Processing method before welding of photovoltaic welding strip, welding method and solar cell module

Abstract

The invention discloses a treatment method before welding of a photovoltaic welding strip, a welding method and a solar cell module, and the treatment method before welding of the photovoltaic welding strip comprises the step of carrying out preheating treatment on the photovoltaic welding strip coated with water-based scaling powder by adopting a preheating process. The photovoltaic welding strip coated with the water-based soldering flux is preheated before welding, so that the surface tension of the water-based soldering flux on the surface of the welding strip can be effectively reduced, uniform spreading of the water-based soldering flux is promoted, moisture in the water-based soldering flux is fully evaporated before entering a high-temperature welding area, the problem of residual watermarks on the surface of a battery piece caused by flowing of the water-based soldering flux is solved, and the quality of the photovoltaic welding strip is improved. And the welding efficiency and the welding quality are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of welding strip technology, and more specifically, to a method for pretreatment of photovoltaic welding strips, a welding method, and a solar cell module. Background Technology

[0002] With increasingly stringent environmental and safety requirements, the electronic soldering industry is transitioning from traditional alcohol-based (ethanol, isopropanol, etc.) water-based fluxes to safer and more environmentally friendly water-based fluxes. Water-based fluxes use deionized water as the main solvent and offer significant advantages such as being non-flammable, non-toxic, and having extremely low VOC (volatile organic compound) emissions. However, the inherent physical properties of water, particularly its high surface tension (approximately 72 mN / m), far exceed that of ethanol (approximately 22 mN / m) and isopropanol (approximately 21 mN / m), posing a significant challenge to the soldering process. 1. Water-based flux is difficult to spread. High surface tension makes it difficult for water-based flux droplets to spread on the surface of photovoltaic solder ribbons. Instead, they tend to shrink into spherical droplets rather than forming a uniform and continuous liquid film. This results in uneven distribution of active substances in the water-based flux. Insufficient activity in some areas may lead to poor soldering, while excessive residue in some areas may lead to subsequent corrosion.

[0003] 2. Welding spatter and defects In the high-temperature zone of soldering, insufficiently preheated water rapidly reaches its boiling point and vaporizes violently. This violent boiling phenomenon causes solder splatter, which easily forms defects such as solder balls and pores around the solder joint, seriously affecting the soldering quality and reliability.

[0004] 3. Watermark residue The heat required for water to evaporate is more than 2.7 times that of alcohols, which results in water evaporating slowly. The liquid carries the solid solute to the edge of the droplet and deposits there, eventually leaving watermarks on the surface of the battery cell. Watermarks not only affect the appearance of the product, but may also bring potential reliability risks. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned deficiencies of the prior art and to provide a method for pretreatment of photovoltaic ribbons, a welding method, and a solar cell module.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] The present invention provides a method for pre-welding photovoltaic solder strips, which includes: preheating the photovoltaic solder strips coated with water-based flux using a preheating process.

[0008] The present invention also provides a welding method for photovoltaic welding strips, which includes: feeding the photovoltaic welding strips, which have undergone sufficient preheating treatment, into a welding area for welding treatment.

[0009] The present invention also provides a solar cell module comprising multiple solar cells, wherein the multiple solar cells are interconnected by photovoltaic solder ribbons, and the photovoltaic solder ribbons are welded to the solar cells by the welding method described above.

[0010] The present invention has the following beneficial effects: This invention provides a method for pre-welding photovoltaic solder ribbons. The method includes preheating the photovoltaic solder ribbon coated with water-based flux using a preheating process. Preheating the photovoltaic solder ribbon coated with water-based flux before welding effectively reduces the surface tension of the flux on the solder ribbon surface, promotes its uniform spreading, and allows the water in the flux to evaporate fully before entering the high-temperature welding zone. This not only avoids the problem of watermark residue on the cell surface caused by the flow of water in the flux, but also fully activates the active substances in the flux, forming a uniform thin solid coating layer on the surface of the photovoltaic solder ribbon, significantly improving welding efficiency and welding quality. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0012] The following is a detailed description of a photovoltaic ribbon pre-welding treatment method, a welding method, and a solar cell module provided by embodiments of the present invention.

