Method for preparing a hall electrode for high-purity germanium hall testing

Abstract

A preparation method of a Hall electrode for high-purity germanium Hall test comprises the following steps: single-wire cutting a Hall sample from a crystal; pouring an alumina polishing solution on a smooth quartz plate to polish both sides of the Hall sample to eliminate scratches formed by single-wire cutting, rinsing with deionized water and drying with nitrogen; cutting a Hall sample at the center and the edge of the Hall sample respectively; cleaning the Hall sample, corroding with a corrosion solution with a volume ratio of HNO3:HF being (2-4):1, immersing in a passivation solution with a volume ratio of HF:water being 1:1, cleaning with pure water and drying with high-purity nitrogen; welding an electrode: preparing a high-purity indium wire, setting a high temperature of an electric iron at 250-280 DEG C, first touching the indium wire, evenly touching the indium wire on four corners of the Hall sample, setting a low temperature of the electric iron at 180-210 DEG C, welding the four corners on a Hall device circuit board in sequence through the indium on the four corners, and forming a Hall electrode.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of semiconductor material detection, and more particularly to a preparation method of a Hall electrode for high-purity germanium Hall testing. BACKGROUND

[0002] A voltage is applied in the length direction of a semiconductor sample, and a magnetic field is applied in the width direction. Due to the magnetic field, a Lorentz force is generated in the height direction, which phenomenon is called Hall effect. The Lorentz force causes carriers moving in the semiconductor sample to accumulate above the semiconductor sample, thus generating an electric field on the upper and lower surfaces (height direction) of the semiconductor sample. The electric force generated by the electric field balances the Lorentz force, and the semiconductor sample is subjected to Hall detection using this phenomenon.

[0003] When performing low-temperature Hall detection, high requirements are placed on the sample and electrode contact, such as uniform sample thickness, smooth sample surface, no holes or grooves, electrode contact position at the sample edge, small electrode contact area, and stable electrode contact.

[0004] The current conventional detection method in this field first cuts a sample piece with a thickness of less than 1 mm, then cuts the sample piece into small square samples, and finally makes electrodes on the four corners of the samples for Hall detection. For example, patent documents CN114577561A and CN114235899A use similar methods.

[0005] The current process has the following problems: During sample piece preparation, single-wire cutting is used to obtain a Hall sample piece, resulting in many scratches on the Hall sample piece and large thickness errors and poor surface flatness. The small Hall samples prepared from the Hall sample piece are not clean after surface treatment in the etching process, and the surface is easily re-oxidized. The Hall samples have virtual welding and voids during electrode welding, resulting in unstable electrode contact. High temperature can cause indium impurities to diffuse into the sample, reducing the purity of the Hall sample, and other problems, which greatly reduce the accuracy and stability of the Hall test results. SUMMARY

[0006] In view of the problems in the background art, an object of the present disclosure is to provide a preparation method of a Hall electrode for high-purity germanium Hall testing, which can completely eliminate the surface scratches formed by single-wire cutting of the Hall sample piece and reduce the thickness error and roughness of the Hall sample piece.

[0007] Another objective of this disclosure is to provide a method for preparing a Hall electrode for high-purity germanium Hall testing, which can eliminate residual oxides on the surface of the Hall sample during the corrosion process, resulting in a clean surface treatment, thereby ensuring the accuracy and stability of the Hall test and improving the repeatability of the Hall test.

[0008] Another object of this disclosure is to provide a method for preparing a Hall electrode for high-purity germanium Hall testing that does not induce indium impurity diffusion.

