Low-temperature circular welding strip and preparation method thereof

Abstract

The invention provides a low-temperature circular welding strip and a preparation method thereof.The method comprises the steps that burdening is conducted according to alloy compositions, and a copper alloy blank is obtained through smelting and continuous casting; carrying out homogenization treatment on the copper alloy blank, namely heating to a copper alloy homogenization temperature and carrying out heat preservation; the blank obtained after heat preservation is subjected to descaling and then is continuously rolled till the target diameter is reached, and a semi-finished wire is obtained; and carrying out surface coating treatment and post-treatment on the semi-finished wire rod to obtain a finished low-temperature circular welding strip. Corrosion resistance and welding reliability can be enhanced, and the method is suitable for efficient and stable connection of photovoltaic modules.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic module manufacturing, and more specifically, to a low-temperature round solder tape and a preparation method thereof. Background Art

[0002] In the fields of modern electronics manufacturing and photovoltaic modules, welding technology plays a crucial role. Traditional welding materials usually use high-melting-point solders, such as pure tin or tin-lead alloys, etc. These materials require relatively high temperatures during the welding process, generally above 200°C. However, this high-temperature welding method has some obvious limitations. First, high-temperature welding may cause excessive thermal stress at the welding site, thus affecting the mechanical strength and reliability of the welding point. Second, for some heat-sensitive electronic components or photovoltaic cells, high-temperature welding may cause thermal damage to them, reducing their performance and service life. In addition, it is difficult for the electrical conductivity and tensile strength of traditional welding materials to simultaneously meet the strict requirements for welding quality in high-precision electronic devices and photovoltaic modules.

[0003] In the manufacturing of photovoltaic modules, the welding process is a key step in connecting solar cells in series or parallel to form a cell string and then assembling it into a photovoltaic module. The commonly used welding method at present is to use high-melting-point solder tapes, but this method is prone to cause thermal damage to the cells during the welding process, affecting the photoelectric conversion efficiency of the cells and the performance of the overall module. At the same time, there are also certain deficiencies in the electrical conductivity and tensile strength of traditional solder tapes, which are difficult to meet the growing demand for high-performance photovoltaic modules.

[0004] In the process of implementing the embodiments of the present invention, at least the following problems or defects exist in the prior art: the melting point of the existing welding materials is too high, which is easy to cause thermal damage to heat-sensitive components and affect the mechanical strength and reliability of the welding points; it is difficult for the electrical conductivity and tensile strength of traditional welding materials to simultaneously meet the strict requirements for welding quality in high-precision electronic devices and photovoltaic modules. Summary of the Invention

[0005] The present invention provides a low-temperature round solder tape and a preparation method thereof.

[0006] In the first aspect of the present invention, a preparation method of a low-temperature round solder tape is provided, which specifically includes the following steps:

[0007] S1: Weigh materials according to the alloy composition, and obtain a copper alloy blank through melting and continuous casting;

[0008] S2: Perform homogenization treatment on the copper alloy blank, that is, heat it to the copper alloy homogenization temperature and keep it warm;

[0009] S3: After descaling the blank after heat preservation, perform continuous rolling until the target diameter to obtain a semi-finished wire rod;

[0010] S4: Perform surface coating treatment and post-treatment on the semi-finished wire rod to obtain a finished low-temperature round solder strip;

[0011] Among them, the surface coating treatment described in step S4 is one of "electroplating nickel-phosphorus alloy layer + hot-dip tin layer" or "electroless plating nickel-phosphorus alloy layer + vacuum evaporation tin layer".

[0012] Furthermore, the alloy composition of the low-temperature round solder strip is by mass percentage: Cu: 98.0% - 99.5%, Ag: 0.5% - 1.5%, Ti: 0.1% - 0.5%, P: ≤0.02%, S: ≤0.005%, and the balance is inevitable impurities; and the mass percentage of Ag and Ti satisfies: 0.6 ≤ Ag + Ti ≤ 2.0.

[0013] Furthermore, the homogenization temperature of the copper alloy described in step S2 is 850 - 950 °C, and the holding time is 1 - 4 h.

[0014] Furthermore, the rolling in step S3 is cold rolling, the heating temperature before rolling is 400 - 500 °C, and the final rolling temperature is 250 - 350 °C.

[0015] Furthermore, the phosphorus content of the electroplated nickel-phosphorus alloy layer is 8% - 12%, and the coating thickness is 0.5 - 2.0 μm; the thickness of the hot-dip tin layer is 3 - 8 μm.

[0016] Furthermore, the phosphorus content of the electroless plating nickel-phosphorus alloy layer is 10% - 15%, and the coating thickness is 1 - 3 μm; the thickness of the vacuum evaporation tin layer is 5 - 10 μm.

[0017] In the second aspect of the present invention, a low-temperature round solder strip is provided, specifically including:

[0018] The solder strip is prepared by the preparation method described in any one of the first aspect.

[0019] Furthermore, the diameter of the solder strip is 0.15 - 0.30 mm, the surface coating structure is a composite layer of a nickel-phosphorus alloy layer and a tin layer, the thickness of the nickel-phosphorus alloy layer is 0.5 - 3.0 μm, and the thickness of the tin layer is 3 - 10 μm.

