A new electrode preparation and wiring process combining indium pressure contact and hot air welding

Abstract

The application discloses a novel electrode preparation and wiring process combining indium compression contact and hot air welding method, and relates to the technical field of condensed state physics and material engineering. The application comprises the following steps: S1: processing a millimeter-level bulk phase material sample to be measured into a regular long strip-shaped Hallbar structure for electrical transport measurement, and performing cleaning treatment on the surface of the processed sample. The application cooperates indium compression contact and hot air welding, relies on the good ductility and low resistance characteristics of high-purity indium, forms a gap-free ohmic contact between indium and the surface of the millimeter-level bulk phase sample under constant pressure at room temperature, simultaneously utilizes the low melting point characteristics of Sn-Bi series low-temperature soldering paste, forms a metallurgical bonding solder joint structure between the metal wire and the indium electrode through a precise temperature control hot air welding process, and forms a mutual melting diffusion layer, which effectively solves the problem of loose contact. Compared with a single contact mode, the application not only retains the advantage of small thermal damage of the indium compression method to the sample, but also has high mechanical stability of the welding connection.

Description

Technical Field

[0001] This invention belongs to the field of condensed matter physics and materials engineering technology, and in particular relates to a novel electrode preparation and wiring process that combines indium-pressed contact and hot air welding. Background Technology

[0002] When measuring electrical transport properties, it is usually necessary to fabricate electrical contact electrodes on the sample surface. The electrode fabrication method and its quality have a decisive influence on the contact resistance, thus directly affecting the accuracy and stability of electrical transport measurement data. Therefore, developing stable and reliable electrode fabrication and wiring processes is of great significance for high-precision transport experiments.

[0003] The most common methods for electrode fabrication and wiring include the following: 1. Indium-indium bonding: This technique utilizes the excellent ductility and low melting point of indium to directly form ohmic contacts on the surface of semiconductors or bulk materials. This method eliminates the need for adhesives or complex curing steps, resulting in minimal thermal damage to the sample surface, making it particularly suitable for testing scenarios requiring repeated contact. However, under wide temperature variations, the difference in thermal expansion coefficients between the sample and indium can lead to contact loosening due to thermal expansion and contraction, resulting in poor contact.

[0004] 2. Silver Paste Method: A commonly used technique for rapidly preparing electrical contacts on material surfaces. This method uses silver powder as the main conductive component, uniformly dispersing silver particles with an organic binder to form a flowable silver paste, which then solidifies to form a conductive connection. This method has the advantages of simple operation, strong adhesion, and good conductivity, making it particularly suitable for electrode fabrication on rough materials. However, in some material systems, it is difficult to form a stable ohmic contact between the silver paste and the sample, thus affecting the accuracy of electrical measurement results.

[0005] 3. Spot welding: A contact bonding technique that uses pulsed current to instantaneously generate high temperatures between the electrode and the metal wire, causing localized metal melting and forming a metal-metal bond under pressure. This method can form relatively stable metal connections, but it has high requirements for equipment and operating procedures, and the mechanical stability of the contact point is not strong.

[0006] Therefore, in actual electrical transport measurement experiments, there is still a need for an electrode fabrication and wiring process that can take into account low contact resistance, structural stability, and adaptability to high temperature change environments, in order to improve the reliability and measurement stability of the device under complex experimental conditions. To address these issues, we provide a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding. Summary of the Invention

[0007] The purpose of this invention is to provide a novel electrode preparation and wiring process that combines indium-indium contact and hot air welding. By combining indium-indium contact and hot air welding, the problems of high electrode contact resistance, insufficient connection stability, and easy loosening and failure under thermal cycling in the prior art are solved.

