Low-temperature welding material for photovoltaic module

Abstract

The invention discloses a low-temperature welding material for a photovoltaic module. Wherein the soldering material comprises a tackifier, the tackifier comprises coumarone resin, and the mass fraction of the tackifier accounts for 15% or above of the total mass fraction of the soldering flux. The tackifier is used for enabling the scaling powder to have certain adhesive force, providing a part of welding activity and forming an effective welding spot protection layer. The coumarone resin and the common rosin have high melting points (the melting point of the coumarone resin is greater than that of the rosin), and the coumarone resin and the common rosin do not volatilize in the using process of the low-temperature scaling powder, so that the low-temperature scaling powder is inevitably remained around a welding spot. However, when coumarone resin serves as a tackifier, it can be guaranteed that residues are few compared with rosin, and the problems that organic components of most scaling powder are left around and on the surface of a welding spot after welding, the organic residues of the welding spot in a high-temperature and high-humidity environment easily corrode the welding spot, and the welding spot loses efficacy are solved. In addition, compared with rosin, the usage amount of coumarone resin is reduced by more than 10%.

Description

Technical Field

[0001] The invention relates to the field of low-temperature welding materials, in particular to a flux for low-temperature solder paste. Background Art

[0002] Low temperature solder paste is a paste-like welding material made by mixing tin alloy powder containing a certain proportion of bismuth, lead, silver, and indium metal elements with flux paste. The welding temperature is 150-180℃ and it has a wide range of applications. With the development of electronic surface mounting technology, the development of solar photovoltaic module technology and the requirements for environmental protection, the requirements for solder paste are becoming increasingly diversified and more detailed. For example, the performance indicators of solder paste must comply with the standards of JIS (Japanese Industrial Standards) and IPC (American Printed Circuit Association), and meet the various environmental regulations promulgated by the government. Therefore, the flux must exclude harmful substances in the use regulations and standards, and meet the specified technical performance requirements. With the increasing demand for energy saving and cost reduction in the production of solar photovoltaic modules, the welding temperature of low temperature solder paste coincides with the packaging temperature of solar photovoltaic modules, realizing the simultaneous welding of solar cell panels and module packaging. It simplifies the module production process and reduces the energy consumption in the module production process. Compared with the high temperature welding process in the production process of traditional solar photovoltaic modules, the use of low temperature solder paste welding reduces the thermal shock damage to the cells and ensures the stable quality of solar photovoltaic modules.

[0003] The existing solder paste flux paste uses 40%-50% rosin (such as one or more combinations of acrylic modified rosin, hydrogenated rosin, polymerized rosin); 30%-40% alcohol ether solvent (such as one or more combinations of diethylene glycol hexyl ether, ethylene glycol phenyl ether, diethylene glycol butyl ether, tetraethylene glycol butyl ether); 4%-15% organic acid, organic amine (such as succinic acid, adipic acid, pimelic acid, citric acid, anyic acid, myristic acid, diethanolamine, triethanolamine, edetic acid, etc.) 0.5%-3% of antioxidant (one or more combinations of antioxidant 245, antioxidant 264, antioxidant 2246); 4%-5% of thickener (one or more combinations of hydrogenated castor oil, modified hydrogenated castor oil, polyamide wax); 0.1%-2% of corrosion inhibitor (benzotriazole); 0.1%-2% of surfactant (one or two combinations of dibromobutylene glycol and dodecylphenol).

[0004] As can be seen from the above, the existing solder paste is generally a high-temperature solder paste. The alcohol ether solvent used in the high-temperature solder paste is such as diethylene glycol hexyl ether, diethylene glycol monobutyl ether, tetraethylene glycol methyl ether, etc. The solvent evaporates less during the solder paste reflow soldering process. The acidic substances in the solder paste continue to corrode the metal surface in the high-boiling point solvent environment during the reflow soldering sintering silver pad process, and the "silver eating" phenomenon is likely to occur, causing the solder joint to fail; 40%-50% of the rosin usage plus the use of high-boiling point organic solvents, during the reflow soldering process, most of the organic components in the solder paste remain around and on the surface of the solder joint, and the acidic organic residues in the solder joint are likely to corrode the solder joint in a high temperature and high humidity environment, causing failure, affecting the reliability and service life of the product. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a low-temperature welding material for photovoltaic modules, which can solve the problem that organic residues in the solder joints are easily corroded and cause failure in the high temperature and high humidity environment.

[0006] According to one aspect of the present invention, a low-temperature soldering material for photovoltaic modules is provided, wherein the soldering material is a flux; the soldering material includes a tackifier, and the tackifier includes coumarone resin, and the tackifier accounts for 15% or more of the total mass fraction of the flux.

