Flexible component solder paste printing method and system

Abstract

This invention discloses a method and system for printing solder paste on flexible components, belonging to the field of flexible battery technology. The method includes printing solder paste onto the electrodes of multiple small battery cells using multiple sequentially arranged stencils; the total area of ​​the multiple stencils matches the area of ​​the battery cells, each stencil has a size of 300mm*600mm-500mm*800mm, the solder paste viscosity is 100-250 Pa·s, and the surface insulation resistance of the solder paste is ≥1×10⁻⁶. 10 Ω. This invention uses a small screen printing plate to directly print solder paste onto small battery cells, significantly reducing solder paste printing deviation, improving soldering quality, avoiding poor contact, and further effectively improving product reliability. The use of a small screen printing plate reduces limitations on solder paste flowability and viscosity. The improved small screen printing plate in this invention also improves the solder paste composition, enhancing its physical and electrical properties, thereby increasing soldering yield and conversion efficiency.

Description

Technical Field

[0001] This invention belongs to the field of flexible battery technology, specifically relating to a method and system for printing solder paste for flexible components. Background Technology

[0002] In existing flexible module manufacturing processes, solar cells and flexible circuit boards need to be bonded together to form flexible modules for winding or unfolding. When bonding the solar cells and flexible circuit boards, solder paste needs to be applied to the connection points beforehand to achieve conductive and mechanical connections. Current technology typically uses screen printing (using a large screen) to form solder joints on the copper layer of the flexible circuit board, aligning them with the positive and negative electrode soldering points on the small solar cell units, before bonding the solar cells and flexible circuit board. However, this process has some areas for improvement.

[0003] First, in existing technologies, only one large screen (with a size of 1200mm×2500mm or more) is typically used to print solder paste on flexible circuit boards. However, the large screen is stretched during the printing process, resulting in a large tolerance in the printing position. At the same time, the flexible circuit board itself also has a certain tolerance. The combination of the two results in a large deviation in solder paste printing.

[0004] Secondly, a solar cell consists of multiple small battery units, each with a size of less than 50mm*50mm. However, each small battery unit has many electrode contact points (6 solder joints per small battery unit). For example, a solar cell with 13*20 arrayed small battery units has 1560 solder joints. When solder paste is printed on a flexible circuit board, it is easy to have poor contact during the mounting process, which affects the reliability of the product.

[0005] Third, the large screen printing plates used in the existing technology have very high requirements for the fluidity and viscosity of the solder paste. They need to meet the requirements of both screen printing and adhesion to the connection parts, which in turn limits the physical and electrical properties of the solder paste and affects the soldering yield and conversion efficiency.

[0006] It should be noted that this part of the present invention only provides background technology related to the present invention, and does not necessarily constitute prior art or known technology. Summary of the Invention

[0007] This invention aims to at least solve the problems of large solder paste printing deviations and poor solder paste performance during the bonding of battery cells and flexible circuit boards in existing technologies. This invention provides a method and system for solder paste printing on flexible components. By optimizing the solder paste printing process and using a small stencil to directly print solder paste onto small battery cells, this invention significantly reduces solder paste printing deviations, improves soldering quality, avoids poor contact, and further effectively enhances product reliability. Simultaneously, the solder paste used in the optimized solder paste printing process of this invention helps improve soldering yield and conversion efficiency.

[0008] To achieve the above objectives, in a first aspect, the present invention provides a method for printing solder paste on flexible components. The flexible component includes a battery cell and a flexible circuit board. The battery cell is composed of multiple small battery cells arranged in an array. The method includes printing solder paste onto the electrodes of the multiple small battery cells using multiple sequentially arranged screens. The total area of ​​the multiple screens matches the area of ​​the battery cell. Each screen has a size of 300mm*600mm-500mm*800mm, the solder paste viscosity is 100-250 Pa·s, and the surface insulation resistance of the solder paste is ≥1×10⁻⁶. 10 Ω.

[0009] Furthermore, the area of ​​the solder paste dots printed on the electrodes of the small battery unit is 0.3mm*0.5mm-0.5mm*0.8mm.

[0010] Further, the solder paste is composed of the following components by mass percentage: 85-90% alloy powder and 10-15% flux; the alloy powder includes 10-30% bismuth, 30-45% lead, and the balance being tin; or it may also contain 0.5-1% other metals, which are one or a combination of silver, copper, nickel, and titanium.

[0011] Furthermore, the alloy powder particle size type is one or more of T2, T3, and T4.

[0012] Furthermore, the flux contains the following components by weight percentage: 30-50% diluent, 10-35% rosin resin, 5-20% organic acid, 2-8% surfactant, 1-5% antioxidant, and 1-3% corrosion inhibitor; wherein the rosin resin comprises synthetic resin and acid-free rosin.

[0013] Furthermore, the diluent is selected from one or a combination of alcohols, esters, alcohol ethers, hydrocarbons, and ketones.

[0014] Furthermore, the synthetic resin is selected from one or a combination of methyl methacrylate copolymer and silicone-modified acrylic resin.

[0015] Furthermore, the acid-free rosin is selected from one or a combination of hydrogenated rosin, polymerized rosin, and disproportionated rosin.

