Tin-based welding powder and preparation method and application thereof

Abstract

The invention provides tin-based welding powder and a preparation method and application thereof, and relates to the technical field of tin-based welding powder preparation, and the tin-based welding powder comprises a spherical tin-based alloy powder inner core, a middle layer formed by organic acid and resin and coated on the inner core, and a polyurea shell coated outside the middle layer. The tin-based welding powder provided by the invention has good suitability with a high-activity soldering flux, the paste is not dried after being centrifuged for 2.5 hours by a solder paste centrifugal machine, and the viscosity amplification is not more than 10% after the paste is placed at 40 DEG C for 72 hours, so that the problem that the solder paste is dried can be effectively avoided, and the production efficiency of the microelectronic interconnection industry and the welding quality and reliability of products are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of tin-based solder powder preparation technology, and in particular to a tin-based solder powder, its preparation method, and its application. Background Technology

[0002] With the rapid breakthroughs in microelectronics technology and very large-scale integrated circuits, electronic components are developing towards miniaturization, high performance, high reliability, and low cost. Solder paste, with its advantage of meeting the requirements of large-scale production in surface mount technology (SMT), has become one of the core materials for electronic assembly / packaging. To meet the requirements of higher soldering quality and reliability, highly active fluxes are widely used, but this has also led to solder paste drying out during storage, transportation, or use. Solder paste drying is mainly due to an imbalance in the uniform mixing of solder powder and flux, resulting in a decrease in the wetting and dispersing ability of the flux, ultimately causing the solder paste to fail to print, coat, or solder properly. Tin-based solder powder is the main raw material for preparing solder paste, so its performance is crucial to the storage stability of the solder paste. Currently, the mainstream technology for preparing solder powder is centrifugal atomization, which has high production efficiency and produces good and stable product performance. However, solder paste prepared with this type of solder powder and some highly active fluxes often suffers from drying out.

[0003] Currently, the main method to prevent solder paste from drying out by controlling the properties of solder powder is to organically coat the solder powder. For example, Japanese invention patent JP,2004-283841,A discloses a coating method for solder paste and solder powder for solder paste. The technical solution involves mixing solder paste with flux and solder powder coated with urea or urea. The powder is prepared by dissolving 1-20 wt.% urea / urea in a solvent to obtain a coating solution, which is then added to the solder powder and thoroughly stirred, filtered, and dried. Japanese invention patent JP,2010-221260,A discloses a coating method for solder paste and solder powder for solder paste. The technical solution involves surface treating the surface of tin-based solder powder with a compound containing both thiol and carboxyl groups. However, the powder obtained through wet coating or coating methods requires time and effort to dry, and the powder particles tend to adhere to each other and form clumps after drying.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] One of the objectives of this invention is to provide a tin-based solder powder to at least solve one of the technical problems existing in the prior art. The tin-based solder powder provided by this invention has good compatibility with highly active fluxes. The paste does not dry out after being centrifuged in a solder paste centrifuge for 2.5 hours, and the viscosity increase does not exceed 10% after being placed at 40°C for 72 hours. Therefore, it can effectively avoid the problem of solder paste drying out, thereby significantly improving the production efficiency, soldering quality, and reliability of products in the microelectronic interconnect industry.

[0006] The second objective of this invention is to provide a method for preparing tin-based solder powder.

[0007] The third objective of this invention is to provide an application of tin-based solder powder prepared by the aforementioned method in the preparation of solder paste.

[0008] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: In a first aspect, the present invention provides a tin-based solder powder, comprising: a spherical tin-based alloy powder core, an intermediate layer formed of an organic acid and a resin coating the core, and a polyurea shell coating the intermediate layer.

[0009] Secondly, the present invention provides a method for preparing tin-based solder powder, comprising the following steps: (a) During the atomization powdering process, a coating agent A containing organic acid and resin is applied to molten tin-based alloy droplets to form spherical tin-based alloy powder with an intermediate layer; (b) During the sieving process after atomization, the tin powder obtained in step (a) is coated with a coating agent B to form a polyurea shell; (c) Curing to obtain the tin-based solder powder.