[0007] In the above technical scheme, the tackifier effect is to make the soldering flux have a certain adhesion, and provide a part of the welding activity and form an effective solder joint protective layer. The melting points of coumarone resin and commonly used rosin are both high (the melting point of coumarone resin is greater than rosin), and they will not volatilize in the process of using low-temperature soldering flux, which will inevitably lead to residues around the solder joint. But the inventor found that the coumarone resin has a higher tackification film-forming efficiency than rosin, reaches the same viscosity and thixotropy in the soldering flux, and the amount used is less than rosin. Rosin will not volatilize during the welding process, and will all remain around the solder joint. The less the amount of this tackifier resin is, the less the residue will be after welding. Coumarone resin also has electrical insulation performance, aging resistance, and excellent water resistance, which ensures that it remains around the solder joint after welding and makes the solder joint stable and reliable for a long time. When coumarone resin is used as a tackifier, it can be guaranteed that the residue is less than rosin, which solves the problem that most of the organic components of the soldering flux remain around and on the surface after welding, and the organic residue of the solder joint is easy to corrode the solder joint in a high temperature and high humidity environment, resulting in failure. In addition, compared with rosin, the usage of coumarone resin is reduced by more than 10%. Therefore, the inventor of this case proposes to use coumarone resin as a tackifier for soldering flux.

[0008] In some embodiments, the soldering flux further includes an activator, which is compounded by one or more alkaline activators and one or more acidic activators.

[0009] In the above technical solution, the role of the activator is to effectively remove tin alloy particles and oxide films on the surface of the metal pad to be welded during the welding process, while keeping the surface of the metal pad to be welded clean during the welding process. The alkaline activator and the acidic activator are used in combination to make the residual flux after welding undergo acid-base neutralization reaction to generate a nearly neutral substance. The residual flux does not show corrosiveness in a high temperature and high humidity environment, solving the problem of the traditional solder paste easily "eating silver" phenomenon.

[0010] In some embodiments, the alkaline active agent includes: 2-ethylimidazole, 2-phenylimidazole;

[0011] The acidic active agents include o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, and trisaccharic acid.

[0012] In the above technical solution, the above acid and alkaline activators can react quickly with metal oxides on pads such as copper oxide, silver oxide, tin oxide, nickel oxide, etc. at 130℃-180℃, remove metal oxides on the pad surface to make welding go smoothly, and the mixed use of acid and alkaline activators makes the flux as a whole nearly neutral at low temperature, does not corrode the tin powder metal particles in the solder paste, and allows the solder paste to be stored stably for a long time and printed continuously for a long time with stable quality. The activation temperature of other activators is not efficient at 130-180℃.

[0013] In some embodiments, the soldering flux also includes a mixed solvent, and the mixed solvent includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, pinene alcohol, and tetraethylene glycol methyl ether. In the above technical scheme, the role of the mixed solvent is to dissolve the resin and other substances in the soldering flux, provide an ion activity environment for the activator during the reflow soldering process, help the welding to proceed effectively, and the electrical insulation performance of the post-welding residue is good, and the electrical performance of the solder joint can be guaranteed to be long-term stable without cleaning. Among them, the reason for selecting the above substances as the mixed solvent is that the above mixed solvent is used in combination with the activator, and the solvent provides an ion activity environment for the activator during the welding process, so that the organic acid can efficiently remove the oxide on the surface of the metal pad, ensuring smooth welding. Most of the mixed solvent volatilizes during the welding process, and the remaining small part has good electrical insulation performance and will not produce electromigration, ensuring the long-term stability and reliability of the solder joint.

[0014] According to another aspect of the present invention, a low-temperature soldering material for a photovoltaic module is provided, wherein the soldering material is a soldering flux; the soldering flux comprises the following components:

[0015]

[0016]

[0017] In some embodiments, the active agent is compounded from an alkaline active agent and an acidic active agent. The soldering flux also includes a mixed solvent, and the mixed solvent includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, and tetraethylene glycol methyl ether.

[0018] The thickening thixotropic agent includes: one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristic acid ester;

[0019] The mixed solvent includes: a mixture of two or more solvents such as tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether, etc.;

[0020] The corrosion inhibitor comprises: one or more combinations of 1-phenyl-5-mercaptotetrazolyl, benzotriazole, and hexadecanethiol;

[0021] The antioxidant includes: one or more combinations of triphosphite, pentaerythritol ester, glycol di-3-propionate;

[0022] The surfactant includes: dibromobutylene glycol, propylparaben surfactant, or a mixture of the two.

[0023] In the above technical solution,

[0024] The thickening thixotropic agent accounts for 3-10% of the soldering flux, preferably 6%, and can be one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristic acid esters. Its function is to form a hydrogen bond network structure in the soldering flux paste, so that high-density tin alloy particles are evenly distributed inside the paste, and no sedimentation occurs during storage and use, which is convenient for high-speed printing or fast spot welding processes. At the same time, compared with conventional solder paste (thixotropic index: 0.4-0.6), the selection of the above components can make the soldering flux have a higher thixotropic index (0.6-0.8) and better printing and demoulding performance, effectively improving the solder paste printing speed and the production efficiency of welding products.

