A low-silver lead-free solder and a method for preparing the same

Abstract

The application belongs to the technical field of solder, and relates to a low-silver lead-free solder and a preparation method thereof, which comprises the following raw materials in percentage by mass: 0.5-1% of Ag, 0.4-0.8% of Cu, 0.1-0.3% of Bi, 0.1-0.3% of a composite refiner, and the balance of Sn and inevitable impurities; wherein the composite refiner is composed of composite rare earth oxides and nano-SiO2, and the raw materials of the composite rare earth oxides comprise La2O3 and CeO2. The application can inhibit the too fast growth of intermetallic compounds at the interface between the copper substrate and the solder by reasonably adjusting the components of the raw materials and adding the composite refiner. Meanwhile, the Bi element and the composite refiner synergistically act to promote the uniform distribution of Ag and Cu elements in the solder, reduce the stress concentration of the IMC layer, improve the mechanical properties of the solder joint interface, improve the strength, toughness and other properties of the solder, enhance the shear and tensile resistance of the solder joint, enhance the reliability and stability of the solder, ensure the stable combination of the solder and the welding material, avoid the cracking of the solder joint, and improve the welding quality of the solder.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of solder, and relates to a low-silver lead-free solder and a preparation method thereof. BACKGROUND

[0002] Low-silver lead-free solder (such as Sn-Ag-Cu alloy) has become a core material for replacing traditional lead-containing solder due to its environmental protection advantage and relatively low cost. Such solder is widely used in the field of electronic device assembly, and is particularly suitable for surface mounting technology and high-density packaging process.

[0003] However, Sn-Ag-Cu series lead-free solder still faces significant challenges in practical application: due to its high melting point, a higher heating temperature needs to be used in the reflow soldering process. The increase of the temperature accelerates the growth rate of copper substrate and solder interface intermetallic compound (IMC), and as the thickness of the IMC layer increases, the brittle characteristics gradually appear, which leads to the decline of the mechanical properties of the solder joint interface, and finally causes cracks and even fracture failure. SUMMARY

[0004] The application aims to provide a low-silver lead-free solder and a preparation method thereof, and aims to improve the mechanical properties of the solder joint interface and enhance the reliability and stability of the solder.

[0005] The purpose of the application can be achieved by the following technical solutions.

[0006] In a first aspect, the application provides a low-silver lead-free solder, which comprises the following raw materials in mass percentage:

[0007]

[0008] The balance is Sn and unavoidable impurities;

[0009] The composite refiner comprises a composite rare earth oxide and nano-SiO2 mixed together, and the raw materials of the composite rare earth oxide comprise La2O3 and CeO2.

[0010] Preferably, the mass ratio of the composite rare earth oxide and nano-SiO2 is (1-3):1.

[0011] Preferably, the mass ratio of La2O3 and CeO2 is (2-4):1.

[0012] Preferably, the particle size of the nano-SiO2 is 20-40 nm.

[0013] Preferably, the preparation of the composite refiner is as follows:

[0014] La2O3, CeO2 and nano-SiO2 are mixed in proportion, ball milled, calcined, and the composite refiner is obtained.

[0015] Preferably, the composite refiner is prepared by ball milling at a speed of 500-800 rpm for 1-2 h.

[0016] Preferably, the composite refiner is prepared by calcining at a temperature of 800-1000 ℃ for 1-2 h.

[0017] Preferably, the composite refiner has a particle size of 0.5-2 μm.

[0018] In a second aspect, the present application provides a method for preparing a low-silver lead-free solder as described above, comprising the following steps:

[0019] S1, weighing Sn, Ag, Cu and Bi according to a certain proportion and heating to complete melting;

[0020] S2, adding the composite refiner to the melt, stirring and uniformly dispersing;

[0021] S3, pouring into a water-cooled copper mold, cooling to obtain a solder material.

[0022] Preferably, in the step S3, the cooling rate is 10-100 ℃ / s.

