Method for producing tin-zinc-cerium composite and solder

Abstract

The application provides a preparation method of a tin-zinc-cerium composite material, comprising the following steps: A) ball milling tin powder, zinc powder and cerium powder under a protective atmosphere to obtain initial mixed powder; B) vacuum drying the initial mixed powder to obtain mixed powder; and C) forming the mixed powder by using a rapid forming process under a protective atmosphere to obtain the tin-zinc-cerium composite material. The application adopts the rapid forming process, a high cooling rate inhibits the precipitation of the zinc phase of the tin-zinc alloy, reduces the mechanical collapse of the formed piece caused by brittleness, and the introduction of cerium can effectively inhibit the oxidation of zinc, thereby improving the wettability in the soldering process. Meanwhile, cerium can also improve the creep resistance, thereby inhibiting the growth of alloy whiskers, so that the tin-zinc-cerium composite material has wide application prospects in the fields of low-temperature soldering technology and high-end chip pin densification.

Description

Technical Field

[0001] This invention relates to the field of solder technology, and more particularly to a method for preparing a tin-zinc-cerium composite material and a solder. Background Technology

[0002] Currently, the development of surface-mount integrated circuits (SMD) is very rapid. Miniaturization, thinness, and narrow pin pitch are the main development directions for SMD.

[0003] Sn-based lead-free solders have been widely used in integrated circuits, such as Sn-Ag-Cu ternary alloys, Sn-Ag eutectic series, and Sn-Cu alloy series. However, compared with leaded solders, they still have problems such as high price, poor wettability, poor surface tension, and relatively high melting point, which limit the development trend of miniaturization, narrow pin pitch, and density of electronic component packaging.

[0004] Sn-Zn alloys have great research potential due to their relatively low melting point (198.5℃), good mechanical properties, good creep resistance, abundant reserves, and low price. However, Zn is prone to oxidation, leading to poor solder wettability. Furthermore, the Zn phase easily precipitates upon cooling; this brittle phase deteriorates the mechanical properties of the solder joint, making it prone to breakage. Therefore, Sn-Zn alloys are still not ideal as solders.

[0005] In view of the above problems, it is of great significance to provide a composite tin material that suppresses tin whiskers and improves wettability. Summary of the Invention

[0006] The technical problem solved by this invention is to provide a method for preparing a tin-zinc-cerium composite material. The preparation method provided by this application can improve the wettability of solder and inhibit the growth of alloy whiskers.

[0007] In view of this, this application provides a method for preparing a tin-zinc-cerium composite material, comprising the following steps:

[0008] A) Under a protective atmosphere, tin powder, zinc powder and cerium powder are ball-milled to obtain an initial mixed powder; based on the mass of the initial mixed powder, the zinc powder is 7 wt%, the cerium powder is 0.5 to 2 wt%, and the balance is tin powder;

[0009] B) Vacuum dry the initial mixed powder to obtain a mixed powder;

[0010] C) Under a protective atmosphere, the mixed powder is molded using a rapid prototyping process to obtain a tin-zinc-cerium composite material.

[0011] Preferably, the tin powder has a particle size of 20-35 μm, the zinc powder has a particle size of 30-50 μm, and the cerium powder has a particle size of 5-10 μm.

[0012] Preferably, in step A), the ball milling process specifically includes:

[0013] After the tin powder and zinc powder are ball-milled for the first time, cerium powder is added and ball-milled for the second time.

[0014] Preferably, the rotational speeds of the first ball milling and the second ball milling are independently 100–200 r / min;

[0015] The first ball milling time is 1 to 3 hours, and the second ball milling time is 1 to 3 hours.

[0016] Preferably, in step A), the process of introducing the protective atmosphere specifically involves: introducing an inert gas into the ball mill jar, and then releasing the mixed gas inside the jar through a gas valve; the protective atmosphere is argon or nitrogen; and anhydrous ethanol is used as a process control agent during the ball milling process.

[0017] Preferably, in step B), the vacuum drying temperature is 100–150°C and the time is 1–6 hours.

