A lead-free solder and its preparation method

Abstract

The present invention discloses a lead-free solder, and its raw materials by weight percentage include: 0.6 - 0.8% of Cu, 0.06 - 0.08% of modified nanoparticles, 0.05 - 0.07% of Zn, 0.07 - 0.08% of Ni, 2.5 - 3% of Bi, 0.02 - 0.025% of Ge, and the balance is Sn. The present invention also discloses a preparation method of the above lead-free solder. The present invention has good wettability and oxidation resistance, a relatively low melting point, and the solder joints are firm and reliable.

Description

Technical Field

[0001] The present invention relates to the technical field of solders, and particularly to a lead-free solder and a preparation method thereof. Background Art

[0002] Sn-Cu based lead-free solders are widely used because of their wide raw material sources, low cost, and non-toxic side effects. Among them, the widely applicable Sn-0.7Cu lead-free solder is commonly used in electronic packaging. However, as electronic packaging gradually develops towards miniaturization, the size of solder joints is getting smaller and smaller. The formation of intermetallic compounds (referred to as IMCs for short) at the interface of micro solder joints during the soldering reaction process is the key to realizing reliable metallurgical interconnection between the solder and the under-bump metal layer. However, the IMCs at the interface have a brittle nature, which will reduce the mechanical properties and reliability of the micro solder joints. Therefore, it is necessary to control their thickness and morphology. The wettability and oxidation resistance of Sn-Cu based lead-free solders still need to be improved, and the high melting point of Sn-Cu based lead-free solders also limits the scope of use of the solder. Summary of the Invention

[0003] Based on the technical problems existing in the background art, the present invention proposes a lead-free solder and a preparation method thereof. The present invention has good wettability and oxidation resistance, a relatively low melting point, and the solder joints are firm and reliable.

[0004] The present invention proposes a lead-free solder, and its raw materials by weight percentage include: 0.6-0.8% of Cu, 0.06-0.08% of modified nanoparticles, 0.05-0.07% of Zn, 0.07-0.08% of Ni, 2.5-3% of Bi, 0.02-0.025% of Ge, and the balance is Sn.

[0005] Preferably, its raw materials by weight percentage include: 0.7% of Cu, 0.07% of modified nanoparticles, 0.06% of Zn, 0.075% of Ni, 2.7% of Bi, 0.023% of Ge, and the balance is Sn.

[0006] Preferably, in the preparation process of the modified nanoparticles, the nano-titanium dioxide grafted with amino groups is mixed with the graphene oxide dispersion, stirred at room temperature for 18-24 h, and solid-liquid separation is carried out to obtain the modified nanoparticles.

[0007] Nanomaterials are prone to agglomeration and are not easily dispersed in the solder, which will affect the welding performance of the solder. In the present invention, nano-titanium dioxide particles are electrostatically assembled on the surface of graphene, so that the originally folded and agglomerated graphene layers are unfolded, and the titanium dioxide nanoparticles can also be evenly dispersed on the surface of graphene, thus avoiding the problem that nanoparticles and graphene are prone to agglomeration. Assembling nano-titanium dioxide on the surface of graphene can improve the dispersibility of graphene and nano-titanium dioxide in other metal raw materials, so as to give full play to the role of nanomaterials in the solder.

[0008] The above-mentioned amino-grafted nano-titanium dioxide can be obtained by grafting and modifying nano-titanium dioxide with an amino-containing silane coupling agent, and the amino-containing silane coupling agent can be 3-aminopropyltriethoxysilane, etc.

[0009] Preferably, in the preparation process of the modified nanoparticles, the weight ratio of the amino-grafted nano-titanium dioxide to graphene oxide is 5-8:1.

[0010] Preferably, in the preparation process of the modified nanoparticles, the pH of the graphene oxide dispersion is 4.5-5.5.

[0011] Preferably, in the preparation process of the modified nanoparticles, the solvent of the graphene oxide dispersion is a mixed solution of ethanol and water.

[0012] Preferably, ultrasonic treatment is carried out after welding.

[0013] Preferably, the ultrasonic power is 200-250w, the ultrasonic frequency is 10000-15000Hz, and the ultrasonic time is 20-25s.

[0014] After welding, ultrasonic treatment is carried out on the solder joints. By selecting appropriate ultrasonic parameters, the grains of IMC in the solder joints can be further refined, and IMC can be promoted to grow and extend towards the middle of the weld seam, so that the tissue grains are broken and dispersed in the middle of the solder joints due to the ultrasonic action, thereby improving the firmness of the solder joints.

[0015] The present invention also provides a preparation method of the above-mentioned lead-free solder, including the following steps: under the protection of an inert gas, first melt Sn and Bi, then sequentially add Ni, Cu, and Ge for smelting, then cool down to 430-450°C and add Zn for smelting, finally add the modified nanoparticles and mix evenly, and then stand for 15-20 minutes, and cast to obtain the lead-free solder.

[0016] The lead-free solder of the present invention can be processed into shapes such as welding rods, welding wires, welding sheets, and welding balls.

