A heat treatment process for improving wettability of a tin-based solder alloy by controlling grain orientation

Abstract

The application discloses a heat treatment process for improving wettability of tin-based solder alloy by regulating grain orientation, and belongs to the technical field of alloy solder.The tin-based solder alloy comprises 62-67.6% of Sn, 0.3-0.8% of Bi, 1.5-2% of Ag, 0.3-0.6% of Cu, 0.02-0.1% of Ni and inevitable impurities according to mass percentage.The heat treatment process for improving wettability of the solder alloy by regulating grain orientation comprises the following steps: eliminating long-range order of grains by applying an external disordered magnetic field, cold rolling after hot rolling, gradient magnetic field annealing and oil quenching cooling processes, and finally, the long-range order of grains is eliminated, the beta-Sn grain is short-range ordered in the (110) crystal direction, and the wetting angle of Cu6Sn5 and the substrate Sn reaches 51.7°, thereby achieving the purpose of improving the wettability of the solder alloy.

Description

Technical Field

[0001] This invention relates to a heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation, belonging to the field of alloy solder technology. Background Technology

[0002] During brazing, molten solder spreads and wets the substrate surface. Good wettability ensures stable interconnection between the substrate and the solder, resulting in a reliable solder joint. Studying the interfacial microstructure and properties of the solder joint and improving the wettability of the solder are currently the key and challenging aspects of solder alloy research. Since magnetic fields can affect the atomic arrangement and orientation at the interface between the solder alloy and the substrate, making it more conducive to wetting in the liquid state, magnetic field control is widely used to improve the wettability of the solder by changing the grain orientation. This has been widely applied to improve the joint quality.

[0003] Currently, tin-based lead-free solders are widely used in the welding industry due to their environmental friendliness and low melting point. However, their poor wettability leads to insufficient welding quality. Therefore, improving the wettability of tin-based lead-free solders is a current focus of the industry and is also the problem addressed by this invention. Research has found that Nd doping affects the wettability of solders, which improves wettability from the perspective of solder composition. In addition, adding nanomaterials can increase the fluidity of the solder and improve wettability. Research has also found that as the Zn content in the substrate increases, the interfacial wetting force first increases and then decreases, while the wetting time first decreases and then increases. This study examines the impact of substrate composition on wettability. Research has also found that as the temperature increases, the interfacial tension of the solder decreases, the atomic diffusion coefficient increases, and the wettability improves. This study explores the improvement of wetting performance by different brazing processes from the perspective of brazing technology. The above research shows that solder wettability is related to factors such as surface energy, surface tension, and interfacial area. Changes in grain orientation can regulate these factors. Therefore, this invention uses magnetic field to regulate grain orientation to improve solder wettability. Summary of the Invention

[0004] To address the problems existing in current solder alloys, this invention provides a heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation. The process involves controlling the grain orientation of the solder alloy through gradient magnetic field heat treatment, combined with hot rolling followed by cold rolling and oil quenching to prepare the solder alloy. The specific processing steps are as follows:

[0005] (1) The solder alloy is obtained by smelting Sn, Bi, Ag, Cu, Ni and unavoidable impurities and water cooling (ordinary smelting and water cooling can be used here).

[0006] (2) The brazing alloy obtained in step (1) is heated using an induction heating furnace.

[0007] (3) Apply a disordered constant magnetic field (the magnetic field is a rotating magnetic field) to the brazing alloy processed in step (2).

[0008] (4) The brazing alloy treated in step (3) is hot rolled, and after the brazing alloy is cooled to room temperature, it is cold rolled in multiple passes to obtain a thin sheet of brazing alloy. The grain strength and hardness are first reduced by hot rolling, making the grains easier to deform, and then cold rolling is performed to form a recrystallization texture. <110> .

[0009] (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing. During the gradient magnetic field annealing process, the magnetic anisotropy will cause a strong energy difference related to orientation, which will provide additional driving force for grain boundary migration.

[0010] (6) The brazing alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain tin-based brazing alloy.

[0011] Preferably, in step (1), the total mass percentage of Sn, Bi, Ag, Cu, Ni and unavoidable impurities is 100%, including 62-67.6% Sn, 0.3-0.8% Bi, 1.5-2% Ag, 0.3-0.6% Cu, 0.02-0.1% Ni, and the balance being unavoidable impurities.