[0018] Preferably, in step C), the protective atmosphere is argon or nitrogen.

[0019] Preferably, in step C), the rapid prototyping process is specifically 3D printing technology, wherein the laser power of the 3D printing technology is 50-100W, the scanning rate is 10-200mm / s, the spot diameter is 50-100μm, the melt pool temperature is 200-800℃, the scanning interval is 0.05-0.08mm, and the powder thickness is 0.1-0.5mm.

[0020] Preferably, in step C), the laser power of the 3D printing technology is 50-70W, the scanning rate is 80-150mm / s, the controlled spot diameter is 60-80μm, the controlled melt pool temperature is 200-500℃, the scanning interval is 0.05-0.06mm, and the powder thickness is 0.1-0.2mm.

[0021] This application also provides a solder, including a tin-zinc-cerium composite material prepared by the preparation method described above.

[0022] This application provides a method for preparing a tin-zinc-cerium composite material. First, tin powder, zinc powder, and cerium powder are ball-milled and mixed to obtain an initial mixed powder. Then, the initial mixed powder is dried to obtain a final mixed powder. Finally, a rapid prototyping process is used to form the tin-zinc-cerium composite material. In this process, the introduction of cerium increases the electrode potential and impedance of the composite material, improves its oxidation resistance, and thus weakens the influence of oxides generated during welding on the wettability of the solder. Furthermore, the introduction of cerium can reduce the critical decomposition shear stress during plastic deformation, activate more cone slip, thereby forming solid dislocations, leading to cumulative strain hardening, improving the creep resistance of the Sn-Zn alloy, and thus inhibiting the growth of alloy whiskers. The rapid prototyping technology introduced in this application ensures that, when the solder is sufficiently cooled, the doped phase does not have time to precipitate and is retained in the Sn matrix, thereby preventing brittle precipitates from affecting the mechanical properties of the solder joint.

[0023] Therefore, the tin-zinc-cerium (Sn-7Zn-0.5-2Ce) composite material prepared in this application not only has good mechanical properties, but also good creep resistance. During the welding process, it can effectively inhibit the growth of Sn whiskers. At the same time, Ce can effectively improve the oxidation resistance of the Zn phase, thereby improving wettability. Attached Figure Description

[0024] Figure 1 Impedance curves of the tin-zinc-cerium composite materials prepared in Examples 1 and 2 of this invention;

[0025] Figure 2 The electrode potential curves are shown for the tin-zinc-cerium composite materials prepared in Examples 1 and 2 of this invention.

[0026] Figure 3 These are creep strain curves of the tin-zinc-cerium composite materials prepared in Examples 1 and 2 of this invention at different times;

[0027] Figure 4 The graphs show the minimum creep strain curves of the tin-zinc-cerium composite materials prepared in Examples 1 and 2 of this invention under different pressures.

[0028] Figure 5 The above are bar graphs showing the shear strength of the tin-zinc-cerium composite materials prepared in Examples 1 and 2 of this invention.

[0029] Figure 6 This is a schematic diagram of the ball milling process in the preparation of the tin-zinc-cerium composite material of the present invention;

[0030] Figure 7This is a schematic diagram of the 3D printing technology in the preparation process of the tin-zinc-cerium composite material of the present invention. In the figure, 1-powder conveying system, 2-rising piston, 3-powder bed, 4-falling piston, 5-part, 6-fiber laser, 7-galvanometer system, 8-laser beam. Detailed Implementation

[0031] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0032] In view of the performance defects of tin-based inorganic lead materials in the prior art, this application provides a method for preparing tin-zinc-cerium composite materials. This method uses tin powder, zinc powder, and cerium powder as raw materials and introduces a rapid prototyping process. A high cooling rate suppresses the precipitation of the zinc phase in the tin-zinc alloy, reducing the mechanical collapse of the molded part due to brittleness. Simultaneously, the introduction of cerium effectively inhibits zinc oxidation, thereby improving wettability during soldering. Furthermore, cerium reduces the critical decomposition shear stress during plastic deformation, activating more cone slip and forming solid dislocations, leading to cumulative strain hardening, improving creep resistance, and inhibiting the growth of alloy whiskers. This reduces the occurrence of short circuits in narrow-pitch QFP and other component leads caused by whiskers in high-temperature, humid, and stressful environments. Specifically, this invention discloses a method for preparing a tin-zinc-cerium composite material, including the following steps:

[0033] A) Under a protective atmosphere, tin powder, zinc powder and cerium powder are ball-milled to obtain an initial mixed powder; based on the mass of the initial mixed powder, the zinc powder is 7 wt%, the cerium powder is 0.5 to 2 wt%, and the balance is tin powder;

[0034] B) Vacuum dry the initial mixed powder to obtain a mixed powder;

[0035] C) Under a protective atmosphere, the mixed powder is molded using a rapid prototyping process to obtain a tin-zinc-cerium composite material.

[0036] In the preparation process of tin-zinc-cerium composite materials, this application first prepares raw materials tin powder, zinc powder, and cerium powder. Zn and Sn can form a eutectic alloy with good solder properties, but Zn is easily oxidized, which easily leads to poor solder wettability. Moreover, the Zn phase is easily precipitated during solidification, which does not significantly improve the creep resistance of Sn. This application introduces Ce to inhibit the precipitation of the Zn phase, thus maximizing the beneficial effects of Sn-Zn. At the same time, Ce can also improve the creep resistance and oxidation resistance of the alloy. In this application, based on the total mass of tin powder, zinc powder, and cerium powder, the zinc powder is 7 wt%, the cerium powder is 0.5 to 2 wt%, more specifically, the cerium powder is 0.5 wt%, 1.0 wt%, 1.5 wt%, or 2.0 wt%, with the balance being tin powder. The above-mentioned amounts of cerium powder can effectively inhibit the growth of tin whiskers by suppressing dislocation movement during the forming process. However, excessive introduction will hinder the above-mentioned effects. This application then ball-mills the tin powder, zinc powder, and cerium powder to obtain an initial mixed powder; the ball-milling process is specifically as follows:

[0037] After the tin powder and zinc powder are ball-milled for the first time, cerium powder is added and ball-milled for the second time.

[0038] In the above process, the rotation speed of the first and second ball milling is independently 100-200 r / min; the time for the first ball milling is 1-3 h, and the time for the second ball milling is 1-3 h; specifically, the rotation speed of the first and second ball milling is independently 120-180 r / min; the time for the first ball milling is 1.5-2.5 h, and the time for the second ball milling is 1.5-2.5 h. The above ball milling process can prevent powder agglomeration caused by oxidation, thus ensuring the forming quality of the solder. A protective atmosphere needs to be introduced during the ball milling process. The specific process is as follows: an inert gas is introduced into the ball milling jar, and then the mixed gas inside the jar is released through a gas valve. The ball milling process of this application is specifically as follows: Figure 6 As shown, Figure 6 As shown, during the ball milling process, the powder particles are continuously squeezed, collided, cold-welded, and refined under the action of the grinding balls, eventually yielding the initial mixed powder.

[0039] According to the present invention, after obtaining the mixed powder, it is vacuum dried to evaporate the anhydrous ethanol, a process control agent during the ball milling process, to obtain the mixed powder. The vacuum drying temperature is 100-150°C and the time is 1-6 hours; more specifically, the vacuum drying temperature is 100-130°C and the time is 2-5 hours.

