A high-efficiency thermally conductive lead-free solder paste and preparation method thereof

Abstract

The present application relates to the field of electronic packaging materials, and more particularly to a highly efficient, thermally conductive, lead-free solder paste and its preparation method. The solder paste comprises a tin alloy and a flux, wherein the flux is 15-25% of the weight of the tin alloy; the flux is composed of the following raw materials in percentage by weight: 42-60% rosin derivative, 5-10% activator, 5-10% liquid polyisobutylene, 2.5-5.5% copolymer containing maleic anhydride, 1-3% ethylene bisstearamide, 1-3% hydrogenated castor oil, and the remainder being solvent. The rosin derivative, liquid polyisobutylene, and maleic anhydride copolymer enhance the synergistic properties of the resulting solder paste, resulting in excellent fluidity, wettability, and film-forming properties. This improves the uniformity of the flux and tin alloy powder dispersion, and during the soldering process, a small amount of volatilization occurs in the solder joint, preventing the possibility of voids and improving the thermal conductivity and stability of the solder joint after soldering.

Description

Technical Field

[0001] The present application relates to the field of electronic packaging materials, and in particular to a high-efficiency thermally conductive lead-free solder paste and a preparation method thereof. Background Art

[0002] Solder paste is widely used in the electronics manufacturing industry, especially in semiconductor packaging and circuit board assembly. As electronic products develop towards miniaturization and high performance, the requirements for solder paste are becoming increasingly higher. Traditional solder paste is mainly composed of tin alloy powder and flux, where the function of flux is to remove oxides on the metal surface and promote good bonding between the solder and the metal surface. However, with the diversification of application scenarios and the improvement of technical requirements, traditional solder paste has gradually exposed its shortcomings in certain specific applications. For example, in high-power electronic devices, especially the inverter modules in new energy vehicles, their core components IGBT (insulated gate bipolar transistor) will generate a lot of heat during operation, and efficient heat dissipation measures are required to ensure its normal operation.

[0003] To address this challenge, existing technologies have proposed a variety of solutions. Common approaches include using solder materials with improved thermal conductivity and optimizing flux formulations to improve soldering quality and heat dissipation efficiency. However, solder paste is prone to voiding after soldering, which reduces thermal conductivity. Excessive volatile components in the flux can cause air bubbles to form in existing solder pastes, leading to voids within the solder joints, which in turn affects heat dissipation efficiency and soldering quality. These issues limit the practical performance of existing technologies, necessitating the development of a highly efficient, thermally conductive, lead-free solder paste to overcome these drawbacks. Summary of the Invention

[0004] The present invention reduces the voiding phenomenon of solder paste after soldering, while ensuring the stability after soldering, and provides a high-efficiency thermal conductive lead-free solder paste and preparation method.

[0005] A high-efficiency thermally conductive lead-free solder paste is composed of a tin alloy and a flux, wherein the flux accounts for 15-25% of the weight of the tin alloy; the flux is composed of the following raw materials in the following weight percentages:

[0006] Rosin derivatives 42-60%

[0007] Active agent 5-10%

[0008] Liquid polyisobutylene 5-10%

[0009] Copolymer containing maleic anhydride 2.5-5.5%

[0010] Ethylene bisstearamide 1-3%

[0011] Hydrogenated castor oil 1-3%

[0012] The balance is solvent.

[0013] By adopting the above technical solution, the high-efficiency thermal conductive lead-free solder paste has the following effects:

[0014] First of all, the flux content of the present application is low, which can achieve full and uniform dispersion of the tin alloy, so that the solder paste has better fluidity, wettability and film-forming properties, avoids the possibility of voids after welding, and improves welding quality and thermal conductivity. The proportion of rosin derivatives is high, and it works synergistically with the copolymer component containing maleic anhydride to further improve adhesion and thermal stability, ensuring reliability during the welding process. The addition of liquid polyisobutylene significantly enhances the wettability and thermal stability of the solder paste, ensures full solder joints during welding, reduces the void rate, and the liquid polyisobutylene works synergistically with the copolymer containing maleic anhydride. The copolymer containing maleic anhydride improves the film-forming property and chemical stability of the flux, effectively prevents oxidation and corrosion of the metal surface during welding, and optimizes the quality of the welded joint. Ethylene bisstearamide and hydrogenated castor oil work together to improve the handling performance of the solder paste, reduce volatilization losses at high temperatures, and improve the consistency and thermal conductivity of the final solder joints.