[0016] Furthermore, the organic acid is selected from one or a combination of succinic acid, methylsuccinic acid, glutaric acid, adipic acid, octanoic acid, sebacic acid, dipropionic acid, itaconic acid, and salicylic acid.

[0017] Furthermore, the surfactant is selected from one or a combination of perfluorooctyl sulfonate ammonium and Thomas Amphoteric Surfactants.

[0018] Furthermore, the antioxidant is selected from one or a combination of hydroquinone, tert-butylhydroquinone, and thiodipropionates.

[0019] Furthermore, the corrosion inhibitor is selected from one or a combination of benzotriazole, triethanolamine, and imidazole compounds.

[0020] Furthermore, after printing the solder paste onto the electrodes of the small battery cell, the process also includes drying the solder paste; wherein the drying temperature is 80-100℃ and the drying time is 3-5 minutes.

[0021] Furthermore, after drying the solder paste, the process also includes: printing insulating adhesive on the small battery cells that have already been printed with solder paste; and bonding the battery cells to the flexible circuit board.

[0022] Secondly, the present invention provides a flexible component solder paste printing system, which is applied to a flexible component solder paste printing method, and the system includes:

[0023] A screen printing apparatus is used to print solder paste onto the electrodes of multiple small battery cells using multiple sequentially arranged screens; wherein the total area of ​​the multiple screens matches the area of ​​the battery cell, and the size of each screen is 300mm*600mm-500mm*800mm.

[0024] The following comparison with existing technologies will explain in detail the beneficial effects of the improved solder paste printing process of this invention from a principle perspective:

[0025] When bonding the battery cells and the flexible circuit board, solder paste needs to be applied to the connection points in advance to achieve conductive and mechanical connection. Currently, it is common practice to use screen printing to form solder joints on the copper layer of the flexible circuit board, which are aligned with the positive and negative electrode soldering points on the small battery cells, and then bond the battery cells and the flexible circuit board together.

[0026] However, this process has some areas for improvement. First, due to equipment compatibility and printing efficiency limitations, existing technologies typically use only one large screen for solder paste printing. However, with the continuous development of the photovoltaic industry, the quality requirements for products are gradually increasing. Large screens, due to uneven tension and poor stability, are prone to excessive solder paste printing deviations, severely affecting product quality. This invention replaces the large screen in existing technologies with multiple small screens of specific sizes, reducing printing deviations caused by the large screen itself, effectively avoiding poor contact problems during component placement, and improving product reliability and soldering quality. Large screens have very large printing deviations, exceeding 1mm, while small screens offer higher printing precision, controlling the deviation below 50μm. Furthermore, the use of small screens reduces solder paste waste, lowering material costs. Simultaneously, small screens are easier to clean and maintain, reducing cleaning time and material loss, further reducing production costs.

[0027] Secondly, a solar cell comprises multiple small battery cells, each with a very small size (typically 5-50mm on each side). These small cells are difficult to arrange perfectly. To maximize printing efficiency, existing technologies typically print solder paste onto flexible circuit boards rather than directly onto the individual battery cells. However, due to the flexibility and bendability of flexible circuit boards, the solder paste placement during printing often exhibits significant deviations. Since the arrangement problem of small battery cells has been largely solved, this invention chooses to directly print solder paste onto the electrodes of the small battery cells. This avoids printing deviations caused by the flexible circuit board itself, ensuring the subsequent solder paste connection effect and quality, and effectively improving the soldering yield.

[0028] It should be noted that existing technologies typically print solder paste onto flexible circuit boards. Besides the arrangement of small battery cells, another reason is that this allows for separate but simultaneous arrangement of the small battery cells and solder paste printing, improving production efficiency. Furthermore, the flexible circuit board and the large screen printing plate work together. Flexible circuit boards are often continuous strip structures, and a single print from the large screen printing plate can cover multiple solder joint areas, avoiding frequent positioning adjustments and aligning with the ductility of the flexible substrate. Using multiple small screen printing plates for segmented calibration of the flexible circuit board would amplify accumulated errors. However, as mentioned above, using a large screen printing plate to print solder paste onto the flexible circuit board results in significant printing deviations. This invention, by directly printing solder paste onto the electrodes of the small battery cells, avoids printing deviations caused by the flexible circuit board itself, ensuring the subsequent solder paste connection effect and quality, and effectively improving the soldering yield.

[0029] Third, existing solder paste printing technologies use large screens, which require high fluidity and viscosity of the solder paste. This is because the large screen size and wide printing area necessitate the solder paste covering a greater distance during printing, requiring better fluidity to ensure even filling of the mesh openings and transfer to the substrate. Furthermore, due to the larger structure and printing deviations of the large screen itself, existing technologies produce solder paste dots with larger areas (0.7mm × 1.6mm). In such cases, solely pursuing high fluidity can easily lead to short circuits between the positive and negative electrodes, especially given the limited space in small battery cells. Therefore, existing technologies demand high fluidity and viscosity of the solder paste, but this limits its physical and electrical properties, thus affecting soldering yield and conversion efficiency. In contrast, this invention uses a small screen with a smaller printing area and solder paste dot area, reducing the limitations on solder paste fluidity. The improved small screen printing technology of this invention also improves the solder paste composition, enhancing its physical and electrical properties, thereby improving soldering yield and conversion efficiency.

