Sn-Pb-Bi series soldering paste with high reliability and high storage stability and preparation method of Sn-Pb-Bi series soldering paste

Abstract

The invention belongs to the field of electronic packaging, and discloses Sn-Pb-Bi series soldering paste with high reliability and high storage stability and a preparation method of the Sn-Pb-Bi series soldering paste, and the Sn-Pb-Bi series soldering paste is composed of, by mass, 85-92 wt% of solder alloy powder and 8-15 wt% of scaling powder. And the solder alloy powder is Sn < 43 > Pb < 43 > Bi < 14 > or Sn < 46 > Pb < 46 > Bi < 8 >. The scaling powder is composed of the following components in percentage by mass: 48 wt%-68 wt% of an organic solvent, 8 wt%-12 wt% of an active agent, 3 wt%-7 wt% of a pH regulator, 10 wt%-15 wt% of a film-forming agent, 5 wt%-8 wt% of a surfactant, 0 wt%-1 wt% of a corrosion inhibitor, 0.1 wt%-0.5 wt% of an antioxidant and 6 wt%-10 wt% of a thixotropic agent. The prepared soldering paste is good in wettability, low in residual rate and free of tin bead and collapse phenomena, and can be stably stored for one month at the temperature of 5-40 DEG C.

Description

Technical Field

[0001] The invention belongs to the field of electronic packaging and manufacturing, and relates to a Sn-Pb-Bi solder paste with high reliability and high storage stability and a preparation method thereof. Background Art

[0002] As electronic products continue to advance toward miniaturization and multifunctionality, surface mount technology (SMT) has become a widely used process in electronics manufacturing due to its simplicity, high integration, and low cost. Solder paste, a key material in the SMT process, serves as the bridge connecting electronic components to circuit boards. It precisely secures components to the circuit board and, after reflow, forms reliable solder joints, ensuring the electrical connection and mechanical stability of electronic products, enabling efficient assembly.

[0003] Sn-Pb-Bi solders are promising medium- and low-temperature solders suitable for applications in aerospace, military, and other fields where the reliability and stability of electronic equipment are critical. However, existing Sn-Pb-Bi solder pastes suffer from poor printability and collapse, which can lead to uneven solder paste application on circuit boards, resulting in cold solder joints and the formation of tin beads around solder joints, which can cause short circuits. Furthermore, they have a high post-solder residue rate, which can corrode solder joints when operated in humid environments, reducing their reliability. After storage for a period of time, the solder paste can experience a sudden increase in viscosity or delamination, seriously affecting solder joint quality.

[0004] An invention patent (patent number CN117139915) for a lead-containing solder paste that prevents tin-blasting and its preparation method has been published. This patent involves immersing a montmorillonite composite material in a formulated resin solution to form a resin layer with strong water-absorbing resistance. The multi-layer structure, interlocked with each other, forms a dense, continuous, and water-absorbing layer. This effectively blocks moisture penetration from the air, reduces water absorption by the solder paste, and thus prevents tin-blasting during soldering. However, halogen compounds are highly reactive and can corrode solder joints, affecting their reliability.

[0005] Generally speaking, there are relatively few patents for Sn-Pb-Bi solder pastes, and most focus on improving a single performance factor. Commercially available Sn-Pb-Bi solder pastes offer only modest overall performance. Therefore, there is an urgent need for a Sn-Pb-Bi solder paste with high reliability and storage stability. Summary of the Invention

[0006] The present invention aims to provide a Sn-Pb-Bi solder paste with high reliability and high storage stability and a preparation method thereof. By optimizing the components and ratios of the activator, film-forming agent and functional additive in the flux, a solder paste with good wettability, low residue rate, and no tin beads and collapse is produced. The solder paste can be stably stored at 5-40°C for one month.

[0007] The technical solution of the present invention:

[0008] A Sn-Pb-Bi solder paste with high reliability and high storage stability comprises the following components: 85-92 wt% of solder alloy powder and 8-15 wt% of soldering flux.

[0009] Preferably, the solder alloy powder is Sn43Pb43Bi14 or Sn46Pb46Bi8.

[0010] Preferably, the soldering flux is composed of the following components in mass fraction: 48-68wt% of an organic solvent, 8-12wt% of an active agent, 3-7wt% of a pH regulator, 10-15wt% of a film-forming agent, 5-8wt% of a surfactant, 0-1wt% of a corrosion inhibitor, 0.1-0.5wt% of an antioxidant, and 6-10wt% of a thixotropic agent.