[0009] Therefore, a method for preparing a Hall electrode for high-purity germanium Hall testing includes the following steps: S1, Hall sample cutting: Select the area to be tested for Hall on the high-purity germanium crystal, and cut a Hall sample perpendicular to the crystal growth axis using a single line. The thickness of the Hall sample is (1.0±0.3)mm-(2.0±0.3)mm; S2, Hall sample surface treatment: Perform physical grinding and polishing on the cut Hall sample. The physical grinding and polishing is done by pouring alumina polishing liquid onto a smooth quartz plate and repeatedly grinding and polishing both sides of the Hall sample until Hall effect is completely eliminated. The surface scratches formed by the single-line cutting of the sample were finally rinsed with deionized water and dried with nitrogen. The thickness error of the Hall sample was less than 0.1 mm and the roughness of the Hall sample was less than 1 μm; S3, Hall sample preparation: Hall samples were cut out from the center and edge of the Hall sample. The Hall sample was a small square with a side length of (10±0.1) mm-(15±0.1) mm; S4, Hall sample cleaning treatment, including the following sub-steps: S41, Etching: Prepare an etching solution with a volume ratio of HNO3:HF = (2-4):1, and place the Hall sample in the etching solution for etching. 2-4 min, until relatively dense yellow smoke is produced; S42, passivation: Prepare a passivation solution with a volume ratio of HF:water = 1:1. Remove the Hall sample that has completed corrosion from the corrosion solution and quickly immerse it in the passivation solution for 5-10 min; S43, pure water rinsing: Remove the passivated Hall sample from the passivation solution and rinse it with pure water for at least 15 min; S44, drying: Finally, dry it with high-purity nitrogen gas; S5, electrode welding: Electrode welding is performed in two sub-steps; S51, indium spotting on the Hall sample: Prepare a high-purity indium wire, so that... The soldering iron is set to a high temperature of 250-280℃. First, the indium wire is brought into contact, and then the molten indium wire is evenly applied to the four corners of the Hall sample. The contact time between the soldering iron and the Hall sample is controlled to be as short as possible. S52, the Hall sample is spot-welded onto the Hall device circuit board: The soldering iron is set to a low temperature of 180-210℃. By applying indium to the four corners of the Hall sample, the melting and resolidification of indium are used to sequentially spot-weld the four corners of the Hall sample onto the Hall device circuit board. The spot-welding process requires meticulous attention and multiple passes to control each corner and avoid incomplete soldering or voids, thus forming the Hall electrode. The beneficial effects of this disclosure are as follows.

[0010] In the method for preparing a Hall electrode for high-purity germanium Hall testing according to the present disclosure, after the Hall sample is cut out by single-line cutting in step S1, the surface is physically ground and polished in step S2 to completely eliminate the surface scratches formed by the single-line cutting of the Hall sample, reduce the thickness error and roughness of the Hall sample, thereby improving the accuracy and stability of Hall testing and improving the repeatability of Hall testing.

[0011] In the method for preparing a Hall electrode for high-purity germanium Hall testing according to the present disclosure, in the surface treatment of the Hall sample in step S4, the sample is first etched with an etching solution with a volume ratio of HNO3:HF = (2-4):1 in sub-step S41, and then passivated with a passivation solution with a volume ratio of HF:water = 1:1. This can fully eliminate the oxides remaining on the surface of the Hall sample during the etching process, making the surface treatment clean. Furthermore, a hydrophobic layer (H-terminus) is generated on the surface of the Hall sample, which can prevent secondary oxidation of germanium, ensure the original properties of germanium, ensure the accuracy and stability of Hall testing, and improve the repeatability of Hall testing.

[0012] In the preparation method of the Hall electrode for high-purity germanium Hall testing according to the present disclosure, in the electrode welding step S5: firstly, indium is spot-welded onto the Hall sample in sub-step S51 at a high temperature of 250-280°C. At this high temperature, the indium wire melts rapidly and solidifies regularly at the four corners of the Hall sample, making the contact points of the four Hall electrodes uniform in size and shape, and minimizing the contact between the soldering iron and the Hall sample to reduce the risk of indium impurity diffusion; then, in sub-step S52, the Hall sample is spot-welded onto the Hall device circuit board at a low temperature of 180-210°C, which does not cause indium impurity diffusion and protects the original performance of the Hall sample. Because the spot-welding process requires meticulousness and multiple times, each corner is controlled to avoid cold solder joints and voids, thus effectively avoiding cold solder joints and voids, making the prepared Hall electrode contact stable. Attached Figure Description

[0013] Figure 1 This is a schematic flowchart illustrating the process of fabricating a Hall sample from high-purity germanium crystals.

[0014] Figure 2 The images shown are surface morphology diagrams of the Hall sample before surface treatment, measured by a 3D profilometer in Example 1. The left image is a perspective view, and the right image is a top view.

