Lead-free solder paste with high QFN (Quad Flat No-lead) chip climbing height and preparation method of lead-free solder paste

Abstract

The invention relates to the technical field of lead-free solder paste, in particular to lead-free solder paste with the high QFN chip climbing height and a preparation method thereof.The lead-free solder paste is prepared from, by weight, 100 parts of tin, 4-8 parts of copper, 4-6 parts of silver and 1-2 parts of lubricant, and the lubricant is composed of lanthanum, cerium and yttrium according to the weight ratio of 1: (3-4): 2; the soldering flux is obtained by mixing hydrogenated rosin methyl ester, a surface active agent, rosin, an anti-oxidation thixotropic agent, organic acid and a solvent according to the weight ratio of (1-2): (0.5-1): (15-20): (2-5): (1-3): 50, the lead-free solder paste has good tin climbing capacity, a more uniform and compact welding spot structure can be formed while the tin climbing height is increased, and the lead-free solder paste has the advantages that the lead-free solder paste is not prone to deformation, and the lead-free solder paste is high in stability, good in stability and good in application prospect. Welding defects can be reduced, and the problems that the wettability is poor and the tin climbing capacity is insufficient when the lead-free soldering paste is used for welding a QFN packaging chip are effectively solved.

Description

Technical Field

[0001] This application relates to the technical field of lead-free solder paste, and more specifically, to a lead-free solder paste for improving the climbing height of high QFN chips and a preparation method thereof. Background Art

[0002] QFN package is a pinless chip package form, which has the characteristics of small size, thinness, and excellent electrical performance. The bottom of the QFN package is made of copper material, which has good heat conduction performance, can effectively dissipate heat, and improve the reliability of the chip. The pins of the QFN package are distributed on the four sides of the chip and are connected to the PCB through the bottom pads, meeting the requirements of miniaturized devices.

[0003] In practical applications, in order to achieve an effective connection between the QFN package chip and the PCB board, traditional methods mainly include directly using ordinary lead-free solder paste for soldering. The use of lead-free solder paste is mainly for environmental protection and health and safety considerations, meeting modern environmental protection regulations and international standards. However, it is found during use that the activity of the flux used in lead-free solder paste is usually stronger than that of the flux in leaded solder paste, and the wettability of the lead-free solder paste alloy is not as good as that of the leaded solder paste alloy. The soldering processability and effect are inferior to those of leaded ones. That is, lead-free solder paste shows poor tin climbing ability when soldering the side pins of QFN package chips, resulting in unstable solder joint quality, easy occurrence of virtual soldering or false soldering phenomena, and further affecting the functional stability and reliability of the final product. Summary of the Invention

[0004] In order to solve the problem that the existing lead-free solder paste does not climb tin on the side pads when soldering the side pins of QFN chips, this application provides a lead-free solder paste for improving the climbing height of QFN chips and a preparation method thereof.

[0005] In the first aspect, this application provides a lead-free solder paste for improving the climbing height of QFN chips, adopting the following technical solution: A lead-free solder paste for improving the climbing height of QFN chips is prepared from the following raw materials in parts by weight: 100 parts of tin 4 - 8 parts of copper 4 - 6 parts of silver 1 - 2 parts of lubricant The lubricant is composed of lanthanum, cerium, and yttrium in a weight ratio of 1:(3 - 4):2.

[0006] 25 - 35 parts of flux The flux is obtained by mixing hydrogenated rosin methyl ester, surfactant, rosin, antioxidant thixotropic agent, organic acid, and solvent in a weight ratio of (1 - 2):(0.5 - 1):(15 - 20):(2 - 5):(1 - 3):50.

[0007] By adopting the above technical solution, the prepared lead-free solder paste has good solder climbing ability. While increasing the solder climbing height, it can form a more uniform and dense solder joint structure, which helps to reduce welding defects and effectively solves the problems of poor wettability and insufficient solder climbing ability existing in lead-free solder paste when welding QFN packaged chips.

[0008] By adjusting the ratio of the lead-free solder paste alloy, during the welding process, the lead-free solder paste can climb up more smoothly along the side pins of the QFN chip, increasing the solder climbing height, thereby improving the connection quality of the solder joints. The lubricant added to the lead-free solder paste is composed of lanthanum, cerium, and yttrium, which can effectively reduce the surface tension between the lead-free solder paste and the solder pad. When welding the side pins of the QFN packaged chip, it makes the lead-free solder paste easier to spread on the surface of the pins, forming uniform and continuous solder joints, and reducing the phenomenon of soldering defects such as dry joints or false soldering caused by poor wetting.