[0040] Finally, the mixed powder is formed under a protective atmosphere using a rapid prototyping process to obtain tin-zinc-cerium composite powder. In this process, the protective atmosphere is nitrogen or argon. The rapid prototyping process is specifically 3D printing technology. Specifically, the laser power of the 3D printing technology is 50–100W, the scanning rate is 10–200 mm / s, the spot diameter is 50–100 μm, the melt pool temperature is 200–800℃, the scanning interval is 0.05–0.08 mm, and the powder thickness is 0.1–0.5 mm. More specifically, the laser power of the 3D printing technology is 50–70W, the scanning rate is 80–150 mm / s, the controlled spot diameter is 60–80 μm, the controlled melt pool temperature is 200–500℃, the scanning interval is 0.05–0.06 mm, and the powder thickness is 0.1–0.2 mm. The above process parameters ensure good forming quality of the tin-zinc-cerium composite material, a stable and continuous molten pool, effective suppression of zinc phase precipitation, and the formation of a stable product. The specific details of the 3D printing technology described in this application are as follows: Figure 7 As shown, 3D printing rapid prototyping technology uses laser as a heat source to melt metal and then rapidly cool it to form a shape. The process involves first designing a part model using 3D software (UG, SW, etc.) and discretizing it into a series of ordered 2D models; then feeding mixed powder under the action of a rising piston, with the powder conveying system controlling the powder spreading process; next, the laser beam emitted by the fiber laser forms digital information through the imported 2D model file, scanning and melting the spread metal powder with a set thickness; then the system performs a pre-set descent operation on the substrate, repeating the above process to finally process a 3D part.

[0041] This application preferably employs 3D printing technology so that Ce is not simply added in mixtures, but rather added through alloying. This causes the crystal lattices of Sn, Zn, and Ce to interfere with each other, resulting in lattice distortion. Furthermore, through rapid 3D printing technology, this binary or even ternary phase is preserved to the greatest extent possible, maximizing the role of Ce: effectively inhibiting zinc oxidation, thereby improving wettability during soldering; and by reducing the critical decomposition shear stress during plastic deformation, cerium activates more cone slip, thereby forming fixed dislocations, leading to cumulative strain hardening and improving creep resistance.

[0042] In this application, the tin powder has a particle size of 20-35 μm, the zinc powder has a particle size of 30-50 μm, and the cerium powder has a particle size of 5-10 μm.

[0043] Furthermore, this application also provides a solder comprising the tin-zinc-cerium composite material prepared by the preparation method described above.

[0044] The method for preparing the tin-zinc-cerium composite material provided by this invention improves the performance of the composite material as a solder by introducing rapid prototyping technology and the rare earth element Ce. The rapid prototyping technology features rapid melting and cooling; when the solder is fully cooled, the dopant phase does not have time to precipitate and is retained in the Sn matrix, thus preventing brittle precipitates from affecting the mechanical properties of the solder joint. The introduction of Ce improves the creep resistance and oxidation resistance of the Sn-Zn alloy. Therefore, the Sn-7Zn-0.5-2Ce solder composite material provided by this invention not only has good mechanical properties but also excellent creep resistance. During the soldering process, it can effectively suppress the growth of Sn whiskers, thereby effectively reducing bridging problems caused by dense pins and small spacing, improving the product's survivability in harsh environments and its application prospects in high-end chips.

[0045] To further understand the present invention, the preparation method of the tin-zinc-cerium composite material provided by the present invention will be described in detail below with reference to the embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0046] Example 1

[0047] The composition of Sn-7Zn-0.5Ce is tin matrix, 7wt% Zn powder and 0.5wt% Ce. The particle sizes are 20-35μm, Zn particle size is 30-50μm and Ce particle size is 5-10μm.

[0048] Tin powder, Zn powder, and Ce powder were mixed, and a certain amount of anhydrous ethanol was added to the ball mill jar as a process control agent. Inert gas N2 was introduced into the ball mill jar to reach a certain pressure, and then the mixed gas in the jar was released through the gas valve. The rotation speed was set to 120 rad / min, and the ball milling time was 1 to 3 hours each time new powder was added. After mixing, the vacuum drying temperature was 100 to 130℃, and the drying time was 2 to 6 hours. The Sn-7Zn-0.5Ce composite material was obtained by 3D printing with a laser power of 60W, a scanning rate of 80mm / s, a controlled spot diameter of 70μm, a controlled melt pool temperature of 200 to 300℃, a scanning interval of 0.05 to 0.06mm, and a powder thickness of 0.1 to 0.2mm.