[0030] The flexible component solder paste printing system of the present invention includes a screen printing device with multiple small screens of specific sizes, which significantly improves the accuracy of solder paste printing, enhances product reliability, and has significant advantages and practical application value. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the metal screen printing plate used in the flexible component solder paste printing method provided in Comparative Example 1 of the present invention.

[0033] Figure 2 This is a schematic diagram of the flexible circuit board structure of the flexible component solder paste printing method provided in Comparative Example 1 of the present invention.

[0034] Figure 3 The schematic diagram of the flexible component solder paste printing method provided in Embodiment 1 of the present invention is a structural diagram of directly printing solder paste onto small battery cells using a small screen printing plate.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1. Battery cell; 1-1 Small battery unit; 1-2 Solder paste dots; 4. Flexible circuit board; 4-2 Copper layer; 4-3 Solder joint; 5. Metal mesh; 5-1 Mesh opening. Detailed Implementation

[0037] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0039] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0040] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0041] This invention provides a method for printing solder paste on flexible components. The flexible component includes a battery cell and a flexible circuit board. The battery cell is composed of multiple small battery cells arranged in an array. The method includes printing solder paste onto the electrodes of the multiple small battery cells using multiple sequentially arranged stencils. The total area of ​​the multiple stencils matches the area of ​​the battery cell. Each stencil has a size of 300mm*600mm-500mm*800mm, the solder paste viscosity is 100-250 Pa·s, and the surface insulation resistance of the solder paste is ≥1×10⁻⁶. 10 Ω.

[0042] This invention employs a small screen printing plate to directly print solder paste onto small battery cells, significantly reducing solder paste printing deviations, improving soldering quality, avoiding poor contact, and further effectively enhancing product reliability. The use of a small screen printing plate reduces solder paste waste and lowers material costs. Simultaneously, the small screen printing plate is easier to clean and maintain, reducing cleaning time and material loss, further lowering production costs. This invention reduces restrictions on solder paste flowability. The improved small screen printing plate used in this invention also improves the solder paste composition, enhancing its physical and electrical properties, thereby increasing soldering yield and conversion efficiency.

[0043] It should be noted that, for the sake of production efficiency, the multiple screens mentioned in this invention generally refer to two or more. The multiple screens are arranged sequentially according to the electrode positions of the small battery cells. The spacing between the screens can be dynamically adjusted according to the number and spacing of the small battery cells in the array. The multiple screens can be arranged horizontally, vertically, or in an array, etc.

[0044] For specific printing methods, refer to conventional screen printing techniques in the existing technology; this invention does not impose any special limitations on them.

[0045] Furthermore, the size of the screen is 300mm*600mm-500mm*800mm, specifically 300mm*600mm, 400mm*700mm, 500mm*800mm and any value between them.

[0046] Furthermore, small screen printing plates have many significant advantages over large screen printing plates. First, the size of small screen printing plates is smaller (about 1 / 5 to 1 / 3 the size of large screen printing plates), which allows them to maintain higher printing precision during production and use, effectively reducing printing deviations caused by screen printing plate factors, thereby significantly improving printing quality.

[0047] Secondly, the tension of the small screen is easier to maintain uniformly, avoiding printing problems caused by uneven tension, and further ensuring the uniformity and consistency of printing.

[0048] Furthermore, the frame of a small screen printing plate has relatively high strength and stability, and is not prone to deformation or movement. This helps maintain the stability of the printing process and reduces printing deviations caused by factors such as equipment impact or aging and loosening.

[0049] Finally, smaller screens have relatively lower operating costs. Not only are they more economical to produce, but they also waste less solder paste during printing and are easier and faster to clean and maintain, thus significantly reducing production and equipment maintenance costs. Specifically, large screens suffer significant solder paste loss during cleaning, exceeding 50g per cleaning cycle and taking over 20 minutes; smaller screens, on the other hand, lose only 1-2g per cleaning cycle, taking only 1-2 minutes. Furthermore, the cost of each large screen is more than 10 times that of each small screen. At the same cost, the total printing area of ​​multiple small screens far exceeds that of a single large screen.

[0050] Furthermore, the viscosity of the solder paste is 100-250 Pa·s, specifically 100 Pa·s, 110 Pa·s, 120 Pa·s, 130 Pa·s, 140 Pa·s, 150 Pa·s, 160 Pa·s, 170 Pa·s, 180 Pa·s, 190 Pa·s, 200 Pa·s, 210 Pa·s, 220 Pa·s, 230 Pa·s, 240 Pa·s, 250 Pa·s, and any value between them.

[0051] Preferably, the viscosity of the solder paste is tested according to JIS-Z-3284 / IPC-TM-650 2.4.34. At 25±1℃, an NDJ-7 type rotary viscometer is used to rotate continuously at 7.5 rpm for 2 minutes, and the reading is taken after stabilization.

[0052] Understandably, generally speaking, the higher the viscosity of solder paste, the lower the fluidity and the higher the tackiness of the adhesive; conversely, the lower the viscosity of solder paste, the higher the fluidity and the lower the tackiness of the adhesive. However, existing solder pastes require a balance between fluidity and tackiness, thus placing stringent requirements on their viscosity.