[0009] The flux composed of hydrogenated rosin methyl ester, surfactant, composite rosin, antioxidant thixotropic agent, organic acid, and solvent can provide good antioxidant performance and thixotropic performance during the welding process, prevent the oxidation and flow of the lead-free solder paste during the climbing process, and ensure the reliability of the solder joints. At the same time, it can effectively remove the oxide layer and impurities on the surface of the solder pad and pins, reduce welding defects such as solder joint voids and solder balls during the welding process, and improve the welding quality.

[0010] Preferably, the flux is obtained by mixing hydrogenated rosin methyl ester, surfactant, rosin, antioxidant thixotropic agent, organic acid, and solvent in a weight ratio of 1.2:0.7:18:3:2.5:50.

[0011] By adopting the above technical solution, optimizing the dosage of each component in the flux can further improve the wettability and solder climbing ability of the lead-free solder paste, thereby increasing the solder climbing height of the solder joints and reducing welding defects such as dry joints, false soldering, and solder balls.

[0012] Preferably, the rosin is composed of hydrogenated rosin and disproportionated rosin in a weight ratio of (4 - 6):3.

[0013] By adopting the above technical solution, optimizing the type of composite rosin can further improve the overall wettability of the lead-free solder paste, promote its solder climbing ability, increase the solder climbing height of the solder joints, and reduce the phenomenon of dry joints or false soldering. At the same time, the composite rosin has higher thermal stability at high temperatures and can effectively remove the oxide layer on the surface of the solder pad and pins, and can remain stable during the welding process without decomposition or volatilization, ensuring the welding quality.

[0014] Preferably, the antioxidant thixotropic agent is composed of hydrogenated castor oil and ethylene bis(16 - hydroxy)stearamide in a weight ratio of 1:(2 - 4).

[0015] By adopting the above technical solutions, optimizing the dosage and types of antioxidant thixotropic agents can reduce the consistency of lead-free solder paste when subjected to shear force, which helps the lead-free solder paste to flow and is easy to construct. After the shear force is removed, the consistency slowly recovers, which can prevent the lead-free solder paste from flowing and the solder joints from collapsing, increase the tin climbing height of the solder joints, and ensure the welding quality. At the same time, it can effectively prevent the oxidation of lead-free solder paste during the welding process and improve the antioxidant performance of lead-free solder paste.

[0016] Preferably, the hydroxyl value of the hydrogenated castor oil is 150 - 165mgKOH / g.

[0017] By adopting the above technical solutions, optimizing the hydroxyl value of the hydrogenated castor oil can further improve the antioxidant performance of lead-free solder paste. At the same time, it can effectively promote the spreading and climbing of lead-free solder paste, improve the welding quality, increase the tin climbing height of the solder joints, and reduce the phenomenon of virtual soldering or false soldering. Moreover, it can improve the fluidity and uniformity of the solder, making the welding process more stable and reliable.

[0018] Preferably, the surfactant is one of trimethyl butylene glycol, oleyl alcohol polyoxyethylene ether, polyethylene glycol, dimethyl silicone oil, glycerol, nonylphenol polyoxyethylene ether, and sec-octylphenol polyoxyethylene ether.

[0019] Preferably, the surfactant is composed of oleyl alcohol polyoxyethylene ether, trimethyl butylene glycol, and poly(ethylene glycol) tert-octylphenyl ether in a weight ratio of (1 - 3):5:(3 - 6).

[0020] By adopting the above technical solutions, optimizing the types and dosage of surfactants can further enhance the emulsification and wetting properties of lead-free solder paste, improve the spreading and tin climbing ability of lead-free solder paste, and increase the tin climbing height. At the same time, the three act synergistically to effectively disperse the solid particles in the lead-free solder paste, improve the uniformity and stability of the lead-free solder paste, ensure the welding quality, and reduce the phenomenon of virtual soldering or false soldering.

[0021] Preferably, the organic acid includes one of tartaric acid, oxalic acid, malic acid, citric acid, ascorbic acid, and caffeic acid.

[0022] By adopting the above technical solutions, optimizing the types of organic acids can improve the fluidity and uniformity of lead-free solder paste. During welding, it can react with the oxides on the metal surface to form soluble salts, thereby promoting the wetting and climbing of lead-free solder paste, increasing the tin climbing height of the solder joints, and reducing the phenomenon of virtual soldering or false soldering. At the same time, it can effectively prevent the oxidation of lead-free solder paste during the welding process and improve the welding quality.

