High-reliability rosin-free no-clean solder paste, flux used therein, and preparation method thereof.

Abstract

This invention belongs to the field of electronic soldering materials technology, specifically relating to a high-reliability rosin-free no-clean solder paste, a flux used therein, and a preparation method thereof. This high-reliability rosin-free no-clean flux for solder paste has high quality and high reliability, and contains no rosin. Solder paste prepared with this flux not only has good wettability, low post-soldering residue, light color, and requires no cleaning, but also possesses excellent printability, release properties, anti-void properties, and corrosion resistance, which can greatly improve the quality of solder joints and ensure the stability of various electronic components.

Description

Technical Field

[0001] This invention relates to the field of electronic soldering materials technology, specifically to a highly reliable rosin-free no-clean solder paste, a flux paste for use therein, and a preparation method thereof. Background Technology

[0002] Solder paste is a widely used welding material in the electronics industry, primarily used to solder tiny, precision electronic components onto circuit boards. In recent years, with the rapid development of electronic information technology, the load and power consumption of various electronic devices have been continuously increasing. High integration, miniaturization, and high power have become the development direction for various electronic devices. Correspondingly, high-precision welding processes have placed higher demands on the applicability and reliability of solder paste.

[0003] Traditional solder paste often suffers from problems such as unstable printability, unsatisfactory soldering results, excessive residue, and poor reliability. Its flux formulation, preparation process, and alloy ratio all determine the final solder joint performance, leading to unstable soldering quality and even ultimately affecting the stability of electronic products. For example, while rosin, one of the components of flux, plays an important role, it also causes a large amount of post-soldering residue, which can potentially lead to insulation aging and corrosion, resulting in a decrease in insulation resistance (SIR) and electrochemical migration (ECM).

[0004] Furthermore, although existing solder pastes may possess excellent environmental friendliness and printability, or excellent reliability, wettability, and reflow performance, none of them fully address all these aspects. Meanwhile, new electronic components and integrated circuits are developing towards high frequency, high speed, multi-functionality, and small size. Therefore, existing solder pastes and fluxes used for them still need improvement. Summary of the Invention

[0005] The main objective of this invention is to provide a highly reliable rosin-free, no-clean solder paste, as well as the flux used therein and its preparation method. The high-quality, high-reliability flux provided by this invention is free of rosin. Solder paste prepared with this flux not only has good wettability, low post-soldering residue, light color, and requires no cleaning, but also has excellent printability, release properties, anti-void properties, and corrosion resistance, which can greatly improve the quality of solder joints and ensure the stability of various electronic components.

[0006] A first aspect of the present invention provides a highly reliable rosin-free no-clean flux for soldering paste, the flux containing no rosin, the flux comprising the following components by weight percentage: 10 wt% to 15 wt% activator, 5 wt% to 10 wt% surfactant, 35 wt% to 45 wt% solvent, 10 wt% to 18 wt% stabilizer, 10 wt% to 15 wt% thixotropic agent, 3 wt% to 5 wt% corrosion inhibitor, and 3 wt% to 5 wt% lubricant.

[0007] In some embodiments of the present invention, the activator includes one or more combinations of stearic acid, propylenediamine phosphate, phenyl succinic acid, 2,2-dimethylolbutyric acid, p-tert-butylbenzoic acid, succinic acid, 4-methyl-2-phenylimidazolium, N-phenyl-o-aminobenzoic acid, triisopropanolamine, 8-hydroxyquinoline, citric acid, azelaic acid, dibromosuccinic acid, and ethylene bis-stearamide.

[0008] In some embodiments of the present invention, the surfactant includes one or more combinations of disodium lauryl sulfosuccinate, potassium monododecyl phosphate, dodecyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, and coconut oil monoethanolamide.

[0009] In some embodiments of the present invention, the solvent includes one or more combinations of isopropanol, n-butanol, rosin alcohol, tripropanol butyl ether, terpineol, ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, 2-ethyl-1,3-hexanediol, glycerol, propylene glycol, divalent esters, butyl formate, amyl formate, diglycidyl ether, dioctyl phthalate, tetraethylene glycol, isohexadecanol, diethylene glycol butyl ether acetate, and nitrobenzene mixed solvents.

[0010] In some embodiments of the present invention, the stabilizer includes one or more combinations of dibutyltin dilaurate, phosphite, and zinc stearate.

[0011] In some embodiments of the present invention, the thixotropic agent includes one or more combinations of polyamide wax and hydrogenated castor oil.