[0013] In a first aspect, the present invention provides a method for pre-welding photovoltaic solder strips, comprising: preheating photovoltaic solder strips coated with water-based flux using a preheating process.

[0014] To overcome the problems of difficult spreading, spattering, and watermark residue associated with water-based flux coatings on photovoltaic solder ribbons during welding, this invention proposes a preheating process to preheat the metal solder ribbon coated with water-based flux. Temperature is a crucial factor affecting the surface tension of liquids; as temperature increases, the surface tension of the liquid decreases significantly. Preheating the photovoltaic solder ribbon coated with water-based flux before welding reduces the surface tension of the flux, weakens its contraction tendency, and transforms it from a "granular" state to a "continuous and uniform liquid film" on the solder ribbon surface, thus completely encapsulating the ribbon. Furthermore, preheating before high-temperature welding allows sufficient time and energy for the water to evaporate relatively slowly. When the photovoltaic solder ribbon enters the high-temperature welding zone, the water-based flux is already a "dry" film, eliminating the need to divert heat to evaporate moisture, thus enabling smooth and rapid welding. At the same time, it avoids the problem that the water in the water-based flux does not evaporate completely before entering the high-temperature zone, thus causing violent boiling at high temperatures, which leads to the splashing and uneven deposition of solid substances in the water-based flux on the surface of the battery cell, ultimately leaving watermarks. This significantly improves the overall welding efficiency and welding quality.

[0015] In some alternative embodiments, the preheating treatment is a stepped heating preheating treatment.

[0016] In some alternative embodiments, the stepped heating preheating treatment is performed in a multi-temperature zone preheating system, preferably using hot air circulation heating, infrared heating, or a combination thereof.

[0017] In some optional embodiments, the stepped heating preheating treatment includes: a first-stage preheating treatment and a second-stage preheating treatment, wherein the temperature of the first-stage preheating treatment is below the boiling point of water, and the temperature of the second-stage preheating treatment is above the boiling point of water. The photovoltaic solder ribbon coated with water-based flux undergoes the first-stage preheating treatment below the boiling point of water. The purpose of this stage is to initially heat the flux droplets, reducing their viscosity, increasing their molecular kinetic energy, initiating initial spreading, and initiating slow evaporation of moisture. Next, the second-stage preheating treatment is performed at a temperature above the boiling point of water. The purpose of this stage is to allow the vast majority of moisture (over 95%) to evaporate smoothly, avoiding violent boiling. Simultaneously, the active substances in the water-based flux are activated at this temperature and form a uniform coating layer on the solder ribbon surface. When the photovoltaic solder ribbon undergoes the above stepped heating preheating treatment and is welded to the electrode grid lines, the welding process can proceed smoothly and quickly, without defects such as spatter, porosity, and surface residue. The bonding strength at the weld position is high, and the welding effect is excellent.

[0018] In some optional embodiments, the stepped heating preheating treatment includes: controlling the temperature of the first stage preheating treatment to be 70℃~90℃ and the preheating time to be 10~30s, and the temperature of the second stage preheating treatment to be 90℃~110℃ and the preheating time to be 15~40s.