[0023] Preferably, the solvent includes one of tetrahydrofurfuryl alcohol, diethylene glycol dibutyl ether, dipropylene glycol dimethyl ether, propylene glycol methyl ether, diethylene glycol monohexyl ether, tetraethylene glycol, N-methylpyrrolidone, 2-hexyldecanol, and 2-ethyl-1,3-hexanediol.

[0024] By using the above solvents, the organic components in the lead-free solder paste can be effectively dissolved, improving the uniformity and stability of the lead-free solder paste and facilitating the climbing of the lead-free solder paste.

[0025] In a second aspect, the present application provides a method for preparing a lead-free solder paste for the climbing height of QFN chips, adopting the following technical solution: A method for preparing a lead-free solder paste for the climbing height of QFN chips includes the following preparation steps: S1. Add tin, silver, copper, and lubricant to a furnace to obtain an alloy melt; S2. Transfer the alloy melt to an atomization chamber filled with nitrogen protection, with a rotation speed of 100,000 - 120,000 revolutions per minute and a gas pressure of 110,000 - 120,000 Pa. Screen the alloy melt through a screening device to obtain alloy powder, and the average particle size of the alloy powder is 5 - 10 microns; S3. Stir the alloy powder and the flux evenly to obtain a lead-free solder paste with a high climbing height for QFN chips.

[0026] By melting tin, silver, copper, and lubricant into an alloy melt, the uniform distribution of alloy components can be ensured, improving the wettability and fluidity of the alloy. Through high-speed atomization and screening, alloy powder with uniform particle size can be obtained. Controlling the particle size within the range of 5 - 10 microns can effectively improve the fluidity and uniformity of the solder, reducing possible defects during the welding process. By fully stirring the alloy powder and the flux evenly, the uniform distribution of the flux in the solder can be ensured, making the welding process more stable and reliable. At the same time, it can effectively remove the oxide layer on the surface of the solder pad and pins, improve the wettability and tin climbing ability of the solder, increase the tin climbing height, and reduce the phenomenon of false soldering or poor soldering.

[0027] In summary, the present application has the following beneficial effects: 1. Improving the tin climbing height: By optimizing the alloy composition and flux formula, the lead-free solder paste shows excellent tin climbing ability when welding the side pins of QFN packaged chips. The tin climbing height can reach 81% of the pin height, meeting the requirements of industry standards.

[0028] 2. Enhancing the wettability: Components such as hydrogenated rosin methyl ester, surfactant, and organic acid are added to the flux. These components can effectively reduce the surface tension between the solder and the solder pad, enhance the wettability, and enable the solder to spread and adhere better to the solder pad.

[0029] 3. Reducing welding defects: By optimizing the alloy composition and flux formula, common welding defects such as false soldering, poor soldering, and solder balls during the welding process are reduced. Detailed implementation mode Embodiment

[0030] The disproportionated rosin was purchased from Hubei Watson Chemical Technology Co., Ltd., and its CAS number is 65997-06-0.

[0031] The hydrogenated rosin was purchased from Wuhan Chengtian Fine Chemical Co., Ltd., and its brand is Seung-tin.

[0032] The fully hydrogenated rosin was purchased from Sichuan Ruikai Bang Chemical Materials Co., Ltd., and its model is fully hydrogenated rosin AX-E.

[0033] In Example 1, the hydroxyl value of hydrogenated castor oil is 150 mg KOH / g; in Example 2, the hydroxyl value of hydrogenated castor oil is 160 mg KOH / g; in Example 3, the hydroxyl value of hydrogenated castor oil is 165 mg KOH / g.

[0034] Example 1 A lead-free solder paste for the climbing height of QFN chips is prepared by the following method: S1. Add 1000 g of tin, 40 g of silver, 40 g of copper and 10 g of lubricant into a furnace, and heat to obtain an alloy melt; S2. Pour the alloy melt into an atomization chamber filled with nitrogen protection, with a rotation speed of 100,000 revolutions per minute and a pressure of 110,000 Pa. Screen the alloy melt through a screening device to obtain alloy powder, and the average particle size of the alloy powder is 5 microns; S3. Stir the alloy powder and 250 g of flux evenly to obtain a lead-free solder paste with a high climbing height of QFN chips.

[0035] The lubricant is composed of lanthanum, cerium and yttrium in a weight ratio of 1:3:2.