[0015] In summary, the present application utilizes a relatively low content of flux to achieve full and uniform dispersion of the tin alloy, and uses raw materials such as rosin derivatives, activators, liquid polyisobutylene, and copolymers containing maleic anhydride to enhance the synergistic effect, so that the resulting solder paste has better fluidity, wettability, and film-forming properties. During the welding process, a small amount of flux evaporates in the solder joints, avoiding the possibility of voids, thereby improving the welding quality, the thermal conductivity of the solder joints after welding, and the stability of the solder joints.

[0016] When a lower content of flux is used, it is difficult to fully mix with the tin alloy powder, and during welding, the wettability and diffusivity are low, resulting in incomplete solder joints and a high void rate.

[0017] Preferably, the chemical elements of the tin alloy are composed of 85-93 wt% tin, 2-6 wt% silver, 1-5 wt% copper, 0.1-3% boron, and 0.5-2.5% silicon.

[0018] The above raw material composition and usage ratio are all within the preferred range of this application. The obtained tin alloy has good comprehensive properties such as thermal conductivity, corrosion resistance, and easy dispersion. It can be mixed evenly with the flux of this application to reduce the occurrence of voids after welding.

[0019] Preferably, the particle size of the tin alloy is 20-38 μm.

[0020] By adopting this technical solution, the tin alloy particle size is controlled within the range of 20-38μm, allowing the solder paste to better fill the gap between the chip and the motherboard during the soldering process, increasing the contact area while reducing the void rate. This optimization has the following benefits: First, the evenly distributed tin particles improve the fullness of the solder joint and reduce the risk of reduced thermal conductivity due to bubbles. Second, the moderate particle size range takes into account the fluidity and stability of the solder paste, ensuring good workability and high heat dissipation efficiency during the soldering process.

[0021] Preferably, the rosin derivative is composed of at least three of hydrogenated rosin methyl ester, rosin-modified phenolic resin, rosin-modified maleic acid resin, and water-white rosin resin.

[0022] By adopting the above technical solution, the rosin derivative is composed of at least three of hydrogenated rosin methyl ester, rosin-modified phenolic resin, rosin-modified maleic acid resin, and water-white rosin resin, which can significantly improve the comprehensive performance of the flux. Specifically:

[0023] The combined use of multiple rosin derivatives enhances the flux's adhesion and film-forming properties, helping to form a more uniform and dense protective film, improving the quality and reliability of the solder joint. The combined effects of different rosin derivatives improve the flux's stability at high temperatures, reducing performance degradation due to temperature fluctuations and ensuring a smooth soldering process. The synergistic effect of these rosin derivatives enhances the flux's wettability, making it easier to evenly distribute the solder across the entire soldering area, improving solder coverage and uniformity. Different rosin derivatives have varying degrees of antioxidant capacity, and their combined use effectively prevents oxidation of the metal surface during soldering, protecting the quality of the solder joint.

[0024] In summary, the combination of various rosin derivatives, along with liquid polyisobutylene and a copolymer containing maleic anhydride, further enhances the flux's wetting, dispersibility, film-forming, and adhesion properties, allowing it to fully mix evenly with the tin alloy. The resulting solder paste exhibits superior soldering properties, reduces post-solder voiding, and improves thermal conductivity. Furthermore, post-soldering, the bond remains stable, preventing the possibility of detachment.

[0025] Preferably, the active agent is one or more of decyl tetradecanoic acid, 1-hydroxybenzotriazole monohydrate, trimethylbutylene glycol, succinic acid, and tartaric acid.

[0026] By employing the above technical solution, the activator, which uses one or more combinations of decyltetradecanoic acid, 1-hydroxybenzotriazole monohydrate, trimethylbutylene glycol, succinic acid, or tartaric acid, significantly enhances the flux's activation performance. These organic acid activators not only effectively remove oxides from metal surfaces but also enhance the wettability and adhesion of solder joints, thereby improving soldering quality and reliability. Furthermore, this selection takes into account environmental protection and lead-free requirements, further enhancing the overall performance of the solder paste.

[0027] Preferably, the liquid polyisobutylene is polyisobutylene 300R.

[0028] By adopting the above technical solution, the liquid polyisobutylene is selected from polyisobutylene 300R, whose excellent wettability and thermal stability significantly improve the soldering performance of the solder paste. It also works synergistically with the copolymer containing maleic anhydride to further enhance the overall performance of the solder.

[0029] Preferably, the maleic anhydride-containing copolymer is a methyl vinyl ether-maleic anhydride copolymer.