[0023] The present application has the following beneficial effects:

[0024] By introducing the composite refiner of composite rare earth oxides and nano-SiO2, the excessive growth of intermetallic compounds (IMC) is effectively inhibited, the interface brittleness is reduced, and thus the shear strength of the solder joint is improved. At the same time, the Bi element and the composite refiner synergistically interfere with the deposition path of Ag / Cu, so that it is more uniformly distributed in the melt, reducing the stress concentration of the IMC layer and the crack of the solder joint; the strength, toughness and other properties of the solder are improved, the shear and tensile resistance of the solder joint is enhanced; the combination of the solder and the welding material is stable, the soldering cracking is avoided, and the soldering quality of the solder is improved. DETAILED DESCRIPTION

[0025] In order to further illustrate the technical means and effects adopted by the present application to achieve the predetermined object, the specific embodiments, structures, features and effects according to the present application are described in detail as follows in combination with preferred embodiments.

[0026] Example 1

[0027] A low-silver lead-free solder comprises the following raw materials in mass percentage, as shown in Table 1.

[0028] Table 1

[0029]

[0030] The composite refiner is prepared by mixing composite rare earth oxide and nano-SiO2, and the raw materials of the composite rare earth oxide include La2O3 and CeO2.

[0031] The particle size of the nano-SiO2 is 20 nm.

[0032] The composite refiner is prepared by mixing composite rare earth oxide and nano-SiO2, and the raw materials of the composite rare earth oxide include La2O3 and CeO2.

[0033] The La2O3, CeO2 and nano-SiO2 are mixed in proportion, put into a ball mill, and ball milled at a speed of 500 rpm for 2 h to make the particle size of the mixture 0.5-2 μm, and then the mixture is transferred to a high-temperature furnace and calcined at 800 ℃ for 2 h to obtain the composite refiner.

[0034] A preparation method of a low-silver lead-free solder includes the following steps:

[0035] S1, Sn, Ag, Cu and Bi are weighed in proportion into a crucible and heated to complete melting;

[0036] S2, the composite refiner is added to the melt in proportion, and fully stirred to make it uniformly dispersed in the melt;

[0037] S3, water-cooled copper mold casting is adopted, and the cooling rate is controlled to be 10 ℃ / s, and the low-silver lead-free solder material is obtained after cooling.

[0038] Example 2

[0039] A low-silver lead-free solder includes the following raw materials in mass percentage, as shown in Table 2.

[0040] Table 2

[0041]

[0042] The composite refiner is prepared by mixing composite rare earth oxide and nano-SiO2, and the raw materials of the composite rare earth oxide include La2O3 and CeO2. The mass ratio of the composite rare earth oxide and nano-SiO2 is 2:1. The mass ratio of La2O3 and CeO2 is 3:1.

[0043] The particle size of the nano-SiO2 is 30 nm.

[0044] The composite refiner is prepared by mixing composite rare earth oxide and nano-SiO2, and the raw materials of the composite rare earth oxide include La2O3 and CeO2.

[0045] La2O3, CeO2 and nano-SiO2 were mixed in proportion and placed in a ball mill. The mixture was ball-milled at 650 rpm for 1.5 h to make the particle size of the mixture 0.5-2 μm. The mixture was then transferred to a high-temperature furnace and calcined at 900 °C for 1.5 h to obtain the composite finer agent.

[0046] A method for preparing a low-silver lead-free solder includes the following steps:

[0047] S1. Weigh Sn, Ag, Cu and Bi in proportion and place them in a crucible and heat until completely melted;

[0048] S2. Add the composite refining agent to the melt in proportion, stir thoroughly to ensure that it is evenly dispersed in the melt;

[0049] S3. Water-cooled copper mold casting is used, and the cooling rate is controlled at 50℃ / s. After cooling, low-silver lead-free solder material is obtained.