[0036] The flux is obtained by mixing hydrogenated rosin methyl ester, surfactant (oleyl alcohol polyoxyethylene ether), rosin (disproportionated rosin), antioxidant thixotropic agent (hydrogenated castor oil), organic acid (tartaric acid) and solvent (tetrahydrofurfuryl alcohol) in a weight ratio of 1:0.5:15:2:1:50.

[0037] The differences between Example 2-3 and Example 1 lie in that the types, dosages and parameters of the raw materials for preparing the lead-free solder paste with a high climbing height of QFN chips are different. The specific differences are shown in Table 1: Table 1 Types, dosages and parameters of the raw materials for preparing the lead-free solder paste with a high climbing height of QFN chips in Examples 1-3 Example 4 A lead-free solder paste for the climbing height of QFN chips. The difference between this example and Example 1 is that the rosin is composed of hydrogenated rosin and disproportionated rosin in a weight ratio of 4:3.

[0038] Example 5 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the rosin is composed of hydrogenated rosin and disproportionated rosin in a weight ratio of 6:3.

[0039] Embodiment 6 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the antioxidant thixotropic agent is composed of hydrogenated castor oil and N,N'-ethylenebis(16-hydroxystearamide) in a weight ratio of 1:2.

[0040] Embodiment 7 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 4 is that the antioxidant thixotropic agent is composed of hydrogenated castor oil and N,N'-ethylenebis(16-hydroxystearamide) in a weight ratio of 1:4.

[0041] Embodiment 8 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the surfactant is composed of oleyl polyoxyethylene ether, trimethylbutenediol, and polyoxyethylene tert-octylphenyl ether in a weight ratio of 1:5:3.

[0042] Embodiment 9 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 7 is that the surfactant is composed of oleyl polyoxyethylene ether, trimethylbutenediol, and polyoxyethylene tert-octylphenyl ether in a weight ratio of 3:5:6.

[0043] Embodiment 10 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the flux is obtained by mixing methyl ester of hydrogenated rosin, surfactant, rosin, antioxidant thixotropic agent, organic acid, and solvent in a weight ratio of 1.2:0.7:18:3:2.5:50.

[0044] Comparative Example Comparative Example 1 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the lubricant is omitted.

[0045] Comparative Example 2 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the lubricant is lanthanum.

[0046] Comparative Example 3 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that neodymium is used instead of lanthanum.

[0047] Comparative Example 4 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that neodymium is used instead of cerium.

[0048] Comparative Example 5 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that neodymium is used instead of yttrium.

[0049] Comparative Example 6 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that the lubricant is composed of lanthanum, cerium, and yttrium in a weight ratio of 1:1:1.

[0050] Comparative Example 7 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that hydrogenated rosin methyl ester is omitted.

[0051] Comparative Example 8 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that organic acid is omitted.

[0052] Comparative Example 9 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that antioxidant thixotropic agent is omitted.

[0053] Comparative Example 10 A lead-free solder paste for the climbing height of QFN chips. The difference between this embodiment and Embodiment 1 is that surfactant is omitted.

[0054] Detection method / Test method for the climbing height of soldering: Select a standard QFN package test board, use lead-free solder paste, print it on the test board according to the standard process, put the test board into the reflow soldering furnace, perform soldering according to the standard temperature curve, use a microscope device to measure the climbing height of soldering, and record the data.

[0055] Detection of soldering quality: Use a discarded PCB board for actual soldering test, perform X-Ray detection on the solder joints, and check whether there are voids, unevenness, or incomplete soldering inside. The experimental data is shown in Table 2: Table 2 Experimental data of Embodiments 1-10 and Comparative Examples 1-10 From the experimental data of Example 1 and Comparative Examples 1-6, it can be seen that in the present application, by blending lanthanum, cerium, and yttrium in a specific weight ratio and adding them as a lubricant to lead-free tin, the height of tin climbing can be greatly increased, while ensuring the welding quality, and the welding is full and the structure is uniform without voids during the welding process.

[0056] From the experimental data of Example 1 and Comparative Examples 7-10, it can be seen that in the present application, by using a specific preparation of flux and sharing it with tin, copper, silver, and lubricant, the height of tin climbing of the lead-free solder paste can be effectively increased, and the welding is ensured to be void-free, with a uniform structure and full welding.

[0057] From the experimental data of Example 1 and Examples 4-5, it can be seen that by mixing hydrogenated rosin and disproportionated rosin in a specific ratio, the height of tin climbing of the lead-free solder paste can be effectively increased.