[0010] Furthermore, the components of the coating agent A include organic acids and resins; Preferably, the mass ratio of the organic acid to the resin is 1:(1-4); Preferably, the organic acid includes one or more of benzoic acid, salicylic acid, and hydroxyethyl sulfonic acid; Preferably, the resin includes one or more of epoxy resin, polyurethane, and phenolic resin; Preferably, the preparation process of the coating agent A includes: mixing the organic acid with ethanol, and then adding resin to obtain the coating agent A.

[0011] Furthermore, the coating agent B comprises polyurea; Preferably, the polyurea is obtained by reacting isocyanate and amino compound; Preferably, the mass ratio of the isocyanate to the amino compound is 1:0.8 to 1:1.2; Preferably, the isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; Preferably, the amino compound includes one or more of diethylenetriamine, triethylenetetramine, diethyltoluenediamine, tallulamine, and piperazine; Preferably, the preparation process of the coating agent B includes: dehydrating the isocyanate and cooling it to room temperature, while dissolving the amino compound in an organic solvent and cooling it to room temperature, and then mixing the two components to form a polyurea coating agent.

[0012] Furthermore, the concentration of coating agent A is 0.01~10 wt.%, and the concentration of coating agent B is 0.01-4 wt.%.

[0013] Furthermore, in step (a), the coating agent A is transported to the atomization chamber of the atomization powdering process via liquid flow, and the coating agent A is vaporized by dispersing the liquid droplets with gas. Preferably, the flow rate of the gas is 0.5 mL / s-100 mL / s; Preferably, the coating agent A is delivered by using a liquid flow controller to control the pumping of liquid, with a control frequency of 10-50Hz and a control flow rate of 0.01mL / s-0.5mL / s.

[0014] In a further step (b), the method of application includes: using a liquid flow controller to control the pumping of liquid, controlling the flow frequency at 60-100Hz, and controlling the flow rate at 0.5mL / s-1.0mL / s.

[0015] Furthermore, prior to step (a), the process includes: smelting pure tin and a tin intermediate alloy as raw materials to obtain a molten tin-based alloy liquid.

[0016] Furthermore, in step (c), the curing is carried out by standing at room temperature for 12-24 hours.

[0017] Thirdly, the present invention provides an application of tin-based solder powder prepared by the aforementioned preparation method in the preparation of solder paste.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The tin-based solder powder provided by this invention has a core-double-layer coating structure. The core, composed of spherical tin-based alloy powder, provides excellent thermal conductivity and solder wetting properties. The middle layer is composed of an organic acid and resin composite. The polar functional groups (such as carboxyl groups) in the organic acid can be effectively adsorbed onto the surface of the metal powder, forming a stable chelate structure, reducing the surface energy of the tin powder, inhibiting its agglomeration tendency, and simultaneously enhancing compatibility with the resin components, achieving a uniform and dense initial coating. The outer polyurea shell is rapidly formed through in-situ reaction, exhibiting excellent film-forming properties, chemical stability, and mechanical strength. It effectively prevents acidic substances or moisture in the highly active flux from oxidizing or undergoing side reactions with the tin powder core during storage and use. This synergistic double-layer coating structure significantly improves the compatibility and long-term stability between the solder powder and the highly active flux, effectively preventing the solder paste from drying out during storage or use, thereby extending the shelf life and working life of the solder paste.

[0019] The method for preparing tin-based solder powder provided by this invention adopts an online coating process, which enables powder preparation and coating to be carried out simultaneously. This is conducive to continuous production and avoids the complex drying and dispersion problems in traditional post-processing coating processes. It is also conducive to the continuous and low-energy preparation of high-quality solder powder. Attached Figure Description

[0020] 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.

[0021] Figure 1 The microstructure of the tin-based solder powder in Example 1; Figure 2 The image shows the state of the solder paste from Example 3 after a 2.5-hour centrifugal drying experiment. Figure 3 The image shows the state of the solder paste from Example 5 after a 2.5-hour centrifugal drying experiment. Figure 4 This is a diagram showing the state of the solder paste from Example 12 after centrifugation for 1 hour until it became dry. Figure 5 This is a diagram showing the state of the solder paste from Comparative Example 1 after centrifugation for 1.5 hours until it became dry. Detailed Implementation

[0022] Unless otherwise defined herein, the scientific and technical terms used in conjunction with this invention shall have the meanings commonly understood by one of ordinary skill in the art. The meaning and scope of terms shall be clear; however, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or foreign definitions. In this application, unless otherwise stated, the use of "or" means "and / or". Furthermore, the use of the term "comprising" and other forms is non-limiting.