[0015] Figure 3 The images shown are surface morphology diagrams of the Hall sample after surface treatment, measured by a 3D profilometer in Example 1. The left image is a perspective view, and the right image is a top view. Detailed Implementation

[0016] It will be understood that the disclosed embodiments are merely examples of this disclosure, which can be implemented in various forms. Therefore, the specific details disclosed herein should not be construed as limiting, but are intended only as the basis for the claims and as an illustrative basis to teach those skilled in the art how to implement this disclosure in various ways.

[0017] [Preparation method of Hall electrode for high-purity germanium Hall effect testing]

[0018] Reference Figure 1 The method for preparing a Hall electrode for high-purity germanium Hall testing according to this disclosure includes the following steps:

[0019] S1, Hall sample cutting: Select the part of the high-purity germanium crystal that needs to be tested for Hall, and cut the crystal into a Hall sample with a single line perpendicular to the crystal growth axis. The thickness of the Hall sample is (1.0±0.3)mm-(2.0±0.3)mm.

[0020] S2, Surface treatment of Hall sample: The cut Hall sample is subjected to physical grinding and polishing. Physical grinding and polishing is carried out by pouring alumina polishing liquid onto a smooth quartz plate and repeatedly grinding and polishing the Hall sample on both sides until the surface scratches formed by the single-line cutting of the Hall sample are completely eliminated. Finally, it is rinsed with deionized water and dried with nitrogen. The thickness error of the Hall sample is less than 0.1 mm and the roughness of the Hall sample is less than 1 μm.

[0021] S3, Hall sample preparation: Hall samples are cut out from the center and edge of the Hall sample piece. The Hall sample is a small square with a side length of (10±0.1)mm-(15±0.1)mm.

[0022] S4, Hall sample cleaning process, including sub-steps:

[0023] S41, Corrosion: Prepare a corrosive solution with a volume ratio of HNO3:HF = (2-4):1, place the Hall sample in the corrosive solution and corrode for 2-4 minutes until a relatively dense yellow fumes are produced;

[0024] S42, passivation: Prepare a passivation solution with a volume ratio of HF:water = 1:1. Take the Hall sample that has been etched out from the etching solution and quickly put it into the passivation solution for 5-10 minutes.

[0025] S43, Pure water rinsing: Remove the passivated Hall sample from the passivation solution and rinse the Hall sample with pure water for no less than 15 minutes.

[0026] S44, Drying: Finally, use high-purity nitrogen to dry;

[0027] S5, Welding Electrode: The welding electrode is produced in two sub-steps;

[0028] S51, Hall effect sample indium application: Prepare a high-purity indium wire, set the soldering iron to a high temperature of 250-280℃, first make contact with the indium wire, then evenly apply the molten indium wire to the four corners of the Hall sample, controlling the application process.

[0029] The contact time between the soldering iron and the Hall sample should be as short as possible;

[0030] S52, Spot welding of Hall sample onto Hall device circuit board: Set the soldering iron to a low temperature of 180-210℃, and spot weld the four corners of the Hall sample onto the Hall device circuit board by applying indium to the four corners of the Hall sample. The melting and resolidification of indium are used to spot weld the four corners of the Hall sample onto the Hall device circuit board in sequence. The spot welding process requires meticulousness and multiple times to control each corner to avoid the presence of cold solder joints or voids, thus forming Hall electrodes.

[0031] In the method for preparing a Hall electrode for high-purity germanium Hall testing according to the present disclosure, after the Hall sample is cut out by single-line cutting in step S1, the surface is physically ground and polished in step S2 to completely eliminate the surface scratches formed by the single-line cutting of the Hall sample, reduce the thickness error and roughness of the Hall sample, thereby improving the accuracy and stability of Hall testing and improving the repeatability of Hall testing.

[0032] In the method for preparing a Hall electrode for high-purity germanium Hall testing according to the present disclosure, in the surface treatment of the Hall sample in step S4, the sample is first etched with an etching solution with a volume ratio of HNO3:HF = (2-4):1 in sub-step S41, and then passivated with a passivation solution with a volume ratio of HF:water = 1:1. This can fully eliminate the oxides remaining on the surface of the Hall sample during the etching process, making the surface treatment clean. Furthermore, a hydrophobic layer (H-terminus) is generated on the surface of the Hall sample, which can prevent secondary oxidation of germanium, ensure the original properties of germanium, ensure the accuracy and stability of Hall testing, and improve the repeatability of Hall testing.