[0020] Furthermore, the tensile strength of the solder strip is 300 - 450 MPa, the conductivity

[0021] ≥90% IACS, and the welding melting point ≤180 °C.

[0022] In the third aspect of the present invention, a connection structure for a photovoltaic module is provided, specifically including:

[0023] The connection structure is made of the low-temperature round solder strip described in any one of the second aspects.

[0024] The above embodiments of the present invention have at least the following beneficial effects:

[0025] 1. By adopting a copper-silver-titanium alloy composition in a specific ratio and combining a high-temperature homogenization treatment process, the microstructural uniformity of the metal material can be effectively improved, and internal stress concentration can be eliminated, thereby enhancing the mechanical strength and electrical conductivity of the solder strip. This enables it to withstand mechanical loads and maintain stable current transmission capabilities during the long-term operation of photovoltaic modules. At the same time, this alloy ratio can also ensure that the material still has good weldability under low-temperature conditions.

[0026] 2. A composite plating structure of a nickel-phosphorus alloy layer and a tin layer is adopted. The nickel-phosphorus alloy layer, as a barrier layer, can effectively prevent the diffusion reaction between the copper substrate and the tin layer, while improving the corrosion resistance of the plating layer. The outer tin layer provides excellent welding wettability and weldability. This dual protection mechanism enables the solder strip to maintain stable electrical connection performance under harsh environmental conditions and is suitable for photovoltaic module interconnection systems with extremely high reliability requirements.

[0027] 3. By precisely controlling the rolling temperature parameters and adopting an optimized plating process, high-precision control of the solder strip size can be achieved, ensuring that the product has excellent geometric consistency and surface quality. This precision manufacturing process not only improves the mechanical property uniformity of the solder strip but also enables it to perfectly adapt to the process requirements of automated welding equipment, thereby enhancing the processing efficiency and product yield of the photovoltaic module production line while reducing production costs. Description of the Drawings

[0028] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs denote the same components.

[0029] Figure 1 It is a schematic structural diagram of the low-temperature round solder strip provided by an embodiment of the present invention;

[0030] Figure 2 It is a flowchart of a method for preparing a low-temperature round solder strip provided by an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the alloy microstructure of the low-temperature round solder strip provided by an embodiment of the present invention. Detailed Embodiments

[0032] The following will specifically describe the preferred embodiments of the present invention in conjunction with the drawings. The drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, not to limit the scope of the present invention.

[0033] The present invention relates to a low-temperature circular soldering tape and a preparation method thereof. The alloy composition of the low-temperature circular soldering tape is as follows by mass percentage: Cu: 98.0% - 99.5%, Ag: 0.5% - 1.5%, Ti: 0.1% - 0.5%, P: ≤0.02%, S: ≤0.005%, and the balance is inevitable impurities; and the mass percentages of Ag and Ti satisfy: 0.6 ≤ Ag + Ti ≤ 2.0. The following is a specific description of the functions and dosage selections of the components contained in the present invention:

[0034] Cu (copper): As the main component of the soldering tape, copper has excellent electrical and thermal conductivity and is the main element constituting the basic properties of the soldering tape. In the present invention, the content of copper is controlled at 98.0% - 99.5% to ensure that the soldering tape has good electrical conductivity, and at the same time provides a sufficient matrix for other alloy elements, enabling them to exert their respective characteristics without affecting the main properties of the soldering tape and realizing the optimization of the comprehensive performance of the soldering tape. The high content of copper ensures the high-efficiency electrical conductivity of the soldering tape in applications such as electronic soldering, and at the same time provides a stable matrix environment for the addition of other alloy elements.

[0035] Ag (silver): The addition of silver can significantly improve the oxidation resistance and corrosion resistance of the soldering tape, enabling the soldering tape to maintain good performance stability in harsh environments such as high temperature and humidity. In addition, silver can also improve the soldering performance of the soldering tape, reduce the soldering melting point, and enable the soldering tape to achieve good soldering effects under low-temperature conditions. In the present invention, the content of silver is controlled at 0.5% - 1.5%, which can not only give full play to the above advantages of silver, but also avoid a large increase in cost due to excessive content, while ensuring that the comprehensive performance of the soldering tape reaches the best balance. The appropriate addition of silver not only improves the oxidation and corrosion resistance of the soldering tape, but also optimizes the soldering performance, enabling it to achieve high-efficiency soldering under low-temperature conditions.

[0036] Ti (titanium): Titanium is a metal element with relatively strong activity. In the soldering tape, it mainly plays the role of refining grains, increasing strength and toughness. By adding an appropriate amount of titanium, the microstructure of the soldering tape can be effectively improved, enabling the soldering tape to have good toughness while having high strength, thereby improving the tensile strength and fatigue resistance of the soldering tape. In the present invention, the content of titanium is controlled at 0.1% - 0.5%, which can not only achieve the above performance improvement, but also avoid problems such as increased brittleness of the soldering tape that may be caused by excessive titanium content, ensuring the performance stability and reliability of the soldering tape. The addition of titanium significantly improves the comprehensive performance of the soldering tape by refining grains and increasing strength and toughness, making it perform excellently in various applications.