[0012] Preferably, in step (2), the brazing alloy is heated to 230-250°C to eliminate the long-range ordered crystal structure in the sample. Before heating, the positive and negative poles of the rotating magnetic field have been connected to both ends of the brazing alloy.

[0013] Preferably, in step (3), the magnetic field strength is controlled at 12 to 16T, the superimposed magnetic field direction is rotated 180° every 200μs, the temperature is controlled between 225 and 250℃, and the temperature is controlled before the recrystallization temperature, so as to facilitate the subsequent magnetic field heat treatment to obtain grains with a certain orientation, and the reaction time is 30 to 50s.

[0014] Preferably, in step (4), the hot rolling temperature is controlled between 225 and 250°C, the cumulative total deformation during rolling is 58%, and the hot rolling is carried out in 5 passes with reductions of 5%, 8%, 10%, 15%, and 20%, respectively.

[0015] Preferably, in step (4), the total deformation of cold rolling is 74%, and five passes are used for rolling, with reductions of 6%, 10%, 14%, 20%, and 24% respectively. Cold rolling is carried out at room temperature, and the entire rolling process is done in an oil bath to prevent grain oxidation.

[0016] Preferably, in step (5), a three-gradient magnetic field annealing is used. The first gradient annealing temperature is 225℃ and the magnetic field strength is 0.1~0.6T. The second gradient annealing temperature is 175℃ and the magnetic field strength is 1.2~5T. The third gradient annealing temperature is 125℃ and the magnetic field strength is 6~12T. The annealing time for each step is 30s.

[0017] Preferably, step (5) needs to be repeated more than 5 times.

[0018] The principle of this invention: Compared to ordinary annealing, gradient magnetic field annealing increases the energy difference between different orientations due to increased magnetic anisotropy during recrystallization; in Sn-based solder alloys, <110> The direction with the highest permeability, lowest magnetic anisotropy, and lowest barrier to increase in magnetic field-induced free energy is achieved through the rolling process before annealing. <110> Texture, <110> The direction is parallel to the rolling direction, therefore <110> The growth of β-Sn grains in the direction of magnetic field is lower; on the other hand, the magnetic order generated by the magnetic field reduces atomic diffusion and reduces grain boundary mobility. <110> The directional texture is enhanced while other high-energy-storage orientations are suppressed.

[0019] Beneficial effects of the present invention

[0020] (1) The present invention obtains a tin-based solder alloy with β-Sn (110) crystal orientation by controlling the grain orientation through gradient magnetic field heat treatment, followed by hot rolling, cold deformation, and oil quenching, thereby achieving the purpose of improving the wettability of the tin-based solder alloy.

[0021] (2) Compared with the conventional tin-based solder alloy production process, magnetic field control and rolling are added. The disordered constant magnetic field makes the atomic long-range more disordered and the grain size smaller. Rolling makes the grains form an orientation relationship, and β-Sn is more inclined to the (110) crystal orientation.

[0022] (3) Compared with the conventional tin-based solder alloy production process, gradient magnetic field heat treatment is adopted, which makes the (110) crystal grow along this direction. At the same time, a combination of strong magnetic field and low temperature is adopted, and heat treatment is carried out in a cycle with increasing magnetic field strength to avoid excessive grain expansion and meet the performance control requirements.

[0023] (4) This invention provides a low-cost and green method for improving the wettability of solder. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the production process of the heat treatment process for the preferred orientation (110) of the tin-based solder alloy of the present invention.

[0025] Figure 2 This is an atomic model of the interface between Cu6Sn5 and the Sn substrate after gradient magnetic field heat treatment. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0027] Example 1

[0028] The chemical composition of a tin-based solder alloy according to this invention is shown in Table 1.

[0029] Table 1 Chemical composition of tin-based solder alloy in Example 1

[0030] Sn Bi Cu Ni Ag margin 62％ 0.5％ 0.3％ 0.02％ 1.75％ Unavoidable impurities

[0031] The specific processing steps are as follows:

[0032] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 1.

[0033] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Connect the positive and negative poles of the rotating magnetic field to both ends of the sample, and place the tin-based brazing alloy into an open heating furnace to heat it to 230°C.

[0034] (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2): the magnetic field strength is 12T, the superimposed magnetic field direction rotates 180° every 200μs, the temperature is controlled at 225℃, and the treatment time is 50s.