[0053] Furthermore, compared to existing technologies that require solder paste with a balance of fluidity and viscosity, the small-screen printing of this invention does not have strict requirements on the fluidity and viscosity of the solder paste. Theoretically, this invention can use solder paste of any viscosity, all of which should be within the scope of protection of this invention. Based on this, this invention selects solder paste with appropriate viscosity, thereby improving the physical and electrical properties of the solder paste.

[0054] Furthermore, the solder paste of this invention, with its suitable viscosity, exhibits better anti-slump properties during printing, effectively preventing issues such as solder paste collapse and overflow during the printing process, thereby improving printing accuracy and consistency. In addition, the solder paste of this invention is also more suitable for fine-pitch printing, ensuring excellent performance in solder joint buildup, forming full and smooth solder joints, reducing soldering defects, and improving soldering quality. Simultaneously, the solder paste of this invention exhibits minimal viscosity change during continuous printing, maintaining stable printing results, reducing printing defects caused by viscosity variations, and improving production efficiency. During storage and use, it has a longer service life, is less prone to drying out, and reduces solder paste waste and production costs.

[0055] Furthermore, the surface insulation resistance of the solder paste is ≥1×10⁻⁶. 10 Ω, specifically 1×10 10 Ω, 5×10 10 Ω, 1×10 11 Ω, 5×10 11 Ω, 1×10 12 Ω, 5×10 12 Ω can be higher than or equal to any value in between.

[0056] Preferably, the test method for the surface insulation resistance of the solder paste refers to GB / T9491-2002. After the solder comb is placed in an environment with a temperature of 40°C and a humidity of 93% for 96 hours, it is taken out and the insulation resistance of the solder paste surface is measured. The test voltage is DC500V.

[0057] Furthermore, the high surface insulation resistance solder paste of the present invention has significant advantages. After curing, the high surface insulation resistance solder paste exhibits excellent surface insulation properties, effectively preventing leakage current caused by accidental conduction between adjacent conductors. Simultaneously, it improves the long-term reliability of soldering, preventing moisture absorption by residues in harsh environments such as humid conditions from causing a decrease in surface insulation resistance, leading to corrosion or short circuits. High surface insulation resistance can also further improve the electrical performance of the battery, effectively increasing battery yield and conversion efficiency.

[0058] Furthermore, the solder paste is composed of the following components by mass percentage: 85-90% alloy powder and 10-15% flux; wherein the alloy powder includes 10-30% bismuth, 30-45% lead, and the balance is tin; or it may also contain 0.5-1% other metals, wherein the other metals are one of silver, copper, nickel, and titanium.

[0059] Preferably, the alloy powder has a mass percentage of 85-90%, which can be 85%, 86%, 87%, 88%, 89%, 90%, and any value between them.

[0060] Preferably, the flux is 10-15%, and can be 10%, 11%, 12%, 13%, 14%, 15%, or any value between them.

[0061] Preferably, the mass percentage of bismuth in the alloy powder is 10-30%, which can be 10%, 15%, 20%, 25%, 30%, or any value between them.

[0062] Preferably, the lead content in the alloy powder is 30-45% by mass, and can be 30%, 35%, 40%, 45% or any value between them.

[0063] Understandably, bismuth, lead, and tin each have unique functions and roles in solder paste. Tin, as the base component of the solder paste alloy, provides the main structural support and conductivity, exhibiting excellent metal bonding ability to form strong solder joints. The addition of bismuth effectively lowers the melting point of the solder paste and improves wettability, which is crucial for solder joint formation and quality improvement during the soldering process. The addition of lead effectively inhibits tin whisker growth and improves the fatigue resistance of the solder joint. Furthermore, other metals, such as silver, are mainly used to improve the wettability of the solder joint during the soldering process, increase its strength and fatigue resistance, and help maintain stability at high temperatures, reducing soldering problems caused by thermal expansion and contraction. Simultaneously, bismuth and silver also enhance the solder's oxidation resistance and inhibit the formation of intermetallic compounds, thereby improving the reliability and durability of the soldering. The addition of copper strengthens the rigidity of the solder, increases solder joint strength, inhibits the growth of intermetallic compounds, and delays solder joint aging.

[0064] The alloy powder has one or more particle size types, namely T2, T3, and T4. It should be noted that currently, alloy powder particle size types range from T2 to T10. For solder paste alloy powders of T2-T6, 80% of the alloy particles must be distributed within a specific range. Specifically, for alloy powder of particle size type T2, 80% of the particle diameter must be between 45-75 μm; for alloy powder of particle size type T3, 80% of the particle diameter must be between 25-45 μm; and for alloy powder of particle size type T4, 80% of the particle diameter must be between 20-38 μm.

[0065] It is understood that the alloy powder of the present invention has a suitable particle size, which helps to improve printing resolution, reduce collapse, increase surface area, and accelerate melting reaction.

[0066] Furthermore, the flux contains the following components by weight percentage: 30-50% diluent, 10-35% rosin resin, 5-20% organic acid, 2-8% surfactant, 1-5% antioxidant, and 1-3% corrosion inhibitor; wherein the rosin resin comprises synthetic resin and acid-free rosin.

[0067] Preferably, the mass percentage of the diluent is 30-50%, and can be 30%, 33%, 35%, 38%, 40%, 43%, 45%, 48%, 50%, and any value between them.