[0012] In some embodiments of the present invention, the corrosion inhibitor includes one or more combinations of boric acid, sodium nitrite, hydroquinone, catechol, 2,6-di-tert-butyl-p-cresol, benzotriazole, and ascorbic acid.

[0013] In some embodiments of the present invention, the lubricant includes one or more combinations of castor oil, erucamide, and polyacrylamide.

[0014] The second aspect of the present invention provides a method for preparing the high-reliability rosin-free no-clean flux for solder paste as described in the first aspect, the method comprising: mixing and melting the components forming the flux in a required ratio to obtain the flux.

[0015] In some embodiments of the present invention, the components forming the flux are added in the following order: surfactant, activator, thixotropic agent, stabilizer, corrosion inhibitor and lubricant are added to the solvent in sequence.

[0016] In some embodiments of the present invention, each component is stirred for 3 to 5 minutes after being added, and stirred for 15 to 20 minutes after all components are added.

[0017] The third aspect of this invention provides a highly reliable rosin-free, no-clean solder paste, the solder paste comprising the following components by weight percentage: 85 wt% to 90 wt% alloy powder, 10 wt% to 15 wt% flux; the flux is the flux described in the first aspect or the flux prepared by the preparation method described in the second aspect.

[0018] The fourth aspect of the present invention provides a method for preparing the high-reliability rosin-free no-clean solder paste described in the third aspect. The preparation method includes: mixing alloy powder and flux in a required ratio, subjecting the mixture to vacuum heating and stirring, and then obtaining the solder paste after vacuum treatment.

[0019] In some embodiments of the present invention, the stirring speed of the vacuum heating stirring is 10 rpm to 20 rpm, the stirring time is 6 min to 18 min, and the vacuum degree is -0.06 MPa to -0.1 MPa.

[0020] This invention provides a high-quality, high-reliability flux paste that is free of rosin. Solder paste prepared with this flux paste not only has good wettability, low post-soldering residue, light color, and requires no cleaning, but also has excellent printability, release properties, anti-void properties, and corrosion resistance, which can greatly improve the quality of solder joints and ensure the stability of various electronic components.

[0021] The solder paste prepared in this invention does not contain rosin, has little residue after soldering, light color, requires no cleaning, is completely halogen-free, and has ultra-low voids; moreover, its online test performance results for reflow characteristics, wetting, printing, demolding, and corrosion resistance are all excellent.

[0022] This invention uses a vacuum heating and stirring method to prepare solder paste, which not only reduces the air content in the solder paste and effectively promotes the bonding between the flux and the solder powder, preventing powder separation during subsequent use, but also effectively reduces the internal void rate, thereby reducing potential hazards in actual use.

[0023] The solder paste prepared by this invention is halogen-free, environmentally friendly, and pollution-free, truly meeting the EU RoHS requirements for zero-halogen flux, reducing the use of harmful substances and lowering environmental pollution.

[0024] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and in order to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 The diagram shows the wettability, solder joints, and residue condition of the solder paste prepared in Example 1. Figure 2 This is a diagram showing the anti-collapse properties of the solder paste prepared in Example 1; Figure 3 This is a diagram showing the number of solder balls in the solder paste prepared in Example 1; Figure 4 The demolding performance diagram is shown for the solder paste prepared in Example 1; Figure 5 This is a diagram showing the void ratio of the solder paste prepared in Example 1; Figure 6 This is a copper plate corrosion diagram of the solder paste prepared in Example 1. Detailed Implementation

[0027] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the invention, are intended to cover non-exclusive inclusion.

[0029] In the description of the embodiments of this invention, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this invention, "multiple" means two or more, unless otherwise explicitly defined.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] In the description of the embodiments of this invention, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0032] In the description of the embodiments of the present invention, the term "multiple" refers to two or more (including two), similarly, "multiple groups" refers to two or more (including two groups), and "multiple pieces" refers to two or more (including two pieces).

[0033] In the description of the embodiments of the present invention, unless otherwise explicitly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present invention can be understood according to the specific circumstances.

[0034] This invention provides a highly reliable rosin-free, no-clean flux for soldering. The flux does not contain rosin and comprises the following components by weight percentage: 10 wt% to 15 wt% activator, 5 wt% to 10 wt% surfactant, 35 wt% to 45 wt% solvent, 10 wt% to 18 wt% stabilizer, 10 wt% to 15 wt% thixotropic agent, 3 wt% to 5 wt% corrosion inhibitor, and 3 wt% to 5 wt% lubricant.