[0035] (4) The brazing alloy processed in step (3) is subjected to hot rolling followed by cold rolling: the hot rolling temperature is controlled at 225℃, and it is rolled in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% each time, and the total deformation of hot rolling is 58%; after the brazing alloy cools to room temperature, it is subjected to 5 passes of cold rolling with a reduction of 6%, 10%, 14%, 20%, and 24% respectively, and the entire cold rolling process is carried out in an oil bath. The total deformation of cold rolling eventually reaches 74%, and the brazing alloy sheet is finally obtained.

[0036] (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing: the first gradient annealing temperature is 225℃ and the magnetic field strength is 0.1T, the second gradient annealing temperature is 175℃ and the magnetic field strength is 1.2T, the third gradient annealing temperature is 125℃ and the magnetic field strength is 6T, and the duration of each annealing is 30s (step (5) is repeated 6 times).

[0037] (6) The solder alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain a tin-based solder alloy with excellent wetting properties.

[0038] The orientation density distribution of β-Sn in tin-based solder alloys measured using the tilted section method in X-ray diffraction is shown in Table 2. The solder wetting angle measurements at different temperatures are shown in Table 3. Table 2 shows that: <110> The orientation density is highest in the crystal direction, indicating that β-Sn achieves a preferred orientation after being controlled by gradient magnetic field heat treatment. <110> As can be seen from Table 3, as the brazing temperature increases, the wetting angle reaches 51.7°, which is smaller than the wetting angle before adjustment, indicating that the wettability of the brazing alloy is improved after the gradient magnetic field heat treatment is controlled.

[0039] Table 2 Orientation density of different textures in tin-based solder alloys in Example 1

[0040] Orientation <110> <111> <112> Ψ(g) 7 4 2

[0041] Table 3 Wetting angle of tin-based solder alloy at different temperatures in Example 1.

[0042] Temperature ℃ 257 287 317 Wetting angle ° 53.7 52.8 51.7

[0043] Example 2

[0044] The chemical composition of the tin-based solder alloy of this invention is shown in Table 4.

[0045] Table 4 Chemical composition of tin-based solder alloy in Example 2

[0046] Sn Bi Cu Ni Ag margin 65％ 0.3％ 0.3％ 0.06％ 1.5％ Unavoidable impurities

[0047] The specific processing steps are as follows:

[0048] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 1.

[0049] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Connect the positive and negative poles of the rotating magnetic field to both ends of the sample, and put the tin-based brazing alloy into an open heating furnace to heat it to 250°C.

[0050] (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2): the magnetic field strength is 16T, the superimposed magnetic field direction rotates 180° every 200μs, the temperature is controlled at 235℃, and the treatment time is 30s.

[0051] (4) The brazing alloy processed in step (3) is subjected to hot rolling followed by cold rolling: the hot rolling temperature is controlled at 235℃, and it is rolled in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% for each pass, resulting in a total hot rolling deformation of 58%; after the brazing alloy cools to room temperature, it is subjected to 5 passes of cold rolling with a reduction of 6%, 10%, 14%, 20%, and 24% for each pass, and the entire cold rolling process is carried out in an oil bath. The total cold rolling deformation eventually reaches 74%, and the brazing alloy sheet is finally obtained.

[0052] (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing: the first gradient annealing temperature is 225℃ and the magnetic field strength is 0.6T, the second gradient annealing temperature is 175℃ and the magnetic field strength is 5T, the third gradient annealing temperature is 125℃ and the magnetic field strength is 12T, and the duration of each annealing is 30s (step (5) is repeated 7 times).

[0053] (6) The solder alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain a tin-based solder alloy with excellent wetting properties.

[0054] The orientation density distribution of β-Sn in tin-based solder alloys measured using the tilted section method in X-ray diffraction is shown in Table 5. The solder wetting angle measurements at different temperatures are shown in Table 6. Table 5 shows that: <110> The orientation density is highest in the crystal direction, indicating that β-Sn achieves a preferred orientation after being controlled by gradient magnetic field heat treatment. <110> As can be seen from Table 6, as the brazing temperature increases, the wetting angle reaches 52.7°, which is smaller than the wetting angle before adjustment, indicating that the wettability of the brazing alloy is improved after the gradient magnetic field heat treatment is controlled.

[0055] Table 5 Orientation density of different textures in tin-based solder alloys in Example 2

[0056] Orientation <110> <111> <112> Ψ(g) 8 4 1

[0057] Table 6 Wetting angle of tin-based solder alloy at different temperatures in Example 2.

