Method for reducing anisotropy of intermetallic compound Cu6Sn5

Abstract

The invention relates to a method for reducing anisotropy of an intermetallic compound Cu6Sn5, and belongs to the technical field of lead-free welding. The method comprises the following steps: doping alloy elements such as Ag, Ni / Co or Ni / Co / Ag into Cu6Sn5, forming a ternary phase intermetallic compound under a high-temperature condition, and stabilizing a Cu6Sn5 crystal structure. The doped elements enhance the structural stability through displacement solid solution and orbital hybridization, inhibit lattice anisotropy and hardness difference, and improve the mechanical properties of the material. The prepared alloy shows that the anisotropy is obviously reduced in the aspects of Vickers hardness, lattice constant, elasticity modulus and the like through verification of a first principle and testing of multiple groups of samples. According to the method, the reliability and the service life of the welding spot structure can be improved and prolonged without a complex processing flow, and the method is suitable for interface stability enhancement and service performance optimization of the lead-free solder welding spot.

Description

Technical Field

[0001] The present invention relates to a method for reducing the anisotropy of the intermetallic compound Cu6Sn5, and belongs to the technical field of aluminum alloys. Background Art

[0002] Lead-free soldering technology is a method to replace traditional lead-based soldering technology. Currently, the most widely used solder in the market is SAC lead-free solder, and the intermetallic compound most easily formed by the reaction of lead-free SAC solder and Cu substrate is Cu6Sn5. Regarding the main failure mode of SAC / Cu solder joints, it is considered that the hard and brittle phase Cu6Sn5 in the interfacial layer undergoes a phase structure transformation during solidification and crystallization in the soldering process, resulting in volume changes and causing microcracks in the interfacial layer. Under the combined action of thermal fatigue, large current, and mechanical shock during long-term service, the continuous growth of the anisotropic structure of Cu6Sn5 will accumulate anisotropy in morphology, as well as anisotropy in thermal and mechanical properties, which will accelerate the fracture of the solder joint interface, thereby reducing reliability and shortening the service life.

[0003] In order to improve the stability of Cu6Sn5 and inhibit the oriented growth of Cu6Sn5 at the interface, alloying is one of the main methods to improve its stability. By adding trace elements to form a solid solution of Cu6Sn5 and form a new ternary phase intermetallic compound, the anisotropy can be weakened during the soldering solidification process, thereby effectively inhibiting problems such as the growth of interfacial intermetallic compounds and voids. Summary of the Invention

[0004] Aiming at the problems of poor mechanical properties of the brazed joint and insufficient solder joint reliability during the welding process of existing Sn-based lead-free solder and Cu substrate, the present invention proposes a method for reducing the anisotropy of the intermetallic compound Cu6Sn5. This method is based on first-principles calculations to determine the optimal doping content and doping position of alloying elements Ag, Ni / Co, or Ni / Co / Ag, and evaluate their effects on the anisotropy of Cu6Sn5. On this basis, by doping the above alloying elements into Cu6Sn5, a ternary phase intermetallic compound (such as (Cu,Ni)6Sn5) is formed by dissolution under high-temperature conditions, stabilizing the crystal structure of Cu6Sn5 from the source and inhibiting the formation of anisotropy. The obtained doped Cu6Sn5 alloy exhibits better structural stability and mechanical properties during aging and service, and can effectively inhibit the excessive growth of interfacial intermetallic compounds and the generation of void defects. By reducing anisotropy and improving mechanical properties, the reliability and service life of the solder joint are synchronously enhanced.

[0005] A method for reducing the anisotropy of the intermetallic compound Cu6Sn5, the specific steps are as follows:

[0006] (1) Use first-principles calculations to study the effect of the content of Ag, Ni / Co, and Ni / Co / Ag on the anisotropy of Cu6Sn5.

[0007] (2) Mix high-purity Sn powder, high-purity Cu powder, and dopant powder by ball milling to obtain a mixed powder; the dopant powder is Ag powder, Ni / Co mixed powder, or Ni / Co / Ag mixed powder.

[0008] (3) Gradually heat the mixed powder at a constant rate to 900 - 1000 °C and keep it at this temperature for 4 - 6 h, then cool it to room temperature to obtain the intermetallic compound Cu6Sn5.

[0009] Preferably, by mass percentage, in the mixed powder of step (1), the Sn powder accounts for 55 - 60%, the Cu powder accounts for 54 - 58%, and the dopant powder accounts for 2 - 8%.

[0010] Preferably, in the Ni / Co mixed powder, the mass ratio of Ni powder to Co powder is 0.5 - 1:1, and in the Ni / Co / Ag mixed powder, the mass ratio of Ni powder, Co powder, and Ag powder is 0.3 - 1:0.6 - 1:1.

