Halogen-free pre-coating soldering lug and preparation method thereof

Abstract

The invention discloses a halogen-free pre-coating soldering lug and a preparation method thereof. The halogen-free pre-coating soldering lug comprises 97-99 wt% of a soldering lug body and 1-3 wt% of flux paste. The flux paste comprises the following components: a film-forming resin agent, an active agent, a flexible plasticizer, an anti-sticking additive and a low-boiling-point solvent, the active agent at least comprises pyridine-2-formic acid. The preparation method comprises the following steps: preparing a mixed solution; freezing, standing and carrying out temperature returning treatment; carrying out coating treatment; and punch forming. According to the method, the breaking capacity and wettability of the halogen-free coating soldering lug on a compact oxide layer are effectively improved, the stamping powder falling rate is reduced, and the problems of drying and adhesion are thoroughly solved; through the improved design of the formula and the process, the halogen-free pre-coating soldering lug which is excellent in oxidation capacity and wettability, free of slag falling during stamping and dry and non-sticky in surface is successfully prepared, and the welding effect can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the field of welding materials, and in particular to a halogen-free pre-coated welding sheet and a preparation method thereof. Background Art

[0002] As electronic packaging rapidly evolves toward higher density, miniaturization, and higher reliability, traditional soldering materials and processes are increasingly exposed to limitations in key applications. This is particularly true in high-end packaging applications such as flip-chips, power device modules, and MEMS devices, which require complex structures, high thermal loads, and high long-term stability. Conventional solder paste printing and flux dispensing processes struggle to meet the requirements for process control precision and soldering consistency. Consequently, pre-coated solder pads have emerged.

[0003] As a functional welding material that evenly attaches flux in solid form to the surface of preformed solder, the pre-coated solder sheet has an integrated design that eliminates the need to add flux separately during the welding process, thereby significantly simplifying the process steps. It has the advantages of high integration and controllable shape, and can control welding accuracy and improve welding consistency. It is especially suitable for scenarios with tiny pads, high-density wiring, limited electrodes or limited space.

[0004] Pre-coated solder pads typically use tin-lead, lead-free tin alloys, or other solder bases, with a 1-4wt% flux coating applied to the surface. This is achieved through precise coating control and drying processes, ensuring excellent solderability for each pad and improving overall assembly yield. As a core auxiliary material in the soldering process, flux primarily removes oxides from the metal surface, reduces the surface tension of molten solder, improves wettability, and inhibits reoxidation during soldering. Therefore, in pre-coated solder pads, an integrated soldering material, the performance of the flux directly determines the reliability, environmental friendliness, and process compatibility of the soldering result.

[0005] The traditional high-activity flux used in existing pre-coated solder sheets is mainly halogen system and halogen-free system. The halogen compounds in the halogen system can effectively break the metal oxide layer at the welding interface, improve the wetting speed and welding quality, but the residual Cl- and Br - Halogen ions such as halogen can significantly reduce the long-term reliability of devices in the working environment. Accordingly, while halogen-free flux systems offer greater applicability, these formulations are generally weak in deoxidation capabilities. This is especially true when dealing with inert or dense metal oxide layers, such as nickel plating. The surface wetting and spreading rate is ≤70%, making it difficult to fully wet the surface. The solder spreading rate often falls below process requirements, even leading to cold or poor solder joints, affecting soldering quality. Furthermore, after applying traditional highly active flux to solder pads, the dried pre-coat layer can experience crystallization, powder loss during stamping (powder loss rate >5%), and sticking during packaging. Summary of the Invention

[0006] The present invention provides a halogen-free pre-coated solder sheet and a preparation method thereof, and for the first time uses pyridine-2-carboxylic acid as a core active agent in conjunction with a -18 to -12°C freezing process, effectively solving the problems of the high-activity halogen-free solder flux in the prior art, such as weak oxide layer removal ability, poor wettability and difficulty in spreading, crystallization after drying, powder loss during punching, and adhesion.

[0007] To solve the above technical problems, the present invention provides a halogen-free pre-coated solder sheet, comprising 97-99 wt% of solder sheet and 1-3 wt% of solder paste; wherein the solder paste comprises the following components:

[0008] Film-forming resin 40-60wt%;

[0009] Active agent 3-10wt%;

[0010] 3-10 wt% flexible plasticizer;

[0011] Anti-stick additive 1-3wt%;

[0012] The balance is low boiling point solvent;

[0013] The active agent includes pyridine-2-carboxylic acid.