[0011] Preferably, the organic solvent is a combination of two or more of isopropyl alcohol, n-butanol, propylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol monobutyl ether, dipropylene glycol dimethyl ether, tetrahydrofurfuryl alcohol, and n-octanol, and the solvents involved in the combination are required to include solvents with a boiling point below 130°C and a boiling point above 130°C.

[0012] Preferably, the active agent is a combination of two or more of stearic acid, DL-glutamic acid, adipic acid, p-hydroxybenzoic acid, methylsuccinic acid, succinic acid, sebacic acid, suberic acid, phenylsuccinic acid, phthalic acid, and 2,5-dihydroxybenzoic acid, and the organic acids involved in the combination are required to include organic acids with a melting point below 130°C and a melting point above 130°C.

[0013] Preferably, the pH adjuster is one or a combination of two or more of monoethanolamine, diethanolamine, and triethanolamine.

[0014] Preferably, the film-forming agent is rosin or polyethylene glycol, the rosin is one or a combination of two or more of polymerized rosin, hydrogenated rosin, disproportionated rosin, ice white rosin, and special rosin, and the polyethylene glycol is polyethylene glycol 2000 and / or polyethylene glycol 4000.

[0015] Preferably, the surfactant is one or a combination of dodecylphenol polyoxyethylene ether and polysorbate 20.

[0016] Preferably, the corrosion inhibitor is one or a combination of two or more of imidazole, benzimidazole, and benzotriazole.

[0017] Preferably, the antioxidant is one or a combination of two or more of hydroquinone, catechol, ascorbic acid, 2,6-di-tert-butyl-p-cresol, and tert-butylhydroquinone.

[0018] Preferably, the thixotropic agent is hydrogenated castor oil or thixotropic agent 6500, and the mass ratio of hydrogenated castor oil to thixotropic agent 6500 is required to be 1 to 3:1.

[0019] A method for preparing a Sn-Pb-Bi solder paste with high reliability and high storage stability is provided. The preparation method is as follows:

[0020] According to the mass fraction of each component in the flux, a solvent, an activator, a pH regulator, a film-forming agent, a surfactant, a corrosion inhibitor, an antioxidant and a thixotropic agent are added in sequence; the mixture is stirred and dissolved in a water bath at 60°C and a speed of 500 r / min, and the next component is added only after each component is completely dissolved; after all components are completely dissolved, the stirring environment is changed to room temperature, the stirring speed is set to 800 r / min, and when the viscosity of the flux increases significantly and the magnet cannot rotate, the stirring is stopped to obtain the flux; the solder alloy powder and the flux are weighed according to the formula ratio and evenly mixed, thereby obtaining a Sn-Pb-Bi solder paste with high reliability and high storage stability.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention adopts halogen-free active substances and prepares a solder paste with good wettability by compounding organic acids with different melting points. While ensuring activity, it avoids the strong corrosion of halogen on the solder joints and improves the reliability of the solder joints.

[0023] (2) The present invention proposes two methods for reducing flux residue: the first method is to use polyethylene glycol as a film-forming agent; the second method is to reduce the amount of rosin added to 10-15wt%. Since the reduction in rosin usage will reduce wettability and affect solder paste forming, the formula needs to be supplemented with dodecylphenol polyoxyethylene ether or polysorbate 20 to work together with organic acids to compensate for the reduced activity caused by the reduction in rosin. At the same time, a certain mass ratio of hydrogenated castor oil and thixotropic agent 6500 is added to coordinately control the viscosity of the solder paste and improve the problem of poor solder paste forming caused by rosin. The formula combination of the present invention not only reduces flux residue, but also does not affect other properties of the solder paste.

[0024] (3) The present invention provides a preparation process for the solder paste, particularly wherein a thixotropic agent is added by dissolving in a 60°C water bath and thickening by stirring at room temperature to prepare a paste-like flux, wherein the flux and solder alloy powder are mixed in a ratio of 8-15wt% of flux and 85-92wt% of solder alloy powder, and the prepared solder paste has good printability and anti-collapse properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 11 and 2, and comparative examples 1, 2, 3, and 4 of the present invention are shown in the figure for the anti-collapse performance test of the solder paste; wherein, (a) Example 1; (b) Example 2; (c) Comparative example 1; (d) Comparative example 2; (e) Comparative example 3; and (f) Comparative example 4.