[0011] Preferably, the heating rate in step (2) is 5 - 10 °C / min.

[0012] The beneficial effects of the present invention are as follows:

[0013] (1) By doping alloying elements (such as Ni, Co, Ag) into Cu6Sn5, ternary-phase intermetallic compounds are formed with Cu6Sn5 at high temperatures. For example, Ni atoms can replace Cu atoms and enter the η-Cu6Sn5 lattice to form η-(Cu,Ni)6Sn5, thereby stabilizing its crystal structure. Orbital hybridization occurs between the doping elements and Cu and Sn atoms, enhancing the bonding stability, effectively reducing the structural anisotropy of Cu6Sn5, improving its mechanical properties, and further inhibiting the abnormal growth of interfacial intermetallic compounds and void defects, thus improving the reliability of lead-free solder joints.

[0014] (2) The present invention uses first-principles calculations to optimize the types and doping ratios of doping elements, providing theoretical guidance for alloy design. Without introducing complex process flows, a significant reduction in the anisotropy of Cu6Sn5 can be achieved, effectively enhancing the stability and service life of the solder joint interface structure. Description of the Drawings

[0015] Figure 1 SEM image of Cu6Sn5 doped with Ni / Co / Ag in Example 1;

[0016] Figure 2 XRD patterns of Cu6Sn5 doped with Ni / Co / Ag in Examples 1 - 2;

[0017] Figure 3 The three-dimensional hardness diagram of Cu6Sn5 doped with Examples 1 and 2 was calculated using first-principles;

[0018] Figure 4 The three-dimensional bulk modulus diagram of Cu6Sn5 doped with Examples 1 and 2 was calculated using first-principles;

[0019] Figure 5 The three-dimensional Young's modulus diagram of Cu6Sn5 doped with Examples 1 and 2 was calculated using first-principles;

[0020] Figure 6 The SEM image of Ni / Co mixed-doped Cu6Sn5 in Example 3;

[0021] Figure 7 The XRD pattern of Ni / Co mixed-doped Cu6Sn5 in Example 3; Figure 8 The SEM image of Ag-doped Cu6Sn5 in Example 4; Figure 9 The XRD pattern of Ag-doped Cu6Sn5 in Example 4. Specific Embodiments

[0022] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0023] Example 1: A method for reducing the anisotropy of the intermetallic compound Cu6Sn5, the specific steps are as follows:

[0024] (1) Use first-principles calculations to study the effect of the content of Ni / Co / Ag on the anisotropy of Cu6Sn5;

[0025] (2) Ball-mill and mix high-purity Sn powder, high-purity Cu powder, and dopant powder (Ni / Co / Ag mixed powder) for 4 h to obtain a mixed powder; by mass percentage, the Sn powder in the mixed powder accounts for 58%, the Cu powder accounts for 36%, the dopant Ni powder accounts for 1%, the dopant Co powder accounts for 2%, and the dopant Ag powder accounts for 3%;

[0026] (3) Heat the mixed powder at a constant heating rate of 8 °C / min to 950 °C and keep it at a constant temperature for 4 h, then cool it to room temperature to obtain Ni / Co / Ag-doped intermetallic compound Cu6Sn5;

[0027] Taking the undoped intermetallic compound Cu6Sn5 as the comparative example, the hardness test data of 10 specimens are shown in Table 1,

[0028] Table 1 Hardness of undoped intermetallic compound Cu6Sn5

[0029]

[0030] The Vickers hardness of the undoped intermetallic compound Cu6Sn5 ranges from 200 to 510 HV;

[0031] The hardness test data of 10 specimens of the Ni / Co / Ag mixed-doped Cu6Sn5 alloy in this example are shown in Table 2.

[0032] Table 2 Hardness of Ni / Co / Ag mixed-doped Cu6Sn5 alloy

[0033]

[0034] As can be seen from Table 2, the Vickers hardness of the Ni / Co / Ag mixed-doped Cu6Sn5 alloy in this example ranges from 600 to 800 HV. Compared with the range of the Vickers hardness of the undoped intrinsic intermetallic compound Cu6Sn5 alloy (200 - 510 HV), the range between the maximum and minimum hardness values has shrunk, indicating that the addition of Ni and Co elements suppresses the anisotropy of hardness and improves the mechanical properties relative to the intrinsic intermetallic compound Cu6Sn5;