[0037] P (Phosphorus): The content of phosphorus in the solder ribbon is controlled to be ≤0.02%. Phosphorus is a harmful element. Excessive content will lead to a decrease in the toughness and plasticity of the solder ribbon, affecting its processing performance and service performance. Therefore, in the present invention, the content of phosphorus is strictly controlled to ensure the excellent performance of the solder ribbon. By strictly controlling the content of phosphorus, the problem of performance degradation during the processing and use of the solder ribbon can be effectively avoided.

[0038] S (Sulfur): The content of sulfur in the solder ribbon is controlled to be ≤0.005%. Sulfur is also a harmful element. It will form a eutectic compound with low melting point with copper, resulting in hot brittleness during the processing of the solder ribbon and reducing the strength and toughness of the solder ribbon. By strictly controlling the content of sulfur, these problems can be effectively avoided, ensuring that the processing performance and service performance of the solder ribbon are not affected. Strictly controlling the content of sulfur helps to improve the strength and toughness of the solder ribbon and avoid the occurrence of hot brittleness.

[0039] Inevitable impurities: During the production process of the solder ribbon, some impurity elements will inevitably be mixed in. The content of these impurity elements is usually low and has little impact on the performance of the solder ribbon. However, in the present invention, the total amount of impurity elements is still strictly controlled to ensure the purity and performance stability of the solder ribbon. By controlling the total amount of impurity elements, the purity and performance stability of the solder ribbon can be further improved, ensuring its reliability in various applications.

[0040] The low-temperature circular solder ribbon of the present invention achieves good welding performance, high tensile strength, excellent electrical conductivity, and excellent oxidation and corrosion resistance under low-temperature conditions through the above specific alloy composition, making it have significant advantages in the applications such as photovoltaic modules. By precisely controlling the content of each component, the solder ribbon of the present invention reaches the best balance in performance and can meet various high-demand application scenarios.

[0041] Specifically, the mass percentages of the Ag and Ti alloy components in the low-temperature circular solder ribbon satisfy: 0.6 ≤ Ag + Ti ≤ 2.0. The above alloy composition ratio can further effectively optimize the welding performance and mechanical properties of the low-temperature circular solder ribbon. The compound addition content of Ag and Ti cannot be too high or too low. Otherwise, on the one hand, their role in improving the welding performance and enhancing the mechanical properties cannot be fully exerted, and on the other hand, when the compound addition content is too high, it may lead to an increase in the brittleness of the solder ribbon, affecting its processing performance and service performance.

[0042] Preferably, in order to exert the strengthening effect of Ti microalloying during the continuous rolling process and match it with Ag microalloying and low-temperature welding performance, for the low-temperature circular solder ribbon manufactured by the method of "continuous rolling + online heat treatment + surface coating treatment", the microalloy ratio of Ag, Ti, and P follows: Ag: 0.5% - 1.5%, Ti: 0.1% - 0.5%, P: ≤0.02%.

[0043] Preferably, in order to exert the synergistic effect of Ti microalloying in the offline heat treatment process to refine the grains and thus improve the strength and toughness of the solder ribbon, and to match and cooperate with the grain refinement effect of Ag microalloying, for the low-temperature circular solder ribbon manufactured by the method of "continuous rolling + offline heat treatment + surface coating treatment", the microalloy ratios of Ag, Ti, and P follow the following two cases: (1) Ag: 0.5% - 1.5%, Ti: 0.1% - 0.5%, P: ≤0.02%; (2) Ag: 1.5% - 2.0%, Ti: 0.1% - 0.3%, P: ≤0.01%.

[0044] Specifically, the diameter of the low-temperature circular solder ribbon is 0.15 - 0.30 mm, and the surface coating structure is a composite layer of a nickel-phosphorus alloy layer and a tin layer. The thickness of the nickel-phosphorus alloy layer is 0.5 - 3.0 μm, and the thickness of the tin layer is 3 - 10 μm. The microstructure of the solder ribbon is a composite structure of a uniform copper matrix, a nickel-phosphorus alloy layer, and a tin layer, without obvious defects, and is uniformly distributed within the diameter range. The composite structure of the nickel-phosphorus alloy layer and the tin layer can significantly improve the antioxidant performance and welding performance of the solder ribbon, achieving the goals of low-temperature welding and high conductivity; however, the thickness of the tin layer should not be too large, which will cause the conductivity of the solder ribbon to decrease. The cross-section of the solder ribbon is circular, and the diameter is uniform. The circular shape is achieved through precise rolling and drawing processes, ensuring that the solder ribbon maintains a circular cross-section as consistent as possible throughout its entire length. The diameter of the circular solder ribbon is usually between 0.15 - 0.30 mm, and the specific dimensions are adjusted according to different application requirements. The surface of the solder ribbon has been finely treated, presenting a smooth and uniform appearance, which not only helps to improve the welding performance but also reduces the resistance and heat loss during the welding process to a certain extent. This circular solder ribbon performs excellently in applications such as photovoltaic modules, can effectively improve the reliability and durability of the modules, and at the same time meet the strict requirements for the appearance and performance of the solder ribbon in industrial production.