[0068] Furthermore, the diluent is selected from one or a combination of alcohols, esters, alcohol ethers, hydrocarbons, and ketones, preferably from one or a combination of ethylene glycol monobutyl ether, ethanol, ethylene glycol, glycerol, and ethylene glycol butyl ether. The main function of the diluent is to dissolve the solid components, adjust the viscosity and evaporation rate to make them easier to coat, and help other components mix evenly, so that they maintain a stable shape during the printing process and prevent collapse and runoff.

[0069] Furthermore, alcohols can be selected from ethanol, 2-butanol, ethylene glycol, propylene glycol, and glycerol, etc.; esters can be selected from ethyl acetate, butyl acetate, etc.; alcohol ethers can be selected from diethylene glycol ethyl ether alcohol, ethylene glycol monoethyl ether, propylene glycol methyl ether, etc.; hydrocarbons can be selected from toluene, etc.; and ketones can be selected from acetone, methyl ethyl ketone, N-aminopyrrolidone, etc.

[0070] It is understood that the present invention uses a small screen printing process. Compared with the large screen printing process that requires high-flow solder paste in the prior art, the present invention significantly reduces the proportion of diluent in the flux (the proportion of diluent in the flux in the prior art is about 70-80%). The lower diluent content can maintain the appropriate viscosity of the solder paste and at the same time significantly reduce the amount of residue after solder paste printing, thereby improving the surface insulation resistance of the solder paste.

[0071] Preferably, the rosin resin has a mass percentage of 10-35%, which can be 10%, 15%, 20%, 25%, 30%, 35%, and any value between them.

[0072] Furthermore, rosin resin includes synthetic resin and acid-free rosin. The synthetic resin is selected from one or a combination of methyl methacrylate copolymer and silicone-modified acrylic resin; the acid-free rosin is selected from one or a combination of hydrogenated rosin, polymerized rosin, and disproportionated rosin. After melting during soldering, rosin resin forms a highly fluid liquid, reducing the interfacial tension between the molten solder and the metal surface. This helps the solder "spread" and coat the pads or component leads, contributing to a complete, smooth, and full solder joint, thus improving soldering quality. After decomposition or melting, rosin resin forms a protective film that isolates the metal from air, preventing re-oxidation and improving the insulation performance of the solder joint, ensuring soldering reliability.

[0073] Preferably, the organic acid has a mass percentage of 5-20%, which can be 5%, 10%, 15%, 20%, or any value between them.

[0074] Furthermore, the organic acid is selected from one or a combination of succinic acid, methylsuccinic acid, glutaric acid, adipic acid, octanoic acid, sebacic acid, dipropionic acid, itaconic acid, and salicylic acid. As an active agent, the organic acid can effectively remove oxides from the metal surface, reduce surface tension during the welding process, and promote the wetting and diffusion of the solder with the metal surface, which helps to improve welding quality and welding strength.

[0075] Preferably, the surfactant is 2-8% by mass, and can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value between them.

[0076] Furthermore, the surfactant is selected from one or a combination of perfluorooctyl sulfonate ammonium and Thomas amphipathic surfactants. Surfactants can reduce surface tension and improve wettability, making it easier for the solder to bond with the battery cell electrode solder joints, improving printout contours and edge collapse behavior. Surfactants can also completely react or vaporize and decompose after soldering, significantly reducing corrosive residues, increasing insulation performance, and improving long-term electrical reliability.

[0077] Preferably, the antioxidant is 1-5% by mass, and can be 1%, 2%, 3%, 4%, 5% or any value between them.

[0078] Furthermore, the antioxidant is selected from one or a combination of hydroquinone, tert-butylhydroquinone, and thiodipropionates. Antioxidants in solder paste can effectively improve oxidation removal efficiency. On one hand, they preferentially react with oxygen or free radicals, inhibiting further oxidation of metal powder and flux components during storage and heating, maintaining the "fresh" state of the solder surface. On the other hand, antioxidants can also stabilize the flux system, preventing its failure at high temperatures, extending flux activity time, and improving the damp heat stability and electrical insulation of residues after soldering, thereby further improving the overall solder joint quality and long-term reliability.

[0079] Preferably, the corrosion inhibitor has a mass percentage of 1-3%, which can be 1%, 1.5%, 2%, 2.5%, 3%, or any value between them.

[0080] Furthermore, the corrosion inhibitor is selected from one or a combination of benzotriazole, triethanolamine, and imidazole compounds. The main function of the corrosion inhibitor is to prevent further oxidation of the metal surface during welding, protecting the base metal. The corrosion inhibitor also reduces corrosive substances generated during welding, ensuring weld quality and extending the service life of the welding equipment.

[0081] It should be noted that, without significantly altering the surface insulation resistance baseline characteristics of the solder paste, other additives can be selectively added to the flux according to the actual application scenario. These additives may include, but are not limited to, thixotropic agents, film-forming agents, tackifiers, leveling agents, and defoamers.

[0082] Furthermore, the thixotropic agent can be hydrophobic nano-silica with a particle size of 10-50 nm. The thixotropic agent can improve the rheological properties of the flux, giving it good flowability and formability during printing. It also prevents sedimentation and separation of the flux after printing, ensuring the uniformity and stability of the flux.