[0019] The stepped preheating treatment for photovoltaic welding provided by this invention involves immediately conveying the photovoltaic welding ribbon coated with water-based flux through a multi-temperature zone preheating system for stepped heating, wherein: The photovoltaic solder ribbon coated with water-based flux is immediately conveyed through the first preheating zone of a multi-temperature zone preheating system, preferably heated by powerful hot air circulation. This method is highly effective in blowing and homogenizing thicker liquid films and can begin to remove surface moisture. In this stage, hot air and heat energy increase the fluidity of the excessively thick water-based flux film, allowing it to spread out under the combined action of surface tension and external force (hot air), forming a uniformly thick liquid film and beginning to evaporate some moisture. This achieves liquid film homogenization and initial evaporation. The set temperature is 70℃~90℃, slightly lower than the boiling point of water, to prevent rapid surface crusting. A more preferable residence time is 10~30 seconds. When the photovoltaic solder ribbon leaves this zone, the surface liquid film has become uniform and flat, but is still completely wet. For example, the preheating temperature in the first stage can be 70℃, 71℃, 72℃, 73℃, 74℃, 75℃, 76℃, 77℃, 78℃, 79℃, 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃, 90℃ or any other value between 70℃ and 90℃, and the preheating time can be 10s, 11s, 12s, 13s, 14s, 15s, 16s, 17s, 18s, 19s, 20s, 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, 30s or any other value between 10 and 30s.

[0020] Next, the photovoltaic ribbon, preheated in the first preheating zone, is fed into the second preheating zone. The preferred heating method is a combination of mid-wave infrared heating and hot air circulation. Infrared heating provides efficient and penetrating energy, rapidly raising the temperature inside the liquid film; the hot air promptly removes evaporated water vapor, preventing condensation. The infrared heater temperature is set at 90℃~110℃, a critical stage for complete moisture evaporation. The uniform liquid film is rapidly heated, resulting in significant moisture evaporation. The active substances in the water-based flux are fully activated at this temperature, forming a uniform, extremely thin solid coating on the photovoltaic ribbon surface. A more preferred residence time is 15~40 seconds. When the photovoltaic ribbon leaves the second preheating zone, the surface temperature reaches 100-103℃, and the surface is visually completely dry, matte, and non-sticky to the touch. Weight monitoring indicates that over 95% of the moisture has been removed after this stage. For example, the preheating temperature in the second stage is 90℃, 91℃, 92℃, 93℃, 94℃, 95℃, 96℃, 97℃, 98℃, 99℃, 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, 110℃ or any other value between 90℃ and 110℃, and the preheating time is 15s, 16s, 17s, 18s, 19s, 20s, 21s, 22s, 23s, 24s, 25s, 26s, 27s, 28s, 29s, 30s, 31s, 32s, 33s, 34s, 35s, 36s, 37s, 38s, 39s, 40s or any other value between 15 and 40s.

[0021] In some alternative embodiments, the water-based flux has a solid content of 5% to 15% and a surface tension of ≥50mN / m.

[0022] In some alternative embodiments, the photovoltaic solder strip is a tin-plated copper strip for photovoltaic modules.

[0023] Secondly, the present invention provides a welding method for photovoltaic welding strips, comprising: feeding the photovoltaic welding strips, which have undergone sufficient preheating treatment, into a welding zone for welding treatment.

[0024] In some alternative embodiments, the welding heat source temperature is controlled at 230°C to 280°C, and the welding time is less than 5 seconds. During high-temperature welding, since the water-based flux layer on the surface of the solder strip is a uniform solid residual film rather than a liquid, there is no spatter during welding. After the solder melts, it can quickly and uniformly wet the entire solder strip and the battery main grid line. For example, the welding heat source temperature can be 230°C, 240°C, 245°C, 250°C, 255°C, 260°C, 265°C, 270°C, 275°C, 280°C, or any other value between 230°C and 280°C, and the welding time can be 1 second, 2 seconds, 3 seconds, 4 seconds, etc. It is worth noting that if the solder strip is directly welded at high temperature, most of the heat is first used to evaporate the large amount of liquid water on the solder strip and pads, and the remaining heat is used to heat and melt the solder. The effective proportion of energy actually used to form the intermetallic compound (IMC) is very low. In this invention, the preheated solder strip has a temperature close to the melting point of the solder, which can significantly shorten the heating time during welding and achieve better welding results.

[0025] In some optional embodiments, the photovoltaic welding strip is cooled and cleaned after welding, preferably by natural cooling or air cooling.