[0045] The diameter specifications of the low-temperature circular solder ribbon for preparing the connection structure of photovoltaic modules are generally 0.15 - 0.30 mm. Among them, the commonly used diameter specifications of the solder ribbon for preparing the internal connection of photovoltaic modules are 0.20 - 0.25 mm; the commonly used diameter specifications of the solder ribbon for preparing the external connection of photovoltaic modules are 0.25 - 0.30 mm.

[0046] The composite structure of the nickel-phosphorus alloy layer and the tin layer has high strength and good antioxidant and welding properties. However, if the thickness of the nickel-phosphorus alloy layer or the tin layer is uneven, these defects will not only damage the antioxidant and welding properties of the solder ribbon but also deteriorate the conductivity of the solder ribbon.

[0047] The low-temperature round solder strip of the present invention obtains excellent low-temperature welding performance and mechanical properties through chemical composition and surface coating treatment control. The composite structure of the nickel-phosphorus alloy layer and the tin layer is formed during the surface coating treatment process, consisting of a nickel-phosphorus alloy layer with high oxidation resistance and a tin layer with high welding performance, having excellent strength-conductivity matching and excellent welding performance.

[0048] Specifically, the tensile strength of the low-temperature round solder strip is 300-450 MPa, the conductivity is ≥90% IACS, and the welding melting point is ≤180 °C. The tensile strength-conductivity matching of the low-temperature round solder strip is excellent, which is beneficial to the preparation of downstream products such as photovoltaic module connection structures with high conductivity and high toughness.

[0049] The low-temperature round solder strip of the present invention will present a black appearance. This black surface is mainly due to the formation of a uniform oxide film or a specific coating on the surface of the solder strip. For example, in the process of electroplating nickel-phosphorus alloy layer + hot-dip tinning layer, during the hot-dip tinning process of the solder strip, a thin tin oxide film may be formed on the surface of the tin layer, and this oxide film presents black or dark gray under specific conditions. Similarly, in the process of electroless plating nickel-phosphorus alloy layer + vacuum evaporation tin layer, a similar oxide layer may also be formed during the cooling process of the vacuum evaporation tin layer, resulting in a black appearance on the surface of the solder strip.

[0050] The present invention also discloses a preparation method of the low-temperature round solder strip, including the following steps:

[0051] S1: According to the alloy composition for batching, through melting and continuous casting, a copper alloy blank is obtained;

[0052] S2: Homogenize the copper alloy blank, that is, heat it to the copper alloy homogenization temperature and keep it warm;

[0053] S3: After descaling the blank after heat preservation, perform continuous rolling until the target diameter to obtain a semi-finished wire rod;

[0054] S4: Perform surface coating treatment and post-treatment on the semi-finished wire rod to obtain the finished low-temperature round solder strip.

[0055] Specifically, in step S1, a copper alloy blank can be obtained by vacuum induction melting and continuous casting.

[0056] Exemplarily, in step S1, an excessive amount of each alloy element raw material can be weighed according to the alloy composition and added to a melting furnace. The alloy is melted, refined, degassed, electromagnetically stirred, and continuously cast into a billet in the melting furnace. By controlling the relevant parameters of melting, refining, and degassing, and performing real-time sampling and analysis on the molten alloy in the furnace, when the component content of each element reaches a preset value / range, the molten alloy is poured out for electromagnetic stirring and continuous casting. The above process and parameter control are relatively mature alloy preparation processes in the prior art, and the parameters can be adjusted during implementation according to practical experience and specific alloy composition.

[0057] Specifically, the homogenization temperature of the copper alloy in step S2 is 850 - 950 °C, and the holding time is 1 - 4 h. When the homogenization temperature is too high, some elements such as Ti in the billet will be completely dissolved, resulting in coarsening of the copper alloy grains and increasing the energy cost at the same time; when the homogenization temperature is too low, elements such as Ag and Ti in the steel will not be sufficiently dissolved, thus affecting the performance of the subsequent finished product. If the homogenization holding time is too long, the copper alloy grains will coarsen, increasing the energy cost and being unfavorable for production efficiency at the same time; if the homogenization holding time is too short, it is difficult to ensure the temperature uniformity of the billet thickness. Therefore, the holding time is controlled to be 1 - 4 h.

[0058] Preferably, when the Ti content in the alloy is 0.1% - 0.5%, the homogenization temperature of the copper alloy is 900 - 950 °C, so that more than 80% of Ti is in a dissolved state.

[0059] Exemplarily, the descaling operation in step S3 can adopt high-pressure water descaling technology or other conventional descaling processes. The role of the descaling operation is to completely remove the oxide scale to prevent it from being pressed into the surface of the alloy / wire rod to generate defects, thereby improving the surface quality of the product.

[0060] Specifically, the pre-rolling heating temperature in step S3 is 400 - 500 °C, and the final rolling temperature is 250 - 350 °C. If the final rolling temperature is too high, the copper alloy grains are relatively coarse during rolling, and the role of Ti microalloying in refining the rolling grains is not significant; if the final rolling temperature is too low, more Ag will precipitate and the rolling force will increase significantly. After rolling, the air cooling speed when cooling to 100 °C is ≥2 °C / s, aiming to avoid the formation of network oxides in the rolled wire rod, thereby avoiding the adverse effects of network oxides on the final performance and the adverse effects on the uncoiling performance before subsequent plating.

