Hot-dip tinned copper strip with a multielement alloy tin layer and a method for producing the same

Abstract

The application discloses a hot-dip tinned copper plate strip multi-element alloy tin layer and a preparation method thereof. The multi-element alloy tin layer comprises 4-6% of Sb, 0.1-1% of Ag, 0.2-0.4% of Ni, and the balance of Sn and inevitable impurities. The multi-element alloy tin layer comprises a Cu3Sn layer, a Cu6Sn5 layer and a Sn layer, and Ag3Sn particles and precipitated phases exist on the surface of the multi-element alloy tin layer. The multi-element alloy tin layer has many advantages such as stable structure, high hardness, high temperature resistance, environmental protection and low cost, and can be applied to the fields of new energy vehicles, electronic components, communication equipment and the like which need high temperature, high pressure and large current service scenes, and has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of hot-dip tin plating technology, specifically to a multi-element alloy tin layer for hot-dip tin-plated copper strip and its preparation method. Background Technology

[0002] Copper alloy sheets and strips are widely used in interconnect and connection devices across various fields, including automotive, communications, new energy batteries, precision instruments, aerospace, and high-end electronics. With the continuous exploration and development of 5G technology, new energy vehicles, and aerospace, the usage of copper alloy sheets and strips is showing a year-on-year growth trend. At the same time, new application areas, more demanding service environments, and the need for more efficient and high-throughput applications are placing higher demands on the performance of traditional copper alloy sheets and strips.

[0003] Taking new energy vehicles as an example, copper alloy strips are widely used in power systems, body systems, information control systems, safety systems, and on-board equipment, serving as the core material for crimping and electrical connection of automotive wiring harness terminals. The number of on-board connectors for new energy vehicles alone (with copper strip conductive assemblies as their core) reaches 800-1000, double the demand for traditional fuel vehicles. As new energy vehicles develop towards electrification and intelligence, the industry urgently demands longer driving range, larger capacity fast-charging batteries, and faster charging speeds. This demand pressure has forced breakthroughs in the mechanical, electrical, stress relaxation, and bending performance of copper alloy strip materials for new energy vehicles. For example, these breakthroughs include: high mating cycles, high contact force, small displacement deformation, small bending angle (for product miniaturization), low contact impedance, good heat dissipation, long-term service in high-temperature environments, and compliance with environmental standards.

[0004] Studies have found that, in addition to improving the yield strength, elastic modulus, conductivity, bending performance, and fatigue resistance of copper alloy strips, tin plating of copper alloy strips to form a well-contacted and uniformly thick tin coating on their surface helps to further address the aforementioned issues. In actual large-scale industrial production, electroplating and hot-dip tin plating are the main methods used. However, electroplating is being phased out by the industry due to its complex production process, strict operational requirements, high equipment costs, complex and costly plating solutions, and significant emissions and environmental pollution. Hot-dip tin plating involves immersing pre-treated copper materials in molten tin at a specific temperature. Through an alloying reaction between the copper and tin, a tin coating is formed on the copper surface. Hot-dip tin plating offers advantages such as good weldability, a dense and strong coating, less pollution, simple production process, short delivery time, and simple and inexpensive equipment. Leading international tin plating companies have widely adopted hot-dip tin plating, and with the continuous improvement of automation in manufacturing, the hot-dip tin plating process is also trending towards automation and intelligence.

[0005] Currently, hot-dip tin-plated copper strips are widely used in intelligent equipment, communications, electronics, and automotive industries, such as for electronic component pins, connectors, and circuit boards. By researching and controlling the composition and microstructure of the tin plating layer, the hardness, insertion and extraction force, conductivity, wear resistance, and corrosion resistance of tin-plated copper strips can be improved. Currently, common tin plating layer compositions for copper strips on the market include pure tin, Sn-Ag, etc., which can meet most application requirements. However, with market demands and technological advancements, faster charging speeds, higher current densities, and longer service lives require copper strips with tin plating layers possessing higher hardness, better conductivity, and high-temperature resistance. Therefore, developing new hot-dip tin plating layer compositions based on market demand will help further improve the performance of tin-plated copper strips, expand their applications in various fields, and has significant social and economic benefits.

[0006] For conductive copper alloy hot-dip tin-plated strips, the most significant factors affecting safety performance during use are service life and rated operating temperature. For example, some electronic connectors for new energy vehicles require temperatures of 105-160℃ to prevent the formation of conductive tin whiskers. Pure tin plating, due to its low hardness and softness, is prone to wear during use, resulting in a limited service life. Lead-tin alloy plating is commonly used and effectively suppresses whiskers, but it has been banned both domestically and internationally due to its lead content. While Sn-Ag plating has good conductivity, its service temperature is limited to 130℃. Summary of the Invention

[0007] The purpose of this invention is to improve upon the shortcomings of the prior art by providing a multi-element alloy tin layer for hot-dip tin-plated copper strips and its preparation method.