[0033] In the preparation method of the Hall electrode for high-purity germanium Hall testing according to the present disclosure, in the electrode welding step S5: firstly, indium is spot-welded onto the Hall sample in sub-step S51 at a high temperature of 250-280°C. At this high temperature, the indium wire melts rapidly and solidifies regularly at the four corners of the Hall sample, making the contact points of the four Hall electrodes uniform in size and shape, and minimizing the contact between the soldering iron and the Hall sample to reduce the risk of indium impurity diffusion; then, in sub-step S52, the Hall sample is spot-welded onto the Hall device circuit board at a low temperature of 180-210°C, which does not cause indium impurity diffusion and protects the original performance of the Hall sample. Because the spot-welding process requires meticulousness and multiple times, each corner is controlled to avoid cold solder joints and voids, thus effectively avoiding cold solder joints and voids, making the prepared Hall electrode contact stable.

[0034] In step S1, for example, single-wire cutting uses diamond wire with a diameter of 0.4-0.8 mm. In step S1, for example, the thickness of the Hall sample is 1.5 mm.

[0035] In step S2, in one example, a suspension of aluminum oxide and water is prepared as a polishing slurry. The aluminum oxide particle size is 10-20 μm, and the weight ratio of aluminum oxide to water is (15-25):100. In step S2, for example, the purity of nitrogen gas is 9N.

[0036] In step S3, in one example, the Hall sample is a small square with a side length of 12 mm.

[0037] In sub-step S41, in one example, a corrosive solution with a volume ratio of HNO3:HF = 3:1 is prepared, and corrosion is carried out for 3 minutes. In sub-step S42, in one example, immersion is performed for 8 minutes. In sub-step S43, in one example, the rinsing time is 20-30 minutes. For example, the rinsing time is 25 minutes. In sub-step S44, for example, the nitrogen purity is 9N.

[0038] In sub-step S51, for example, the purity of the high-purity indium wire is 5N or higher. In sub-step S51, in one example, the soldering iron is set to a high temperature of 270°C. In sub-step S52, in one example, the soldering iron is set to a low temperature of 195°C.

[0039] [test]

[0040] Example 1

[0041] The preparation method of the Hall electrode for high-purity germanium Hall testing in Example 1 adopts the following steps:

[0042] S1, Hall sample cutting: Select the part of the high-purity germanium crystal that needs to be tested for Hall, and cut the crystal into a Hall sample with a diamond wire of 0.6 mm in diameter perpendicular to the crystal growth axis. The thickness of the Hall sample is 1.5 mm.

[0043] S2, Hall sample surface treatment: The cut Hall sample is subjected to physical grinding and polishing. A suspension of aluminum oxide and water is prepared as the grinding and polishing liquid. The particle size of aluminum oxide is 15μm and the weight ratio of aluminum oxide to water is 20:100. Physical grinding and polishing is carried out by pouring the aluminum oxide polishing liquid onto a smooth quartz plate and repeatedly grinding and polishing the Hall sample on both sides until the surface scratches formed by the single-line cutting of the Hall sample are completely eliminated. Finally, it is rinsed with deionized water and dried with nitrogen gas of purity 9N. The thickness error of the Hall sample is less than 0.1mm and the roughness of the Hall sample is less than 1μm.

[0044] S3, Hall sample preparation: Hall samples are cut out from the center and edge of the Hall sample piece. The Hall sample is a small square with a side length of 12mm.

[0045] S4, Hall sample cleaning process, using the following sub-steps:

[0046] S41, Corrosion: Prepare a corrosion solution with a volume ratio of HNO3:HF = 3:1, place the Hall sample in the corrosion solution and corrode for 3 minutes until a relatively dense yellow fumes are produced;

[0047] S42, passivation: Prepare a passivation solution with a volume ratio of HF:water = 1:1. Take the Hall sample that has been etched out from the etching solution and quickly put it into the passivation solution for 8 minutes.