[0023] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] The first aspect of the present invention provides a tin-based solder powder, comprising: a spherical tin-based alloy powder core, an intermediate layer formed of organic acid and resin covering the core, and a polyurea shell covering the intermediate layer.

[0025] The tin-based solder powder provided by this invention is a tin-based solder powder compatible with highly active fluxes. This tin-based solder powder consists of a core formed by spherical tin-based alloy powder, an intermediate layer formed by a mixture of organic acid and resin, and a shell formed by polyurea. This tin-based solder powder has good compatibility with highly active fluxes, effectively preventing the problem of solder paste drying.

[0026] The tin-based solder powder provided by this invention has an intermediate layer in which the polar groups of organic acids can be well adsorbed on the surface of the tin powder or form stable chelates, thereby reducing the surface energy of the metal powder and facilitating uniform dispersion of the powder in the resin. Simultaneously, the resin in the intermediate layer helps form a dense, non-detachable coating film. Polyurea, as the outer shell, has the advantages of rapid curing and environmental friendliness. This double-layer film effectively prevents the metal core of the tin powder from reacting with the active substances in the highly active flux during use, thus avoiding the drying phenomenon of the solder paste. The preparation method of the tin-based solder powder described in this application is mainly through online production. Compared with existing wet-process post-coating or coating processes, its core advantages are a more uniform coating layer, a shorter production process, lower energy consumption, and smaller batch-to-batch variations.

[0027] A second aspect of this invention provides a method for preparing tin-based solder powder, comprising the following steps: (a) During the atomization powdering process, a coating agent A containing organic acid and resin is applied to molten tin-based alloy droplets to form spherical tin-based alloy powder with an intermediate layer; (b) During the sieving process after atomization, the tin powder obtained in step (a) is coated with a coating agent B to form a polyurea shell; (c) Curing to obtain the tin-based solder powder.

[0028] The preparation method provided by this invention achieves integrated online production of powder preparation and double-layer coating by simultaneously applying coating agent A during the atomization powder preparation process and continuously applying coating agent B during the sieving stage. This method avoids the lengthy processes of drying and dispersion after traditional wet coating, significantly shortens the process flow, reduces energy consumption, and effectively ensures the uniformity and integrity of the coating layer, improving batch stability and facilitating large-scale continuous manufacturing.

[0029] In some preferred embodiments, the components of the coating agent A include organic acids and resins; Preferably, the mass ratio of the organic acid to the resin is 1:(1-4), for example, it can be 1:1, 1:2, 1:3, 1:4, etc.; Preferably, the organic acid includes one or more of benzoic acid, salicylic acid, and hydroxyethyl sulfonic acid; Preferably, the resin includes one or more of epoxy resin, polyurethane, and phenolic resin; Preferably, the preparation process of the coating agent A includes: first stirring the organic acid and 92% ethanol evenly, then adding the resin and mixing thoroughly.

[0030] In some preferred embodiments, the coating agent B comprises polyurea; Preferably, the polyurea is obtained by reacting isocyanate and amino compound; Preferably, the mass ratio of the isocyanate to the amino compound is 1:0.8 to 1:1.2, for example, it can be 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, etc.; Preferably, the isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; Preferably, the amino compound includes one or more of diethylenetriamine, triethylenetetramine, diethyltoluenediamine, tallulamine, and piperazine; Preferably, the preparation process of the coating agent B includes: dehydrating the isocyanate and cooling it to room temperature, while dissolving the amino compound in an organic solvent and cooling it to room temperature, and then mixing the two components to form a polyurea coating agent.

[0031] In some preferred embodiments, the concentration of the coating agent A is 0.01~10 wt.%, for example, it can be 0.01 wt.%, 0.1 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, etc.; In some preferred embodiments, the concentration of the coating agent B is 0.01-4 wt.%, for example, it can be 0.01 wt.%, 0.1 wt.%, 1 wt.%, 2 wt.%, 3 wt.%, 4 wt.%, etc.