[0030] By adopting the above technical solution, the use of methyl vinyl ether-maleic anhydride copolymer significantly improves the film-forming properties, wettability, and thermal stability of the flux. It also works synergistically with polyisobutylene 300R to further enhance the flux's overall performance, reducing the likelihood of voids after soldering and providing excellent adhesion stability.

[0031] Specifically, film-forming property: methyl vinyl ether-maleic anhydride copolymer forms a uniform and dense film on the metal surface, effectively preventing the metal from oxidation and corrosion during the welding process and protecting the quality of the welded joint.

[0032] Wettability: The copolymer improves the fluidity of the flux, allowing it to better wet the metal surface, helping the solder to be more evenly distributed on the metal joint, improving the reliability and quality of soldering.

[0033] Thermal stability: Methyl vinyl ether-maleic anhydride copolymer has excellent chemical and thermal stability, and can withstand the high temperature and chemical reactions during the welding process, ensuring that the flux maintains stable performance during the welding process, reducing the volatilization and decomposition of the flux, thereby improving the welding quality and the thermal conductivity of the solder joint.

[0034] Preferably, the ethylene bisstearamide is ethylene bis(12-hydroxy)stearamide and / or ethylene bis(16-hydroxy)stearamide.

[0035] By adopting the above technical solution, ethylene bis(12-hydroxy) stearamide and / or ethylene bis(16-hydroxy) stearamide are specifically selected as ethylene bisstearamide, which can significantly improve the lubricity and thermal stability of the flux.

[0036] In summary, the selection of ethylene bis(12-hydroxy) stearamide and / or ethylene bis(16-hydroxy) stearamide as the specific components of ethylene bisstearamide not only improves the comprehensive performance of the flux, but also further improves the saturation and thermal conductivity of the solder joint and reduces the occurrence of voids.

[0037] Preferably, the maleic anhydride-containing copolymer is prepared from the following raw materials in percentage by weight:

[0038] Contains 3-5% acrylate-based diluent

[0039] Methacryloyloxypropyl double-terminated polydimethylsiloxane 5-10%

[0040] Maleic anhydride 2-5%

[0041] Initiator 0.02-0.05%

[0042] The balance was methyl vinyl ether-maleic anhydride copolymer.

[0043] Methacryloyloxypropyl double-terminated polydimethylsiloxane, an acrylate-based diluent, and maleic anhydride can undergo a copolymerization reaction under the action of an initiator to generate a copolymer with excellent film-forming properties, wettability, and thermal stability. The copolymer synergistically acts with a methyl vinyl ether-maleic anhydride copolymer. The obtained copolymer containing maleic anhydride is used in a soldering flux to further improve the overall performance of the soldering flux, reduce the phenomenon of wire voids in the solder paste after soldering, maintain stable adhesion on the PCB board, and improve the thermal conductivity of the solder paste after application.

[0044] In a second aspect, a method for preparing a high-efficiency thermally conductive lead-free solder paste is provided, which is prepared by the following method:

[0045] The rosin derivative, the activator, the liquid polyisobutylene, the copolymer containing maleic anhydride, the ethylene bisstearamide, the hydrogenated castor oil, and the solvent are weighed and mixed uniformly according to weight percentage to obtain a soldering flux;

[0046] The flux and the tin alloy are weighed and mixed evenly according to weight percentage to obtain a tin paste.

[0047] By adopting the above technical solution, the highly efficient thermal conductive lead-free solder paste prepared has the following effects:

[0048] Flux Optimization: The flux's rational compositional ratios ensure synergistic effects, including the rosin derivative, activator, liquid polyisobutylene, and copolymer containing maleic anhydride, enhancing the flux's film-forming properties, wettability, and thermal stability. The combination of liquid polyisobutylene and methyl vinyl ether-maleic anhydride copolymer, in particular, enhances wettability and thermal stability, ensuring uniform solder distribution during soldering, reducing voiding, and improving soldering quality and thermal conductivity.

[0049] Tin Alloy Optimization: The chemical composition and particle size range of the tin alloy are precisely controlled to ensure high thermal conductivity and excellent solderability. The presence of elements such as silver, copper, boron, and silicon in the tin alloy not only increases the melting point and mechanical strength, but also enhances the corrosion and oxidation resistance of the solder joint.

[0050] Improved overall performance: Through a reasonable ratio of flux and tin alloy, the final lead-free solder paste has high thermal conductivity, good fluidity and wettability, while reducing volatilization and voids during the soldering process, significantly improving the thermal conductivity and reliability after soldering.

