A method and system for pre-activation welding of photovoltaic ribbon

Abstract

This invention provides a pre-activation welding method and system for photovoltaic solder ribbons, belonging to the field of surface treatment technology. The method adds an online pre-activation step after the solder ribbon is unwound and before flux spraying. Organic acid vapor with a concentration of 100-500 ppm is mixed with an inert carrier gas and uniformly sprayed onto the solder ribbon surface through a fan-shaped atomizing nozzle. Simultaneously, an independent temperature control unit precisely maintains the solder ribbon surface temperature at 90-110°C for 1-2 seconds, causing a reduction reaction between the acid vapor and the oxide layer to generate thermally decomposable organometallic acid salts, achieving in-situ surface regeneration. The system is a modular device, including gas mixing, atomizing spraying, closed-loop temperature control, and safety emission units, and can be directly installed on a string welding machine. This invention solves the problem of open welds caused by corrosion and oxidation of the inner layer of the solder ribbon.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology, and more specifically to a pre-activation welding method and system for photovoltaic solder ribbons. Background Technology

[0002] In the automated stringing production of photovoltaic modules, tin-lead alloy solder ribbons are commonly used to connect the main grid of the cells. The solderability of the solder ribbon surface directly determines the connection resistance and long-term reliability, which are key factors affecting the power output and warranty period of the module. However, during the storage, transportation and workshop storage of the solder ribbon after tin plating, its surface is very prone to oxidation, forming a dense oxide layer mainly composed of SnO2, PbO and its hydroxyl oxides. This problem is particularly serious in high temperature and high humidity environments. Moreover, for the inner layer of the solder ribbon roll, due to the closed state, a more stubborn closed corrosion oxide layer will form, which has a loose structure, uneven thickness and is rich in hydroxyl groups, with low chemical reactivity.

[0003] Current mainstream solutions to the problem of solder strip oxidation in the industry all have flaws. For example, spraying rosin-based or organic acid-based flux at the moment of welding presents a fundamental contradiction under standard high-speed production cycles. To protect the cells from corrosion, the activity of the flux is limited. The limited activity and extremely short contact time are completely insufficient to reduce the already formed dense oxide layer, especially the aforementioned sealed corrosion layer. This directly leads to batch defects of open soldering, that is, the solder strip and the main grid are not metallurgically bonded and fall off as a whole, resulting in a serious loss of yield.

[0004] Other methods include passive protection and material replacement. One method requires solder ribbon suppliers to use vacuum or nitrogen-filled packaging, which significantly increases procurement costs. The other method is to replace it with Sn63Pb37 eutectic solder ribbon, which has slightly better oxidation resistance, but this also increases material costs. Both of these methods are cost shifting and do not solve the problem technically. Furthermore, they cannot handle the oxidized solder ribbon inventory.

[0005] They also tried to force welding by increasing the welding temperature, extending the welding time, or modifying the pressure needle mechanism. This method sacrifices the process window, which can easily lead to microcracks in the battery cells and an increased risk of hot spots. In addition, the equipment modification costs are high and the cycle is long, which affects the continuity of production.

[0006] Therefore, there is an urgent need in the field for a method and system that can instantly reduce the oxide layer on the surface of the solder strip to near-factory solderability without interrupting production or changing the properties of the solder strip itself. Summary of the Invention

[0007] This invention aims to completely solve the aforementioned technical bottlenecks and provide an innovative pre-activation welding method for photovoltaic solder ribbons. The core of this method is to instantly perform online, in-situ chemical reduction of the oxide layer on the surface of the solder ribbon before welding, restoring it to a weldability close to its factory condition, without interrupting production or altering the properties of the solder ribbon itself.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A pre-activation welding method for photovoltaic solder ribbons includes the following steps:

[0010] Step a: On the continuous travel path of the welding strip, before the flux spraying station, volatile organic acid vapor and inert carrier gas are mixed in proportion by a mass flow controller to form an activation gas with an organic acid concentration of 100-500 ppm.