[0025] The active agent accounts for 2-8% of the flux, preferably 7%, and can be one or more combinations of o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, trisaccharide, 2-ethylimidazole, and 2-phenylimidazole. Its function is to effectively remove tin alloy particles and oxide films on the surface of the metal pad to be welded during the welding process, while keeping the surface of the metal pad to be welded clean during the welding process. The compound use of imidazole alkaline active agents and o-iodophenylacetic acid and other acidic active agents causes the residual flux after welding to undergo acid-base neutralization reaction to generate a nearly neutral substance. The residual flux does not show corrosion in a high temperature and high humidity environment, solving the problem that the traditional solder paste is prone to "eating silver". At the same time, the use of this method can effectively weld and sinter silver pads to form a thinner IMC layer, improve the strength of the solder joints, improve the quality of the welded products, and extend the service life of the welded products. It is particularly suitable for the welding and assembly of solar photovoltaic component products.

[0026] The mixed solvent accounts for 40-60% of the soldering flux, preferably 53.3%, and can be a mixture of two or more of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether and the like. The mixed solvent dissolves resin, activator, corrosion inhibitor, antioxidant, and thickening thixotropic agent, provides an ion activity environment for the activator during the reflow soldering process, helps the soldering to proceed effectively, and the electrical insulation performance of the residue after soldering is good, and the electrical performance of the solder joint can be ensured to be stable for a long time without cleaning.

[0027] The corrosion inhibitor accounts for 0.1-1.5% of the soldering flux, preferably 1%, and can be one or more combinations of 1-phenyl-5-mercaptotetrazole, benzotriazole, and hexadecanethiol, and its function is to protect the solder joints and prevent the corrosion of the welded metal.

[0028] The antioxidant accounts for 1-3% of the flux, preferably 2%, and can be one or more combinations of tris(2,4-di-tert-butylphenyl)phosphite, pentaerythritol 〖3-(3,5-di-tert-butyl-4-hydroxy)propionate〗, glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and its function is to effectively protect the various substances in the solder paste from chemical reactions and deterioration during storage, thereby ensuring the storage stability of the solder paste and the stable quality during use.

[0029] The surfactant accounts for 0.1-1% of the soldering flux, preferably 0.5%, and can be one or a mixture of dibromobutylene glycol and propylparaben surfactant, which functions to reduce the surface tension of the pad, enhance the soldering activity, and form a smooth and round solder joint.

[0030] The tackifier is coumarone resin, which has the function of making the soldering flux have a certain adhesion, providing a part of the soldering activity and forming an effective solder joint protective layer. Among them, coumarone resin and rosin have high melting points, and will not volatilize during the use of low-temperature soldering flux, which will inevitably lead to residues around the solder joints. The amount of coumarone resin used is reduced by more than 10% compared with rosin. Therefore, the soldering flux using coumarone resin has less residues, which solves the problem that most of the organic components of the soldering flux remain around and on the surface of the solder joint after soldering, and the organic residues of the solder joints are easy to corrode the solder joints in a high temperature and high humidity environment, resulting in failure.

[0031] According to another aspect of the present invention, a method for preparing a low-temperature soldering material for a photovoltaic module is provided, which is used to prepare the above-mentioned low-temperature soldering material for a photovoltaic module, comprising:

[0032] The coumarone resin, thickening thixotropic agent and mixed solvent are uniformly heated to 160° C., and a mixture A is obtained after all the materials are dissolved;

[0033] The temperature is lowered to 130°C, and an active agent, a corrosion inhibitor, an antioxidant, and a surfactant are added to the mixture A, and the mixture is heated and stirred until the materials are dissolved to obtain a mixture B; the mixture B has a uniform and clear liquid appearance;

[0034] The completely dispersed and dissolved mixture B is filtered through a 100-mesh filter and poured into a high-temperature resistant plastic bag. The bag containing the mixture B is placed in a cooling water circulation pool and quickly cooled to below 20° C. to obtain a soldering flux.

[0035] In the above technical solution, a heating and dissolving process is adopted, which is simple, low-cost and suitable for large-scale production.

[0036] According to another aspect of the present invention, there is provided a low-temperature solder paste for photovoltaic module assembly, comprising any one of the above-mentioned low-temperature soldering materials for photovoltaic modules.

[0037] In the above technical solution, the solder paste prepared based on the above flux has reduced organic residue after welding, thereby improving the reliability of solder joints. DETAILED DESCRIPTION

[0038] The present invention will be further described in detail below in conjunction with the embodiments. It is particularly noted that the following embodiments are only used to illustrate the present invention, but are not intended to limit the scope of the present invention. Similarly, the following embodiments are only partial embodiments of the present invention rather than all embodiments, and all other embodiments obtained by those of ordinary skill in the art without creative work are within the scope of protection of the present invention.

[0039] The invention provides a soldering flux which can solve the problem that organic residues in solder joints are prone to corrode the solder joints and cause failure in a high-temperature and high-humidity environment.

[0040] Embodiment 1

[0041] A soldering flux includes: the soldering flux includes a tackifier, the tackifier includes coumarone resin, and the tackifier accounts for 15% or more of the total mass fraction of the soldering flux.