[0035] In an embodiment of the present invention, a high-quality, high-reliability flux paste is provided first, which does not contain rosin. Solder paste prepared with this flux paste not only has good wettability, little residue after soldering, light color, and no cleaning required, but also has excellent printability, release properties, anti-void properties, and corrosion resistance, which can greatly improve the quality of solder joints and ensure the stability of various electronic components.

[0036] In embodiments of the present invention, the mass percentage of the surfactant is 10 wt% to 15 wt%. Exemplarily, the mass percentage of the surfactant can be one of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, or any value satisfying the above range.

[0037] In embodiments of the present invention, the activator includes one or more combinations of stearic acid, propylene diamine phosphate, phenyl succinic acid, 2,2-dimethylolbutyric acid, p-tert-butylbenzoic acid, succinic acid, 4-methyl-2-phenylimidazolium, N-phenyl-o-aminobenzoic acid, triisopropanolamine, 8-hydroxyquinoline, citric acid, azelaic acid, dibromosuccinic acid, and ethylene bis-stearamide.

[0038] In embodiments of the present invention, the mass percentage of the surfactant is 5 wt% to 10 wt%. Exemplarily, the mass percentage of the surfactant can be one of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any value satisfying the above range.

[0039] In embodiments of the present invention, the surfactant includes one or more combinations of disodium lauryl sulfosuccinate, potassium monododecyl phosphate, dodecyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, and coconut oil monoethanolamide.

[0040] In embodiments of the present invention, the mass percentage of the solvent is 35 wt% to 45 wt%. Exemplarily, the mass percentage of the solvent can be one of 35 wt%, 36 wt%, 37 wt%, 38 wt%, 39 wt%, 40 wt%, 41 wt%, 42 wt%, 43 wt%, 44 wt%, or 45 wt%, or any value satisfying the above range.

[0041] In embodiments of the present invention, the solvent includes one or more combinations of isopropanol, n-butanol, rosin alcohol, tripropanol butyl ether, terpineol, ethylene glycol methyl ether, diethylene glycol ethyl ether, diethylene glycol butyl ether, 2-ethyl-1,3-hexanediol, glycerol, propylene glycol, divalent esters, butyl formate, amyl formate, diglycidyl ether, dioctyl phthalate, tetraethylene glycol, isohexadecanol, diethylene glycol butyl ether acetate, and nitroethane mixed solvents.

[0042] In embodiments of the present invention, the mass percentage of the stabilizer is 10 wt% to 18 wt%. Exemplarily, the mass percentage of the stabilizer can be one of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 16 wt%, 17 wt%, or 18 wt%, or any value satisfying the above range.

[0043] In embodiments of the present invention, the stabilizer includes one or more combinations of dibutyltin dilaurate, phosphite, and zinc stearate.

[0044] In embodiments of the present invention, the mass percentage of the thixotropic agent is 10 wt% to 15 wt%. Exemplarily, the mass percentage of the thixotropic agent can be one of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, or any value satisfying the above range.

[0045] In embodiments of the present invention, the thixotropic agent includes one or more combinations of polyamide wax and hydrogenated castor oil.

[0046] In embodiments of the present invention, the mass percentage of the corrosion inhibitor is 3 wt% to 5 wt%. Exemplarily, the mass percentage of the corrosion inhibitor can be one of 3 wt%, 4 wt%, 5 wt%, or any value satisfying the above range.

[0047] In embodiments of the present invention, the corrosion inhibitor includes one or more combinations of boric acid, sodium nitrite, hydroquinone, catechol, 2,6-di-tert-butyl-p-cresol, benzotriazole, and ascorbic acid.

[0048] In embodiments of the present invention, the mass percentage of the lubricant is 3 wt% to 5 wt%. Exemplarily, the mass percentage of the lubricant can be one of 3 wt%, 4 wt%, 5 wt%, or any value satisfying the above range.

[0049] In embodiments of the present invention, the lubricant includes one or more combinations of castor oil, erucamide, and polyacrylamide.

[0050] The present invention also provides a method for preparing a highly reliable rosin-free, no-clean flux for solder paste, the key being to mix and melt the components forming the flux according to the required ratio to obtain the flux paste.

[0051] The method for preparing a highly reliable rosin-free, no-clean flux for soldering paste in this invention is carried out according to the following steps.

[0052] S1: First, use a balance to accurately weigh the mass of each component according to the ratio.

