressure is 20-60N; S3. Pretreatment: Clean and activate the copper strip after punching to remove surface impurities. Immerse the copper strip after punching in alkaline cleaning agent for electrolytic cleaning at 45°C for 1-2 minutes, and then soak the copper strip in acid activator for 0.5-1 minute for surface activation. S4. Electroplating tin: Pulse electroplating technology is used. The plating solution contains 50-60g / L potassium tin sulfonate, 100-150g / L potassium sulfonic acid and 1-5g / L additives. The current density is 1-5A / dm 2 , the pulse frequency is 50-200Hz, and the tinning time is 3-10 minutes; S5. Post-processing: After cleaning the tinned copper strip, soak it in a passivation solution for 0.5-1 minute to form a passivation layer of 0.1-0.3 μm, and then dry it.

5. The method for preparing a punched tinned copper strip according to claim 3, wherein: The punching edge of the S2 medium-high precision mold is designed as a double chamfer structure, the edge angle is 15-25°, the edge roughness Ra≤0.4μm, and the mold material is cemented carbide (WC-Co) or high-speed steel (M2) with a hardness ≥60HRC.

6. The method for preparing a punched tinned copper strip according to claim 3, characterized in that: The acidic activator in S3 is a sulfuric acid solution with a concentration of 10-15 wt%.

7. The method for preparing a punched tinned copper strip according to claim 3, characterized in that: The alkaline cleaning agent in S3 contains sodium hydroxide with a concentration of 10-20 g / L, sodium carbonate with a concentration of 5-15 g / L, and sodium citrate with a concentration of 1-3 g / L.

8. The method for preparing a punched tinned copper strip according to claim 3, characterized in that: The additives of the electroplating solution in S4 include thiourea derivatives and polyethylene glycol, and the addition amount is 1-3 g / L.

9. The method for preparing a punched tinned copper strip according to claim 3, characterized in that: The passivating agent in S5 is a bismuth nitrate-citric acid composite solution, comprising 10-20 g / L bismuth nitrate, 5-10 g / L citric acid, and 1-3 g / L potassium sodium tartrate. The pH value of the solution is controlled at 2.5-3.5, and the treatment temperature is 40-60°C.

10. The method for preparing a punched tinned copper strip according to claim 3, characterized in that: The drying step of the passivation treatment in S5 is to use hot air circulation drying, control the temperature to 60-80° C., and dry for 3-5 minutes, so that the passivation layer (1) is completely solidified and no water marks remain on the surface.

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