[0042] In the present embodiment, the role of the tackifier is to give the soldering flux a certain adhesion, provide a portion of the welding activity and form an effective solder joint protective layer. The melting points of coumarone resin and commonly used rosin are both relatively high (the melting point of coumarone resin is greater than that of rosin), and they will not volatilize during the use of low-temperature soldering flux, which will inevitably lead to residues around the solder joints. However, the inventors found that when coumarone resin is used as a tackifier, it can ensure less residue than rosin, solving the problem that most of the organic components of the soldering flux remain around and on the surface of the solder joint after welding, and the organic residues in the solder joint are prone to corrode the solder joint and cause failure in a high temperature and high humidity environment. In addition, compared with rosin, the amount of coumarone resin used is reduced by more than 10%. Therefore, the inventors of this case proposed to use coumarone resin as a tackifier for the soldering flux.

[0043] In this embodiment, the soldering flux further includes an activator, which is a compound of one or more alkaline activators and one or more acidic activators. The activator is used to effectively remove tin alloy particles and oxide films on the surface of the metal pad to be soldered during the soldering process, while keeping the surface of the metal pad to be soldered clean during the soldering process. The alkaline activator and the acidic activator are compounded to cause the residual soldering flux after soldering to undergo an acid-base neutralization reaction to generate a nearly neutral substance. The residual soldering flux does not show corrosiveness in a high temperature and high humidity environment, which solves the problem of the traditional solder paste being prone to "silver eating" phenomenon.

[0044] In this embodiment, the alkaline active agent includes: 2-ethylimidazole, 2-phenylimidazole;

[0045] The acidic activators include o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, and trisaccharide. These acidic and alkaline activators can react quickly with metal oxides on pads such as copper oxide, silver oxide, tin oxide, and nickel oxide at 130°C-180°C, remove metal oxides on the pad surface to make welding go smoothly, and the mixed use of acidic and alkaline activators makes the flux as a whole nearly neutral at low temperature, does not corrode the tin powder metal particles in the solder paste, and allows the solder paste to be stored stably for a long time and printed continuously for a long time with stable quality. The activation temperature of other activators is not efficient at 130-180°C. .

[0046] In the present embodiment, the soldering flux also includes a mixed solvent, and the mixed solvent includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, pinene alcohol, and tetraethylene glycol methyl ether. The role of the mixed solvent is to dissolve the resin and other substances in the soldering flux, provide an ion activity environment for the activator during the reflow soldering process, help the welding to proceed effectively, and the electrical insulation performance of the residue after welding is good, and the electrical performance of the solder joint can be guaranteed to be long-term stable without cleaning. Among them, the reason for selecting the above-mentioned substances as the mixed solvent is that the above-mentioned mixed solvent is used in combination with the activator, and the solvent provides an ion activity environment for the activator during the welding process, so that the organic acid can efficiently remove the oxide on the surface of the metal pad, ensuring that the welding proceeds smoothly. Most of the mixed solvent volatilizes during the welding process, and the remaining small part has good electrical insulation performance and will not produce electromigration, ensuring the long-term stability and reliability of the solder joint.

[0047] Embodiment 2

[0048] A soldering flux comprising the following components:

[0049]

[0050] In this embodiment, the activator is compounded from an alkaline activator and an acidic activator. The soldering flux also includes a mixed solvent, which includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, and tetraethylene glycol methyl ether.

[0051] The thickening thixotropic agent includes: one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristic acid ester;

[0052] The mixed solvent includes: a mixture of two or more solvents such as tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether, etc.; the corrosion inhibitor includes: one or more combinations of 1-phenyl-5-mercaptotetrazole, benzotriazole, and hexadecanethiol; the antioxidant includes: one or more combinations of triphosphite, pentaerythritol ester, and glycol di-3-propionate; the surfactant includes: one or a mixture of two surfactants such as dibromobutylene glycol and propylparaben.

[0053] In this embodiment, the thickening thixotropic agent accounts for 3-10% of the soldering flux, preferably 6%, which can be one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, cetyl myristate, and its function is to form a hydrogen bond network structure in the soldering flux paste, so that high-density tin alloy particles are evenly distributed inside the paste, and no sedimentation occurs during storage and use, which is convenient for high-speed printing or fast spot welding process. At the same time, compared with conventional solder paste (thixotropic index: 0.4-0.6), the selection of the above components can make the soldering flux have a higher thixotropic index (0.6-0.8) and better printing and demoulding performance, effectively improving the solder paste printing speed and improving the production efficiency of welding products.

[0054] The active agent accounts for 2-8% of the flux, preferably 7%, and can be one or more combinations of o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, trisaccharide, 2-ethylimidazole, and 2-phenylimidazole. Its function is to effectively remove tin alloy particles and oxide films on the surface of the metal pad to be welded during the welding process, while keeping the surface of the metal pad to be welded clean during the welding process. The compound use of imidazole alkaline active agents and o-iodophenylacetic acid and other acidic active agents causes the residual flux after welding to undergo acid-base neutralization reaction to generate a nearly neutral substance. The residual flux does not show corrosion in a high temperature and high humidity environment, solving the problem that the traditional solder paste is prone to "eating silver". At the same time, the use of this method can effectively weld and sinter silver pads to form a thinner IMC layer, improve the strength of the solder joints, improve the quality of the welded products, and extend the service life of the welded products. It is particularly suitable for the welding and assembly of solar photovoltaic component products.