[0011] Step b: Then, through a fixed fan-shaped atomizing nozzle, the activation gas is evenly sprayed onto the surface of the welding strip in a manner that covers the full width of the welding strip;

[0012] Step c: Next, an independent temperature control unit is used to synchronously heat the area where the solder ribbon is sprayed, and a closed-loop control is formed by temperature sensor feedback to precisely maintain the surface temperature of the solder ribbon within the range of 90-110°C for 1-2 seconds.

[0013] Step d: Next, based on the oxidation risk level determined by the solder strip batch information, the preset process formula is automatically matched and called to set the gas concentration in step a and the temperature value in step c.

[0014] Step e: Finally, the solder strip that has undergone the pre-activation treatment in step a is moved to the subsequent station for flux spraying and heating welding.

[0015] Preferably, in step a, the volatile organic acid vapor is formic acid or acetic acid with a concentration of 300-500 ppm, and the inert carrier gas is nitrogen.

[0016] Preferably, in step c, the independent temperature control unit achieves heating by reusing the original preheating platform of the string welding machine or by adding an infrared heater, and the closed-loop control keeps the temperature fluctuation within ±2°C.

[0017] Preferably, step a is particularly suitable for processing weld strip coils that have developed a dense, hydroxyl-rich, closed-loop corroded oxide layer on the inner layer due to long-term storage.

[0018] This invention also provides a pre-activation welding system for photovoltaic welding ribbons, wherein the system is integrated as an independent functional module between the ribbon unwinding and flux spraying stations of a string welding machine, comprising:

[0019] The gas supply and precision mixing unit includes an organic acid storage tank, an inert gas source, a dual-channel mass flow controller, and a static mixing chamber, used to generate and deliver a stable concentration of organic acid mixed gas.

[0020] The atomizing spray unit includes at least one fan-shaped atomizing nozzle and an adjustable mounting bracket, which is adapted to the existing structure of the string welding machine so that the nozzle is aligned with the surface of the welding strip.

[0021] The local micro-area closed-loop temperature control unit includes an independent heater, a temperature sensor and a PID controller, which is used to perform precise temperature control of the solder ribbon activation micro-area independently of the string welding machine.

[0022] The instant safety purification unit includes an exhaust hood located above the injection point to create local negative pressure and immediately expel residual gas.

[0023] Preferably, in the local micro-area closed-loop temperature control unit, the independent heater is an infrared heating tube or hot air nozzle with a power of no more than 50W, the temperature sensor is an infrared thermometer, and the PID controller dynamically adjusts the heater power according to the sensor feedback signal.

[0024] Preferably, the system also includes a parameter adaptive control unit, which has multiple sets of process recipes corresponding to different solder strip oxidation risk levels and can receive external level signals to automatically drive the gas supply and precision mixing unit and the local micro-area closed-loop temperature control unit to execute the corresponding parameters.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention introduces a low-temperature organic acid vapor pre-activation step to reduce oxides such as SnO2 and PbO on the surface of the solder strip in situ before welding. This solves the technical bottleneck that conventional liquid flux cannot treat such dense oxide layers due to insufficient reaction time within the standard process window, and fundamentally avoids defects such as incomplete soldering or open soldering caused by solder strip oxidation.

[0027] The activation temperature of 90-110°C is much lower than the melting point of the welding strip alloy, ensuring that the welding strip does not melt or deteriorate in mechanical properties during the activation process. The organic acid concentration of 100-500 ppm ensures sufficient reducing power while minimizing reagent consumption and achieving complete decomposition, thus avoiding corrosion risks and residue problems.

[0028] The pre-activation system adopts a modular design, and its gas injection and temperature control units can be installed in the original guide wheels and other positions of the string welding machine without modifying the main structure of the equipment, electrical control system or production cycle, thus reducing the complexity, cost and downtime of production line upgrades.

[0029] This method directly processes oxidized incoming welding strips, avoiding the increased material costs associated with changing welding strip alloys or requiring special packaging. It also eliminates rework or scrap losses due to poor welding. The consumption of trace amounts of organic acid results in extremely low operating material costs.