[0008] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0009] This invention discloses a novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding, comprising the following steps: S1: The sample of the bulk material to be tested at the millimeter scale is processed into a regular long strip Hallbar structure for electrical transport measurement. The surface of the processed sample is cleaned. Mechanical peeling, solvent cleaning or other surface cleaning methods can be used to remove the contamination layer or oxide layer on the sample surface to ensure the surface cleanliness of the sample area to be processed. S2: On the cleaned sample surface, soft indium is pressed at predetermined electrode points using the indium pressing method to form a regular electrode layout that meets the requirements of Hallbar testing. Taking advantage of the good ductility of indium, a stable and gapless ohmic contact is formed between indium and the sample surface under constant pressure. S3: On the sample and the surface of the indium electrode after the indium electrode preparation is completed, an insulating coating is uniformly coated to form a complete coverage of the non-electrode area of ​​the sample and the non-contact area of ​​the indium electrode. The coated insulating coating is then irradiated with ultraviolet light to complete the curing process, forming a stable insulating protective layer on the sample surface. S4: Locally remove the cured insulating coating covering the surface of the indium electrode to expose the preset contact area of ​​the indium electrode, forming an electrode welding window. Ensure that there is no residue of the insulating coating in the removed area, so that the contact area of ​​the indium electrode is completely exposed, providing a clean contact interface for subsequent welding. S5: Apply low-temperature solder paste to the exposed indium electrode contact area, place the end of the metal wire in the solder paste position, and make the end of the wire fully adhere to the surface of the indium electrode to ensure that the solder paste evenly covers the contact area and there is no gap between the end of the wire and the indium electrode, forming a stable pre-contact structure. S6: The hot air welding method is used to precisely heat the solder paste area, so that the low-temperature solder paste is fully melted, wets the indium electrode and the metal wire, and after heating is stopped, it is naturally cooled at room temperature to form a stable welded connection structure between the metal wire and the indium electrode.

[0010] The present invention is further configured such that, in step S1, the reference size of the processed Hallbar structure sample is 1mm × 2mm. The mechanical peeling process must completely remove the contamination layer and natural oxide layer on the sample surface to ensure the surface flatness of the area to be pressed into indium and avoid surface impurities affecting the contact effect between the indium electrode and the sample. This cleaning method does not require the use of chemical reagents and will not cause corrosion or damage to the surface structure of the millimeter-scale bulk sample. Compared with the chemical cleaning process required by the existing silver paste method, it can better protect the integrity of the sample and lay the foundation for the formation of a stable ohmic contact in the subsequent indium pressing contact.

[0011] The present invention is further configured such that, in step S2, the electrode layout for the Hallbar test is a standard six-electrode layout. The four indium electrodes for voltage testing are 0.2mm × 0.2mm in size, and the two electrodes for applying the current source use indium blocks of 0.2mm × 1mm in size, ensuring uniform current distribution in the sample. This electrode size design is adapted to the size characteristics of millimeter-scale bulk samples, avoiding stress concentration on the sample surface due to excessively large electrode sizes. Simultaneously, through differentiated size design, the accuracy of voltage testing and the stability of current application are balanced, solving the measurement data deviation problem caused by unreasonable electrode layout in existing indium-pressed methods.

[0012] The present invention is further configured such that, in step S2, the soft metal indium used for pressing the electrode is high-purity indium, and the pressing process of the indium electrode is completed at room temperature. By pressing with constant pressure, the indium is tightly bonded to the sample surface to form a gapless contact interface. The selection of high-purity indium can effectively reduce the resistance of the indium electrode itself and avoid impurity elements from affecting the contact effect. The room temperature pressing process minimizes thermal damage. Compared with the high-temperature operation of the existing spot welding method, it is more suitable for temperature-sensitive millimeter-scale bulk materials. At the same time, by utilizing the good ductility of indium, a tight bond between the electrode and the sample surface is achieved, solving the problem of weak contact in the existing indium pressing method.

[0013] The present invention is further configured such that, in step S3, the insulating coating uses a UV-curable insulating adhesive, the coating thickness is controlled between 50μm and 100μm, and the UV irradiation curing time is controlled between 30s and 90s. The cured insulating coating completely covers the non-test area of ​​the sample and the non-contact area of ​​the indium electrode, without any defects such as missed coating or blistering. The coating thickness and curing parameters of the insulating coating are precisely matched, which can effectively isolate the interference of dust and moisture in the external environment to the electrode and avoid short circuits of the electrode. At the same time, the coating thickness will not affect the subsequent insulation layer removal operation. Compared with traditional thermal curing, the UV curing method has a faster curing speed and will not cause thermal damage to the prepared indium electrode, further ensuring the integrity of the electrode structure.