[0035] The SEM image of Ni / Co / Ag mixed-doped Cu6Sn5 is shown in Figure 1 , and the XRD pattern Figure 2 ; The lattice constants calculated from the Cu6Sn5 diffraction peaks are shown in Table 3. After doping with Ni, Co, and Ag elements, the lattice constants shrink in all three directions of a, b, and c, and the unit cell volume decreases accordingly, and the shrinkage amplitude of each axis is close, indicating that the crystal structure tends to be uniform and the structural anisotropy is significantly suppressed; The mechanical properties of this structure are simulated using the first-principles method. Figures 3 to 5 They are three-dimensional visualization diagrams of the hardness (H), bulk modulus (B), and Young's modulus (E) of the doped samples respectively. It can be observed from the figures that the anisotropy shows a decreasing trend in all three modulus dimensions, which is highly consistent with the measured hardness data, further verifying the positive regulation effect of the doping design on the structural stability and mechanical properties of Cu6Sn5.

[0036] Example 2: A method for reducing the anisotropy of the intermetallic compound Cu6Sn5, the specific steps are as follows:

[0037] (1) Calculate the influence of the content of Ni / Co / Ag on the anisotropy of Cu6Sn5 using first-principles calculations; Mix high-purity Sn powder, high-purity Cu powder, and dopant powder (Ni / Co / Ag mixed powder) by ball milling for 4 h to obtain a mixed powder; By mass percentage, the Sn powder in the mixed powder accounts for 59%, the Cu powder accounts for 38%, the dopant Ni powder accounts for 1%, the dopant Co powder accounts for 1%, and the dopant Ag powder accounts for 1%;

[0038] (2) The mixed powder is heated uniformly at a heating rate of 10 °C / min to a temperature of 900 °C and kept at a constant temperature for melting for 5 h, and then cooled to room temperature to obtain Ni / Co / Ag-doped intermetallic compound Cu6Sn5;

[0039] The XRD pattern of the Ni / Co / Ag mixed-doped Cu6Sn5 alloy in this example is shown in Figure 2 , and the lattice constants are calculated from the experimental diffraction peaks of Cu6Sn5 as shown in Table 3 below,

[0040] Table 3 Lattice constants of Ni / Co / Ag mixed-doped Cu6Sn5 alloys in Examples 1-2

[0041]

[0042] After doping with Ni / Co / Ag elements, the lattice constants contract in all three directions of a, b, and c, resulting in an overall reduction in the unit cell volume. Since the contraction amplitudes in each axis direction are close, the unit cell shape becomes more uniform, thus suppressing the anisotropy of the crystal structure.

[0043] The hardness test data of 10 specimens of the Ni / Co / Ag mixed-doped Cu6Sn5 alloy in this example are shown in Table 4,

[0044] Table 4 Hardness of Ni / Co mixed-doped Cu6Sn5 alloy

[0045]

[0046] As can be seen from Table 4, the Vickers hardness range of the Ni / Co / Ag mixed-doped Cu6Sn5 alloy in this example is 500 - 670 HV. Compared with the Vickers hardness range (200 - 510 HV) of the undoped intrinsic intermetallic compound Cu6Sn5 alloy, the range between the maximum and minimum hardness values has shrunk, indicating that the addition of Ni, Co, and Ag elements suppresses the anisotropy of hardness and improves the mechanical properties relative to the intrinsic intermetallic compound Cu6Sn5;

[0047] Calculate the structural stiffness coefficient of this doping system using first-principles calculations, and perform three-dimensional visualization analysis on the hardness (H), bulk modulus (B), and Young's modulus (E) respectively. The results are shown in Figure 3 、Figure 4 and Figure 5 As shown in Figure 5 , it can be seen that the distributions of various moduli in different crystal axis directions tend to be consistent, indicating that the doping treatment effectively reduces the anisotropy of the crystal structure, which is in good agreement with the hardness results obtained from experiments.

[0048] Example 3: A method for reducing the anisotropy of intermetallic compound Cu6Sn5, the specific steps are as follows:

[0049] (1) Use first-principles calculations to study the effect of the content of Ni / Co on the anisotropy of Cu6Sn5; ball-mill and mix high-purity Sn powder, high-purity Cu powder, and dopant powder (Ni / Co powder) for 4 h to obtain a mixed powder; by mass percentage, the Sn powder in the mixed powder accounts for 59%, the Cu powder accounts for 38%, the dopant Ni powder accounts for 1.5%, and the dopant Co powder accounts for 1.5%;

[0050] (2) The mixed powder is heated at a uniform heating rate of 8 °C / min to a temperature of 900 °C and held for 4 h for constant-temperature melting, and then cooled to room temperature to obtain Ni / Co-doped intermetallic compound Cu6Sn5;

[0051] The hardness test data of 10 specimens of the Ni / Co-doped Cu6Sn5 alloy in this example are shown in Table 5,