[0014] In a preferred embodiment of the present invention, the active agent further comprises at least one of methylsuccinic acid, 2-hydroxysuccinic acid, lactic acid, tartaric acid, citric acid or succinic acid.

[0015] In a preferred embodiment of the present invention, the flexible plasticizer includes at least one of polyvinyl butyral, a polymer of lauric acid and 1,6-hexanediol, PEG-400, PEG-2000, vinyl bisstearamide or methylene stearamide.

[0016] In a preferred embodiment of the present invention, the film-forming resin agent includes at least one of pentaerythritol-modified rosin ester, rosin glycerol ester, high softening point rosin, polymerized rosin, acrylic acid-modified rosin resin or maleic acid rosin resin.

[0017] In a preferred embodiment of the present invention, the anti-sticking additive includes at least one of microcrystalline wax powder or ultrafine hydrophobic silica.

[0018] In a preferred embodiment of the present invention, the low boiling point solvent component includes at least one of diethylene glycol dibutyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethyl acetate, dipropylene glycol methyl ether or propylene glycol methyl ether acetate.

[0019] In a preferred embodiment of the present invention, the material of the soldering sheet is: Sn 96.5 Ag 3.0 Cu 0.5 .

[0020] To solve the above technical problems, the present invention also provides a method for preparing a halogen-free pre-coated solder sheet, comprising the following steps:

[0021] (1) Preparing a mixed solution: Heat and stir the film-forming resin, flexible plasticizer, and low-boiling-point solvent in the formulated amount until the film-forming resin is completely dissolved, cool to 80-100°C, add the active agent and anti-sticking additive, and continue stirring until all components are fully dissolved and mixed;

[0022] (2) Freezing and cooling: The obtained mixed solution is transferred to a sealed container and cooled and cooled. After freezing, the mixed solution is taken out and cooled and cooled at room temperature to obtain a coating flux paste.

[0023] (3) Coating treatment: evenly coating the obtained solder paste on the surface of the solder strip, controlling the coating amount of the solder paste to be 1.0-1.5wt% of the mass of the solder strip, and drying to obtain a pre-coated solder strip;

[0024] (4) Stamping: The obtained pre-coated solder strip is punched using a fully automatic stamping machine to obtain the pre-coated solder sheet.

[0025] In a preferred embodiment of the present invention, in step (2), the freezing and standing conditions are: temperature -18 to -12°C, time 22 to 28 hours.

[0026] In a preferred embodiment of the present invention, in step (3), the drying process conditions are: temperature 120-150° C., time 10-15 min.

[0027] The beneficial effects of the present invention are as follows: a halogen-free pre-coated solder sheet and a preparation method thereof adopt pyridine-2-carboxylic acid as a core active agent, which effectively improves the ability of the halogen-free coated solder sheet to break dense oxide layers and the wettability, especially on the surface of dense metal oxide layers such as nickel plating, the wetting and spreading rate reaches 93-97%, overcoming the technical bottlenecks of poor wettability and high false solder joint rate of traditional halogen-free solder sheets; the flexible plasticizer compounding system gives the coating super-strong and super-tough properties, effectively reducing the stamping powder loss rate; the freezing treatment eliminates solvent crystallization, significantly improving the drying and adhesion problems; the present invention successfully prepares a halogen-free pre-coated solder sheet with excellent oxidation ability and wettability, no slag during stamping, and a dry and non-adhesive surface through improved design of the formula and process, which can effectively improve the welding effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The present invention is a schematic flow chart of a method for preparing a halogen-free pre-coated solder sheet. DETAILED DESCRIPTION

[0029] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0030] The invention discloses a halogen-free pre-coated solder sheet with non-sticky dry film, high adhesion and no slag. The solder sheet comprises 97-99 wt % of the solder sheet and 1-3 wt % of the solder paste uniformly coated on the surface of the solder sheet.

[0031] The material of the soldering sheet is: Sn 96.5 Ag 3.0 Cu 0.5 .

[0032] The solder paste comprises the following components: 40-60 wt% of film-forming resin, 3-10 wt% of active agent, 3-10 wt% of flexible plasticizer, 1-3 wt% of anti-sticking additive and the balance of low boiling point solvent, the total amount of each component being 100%.