[0014] The present invention is further configured such that, in step S4, the local removal of the insulating coating is performed using a mechanical micromanipulation method. The removal of the insulating coating is completed under a stereomicroscope using a micro tungsten carbide probe. The area of ​​the resulting electrode welding window does not exceed 80% of the corresponding indium electrode surface area. There is no residual insulating layer or damage to the indium electrode at the edge of the window. The combined use of the stereomicroscope and the micro tungsten carbide probe enables precise positioning of the insulating layer removal, avoiding damage to the indium electrode or sample surface during the removal process. The control of the welding window area takes into account both the contact area requirements for subsequent welding and the overall structural stability of the indium electrode. This ensures effective contact between the wire and the indium electrode while avoiding the risk of short circuits caused by excessive electrode exposure due to an excessively large window.

[0015] The present invention is further configured such that, in step S5, the low-temperature solder paste is Sn-Bi series low-temperature solder paste, with a solid-phase melting point between 120°C and 140°C. The metal wire is any one of high-purity gold wire, high-purity copper wire, or gold-plated copper wire, with the wire diameter controlled between 20μm and 50μm. The end of the wire needs to be deoxidized before contacting the solder paste and indium electrode. The low melting point of the Sn-Bi series low-temperature solder paste avoids damage to the sample and indium electrode caused by high temperature during the welding process. Compared with existing high-temperature solder paste, it is more suitable for the low-temperature operation requirements of this process. The selection of the wire diameter is suitable for the electrode size of the millimeter-level bulk sample. The deoxidation treatment effectively removes the oxide layer at the end of the wire, ensuring a good electrical connection between the wire and the indium electrode and solder paste, thus solving the problem of poor wire contact in existing welding processes.

[0016] The present invention is further configured such that, in step S6, the hot air temperature for hot air welding is precisely controlled between 130°C and 150°C, the vertical distance between the hot air gun outlet and the welding window is 5mm to 10mm, and the heating time is controlled between 5s and 15s. Heating is stopped after the low-temperature solder paste has completely melted and fully wetted the indium electrode and the metal wire. During the cooling process, the metal wire is kept without displacement to avoid defects such as cold solder joints. These hot air welding parameters are precisely adjusted to ensure that the low-temperature solder paste can fully melt and form a good metallurgical bond with the indium electrode, while preventing the indium electrode from melting or the sample from being damaged due to excessively high temperature or heating time. The control of the hot air gun distance ensures the uniformity of heating and avoids local overheating. The fixing of the wire during the cooling process further ensures the stability of the welded structure, solving the problems of poor welding stability and easy cold solder joints in the existing spot welding method.

[0017] The present invention is further configured such that, in step S6, the weld joint formed after cooling is a solid-bonded metallurgical structure, the molten solder and the indium electrode form an interfusion diffusion layer, the weld joint completely covers the end of the metal wire, the boundary of the weld joint does not exceed the range of the electrode welding window, there are no defects of solder overflow or cold welding, and low resistance connection between the electrode and the wire is achieved. The formation of the interfusion diffusion layer makes the connection between the indium electrode and the metal wire more solid. Compared with the mechanical contact of the existing indium pressing method, it improves the mechanical stability and thermal cycling resistance of the connection. The control of the weld joint boundary avoids electrode short circuit caused by solder overflow. The low resistance connection characteristic effectively reduces the contact resistance, ensures the accuracy of electrical transmission measurement data, and solves the problems of high contact resistance and poor stability of the existing process.

[0018] The present invention is further configured such that, after step S6 is completed, the contact resistance of each electrode is tested using a four-probe method, and the contact resistance between a single electrode and the wire is no higher than 1Ω. After the contact resistance test is completed, the sample is subjected to more than 10 thermal cycling tests. The fluctuation range of the electrode contact resistance after the cycles does not exceed 5%. The use of the four-probe method ensures the accuracy of the contact resistance test. Compared with the ordinary two-probe test, it effectively eliminates the interference of the wire's own resistance. The numerical limitation of the contact resistance and the requirements of the thermal cycling test directly reflect the core advantages of this process, proving that the electrode structure prepared by this process can maintain stable ohmic contact in a wide temperature range variable temperature test environment. This solves the problem of loose contact and large fluctuation of contact resistance in the existing indium pressing method under temperature change environment, and meets the needs of high-precision electrical transport experiments.

[0019] The present invention has the following beneficial effects.