[0052] Table 5 Hardness of Ni / Co-doped Cu6Sn5 alloy

[0053]

[0054] As can be seen from Table 5, the Vickers hardness range of the Ni / Co mixed-doped Cu6Sn5 alloy in this example is 380 - 440 HV. Compared with the Vickers hardness range (200 - 510 HV) of the undoped intrinsic intermetallic compound Cu6Sn5 alloy, the range between the maximum and minimum hardness values is reduced, indicating that the addition of Ni / Co elements suppresses the anisotropy of hardness relative to the intrinsic intermetallic compound Cu6Sn5;

[0055] Perform SEM scanning on the surface morphology of the alloy sample, and the results are shown in Figure 6 , XRD is shown in Figure 7 , and the lattice constants are calculated from the experimental diffraction peaks of Cu6Sn5 as shown in Table 6,

[0056] Table 6 Lattice constant table of Ni / Co-doped Cu6Sn5 alloy

[0057]

[0058] After doping with Ni / Co atoms, its lattice constants contract in both the a and c directions, and the unit cell volume also becomes smaller, which suppresses its structural anisotropy.

[0059] Example 4: A method for reducing the anisotropy of intermetallic compound Cu6Sn5, the specific steps are as follows:

[0060] (1) Use first-principles calculations to study the effect of Ag content on the anisotropy of Cu6Sn5; mix high-purity Sn powder, high-purity Cu powder, and dopant powder (Ag powder) by ball milling for 4 h to obtain a mixed powder; by mass percentage, the Sn powder in the mixed powder accounts for 58%, the Cu powder accounts for 36%, and the dopant Ag powder accounts for 6%;

[0061] (2) Heat the mixed powder at a uniform heating rate of 5 °C / min to 950 °C and keep it at a constant temperature for 6 h, then cool it to room temperature to obtain Ag-doped intermetallic compound Cu6Sn5;

[0062] The hardness test data of 10 specimens of the Ag-doped Cu6Sn5 alloy in this example are shown in Table 7,

[0063] Table 7 Hardness of Ag-doped Cu6Sn5 alloy

[0064]

[0065] As can be seen from Table 7, the Vickers hardness range of the Ag-mixed doped Cu6Sn5 alloy in this example is 450 - 560 HV. Compared with the Vickers hardness range of the undoped intrinsic intermetallic compound Cu6Sn5 alloy (200 - 510 HV), the range between the maximum and minimum hardness values shrinks, indicating that adding Ag element suppresses the hardness anisotropy relative to the intrinsic intermetallic compound Cu6Sn5;

[0066] Perform SEM scanning on the surface morphology of the alloy sample, and the results are shown in Figure 8 , XRD is shown in Figure 9 , and the lattice constants obtained from the experimental diffraction peaks of Cu6Sn5 are calculated as shown in Table 8,

[0067] Table 8 Lattice constant table of Ag-doped Cu6Sn5 alloy

[0068]

[0069] The lattice constants contract in both the a and c directions, and the unit cell volume becomes smaller, which suppresses its structural anisotropy.

[0070] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present invention within the scope of knowledge possessed by those of ordinary skill in the art.

Claims

1. A method for reducing the anisotropy of the intermetallic compound Cu6Sn5, characterized in that The specific steps are as follows: (1) Use first-principles calculations to study the effect of the contents of Ag, Ni / Co, and Ni / Co / Ag on the anisotropy of Cu6Sn5; (2) Ball-mill and mix high-purity Sn powder, high-purity Cu powder, and dopant powder to obtain a mixed powder; the dopant powder is Ag powder, Ni / Co mixed powder, or Ni / Co / Ag mixed powder; (3) Heat the mixed powder at a constant rate to 900-1000 °C and keep it molten for 4-6 h, then cool it to room temperature to obtain the intermetallic compound Cu6Sn5.

2. The method for reducing the anisotropy of the intermetallic compound Cu6Sn5 according to claim 1, wherein: By mass percentage, in the mixed powder of step (1), the Sn powder accounts for 55-60%, the Cu powder accounts for 54-58%, and the dopant powder accounts for 2-8%.

3. The method for reducing the anisotropy of the intermetallic compound Cu6Sn5 according to claim 1 or 2, characterized in that: In the Ni / Co mixed powder, the mass ratio of Ni powder to Co powder is 0.5-1:1, and in the Ni / Co / Ag mixed powder, the mass ratio of Ni powder, Co powder, and Ag powder is 0.3-1:0.6-1:

1.

4. The method for reducing the anisotropy of the intermetallic compound Cu6Sn5 according to claim 1, wherein: In step (2), the heating rate is 5-8 °C / min.

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