[0033] Specifically, the film-forming resin agent includes at least one of pentaerythritol-modified rosin ester, rosin glycerol ester, high softening point rosin, polymerized rosin, acrylic acid-modified rosin resin, or maleic acid rosin resin. The film-forming resin agent imparts excellent adhesion, flexibility, and thermal stability to the soldering paste.

[0034] The active agent is pyridine-2-carboxylic acid or a combination of pyridine-2-carboxylic acid and at least one of methylsuccinic acid, 2-hydroxysuccinic acid, lactic acid, tartaric acid, citric acid, or succinic acid. The pyridine ring nitrogen atom and the carboxyl group of the active agent pyridine-2-carboxylic acid synergistically chelate metal oxides, imparting excellent deoxidation capability to the solder flux paste. Furthermore, the synergistic effect with other active agents further enhances the film breaking and complexing effect on the oxide layer, improving wettability, thereby effectively resolving the problem of halogen-free fluxes having weak deoxidation capability or difficulty in fully wetting dense metal oxide layers.

[0035] The flexible plasticizer includes at least one of polyvinyl butyral, a polymer of lauric acid and 1,6-hexanediol, PEG-400, PEG-2000, vinyl bisstearamide, or methylene stearamide. Preferably, the flexible plasticizer is a combination of polyvinyl butyral and a polymer of lauric acid and 1,6-hexanediol, with the weight ratio of the two being 1:3 to 1:5. The polymer of polyvinyl butyral, lauric acid, and 1,6-hexanediol is used to improve the flexibility and crack resistance of the cured solder paste film, thereby preventing slag.

[0036] The anti-sticking additive is used to reduce the surface energy of the film layer formed after the soldering paste is applied, and to improve the handling feel after drying.

[0037] The low boiling point solvent is used to form a uniform film after the solder paste is coated, and is easy to dry, thereby improving the drying efficiency.

[0038] The present invention uses the synergistic effect of the above components to make the prepared halogen-free pre-coated solder sheet have good oxidation ability and wettability, and the coating layer thereon has uniform texture and high adhesion strength, effectively avoiding the problems of crystallization, powder loss during punching and adhesion during packaging.

[0039] The method for preparing the halogen-free pre-coated solder sheet specifically comprises the following steps:

[0040] (1) preparing a mixed solution: heating the film-forming resin agent, the flexible plasticizer and the low-boiling-point solvent in the formulated amount to 130-150° C., stirring until the film-forming resin agent is completely dissolved to obtain a uniform film-forming resin solution; stopping heating, cooling the obtained film-forming resin solution to 80-100° C., rapidly adding the formulated amount of the active agent and the anti-sticking additive, and continuing stirring until the components are fully dissolved and mixed to obtain a mixed solution;

[0041] (2) Freezing and standing and returning to temperature: the obtained mixed solution is transferred to a sealed container and frozen and stood at -20 to -10°C for 20 to 36 hours; after the freezing is completed, the sealed container is taken out and allowed to stand and return to room temperature to obtain a coating flux paste; freezing causes the solvent to crystallize directionally, forming a microporous structure, thereby improving the dispersion uniformity of the flux and preventing crystallization;

[0042] (3) Coating treatment: The obtained flux paste is evenly coated on the surface of the soldering strip by an adjustable thin film coating machine, and then baked in an oven at 120-150°C for 10-15 minutes to obtain a pre-coated soldering strip;

[0043] (4) Stamping: The obtained pre-coated solder strip is punched using a fully automatic stamping machine to obtain a pre-coated solder sheet in the shape of a mold.

[0044] The technical content of the present invention is described in detail below through specific embodiments.

[0045] Example 1

[0046] Add 35.0g of pentaerythritol-modified rosin ester, 10.0g of high-softening-point rosin, 2.0g of polyvinyl butyral, 8.0g of a polymer of lauric acid and 1,6-hexanediol, 20.0g of diethylene glycol dibutyl ether, and 16.5g of propylene glycol monomethyl ether to a beaker. Heat to 140°C and stir until the film-forming resins, pentaerythritol-modified rosin ester and high-softening-point rosin, are completely dissolved, resulting in a uniform film-forming resin solution. Stop heating and cool the film-forming resin solution to 80°C. Quickly add 8.0g of pyridine-2-carboxylic acid (active agent) and 0.5g of microcrystalline wax powder (anti-stick additive), and continue stirring until the mixture is fully dispersed and dissolved.