[0048] S43, Pure water rinsing: Remove the passivated Hall sample from the passivation solution and rinse the Hall sample with pure water for 25 minutes;

[0049] S44, Drying: Finally, use high-purity nitrogen gas with a purity of 9N to dry;

[0050] S5, Welding Electrode: The welding electrode is produced in two sub-steps;

[0051] S51, Hall sample indium application: Prepare a high-purity indium wire with a purity of 5N. Set the soldering iron to a high temperature of 270℃, first make contact with the indium wire, and then evenly apply the molten indium wire to the four sides of the Hall sample.

[0052] At each corner, the contact time between the soldering iron and the Hall sample should be kept as short as possible;

[0053] S52, Spot welding of Hall sample onto Hall device circuit board: Set the soldering iron to a low temperature of 195℃, and spot weld the four corners of the Hall sample onto the Hall device circuit board by applying indium to the four corners of the Hall sample. The melting and resolidification of indium are used to spot weld the four corners of the Hall sample onto the Hall device circuit board in sequence. The spot welding process requires meticulousness and multiple times to control each corner to avoid the presence of cold solder joints or voids, thus forming Hall electrodes.

[0054] Comparative Example 1

[0055] Except for not performing the Hall sample surface treatment in step S2, the rest is the same as in Example 1.

[0056] Comparative Example 2

[0057] Except that the passivation in sub-step S42 is not performed in the Hall sample cleaning process in step S4, and the phrase "remove the Hall sample that has been passivated from the passivation solution" in step S43 is changed to "remove the Hall sample that has been etched from the etching solution", the rest is the same as in Example 1.

[0058] Comparative Example 3

[0059] Except for changing "set the soldering iron to a low temperature of 195°C" to "set the soldering iron to a high temperature of 270°C" in sub-step S52 of the welding electrode in step S5, the rest is the same as in Example 1.

[0060] Comparative Example 4

[0061] Except for changing "set the soldering iron to a high temperature of 270°C" to "set the soldering iron to a low temperature of 195°C" in sub-step S51 of the welding electrode in step S5, the rest is the same as in Example 1.

[0062] In Examples 1 and 1-4, five Hall electrodes (A, B, C, D, and E) were prepared from the same cross-section of the same crystal. Hall electrodes were fabricated using the methods described in Examples 1 and 1-4, respectively, and each Hall electrode was tested four times. Carrier concentration and type were determined using an HL9900 from Toho Technology, USA.

[0063] Table 1. Hall effect test results for Example 1 and Comparative Examples 1-4

[0064]

[0065]

[0066] The comparison of the deviations of the four tests in Example 1 and Comparative Example 1 shows that the surface treatment of the Hall sample in step S2 in Example 1 significantly improved the accuracy and stability of the Hall test results.

[0067] The average carrier concentration and the deviation of the four tests in Example 1 and Comparative Example 2 show that the accuracy and stability of the Hall test results and the repeatability of the test are improved by immersing the sample in passivation solution after corrosion in Example 1. This is because it fully eliminates the oxides remaining on the sample surface during the corrosion process and generates a hydrophobic layer (H-terminus) on the germanium surface, which prevents secondary oxidation of germanium and ensures the original performance of the germanium sheet.

[0068] The average carrier concentration from the four tests in Example 1 and Comparative Example 3 shows that Comparative Example 3 only used a single high-temperature setting. After the high-temperature soldering iron was in contact with the Hall sample for a long time, indium impurity diffusion occurred, which greatly affected the accuracy of the sample.

[0069] The deviations from the four tests in Example 1 and Comparative Example 4 show that Comparative Example 4 only used a single low-temperature setting. During the soldering process, the four corners of the sample solidified irregularly, resulting in uneven size and shape of the four electrode contact points. This affected the stability and accuracy of the Hall effect test results.

[0070] also, Figure 2 and Figure 3Photos of the Hall sample from Example 1 before and after processing in step S2 are provided. Figure 2 The images shown are surface morphology diagrams of the Hall sample before surface treatment, measured by a 3D profilometer in Example 1. The left image is a perspective view, and the right image is a top view. Figure 3 The images shown are surface morphology diagrams of the Hall sample after surface treatment, measured by a 3D profilometer in Example 1. The left image is a perspective view, and the right image is a top view. Figure 2 A distinct linear concavity and convexity can be observed. Figure 3 The sample surface is flat and has low roughness.