[0055] The mixed solvent accounts for 40-60% of the soldering flux, preferably 53.3%, and can be a mixture of two or more of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether and the like. The mixed solvent dissolves resin, activator, corrosion inhibitor, antioxidant, and thickening thixotropic agent, provides an ion activity environment for the activator during the reflow soldering process, helps the soldering to proceed effectively, and the electrical insulation performance of the residue after soldering is good, and the electrical performance of the solder joint can be ensured to be stable for a long time without cleaning.

[0056] The corrosion inhibitor accounts for 0.1-1.5% of the soldering flux, preferably 1%, and can be one or more combinations of 1-phenyl-5-mercaptotetrazole, benzotriazole, and hexadecanethiol, and its function is to protect the solder joints and prevent the corrosion of the welded metal.

[0057] The antioxidant accounts for 1-3% of the flux, preferably 2%, and can be one or more combinations of tris(2,4-di-tert-butylphenyl)phosphite, pentaerythritol 〖3-(3,5-di-tert-butyl-4-hydroxy)propionate〗, glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and its function is to effectively protect the various substances in the solder paste from chemical reactions and deterioration during storage, thereby ensuring the storage stability of the solder paste and the stable quality during use.

[0058] The surfactant accounts for 0.1-1% of the soldering flux, preferably 0.5%, and can be one or a mixture of dibromobutylene glycol and propylparaben surfactant, which functions to reduce the surface tension of the pad, enhance the soldering activity, and form a smooth and round solder joint.

[0059] The tackifier is coumarone resin, which has the function of making the soldering flux have a certain adhesion, providing a part of the soldering activity and forming an effective solder joint protective layer. Among them, coumarone resin and rosin have high melting points, and will not volatilize during the use of low-temperature soldering flux, which will inevitably lead to residues around the solder joints. The amount of coumarone resin used is reduced by more than 10% compared with rosin. Therefore, the soldering flux using coumarone resin has less residues, which solves the problem that most of the organic components of the soldering flux remain around and on the surface of the solder joint after soldering, and the organic residues of the solder joints are easy to corrode the solder joints in a high temperature and high humidity environment, resulting in failure.

[0060] Embodiment 3

[0061] A method for preparing a soldering flux, used for preparing the above-mentioned soldering flux,

[0062] S1. Uniformly heat the coumarone resin, thickening thixotropic agent and mixed solvent to 160° C., and obtain a mixture A after all the materials are dissolved;

[0063] S2. The temperature is lowered to 130° C., and an active agent, a corrosion inhibitor, an antioxidant, and a surfactant are added to the mixture A. The mixture is heated and stirred until the materials are dissolved to obtain a mixture B. The mixture B has a uniform and clear liquid appearance.

[0064] S3. Filter the completely dispersed and dissolved mixture B through a 100-mesh filter and pour it into a high-temperature resistant plastic bag. Put the bag containing the mixture B into a cooling water circulation pool and quickly cool it to below 20° C. to obtain a soldering flux.

[0065] In this embodiment, a heating dissolution process is adopted, which is simple, low-cost and suitable for large-scale production.

[0066] Embodiment 4

[0067] A low-temperature solder paste for photovoltaic module assembly includes any one of the fluxes in the first embodiment or the second embodiment. The solder paste prepared based on the flux has reduced organic residue after welding, thereby improving the reliability of solder joints.

[0068] In order to better understand the present invention, the following is a detailed description based on Embodiments 1 to 4:

[0069] The purpose of the invention is to disclose a low-temperature solder paste with flux (welding temperature is 150-180°C) that meets performance standards, has low solder joint void rate, and high welding reliability. When sintering silver for BC-type solar photovoltaic cells, the cells generally use low-temperature solder paste (welding temperature is below 170°C), which can solve energy saving, warping deformation, and thermal stress problems. The tin alloy powder in the low-temperature solder paste is 42% tin and 58% bismuth (Sn42Bi58), 42% tin and 57.6% bismuth and 0.4% silver (Sn42Bi57.6Ag0.4), 42% tin and 57% bismuth and 1% silver (Sn42Bi57Ag1), 43% tin and 43% lead and 14% bismuth (Sn43Pb43Bi14), and the flux in the solder paste uses the following ingredients:

[0070] The technical solution to realize the present invention is as follows: the components of the soldering flux are (by weight percentage):

[0071]

[0072] The thickening thixotropic agent is one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristic ester.

[0073] The active agent is one or more combinations of o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, trispropane, 2-ethylimidazole and 2-phenylimidazole.

[0074] The mixed solvent is a mixture of two or more solvents selected from tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether and the like.

[0075] The corrosion inhibitor is one or more combinations of 1-phenyl-5-mercaptotetrazole, benzotriazole and hexadecanethiol.