[0053] S2: First, add the solvent to the reactor, then add the surfactant, activator, thixotropic agent, stabilizer, corrosion inhibitor, and lubricant respectively. After each component is added, stir at 80℃~100℃ for 3 min~5 min. After all components are added, stir for another 15 min~20 min to obtain the flux paste.

[0054] It is worth mentioning that the prepared flux can be finely ground and left to stand for 24 hours before use.

[0055] In embodiments of the present invention, the stirring time after the addition of each component can be one of 3 min, 4 min, 5 min, or any value within the above range. The stirring time after all components have been added can be one of 15 min, 16 min, 17 min, 18 min, 19 min, 20 min, or any value within the above range. The stirring temperature can be one of 80℃, 85℃, 90℃, 95℃, 100℃, or any value within the above range.

[0056] The present invention also provides a highly reliable rosin-free no-clean solder paste, which comprises the following components by weight percentage: 85 wt% to 90 wt% alloy powder and 10 wt% to 15 wt% flux; the flux is the above-mentioned flux or the flux prepared by the above-mentioned preparation method.

[0057] In the embodiments of this invention, the solder paste provided by this invention is a zero-halogen solder paste, which is environmentally friendly and pollution-free, truly meeting the EU RoHS requirements for zero-halogen flux, reducing the use of harmful substances and lowering environmental pollution. Furthermore, this solder paste does not contain rosin, resulting in minimal residue and a light color after soldering. It requires no cleaning, is completely halogen-free, and has ultra-low voids. Simultaneously, its online testing performance results, including reflow characteristics, wetting, printing, release, and corrosion resistance, are all excellent.

[0058] In embodiments of the present invention, the alloy powder includes, but is not limited to, Sn96.5Ag3Cu0.5 powder.

[0059] In embodiments of the present invention, the mass percentage of the alloy powder is 85 wt% to 90 wt%. Exemplarily, the mass percentage of the alloy powder can be one of 85 wt%, 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, or any value satisfying the above range.

[0060] In embodiments of the present invention, the mass percentage of the flux paste is 10 wt% to 15 wt%. Exemplarily, the mass percentage of the flux paste can be one of 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, or 15 wt%, or any value satisfying the above range.

[0061] The present invention also provides a method for preparing a highly reliable rosin-free, no-clean solder paste. The key is to mix alloy powder and flux in the required proportion, heat and stir under vacuum, and then vacuum process the mixture to obtain the solder paste. The resulting solder paste has high reliability and better soldering effect.

[0062] The preparation method of the high-reliability rosin-free no-clean solder paste of the present invention is carried out according to the following steps.

[0063] Step 1) Weigh the alloy powder and flux according to the required ratio and then heat and stir them under vacuum. The heating temperature is 30℃~40℃ and the vacuum degree is within the range of -0.06 MPa~-0.1 MPa to ensure a good mixing effect and improve its uniformity and stability.

[0064] In the solder paste preparation method of the present invention, the use of vacuum heating and stirring not only reduces the air content in the solder paste and effectively promotes the bonding of flux and solder powder, preventing powder separation during subsequent use, but also effectively reduces the void ratio.

[0065] In embodiments of the present invention, the heating temperature for vacuum heating and stirring can be one of 30°C, 35°C, and 40°C, or any value satisfying the above range. The vacuum degree can be one of -0.06 MPa, -0.07 MPa, -0.08 MPa, -0.09 MPa, and -0.1 MPa, or any value satisfying the above range.

[0066] In embodiments of the present invention, the stirring speed of the vacuum heating stirring is 10 rpm to 20 rpm, and the stirring time is 6 min to 18 min. Exemplarily, the stirring speed can be one of 10 rpm, 11 rpm, 12 rpm, 13 rpm, 14 rpm, 15 rpm, 16 rpm, 17 rpm, 18 rpm, 19 rpm, or 20 rpm, or any value satisfying the above range. The stirring time can be one of 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, 17 min, or 18 min, or any value satisfying the above range.

[0067] Step 2) Vacuum the mixed solder paste to remove internal air bubbles and prepare the above-mentioned solder paste.

[0068] Unless otherwise defined, the technical terms used in the following embodiments have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are all conventional biochemical reagents; the raw materials, instruments, and equipment used in the following embodiments can all be obtained commercially or through existing methods; unless otherwise specified, the amounts of experimental reagents used are the amounts used in conventional experimental operations; unless otherwise specified, the experimental methods are all conventional methods.