[0071] Several exemplary embodiments have been described in detail above, but this document is not intended to limit itself to the explicitly disclosed combinations. Therefore, unless otherwise stated, the various features disclosed herein can be combined to form several other combinations, which are not shown for simplicity.

Claims

1. A method for preparing a Hall electrode for high-purity germanium Hall effect testing, characterized in that, Including the following steps: S1, Hall sample cutting: Select the part of the high-purity germanium crystal that needs to be tested for Hall, and cut the crystal into a Hall sample with a single line perpendicular to the crystal growth axis. The thickness of the Hall sample is (1.0±0.3)mm-(2.0±0.3)mm. S2, Surface treatment of Hall sample: The cut Hall sample is subjected to physical grinding and polishing. Physical grinding and polishing is carried out by pouring alumina polishing liquid onto a smooth quartz plate and repeatedly grinding and polishing the Hall sample on both sides until the surface scratches formed by the single-line cutting of the Hall sample are completely eliminated. Finally, it is rinsed with deionized water and dried with nitrogen. The thickness error of the Hall sample is less than 0.1 mm and the roughness of the Hall sample is less than 1 μm. S3, Hall sample preparation: Hall samples are cut out from the center and edge of the Hall sample piece. The Hall sample is a small square with a side length of (10±0.1)mm-(15±0.1)mm. S4, Hall sample cleaning process, including sub-steps: S41, Corrosion: Prepare a corrosive solution with a volume ratio of HNO3:HF = (2-4):1, place the Hall sample in the corrosive solution and corrode for 2-4 minutes until a relatively dense yellow fumes are produced; S42, passivation: Prepare a passivation solution with a volume ratio of HF:water = 1:

1. Take the Hall sample that has been etched out from the etching solution and quickly put it into the passivation solution for 5-10 minutes. S43, Pure water rinsing: Remove the passivated Hall sample from the passivation solution and rinse the Hall sample with pure water for no less than 15 minutes. S44, Drying: Finally, use high-purity nitrogen to dry; S5, Welding Electrode: The welding electrode is produced in two sub-steps; S51, Hall sample indium application: Prepare high-purity indium wire, set the soldering iron to a high temperature of 250-280℃, first make contact with the indium wire, and then evenly apply the molten indium wire to the four corners of the Hall sample, controlling the contact time between the soldering iron and the Hall sample to be as short as possible. S52, Hall effect sample spot soldered onto Hall effect device circuit board: Set soldering iron to a low temperature of 180-210℃, and apply solder to the indium at the four corners of the Hall effect sample, utilizing the melting and resolidification of indium. The four corners of the Hall sample are spot-welded onto the circuit board of the Hall device in sequence. The spot-welding process requires meticulousness and is performed multiple times to control each corner to avoid incomplete soldering or voids, thus forming Hall electrodes.

2. The method for preparing the Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In step S1, single-wire cutting uses diamond wire with a diameter of 0.4-0.8 mm; and / or In step S1, the thickness of the Hall sample is 1.5 mm.

3. The method for preparing the Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In step S2, a suspension of aluminum oxide and water is prepared as a grinding and polishing liquid. The particle size of aluminum oxide is 10-20 μm, and the weight ratio of aluminum oxide to water is (15-25):

100.

4. The method for preparing the Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In step S2, the purity of nitrogen is 9N.

5. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In step S3, the Hall sample is a small square with a side length of 12 mm.

6. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In sub-step S41, a corrosive solution with a volume ratio of HNO3:HF = 3:1 is prepared, and corrosion is carried out for 3 minutes; and / or In sub-step S42, soak for 8 minutes.

7. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In sub-step S43, the rinsing time is 20-30 minutes.

8. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 7, characterized in that, In sub-step S43, the rinsing time is 25 minutes.

9. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In sub-step S44, the purity of nitrogen is 9N.

10. The method for preparing a Hall electrode for high-purity germanium Hall testing according to claim 1, characterized in that, In sub-step S51, the purity of the high-purity indium wire is 5N or higher; and / or In sub-step S51, the soldering iron is set to a high temperature of 270°C; and / or In sub-step S52, the soldering iron is set to a low temperature of 195°C.

Images