[0076] The antioxidant is one or more combinations of tris(2,4-di-tert-butylphenyl)phosphite, pentaerythritol [3-(3,5-di-tert-butyl-4-hydroxy)propionate, and glycol bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate.

[0077] The surfactant is one or a mixture of dibromobutylene glycol and propylparaben surfactant.

[0078] The tackifier is gumaron resin.

[0079] The thickening thixotropic agent accounts for 6% of the soldering flux, which can be one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristyl esters. Its function is to form a hydrogen bond network structure in the soldering flux paste, so that high-density tin alloy particles are evenly distributed inside the paste, and no sedimentation occurs during storage and use, which is convenient for high-speed printing or fast spot welding. The activating agent accounts for 7% of the soldering flux, which can be one or more combinations of o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, trispropane, 2-ethylimidazole, and 2-phenylimidazole. Its function is to effectively remove tin alloy particles and oxide films on the surface of the metal pad to be welded during the welding process, while keeping the surface of the metal pad to be welded clean during the welding process. The imidazole alkaline activating agent is compounded with the acidic activating agent such as o-iodophenylacetic acid to cause the residual soldering flux after welding to undergo an acid-base neutralization reaction to generate a nearly neutral substance. The residual soldering flux does not show corrosion in a high temperature and high humidity environment, which solves the problem that the traditional solder paste is prone to "eating silver". The mixed solvent accounts for 53.3% of the soldering flux, which can be a mixture of two or more solvents such as tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether, etc., and its function is to dissolve resin, active agent, corrosion inhibitor, antioxidant, thickening thixotropic agent, provide ion activity environment for active agent in the reflow soldering process, help soldering to be carried out effectively, and the electrical insulation performance of the post-welding residue is good, and the electrical performance of the solder joint can be guaranteed to be long-term stable without cleaning. The corrosion inhibitor accounts for 1% of the soldering flux, which can be one or more combinations of 1-phenyl-5-mercaptotetrazole, benzotriazole, hexamethylenethiol, and its function is to protect the solder joint and prevent corrosion of the welded metal. The antioxidant accounts for 2% of the soldering flux, which can be one or more combinations of tris(2,4-di-tert-butylphenyl)phosphite, pentaerythritol〖3-(3,5-di-tert-butyl-4-hydroxy)propionate〗, glycol di-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, and its function is to effectively protect the various substances in the solder paste from chemical reactions and deterioration in the storage state, and ensure the storage stability of the solder paste and the quality stability during use. The surfactant accounts for 0.5% of the soldering flux, which can be one or a mixture of dibromobutylene glycol and propylparaben surfactant, and its function is to reduce the surface tension of the pad, enhance the welding activity, and form a smooth and round solder joint. The tackifier is coumarone resin, which is 30% in the soldering flux, and its function is to make the soldering flux have a certain adhesion, provide a part of the welding activity and form an effective solder joint protection layer. Among them, coumarone resin and rosin have higher melting points and will not volatilize during the use of low-temperature flux, which will inevitably lead to residues around the solder joints. The use of coumarone resin is more than 10% less than that of rosin. Therefore, the flux using coumarone resin has less residues, which solves the problem that most of the organic components of the flux remain around and on the surface of the solder joint after welding. The organic residues in the solder joint are prone to corrode the solder joint and cause failure in a high temperature and high humidity environment.

[0080] The preparation process of the above soldering flux is: uniformly heat the tackifier, thickening thixotropic agent and solvent to 160°C, and after all the materials are dissolved, reduce the temperature to 130°C, then add the activator, corrosion inhibitor, antioxidant, surfactant and other materials, heat and stir all the materials to dissolve, and the appearance is a uniform and clear liquid. The completely dispersed and dissolved soldering flux is filtered with a 100-mesh filter and poured into a high-temperature resistant plastic bag, and the bag containing the soldering flux is placed in a cooling water circulation pool and quickly cooled to below 20°C. The soldering flux of the present invention is more suitable for solder alloy powder with a melting point of 100-180°C for tin-based alloys. 80-90% of the tin alloy powder is mixed with the remaining amount of the above soldering flux to form a low-temperature solder paste.

[0081] To further understand the embodiments of the present invention, specific examples are given below.

[0082] Example 1:

[0083] (1) Soldering flux: Prepare the following flux raw materials by mass fraction: 30% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 1% adipic anhydride, 1% malic acid, 2% 2-ethylimidazole), 57% mixed solvent (32% tetrahydrofurfuryl alcohol, 25% pineol), 5% thickener, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant. Heat the coumarone resin, thickener, and solvent evenly to 160°C. After all the materials are dissolved, lower the temperature to 130°C, add the activator, corrosion inhibitor, antioxidant, surfactant, etc., heat and stir until all the materials are dissolved, and the appearance is a uniform and clear liquid. Filter the completely dispersed and dissolved solder flux with a 100-mesh filter and pour it into a high-temperature resistant plastic bag. Put the bag containing the solder flux into a cooling water circulation pool and quickly cool it to below 20°C. This is the spare solder flux.