[0050] Example 3

[0051] A low-silver lead-free solder comprises the following raw materials in the following weight percentages, as shown in Table 3.

[0052] Table 3

[0053]

[0054] The composite refining agent comprises a mixture of composite rare earth oxides and nano-SiO2, wherein the raw materials for the composite rare earth oxides include La2O3 and CeO2. The mass ratio of the composite rare earth oxides to nano-SiO2 is 3:1, and the mass ratio of La2O3 to CeO2 is 4:1.

[0055] The particle size of nano-SiO2 is 40 nm.

[0056] The preparation of the composite refining agent is as follows:

[0057] La2O3, CeO2 and nano-SiO2 were mixed in proportion and placed in a ball mill. The mixture was ball-milled at 800 rpm for 1 hour to make the particle size of the mixture 0.5-2 μm. The mixture was then transferred to a high-temperature furnace and calcined at 1000℃ for 1 hour to obtain the composite finer agent.

[0058] A method for preparing a low-silver lead-free solder includes the following steps:

[0059] S1. Weigh Sn, Ag, Cu and Bi in proportion and place them in a crucible and heat until completely melted;

[0060] S2. Add the composite refining agent to the melt in proportion, stir thoroughly to ensure that it is evenly dispersed in the melt;

[0061] S3. Water-cooled copper mold casting is used, and the cooling rate is controlled at 100℃ / s. After cooling, low-silver lead-free solder material is obtained.

[0062] Example 4

[0063] A low-silver lead-free solder comprises the following raw materials in the following weight percentages, as shown in Table 4.

[0064] Table 4

[0065]

[0066] The composite refining agent comprises a mixture of composite rare earth oxides and nano-SiO2, wherein the raw materials for the composite rare earth oxides include La2O3 and CeO2. The mass ratio of the composite rare earth oxides to nano-SiO2 is 1.5:1, and the mass ratio of La2O3 to CeO2 is 2.5:1.

[0067] The particle size of nano-SiO2 is 25 nm.

[0068] The preparation of the composite refining agent is as follows:

[0069] La2O3, CeO2 and nano-SiO2 were mixed in proportion and placed in a ball mill. The mixture was ball-milled at 550 rpm for 1.8 hours to make the particle size of the mixture 0.5-2 μm. The mixture was then transferred to a high-temperature furnace and calcined at 850°C for 1.8 hours to obtain the composite finer agent.

[0070] A method for preparing a low-silver lead-free solder includes the following steps:

[0071] S1. Weigh Sn, Ag, Cu and Bi in proportion and place them in a crucible and heat until completely melted;

[0072] S2. Add the composite refining agent to the melt in proportion, stir thoroughly to ensure that it is evenly dispersed in the melt;

[0073] S3. Water-cooled copper mold casting is used, and the cooling rate is controlled at 30℃ / s. After cooling, low-silver lead-free solder material is obtained.

[0074] Example 5

[0075] A low-silver lead-free solder comprises the following raw materials in the following weight percentages, as shown in Table 5.

[0076] Table 5

[0077]

[0078]

[0079] The composite refining agent comprises a mixture of composite rare earth oxides and nano-SiO2, wherein the raw materials for the composite rare earth oxides include La2O3 and CeO2. The mass ratio of the composite rare earth oxides to nano-SiO2 is 2.5:1, and the mass ratio of La2O3 to CeO2 is 3.5:1.

[0080] The particle size of nano-SiO2 is 25 nm.

[0081] The preparation of the composite refining agent is as follows:

[0082] La2O3, CeO2 and nano-SiO2 were mixed in proportion and placed in a ball mill. The mixture was ball-milled at 750 rpm for 1.2 h to make the particle size of the mixture 0.5-2 μm. Then the mixture was transferred to a high-temperature furnace and calcined at 950 °C for 1.2 h to obtain the composite finer agent.