[0051] Simple process: The preparation method is simple and easy. The preparation of flux and solder paste can be completed by weighing each component and mixing them evenly, which is convenient for large-scale production and application.

[0052] In summary, this application includes at least one of the following beneficial technical effects:

[0053] 1. By adopting a lower flux content and optimizing the formula design, the tin alloy components are fully and evenly dispersed, forming a welding effect with full solder joints and low porosity, which significantly improves the thermal conductivity and heat dissipation efficiency; the rosin derivative and the copolymer containing maleic anhydride work synergistically to enhance the film-forming and adhesion properties of the flux, and improve the stability of the solder joints in high-temperature environments; liquid polyisobutylene and the copolymer containing maleic anhydride jointly improve the wettability of the flux, promote the effective bonding of the solder and the metal surface, and further ensure the welding quality.

[0054] 2. Methacryloyloxypropyl double-terminated polydimethylsiloxane, an acrylate-based diluent, and maleic anhydride can undergo a copolymerization reaction under the action of an initiator to generate a copolymer with excellent film-forming properties, wettability, and thermal stability. The copolymer synergistically acts with a methyl vinyl ether-maleic anhydride copolymer. The obtained copolymer containing maleic anhydride is used in a flux to further improve the comprehensive performance of the flux, reduce the phenomenon of wire voids in the solder paste after soldering, and maintain stable adhesion on the PBC board, thereby improving the thermal conductivity of the solder paste after application. DETAILED DESCRIPTION

[0055] The present application is further described in detail below with reference to the embodiments.

[0056] Liquid polyisobutylene is polyisobutylene 300R, Japanese Idemitsu polyisobutylene 300R;

[0057] Hydrogenated castor oil Jiangsu Minglin Chemical Technology Co., Ltd. EL-40

[0058] Hydrogenated rosin methyl ester CAS: 8050-15-5;

[0059] Rosin modified phenolic resin Sanming Senke New Materials Co., Ltd. F-2136

[0060] Rosin modified maleic acid resin Deqing County Haizhuo Chemical Co., Ltd. ML-103;

[0061] Water-white rosin resin Komao KA100W;

[0062] Methyl vinyl ether-maleic anhydride copolymer CAS No. 9011-16-9

[0063] Methacryloyloxypropyl di-terminated polydimethylsiloxane has a molecular weight of 8000-10000; CAS number 58130-03-3.

[0064] Preparation Example of Copolymer Containing Maleic Anhydride

[0065] Preparation Example 1

[0066] A copolymer containing maleic anhydride is prepared by the following method:

[0067] 5% methacryloyloxypropyl di-terminated polydimethylsiloxane, 2% maleic anhydride, 5% acrylate-containing diluent, and 0.05% initiator were weighed and mixed uniformly, heated to 60°C, and reacted for 2 hours. 87.95% methyl vinyl ether-maleic anhydride copolymer was then added and mixed uniformly to obtain a copolymer containing maleic anhydride. The initiator was dibenzoyl peroxide, and the acrylate-containing diluent was dipropylene glycol diacrylate.

[0068] Preparation Example 2

[0069] Preparation Example 2 differs from Preparation Example 1 in that the amounts of raw materials used are different, specifically: 7% methacryloyloxypropyl di-terminated polydimethylsiloxane, 3% maleic anhydride, 4% acrylate-based diluent, 0.03% initiator, and 85.97% methyl vinyl ether-maleic anhydride copolymer are weighed in weight percentage.

[0070] Preparation Example 3

[0071] Preparation Example 3 differs from Preparation Example 1 in that the amounts of raw materials used are different, specifically: 10% methacryloyloxypropyl di-terminated polydimethylsiloxane, 2% maleic anhydride, 3% acrylate-based diluent, 0.02% initiator, and 84.92% methyl vinyl ether-maleic anhydride copolymer are weighed in weight percentage.

[0072] Preparation Comparative Example

[0073] Preparation Comparative Example 1

[0074] The difference between Preparation Comparative Example 1 and Preparation Example 1 is that an equal amount of methacryloyloxypropyl di-terminated polydimethylsiloxane is replaced by maleic anhydride.