[0061] Specifically, the post-treatment method in step S4 is one of "electroplated nickel-phosphorus alloy layer + hot-dip tin layer" or "electroless nickel-phosphorus alloy layer + vacuum tin plating layer".

[0062] Combined process of electroplated nickel-phosphorus alloy layer and hot-dip tin layer. First, an electroplating process is used to form a nickel-phosphorus alloy layer on the surface of the solder strip. This process utilizes electrolysis to reduce and deposit nickel and phosphorus ions from the electrolyte onto the surface of the solder strip, forming an alloy layer with high hardness, wear resistance, and corrosion resistance. Its hardness can reach above HV700, providing a solid substrate for the subsequent hot-dip tin layer. Subsequently, hot-dip tinning is carried out by immersing the solder strip in molten tin, causing tin to form a uniform coating on the surface of the solder strip. By controlling the dipping time and temperature, the thickness of the tin layer can be precisely adjusted, usually between 3 and 8 μm. This tin layer has strong adhesion and excellent welding performance, and can significantly reduce the welding melting point of the solder strip.

[0063] Combined process of electroless nickel-phosphorus alloy layer and vacuum-evaporated tin layer. First, an electroless plating process is used to generate a nickel-phosphorus alloy layer on the surface of the solder strip. Nickel and phosphorus are deposited on the surface of the solder strip from the plating solution through chemical reactions, forming a uniform alloy layer. This process does not require an external power supply and is suitable for solder strips with complex shapes, capable of uniformly covering the surface of the solder strip. The thickness of the coating can be precisely controlled by the concentration of the plating solution and the reaction time, generally between 1 and 3 μm. Then, vacuum evaporation of tin is carried out. In a high-vacuum environment, tin is heated to the evaporation state and deposited on the surface of the solder strip, forming a uniform tin layer. By controlling the evaporation time and temperature, the thickness of the tin layer can be precisely controlled between 5 and 10 μm. This tin layer has strong adhesion and good welding performance, and can effectively reduce the welding melting point of the solder strip.

[0064] Specifically, the phosphorus content of the electroplated nickel-phosphorus alloy layer is 8% - 12%, and the coating thickness is 0.5 - 2.0 μm; the thickness of the hot-dip tin layer is 3 - 8 μm. A coating thickness ≥ 0.5 μm can ensure that the solder strip has good antioxidant and welding performance; when the coating thickness ≥ 8 μm, it will increase costs and may also affect the electrical conductivity of the solder strip. The formation of the tin coating should be strictly controlled in the subsequent hot-dip or vacuum evaporation stage to facilitate controlling its thickness to be appropriate.

[0065] Specifically, when the post-treatment method is "electroplated nickel-phosphorus alloy layer + hot-dip tin layer", the phosphorus content of the electroplated nickel-phosphorus alloy layer is controlled to be 8% - 12%, and the electroplating time is controlled to be 10 - 60 minutes. According to the preset chemical composition of the present invention, a nickel-phosphorus alloy layer with uniform thickness can be obtained by selecting an appropriate phosphorus content and time range. For the chemical composition of the present invention, the higher the phosphorus content, the greater the hardness of the nickel-phosphorus alloy layer. Since the present invention aims at low-temperature round solder tapes, the phosphorus content does not exceed 12%, and this upper limit of phosphorus content does not exceed the optimal hardness range. On the other hand, the phosphorus content is not less than 8% as the lower limit of phosphorus content. Since the phosphorus content is lower than 8%, the lower the phosphorus content, the worse the oxidation resistance of the nickel-phosphorus alloy layer. The oxidation resistance of the nickel-phosphorus alloy layer at the lower limit of phosphorus content of 8% meets the requirements, and the hardness of the nickel-phosphorus alloy layer reaches the best at the upper limit of phosphorus content of 12%. Combined with the subsequent hot-dip tin layer, the thickness of the nickel-phosphorus alloy layer can reach more than 0.5 μm. It is worth emphasizing that when using this post-treatment method, there is no need to cool the wire to room temperature after final rolling, and it can be directly air-cooled online to the preset electroplating temperature.

[0066] Specifically, when the post-treatment method is "electroless nickel-phosphorus alloy layer + vacuum tin evaporation layer", the phosphorus content of the electroless nickel-phosphorus alloy layer is controlled to be 10% - 15%, the electroless plating time is controlled to be 5 - 30 minutes, the air-cooling speed before entering the vacuum tin evaporation is ≥ 2 °C / s to avoid the formation of oxide scale, and the thickness of the vacuum tin evaporation layer is controlled to be 5 - 10 μm. It is worth emphasizing that before vacuum tin evaporation, the wire after final rolling needs to be air-cooled to room temperature before electroless plating.

[0067] The principle for controlling the vacuum tin evaporation temperature is as follows: the lower limit is 50 °C - 100 °C above the equilibrium phase transition temperature at which the solder tape of the present invention is completely evaporated, so that complete evaporation of the tin layer can occur at this temperature during the vacuum tin evaporation of the solder tape; the upper limit cannot be too high. On the one hand, it is based on controlling the tin layer grains to be fine, and on the other hand, it is to control energy consumption. The vacuum tin evaporation time is matched with the vacuum tin evaporation temperature. The higher the temperature, the shorter the time. Vacuum tin evaporation at 100 °C is matched with a holding time of 5 minutes, and vacuum tin evaporation at 50 °C is matched with a holding time of 30 minutes. High temperature and short time can control the tin layer grains to be fine and energy consumption, and at the same time, it is sufficient to fully evaporate the tin layer and achieve compositional homogenization.