[0020] 1. This invention utilizes the synergistic combination of indium-pressed contact and hot air welding. Leveraging the excellent ductility and low resistance of high-purity indium, it enables the indium to form a gapless ohmic contact with the surface of a millimeter-scale bulk sample under constant pressure at room temperature. Simultaneously, by utilizing the low melting point of Sn-Bi series low-temperature solder paste, a precisely temperature-controlled hot air welding process is used to form a metallurgically bonded solder joint structure between the metal wire and the indium electrode. The formation of the interfusion diffusion layer effectively solves the problem of contact loosening. Compared with a single contact method, it retains the advantage of minimal thermal damage to the sample from the indium-pressed method while possessing the high mechanical stability of the welded connection. This achieves a dual improvement in low contact resistance and structural stability, significantly enhancing the accuracy and repeatability of electrical transport measurement data.

[0021] 2. This invention utilizes a structural combination of insulating coating, precise windowing, and parametric welding. It employs UV-curable insulating adhesive to completely encapsulate the non-electrode areas of the sample, effectively isolating external environmental interference and the risk of electrode short circuits, protecting the shape of the indium electrode, and limiting the solder diffusion range. This ensures the stability of the welding position and prevents damage to the electrode structure. Simultaneously, precise windowing under the assistance of a stereomicroscope ensures the welding contact area while avoiding damage to the indium electrode and sample surface. Combined with electrode size design and wire selection adapted to millimeter-scale samples, the process adaptability is further optimized. The operation is simple and requires no complex equipment. It solves the problems of unstable contact and large measurement deviations in some material systems while also protecting temperature-sensitive samples. It is suitable for the fabrication of electrical transport devices using various millimeter-scale bulk materials, making it widely applicable and highly practical. Attached Figure Description

[0022] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0023] Figure 1 This is a flowchart illustrating the overall process flow of a novel electrode fabrication and wiring technique that combines indium-pressed contact and hot air welding.

[0024] Figure 2 This is a detailed flowchart of stage S1 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0025] Figure 3 This is a detailed flowchart of stage S2 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0026] Figure 4 This is a detailed flowchart of stage S3 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0027] Figure 5 This is a detailed flowchart of stage S4 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0028] Figure 6 This is a detailed flowchart of stage S5 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0029] Figure 7 This is a detailed flowchart of stage S6 in a novel electrode fabrication and wiring process that combines indium-pressed contact and hot air welding.

[0030] Figure 8 This image shows an actual sample with indium-plated contacts in a novel electrode fabrication and wiring process that combines indium-plated contact and hot air welding.

[0031] Figure 9 This image shows an indium block coated with solder resist and cured under ultraviolet light in a novel electrode fabrication and wiring process that combines indium contact and hot air welding.

[0032] Figure 10 This image shows a physical sample of indium block solder resist removal during a novel electrode fabrication and wiring process that combines indium contact and hot air welding.

[0033] Figure 11 This is a photograph of a novel electrode fabrication and wiring process that combines indium contact and hot air welding, in which gold wires and solder paste are placed on an indium block.

[0034] Figure 12 This image shows a physical example of a novel electrode fabrication and wiring process that combines indium contact and hot air welding, in which a hot air gun heats the gold wire and solder paste on an indium block at 135°C. Detailed Implementation

[0035] The technical solutions of the present invention will be described below with reference to the accompanying drawings. The described embodiments are only some embodiments of the present invention, and not all embodiments.

[0036] Example 1 Please see Figure 1-12 This invention discloses a novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding, comprising the following steps: S1: The sample of the bulk material to be tested at the millimeter scale is processed into a regular long strip Hallbar structure for electrical transport measurement. The surface of the processed sample is cleaned. Mechanical peeling, solvent cleaning or other surface cleaning methods can be used to remove the contamination layer or oxide layer on the sample surface to ensure the surface cleanliness of the sample area to be processed. S2: On the cleaned sample surface, soft indium is pressed at predetermined electrode points using the indium pressing method to form a regular electrode layout that meets the requirements of Hallbar testing. Taking advantage of the good ductility of indium, a stable and gapless ohmic contact is formed between indium and the sample surface under constant pressure. S3: On the sample and the surface of the indium electrode after the indium electrode preparation is completed, an insulating coating is uniformly coated to form a complete coverage of the non-electrode area of ​​the sample and the non-contact area of ​​the indium electrode. The coated insulating coating is then irradiated with ultraviolet light to complete the curing process, forming a stable insulating protective layer on the sample surface. S4: Locally remove the cured insulating coating covering the surface of the indium electrode to expose the preset contact area of ​​the indium electrode, forming an electrode welding window. Ensure that there is no residue of the insulating coating in the removed area, so that the contact area of ​​the indium electrode is completely exposed, providing a clean contact interface for subsequent welding. S5: Apply low-temperature solder paste to the exposed indium electrode contact area, place the end of the metal wire in the solder paste position, and make the end of the wire fully adhere to the surface of the indium electrode to ensure that the solder paste evenly covers the contact area and there is no gap between the end of the wire and the indium electrode, forming a stable pre-contact structure. S6: The hot air welding method is used to precisely heat the solder paste area, so that the low-temperature solder paste is fully melted, wets the indium electrode and the metal wire, and after heating is stopped, it is naturally cooled at room temperature to form a stable welded connection structure between the metal wire and the indium electrode.