[0075] Example

[0076] Example 1

[0077] A method for preparing a high-efficiency thermally conductive lead-free solder paste comprises the following steps:

[0078] According to weight percentage, 42% of rosin derivative, 5% of active agent, 10% of liquid polyisobutylene, 5.5% of copolymer containing maleic anhydride, 3% of ethylene bisstearamide, 3% of hydrogenated castor oil, and 31.5% of solvent are weighed and evenly mixed to obtain a soldering flux, wherein the rosin derivative consists of hydrogenated rosin methyl ester, hydrogenated rosin methyl ester, and water-white rosin resin in a weight ratio of 1:1:3; the active agent is decyltetradecanoic acid; the solvent is diethylene glycol monohexyl ether; the liquid polyisobutylene is polyisobutylene 300R; the ethylene bisstearamide is ethylene bis(12-hydroxy)stearamide; and the copolymer containing maleic anhydride is methyl vinyl ether-maleic anhydride copolymer.

[0079] According to weight percentage, soldering flux and tin alloy are weighed and mixed evenly, with the soldering flux accounting for 15% of the weight of the tin alloy, to obtain solder paste.

[0080] The particle size of the tin alloy may be 20-38 μm, and in this embodiment, preferably 25 μm.

[0081] In terms of weight percentage, the chemical elements of the tin alloy are composed of 85 wt % tin, 6 wt % silver, 5 wt % copper, 3 % boron, and 1 % silicon.

[0082] Example 2

[0083] The difference between Example 2 and Example 1 is that the soldering flux is 21% of the weight of the tin alloy; in terms of weight percentage, the chemical elements of the tin alloy are composed of 89wt% tin, 5wt% silver, 3wt% copper, 2% boron, and 1% silicon.

[0084] Example 3

[0085] The difference between Example 3 and Example 1 is that the soldering flux is 25% of the weight of the tin alloy; in terms of weight percentage, the chemical elements of the tin alloy are composed of 93wt% tin, 2wt% silver, 1wt% copper, 3% boron, and 1% silicon.

[0086] Example 4

[0087] The difference between Example 4 and Example 2 is that the rosin derivative consists of rosin-modified phenolic resin, rosin-modified maleic acid resin, and hydrogenated rosin methyl ester in a weight ratio of 1:1:3.

[0088] Example 5

[0089] The difference between Example 5 and Example 2 is that the active agent consists of decyltetradecanoic acid and succinic acid in a weight ratio of 1:1.

[0090] Example 6

[0091] The difference between Example 6 and Example 2 is that ethylene bisstearamide is composed of ethylene bis(12-hydroxy)stearamide and ethylene bis(16-hydroxy)stearic acid in a weight ratio of 1:1.

[0092] Examples 7-8

[0093] The difference between Example 7-8 and Example 2 is that the raw material composition of the flux is different, as shown in Table 1;

[0094] Table 1 Raw material composition of the flux of Example 2, Example 7-8 (%)

[0095]

[0096] Example 9

[0097] The difference between Example 9 and Example 7 is that the source of the copolymer containing maleic anhydride is Preparation Example 1.

[0098] Example 10

[0099] The difference between Example 10 and Example 7 is that the source of the copolymer containing maleic anhydride is Preparation Example 2.

[0100] Example 11

[0101] The difference between Example 11 and Example 7 is that the source of the copolymer containing maleic anhydride is Preparation Example 3.

[0102] Example 12

[0103] The difference between Example 12 and Example 7 is that the source of the copolymer containing maleic anhydride is the preparation of Comparative Example 1.

[0104] Comparative Example

[0105] Comparative Example 1

[0106] The difference between Comparative Example 1 and Example 1 is that the liquid polyisobutylene is replaced by an equal amount of a copolymer containing maleic anhydride.

[0107] Comparative Example 2

[0108] The difference between Comparative Example 2 and Example 1 is that the copolymer containing maleic anhydride is replaced by liquid polyisobutylene in equal amounts.

[0109] Comparative Example 3

[0110] The difference between Comparative Example 3 and Example 1 is that the liquid polyisobutylene and the copolymer containing maleic anhydride are replaced by rosin in equal amounts.

[0111] Comparative Example 4

[0112] The difference between Comparative Example 4 and Example 1 is that the soldering flux accounts for 40% of the weight of the tin alloy.

[0113] Comparative Example 5

[0114] The difference between Comparative Example 5 and Example 1 is that the soldering flux accounts for 8% of the weight of the tin alloy.

[0115] Performance testing

[0116] The solder pastes obtained in Examples 1-12 and Comparative Examples 1-5 were soldered on PCB boards at 200° C. to form solder joints, and then the following tests were performed.