[0032] In some preferred embodiments, in step (a), the coating agent A is delivered to the atomizing chamber of the atomizing powder by liquid flow, and the coating agent A is vaporized by gas dispersion of liquid droplets; Preferably, the flow rate of the gas is 0.5 mL / s to 100 mL / s, for example, it can be 0.5 mL / s, 5 mL / s, 50 mL / s, 100 mL / s, etc.; Preferably, the delivery of the coating agent A is controlled by a liquid flow controller to pump the liquid, with a flow control frequency of 10-50Hz and a flow rate of 0.01mL / s-0.5mL / s, for example, 0.01 mL / s, 0.1 mL / s, 0.2 mL / s, 0.3 mL / s, 0.4 mL / s, 0.5 mL / s, etc.

[0033] In some preferred embodiments, in step (b), the method of application includes: using a liquid flow controller to control the pumping of liquid, controlling the flow frequency at 60-100Hz, and controlling the flow rate at 0.5mL / s-1.0mL / s, for example, 0.5 mL / s, 0.6 mL / s, 0.7 mL / s, 0.8 mL / s, 0.9 mL / s, 1 mL / s, etc.

[0034] In some preferred embodiments, before step (a), the process further includes: smelting pure tin and a tin intermediate alloy as raw materials to obtain a molten tin-based alloy liquid.

[0035] In some preferred embodiments, in step (c), curing is performed by standing at room temperature for 12-24 hours, for example, 12 hours, 18 hours, 24 hours, etc.

[0036] In a preferred embodiment of the present invention, the method for preparing the tin-based solder powder includes: (1) Prepare tin-based solder powder online coating solutions A and B; (2) Melt the alloy in an intermediate frequency furnace; (3) Online coating of coating solution A; (4) Online coating of coating solution B; (5) Place at room temperature to obtain solder powder suitable for high-activity flux.

[0037] Furthermore, in a preferred embodiment of the present invention, the method for preparing the tin-based solder powder includes the following steps: (1) Prepare tin-based solder powder online coating agents A and B; (2) Using pure tin and tin intermediate alloy as raw materials, according to the composition of the prepared tin-based alloy, the alloy raw materials are smelted in a medium frequency furnace, and the smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously and precisely conveyed into the atomization chamber through the external conveying equipment to achieve immediate coating; (4) While tin powder is being prepared by sieving and atomization, coating agent B is being uniformly conveyed onto the screen using appropriate conveying equipment; (5) Allow the coating to stand at room temperature to fully cure, and obtain tin-based solder powder suitable for high-activity flux.

[0038] A third aspect of the present invention provides the application of tin-based solder powder prepared by the aforementioned preparation method in the preparation of solder paste.

[0039] Furthermore, this tin-based solder powder can be used as a solder paste for surface mount technology.

[0040] The present invention will be further illustrated by the following examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0041] Example 1 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve benzoic acid in 92% ethanol, then add epoxy resin and mix thoroughly. The mass ratio of organic acid to resin is 1:1, and the concentration of coating agent A is 0.01 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120℃ for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:0.8. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 0.01 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The flow control frequency is 10Hz, the flow rate is 0.01mL / s, and the gas flow rate used to disperse the coating agent A is 0.5mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 60Hz and the flow rate is 0.5mL / s. (5) Let stand at room temperature for 12 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0042] in, Figure 1 The microstructure of the tin-based solder powder in Example 1 is shown.

[0043] Example 2 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:1, and the concentration of coating agent A is 0.5 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:0.85. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 0.05 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The flow control frequency is 15Hz, the flow rate is 0.05mL / s, and the gas flow rate used to disperse the coating agent A is 4mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 65Hz and the flow rate is 0.55mL / s. After standing at room temperature for 14 hours, the coating layer is fully cured to obtain tin-based solder powder suitable for highly active flux.