[0084] (2) Place the tin-bismuth (Sn42Bi58) eutectic alloy powder and flux in a weight ratio of 9:1 into the solder paste mixing equipment. Stir at 30 rpm for 10 minutes, raise the stirring rotor, and manually scrape the unmixed solder paste on the rotor and the wall of the stirring pot into the stirring pot with a plastic scraper. Then seal the stirring pot, evacuate to -0.07Mpa, stir at 35 rpm for 25 minutes, and then package into finished solder paste packaging. Store the packaged solder paste in a dry environment at 0-10°C for ready use.

[0085] Example 2:

[0086] The main difference from Example 1 is that the raw materials of the flux are: 33% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 1% adipic anhydride, 2% malic acid, 1% 2-ethylimidazole), 54% mixed solvent (32% tetrahydrofurfuryl alcohol, 22% pineol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0087] Example 3:

[0088] The main difference from Example 1 is that the raw materials of the flux are: 28% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 1% adipic anhydride, 2% malic acid, 1% 2-ethylimidazole), 59% mixed solvent (34% tetrahydrofurfuryl alcohol, 25% pineneol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0089] Example 4:

[0090] The main difference from Example 1 is that the raw materials of the flux are: 38.5% coumarone resin, 3.5% activator (1% o-iodophenylacetic acid, 1% adipic anhydride, 1% malic acid, 0.5% 2-ethylimidazole), 50% mixed solvent (25% tetrahydrofurfuryl alcohol, 25% pineneol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0091] Example 5:

[0092] The main difference from Example 1 is that the raw materials of the flux are: 37% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 2% adipic anhydride, 1% malic acid, 1% 2-ethylimidazole), 50% mixed solvent (20% tetrahydrofurfuryl alcohol, 30% pineol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0093] Example 6:

[0094] The main difference from Example 1 is that the raw materials of the flux are: 37% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 2% adipic anhydride, 1% malic acid, 1% 2-ethylimidazole), 50% mixed solvent (30% tetrahydrofurfuryl alcohol, 20% pineol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0095] Example 7:

[0096] The main difference from Example 1 is that the raw materials of the flux are: 20% coumarone resin, 17% polymerized rosin, 5% activator (1% o-iodophenylacetic acid, 2% adipic anhydride, 1% malic acid, 1% 2-ethylimidazole), 50% mixed solvent (30% tetrahydrofurfuryl alcohol, 20% terpineol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0097] Example 8:

[0098] The main difference from Example 1 is that the raw materials of the flux are: 17% coumarone resin, 20% polymerized rosin, 5% activator (1% o-iodophenylacetic acid, 2% adipic anhydride, 1% malic acid, 1% 2-ethylimidazole), 50% mixed solvent (25% tetrahydrofurfuryl alcohol, 25% terpineol), 5% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0099] Example 9:

[0100] The main difference from Example 1 is that the raw materials of the flux are: 38% coumarone resin, 5% activator (1% o-iodophenylacetic acid, 2% adipic anhydride, 1% malic acid, 1% 2-ethylimidazole), 50% mixed solvent (25% tetrahydrofurfuryl alcohol, 25% pineneol), 4% thickening thixotropic agent, 0.5% corrosion inhibitor, 2% antioxidant, and 0.5% surfactant.

[0101] Comparative Example:

[0102] Prepare solder paste as follows:

[0103] (1) Preparation of ordinary soldering paste: Prepare the following soldering paste raw materials by mass fraction: rosin 45%, activator 6% (including succinic acid 2%, citric acid 1%, benzoic acid 1%, diethanolamine 2%), thickener thixotropic agent (modified hydrogenated castor oil) 5%, corrosion inhibitor 0.5%, antioxidant 2%, surfactant 1%, solvent 40.5% (including diethylene glycol methyl ether 30%, tetraethylene glycol butyl ether 10.5%). Evenly heat the rosin, thickener thixotropic agent and solvent to 120°C, and use an emulsifier to emulsify and disperse the materials. When the material temperature rises to 140°C and the material is in a uniform paste state, add the activator, corrosion inhibitor, antioxidant, surfactant and other materials, continue to emulsify and disperse until it is in a uniform paste state, and stop emulsification. Pour the prepared soldering paste into a high-temperature resistant plastic bag, and put the bag containing the soldering paste into a cooling water circulation pool to quickly cool it to room temperature for use at any time.

[0104] (2) Place the tin-bismuth (Sn42Bi58) eutectic alloy powder and flux in a weight ratio of 89:11 into the solder paste mixing equipment. Stir at 25 rpm for 5 minutes, raise the stirring rotor, and manually scrape the unmixed solder paste on the rotor and the wall of the stirring pot into the stirring pot with a plastic scraper. Then seal the stirring pot, evacuate to -0.08Mpa, stir at 35 rpm for 25 minutes, and then package into finished solder paste packaging. Store the packaged solder paste in a dry environment at 0-10°C for later use.

[0105] The flux raw materials used in the above examples and comparative examples are shown in Table 1.