[0058] Temperature ℃ 257 287 317 Wetting angle ° 56 53.2 52.7

[0059] Example 3

[0060] The chemical composition of the tin-based solder alloy of this invention is shown in Table 7.

[0061] Table 7 Chemical composition of tin-based solder alloy in Example 3

[0062] Sn Bi Cu Ni Ag margin 67.6％ 0.8％ 0.6 0.1％ 2％ Unavoidable impurities

[0063] The specific processing steps are as follows:

[0064] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 1.

[0065] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Connect the positive and negative poles of the rotating magnetic field to both ends of the sample, and put the tin-based brazing alloy into an open heating furnace to heat it to 250°C.

[0066] (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2): the magnetic field strength is 16T, the superimposed magnetic field direction rotates 180° every 180μs, the temperature is controlled at 250℃, and the treatment time is 30s.

[0067] (4) The brazing alloy processed in step (3) is subjected to hot rolling followed by cold rolling: the hot rolling temperature is controlled at 250℃, and it is rolled in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% each time, and the total deformation of hot rolling is 58%; after the brazing alloy cools to room temperature, it is subjected to 5 passes of cold rolling with a reduction of 6%, 10%, 14%, 20%, and 24% respectively, and the entire cold rolling process is carried out in an oil bath. The total deformation of cold rolling eventually reaches 74%, and the brazing alloy sheet is finally obtained.

[0068] (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing: the first gradient annealing temperature is 225℃ and the magnetic field strength is 0.6T, the second gradient annealing temperature is 175℃ and the magnetic field strength is 5T, the third gradient annealing temperature is 125℃ and the magnetic field strength is 12T, and the duration of each annealing is 30s (step (5) is repeated 8 times).

[0069] (6) The solder alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain a tin-based solder alloy with excellent wetting properties.

[0070] The orientation density distribution of β-Sn in tin-based solder alloys measured using the tilted section method in X-ray diffraction is shown in Table 8. The solder wetting angle measurements at different temperatures are shown in Table 9. Table 8 shows that: <110> The orientation density is highest in the crystal direction, indicating that β-Sn achieves a preferred orientation after being controlled by gradient magnetic field heat treatment. <110> As can be seen from Table 9, as the brazing temperature increases, the wetting angle reaches 53.6°, which is smaller than the wetting angle before adjustment, indicating that the wettability of the brazing alloy is improved after the gradient magnetic field heat treatment is controlled.

[0071] Table 8 Orientation density of different textures in tin-based solder alloys in Example 3

[0072] Orientation <110> <111> <112> Ψ(g) 9 6 3

[0073] Table 9 Wetting angle of tin-based solder alloy at different temperatures in Example 3

[0074] Temperature ℃ 257 287 317 Wetting angle ° 54.2 53.9 53.6

[0075] Comparative Example 1

[0076] In contrast, this embodiment differs from Embodiment 1 only in that step (5) is not gradient magnetic field annealing, but ordinary magnetic field annealing. The other preparation processes and the chemical composition of the alloy are the same as in Embodiment 1. The specific processing steps are as follows:

[0077] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 1.

[0078] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Connect the positive and negative poles of the rotating magnetic field to both ends of the sample, and place the tin-based brazing alloy into an open heating furnace to heat it to 230°C.

[0079] (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2): the magnetic field strength is 12T, the superimposed magnetic field direction rotates 180° every 200μs, the temperature is controlled at 225℃, and the treatment time is 50s.

[0080] (4) The brazing alloy processed in step (3) is subjected to hot rolling followed by cold rolling: the hot rolling temperature is controlled at 225℃, and the rolling is performed in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% each time, and the total deformation of hot rolling is 58%; after the brazing alloy cools to room temperature, it is subjected to 5 passes of cold rolling with a reduction of 6%, 10%, 14%, 20%, and 24% respectively. The entire cold rolling process is carried out in an oil bath, and the total deformation of cold rolling finally reaches 74%, and the brazing alloy sheet is finally obtained.

[0081] (5) The brazing alloy sheet obtained in step (4) is subjected to magnetic field annealing: the annealing temperature is 225℃, the magnetic field strength is 0.1T, and the annealing time is 30s.

[0082] (6) The brazing alloy sheet after magnetic field annealing is cooled by oil quenching to obtain tin-based brazing alloy.