[0008] The technical solution adopted in this invention is: a hot-dip tin-plated copper strip with a multi-element alloy tin layer, wherein the weight percentage composition of the multi-element alloy tin layer is Sb: 4-6%, Ag: 0.1-1%, Ni: 0.2-0.4%, and the balance is Sn and unavoidable impurities.

[0009] Preferably, the multi-element alloy tin layer includes a Cu3Sn layer, a Cu6Sn5 layer, and a Sn layer, and the surface of the multi-element alloy tin layer contains Ag3Sn particles and precipitated phases.

[0010] Preferably, the thickness of the multi-element alloy tin layer is 0.5-10 μm, the precipitated phase is Sn-Sb phase, and the size of the Ag3Sn particles is 0.05-0.3 μm.

[0011] A method for preparing a multi-element alloy tin layer on a hot-dip tin-plated copper strip includes the following steps:

[0012] Step 1: Degrease and remove impurities from the copper strip, clean it, and acid-wash it;

[0013] Step 2: Apply a flux to the copper strip and dry it to obtain a pretreated copper strip;

[0014] Step 3: Immerse the pretreated copper strip in a multi-element alloy tin layer molten metal for hot-dip plating. After plating, remove the plated copper strip and air-cool it to room temperature to obtain a copper strip with a multi-element alloy tin layer.

[0015] Preferably, the hot-dip immersion temperature is 260-300℃, the immersion and leaching rates are 20-120 m / min, and the immersion time is 0.02-0.1 min.

[0016] Preferably, the method for preparing the multi-element alloy tin layer liquid includes the following steps:

[0017] Step (1): Calculate and weigh different intermediate alloy raw materials according to the composition of the multi-element alloy tin layer;

[0018] Step (2): Heat the metallic tin in the raw material in the furnace until it is completely melted to obtain a molten tin alloy;

[0019] Step (3): Heat to 280-350℃, add the remaining preheated intermediate alloy raw materials to the molten tin alloy, stir and mix evenly to obtain multi-element alloy tin layer metal liquid.

[0020] Preferably, the preheating temperature in step (3) is 130-190℃ and the preheating time is 5-10 min.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The various phases in this novel quaternary tin alloy coating are uniformly distributed, without serious component segregation or structural defects. These uniformly distributed hard phases help to improve the hardness and wear resistance of the coating.

[0023] 2. This new tin alloy has a higher melting point, 40°C higher than pure tin, so it can operate at higher temperatures, thus contributing to its high-temperature performance.

[0024] 3. This novel tin alloy has a low Ag content, but the fine Ag3Sn phase formed in the coating is mainly concentrated on the surface of the coating, which can achieve a conductivity effect similar to Sn-Ag3.5, thus saving overall costs.

[0025] 4. This new tin alloy coating can form a good interface bond with the copper strip substrate and has good solderability.

[0026] 5. This novel tin alloy coating, within a preferred thickness range, not only provides excellent conductivity, corrosion resistance, and reliability, but is also a low-cost solution for thin coatings, suitable for various application scenarios, and highly competitive in the market. Attached Figure Description

[0027] Figure 1 The surface morphology of the multi-element alloy tin layer in Example 1;

[0028] Figure 2 for Figure 1 EDS point scan composition analysis of different tissues in China;

[0029] Figure 3 The SEM morphology of the cross-section of the multi-element alloy tin layer in Example 1 at different magnifications;

[0030] Figure 4 for Figure 3 Point scan component analysis at different locations in d;

[0031] Figure 5 Comparison of the microstructure of cross-sections of tin-plated copper strips with different types of plating. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions provided by the present invention, specific embodiments are described below. Example 1

[0033] A 1.5mm thick, 200mm wide C10300 copper strip was used. The copper strip was degreased, cleaned, and acid-washed. A flux was used to ferrule the copper strip, which was then dried. The copper strip was then immersed in a multi-element alloy tin-plated molten metal for hot-dip plating. After plating, the copper strip was removed and air-cooled to room temperature to obtain a copper strip with a multi-element alloy tin layer. The immersion and leaching rates were 20m / min, the hot-dip plating temperature was 300℃, and the plating time was 0.1min. Finally, a tin-plated copper strip with a plating thickness of 5μm was obtained. Example 2