[0058] From the experimental data of Example 1 and 6, and Example 4 and 7, it can be seen that by using hydrogenated castor oil and N,N'-ethylenebis(16-hydroxy)stearamide in a specific ratio, it is beneficial to improve the tin climbing ability of the lead-free solder paste.

[0059] From the experimental data of Example 1 and 8, and Example 7 and 9, it can be seen that by using polyoxyethylene oleyl ether, trimethylbutenediol, and poly(ethylene glycol) tert-octylphenyl ether in a specific ratio, it is beneficial to improve the tin climbing ability of the lead-free solder paste.

[0060] From the experimental data of Example 1 and Example 10, it can be seen that by optimizing the dosage of the components in the flux, it is beneficial to further improve the tin climbing ability of the lead-free solder paste.

[0061] This specific embodiment is only an explanation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A lead-free solder paste for the climbing height of a high QFN chip, characterized in that Prepared from the following raw materials by weight: 100 parts of tin 4 - 8 parts of copper 4 - 6 parts of silver 1 - 2 parts of lubricant The lubricant is composed of lanthanum, cerium and yttrium in a weight ratio of 1:(3 - 4):2; 25 - 35 parts of flux The flux is obtained by mixing hydrogenated rosin methyl ester, surfactant, rosin, antioxidant thixotropic agent, organic acid and solvent in a weight ratio of (1 - 2):(0.5 - 1):(15 - 20):(2 - 5):(1 - 3):

50.

2. The lead-free solder paste for the climbing height of a high QFN chip according to claim 1, wherein: The rosin is composed of hydrogenated rosin and disproportionated rosin in a weight ratio of (4 - 6):

3.

3. The lead-free solder paste for the climbing height of a high QFN chip according to claim 1, wherein: The antioxidant thixotropic agent is composed of hydrogenated castor oil and ethylene bis(16 - hydroxy) stearamide in a weight ratio of 1:(2 - 4).

4. A lead-free solder paste for the climbing height of a high QFN chip according to claim 1, characterized in that: The hydroxyl value of the hydrogenated castor oil is 150 - 165mgKOH / g.

5. The lead-free solder paste for the climbing height of a high QFN chip according to claim 1, characterized in that: The surfactant is one of trimethyl butene diol, oleyl polyoxyethylene ether, polyethylene glycol, dimethyl silicone oil, glycerol, nonylphenol polyoxyethylene ether and sec - octylphenol polyoxyethylene ether.

6. The lead-free solder paste for the climbing height of a high QFN chip according to claim 5, characterized in that: The surfactant is composed of oleyl polyoxyethylene ether, trimethyl butene diol and polyglycol tert - octylphenyl ether in a weight ratio of (1 - 3):5:(3 - 6).

7. An unleaded solder paste for the climbing height of a high QFN chip according to claim 1, characterized in that: The organic acid includes one of tartaric acid, oxalic acid, malic acid, citric acid, ascorbic acid and caffeic acid.

8. The lead-free solder paste for the climbing height of a high QFN chip according to claim 1, characterized in that: The solvent includes at least one of tetrahydrofurfuryl alcohol, diethylene glycol dibutyl ether, dipropylene glycol dimethyl ether, propylene glycol methyl ether, diethylene glycol monohexyl ether, tetraethylene glycol, N - methylpyrrolidone, 2 - hexyl - decanol and 2 - ethyl - 1,3 - hexanediol.

9. An unleaded solder paste for the climbing height of a high QFN chip according to claim 1, characterized in that: The flux is obtained by mixing hydrogenated rosin methyl ester, surfactant, rosin, antioxidant thixotropic agent, organic acid and solvent in a weight ratio of 1.2:0.7:18:3:2.5:

50.

10. A method for preparing a lead-free solder paste for the climbing height of a high QFN chip as described in any one of claims 1-9, characterized in that, Including the following preparation steps: S1. Add tin, silver, copper and lubricant into a furnace to obtain an alloy melt; S2. Transfer the alloy melt to an atomization chamber filled with nitrogen protection, with a rotation speed of 100,000 - 120,000 revolutions per minute and a gas pressure of 110,000 - 120,000 Pa. Screen the alloy melt through a screening device to obtain alloy powder, and the average particle size of the alloy powder is 5 - 10 microns; S3. Stir the alloy powder and the flux evenly to obtain a lead - free solder paste with a high QFN chip climbing height.

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