[0047] The mixed solution was transferred to a sealed container and frozen at -15°C for 24 hours. After the freezing was complete, the sealed container was taken out and allowed to stand at room temperature to return to room temperature to obtain a coating flux paste.

[0048] The obtained coating flux paste is evenly applied on the Sn by an adjustable film coater. 96.5 Ag 3.0 Cu 0.5 The coating amount on the surface of the solder strip is 1.25wt%, and then the oven temperature is set to 120℃, and the coated solder strip is placed in the oven and baked for 15 minutes to obtain Sn 96.5 Ag 3.0 Cu 0.5 Pre-coated solder ribbon.

[0049] The pre-coated solder strip is punched with a fully automatic punching machine to obtain a mold-shaped Sn 96.5 Ag 3.0 Cu 0.5 Pre-applied solder pads.

[0050] Example 2

[0051] Add 35.0g of pentaerythritol-modified rosin ester, 10.0g of high-softening-point rosin, 2.0g of polyvinyl butyral, 8.0g of a polymer of lauric acid and 1,6-hexanediol, 20.0g of diethylene glycol dibutyl ether, and 16.5g of propylene glycol monomethyl ether to a beaker. Heat to 140°C and stir until the film-forming resins, pentaerythritol-modified rosin ester and high-softening-point rosin, are completely dissolved, resulting in a uniform film-forming resin solution. Stop heating and cool the film-forming resin solution to 80°C. Quickly add 2.0g of pyridine-2-carboxylic acid (active agent), 6.0g of methylsuccinic acid, and 0.5g of microcrystalline wax powder (anti-stick additive), and continue stirring until the mixture is fully dispersed and dissolved.

[0052] The mixed solution was transferred to a sealed container and frozen at -15°C for 24 hours. After the freezing was complete, the sealed container was taken out and allowed to stand at room temperature to return to room temperature to obtain a coating flux paste.

[0053] The obtained solder paste is evenly applied on the Sn by an adjustable film coater. 96.5 Ag 3.0 Cu 0.5 The coating amount on the surface of the solder strip is 1.25wt%, and then the oven temperature is set to 120℃, and the coated solder strip is placed in the oven and baked for 15 minutes to obtain Sn 96.5 Ag 3.0 Cu 0.5 Pre-coated solder ribbon.

[0054] The pre-coated solder strip is punched with a fully automatic punching machine to obtain a mold-shaped Sn 96.5 Ag3.0 Cu 0.5 Pre-applied solder pads.

[0055] Example 3

[0056] Add 35.0g of pentaerythritol-modified rosin ester, 10.0g of rosin glycerol ester, 10.0g of a polymer of dodecanoic acid and 1,6-hexanediol, 20.0g of diethylene glycol dibutyl ether, and 16.5g of propylene glycol monomethyl ether to a beaker. Heat to 140°C and stir until the film-forming resins, pentaerythritol-modified rosin ester and rosin glycerol ester, are completely dissolved, resulting in a uniform film-forming resin solution. Stop heating and cool the film-forming resin solution to 80°C. Quickly add 2.0g of pyridine-2-carboxylic acid (active agent), 6.0g of methylsuccinic acid (methylsuccinic acid), and 0.5g of ultrafine hydrophobic silica (anti-sticking additive), and continue stirring until fully dispersed and dissolved.

[0057] The mixed solution was transferred to a sealed container and frozen at -15°C for 24 hours. After the freezing was complete, the sealed container was taken out and allowed to stand at room temperature to return to room temperature to obtain a coating flux paste.

[0058] The obtained solder paste is evenly applied on the Sn by an adjustable film coater. 96.5 Ag 3.0 Cu 0.5 The coating amount on the surface of the solder strip is 1.25wt%, and then the oven temperature is set to 120℃, and the coated solder strip is placed in the oven and baked for 15 minutes to obtain Sn 96.5 Ag 3.0 Cu 0.5 Pre-coated solder ribbon.

[0059] The pre-coated solder strip is punched with a fully automatic punching machine to obtain a mold-shaped Sn 96.5 Ag 3.0 Cu 0.5 Pre-applied solder pads.