[0069] Example 1 A highly reliable rosin-free, no-clean solder paste comprises the following components by weight percentage: 88.5% Sn96.5Ag3Cu0.5 powder and 11.5 wt% flux. The flux comprises the following components by weight percentage: 10% azelaic acid, 10% dodecyltrimethylammonium chloride, 45% diethylene glycol ethyl ether, 12% dibutyltin dilaurate, 14% hydrogenated castor oil, 4% 2,6-di-tert-butyl-p-cresol, and 5% polyacrylamide.

[0070] Method for preparing solder paste: S1: First, use a balance to accurately weigh the mass of each component according to the ratio.

[0071] S2: First, add diethylene glycol ethyl ether to the reactor. Then, add the following components in sequence to the diethylene glycol ethyl ether: dodecyltrimethylammonium chloride, azelaic acid, hydrogenated castor oil, dibutyltin dilaurate, 2,6-di-tert-butyl-p-cresol, and polyacrylamide. Stir at 90°C for 4 minutes after each addition, and finally stir for another 20 minutes to obtain the flux.

[0072] Preparation method of high-reliability rosin-free no-clean solder paste: Step 1) Weigh the alloy powder and flux according to the required ratio, and then heat and stir them under vacuum at 40℃ and a vacuum degree of -0.1 MPa for 10 min at a stirring speed of 15 rpm.

[0073] Step 2) Vacuum the mixed solder paste to remove internal air bubbles again, and prepare the solder paste.

[0074] Example 2 The remaining operations are the same as in Example 1, except that the vacuum heating and stirring speed in the preparation of the high-reliability rosin-free no-clean solder paste is 20 rpm and the stirring time is 6 min.

[0075] Example 3 The remaining operations are the same as in Example 1, except that the vacuum heating and stirring speed in the preparation of the high-reliability rosin-free no-clean solder paste is 10 rpm and the stirring time is 18 min.

[0076] Comparative Example 1 The remaining operations are the same as in Example 1, except that the flux contains the following components by weight percentage: azelaic acid 15%, dodecyltrimethylammonium chloride 8%, diethylene glycol ethyl ether 35%, dibutyltin dilaurate 18%, hydrogenated castor oil 10%, 2,6-di-tert-butyl-p-cresol 3%, polyacrylamide 3%, and hydrogenated rosin 8%.

[0077] Comparative Example 2 The remaining operations are the same as in Example 1, except that the flux contains the following components by weight percentage: azelaic acid 13%, dodecyltrimethylammonium chloride 5%, diethylene glycol ethyl ether 40%, dibutyltin dilaurate 10%, hydrogenated castor oil 13%, 2,6-di-tert-butyl-p-cresol 5%, polyacrylamide 4%, and hydrogenated rosin 10%.

[0078] Comparative Example 3 The remaining operations are the same as in Example 1, except that the preparation method of the solder paste does not use vacuum heating and stirring. Instead, it uses conventional room temperature stirring at a speed of 15 rpm for 10 min.

[0079] Comparative Example 4 The remaining operations were the same as in Comparative Example 1, except that the preparation method of the solder paste did not use vacuum heating and stirring. Instead, a conventional room temperature stirring method was used, with a stirring speed of 15 rpm and a stirring time of 10 min.

[0080] Comparative Example 5 The remaining operations were the same as in Comparative Example 2, except that the preparation method of the solder paste did not use vacuum heating and stirring. Instead, a conventional room temperature stirring method was used, with a stirring speed of 15 rpm and a stirring time of 10 min.

[0081] The composition and mixing method of the flux and solder paste in the examples and comparative example 1 are detailed in Table 1.

[0082] Table 1 Summary of the composition and mixing method of flux and solder paste in the examples and comparative examples

[0083] Performance testing Testing standards: Viscosity: Tested using IPC-TM-650 (2.4.34.3).

[0084] Collapse resistance: Tested using IPC-TM-650 (2.4.35).

[0085] Wetting: Tested using IPC-TM-650 (2.4.45).

[0086] Solder balls: Tested using T5-T6: IPC-TM-650 (2.4.43).

[0087] Copper plate corrosion: Tested using IPC-TM-650 (2.6.15C:2004).