[0030] By pre-setting and associating the oxidation risk level of different solder strip types with activation parameters (such as acid concentration and temperature), the system can automatically match the optimal process conditions, simplifying operation, reducing reliance on personnel experience, and enhancing the adaptability and consistency of the production process to different incoming material conditions. Attached Figure Description

[0031] Figure 1 This is a flowchart of an embodiment of the method of the present invention;

[0032] Figure 2 This is a structural block diagram of a system embodiment of the present invention;

[0033] Figure 3 This is a block diagram illustrating the composition and structure of the gas supply and precision mixing unit of the present invention;

[0034] Figure 4 This is a block diagram showing the composition and structure of the atomizing spray unit of the present invention;

[0035] Figure 5 This is a block diagram of the composition structure of the local micro-area closed-loop temperature control unit of the present invention;

[0036] Figure 6 This is a structural unit of the instant safety purification unit of the present invention.

[0037] In the diagram: 1. Gas supply and precision mixing unit; 11. Organic acid storage tank; 12. Inert gas source; 13. Dual-channel mass flow controller; 14. Static mixing chamber; 2. Atomizing injection unit; 21. Fan-shaped atomizing nozzle; 22. Direction-adjustable mounting bracket; 3. Local micro-zone closed-loop temperature control unit; 31. Independent heater; 32. Temperature sensor; 33. PID controller; 4. Instant safety purification unit; 41. Exhaust hood; 5. Parameter adaptive control unit. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0039] Examples, such as Figures 1-6As shown, this embodiment provides a pre-activation welding method for photovoltaic solder ribbons, including the following steps:

[0040] Step a: On the continuous travel path of the welding strip, before the flux spraying station, volatile organic acid vapor and inert carrier gas are mixed in proportion by a mass flow controller to form an activation gas with an organic acid concentration of 100-500ppm.

[0041] Step b: Then, through the fixed fan-shaped atomizing nozzle 21, the activation gas is evenly sprayed onto the surface of the welding strip in a manner that covers the full width of the welding strip;

[0042] Step c: Next, an independent temperature control unit is used to synchronously heat the area where the solder ribbon is sprayed, and a closed-loop control is formed by the feedback of temperature sensor 32 to precisely maintain the surface temperature of the solder ribbon within the range of 90-110°C for 1-2 seconds.

[0043] Step d: Next, based on the oxidation risk level determined by the solder strip batch information, the preset process formula is automatically matched and called to set the gas concentration in step a and the temperature value in step c.

[0044] Step e: Finally, the solder strip that has undergone the pre-activation treatment in step a is moved to the subsequent station for flux spraying and heating welding.

[0045] In step a, the volatile organic acid vapor is formic acid or acetic acid with a concentration of 300-500 ppm, and the inert carrier gas is nitrogen.

[0046] In step c, the independent temperature control unit achieves heating by reusing the original preheating platform of the string welding machine or by adding an infrared heater, and the closed-loop control keeps the temperature fluctuation within ±2°C.

[0047] Step a is particularly suitable for processing solder strip coils that have developed a dense, hydroxyl-rich, closed-off corroded oxide layer on the inner layer due to long-term storage.

[0048] This invention also provides a pre-activation welding system for photovoltaic welding ribbons. The system is integrated as an independent functional module between the ribbon unwinding and flux spraying stations of a string welding machine, comprising:

[0049] The gas supply and precision mixing unit 1 includes an organic acid storage tank 11, an inert gas source 12, a dual-channel mass flow controller 13, and a static mixing chamber 14, for generating and delivering a stable concentration of organic acid mixed gas.

[0050] The atomizing spray unit 2 includes at least one fan-shaped atomizing nozzle 21 and an adjustable mounting bracket 22, which is adapted to the existing structure of the string welding machine so that the nozzle is aligned with the surface of the welding strip.

[0051] The local micro-area closed-loop temperature control unit 3 includes an independent heater 31, a temperature sensor 32 and a PID controller 33, which is used to perform precise temperature control of the solder ribbon activation micro-area independently of the string welding machine.