[0037] Example 2 This embodiment provides a novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding, applied to the fabrication of electrical transport Hallbar devices for millimeter-scale bulk thermoelectric materials. The specific steps are as follows: First, the millimeter-scale bulk thermoelectric material sample to be tested is processed into a regular elongated Hallbar structure with a reference size of 1.2mm × 2.2mm. Mechanical peeling, solvent cleaning, or other surface cleaning methods can be used to remove the contaminant or oxide layer from the sample surface. Complete removal of the surface contaminant and natural oxide layers ensures the surface flatness of the area to be pressed with indium, preventing surface impurities from affecting the contact effect between the indium electrode and the sample. Then, on the cleaned sample surface, high-purity indium (99.995%) is pressed under constant pressure at room temperature to form an indium electrode with a six-electrode layout conforming to the Hallbar testing standard at predetermined electrode locations. The indium electrodes for the four voltage testing terminals are 0.2mm × 0.2mm in size, and the indium electrodes for the two current application terminals are 0.A 2mm × 1mm electrode is used to create a stable, gapless ohmic contact between the indium electrode and the sample surface, utilizing the good ductility of indium. The use of high-purity indium effectively reduces the resistance of the indium electrode itself and avoids the influence of impurities on the contact effect. Next, an 80μm thick UV-curable insulating adhesive is uniformly coated onto the sample and the surface of the indium electrode, completely covering the non-electrode areas of the sample and the non-contact areas of the indium electrode. The coated insulating coating is then irradiated with UV light for 60 seconds to complete the curing process, forming a stable insulating protective layer on the sample surface. The cured insulating coating completely covers the non-test areas of the sample and the non-contact areas of the indium electrode, without any missed areas or bulging. The defects were identified. Subsequently, the cured insulating coating covering the indium electrode surface was locally removed using a mechanical micromanipulation method. Under a stereomicroscope, a micro-tungsten carbide probe was used to remove the insulating coating from a predetermined area on the indium electrode surface, exposing the predetermined contact area of ​​the indium electrode and forming an electrode welding window. The window area did not exceed 80% of the corresponding indium electrode surface area, and there was no residual insulating layer or damage to the indium electrode at the window edge. Then, Sn-Bi-based lead-free low-temperature solder paste with a solid-phase melting point of 135℃ was applied to the exposed indium electrode contact area. A 40μm diameter gold-plated copper wire end, after plasma deoxidation treatment, was placed at the solder paste location, ensuring the wire end was fully bonded to the indium electrode surface. The solder paste is evenly applied to the contact area, ensuring no gaps between the wire tip and the indium electrode, forming a stable pre-contact structure. The oxidation resistance of the gold-plated copper wire is suitable for high-temperature testing environments. Finally, hot air welding is used to precisely heat the solder paste area, controlling the hot air temperature precisely at 145℃. The vertical distance between the hot air gun outlet and the welding window is 8mm, and the heating time is controlled at 12s. Heating is stopped after the low-temperature solder paste has completely melted and fully wetted the indium electrode and the metal wire. It is then allowed to cool naturally at room temperature, maintaining no displacement of the metal wire during cooling to avoid cold solder joint defects, thus forming a stable welded connection structure between the metal wire and the indium electrode. The resulting weld joint is a solid-metallic structure where the molten solder and indium electrode form an interfusion diffusion layer. The weld joint completely covers the end of the metal wire, and its boundary does not exceed the electrode welding window, exhibiting no solder overflow, incomplete soldering, or cold soldering defects. After the process, the contact resistance of each electrode was tested using the four-probe method. The contact resistance between a single electrode and the wire was 0.9Ω. After 10 cycles of thermal cycling from -50℃ to 150℃, the contact resistance fluctuation was 4%. This electrode structure maintains stable ohmic contact in a high-temperature variable-temperature testing environment of 300K-400K, meeting the long-term stability requirements of high-temperature electrical transport measurements of thermoelectric materials.