[0017] Beneficial effects:

[0018] 1. By modifying nano-titanium dioxide and graphene, the present invention greatly improves the dispersibility of nano-titanium dioxide and graphene in the solder;

[0019] 2. Uniformly dispersed nano-titanium dioxide can be adsorbed at the grooves of IMC (such as Cu6Sn5) and form a firm connection with IMC, thereby hindering the element diffusion between the substrate and the solder, reducing the probability of forming brittle IMC, and thus improving the firmness of the solder joint; nano-titanium dioxide also cooperates with appropriate amounts of Zn and Ni to further inhibit the growth of brittle IMC, and Ni can react with Sn and Zn and adsorb on the surfaces of Sn and Zn to further improve the problem of easy oxidation of Sn-Cu solder and Zn; and an appropriate amount of Ge is added to cooperate with Ni to further improve the problem of easy oxidation of Sn-Cu solder and Zn.

[0020] 3. In the present invention, by adding a relatively large content of Bi, the melting point of the solder is reduced, and the cooperation of Bi and uniformly dispersed graphene can improve the wettability of the solder. However, too high a Bi content is likely to cause the solder joint to become brittle, and the addition of graphene can improve the compactness and toughness of the solder joint, avoiding the problem of the solder joint becoming brittle caused by a high Bi content; 4. After welding, the solder joint is ultrasonically treated to further improve the firmness of the solder joint. Specific embodiments

[0021] Next, the technical solutions of the present invention will be described in detail through specific embodiments.

[0022] The formulations of Examples 1-3 and Comparative Examples 1-8 are shown in Table 1.

[0023] Table 1 Formulations of each group (by weight percentage, the balance is Sn)

[0024]

[0025]

[0026] The preparation methods of the above Examples 1-3 and Comparative Examples 1-8 are the same, which are: in a vacuum melting furnace, under argon protection, first melt Sn and Bi, and then successively add Ni, Cu, and Ge for melting; then cool down to 450 °C and add Zn for melting, and finally add modified nano-particles, stir well and mix evenly, then let stand for 15 min, cast, and process to obtain lead-free welding wires.

[0027] The preparation methods of the modified nano-particles in the above Examples 1-3 are the same, which are: adding graphene oxide into ethanol water and ultrasonically dispersing it evenly, adjusting the pH = 4.5 - 5.5, and then adding nano-titanium dioxide modified by 3-aminopropyltriethoxysilane and mixing evenly, stirring at room temperature for 22 h, filtering, and taking the filter cake, washing and drying to obtain modified nano-particles.

[0028] Respectively take the welding wires of Examples 1-3 and Comparative Examples 1-8, weld the copper alloy, and then ultrasonically treat for 25 s under the conditions of 220 w and 12,000 Hz, and use a universal testing machine to detect the shear strength of the solder joint.

[0029] The wettability was detected according to the method of GB11364-89.

[0030] The static oxidation experiments were carried out on the welding wires of Examples 1-3 and Comparative Examples 1-8 at 270 °C. Each time, 300 g of the material was weighed and placed in a corundum crucible, and then the crucible was placed in a tin bath for the experiment. The slag was scraped once every 30 min, and the slag was skimmed and weighed once every 1 h. Each group of experiments lasted for 10 h, and the antioxidant property of the lead-free solder was evaluated according to the amount of oxidation slag. The results are shown in Table 2.

[0031] Table 2 Detection Results

[0032]

[0033] As can be seen from Table 1, in the present invention, through the proper combination of various elements and modified nanoparticles, the solder has good wettability and antioxidant property, and the solder joint has good firmness.

[0034] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and all should be covered within the protection scope of the present invention.

Claims

1. A lead-free solder, characterized in that, Its raw materials by weight percentage include: 0.6 - 0.8% of Cu, 0.06 - 0.08% of modified nanoparticles, 0.05 - 0.07% of Zn, 0.07 - 0.08% of Ni, 2.5 - 3% of Bi, 0.02 - 0.025% of Ge, and the balance is Sn; In the preparation process of the modified nanoparticles, grafted amino - functionalized titanium dioxide nanoparticles and graphene oxide dispersion are mixed evenly, stirred at room temperature for 18 - 24 h, and then solid - liquid separated to obtain the modified nanoparticles; In the preparation process of the modified nanoparticles, the weight ratio of grafted amino - functionalized titanium dioxide nanoparticles to graphene oxide is 5 - 8:1; In the preparation process of the modified nanoparticles, the pH of the graphene oxide dispersion is 4.5 - 5.5; In the preparation process of the modified nanoparticles, the solvent of the graphene oxide dispersion is a mixed solution of ethanol and water; The grafted amino - functionalized titanium dioxide nanoparticles are 3 - aminopropyltriethoxysilane - modified titanium dioxide nanoparticles.

2. The lead-free solder according to claim 1, wherein Ultrasonic treatment is carried out after welding.

3. The lead-free solder according to claim 2, wherein The ultrasonic power is 200 - 250 w, the ultrasonic frequency is 10000 - 15000 Hz, and the ultrasonic time is 20 - 25 s.

4. A method for preparing a lead-free solder according to any one of claims 1-3, characterized in that, It includes the following steps: Under the protection of inert gas, first melt Sn and Bi, then successively add Ni, Cu, and Ge for melting, then cool down to 430 - 450 °C, add Zn for melting, finally add the modified nanoparticles and mix evenly, then stand for 15 - 20 min, and cast to obtain the lead - free solder.

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