[0049] Electrochemical test results showed that the impedance and electrode potential of Sn were -0.16 V and 87 Ω·cm, respectively. 2 Sn-7Zn has a voltage of -0.20V and an Ω·cm, respectively. 2 Sn-7Zn-0.5Ce have values ​​of -0.21V and 130Ω·cm, respectively. 2 ,like Figure 1 and 2As shown, the introduction of Ce significantly improves the oxidation resistance of solder and effectively reduces the influence of oxides on solder wettability.

[0050] Creep resistance test results show that at room temperature and under a constant creep force of 30 MPa, Sn-7Zn-0.5Ce exhibits a creep resistance of nearly 10%. Figure 3 and 4 As shown, it is significantly higher than Sn and Sn-7Zn.

[0051] Mechanical test results show that the shear strength of Sn-7Zn-0.5Ce reaches 25 MPa. Figure 5 As shown, it is higher than Sn and Sn-7Zn.

[0052] In the above embodiments, the relevant properties of Sn and Sn-7Zn in terms of electrochemical performance, creep resistance and mechanical properties are described in the prior art.

[0053] Example 2

[0054] The formulations consisting of a tin matrix, 7 wt% Zn powder, and 0.5 wt%, 1 wt%, and 2 wt% Ce are Sn-7Zn-0.5Ce, Sn-7Zn-1Ce, and Sn-7Zn-2Ce; the particle sizes of Sn, Zn, and Ce are 20–35 μm, 30–50 μm, and 5–10 μm, respectively.

[0055] Tin powder, Zn powder, and Ce powder were mixed, and a certain amount of anhydrous ethanol was added to the ball mill jar as a process control agent. Inert gas N2 was introduced into the ball mill jar to reach a certain pressure, and then the mixed gas in the jar was released through the gas valve. The rotation speed was set to 120 rad / min, and the ball milling time was 1 to 3 hours each time new powder was added. After mixing, the vacuum drying temperature was 100 to 130℃, and the drying time was 2 to 6 hours. Laser printing was performed with a laser power of 60W, a scanning rate of 80mm / s, a controlled spot diameter of 70μm, a controlled melt pool temperature between 200 and 300℃, a scanning interval of 0.05 to 0.06mm, and a powder thickness of 0.1 to 0.2mm to obtain Sn-7Zn-0.5Ce, Sn-7Zn-1Ce, and Sn-7Zn-2Ce, respectively.

[0056] Electrochemical test results showed that the impedance and electrode potential of Sn-7Zn-0.5Ce were -0.21V and 130Ω·cm, respectively. 2 Sn-7Zn-1Ce are respectively 170Ω·cm 2 And -0.21V, Sn-7Zn-2Ce are 140Ω·cm 2 and -0.28V, such as Figure 1 and 2As shown, compared to the previous method, the introduction of Ce resulted in higher electrode potential and impedance values, indicating a significant improvement in the oxidation resistance of the solder and effectively reducing the impact of oxides on the solder's wettability.

[0057] Creep resistance test results show that, at room temperature and under a constant creep force of 30 MPa, the creep resistance of Sn-7Zn-1Ce is significantly higher than that of Sn-7Zn-0.5Ce and Sn-7Zn-2Ce, reaching 18%. Meanwhile, the strain-time relationship was described using a power-law equation.

[0058] ε=Aσ n exp(-Q / RT)

[0059] Where ε is the minimum creep rate, A is a dimensionless constant, σ is the applied creep stress, n is the stress exponent, Q is the creep activation energy, and R and T are the gas constant (8.31 J / mol) and absolute temperature, respectively. Figure 3 and 4 As shown, the introduction of Ce can further improve the creep resistance of Sn, thereby effectively suppressing the growth of Sn whiskers during the welding process after rapid melting and cooling.

[0060] Mechanical test results show that Sn-7Zn-1Ce has better mechanical properties, reaching 33 MPa. Figure 5 As shown, this is because the precipitation of the initial Zn phase is suppressed.