[0044] Example 3 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:2, and the concentration of coating agent A is 1 wt.%. When preparing coating agent B, first heat toluene diisocyanate at 120°C under vacuum for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:0.9. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 0.15 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 20Hz, the flow rate is 0.1mL / s, and the gas flow rate used to disperse the coating agent A is 10mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 70Hz and the flow rate is 0.6mL / s. (5) Let stand at room temperature for 15 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0045] Example 4 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:2, and the concentration of coating agent A is 2 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:0.95. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 0.6 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 25Hz, the flow rate is 0.15mL / s, and the gas flow rate used to disperse the coating agent A is 18mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 75Hz and the flow rate is 0.65mL / s. (5) Let stand at room temperature for 16 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0046] Example 5 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:2.5, and the concentration of coating agent A is 3 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 1 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 30Hz, the flow rate is 0.2mL / s, and the gas flow rate used to disperse the coating agent A is 30mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 80Hz and the flow rate is 0.7mL / s. (5) Let stand at room temperature for 18 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0047] Example 6 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:2.5, and the concentration of coating agent A is 4 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1.05. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 1.5 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 35Hz, the flow rate is 0.25mL / s, and the gas flow rate used to disperse the coating agent A is 45mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 80Hz and the flow rate is 0.75mL / s. (5) Let stand at room temperature for 20 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0048] Example 7 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:3, and the concentration of coating agent A is 5 wt.%. When preparing coating agent B, first heat toluene diisocyanate at 120°C under vacuum for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1.1. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 2 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The flow control frequency is 40Hz, the flow rate is 0.3mL / s, and the gas flow rate used to disperse the coating agent A is 60mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 85Hz and the flow rate is 0.8mL / s. (5) Let stand at room temperature for 21 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0049] Example 8 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:3, and the concentration of coating agent A is 7 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1.15. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 2.5 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 45Hz, the flow rate is 0.35mL / s, and the gas flow rate used to disperse the coating agent A is 70mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 90Hz and the flow rate is 0.85mL / s. (5) Let stand at room temperature for 22 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0050] Example 9 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:3.5, and the concentration of coating agent A is 9 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1.2. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 3 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The flow control frequency is 50Hz, the flow rate is 0.4mL / s, and the gas flow rate used to disperse the coating agent A is 85mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 95Hz and the flow rate is 0.9mL / s; (5) Let stand at room temperature for 23 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0051] Example 10 This embodiment provides a tin-based solder powder, the preparation process of which is as follows: (1) When preparing coating agent A, first dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly. The mass ratio of organic acid to resin is 1:4, and the concentration of coating agent A is 10 wt.%. When preparing coating agent B, first heat toluene diisocyanate under vacuum at 120°C for 3 hours, then dissolve diethylenetriamine in dimethylformamide. The mass ratio of the former to the latter is 1:1. After cooling to room temperature, mix the two thoroughly. The concentration of coating agent B is 4 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 50Hz, the flow rate is 0.5mL / s, and the gas flow rate used to disperse the coating agent A is 100mL / s; (4) While tin powder is prepared by sieving and atomization, coating agent B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 100Hz and the flow rate is 1.0mL / s. (5) Let stand at room temperature for 24 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0052] Example 11 This embodiment provides a tin-based solder powder, which differs from Embodiment 10 in that the mass ratio of organic acid to resin is 1:5.

[0053] Example 12 This embodiment provides a tin-based solder powder, which differs from Embodiment 10 in that the mass ratio of organic acid to resin is 0.5:1.

[0054] Example 13 This embodiment provides a tin-based solder powder, which differs from Embodiment 10 in that the concentration of coating agent A is 11 wt.% and the concentration of coating agent B is 5 wt.%.