[0026] Figure 2 These are the surface morphologies of the solder joints of Example 1, Example 2 and Comparative Examples 1, 2, 3 and 4 of the present invention; wherein, (a) Example 1; (b) Example 2; (c) Comparative Example 1; (d) Comparative Example 2; (e) Comparative Example 3; and (f) Comparative Example 4. Figure 3 These are the solder paste tin ball test result diagrams of Example 1 and Example 2 of the present invention and Comparative Examples 1, 2, 3 and 4; wherein, (a) Example 1; (b) Example 2; (c) Comparative Example 1; (d) Comparative Example 2; (e) Comparative Example 3; and (f) Comparative Example 4. DETAILED DESCRIPTION

[0027] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0028] Example 1

[0029] A Sn-Pb-Bi solder paste with high reliability and high storage stability is provided. The components of the solder paste are as follows, in terms of mass percentage:

[0030]

[0031]

[0032] The specific preparation method is as follows:

[0033] Step 1: Prepare the solvent: weigh n-butanol and tetrahydrofurfuryl alcohol in a mass ratio of 1:2 and mix them evenly using a magnetic stirrer.

[0034] Step 2: Prepare the flux: Add the organic acid, organic amine, film-forming agent, surfactant, corrosion inhibitor, antioxidant, and thixotropic agent in the above proportions to the solvent in sequence. Stir and dissolve in a 60°C water bath at 500 rpm. Ensure each component is completely dissolved before adding the next. Once all components are completely dissolved, return the stirring environment to room temperature and set the stirring speed to 800 rpm. Stir until the flux viscosity increases significantly and the magnet cannot rotate.

[0035] Step 3: Prepare solder paste: Weigh the solder alloy powder and flux according to the formula ratio and mix them evenly.

[0036] Example 2

[0037] A Sn-Pb-Bi solder paste with high reliability and high storage stability is provided. The components of the solder paste are as follows, in terms of mass percentage:

[0038]

[0039] Please refer to Example 1 for the specific preparation method.

[0040] Comparative Example 1

[0041] A Sn-Pb-Bi solder paste with high reliability and high storage stability is provided. The components of the solder paste are as follows, in terms of mass percentage:

[0042]

[0043]

[0044] Please refer to Example 1 for the specific preparation method.

[0045] Comparative Example 2

[0046] A Sn-Pb-Bi solder paste, wherein the components in the solder paste are composed as follows in terms of mass percentage:

[0047] Please refer to Example 1 for the specific preparation method.

[0048] Comparative Example 3

[0049] A Sn-Pb-Bi solder paste, wherein the components in the solder paste are composed as follows in terms of mass percentage:

[0050]

[0051] Specific preparation method refers to Example 1

[0052] Comparative Example 4

[0053] A Sn-Pb-Bi solder paste, wherein the components in the solder paste are composed as follows in terms of mass percentage:

[0054]

[0055] Specific preparation method refers to Example 1

[0056] Performance tests were performed on Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. The tests for wettability, viscosity, solder beads, collapse, dryness, and corrosion followed the test methods and test rules in standards GB / T31475-2015 and SJ / T11186-2019. In addition, the halogen content in the flux, the flux residue rate, and the storage time of the solder paste were tested. The flux residue rate was calculated as follows: η=1-[(m1-m2) / ρ(m1-m0)], where m0 is the mass of the substrate, m1 is the total mass of the solder paste coated on the substrate, m2 is the total mass of the substrate and solder joints after reflow, and ρ is the mass fraction of the flux. The solder paste's low-temperature storage life test involves placing the paste in a sealed refrigerated container at 5°C and determining if the paste has delaminated, crusted, or experienced a sudden increase in viscosity. The high-temperature storage life test involves placing the paste in a sealed, insulated container at 40°C and determining if the paste has delaminated, crusted, or experienced a sudden increase in viscosity. The test results are shown in Table 1.

[0057] Table 1 Performance test results of solder paste in Examples and Comparative Examples

[0058]

[0059] As can be seen from the test results in Table 1, the solder paste prepared by the present invention has excellent comprehensive properties. It is compounded with halogen-free organic acids with different melting points, has good wettability and can avoid halogen corrosion to the substrate. By using polyethylene glycol to replace rosin or reducing the amount of rosin, adding dodecylphenol polyoxyethylene ether or polysorbate 20 to work together with the organic acid to make up for the lack of activity, the post-soldering residual rate of the flux can be reduced, and the residue is dry and easy to clean. By adding hydrogenated castor oil and thixotropic agent 6500 in a mass ratio of 1 to 3:1 by high-temperature dissolution and room-temperature stirring and thickening, the viscosity of the solder paste is synergistically controlled, the printability and anti-collapse properties of the solder paste are improved, and the solder paste is not prone to bridging during printing and there are no tin beads around the solder joints, which greatly improves the reliability of the solder joints. At the same time, the prepared solder paste does not show delamination, skinning, or sudden increase in viscosity after being stored at room temperature for 1 month or at low temperature for 6 months, and has good storage stability.