[0088] Table 2 Summary of performance tests of solder pastes prepared in the examples and comparative examples

[0089] Combination Figure 1-6 As shown in Table 2, the solder pastes in Examples 1-3 are unique in that they are prepared without rosin and using a vacuum heating and stirring process. This combination not only significantly reduces post-soldering residue and lightens the color, achieving the convenience of no-cleaning, but also demonstrates excellent online performance in areas such as reflow characteristics, wettability, printability, release properties, copper corrosion resistance, and void ratio. Furthermore, this solder paste is completely halogen-free, meeting current environmental protection requirements. In contrast, although Comparative Examples 1-2 also used vacuum heating and stirring technology, the replacement of some solvents with different proportions of rosin resulted in a significant increase in post-soldering residue, which was widely spread above and around the solder joints. Simultaneously, the void ratio and the number of solder balls also increased to some extent.

[0090] On the other hand, Comparative Example 3, based on Example 1, omitted the crucial step of vacuum heating and stirring, resulting in solder pastes that all showed some residue after soldering. Furthermore, compared to the examples, Comparative Examples 1-5 showed an increase in void ratio, further confirming the positive effect of the vacuum heating and stirring process in reducing void ratio.

[0091] In summary, the solder pastes provided in Examples 1-3 not only excel in environmental friendliness and convenience but also achieve high levels of performance across various indicators. The solder paste of this invention is primarily used in 5G electronic products and surface mount technology (SMT) assembly processes. Currently, almost all circuit boards for electronic and electrical products utilize SMT technology, resulting in a very wide market application. The zero-halogen solder paste prepared by this invention fulfills the requirement of zero-halogen flux; moreover, it contains no rosin, resulting in minimal post-soldering residue, a light color, no need for cleaning, and ultra-low voids; furthermore, its online test results for reflow characteristics, wetting, printing, demolding, and corrosion resistance are all excellent.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. The present invention is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A highly reliable rosin-free, no-clean flux for soldering paste, characterized in that, The flux does not contain rosin and is composed of the following components by weight percentage: 10 wt%~15 wt% activator, 5 wt%~10 wt% surfactant, 35 wt%~45 wt% solvent, 10 wt%~18 wt% stabilizer, 10 wt%~15 wt% thixotropic agent, 3 wt%~5 wt% corrosion inhibitor, and 3 wt%~5 wt% lubricant. The active agent is azelaic acid; the solvent is diethylene glycol ethyl ether; the surfactant is one or more of disodium lauryl sulfosuccinate, potassium monododecyl phosphate, dodecyltrimethylammonium chloride, fatty alcohol polyoxyethylene ether, and coconut oil monoethanolamide; the stabilizer is one or more of dibutyltin dilaurate, phosphite, and zinc stearate. The preparation method of the aforementioned high-reliability rosin-free no-clean flux includes: The components that form the flux paste are mixed and melted according to the required ratio to obtain the flux paste. The components that form the flux paste are added in the following order: surfactant, activator, thixotropic agent, stabilizer, corrosion inhibitor and lubricant are added to the solvent in sequence. After each component is added, the mixture is stirred for 3 min to 5 min. After all components are added, the mixture is stirred for 15 min to 20 min.

2. The high-reliability rosin-free, no-clean flux for soldering paste as described in claim 1, characterized in that, The thixotropic agent includes one or more combinations of polyamide wax and hydrogenated castor oil.

3. The high-reliability rosin-free, no-clean flux for soldering paste as described in claim 1, characterized in that, The corrosion inhibitor includes one or more combinations of boric acid, sodium nitrite, hydroquinone, catechol, 2,6-di-tert-butyl-p-cresol, benzotriazole, and ascorbic acid.

4. The high-reliability rosin-free, no-clean flux for soldering paste as described in claim 1, characterized in that, The lubricant includes one or more combinations of castor oil, erucamide, and polyacrylamide.

5. A method for preparing a high-reliability rosin-free, no-clean flux for solder paste according to any one of claims 1-4, characterized in that, The preparation method includes: The components that form the flux paste are mixed and melted according to the required ratio to obtain the flux paste.

6. A highly reliable rosin-free, no-clean solder paste, characterized in that, The solder paste is composed of the following components by weight percentage: Alloy powder 85 wt%~90 wt%, flux 10 wt%~15 wt%; The flux is the flux according to any one of claims 1-4 or the flux prepared by the preparation method according to claim 5.

7. A method for preparing the high-reliability rosin-free no-clean solder paste according to claim 6, characterized in that, The preparation method includes: The solder paste is prepared by mixing alloy powder and flux in the required proportions, then heating and stirring under vacuum, followed by vacuum treatment.

8. The preparation method according to claim 7, characterized in that, The stirring speed of the vacuum heating and stirring is 10 rpm to 20 rpm, the stirring time is 6 min to 18 min, and the vacuum degree is -0.06 MPa to -0.1 MPa.

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