[0083] The orientation density distribution of β-Sn in tin-based solder alloys measured using the tilted section method in X-ray diffraction is shown in Table 10. The solder wetting angle measurements at different temperatures are shown in Table 11. Table 10 shows that: <110> The orientation density of the crystal orientation is not at its maximum, indicating that β-Sn will not preferentially oriented without gradient magnetic field heat treatment. As can be seen from Table 11, as the brazing temperature increases, the wetting angle reaches 53.6°, which is greater than the wetting angle of Example 1. Comparing the results of Example 1 and Comparative Example 1, we can conclude that the brazing alloy after gradient magnetic field heat treatment has better wettability than the brazing alloy after ordinary magnetic field heat treatment.

[0084] Table 10 Orientation density of different textures in tin-based solder alloys (Comparative Example 1)

[0085] Orientation <110> <111> <112> Ψ(g) 3 6 4

[0086] Table 11 Comparative Example 1: Wetting angle of tin-based solder alloy at different temperatures

[0087] Temperature ℃ 257 287 317 Wetting angle ° 54.9 54.0 53.6

[0088] Comparative Example 2

[0089] In contrast, this embodiment differs from Embodiment 2 only in that the disordered constant magnetic field treatment in step (3) is omitted. All other preparation processes and the chemical composition of the alloy are the same as in Embodiment 2. The specific processing steps are as follows:

[0090] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 4.

[0091] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Place the tin-based brazing alloy into an open heating furnace and heat it to 250°C.

[0092] (3) The brazing alloy processed in step (2) is subjected to hot rolling followed by cold rolling: the hot rolling temperature is controlled at 235℃, and it is rolled in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% for each pass, resulting in a total hot rolling deformation of 58%; after the brazing alloy cools to room temperature, it is subjected to 5 passes of cold rolling with a reduction of 6%, 10%, 14%, 20%, and 24% for each pass, and the entire cold rolling process is carried out in an oil bath. The total cold rolling deformation eventually reaches 74%, and the brazing alloy sheet is finally obtained.

[0093] (4) The brazing alloy sheet obtained in step (3) is subjected to gradient magnetic field annealing: the first gradient annealing temperature is 225℃ and the magnetic field strength is 0.6T, the second gradient annealing temperature is 175℃ and the magnetic field strength is 5T, the third gradient annealing temperature is 125℃ and the magnetic field strength is 12T, and the duration of each annealing is 30s (step (5) is repeated 7 times).

[0094] (5) The solder alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain tin-based solder alloy.

[0095] The orientation density distribution of β-Sn in the tin-based solder alloy was measured using the tilted section method in X-ray diffraction, as shown in Table 11. The wetting angle of the solder at different temperatures is shown in Table 12. Table 11 shows that β-Sn does not exhibit a preferred orientation, indicating that the β-Sn grain orientation is disordered without the disordered magnetic field treatment. Table 12 shows that as the brazing temperature increases, the wetting angle reaches 54.1°, which is greater than that of Example 2. Comparing the results of Example 2 and Comparative Example 2, it can be concluded that the solder alloy treated with a disordered constant magnetic field eliminates the disordered crystal orientation and exhibits better wettability.

[0096] Table 11 Orientation density of different textures in tin-based solder alloys (Comparative Example 2)

[0097] Orientation <110> <111> <112> Ψ(g) 8 8 7

[0098] Table 12 Comparative Example 2: Wetting angle of tin-based solder alloy at different temperatures

[0099] Temperature ℃ 257 287 317 Wetting angle ° 56.2 55.7 54.1

[0100] Comparative Example 3

[0101] In contrast, this embodiment differs from Embodiment 3 only in that step (4) involves only hot rolling. The other preparation processes and the chemical composition of the alloy are the same as in Embodiment 3. The specific processing steps are as follows:

[0102] (1) The brazing alloy was obtained by smelting and water cooling according to the composition in Table 7.

[0103] (2) Heat the brazing alloy obtained in step (1) using an induction heating furnace: Connect the positive and negative poles of the rotating magnetic field to both ends of the sample, and put the tin-based brazing alloy into an open heating furnace to heat it to 250°C.

[0104] (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2): the magnetic field strength is 16T, the superimposed magnetic field direction rotates 180° every 180μs, the temperature is controlled at 250℃, and the treatment time is 30s.