[0052] The instant safety purification unit 4 includes an exhaust hood 41 located above the injection point, which is used to create a local negative pressure and immediately discharge residual gas.

[0053] In the local micro-zone closed-loop temperature control unit 3, the independent heater 31 is an infrared heating tube or hot air nozzle with a power of no more than 50W, the temperature sensor 32 is an infrared thermometer, and the PID controller 33 dynamically adjusts the heater power according to the sensor feedback signal.

[0054] It also includes a parameter adaptive control unit 5, which has multiple sets of process formulas corresponding to different solder strip oxidation risk levels. It can also receive external level signals and automatically drive the gas supply and precision mixing unit 1 and the local micro-area closed-loop temperature control unit 3 to execute the corresponding parameters.

[0055] The specific implementation principles and processes are as follows:

[0056] Gas source and pretreatment:

[0057] Step a: The organic acid vapor source comes from the organic acid storage tank. Since formic acid (boiling point 100.8°C) or acetic acid (boiling point 118°C) has significant volatility at room temperature, the upper space of the storage tank naturally contains saturated vapor of the organic acid. In order to achieve a stable supply, a small flow of high-purity nitrogen gas (called carrier gas) can be introduced into the upper space above the liquid surface of the storage tank to carry out the organic acid vapor, forming a mixed gas flow of organic acid vapor and nitrogen gas (which can be regarded as saturated or high-concentration mother gas).

[0058] The dilution gas source is high-purity nitrogen directly from the nitrogen source;

[0059] Core Hybridization and Proportional Control (implemented by MFC):

[0060] The system is configured with a mass flow controller (MFC) with at least two independent control channels.

[0061] Channel 1 is used to precisely control the flow rate (Q_acid) of the mixed mother gas containing organic acid vapor drawn from the organic acid storage tank.

[0062] Channel 2 is used to precisely control the flow rate of pure nitrogen dilution gas (Q_diluent).

[0063] Concentration control principle: The target volume concentration (C_target, unit ppm) of organic acid in the final output activated gas is determined by the following formula:

[0064] C_target=(Q_acid*C_sat) / (Q_acid+Q_diluent)*10^6

[0065] Wherein, C_sat is the saturation concentration (volume fraction) of organic acid in the mother gas. This value is related to the temperature and pressure of the storage tank and can be regarded as a constant under constant temperature conditions.

[0066] The user or control system sets the target concentration (e.g., 300 ppm) on the device's HMI. The control unit automatically calculates a set of flow rate setpoints for Q_acid and Q_diluent that meet the requirements based on the known or calibrated C_sat value using the formula mentioned above, and sends instructions to the two MFCs respectively. The MFCs execute with high precision (e.g., ±1% of full scale) and adjust the flow rates of the two gas streams to the setpoints respectively. Since the MFC performs closed-loop precision control of the flow rate, it can achieve and stably output a uniform mixed gas with any set concentration in the range of 100-500 ppm.

[0067] Step b: Select a fan-shaped atomizing nozzle 21 with a diffusion angle greater than the width of the welding strip, and rigidly fix it on the body of the string welding machine with a bracket. The installation position is behind the welding strip guide wheel and directly in front of the flux spraying station.

[0068] Adjust the installation position and angle of the nozzle so that the wide side of its fan-shaped spray is perpendicular to the direction of the welding strip's travel, and align the central axis of the spray with the center of the welding strip. Through actual testing or geometric calculation, ensure that within the working distance (e.g., 10-30mm) from the nozzle outlet to the surface of the welding strip, the width of the spray completely covers the entire surface of the welding strip with a slight margin.

[0069] Connect the activated gas pipeline generated in step a to the air inlet of the nozzle. The system provides appropriate and stable gas pressure and total flow rate according to the flow-pressure characteristics of the nozzle to ensure that the fan-shaped spray is fully widened and the flow rate is uniform.

[0070] By observation or using thin plate testing, it was confirmed that the spray could continuously and completely cover the upper surface and both sides of the moving solder strip without any missed areas.