[0061] Comparative Example 1

[0062] Sn-7Zn-1Ce is prepared by fixing 7wt% Zn powder and 1wt% Ce onto a tin matrix. The particle sizes of Sn, Zn and Ce are 20-35 μm, 30-50 μm and 5-10 μm, respectively.

[0063] Tin powder, Zn powder, and Ce powder were mixed, and a certain amount of anhydrous ethanol was added to the ball mill jar as a process control agent. Inert gas N2 was introduced into the ball mill jar to reach a certain pressure, and then the mixed gas in the jar was released through the gas valve. The rotation speed was set to 120 rad / min, and the ball milling time was 1 to 3 hours each time new powder was added. After mixing, the vacuum drying temperature was 100 to 130℃, and the drying time was 2 to 6 hours. Laser printing was performed with a laser power of 120W, a scanning rate of 40 mm / s, a controlled spot diameter of 70 μm, a controlled melt pool temperature between 200 and 300℃, a scanning interval of 0.05 to 0.06 mm, and a powder thickness of 0.1 to 0.2 mm to obtain Sn-7Zn-1Ce.

[0064] Under forming parameters of 120W laser power and 40mm / s scanning rate, the printed surface of Sn-7Zn-1Ce has large cracks and pores formed by element vaporization, making it almost impossible to form and impossible to evaluate other properties.

[0065] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0066] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a tin-zinc-cerium composite material, comprising the following steps: A) Under a protective atmosphere, tin powder, zinc powder and cerium powder are ball-milled to obtain an initial mixed powder; based on the mass of the initial mixed powder, the zinc powder is 7 wt%, the cerium powder is 0.5~2 wt%, and the balance is tin powder; B) Vacuum dry the initial mixed powder to obtain a mixed powder; C) Under a protective atmosphere, the mixed powder is formed using a rapid prototyping process to obtain a tin-zinc-cerium composite material; the rapid prototyping process allows Ce to be added in an alloying manner, causing the crystal lattices of the three elements Sn-Zn-Ce to interfere with each other, producing crystal lattice distortion, and through rapid 3D printing technology, this binary or even ternary phase is preserved to the greatest extent, maximizing the role of Ce. The rapid prototyping process is specifically 3D printing technology, wherein the laser power of the 3D printing technology is 60~70W, the scanning rate is 10~200mm / s, the spot diameter is 50~100μm, the melt pool temperature is 200~800℃, the scanning interval is 0.05~0.08mm, and the powder thickness is 0.1~0.5mm.

2. The preparation method according to claim 1, characterized in that, The tin powder has a particle size of 20-35 μm, the zinc powder has a particle size of 30-50 μm, and the cerium powder has a particle size of 5-10 μm.

3. The preparation method according to claim 1, characterized in that, In step A), the ball milling process specifically includes: After the tin powder and zinc powder are ball-milled for the first time, cerium powder is added and ball-milled for the second time.

4. The preparation method according to claim 3, characterized in that, The rotational speeds of the first and second ball milling processes are independently 100-200 r / min; The first ball milling time is 1-3 hours, and the second ball milling time is 1-3 hours.

5. The preparation method according to claim 1 or 3, characterized in that, In step A), the process of introducing the protective atmosphere specifically involves: introducing an inert gas into the ball mill jar, and then releasing the mixed gas inside the jar through a gas valve; the protective atmosphere is argon or nitrogen; and anhydrous ethanol is used as a process control agent during the ball milling process.

6. The preparation method according to claim 1, characterized in that, In step B), the vacuum drying temperature is 100~150℃ and the time is 1~6h.

7. The preparation method according to claim 1, characterized in that, In step C), the protective atmosphere is argon or nitrogen.

8. The preparation method according to claim 1, characterized in that, In step C), the laser power of the 3D printing technology is 50~70W, the scanning rate is 80~150mm / s, the controlled spot diameter is 60~80μm, the controlled melt pool temperature is 200~500℃, the scanning interval is 0.05~0.06mm, and the powder thickness is 0.1~0.2mm.

9. A solder comprising a tin-zinc-cerium composite material prepared by the preparation method according to any one of claims 1 to 8.

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