[0055] Comparative Example 1 This comparative example provides a tin-based solder powder, the preparation process of which is as follows: (1) Dissolve salicylic acid in 92% ethanol, then add polyurethane and mix thoroughly to prepare coating agent A. The mass ratio of organic acid to resin is 1:2, and the concentration of coating agent A is 2 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) The molten alloy liquid is slowly introduced into the atomization powder making process through the intermediate ladle, and at the same time, the coating agent A is continuously delivered into the atomization chamber by the liquid flow controller to achieve immediate coating. The control flow frequency is 25Hz, the flow rate is 0.15mL / s, and the gas flow rate used to disperse the coating agent A is 18mL / s; (4) Tin powder is prepared by sieving and atomization. (5) Let stand at room temperature for 16 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0056] Comparative Example 2 This comparative example provides a tin-based solder powder, the preparation process of which is as follows: (1) Toluene diisocyanate was heated under vacuum at 120°C for 3 hours, and then diethylenetriamine was dissolved in dimethylformamide at a mass ratio of 1:1.2. After cooling to room temperature, the two were thoroughly mixed to prepare coating agent B with a concentration of 3 wt.%. (2) Using pure tin and tin intermediate alloy as raw materials, SnAg3Cu0.5 alloy is prepared and the alloy raw materials are smelted in a medium frequency furnace. The smelting temperature is set to ensure that the alloy melts uniformly. (3) While tin powder is prepared by sieving and atomization, coating liquid B is uniformly conveyed to the screen through the corresponding conveying equipment, wherein the flow frequency is controlled at 75Hz and the flow rate is 0.65mL / s. (4) Let stand at room temperature for 23 hours to allow the coating layer to fully solidify and obtain tin-based solder powder suitable for high-activity flux.

[0057] Experimental Example (a) Experimental subjects: The solder paste prepared by uniformly mixing the tin powder (88.5 wt.%) prepared in Examples 1 to 13 with the EM887 flux (11.5 wt.%) of Advanced Micro-Tech Materials Co., Ltd. was used as experimental group 1-13, and the solder paste prepared by uniformly mixing the tin powder (88.5 wt.%) prepared in Comparative Examples 1 to 2 with the above flux was used as control group 1-2.

[0058] (II) Experimental Methods: 1. Centrifugal stability test a) Refrigerated solder paste products should be left to stand for no less than 4 hours in an environment with a temperature of (25±5)℃ and a relative humidity of (50±10)%. b) Start the solder paste centrifuge and run it idle for 3 minutes to bring the equipment to a good working condition; c) Place the entire bottle of solder paste to be tested in a centrifuge, with the weight difference between the two sides of the sample not exceeding 2 g, and set the centrifuge speed to 500 r / min. d) After 30 minutes, remove the solder paste and observe its drying process; e) Repeat step d) 4 times and record the drying time of the solder paste.

[0059] 2. Viscosity increase test a) Immerse the sensor of the Malcom spiral pump viscometer into the solder paste sample and set the rotation speed to 10 r / min; b) Start the viscometer. When the reading stabilizes for more than 1 minute and no longer changes, record the solder paste viscosity as the initial viscosity value (η0). c) Tighten the lid of the test container holding the sample and place it in a 40 ℃ constant temperature chamber; d) After 72 hours, remove the sample from the constant temperature chamber and let it stand for no less than 2 hours in an environment with a temperature of (25±5)℃ and a relative humidity of (50±10%). e) Open the test container lid, observe the appearance of the solder paste, and test the viscosity of the solder paste according to steps a) and b), which will be the final viscosity value η of the solder paste.

[0060] (III) Experimental Results The experimental results for the experimental and control groups were statistically analyzed. The centrifugation stability test results for experimental groups 1-13 and control groups 1-2 are shown in Table 1. Figure 2 The image shows the state of the solder paste from Example 3 after a 2.5-hour centrifugal drying experiment. Figure 3 The image shows the state of the solder paste from Example 5 after a 2.5-hour centrifugal drying experiment. Figure 4 This is a diagram showing the state of the solder paste from Example 12 after centrifugation for 1 hour until it became dry. Figure 5 This is a diagram showing the state of the solder paste from Comparative Example 1 after centrifugation for 1.5 hours until it became dry.

[0061] Table 1. Centrifugation stability test results for the experimental and control groups.

[0062] Table 2. Results of viscosity increase test in experimental and control groups

[0063] As shown in Tables 1 and 2, experimental groups 1 to 10 all achieved good overall performance under the optimized parameters. While experimental groups 1-4 met the basic requirements, their viscosity increase was relatively high (9.4%~10%). Among all the compliant embodiments, experimental group 5 exhibited the best overall performance balance: it did not dry out after 2.5 hours of centrifugation, and its viscosity increase after 72 hours was only 8.2%. In contrast, although experimental group 10 had the lowest viscosity increase (8%), its coating agent concentration had reached the upper limit of the parameters required by this invention (10wt.% / 4wt.%), posing a potential risk of clogging, brittleness, or increased costs. Therefore, under the premise of excellent performance and comprehensive manufacturing requirements, Example 5 is the optimal overall solution of this invention.