[0034] A 0.2mm thick, 350mm wide C19010 copper strip was used. The copper strip was degreased, cleaned, and acid-washed. A flux was used to ferrule the copper strip, which was then dried. The copper strip was then immersed in a multi-element alloy tin-plated molten metal for hot-dip plating. After plating, the copper strip was removed and air-cooled to room temperature to obtain a copper strip with a multi-element alloy tin layer. The immersion and leaching rates were 120m / min, the hot-dip plating temperature was 260℃, and the plating time was 0.02min. Finally, a tin-plated copper strip with a plating thickness of 1μm was obtained. Example 3

[0035] A 0.5mm thick, 370mm wide C19400 copper strip was used. The copper strip was degreased, cleaned, and acid-washed. A flux was used to ferrule the copper strip, which was then dried. The copper strip was then immersed in a multi-element alloy tin-plated molten metal for hot-dip plating. After plating, the copper strip was removed and air-cooled to room temperature to obtain a copper strip with a multi-element alloy tin layer. The immersion and leaching rates were 60m / min, the hot-dip plating temperature was 275℃, and the plating time was 0.05min. Finally, a tin-plated alloy copper strip with a plating thickness of 3μm was obtained.

[0036] Comparative Examples 1-3 used pure tin plating, while Comparative Examples 4-6 used tin-silver plating.

[0037] The conductivity, hardness, and corrosion resistance of each embodiment and comparative example were tested, and the results are shown in Table 1.

[0038] Conductivity: The conductivity of each embodiment and comparative example was tested using a conductivity meter with the eddy current method at room temperature.

[0039] Coefficient of friction: The coefficient of friction is measured using a friction coefficient measuring instrument and the planar friction coefficient test method, in accordance with GB / T10006 "Determination of the coefficient of friction of plastic films and sheets";

[0040] Microhardness: Tested using a microhardness tester according to GB / T4342-1991 "Metallic materials - Micro Vickers hardness test method";

[0041] Neutral salt spray test: The test shall be conducted in accordance with GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", with NaCl concentration of 5%, test temperature ±35℃, and pH value of 6.8±0.2.

[0042] Anti-aging ability: Tested under dry heat conditions according to the test method in IEC 60068-2-2, the test temperature is 160 degrees Celsius and the heat preservation time is 96 hours.

[0043] Table 1 Performance tests of the embodiments and comparative examples of the present invention

[0044]

[0045] Figure 1The surface morphology of the multi-element alloy tin layer in Example 1 is shown. Overall, the surface of the multi-element alloy tin layer is relatively flat, but there are certain solidification undulations. Different microstructures can also be observed on the surface of the multi-element alloy tin layer: (1) large bright white circular spots with a diameter of about 0.5 μm; (2) above the solidification undulations, densely distributed fine feather-like grayish-white spots with a size of about 0.1 μm can also be observed; (3) densely distributed lath-like precipitation stripes with a length of about 5-10 μm; (4) the remainder is the matrix microstructure. Figure 1 b is Figure 1 The magnified image of phase a clearly shows the bright white circular spots, the fine, feather-like distribution of grayish-white spots, and the detailed distribution of the precipitated phase and matrix. To confirm the basic composition of each phase, EDS point scans were performed on these phases, and the results are as follows: Figure 2 As shown.

[0046] Figure 2 a shows the point scan results of a large bright white circular spot. The compositional analysis results indicate that the bright white circular spot is mainly composed of Sn and Cu. Figure 2 b shows the point scan results of the fine, feather-like grayish-white spots. The compositional analysis results indicate that the fine grayish-white spot tissue is mainly composed of Sn and Ag. Figure 2 c represents the point scan result at any matrix tissue location. The compositional analysis results show that it is mainly composed of two elements, Sn and Sb, and the Ag content is low. Figure 2 d represents the compositional analysis results of the lath-shaped precipitation stripes. Its composition is basically consistent with the matrix structure, mainly composed of Sn and Sb elements. It can be considered as the preferential precipitation morphology generated during the solidification process.

[0047] Figure 3 The cross-sectional morphology of the copper-plated strip with a multi-element alloy tin layer in Example 1 is shown. The thickness of the tin-plated copper strip is approximately 5 μm. Through analysis and observation, it can be seen that the overall structure of the plating can be divided into 5 layers, from bottom to top: (1) copper substrate layer, (2) a relatively uniform solder layer with a thickness of approximately 0.5 μm, (3) a rod-shaped transition layer that extends into the plating structure with a thickness of approximately 1.0 μm, (4) the substrate alloy plating structure, and (5) a surface solidification structure with bright white fine particles. It is worth noting that a small amount of rod-shaped solder structure also exists in the alloy plating structure, and a small amount can extend to the plating surface. Upon careful observation, it can also be found that no rod-shaped precipitates are found in the cross-sectional structure of the alloy plating. In order to further distinguish the specific composition of each layer, detailed EDS selected area composition analysis was performed in each plating layer layer area, and the results are as follows. Figure 4 As shown.