[0105] (4) The brazing alloy processed in step (3) is hot rolled: the hot rolling temperature is controlled at 250°C, and it is rolled in 5 passes with a reduction of 5%, 8%, 10%, 15%, and 20% each time, and the total hot rolling deformation is 58%; finally, a brazing alloy sheet is obtained.

[0106] (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing: the first gradient annealing temperature is 225℃ and the magnetic field strength is 0.6T, the second gradient annealing temperature is 175℃ and the magnetic field strength is 5T, the third gradient annealing temperature is 125℃ and the magnetic field strength is 12T, and the duration of each annealing is 30s (step (5) is repeated 8 times).

[0107] (6) The solder alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain tin-based solder alloy.

[0108] The orientation density distribution of β-Sn in tin-based solder alloys was measured using the tilted section method in X-ray diffraction. Table 13 shows the distribution, and Table 14 shows the measured wetting angle of the solder at different temperatures. Table 13 shows that the orientation density distribution of β-Sn... <110> The low orientation density indicates that the β-Sn grains do not exhibit preferential orientation without cold rolling. Table 14 shows that as the brazing temperature increases, the wetting angle reaches 54.0°, which is greater than that of Example 3. Comparing the results of Example 3 and Comparative Example 3, it can be concluded that the brazing alloy undergoing cold rolling exhibits preferential orientation. <110> It has better wettability.

[0109] Table 13 Orientation density of different textures in tin-based solder alloys (Comparative Example 3)

[0110] Orientation <110> <111> <112> Ψ(g) 2 8 4

[0111] Table 14 Comparative Example 3: Wetting angle of tin-based solder alloy at different temperatures

[0112] Temperature ℃ 257 287 317 Wetting angle ° 54.9 54.6 54.0

Claims

1. A heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation, characterized in that: Preferred grain orientation can be controlled by directional magnetic field heat treatment. The specific processing steps are as follows: (1) The solder alloy is obtained by smelting Sn, Bi, Ag, Cu, Ni and unavoidable impurities and water cooling; (2) The brazing alloy obtained in step (1) is heated using an induction heating furnace; (3) Apply a disordered constant magnetic field to the brazing alloy treated in step (2); (4) The brazing alloy processed in step (3) is hot rolled, and after the brazing alloy is cooled to room temperature, it is cold rolled in multiple passes to obtain a brazing alloy sheet. (5) The brazing alloy sheet obtained in step (4) is subjected to gradient magnetic field annealing; (6) The brazing alloy sheet after gradient magnetic field annealing is cooled by oil quenching to obtain tin-based brazing alloy; In step (1), the total mass percentage of Sn, Bi, Ag, Cu, Ni and unavoidable impurities is 100%, including 62~67.6% Sn, 0.3~0.8% Bi, 1.5~2% Ag, 0.3~0.6% Cu, 0.02~0.1% Ni, with the balance being unavoidable impurities; In step (3), the magnetic field strength is controlled at 12~16T, the superimposed magnetic field direction is rotated 180° every 200μs, the temperature is controlled between 225~250℃, and the reaction time is 30~50s; In step (5), a three-gradient magnetic field annealing is used. The first gradient annealing temperature is 225℃ and the magnetic field strength is 0.1~0.6T. The second gradient annealing temperature is 175℃ and the magnetic field strength is 1.2~5T. The third gradient annealing temperature is 125℃ and the magnetic field strength is 6~12T. The annealing time for each step is 30s.

2. The heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation according to claim 1, characterized in that: In step (2), the brazing alloy is heated to 230~250℃. Before heating, the positive and negative poles of the rotating magnetic field have been connected to both ends of the brazing alloy.

3. The heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation according to claim 1, characterized in that: In step (4), the hot rolling temperature is controlled between 225 and 250°C, the total cumulative deformation during rolling is 58%, and the hot rolling is carried out in 5 passes with reductions of 5%, 8%, 10%, 15%, and 20%, respectively.

4. The heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation according to claim 1, characterized in that: In step (4), the total deformation of cold rolling is 74%, and five passes are used for rolling. The reduction amounts are 6%, 10%, 14%, 20%, and 24%, respectively. Cold rolling is carried out at room temperature, and the entire rolling process is done in an oil bath.

5. The heat treatment process for improving the wettability of tin-based solder alloys by controlling grain orientation according to claim 1, characterized in that: Step (5) needs to be repeated more than 5 times.

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