[0083] Furthermore, ordinary silica surfaces are rich in hydroxyl groups (-OH), which easily adsorb moisture and react with organic acids, leading to unstable solder paste viscosity or agglomeration. This invention, through silanization hydrophobic modification (such as grafting long-chain alkyl or fluorocarbon groups), firstly, significantly reduces particle surface polarity to prevent moisture absorption and clumping, reducing flowability degradation caused by moisture absorption during storage; secondly, it avoids side reactions with organic acids and diluents in the flux, ensuring long-term viscosity stability and improving compatibility with organic systems; thirdly, the hydrophobic surface more easily forms a three-dimensional network structure through van der Waals forces, enhancing thixotropic efficiency, maintaining suitable viscosity under static conditions, and rapidly thinning during dynamic shearing, adapting to the high-precision printing requirements of small screen printing.

[0084] Furthermore, nano-sized particles have a higher specific surface area, allowing for the efficient construction of a dense thixotropic network with only a small amount added, enabling precise control of solder paste flowability. The small-diameter particles can disperse rapidly under the pressure of the printing squeegee, instantly increasing flowability and ensuring rapid filling of the stencil micropores with solder paste. Simultaneously, the network can be quickly reconstructed after the external force is removed, inhibiting solder paste collapse after printing and improving the clarity of solder joint edges. At the same time, the nanoparticles are uniformly suspended in the solder paste, exhibiting higher anti-settling stability and avoiding component segregation caused by alloy powder sedimentation, thus ensuring printing consistency.

[0085] Furthermore, after printing the solder paste onto the electrodes of the small battery cell, the process also includes drying the solder paste; the drying temperature is 80-100℃, and the drying time is 3-5 minutes. Drying the solder paste after printing it onto the electrodes of the small battery cell effectively removes diluent and moisture, improves the viscosity and wettability of the solder paste, enhances soldering quality, and increases production efficiency and product reliability.

[0086] Furthermore, the present invention rationally sets the drying temperature and drying time to avoid the solder paste from turning into tin and affecting the subsequent hot pressing effect.

[0087] Furthermore, after drying the solder paste, the process also includes:

[0088] Print insulating adhesive onto the small battery cells after solder paste has been applied;

[0089] The battery cells are bonded to the flexible circuit board.

[0090] Furthermore, compared with the prior art, the present invention pre-prints solder paste on the electrodes of the small battery cell when printing insulating adhesive on the small battery cell, thus avoiding the problem that solder paste may overflow into the insulating area and cause short circuits between adjacent electrodes when the insulating adhesive is applied first and then the solder paste is printed.

[0091] Furthermore, the area of ​​the solder paste dots printed on the electrodes of the small battery cell is 0.3mm*0.5mm-0.5mm*0.8mm, specifically 0.3mm*0.5mm, 0.4mm*0.5mm, 0.4mm*0.6mm, 0.4mm*0.7mm, 0.5mm*0.8mm, and any value between them. Because this invention uses a small screen to directly print solder paste onto the small battery cell, the area of ​​the solder paste dots can be significantly reduced (equivalent to about 1 / 3 to 1 / 7 of the area of ​​solder paste dots on a large screen). Although the organic acids in the solder paste can remove metal oxides to improve soldering, residual acidic substances can easily lead to increased contact resistance, causing short circuits or leakage. Reducing the area of ​​the solder paste dots directly reduces the total amount of organic acid per unit solder joint, effectively reducing the reliability risks caused by residual organic acids.

[0092] Understandably, based on small-screen printing, this invention can reduce the area of ​​each solder paste dot by controlling the amount of solder paste printed, adjusting the squeegee pressure, and screen spacing, etc. For details, please refer to the existing technology. This can effectively avoid leakage current caused by accidental conduction between adjacent conductors, while reducing the amount of solder paste used and lowering costs.

[0093] It should be noted that using a large stencil and printing solder paste on a flexible circuit board are mutually compatible. Specifically, the large stencil, due to its structure, makes it difficult to print small solder paste dots, while flexible circuit boards, due to their larger printing tolerances, require larger solder paste dots. Furthermore, flexible circuit boards have relatively lower precision requirements for solder paste printing, thus the two are well-matched. However, excessively large solder paste dot areas can lead to accidental continuity between adjacent conductors, causing leakage current and increasing solder paste usage. The technical solution of this invention effectively solves this problem.

[0094] Secondly, the present invention provides a flexible component solder paste printing system, which is applied to a flexible component solder paste printing method, and the system includes:

[0095] A screen printing apparatus is used to print solder paste onto the electrodes of multiple small battery cells using multiple sequentially arranged screens; the total area of ​​the multiple screens matches the area of ​​the battery cells, and the size of each screen is 300mm*600mm-500mm*800mm.

[0096] Furthermore, the flexible component solder paste printing system may also include a drying device for drying the solder paste, an insulating adhesive printing device for printing insulating adhesive on the small battery cells after the solder paste has been printed, and a bonding device for bonding the battery cells to the flexible circuit board. This invention does not impose any particular limitation on the above-mentioned devices; commonly used devices in the prior art can be employed.