[0106] Table 1. Raw materials of soldering flux in various embodiments and comparative examples

[0107]

[0108]

[0109]

[0110] Example 1 (best effect), Example 2 (changing the tackifier and solvent content compared with Example 1), Example 3 (changing the tackifier and solvent content compared with Example 1), Example 4 (changing the tackifier and active agent content compared with Example 1), Example 5 (changing the tackifier and solvent content compared with Example 1), Example 6 (changing the tackifier and solvent content compared with Example 1), Example 7 (changing the content of the type of tackifier compared with Example 1), Example 8 (changing the content of the type of tackifier compared with Example 1), Example 9 (changing the content of the tackifier and thixotropic agent compared with Example 1).

[0111] The solder paste prepared in the above comparative example was used to perform the sintering silver pad welding of the battery cell, and the welding sample was subjected to the following experiment to test its effect. The main experimental contents and methods are shown in Table 2.

[0112] Table 2 Main experimental methods used in the experimental examples

[0113]

[0114] The specific experimental results obtained from the above experimental example are shown in Table 3

[0115] Table 3 Experimental structure of each experimental example

[0116]

[0117]

[0118] From the above tests, it can be seen that the solder joint tensile force of Example 1 is higher than that of other examples and comparison examples. The solder joint tensile force is high, the solder joint mechanical strength and electrical conductivity are high, the solder joint reliability is high in practical applications, and the reliability of products using this solder paste is also high; Examples 7 and 8 have smaller expansion rates than Example 1, which proves that the wetting performance of the solder pastes of Examples 7 and 8 on the pads is slightly poor; the copper plate of the comparison example has slight copper plate corrosion, and the welding tensile force is small, which proves that the comparison example has slight over-soldering, resulting in a decrease in solder joint strength.

[0119] The above descriptions are only some embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any equivalent device or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A low-temperature welding material for photovoltaic modules, characterized in that: The welding material is a soldering flux; the soldering flux includes a tackifier, and the tackifier includes coumarone resin, and the tackifier accounts for 15% or more of the total mass fraction of the soldering flux.

2. A low-temperature soldering material for photovoltaic modules as claimed in claim 1, characterized in that: The soldering flux also includes an activator, which is compounded by one or more alkaline activators and one or more acidic activators.

3. A low-temperature soldering material for photovoltaic modules as claimed in claim 2, characterized in that: The alkaline active agent includes: 2-ethylimidazole, 2-phenylimidazole; The acidic active agents include o-iodophenylacetic acid, chlorendic acid, adipic anhydride, citric acid, malic acid, and trisaccharic acid.

4. A low-temperature soldering material for photovoltaic modules as claimed in claim 1, characterized in that: The soldering flux also includes a mixed solvent, and the mixed solvent includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, and tetraethylene glycol methyl ether.

5. A low-temperature welding material for photovoltaic modules, characterized in that: The welding material is a soldering flux; the soldering flux comprises the following components:

6. A low-temperature soldering material for photovoltaic modules as claimed in claim 5, characterized in that: The active agent is compounded by an alkaline active agent and an acidic active agent.

7. A low-temperature soldering material for photovoltaic modules as claimed in claim 5, characterized in that: The soldering flux also includes a mixed solvent, and the mixed solvent includes a mixture of at least two of tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, and tetraethylene glycol methyl ether.

8. A low-temperature soldering material for photovoltaic modules as claimed in claim 5, characterized in that: The thickening thixotropic agent includes: one or more combinations of palmitic acid wax, white carbon black, polyamide wax, palmitamide, and cetyl myristic acid ester; The mixed solvent includes: a mixture of two or more solvents such as tetrahydrofurfuryl alcohol, cyclopentane sulfone, dipropylene glycol, terpineol, tetraethylene glycol methyl ether, etc.; The corrosion inhibitor comprises: one or more combinations of 1-phenyl-5-mercaptotetrazolyl, benzotriazole, and hexadecanethiol; The antioxidant includes: one or more combinations of triphosphite, pentaerythritol ester, glycol di-3-propionate; The surfactant includes: dibromobutylene glycol, propylparaben surfactant, or a mixture of the two.

9. A method for preparing a low-temperature welding material for a photovoltaic module, characterized in that: Used to prepare a low-temperature welding material for photovoltaic modules according to any one of claims 5 to 8, characterized in that: The coumarone resin, thickening thixotropic agent and mixed solvent are uniformly heated to 160° C., and a mixture A is obtained after all the materials are dissolved; The temperature is lowered to 130°C, and an active agent, a corrosion inhibitor, an antioxidant, and a surfactant are added to the mixture A, and the mixture is heated and stirred until the materials are dissolved to obtain a mixture B; the mixture B has a uniform and clear liquid appearance; The completely dispersed and dissolved mixture B is filtered through a 100-mesh filter and poured into a high-temperature resistant plastic bag. The bag containing the mixture B is placed in a cooling water circulation pool and quickly cooled to below 20° C. to obtain a soldering flux.

10. A low-temperature solder paste for photovoltaic module assembly, characterized in that: The invention relates to a low-temperature welding material for a photovoltaic module according to any one of claims 1 to 4 or a low-temperature welding material for a photovoltaic module according to any one of claims 5 to 8.

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