[0071] Step c: The solder ribbon enters the activation zone, and the infrared thermometer collects its surface temperature T_actual in real time.

[0072] Deviation calculation and decision: The PID controller 33 compares T_actual with the set value T_set (within 90-110°C) to obtain the deviation e, and calculates the required heating power output P_out accordingly;

[0073] The controller converts P_out into a control signal to adjust the power of the infrared heater (or preheating platform) in real time.

[0074] The above process cycles at a frequency of milliseconds to keep T_actual stable within the range of T_set±ΔT;

[0075] By designing the ratio of the physical length L of the heating zone to the travel speed V of the welding strip (t=L / V), it is ensured that the welding strip stays in the stable temperature zone for 1-2 seconds.

[0076] Step d: In the parameter storage module of the independent temperature control unit or the main control system of the string welding machine, a process recipe table is pre-created and stored. This table binds the qualitative or semi-quantitative oxidation risk level (such as low, medium, high) to the specific activation process parameters one by one;

[0077] For example:

[0078] Low risk level → Bound formula parameters: {Formic acid concentration: 300ppm, activation temperature: 95°C}

[0079] Risk level → Bound formulation parameters: {Formic acid concentration: 400ppm, activation temperature: 100°C}

[0080] High risk level → Bound formula parameters: {Formic acid concentration: 500ppm, activation temperature: 105°C}

[0081] Based on batch information such as the supplier, packaging method, and storage duration of the welding strip coil, operators manually determine the oxidation risk level of the batch of welding strip according to experience or work instructions.

[0082] It should be noted that the determination of the above-mentioned oxidation risk level does not rely on the operator's subjective guess, but is based on a pre-established work instruction, which converts objective batch information into a risk level. The work instruction is based on the following well-known technical principles in the field:

[0083] (1) Supplier factors: The tin plating processes of different suppliers are different, resulting in different initial oxide film thickness and density when the solder ribbon leaves the factory. This is a common consideration for those skilled in the art when selecting solder ribbon suppliers.

[0084] (2) Packaging method factors: Vacuum packaging or nitrogen-filled packaging can effectively isolate oxygen and moisture, significantly delaying the oxidation of the solder strip surface; while ordinary wrapping packaging cannot prevent air penetration, and the oxidation rate is faster;

[0085] (3) Storage time factor: The oxidation of tin-lead alloy solder strip in the air is a chemical process that accumulates over time. The longer the storage time, the thicker the oxide layer, and the inner layer is more likely to form hydroxyl oxides that are more difficult to reduce due to the sealing effect.

[0086] Based on the aforementioned well-known principles, those skilled in the art can determine the judgment threshold applicable to the incoming material situation of the plant through a limited number of process experiments. Table 1 below provides an example of the judgment rules for a certain production scenario, which are the product of applying the aforementioned well-known principles to specific production conditions.

[0087] Table 1. Example of rules for determining the oxidation risk level of weld strips:

[0088] supplier Packaging Storage time Oxidation risk level Company A Vacuum packaging ≤1 month Low Company A Vacuum packaging 1-3 months middle Company A Vacuum packaging >3 months high Company B Ordinary winding ≤15 days middle Company B Ordinary winding >15 days high Company C Nitrogen-filled packaging ≤2 months Low Company C Nitrogen-filled packaging >2 months middle

[0089] The table above is for illustrative purposes only. In actual production, the specific judgment threshold can be calibrated and adjusted based on the oxide layer thickness data of incoming material inspection, the solderability test results, and the activation effect feedback. This method of formulating work instructions based on objective data and well-known laws is a routine skill of those skilled in the art and can be completed without creative labor.

[0090] Subsequently, on the device's human-machine interface (HMI), the user manually selects and enters the risk level (e.g., clicks "high risk") via drop-down menus, buttons, etc.

[0091] The HMI sends the received high-risk level signal to the system's control unit, which then performs the following automatic operations:

[0092] Formula recall: Based on the high input signal, automatically index and recall the corresponding preset parameters from the stored process formula table, namely {formic acid concentration: 500ppm, activation temperature: 105°C};

[0093] Parameter distribution: The control unit distributes the invoked parameters to the corresponding execution modules.