[0060] Example 4

[0061] Add 35.0g of pentaerythritol-modified rosin ester, 10.0g of rosin glycerol ester, 2.0g of polyvinyl butyral, 8.0g of a polymer of lauric acid and 1,6-hexanediol, 20.0g of diethylene glycol dibutyl ether, and 16.5g of propylene glycol monomethyl ether to a beaker. Heat to 140°C and stir until the film-forming resins, pentaerythritol-modified rosin ester and rosin glycerol ester, are completely dissolved, resulting in a uniform film-forming resin solution. Stop heating, cool the film-forming resin solution to 80°C, and quickly add 2.0g of pyridine-2-carboxylic acid (active agent), 6.0g of methylsuccinic acid, and 0.5g of ultrafine hydrophobic silica (anti-stick additive). Continue stirring to fully disperse and dissolve.

[0062] The mixed solution was transferred to a sealed container and frozen at -15°C for 24 hours. After the freezing was complete, the sealed container was taken out and allowed to stand at room temperature to return to room temperature to obtain a coating flux paste.

[0063] The obtained solder paste is evenly applied on the Sn by an adjustable film coater. 96.5 Ag 3.0 Cu 0.5 The coating amount on the surface of the solder strip is 1.25wt%, and then the oven temperature is set to 120℃, and the coated solder strip is placed in the oven and baked for 15 minutes to obtain Sn 96.5 Ag 3.0 Cu 0.5 Pre-coated solder ribbon.

[0064] The pre-coated solder strip is punched with a fully automatic punching machine to obtain a mold-shaped Sn 96.5 Ag 3.0 Cu 0.5 Pre-applied solder pads.

[0065] Comparative Example 1

[0066] Add 35.0g of pentaerythritol-modified rosin ester, 10.0g of high-softening-point rosin, 2.0g of polyvinyl butyral, 8.0g of a polymer of lauric acid and 1,6-hexanediol, 20.0g of diethylene glycol dibutyl ether, and 16.5g of propylene glycol monomethyl ether to a beaker. Heat to 140°C and stir until the film-forming resins, pentaerythritol-modified rosin ester and high-softening-point rosin, are completely dissolved, resulting in a uniform film-forming resin solution. Stop heating and cool the film-forming resin solution to 80°C. Quickly add 8.0g of methylsuccinic acid (active agent) and 0.5g of microcrystalline wax powder (anti-stick additive), and continue stirring until the mixture is fully dispersed and dissolved.

[0067] The mixed solution was transferred to a sealed container and frozen at -15°C for 24 hours. After the freezing was complete, the sealed container was taken out and allowed to stand at room temperature to return to room temperature to obtain a coating flux paste.

[0068] After the freezing is completed, the sealed container is taken out and allowed to stand at room temperature to return to normal temperature to obtain the coating flux paste.

[0069] The obtained solder paste is evenly coated on the Sn by an adjustable thin film coater. 96.5 Ag 3.0 Cu 0.5 The coating amount on the surface of the solder strip is 1.25wt%, and then the oven temperature is set to 120℃, and the coated solder strip is placed in the oven and baked for 15 minutes to obtain Sn 96.5 Ag 3.0 Cu 0.5 Pre-coated solder ribbon.

[0070] The pre-coated solder strip is punched with a fully automatic punching machine to obtain a mold-shaped Sn 96.5 Ag 3.0 Cu 0.5 Pre-applied solder pads.

[0071] Comparative Example 2

[0072] Compared with Example 1, the freezing step was omitted. The subsequent coating and drying processes were the same as in Example 1.

[0073] Comparative Example 3

[0074] Compared with Example 1, no anti-sticking additive was added. The process conditions were the same as those in Example 1.

[0075] The Sn prepared in Examples 1-3 and Comparative Examples 1-2 96.5 Ag 3.0 Cu 0.5 The pre-coated solder sheets were tested for halogen content (tested according to IPC-4101), nickel plating wettability (tested according to IPC-TM-6502.4.46), stamping powder loss rate (mass loss after stamping method), and adhesion (tested according to IPC-J-STD-004 wax paper test method). The results are shown in Table 1 below.

[0076] Table 1

[0077] Halogen content Nickel plating spreading rate % Fan loss rate% Adhesion Example 1 ND 93 0.3 No adhesion Example 2 ND 97 0.2 No adhesion Example 3 ND 91 2.0 Slight adhesion on the edges Comparative Example 1 ND 70 0.5 qualified Comparative Example 2 ND 84 8.8 Severe adhesions Comparative Example 3 ND 90 0.4 Slight adhesion

[0078] Note: ND means not detected or below the detection limit of the method.