[0038] Example 3 This embodiment provides a novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding, applied to the fabrication of electrical transport Hallbar devices for millimeter-scale bulk oxide ceramic materials. The specific steps are as follows: First, the millimeter-scale bulk oxide ceramic material sample to be tested is processed into a regular elongated Hallbar structure with a reference size of 1mm × 2mm. Mechanical peeling, solvent cleaning, or other surface cleaning methods can be used to remove the contaminant or oxide layer from the sample surface. Complete removal of the surface contaminant and natural oxide layers ensures the surface flatness of the area to be pressed with indium. This cleaning method will not damage the surface structure of the oxide ceramic sample. Subsequently, on the cleaned sample surface, high-purity indium (99.992%) is pressed under constant pressure at room temperature to form an indium electrode layout conforming to the Hallbar testing standard at predetermined electrode locations. The indium electrodes for the four voltage testing terminals are 0.2mm × 0.2mm in size, and the indium electrodes for the two current application terminals are 0.The 2mm × 1mm indium electrode utilizes its excellent ductility to form a stable, gapless ohmic contact between indium and the sample surface. The room temperature pressing process minimizes thermal damage, making it suitable for temperature-sensitive oxide ceramic materials. Next, a 100μm thick UV-curable insulating adhesive is uniformly coated onto the sample and the surface of the indium electrode, completely covering the non-electrode areas and the non-contact areas of the indium electrode. The coated insulating layer is then irradiated with UV light for 90 seconds to complete the curing process, forming a stable insulating protective layer on the sample surface. Compared to traditional thermal curing, UV curing is faster and does not damage the prepared sample. The indium electrode suffered thermal damage. Subsequently, the cured insulating coating covering the indium electrode surface was locally removed using a mechanical micromanipulation method. Under a stereomicroscope, a miniature tungsten carbide probe was used to remove the insulating coating from a predetermined area on the indium electrode surface, exposing the predetermined contact area of ​​the indium electrode and forming an electrode welding window. The window area did not exceed 80% of the corresponding indium electrode surface area, and there was no insulating layer residue or indium electrode damage at the window edge. Then, a Sn-Bi-based lead-free low-temperature solder paste with a solid-phase melting point of 140℃ was applied to the exposed indium electrode contact area. A 50μm diameter high-purity copper wire end, after plasma deoxidation treatment, was placed at the solder paste location to conduct the solder. The wire tip is fully in contact with the indium electrode surface to ensure uniform solder paste coverage of the contact area. There is no gap between the wire tip and the indium electrode, forming a stable pre-contact structure. Finally, hot air welding is used to precisely heat the solder paste area, with the hot air temperature precisely controlled at 150℃. The vertical distance between the hot air gun outlet and the welding window is 10mm, and the heating time is controlled at 15s. Heating is stopped after the low-temperature solder paste has completely melted and fully wetted the indium electrode and the metal wire. It is then allowed to cool naturally at room temperature, maintaining no displacement of the metal wire during cooling to avoid cold solder joint defects. This forms a stable welded connection structure between the metal wire and the indium electrode. The resulting structure after cooling... The welding joint is a solid-metallic structure where the molten solder forms an interfusion diffusion layer with the indium electrode. The solder joint completely covers the end of the metal wire, and its boundary does not exceed the electrode welding window, eliminating defects such as solder overflow, incomplete soldering, and cold soldering. After the process is completed, the contact resistance of each electrode is tested using the four-probe method. The contact resistance between a single electrode and the wire is 1.0Ω. After 10 cycles of thermal cycling from -50℃ to 150℃, the contact resistance fluctuation is 5%. This electrode structure maintains stable ohmic contact in a low-temperature variable-temperature testing environment of 80K-200K, meeting the accuracy requirements of low-temperature electrical transport measurements using oxide ceramic materials.