[0068] The present invention also discloses a low-temperature round solder tape for a photovoltaic module, and the solder tape is made of the low-temperature round solder tape.

[0069] Specifically, the low-temperature round solder tape is made into a low-temperature round solder tape for a photovoltaic module through surface treatment and welding performance testing. The specific operations and parameters are as follows:

[0070] Surface treatment: Before surface treatment, cleaning is carried out. The cleaning time is 10 - 20 minutes to clean the oil stains and impurities on the surface and improve the surface quality of the solder tape. Due to the high requirements for the surface of the solder tape, in order to establish better welding conditions, the cleaned solder tape is subjected to surface activation treatment. The surface activation treatment time is 3 - 8 minutes to form a good activation layer on the surface of the solder tape. After activation, welding performance testing is carried out, and the testing speed is 1 - 3 m / min.

[0071] Welding performance testing: During welding testing, a simulated photovoltaic module welding environment is adopted. The testing temperature is 200 - 250 °C and the time is 10 - 30 s. The welding performance testing process is matched with the precipitation of Ag and Ti microalloys. The temperature and time are matched. When the temperature is high, the time is short; when the temperature is low, the time is long, which is beneficial to the precipitation of Ag and Ti nanoparticles to improve welding performance.

[0072] Specifically, the diameter of the low-temperature circular solder tape for photovoltaic modules is 0.15 - 0.30 mm, the tensile strength is 300 - 450 MPa, the conductivity is ≥90% IACS, and the welding melting point is ≤180 °C. The welding performance of the solder tape meets the following requirements: According to the welding tensile strength test specified in the photovoltaic industry standard, the number of test groups is not less than 5 groups. The minimum value of the welding tensile strength of the solder tape is ≥2 N, and the median value is ≥5 N.

[0073] Specifically, the low-temperature circular solder tape is made into the low-temperature circular solder tape for photovoltaic modules through surface treatment, coating performance testing and welding performance testing. The specific operations and parameters are as follows:

[0074] Surface treatment: Before surface treatment, cleaning is carried out. The cleaning time is 10 - 20 minutes to clean the oil stains and impurities on the surface and improve the surface quality of the solder tape. Due to the high requirements for the surface of the solder tape, in order to establish better welding conditions, the cleaned solder tape is subjected to surface activation treatment. The surface activation treatment time is 3 - 8 minutes to form a good activation layer on the surface of the solder tape. After activation, coating performance testing is carried out, and the testing speed is 1 - 3 m / min.

[0075] Coating performance testing: During coating testing, a simulated photovoltaic module welding environment is adopted. The testing temperature is 150 - 200 °C and the time is 5 - 15 s. The coating performance testing process is matched with the composite structure of the nickel-phosphorus alloy layer and the tin layer. The temperature and time are matched. When the temperature is high, the time is short; when the temperature is low, the time is long, which is beneficial to the uniformity and adhesion of the coating.

[0076] Welding performance testing: During welding testing, a simulated photovoltaic module welding environment is adopted. The testing temperature is 200 - 250 °C and the time is 10 - 30 s. The welding performance testing process is matched with the precipitation of Ag and Ti microalloys. The temperature and time are matched. When the temperature is high, the time is short; when the temperature is low, the time is long, which is beneficial to the precipitation of Ag and Ti nanoparticles to improve welding performance.

[0077] The low-temperature round solder ribbon for photovoltaic modules, which has undergone surface treatment, coating performance testing, and welding performance testing, has a diameter of 0.15 - 0.30 mm, a tensile strength of 300 - 450 MPa, a conductivity of ≥90% IACS, a welding melting point of ≤180°C, and a welding tensile force of ≥20 N.

[0078] The following will use specific examples and comparative examples to demonstrate the advantages of precise control of the composition and process parameters of the low-temperature round solder ribbon of the present invention. The chemical compositions of the solder ribbons of Examples 1 - 8 and Comparative Example 1 are shown in Table 1, the specific rolling and cooling process parameters are shown in Table 2, the surface treatment process parameters are shown in Table 3, and the performance test results are shown in Table 4.

[0079] Ordinary copper alloy solder ribbons are selected as Comparative Examples 1 and 3 for the composition, process, and performance. Comparative Examples 2, 4, and 5 have a higher silver content and little or no addition of microalloying elements.

[0080] Specifically, it is described as follows:

[0081] Examples 1 - 2

[0082] Using vacuum induction melting and continuous casting, a copper alloy billet with a diameter of 20 mm is obtained. A billet with a length of 1000 mm is cut, heated to 880 - 890°C and held for 1 - 1.5 h. After being taken out of the furnace, it is continuously rolled into a wire with a diameter of 0.20 - 0.25 mm, the final rolling temperature is 280 - 290°C, and the air-cooling speed when cooled to 100°C after rolling is 3.0 - 3.5°C / s. Subsequently, an electroplated nickel-phosphorus alloy layer treatment is carried out, the phosphorus content is controlled at 10%, the electroplating time is 15 - 20 min, and after electroplating, a hot-dip tin layer treatment is carried out, and the thickness is controlled at 5 - 7 μm.