[0079] From the comparison of the data of Example 1 and Comparative Example 1 in Table 1 above, it can be seen that pyridine-2-carboxylic acid increases the nickel plating spreading rate by 23%, and the oxide layer removal rate changes from "partial residue" to "complete removal", proving that it has an excellent chelating effect on the metal oxide layer.

[0080] Comparing the data from Examples 1 and 2 in Table 1, we can see that the active agent combination system containing pyridine-2-carboxylic acid further increased the spreading rate of the solder paste by 4%, demonstrating that this active agent combination design achieves excellent film breaking and wetting effects, comparable to the performance of halogen-containing solder sheets. In Examples 1-3, the stamping dust loss rate was reduced to below 5%. In Example 3, due to the lack of polyvinyl butyral, the coating's lack of flexibility resulted in a stamping dust loss rate of 2.0%.

[0081] From the comparison of the data in Example 1 and Comparative Example 2 in Table 1, it can be seen that the freezing process reduces the stamping powder loss rate from 8.8% in Comparative Example 2 to 0.3%, a decrease of more than 96%, which effectively enhances the adhesion between the coating and the solder joint interface.

[0082] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention's description and drawings, 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 halogen-free pre-coated solder sheet, characterized in that: The invention comprises 97-99 wt% of solder sheet and 1-3 wt% of solder paste; wherein the solder paste comprises the following components: Film-forming resin 40-60wt%; Active agent 3-10wt%; 3-10 wt% flexible plasticizer; Anti-stick additive 1-3wt%; The balance is low boiling point solvent; The active agent includes pyridine-2-carboxylic acid.

2. The halogen-free pre-coated solder sheet according to claim 1, characterized in that: The active agent further comprises at least one of methylsuccinic acid, 2-hydroxysuccinic acid, lactic acid, tartaric acid, citric acid or succinic acid.

3. The halogen-free pre-coated solder sheet according to claim 1, characterized in that: The flexible plasticizer includes at least one of polyvinyl butyral, a polymer of lauric acid and 1,6-hexanediol, PEG-400, PEG-2000, vinyl bisstearamide or methylene stearamide.

4. The halogen-free pre-coated solder sheet according to claim 1, characterized in that: The film-forming resin agent includes at least one of pentaerythritol-modified rosin ester, rosin glycerol ester, high softening point rosin, polymerized rosin, acrylic acid-modified rosin resin or maleic acid rosin resin.

5. The halogen-free pre-coated solder sheet according to claim 1, characterized in that: The anti-sticking additive includes at least one of microcrystalline wax powder or ultrafine hydrophobic silica.

6. The halogen-free pre-coated solder sheet according to claim 1, characterized in that: The low boiling point solvent component includes at least one of diethylene glycol dibutyl ether, propylene glycol monomethyl ether, diethylene glycol dimethyl ether, ethylene glycol monomethyl ether, ethyl acetate, dipropylene glycol methyl ether or propylene glycol methyl ether acetate.

7. The halogen-free pre-coated solder sheet according to any one of claims 1 to 6, characterized in that: The material of the soldering sheet is: Sn 96.5 Ag 3.0 Cu 0.5 .

8. A method for preparing a halogen-free pre-coated solder sheet according to any one of claims 1 to 6, characterized in that: The steps include: (1) Preparing a mixed solution: Heat and stir the film-forming resin, flexible plasticizer, and low-boiling-point solvent in the formulated amount until the film-forming resin is completely dissolved, cool to 80-100°C, add the active agent and anti-sticking additive, and continue stirring until all components are fully dissolved and mixed; (2) Freezing and cooling: The obtained mixed solution is transferred to a sealed container and cooled and cooled. After freezing, the mixed solution is taken out and cooled and cooled at room temperature to obtain a coating flux paste. (3) Coating treatment: evenly coating the obtained solder paste on the surface of the solder strip, controlling the coating amount of the solder paste to be 1.0-1.5wt% of the mass of the solder strip, and drying to obtain a pre-coated solder strip; (4) Stamping: The obtained pre-coated solder strip is punched using a fully automatic stamping machine to obtain the pre-coated solder sheet.

9. The preparation method according to claim 8, characterized in that In step (2), the freezing and standing conditions are: temperature -18 to -12°C, time 22 to 28 hours.

10. The preparation method according to claim 8, characterized in that In step (3), the drying process conditions are: temperature 120-150° C., time 10-15 min.

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