[0060] The above-described embodiments merely express the implementation methods of the present invention, but should not be understood as limiting the scope of the patent of the present invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A Sn-Pb-Bi solder paste with high reliability and high storage stability, characterized in that: The Sn-Pb-Bi solder paste comprises the following components: 85-92 wt% of solder alloy powder and 8-15 wt% of flux; The solder alloy powder is Sn43Pb43Bi14 or Sn46Pb46Bi8; The soldering flux is composed of the following components in mass fraction: 48-68 wt% of an organic solvent, 8-12 wt% of an activator, 3-7 wt% of a pH regulator, 10-15 wt% of a film-forming agent, 5-8 wt% of a surfactant, 0-1 wt% of a corrosion inhibitor, 0.1-0.5 wt% of an antioxidant, and 6-10 wt% of a thixotropic agent.

2. The Sn-Pb-Bi solder paste according to claim 1, characterized in that The organic solvent is a combination of two or more of isopropyl alcohol, n-butanol, propylene glycol methyl ether, ethylene glycol ethyl ether, ethylene glycol monobutyl ether, dipropylene glycol dimethyl ether, tetrahydrofurfuryl alcohol, and n-octanol. The organic solvent is required to include solvents with a boiling point lower than 130° C. and a boiling point higher than 130° C.

3. The Sn-Pb-Bi solder paste according to claim 1, wherein: The active agent is a combination of two or more of stearic acid, DL-glutamic acid, adipic acid, p-hydroxybenzoic acid, methylsuccinic acid, succinic acid, sebacic acid, suberic acid, phenylsuccinic acid, phthalic acid, and 2,5-dihydroxybenzoic acid. The active agent is required to include organic acids with a melting point below 130°C and a melting point above 130°C.

4. The Sn-Pb-Bi solder paste according to claim 1, wherein: The pH regulator is one or a combination of two or more of monoethanolamine, diethanolamine and triethanolamine.

5. The Sn-Pb-Bi solder paste according to claim 1, wherein: The film-forming agent is rosin or polyethylene glycol, the rosin is one or a combination of two or more of polymerized rosin, hydrogenated rosin, disproportionated rosin, ice white rosin, and special rosin, and the polyethylene glycol is polyethylene glycol 2000 and / or polyethylene glycol 4000.

6. The Sn-Pb-Bi solder paste according to claim 1, wherein The surfactant is one of dodecylphenol polyoxyethylene ether and polysorbate 20 or a combination of the two.

7. The Sn-Pb-Bi solder paste according to claim 1, wherein: The corrosion inhibitor is one or a combination of two or more of imidazole, benzimidazole and benzotriazole.

8. The Sn-Pb-Bi based solder paste according to claim 1, wherein: The antioxidant is one or a combination of two or more of hydroquinone, catechol, ascorbic acid, 2,6-di-tert-butyl-p-cresol, and tert-butylhydroquinone.

9. The Sn-Pb-Bi based solder paste according to claim 1, characterized in that: The thixotropic agents are hydrogenated castor oil and thixotropic agent 6500, and the mass ratio of hydrogenated castor oil to thixotropic agent 6500 is required to be 1 to 3:

1.

10. A method for preparing a Sn-Pb-Bi solder paste with high reliability and high storage stability, characterized in that: Here are the steps: According to the mass fraction of each component in the flux, the solvent, activator, pH regulator, film-forming agent, surfactant, corrosion inhibitor, antioxidant and thixotropic agent are added in sequence; the mixture is stirred and dissolved in a water bath at 60°C and 500 r / min, and the next component is added only after each component is completely dissolved; after all components are completely dissolved, the stirring environment is changed to room temperature and the stirring speed is set to 800 r / min. When the viscosity of the flux increases significantly and the magnet cannot rotate, the stirring is stopped to obtain the flux; Solder alloy powder and flux are weighed according to a formula ratio and uniformly mixed to prepare a Sn-Pb-Bi solder paste with high reliability and high storage stability.

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