[0083] A method for preparing a low-silver lead-free solder includes the following steps:

[0084] S1. Weigh Sn, Ag, Cu and Bi in proportion and place them in a crucible and heat until completely melted;

[0085] S2. Add the composite refining agent to the melt in proportion, stir thoroughly to ensure that it is evenly dispersed in the melt;

[0086] S3. Water-cooled copper mold casting is used, and the cooling rate is controlled at 80℃ / s. After cooling, low-silver lead-free solder material is obtained.

[0087] Comparative Example 1

[0088] The difference from Example 1 is that Sn is used instead of Bi and the composite refining agent in equal amounts.

[0089] Comparative Example 2

[0090] The difference from Example 1 is that an equal amount of Sn is used instead of Bi.

[0091] Comparative Example 3

[0092] The difference from Example 1 is that an equal amount of Sn is used instead of the composite refining agent.

[0093] Comparative Example 4

[0094] The difference from Example 1 is that the composite refining agent contains only La2O3.

[0095] Comparative Example 5

[0096] The difference from Example 1 is that the composite refining agent contains only CeO2.

[0097] Comparative Example 6

[0098] The difference from Example 1 is that the composite refining agent contains only nano-SiO2.

[0099] Comparative Example 7

[0100] The difference from Example 1 is that the composite refining agent contains only La2O3 and nano-SiO2.

[0101] Comparative Example 8

[0102] The difference from Example 1 is that the composite refining agent contains only CeO2 and nano-SiO2.

[0103] Comparative Example 9

[0104] The difference from Example 1 is that the composite refining agent contains only La2O3 and CeO2.

[0105] Comparative Example 10

[0106] The difference from Example 1 is that the Bi content is 0.5%.

[0107] Comparative Example 11

[0108] The difference from Example 1 is that in S3 of the method for preparing low-silver lead-free solder, the cooling rate is 5°C / s.

[0109] Performance testing

[0110] 1. IMC layer thickness test

[0111] Take 0.3g of solder from each example and comparative example, and use a TYD-KW600 reflow oven to solder the solder onto a 1cm x 1cm copper sheet to form a good solder joint. Then, place the samples in a 150℃ electric heating drying oven for 300h for aging. After aging, mount, grind, and polish the samples. Use an etching solution of 60ml anhydrous ethanol + 30ml deionized water + 5mL concentrated hydrochloric acid + 2g ferric chloride for etching. Take pictures under a PHENOM PW-100-001 scanning electron microscope and measure the IMC thickness based on the pictures.

[0112] 2. Shear strength test

[0113] The solders of each embodiment and comparative example were bonded to the substrate by TYD-KW600 reflow soldering, and then the shear strength was tested using a PTR-1101 solder joint shear strength tester at a shear rate of 0.05 mm / s.

[0114] 3. Wettability test

[0115] The wettability test was conducted using the solder ball balance method on a SAT-5200T Solderability Tester. The solder balls used had a mass of 0.2g and the copper rod had a diameter of 8mm.

[0116] 4. Tensile property test

[0117] Uniaxial static tensile tests were performed on the solders of each embodiment and comparative example using an INSTRON 5966 universal testing machine at a tensile rate of 0.01 mm / s to obtain the tensile strength of the solders.

[0118] The performance test data for each embodiment and comparative example are shown in Table 6.

[0119] Table 6

[0120]

[0121]

[0122] As shown in Table 6:

[0123] IMC layer thickness: The IMC layer thicknesses in Examples 1-5 ranged from 0.8 to 1.2 μm, significantly less than those in Comparative Examples 1-3, indicating that the addition of the composite refining agent and Bi element effectively inhibited excessive IMC growth. In Comparative Examples 4-9, even with only a single or partial composite refining agent component, the IMC layer thickness was still greater than in the examples, indicating that the synergistic effect of the components of the composite refining agent is crucial for inhibiting IMC growth. In Comparative Example 10, the increased Bi content resulted in a slight decrease in IMC layer thickness, but the effect was not as good as in the examples, indicating that the components need to work synergistically in appropriate proportions. In Comparative Example 11, a change in cooling rate increased the IMC layer thickness, indicating that a suitable cooling rate also affects the inhibition of IMC growth.