[0026] Thirdly, the present invention provides a solar cell module comprising multiple solar cells, wherein the multiple solar cells are interconnected by photovoltaic solder ribbons, and the photovoltaic solder ribbons are welded to the solar cells by the welding method described above.

[0027] Welding results show that the photovoltaic ribbon obtained using the solution provided by this invention is quiet and stable during the welding process in the welding zone, with no spatter. The surface of the photovoltaic ribbon is smooth and bright, and the solder joints are full. After welding, the surface of the solar cell is uniform and bright, without any visible cloud-like watermarks or mottled residue. The surface color difference is uniform, and the appearance quality meets the Grade A standard. The bonding strength between the solder and the photovoltaic ribbon and the main busbar of the solar cell is higher and stronger.

[0028] The present invention will be further described below with reference to embodiments.

[0029] Example 1 A detailed explanation is given using a fully automated photovoltaic string welder for welding polycrystalline silicon solar cells as an example: (1) Sample preparation: Prepare a water-based flux with a solid content of 10% and a surface tension of approximately 65 mN / m. (2) Water-based flux dipping: The photovoltaic ribbon first passes through a sealed water-based flux tank to fully wet its surface with water-based flux. Then, the photovoltaic ribbon passes through a quantitative scraping device consisting of a uniform roller or a precision scraper to remove excess water-based flux from the surface and precisely control the amount of flux adhered. (3) Stepped preheating: The photovoltaic soldering strip, after being dipped in water-based flux, is immediately conveyed into the preheating furnace. The conveyor belt speed is set to 3800 mm / min. Wherein: First preheating zone (liquid film homogenization and initial evaporation): Heating method: powerful hot air circulation heating. This method is highly effective in blowing and homogenizing thicker liquid films and can begin to remove surface moisture. Set temperature: 75℃, residence time: 20s.

[0030] The second preheating zone (core evaporation and activation zone) uses a combination of mid-wave infrared heating and hot air circulation. Infrared heating provides efficient and penetrating energy, rapidly raising the temperature inside the liquid film; the hot air promptly removes the evaporated water vapor, preventing condensation. The infrared heater temperature is set at 105℃, and the residence time is 35 seconds.

[0031] (4) High temperature welding: Welding is carried out using an infrared welding gun. The welding temperature is set to 265℃, the actual welding temperature is about 240±5℃, and the welding time is 3s.

[0032] (5) Cooling: The welded battery string is forced to cool by a cooling fan.

[0033] Example 2: Let's take the welding of polycrystalline silicon solar cells by a fully automated photovoltaic string welder as an example for a detailed explanation: (1) Sample preparation: A highly active water-based flux with a solid content of 15% and a surface tension of about 70 mN / m was used. This flux has strong deoxidation ability but is more difficult to dry and is prone to residue.

[0034] (2) Conveyor belt speed: To allow sufficient drying time, the speed should be appropriately reduced to 3500 mm / min.

[0035] (3) First preheating zone: set temperature 85℃, dwell time extended to 28s.

[0036] (4) Second preheating zone: Set the infrared heater temperature to 110℃ and extend the dwell time to 40s.

[0037] (5) High temperature welding: The welding temperature is set to 265℃, the actual welding temperature is about 240±5℃, and the welding time is 3s.

[0038] The remaining processes are the same as in Example 1.

[0039] Example 3: Similar to the steps in Example 1, the same equipment, the same batch of materials and water-based flux were used, and the coverage and conveying speed remained unchanged. The only difference was that the temperature of the first preheating zone was slightly adjusted to 80°C and the dwell time was 20s; the temperature of the second preheating zone was increased to 110°C and the dwell time was still 35s; the high-temperature welding temperature was set to 275°C, the actual welding temperature was about 245±5°C, and the welding time was shortened to 1.5s.

[0040] Comparative Example 1: Similar to the steps in Example 1, the same equipment, the same batch of materials and water-based flux are used, and the coating amount, welding temperature and conveying speed remain unchanged. The only difference is that the preheating system is shut down during the shutdown phase, and only the welding heater is turned on.