[0097] The embodiments of the present invention described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0098] Example 1

[0099] like Figure 3 As shown, a method for printing solder paste for flexible components includes:

[0100] Solder paste is printed onto the electrodes of multiple small battery cells 1-1 using multiple stencils arranged in sequence; wherein the total area of ​​the multiple stencils matches the area of ​​the battery cell 1, and the size of each stencil is 400mm*700mm.

[0101] There are four screens arranged in an array, and the battery cell 1 is located below the four screens.

[0102] The area of ​​solder paste dots 1-2 printed on the electrodes of the small battery unit 1-1 is 0.4mm*0.6mm.

[0103] The solder paste is dried at a temperature of 100°C for 5 minutes.

[0104] Print insulating adhesive onto the small battery cell 1-1 after the solder paste has been printed;

[0105] The battery cell 1 is bonded to the flexible circuit board.

[0106] The solder paste of this embodiment is composed of the following components by weight percentage: 90% alloy powder and 10% flux; wherein the alloy powder includes 30% bismuth, 30% lead, and the balance is tin.

[0107] The alloy powder particle size type is T3.

[0108] The flux in this embodiment contains the following components by weight percentage: 40% diluent, 35% rosin resin, 15% organic acid, 5% surfactant, 3% antioxidant, and 2% corrosion inhibitor; the rosin resin includes synthetic resin and acid-free rosin.

[0109] The diluent in this embodiment is glycerol.

[0110] The synthetic resin in this embodiment is methyl methacrylate copolymer; the acid-free rosin is hydrogenated rosin.

[0111] The organic acid in this embodiment is succinic acid.

[0112] The surfactant in this embodiment is ammonium perfluorooctyl sulfonate.

[0113] The antioxidant in this embodiment is hydroquinone.

[0114] The corrosion inhibitor in this embodiment is benzotriazole.

[0115] The solder paste has a viscosity of 200 Pa·s and a surface insulation resistance of 5 × 10⁻⁶. 10 Ω.

[0116] Example 2

[0117] The flexible component solder paste printing method in Example 2 is the same as the method provided in Example 1, except that the size of the screen in Example 2 is 300mm*600mm.

[0118] Example 3

[0119] The flexible component solder paste printing method in Example 3 is the same as the method provided in Example 1, except that the size of the screen in Example 3 is 500mm*800mm.

[0120] Example 4

[0121] The flexible component solder paste printing method in Example 4 is carried out in accordance with the method provided in Example 1, except that the area of ​​the solder paste dots printed on the electrodes of the small battery unit in Example 4 is 0.3mm*0.5mm.

[0122] Example 5

[0123] The flexible component solder paste printing method in Example 5 is carried out in accordance with the method provided in Example 1, except that the area of ​​the solder paste dots printed on the electrodes of the small battery unit in Example 5 is 0.5mm*0.8mm.

[0124] Example 6

[0125] The flexible component solder paste printing method of Example 6 is carried out in accordance with the method provided in Example 1, except that the flux of Example 6 contains the following components by mass percentage: 40% diluent, 25% rosin resin, 10% organic acid, 8% surfactant, 5% antioxidant, 2% corrosion inhibitor, and 10% thixotropic agent;

[0126] The thixotropic agent is hydrophobic nano-silica with a particle size of 30 nm.

[0127] The solder paste has a viscosity of 190 Pa·s and a surface insulation resistance of 4 × 10⁻⁶. 10 Ω.

[0128] Example 7

[0129] The flexible component solder paste printing method of Example 7 is carried out in accordance with the method provided in Example 1, except that the solder paste of Example 7 is composed of the following components by mass percentage: 85% alloy powder and 15% flux;

[0130] The flux contains the following components by weight percentage: 50% diluent, 30% rosin resin, 5% organic acid, 8% surfactant, 5% antioxidant, and 2% corrosion inhibitor;

[0131] The solder paste has a viscosity of 100 Pa·s and a surface insulation resistance of 1.5 × 10⁻⁶. 10 Ω.

[0132] Example 8

[0133] The flexible component solder paste printing method of Example 8 is carried out in accordance with the method provided in Example 1, except that the flux of Example 8 contains the following components by mass percentage: 30% diluent, 35% rosin resin, 20% organic acid, 8% surfactant, 5% antioxidant, and 2% corrosion inhibitor;

[0134] The solder paste has a viscosity of 250 Pa·s and a surface insulation resistance of 1 × 10⁻⁶. 11 Ω.

[0135] Comparative Example 1

[0136] like Figure 1 and Figure 2 As shown, Comparative Example 1 uses existing technology to print solder paste on flexible components. The method includes the following steps:

[0137] The metal screen 5 is mounted on the solder paste printing machine, and the flexible circuit board 4 is placed under the metal screen 5 for alignment. Solder paste is printed through the mesh 5-1, and solder joints 4-3 are formed on the copper layer 4-2 to be aligned and soldered with the positive and negative electrode soldering points of the small battery unit. The size of the screen is 1400mm*3000mm.

[0138] The area of ​​the solder joint 4-3 printed on the copper layer 4-2 is 0.7mm*1.6mm;

[0139] Insulating adhesive is printed onto the small battery cells;

[0140] The battery cells are bonded to the flexible circuit board.

[0141] The solder paste used is a commonly used solder paste in existing technologies, with a viscosity of 50 Pa·s and a surface insulation resistance of 1 × 10⁻⁶. 9 Ω.