[0117] Detection method / test method

[0118] (1) Void test: The void ratio of the solder joints formed by soldering the solder pastes of Examples 1-12 and Comparative Examples 1-5 was measured respectively according to the section microscopic observation method. The judgment criteria were as follows: the soldering condition after sectioning was observed using an electron metallographic microscope, the void ratio did not exceed 20% of the solder ball area, intermetallic was formed, and there was no void crack phenomenon.

[0119] Table 2 IPC void standards for BGA: IPC 7095 7.4.1.6

[0120]

[0121]

[0122] 1. Quality inspection

[0123] Table 3 Quality inspection

[0124]

[0125] (3) Adhesion: Test conditions based on JIS-Z-3284; Test equipment: Adhesion tester; Pressing speed: 2.0 mm / s; Pressing time: 0.2 s; Measurement load: 0.49 N;

[0126] Lifting speed: 10.0 mm / s; Test environment: 25°C, 50% RH;

[0127] Table 4 Experimental data of Examples 1-12 and Comparative Examples 1-5

[0128]

[0129]

[0130] Combining Example 1 and Comparative Examples 1-5 with Table 4, it can be seen that the quality of Comparative Examples 1-3 is unqualified and the void rate is high, indicating that the present application uses a lower content of flux to achieve full and uniform dispersion of the tin alloy, and the rosin derivative, liquid polyisobutylene, and maleic anhydride-containing copolymer of the present application are compounded to achieve a synergistic effect, which can reduce a small amount of volatilization in the solder joint during the welding process, avoid the possibility of voids, and improve the welding quality, the thermal conductivity of the solder joint after welding, and the stability of the solder joint.

[0131] Combining Example 9 with Example 7 and Table 4, it can be seen that Example 9 has higher adhesion than Example 7, while the void rate is lower than that of Example 7. This shows that the maleic anhydride-containing copolymer prepared by using methacryloyloxypropyl di-terminated polydimethylsiloxane, maleic anhydride, an acrylate-based diluent, and methyl vinyl ether-maleic anhydride copolymer in the flux further improves the overall performance and other physical interactions, thereby improving the adhesion stability of the solder paste after soldering, reducing the generation of voids, and improving its thermal conductivity.

[0132] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-efficiency thermally conductive lead-free solder paste, characterized in that: It is composed of tin alloy and flux, with the flux accounting for 15-25% of the weight of the tin alloy; the flux is composed of the following raw materials in the following weight percentages: Rosin derivatives 42-60%, Active agent 5-10%, Liquid polyisobutylene 5-10%, Copolymer containing maleic anhydride 2.5-5.5%, Ethylene bisstearamide 1-3%, Hydrogenated castor oil 1-3%, The balance is solvent; The maleic anhydride-containing copolymer is a methyl vinyl ether-maleic anhydride copolymer; The maleic anhydride-containing copolymer is prepared from the following raw materials in percentage by weight: Contains 3-5% acrylate-based diluent, Methacryloyloxypropyl double-terminated polydimethylsiloxane 5-10%, Maleic anhydride 2-5%, Initiator 0.02-0.05%, The balance was methyl vinyl ether-maleic anhydride copolymer.

2. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The chemical elements of the tin alloy are composed of 85-93 wt% tin, 2-6 wt% silver, 1-5 wt% copper, 0.1-3% boron, and 0.5-2.5% silicon.

3. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The particle size of the tin alloy is 20-38 μm.

4. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The rosin derivative consists of at least three of hydrogenated rosin methyl ester, rosin-modified phenolic resin, rosin-modified maleic acid resin and water-white rosin resin.

5. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The active agent is one or more of decyl tetradecanoic acid, 1-hydroxybenzotriazole monohydrate, trimethylbutylene glycol, succinic acid, and tartaric acid.

6. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The liquid polyisobutylene is polyisobutylene 300R.

7. The high-efficiency thermally conductive lead-free solder paste according to claim 1, characterized in that: The ethylene bisstearic acid amide is ethylene bis(12-hydroxy)stearic acid amide and / or ethylene bis(16-hydroxy)stearic acid amide.

8. A method for preparing a high-efficiency thermally conductive lead-free solder paste according to any one of claims 1 to 7, characterized in that: Prepared by the following method: The rosin derivative, the activator, the liquid polyisobutylene, the copolymer containing maleic anhydride, the ethylene bisstearamide, the hydrogenated castor oil, and the solvent are weighed and mixed uniformly according to weight percentage to obtain a soldering flux; The flux and the tin alloy are weighed and mixed evenly according to weight percentage to obtain a tin paste.

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