[0094] The concentration value of 500 ppm is sent to the mass flow controller (MFC) of the gas supply and precision mixing unit 1. The MFC automatically adjusts the flow ratio to output gas of that concentration.

[0095] The 105°C temperature setpoint is sent to the PID controller 33 of the local micro-zone closed-loop temperature control unit 3, and the temperature control unit begins to perform closed-loop control according to this target temperature.

[0096] Step e: The pre-activated solder strip moves naturally to the next adjacent workstation according to the original conveying rhythm of the production line, and the string welding machine automatically completes the conventional flux spraying and welding according to the original program.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A pre-activation soldering method of a photovoltaic solder ribbon, characterized in that, Includes the following steps: Step a: On the continuous travel path of the welding strip, before the flux spraying station, volatile organic acid vapor and inert carrier gas are mixed in proportion by a mass flow controller to form an activation gas with an organic acid concentration of 100-500 ppm. Step b: Then, the activation gas is uniformly sprayed onto the surface of the welding strip in a manner that covers the full width of the welding strip through a fixed fan-shaped atomizing nozzle (21); Step c: Then, the area where the solder strip is sprayed is synchronously heated by an independent temperature control unit, and closed-loop control is formed by the feedback of temperature sensor (32) to accurately maintain the surface temperature of the solder strip within the range of 90-110°C for 1-2 seconds. Step d: Next, based on the oxidation risk level determined by the solder strip batch information, the preset process formula is automatically matched and called to set the gas concentration in step a and the temperature value in step c. Step e: Finally, the solder strip that has undergone the pre-activation treatment in step a is introduced into the subsequent station for flux spraying and heating welding in sequence; In step a, the volatile organic acid vapor is formic acid or acetic acid with a concentration of 300-500 ppm, and the inert carrier gas is nitrogen.

2. A pre-activation soldering method of a photovoltaic solder tab according to claim 1, characterized in that, In step c, the independent temperature control unit achieves heating by reusing the original preheating platform of the string welding machine or by adding an infrared heater, and the closed-loop control keeps the temperature fluctuation within ±2°C.

3. A pre-activation soldering system of photovoltaic soldering strips, using a pre-activation soldering method of photovoltaic soldering strips according to any one of claims 1-2, characterized in that, The system is integrated as an independent functional module between the strip unwinding and flux spraying stations of the string welding machine, including: The gas supply and precision mixing unit (1) includes an organic acid storage tank (11), an inert gas source (12), a dual-channel mass flow controller (13), and a static mixing chamber (14) for generating and delivering a stable concentration of organic acid mixed gas. The atomizing spray unit (2) includes at least one fan-shaped atomizing nozzle (21) and a direction-adjustable mounting bracket (22), which is adapted to the existing structure of the string welding machine so that the nozzle is aligned with the surface of the welding strip; The local micro-area closed-loop temperature control unit (3) includes an independent heater (31), a temperature sensor (32) and a PID controller (33), which is used to perform precise temperature control of the solder ribbon activation micro-area independently of the string welding machine. The instant safety purification unit (4) includes an exhaust hood (41) located above the injection point, which is used to create a local negative pressure and immediately discharge residual gas.

4. A pre-activation welding system for photovoltaic bussing as defined in claim 3, wherein, In the local micro-area closed-loop temperature control unit (3), the independent heater (31) is an infrared heating tube or hot air nozzle with a power of no more than 50W, the temperature sensor (32) is an infrared thermometer, and the PID controller (33) dynamically adjusts the heater power according to the sensor feedback signal.

5. The pre-activation welding system for photovoltaic ribbons according to claim 3, characterized in that, It also includes a parameter adaptive control unit (5), which has multiple sets of process formulas corresponding to different solder strip oxidation risk levels, and can receive external level signals to automatically drive the gas supply and precision mixing unit (1) and the local micro-area closed-loop temperature control unit (3) to execute the corresponding parameters.

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