[0142] Comparative Example 2

[0143] The flexible component solder paste printing method of Comparative Example 2 is carried out in accordance with the method provided in Example 1, except that the flux in Comparative Example 2 is composed of the following components by mass percentage: 70% diluent, 10% rosin resin, 10% organic acid, 5% surfactant, 3% antioxidant, and 2% corrosion inhibitor.

[0144] The solder paste has a viscosity of 80 Pa·s and a surface insulation resistance of 2 × 10⁻⁶. 9 Ω.

[0145] Test case

[0146] The flexible components obtained in the embodiments and comparative examples were tested, and the results are shown in Table 1.

[0147] Table 1

[0148]

[0149] As shown in Table 1, according to Examples 1 to 8, the preferred technical solutions of the present invention help to further reduce solder paste printing accuracy, improve soldering yield and battery conversion efficiency.

[0150] A comparison of Comparative Example 1 and Example 1 shows that the present invention, by directly printing solder paste onto small battery cells using multiple small stencils of specific sizes, reduces printing deviations caused by large stencils and the flexible circuit board itself, effectively avoiding contact problems during surface mount assembly, and improving product reliability and soldering quality. The use of small stencils in this invention reduces restrictions on solder paste flowability. The improved small stencil printing method of this invention also improves the solder paste composition, enhancing its physical and electrical properties, thereby increasing soldering yield and conversion efficiency.

[0151] Based on the comparison between Comparative Example 2 and Example 1, it can be seen that the use of a small screen printing plate in this invention reduces the restrictions on the fluidity and viscosity of the solder paste. The improved small screen printing plate of this invention improves the composition of the solder paste, enhances the physical and electrical properties of the solder paste, and thus improves the soldering yield and conversion efficiency.

[0152] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for printing solder paste for a flexible component, the flexible component comprising a battery cell and a flexible circuit board, the battery cell being composed of multiple small battery cells arranged in an array, characterized in that, The method involves using multiple sequentially arranged screens to print solder paste onto the electrodes of multiple small battery cells; The total area of ​​the multiple stencils matches the area of ​​the solar cell. Each stencil has a size of 300mm*600mm-500mm*800mm. The solder paste has a viscosity of 100-250 Pa·s and a surface insulation resistance ≥1×10⁻⁶. 10 Ω.

2. The flexible component solder paste printing method according to claim 1, characterized in that, The area of ​​the solder paste dots printed on the electrodes of the small battery unit is 0.3mm*0.5mm-0.5mm*0.8mm.

3. The flexible component solder paste printing method according to claim 1, characterized in that, The solder paste is composed of the following components by weight percentage: 85-90% alloy powder and 10-15% flux; The alloy powder comprises 10-30% bismuth, 30-45% lead, and the balance being tin; or may also contain 0.5-1% other metals, wherein the other metals are one or a combination of silver, copper, nickel, and titanium.

4. The flexible component solder paste printing method according to claim 3, characterized in that, The alloy powder particle size type is one or a combination of T2, T3, and T4.

5. The flexible component solder paste printing method according to claim 3, characterized in that, The flux comprises the following components by weight percentage: 30-50% diluent, 10-35% rosin resin, 5-20% organic acid, 2-8% surfactant, 1-5% antioxidant, and 1-3% corrosion inhibitor; the rosin resin comprises synthetic resin and acid-free rosin.

6. The flexible component solder paste printing method according to claim 5, characterized in that, The diluent is selected from one or a combination of alcohols, esters, alcohol ethers, hydrocarbons, and ketones; And / or, The synthetic resin is selected from one or a combination of methyl methacrylate copolymer and silicone-modified acrylic resin; And / or, The acid-free rosin is selected from one or a combination of hydrogenated rosin, polymerized rosin, and disproportionated rosin. And / or, The organic acid is selected from one or a combination of succinic acid, methylsuccinic acid, glutaric acid, adipic acid, octanoic acid, sebacic acid, bipropionic acid, itaconic acid, and salicylic acid.

7. The flexible component solder paste printing method according to claim 5, characterized in that, The surfactant is selected from one or a combination of perfluorooctyl sulfonate ammonium and Thomas Amphoteric Surfactants. And / or, The antioxidant is selected from one or a combination of hydroquinone, tert-butylhydroquinone, and thiodipropionates. And / or, The corrosion inhibitor is selected from one or a combination of benzotriazole, triethanolamine, and imidazole compounds.

8. The flexible component solder paste printing method according to claim 1, characterized in that, The process of printing solder paste onto the electrodes of the small battery cell also includes drying the solder paste. The drying temperature is 80-100℃, and the drying time is 3-5 minutes.

9. The flexible component solder paste printing method according to claim 8, characterized in that, After the solder paste is dried, the process further includes: Print insulating adhesive onto the small battery cells after solder paste has been applied; The battery cells are bonded to the flexible circuit board.

10. A flexible component solder paste printing system, said system being applied to the flexible component solder paste printing method as described in any one of claims 1 to 9, characterized in that, The system includes: A screen printing apparatus is used to print solder paste onto the electrodes of multiple small battery cells using multiple sequentially arranged screens. The total area of ​​multiple screens is matched with the area of ​​the solar cell, and the size of each screen is 300mm*600mm-500mm*800mm.

Images