[0083] Examples 3 - 4

[0084] Using a melting furnace for melting, through refining, degassing, electromagnetic stirring, and continuous casting into a copper alloy billet with a diameter of 20 mm. A billet with a length of 12000 mm is cut, heated to 850 - 870°C, held for 2 h. After being taken out of the furnace, it is continuously rolled into a wire with a diameter of 0.15 - 0.20 mm, the final rolling temperature is 270 - 280°C. The air-cooling speed before cooling to 100°C after rolling is 3.2 - 3.8°C / s. A chemical nickel-phosphorus alloy layer treatment is used, the phosphorus content is controlled at 12%, the chemical plating time is 10 - 15 min, and after chemical plating, a vacuum tin plating layer treatment is carried out, and the thickness is controlled at 7 - 10 μm.

[0085] Examples 5 - 6

[0086] Smelt using a melting furnace, followed by refining, degassing, electromagnetic stirring, and continuous casting into a copper alloy billet with a diameter of 20 mm. Cut a billet with a length of 12000 mm, heat it to 900 - 920 °C, hold for 0.5 - 1.5 h respectively, and then continuously roll it into a wire with a diameter of 0.22 - 0.25 mm after discharging from the furnace. The final rolling temperature is 290 - 310 °C. The air cooling speed before cooling to 100 °C after rolling is 3.5 - 4.0 °C / s. Then, perform electroplating of nickel - phosphorus alloy layer treatment, control the phosphorus content to 11%, with an electroplating time of 20 - 25 min. After electroplating, perform hot dip tinning layer treatment, with the thickness controlled to 6 - 8 μm.

[0087] Examples 7 - 8

[0088] Smelt using a melting furnace, followed by refining, VD degassing, electromagnetic stirring, and continuous casting into a copper alloy billet with a diameter of 20 mm. Cut a billet with a length of 12000 mm, heat it to 910 - 920 °C, hold for 2 - 3 h, and then continuously roll it into a wire with a diameter of 0.25 mm after discharging from the furnace. The final rolling temperature is 300 - 310 °C. The air cooling speed before cooling to 100 °C after rolling is 4.0 - 4.5 °C / s. Use electroless plating of nickel - phosphorus alloy layer treatment, control the phosphorus content to 13%, with an electroless plating time of 15 - 20 min. After electroless plating, perform vacuum evaporation tinning layer treatment, with the thickness controlled to 8 - 10 μm.

[0089] Table 1 Chemical composition (mass percentage)

[0090]

[0091] Table 2 Rolling and cooling process parameters

[0092]

[0093]

[0094] Table 3 Surface treatment process parameters

[0095]

[0096]

[0097] Table 4 Performance test results

[0098]

[0099] As can be seen from Tables 2, 3 and 4, the solder tapes of Examples 1, 2 and 5-8 are "primary air cooling + offline isothermal heat treatment + secondary air cooling + surface treatment" solder tapes, meeting the tensile strength of 300-450 MPa grade (for example, 320-430 MPa), conductivity ≥ 90% IACS (for example, 91.5%-94.0%), diameter specification of 0.15-0.30 mm, and the surface coating structure is nickel-phosphorus alloy layer + tin layer, where the thickness of the nickel-phosphorus alloy layer is 0.5-3.0 μm and the thickness of the tin layer is 3-10 μm.

[0100] Comparative Example 2 is a "primary air cooling + offline isothermal heat treatment + secondary air cooling + surface treatment" solder tape. The solder tape with a diameter of 0.20 mm has a tensile strength of 360-380 MPa grade, but the conductivity is only 88.0%-90.0%. Due to the long surface treatment time, the surface coating structure is only a tin layer.

[0101] Examples 3 and 4 are "online air cooling + surface treatment" solder tapes, meeting the tensile strength of 300-400 MPa grade (for example, 310-390 MPa), conductivity ≥ 90% IACS (for example, 92.0%-95.0%), diameter specification of 0.15-0.25 mm, and the surface coating structure is nickel-phosphorus alloy layer + tin layer, where the thickness of the nickel-phosphorus alloy layer is 1.0-2.5 μm and the thickness of the tin layer is 5-8 μm.

[0102] As can be seen from Tables 2, 3 and 4, after cold drawing and stabilization heat treatment, the low-temperature round solder tapes of Examples 1, 2 and 5-8 with a diameter of 0.15-0.30 mm have a tensile strength reaching 300-450 MPa grade, conductivity ≥ 90% IACS, and welding melting point ≤ 180°C. Since the solder tape of the present invention precisely controls the addition amount of microalloying elements such as Ag and Ti and optimizes the surface treatment process, the solder tape can still maintain good welding performance and mechanical properties under low-temperature conditions. The performance of the ordinary copper alloy solder tapes of Comparative Examples 1 and 3 is far inferior to that of the inventive examples due to the lack of optimization of microalloying elements and fine control of the surface treatment process.