[0048] Figure 4 for Figure 3 EDS point scan composition analysis results at different locations of coating layer delamination in d, with the location near the coating surface being the most significant. Figure 4 a and Figure 4 The high and consistent Ag content at points b indicates that the fine Ag-containing particles are mainly distributed near the surface. Meanwhile, the Cu content at position 1, which is closer to the internal dark gray phase, is significantly higher than the copper content at position 2, which is closer to the surface, indicating that the dark gray phase in the coating is mainly Cu-Sn phase. Figure 4 c represents the compositional analysis results at position 3 of the intermediate coating structure. The Ag and Cu contents at this position are both low, indicating that it is mainly composed of Sn-Sb elements. Figure 4 d is the bonding layer, which is mainly composed of Cu and Sn elements. However, the Ni content at this location is much higher than at other locations. In the multi-element alloy tin layer, Ni plays a role in enhancing the alloying of the coating with Cu. Figure 4 e represents the composition result at the copper substrate location in Example 1, with the main components including Cu, Ni, and a small amount of Si.

[0049] Figure 5 Comparative microstructures of cross-sections of tin-plated copper strips with different plating types (pure tin plating, tin-silver plating, and this multi-element alloy tin layer). As shown in the figures, the ordinary pure tin plating has a four-layer microstructure, but its surface tin layer is relatively soft, resulting in limited hardness, poor insertion / removal resistance, and generally poor service performance. The tin-silver plating has more uniformly distributed Ag3Sn particles on its surface than the pure tin plating, giving it better conductivity and improved wear resistance. This coating (multi-element alloy tin layer), like the pure tin plating, has a four-layer microstructure. Compared to the tin-silver plating, the Ag3Sn particles on the surface of this coating are finer and denser, thus significantly reducing Ag consumption. Furthermore, the Cu-Sn and Sn-Sb precipitates present only on the surface effectively enhance the hardness of this coating. Therefore, compared to pure tin and tin-silver plating, this multi-element alloy tin layer not only possesses higher hardness but also retains excellent conductivity with a lower Ag addition amount.

Claims

1. A hot-dip tin-plated copper strip with a multi-element alloy tin layer, characterized in that, The multi-element alloy tin layer is made of multi-element alloy tin liquid metal, wherein the weight percentage composition of the multi-element alloy tin liquid metal is Sb: 4-6%, Ag: 0.1-1%, Ni: 0.2-0.4%, and the balance is Sn and unavoidable impurities; the multi-element alloy tin layer includes a Cu3Sn layer, a Cu6Sn5 layer and a Sn layer, and Ag3Sn particles and precipitated phases exist on the surface of the multi-element alloy tin layer; the thickness of the multi-element alloy tin layer is 0.5-10μm, the precipitated phase is Sn-Sb phase, and the size of the Ag3Sn particles is 0.05-0.3μm.

2. A method for preparing a multi-element alloy tin layer on a hot-dip tin-plated copper strip as described in claim 1, characterized in that, Includes the following steps: Step 1: Degrease and remove impurities from the copper strip, clean it, and acid-wash it; Step 2: Apply a flux to the copper strip and dry it to obtain a pretreated copper strip; Step 3: Immerse the pretreated copper strip in a multi-element alloy tin layer molten metal for hot-dip plating. After plating, remove the plated copper strip and air-cool it to room temperature to obtain a copper strip with a multi-element alloy tin layer.

3. The method for preparing a multi-element alloy tin layer on a hot-dip tin-plated copper strip according to claim 2, characterized in that, The hot-dip galvanizing temperature is 260-300℃, the immersion and leaching rates are 20-120 m / min, and the immersion time is 0.02-0.1 min.

4. The method for preparing a multi-element alloy tin layer on a hot-dip tin-plated copper strip according to claim 2, characterized in that, The preparation method of the multi-element alloy tin layer liquid includes the following steps: Step (1): Calculate and weigh different intermediate alloy raw materials according to the composition of the multi-element alloy tin layer; Step (2): Heat the metallic tin in the raw material in the furnace until it is completely melted to obtain a molten tin alloy; Step (3): Heat to 280-350℃, add the remaining preheated intermediate alloy raw materials to the molten tin alloy, stir and mix evenly to obtain multi-element alloy tin layer metal liquid.

5. The method for preparing a multi-element alloy tin layer on a hot-dip tin-plated copper strip according to claim 4, characterized in that, The preheating temperature in step (3) is 130-190℃ and the preheating time is 5-10 min.

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