[0041] Comparative Example 2: Similar to the steps in Example 1, the same equipment, the same batch of materials and water-based flux are used, and the coating amount, welding temperature and conveying speed remain unchanged. The only difference is that only the first-stage preheating system is turned on, and the welding strip is directly welded at high temperature after being preheated in the first preheating zone.

[0042] Comparative Example 3: Similar to the steps in Example 1, the same equipment, the same batch of materials and water-based flux are used, and the coating amount, welding temperature and conveying speed remain unchanged. The only difference is that only the second-stage preheating system is turned on, and the welding strip is directly welded at high temperature after being preheated in the second preheating zone.

[0043] result (1) Welding process Comparative Example 1: A dense "crackling" sound can be heard at the moment of welding, and tiny solder particles are visible to the naked eye. The surface of the photovoltaic solder strip after welding has uneven gloss.

[0044] Comparative Example 2: During the welding process, uneven spreading of the solder strip can be observed. In some areas, the solder strip is not fully coated with flux, resulting in incomplete welding.

[0045] Comparative Example 3: Intermittent "crackling" sounds can be heard at the moment of welding. Moisture evaporates rapidly, generating a large amount of steam. The rapid escape of steam leaves a large number of micropores or channels in the flux layer.

[0046] Example 1: The welding process was quiet and stable, with no spatter. The surface of the photovoltaic welding strip was smooth and bright, and the weld joints were full.

[0047] Example 2: The welding process produces almost no visible steam, melts smoothly without splashing, and produces full, smooth welds with a bright metallic luster, regular and consistent shapes, and no pores.

[0048] Example 3: The welding process was completed quickly without any spatter. After welding, the surface of the photovoltaic welding strip remained smooth and bright, and the weld points were rounded and had clear outlines.

[0049] (2) Watermark removal effect Comparative Example 1: After welding, large areas of cloud-like and mottled watermarks appeared on the surface of the battery cells, which were particularly noticeable under light and seriously affected the product's appearance.

[0050] Comparative Example 2: The watermark was somewhat reduced, but new "ring-shaped" or "edge-accumulation" marks appeared. The reason is that the moisture partially evaporated in the low-temperature zone, but the remaining moisture and flux still boiled violently when directly entering the high-temperature zone, and because the flux was not fully activated, the chemical composition of the residue was complex.

[0051] Comparative Example 3: The watermark appears as dense, fine spots or "popcorn"-like marks. This is because while high-temperature preheating activates the flux, excessive moisture evaporation leads to micro-splattering. Simultaneously, localized micro-deformation of the solder strip may occur due to thermal shock.

[0052] Example 1: After welding, the surface of the battery cell is uniform and bright, without any visible cloud-like watermarks or mottled residue. The surface color is uniform, and the appearance quality meets the Grade A standard.

[0053] Example 2: After welding, the surface of the solar cells exhibited a highly consistent, clean, and bright appearance. A visual inspection of 1000 consecutively sampled solar cells revealed that 99.8% of the samples had no visible watermarks or blemishes, achieving an appearance rating of Grade A.

[0054] Example 3: The flux evaporates completely, the surface of the solder strip is bright after soldering, there are very few residues, no obvious watermarks or contamination, and the appearance quality meets the Grade A standard.

[0055] (3) Peel force test To quantitatively assess the mechanical connection reliability of the weld joints, photovoltaic solder strip peel strength tests were conducted on the battery strings prepared in the examples and comparative examples. Using a universal testing machine, the photovoltaic solder strip was peeled from the main busbar of the battery cell at a uniform speed at a 180-degree angle. The force changes throughout the peeling process were recorded, and the maximum force value was taken as the peel strength (unit: Newtons, N). Each test group included at least 30 valid data points for statistical analysis. The statistical results are shown in Table 1 below:

[0056] The results above show that the average peel force of the photovoltaic ribbon after welding in Example 1 was 1.85 N, the maximum peel force was 2.10 N, and the minimum peel force was 1.60 N, indicating that the photovoltaic ribbon and the main grid line of the solar cell had high bonding strength and good welding effect. Compared with Example 1, Example 2 used a highly active water-based flux with a solid content of 15% and a surface tension of about 70 mN / m. This flux has strong deoxidation ability but is more difficult to dry and is prone to residue. Good welding effect can also be obtained by appropriately increasing the gradient preheating temperature and welding temperature. Compared with Example 1, Example 3 increased the corresponding preheating temperature and time, shortened the welding time, and the final obtained ribbon still maintained a comparable level in terms of appearance and welding tensile strength.

[0057] Compared to Comparative Example 1, the average peel force of the photovoltaic solder ribbon after welding in Example 1 was 1.85 N, while the average peel force of the photovoltaic solder ribbon after welding in Comparative Example 1 was 1.55 N, representing an improvement of approximately 19%. This result indicates that after the photovoltaic solder ribbon coated with water-based flux underwent a stepped preheating treatment in this embodiment of the invention, the active substances in the water-based flux were evenly distributed, effectively removing the oxide layer on the surface of the photovoltaic solder ribbon. This resulted in a stronger and more robust solder joint between the solder and the copper solder ribbon and the main grid lines of the battery. Furthermore, comparing the results of Example 1 with those of Comparative Examples 2 and 3, it can be seen that the two-stage gradient preheating treatment of the solder ribbon in Example 1, with its uniform and stable temperature rise, allowed the flux to spread rapidly and form a strong intermetallic compound layer, resulting in a higher average peel force of the solder ribbon after welding. In Comparative Examples 2 and 3, only one-stage or two-stage preheating was performed. Compared with Example 1, which underwent two-stage gradient preheating, the peeling force had a higher degree of dispersion and greater fluctuation (the difference between the maximum and minimum peeling forces was larger).

[0058] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for pretreatment of photovoltaic welding strips before welding, characterized in that, It includes: A preheating process is used to preheat the photovoltaic solder ribbon coated with water-based flux.

2. The processing method according to claim 1, characterized in that, The preheating treatment is a stepped heating preheating treatment.

3. The processing method according to claim 2, characterized in that, The stepped heating preheating treatment is carried out in a multi-temperature zone preheating system, preferably using hot air circulation heating, infrared heating, or a combination thereof.

4. The processing method according to claim 3, characterized in that, The stepped heating preheating treatment includes: a first stage preheating treatment and a second stage preheating treatment, wherein the temperature of the first stage preheating treatment is lower than the boiling point of water, and the temperature of the second stage preheating treatment is higher than the boiling point of water.

5. The processing method according to claim 4, characterized in that, The stepped heating preheating process includes: controlling the temperature of the first stage preheating process to be 70℃~90℃ and the preheating time to be 10~30s, and the temperature of the second stage preheating process to be 90℃~110℃ and the preheating time to be 15~40s.

6. The processing method according to claim 1, characterized in that, The photovoltaic solder strip is a tin-plated copper strip for photovoltaic modules, and the solid content of the water-based flux is 5%~15%, with a surface tension ≥50mN / m.

7. A method for welding photovoltaic strips, characterized in that, It includes: The photovoltaic welding strip, which has undergone sufficient preheating treatment as described in any one of claims 1-6, is fed into the welding area for welding.

8. The welding method according to claim 7, characterized in that, The welding heat source temperature should be controlled at 230℃~280℃, and the welding time should be less than 5 seconds.

9. The welding method according to claim 7, characterized in that, Also includes: After welding is completed, the material is cooled and cleaned. Natural cooling or air cooling is the preferred cooling method.

10. A solar cell module, characterized in that, It includes multiple solar cells, which are interconnected by photovoltaic welding ribbons, and the photovoltaic welding ribbons are welded to the solar cells by the welding method described in any one of claims 7-9.

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