[0064] In contrast, experimental groups 1 to 10 showed significantly better performance than control groups 1 and 2 in terms of centrifugal stability and viscosity increase. Control group 1, lacking a polyurea shell and relying solely on an organic acid-resin interlayer for coating, dried out in 1.5 hours with a viscosity increase of 18%. Comparative example 2, although possessing a polyurea shell, lacked an effective interlayer and dried out in 1 hour with a viscosity increase as high as 22%, indicating that a single coating structure cannot achieve long-term stability. While examples 11 to 13 possessed a bilayer structure, the deviation of the organic acid to resin mass ratio from the preferred range, or the excessively high concentration of the coating agent, led to uneven film formation or increased internal stress in the coating layer, resulting in a drying time shortened to 1-1.5 hours and a viscosity increase exceeding 19%. This demonstrates that parameters exceeding the reasonable range will disrupt the synergistic effect of the bilayer structure.

[0065] 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; and 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.

Claims

1. A tin-based solder powder, characterized in that, include: The core consists of a spherical tin-based alloy powder core, an intermediate layer formed by organic acid and resin covering the core, and a polyurea shell covering the intermediate layer.

2. The method for preparing tin-based solder powder as described in claim 1, characterized in that, Includes the following steps: (a) During the atomization powdering process, a coating agent A containing organic acid and resin is applied to molten tin-based alloy droplets to form spherical tin-based alloy powder with an intermediate layer; (b) During the sieving process after atomization, the tin powder obtained in step (a) is coated with a coating agent B to form a polyurea shell; (c) Curing to obtain the tin-based solder powder.

3. The preparation method according to claim 2, characterized in that, The components of the coating agent A include organic acids and resins; Preferably, the mass ratio of the organic acid to the resin is 1:(1-4); Preferably, the organic acid includes one or more of benzoic acid, salicylic acid, and hydroxyethyl sulfonic acid; Preferably, the resin includes one or more of epoxy resin, polyurethane, and phenolic resin; Preferably, the preparation process of the coating agent A includes: mixing the organic acid with ethanol, and then adding resin to obtain the coating agent A.

4. The preparation method according to claim 2, characterized in that, The coating agent B includes polyurea; Preferably, the polyurea is obtained by reacting isocyanate and amino compound; Preferably, the mass ratio of the isocyanate to the amino compound is 1:0.8 to 1:1.2; Preferably, the isocyanate includes one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and lysine diisocyanate; Preferably, the amino compound includes one or more of diethylenetriamine, triethylenetetramine, diethyltoluenediamine, tallulamine, and piperazine; Preferably, the preparation process of the coating agent B includes: dehydrating the isocyanate and cooling it to room temperature, while dissolving the amino compound in an organic solvent and cooling it to room temperature, and then mixing the two components to form a polyurea coating agent.

5. The preparation method according to claim 2, characterized in that, The concentration of coating agent A is 0.01~10 wt.%, and the concentration of coating agent B is 0.01-4 wt.%.

6. The preparation method according to claim 2, characterized in that, In step (a), the coating agent A is transported to the atomization chamber of the atomization powdering process by liquid flow, and the coating agent A is vaporized by gas dispersion of liquid droplets; Preferably, the flow rate of the gas is 0.5 mL / s-100 mL / s; Preferably, the coating agent A is delivered by using a liquid flow controller to control the pumping of liquid, with a control frequency of 10-50Hz and a control flow rate of 0.01mL / s-0.5mL / s.

7. The preparation method according to claim 2, characterized in that, In step (b), the application method includes: using a liquid flow controller to control the pumping of liquid, controlling the flow frequency at 60-100Hz, and controlling the flow rate at 0.5mL / s-1.0mL / s.

8. The preparation method according to claim 2, characterized in that, Before step (a), the process further includes: smelting pure tin and a tin intermediate alloy as raw materials to obtain a molten tin-based alloy liquid.

9. The preparation method according to claim 2, characterized in that, In step (c), the curing process involves standing at room temperature for 12-24 hours.

10. The application of the tin-based solder powder prepared by the preparation method according to any one of claims 2-9 in the preparation of solder paste.

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