[0124] Shear strength: The shear strength of Examples 1-5 ranged from 38.7 to 45.1 MPa, higher than that of Comparative Examples 1-3, indicating that the addition of the composite refining agent and Bi element improved the shear strength of the weld joint. The shear strength of Comparative Examples 4-9 was lower than that of the Examples, further demonstrating the importance of the synergistic effect of the components of the composite refining agent. The shear strength of Comparative Example 10 was improved, but still lower than that of the Examples. The shear strength of Comparative Example 11 decreased significantly, indicating that the cooling rate has a significant impact on shear strength.

[0125] Wettability: The wettability of Examples 1-5 is better than that of Comparative Examples 1-3, indicating that the solder has better wettability, which is beneficial for welding. The wettability of Comparative Examples 4-9 is also worse than that of the Examples, indicating that the composition and ratio of the composite refining agent have an impact on wettability. The contact angle of Comparative Example 10 is reduced, but it is still not as good as that of the Examples. The wettability of Comparative Example 11 is significantly worse, indicating that the cooling rate also has a certain effect on wettability.

[0126] Tensile strength: The tensile strength of Examples 1-5 ranged from 45.2 to 51.4 MPa, which was higher than that of Comparative Examples 1-3, indicating that the solder had good tensile strength. The tensile strength of Comparative Examples 4-9 was lower than that of the Examples, indicating that the components of the composite refining agent affected the tensile strength. The tensile strength of Comparative Example 10 was close to that of Example 1, while the tensile strength of Comparative Example 11 decreased, indicating that the cooling rate affected the tensile strength.

[0127] In summary, the low-silver lead-free solder of the present invention, through reasonable composition design and preparation process, especially the synergistic effect of composite refiner and Bi element, and appropriate cooling rate, effectively improves the mechanical properties of the solder joint interface, enhances the reliability and stability of the solder, and also performs well in terms of wettability, and has good application prospects.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A low-silver lead-free solder, characterized in that, Including the following percentages by weight of raw materials: Ag 0.5-1% Cu 0.4-0.8% Bi 0.1-0.3% Composite refining agent 0.1-0.3% The balance is Sn and unavoidable impurities; The composite refining agent is composed of a composite rare earth oxide and nano-SiO2 in a mass ratio of (1-3):1, and the raw materials of the composite rare earth oxide include La2O3 and CeO2 in a mass ratio of (2-4):

1.

2. The low-silver lead-free solder according to claim 1, characterized in that, The particle size of the nano-SiO2 is 20-40 nm.

3. The low-silver lead-free solder according to claim 1, characterized in that, The preparation of the composite refining agent is as follows: La2O3, CeO2 and nano-SiO2 were mixed in proportion, ball-milled and calcined to obtain a composite refining agent.

4. The low-silver lead-free solder according to claim 3, characterized in that, During the preparation of the composite refining agent, ball milling is performed at a speed of 500-800 rpm for 1-2 hours.

5. The low-silver lead-free solder according to claim 3, characterized in that, During the preparation of the composite refining agent, it is calcined at 800-1000℃ for 1-2 hours.

6. The low-silver lead-free solder according to claim 1, characterized in that, The particle size of the composite refining agent is 0.5-2 μm.

7. A method for preparing a low-silver lead-free solder according to any one of claims 1-6, characterized in that, Includes the following steps: S1. Weigh Sn, Ag, Cu and Bi in proportion and heat until completely melted; S2. Add the composite refining agent to the melt, stir, and disperse evenly; S3. The solder material is obtained by casting and cooling using a water-cooled copper mold.

8. The method for preparing a low-silver lead-free solder according to claim 7, characterized in that, In step S3, the cooling rate is 10-100℃ / s.

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