[0103] As shown in Table 5, after cold drawing and stabilization heat treatment, the low-temperature round solder tapes of Examples 1, 2, 5-7 with a diameter of 0.15-0.25 mm have a welding tensile force reaching 5-9 N and a welding melting point ≤ 180°C. The solder tapes of Comparative Examples 1 and 3 have a welding tensile force of only 3-4 N and a welding melting point ≥ 200°C, indicating their poor welding performance.

[0104] After cold drawing, hot galvanizing, and stabilization heat treatment, the low-temperature round welding tapes of Examples 3, 4, and 8 with a diameter of 0.15 - 0.30 mm have a tensile strength reaching 300 - 400 MPa, a conductivity ≥ 90% IACS, and a welding tensile force ≥ 20 N. For the welding tapes of Comparative Examples 2 and 5, the tensile strength is only 280 - 320 MPa, and the welding tensile force is only 8 - 10 N, indicating that their mechanical properties and welding properties are inferior to those of the inventive examples.

[0105] Comparative Example 1 is also an ordinary copper alloy welding tape. For the welding tape with a diameter of 0.20 mm, the tensile strength level is only 280 - 300 MPa, and the conductivity is only 90.0% - 92.0%. The surface coating structure of Comparative Example 1 is without coating.

[0106] Table 5 Stabilization Heat Treatment Parameters and Performance Test Results

[0107]

[0108]

[0109] As can be seen from Table 5, after cold drawing and stabilization heat treatment, the low-temperature round welding tapes of Examples 1, 2, 5 - 7 with a diameter of 0.15 - 0.25 mm have a welding tensile force reaching 5 - 9 N, and a welding melting point ≤ 180°C. For the welding tapes of Comparative Examples 1 and 3, the welding tensile force is only 3 - 4 N, and the welding melting point ≥ 200°C, indicating that their welding performance is poor.

[0110] After cold drawing, hot galvanizing, and stabilization heat treatment, the low-temperature round welding tapes of Examples 3, 4, and 8 with a diameter of 0.15 - 0.30 mm have a tensile strength reaching 300 - 400 MPa, a conductivity ≥ 90% IACS, and a welding tensile force ≥ 20 N. For the welding tapes of Comparative Examples 2 and 5, the tensile strength is only 280 - 320 MPa, and the welding tensile force is only 8 - 10 N, indicating that their mechanical properties and welding properties are inferior to those of the inventive examples.

[0111] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature circular solder strip, characterized in that, The following steps are involved: S1: Prepare the materials according to the alloy composition, and obtain the copper alloy billet through smelting and continuous casting; S2: homogenizing the copper alloy billet, i.e. heating it to the copper alloy homogenization temperature and keeping it warm; S3: Descaling the billet after holding and continuously rolling it until the target diameter is reached to obtain a semi-finished wire rod; S4: Surface coating and post-processing are performed on the semi-finished wire to obtain a finished low-temperature round welding strip; The surface coating treatment in step S4 is one of "electroplating nickel-phosphorus alloy layer + hot-dip tin layer" or "chemical nickel-phosphorus alloy layer + vacuum evaporation tin layer".

2. The preparation method according to claim 1, wherein: The alloy composition of the low-temperature circular welding strip is as follows by mass percentage: Cu: 98.0% to 99.5%, Ag: 0.5% to 1.5%, Ti: 0.1% to 0.5%, P: ≤ 0.02%, S: ≤ 0.005%, and the balance is unavoidable impurities; And the mass percentage of Ag and Ti satisfies: 0.6≤Ag+Ti≤2.

0.

3. The preparation method according to claim 1, characterized in that: The copper alloy homogenization temperature in step S2 is 850-950° C., and the holding time is 1-4 hours.

4. The preparation method according to claim 1, characterized in that: The rolling in step S3 is cold rolling, the heating temperature before rolling is 400-500°C, and the final rolling temperature is 250-350°C.

5. The preparation method according to claim 1, characterized in that: The phosphorus content of the electroplated nickel-phosphorus alloy layer is 8% to 12%, and the thickness of the coating is 0.5 to 2.0 μm; the thickness of the hot-dip tin coating is 3 to 8 μm.

6. The preparation method according to claim 1, characterized in that: The phosphorus content of the chemically plated nickel-phosphorus alloy layer is 10% to 15%, and the thickness of the plated layer is 1 to 3 μm; the thickness of the vacuum evaporated tin layer is 5 to 10 μm.

7. A low-temperature circular welding tape, characterized in that: The welding strip is prepared by the preparation method according to any one of claims 1 to 6.

8. The low-temperature circular solder strip according to claim 7, wherein: The diameter of the welding strip is 0.15-0.30 mm, and the surface coating structure is a composite layer of a nickel-phosphorus alloy layer and a tin layer. The thickness of the nickel-phosphorus alloy layer is 0.5-3.0 μm, and the thickness of the tin layer is 3-10 μm.

9. The low-temperature circular solder strip according to claim 7, characterized in that: The welding strip has a tensile strength of 300-450 MPa, a conductivity of ≥90% IACS, and a welding melting point of ≤180°C.

10. A connection structure for a photovoltaic module, characterized in that: The connection structure is made of the low-temperature circular welding strip according to any one of claims 7 to 9.

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