Claims

1. A novel electrode preparation and wiring process combining the process of compression indium contact and hot air soldering method, characterized in that: Includes the following steps: S1: The sample of the bulk material to be tested at the millimeter scale is processed into a regular long strip Hallbar structure for electrical transport measurement. The surface of the processed sample is cleaned. Mechanical peeling, solvent cleaning or other surface cleaning methods can be used to remove the contamination layer or oxide layer on the sample surface to ensure the surface cleanliness of the sample area to be processed. S2: On the cleaned sample surface, soft indium is pressed at predetermined electrode points using the indium pressing method to form a regular electrode layout that meets the requirements of Hallbar testing. Taking advantage of the good ductility of indium, a stable and gapless ohmic contact is formed between indium and the sample surface under constant pressure. S3: On the sample and the surface of the indium electrode after the indium electrode preparation is completed, an insulating coating is uniformly coated to form a complete coverage of the non-electrode area of ​​the sample and the non-contact area of ​​the indium electrode. The coated insulating coating is then irradiated with ultraviolet light to complete the curing process, forming a stable insulating protective layer on the sample surface. S4: Locally remove the cured insulating coating covering the surface of the indium electrode to expose the preset contact area of ​​the indium electrode, forming an electrode welding window. Ensure that there is no residue of the insulating coating in the removed area, so that the contact area of ​​the indium electrode is completely exposed, providing a clean contact interface for subsequent welding. S5: Apply low-temperature solder paste to the exposed indium electrode contact area, place the end of the metal wire in the solder paste position, and make the end of the wire fully adhere to the surface of the indium electrode to ensure that the solder paste evenly covers the contact area and there is no gap between the end of the wire and the indium electrode, forming a stable pre-contact structure. S6: The hot air welding method is used to precisely heat the solder paste area, so that the low-temperature solder paste is fully melted, wets the indium electrode and the metal wire, and after heating is stopped, it is naturally cooled at room temperature to form a stable welded connection structure between the metal wire and the indium electrode.

2. A novel electrode preparation and wiring process combining pressure indium contact and hot air soldering method as claimed in claim 1, wherein: In step S1, the reference size of the processed Hallbar structure sample is 1mm × 2mm. The mechanical peeling process must completely remove the contamination layer and natural oxide layer on the sample surface to ensure the surface flatness of the indium area to be pressed and avoid surface impurities affecting the contact effect between the indium electrode and the sample.

3. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding as described in claim 1, characterized in that: In step S2, the Hallbar test uses a standard six-electrode layout. The four voltage test terminals have indium electrodes measuring 0.2mm × 0.2mm, while the two electrodes for applying the current source use indium blocks measuring 0.2mm × 1mm to ensure uniform current distribution within the sample.

4. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding as described in claim 1, characterized in that: In step S2, the soft metal indium used to press the electrode is high-purity indium. The pressing process of the indium electrode is completed at room temperature. By pressing with constant pressure, the indium is tightly bonded to the sample surface to form a gapless contact interface.

5. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding as described in claim 1, characterized in that: In step S3, the insulating coating uses UV-curable insulating adhesive, and the coating thickness is controlled between 50μm and 100μm. The UV irradiation curing time is controlled between 30s and 90s. The cured insulating coating completely covers the non-test area of ​​the sample and the non-contact area of ​​the indium electrode, without any defects such as missed coating or bubbling.

6. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding according to claim 1, characterized in that: In step S4, the local removal of the insulating coating is carried out using mechanical micromanipulation. The removal of the insulating coating is performed under a stereomicroscope using a micro tungsten carbide probe. The area of ​​the electrode welding window formed does not exceed 80% of the surface area of ​​the corresponding indium electrode, and there is no residual insulating layer or damage to the indium electrode at the edge of the window.

7. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding according to claim 1, characterized in that: In step S5, the low-temperature solder paste is Sn-Bi series low-temperature solder paste with a solid-phase melting point between 120°C and 140°C. The metal wire is any one of high-purity gold wire, high-purity copper wire, or gold-plated copper wire. The wire diameter is controlled between 20μm and 50μm. The wire end needs to be deoxidized before contacting the solder paste and indium electrode.

8. The novel electrode preparation and wiring process combining indium-pressed contact and hot air welding according to claim 1, characterized in that: In step S6, the hot air temperature for hot air welding is precisely controlled between 130°C and 150°C, the vertical distance between the hot air gun outlet and the welding window is 5mm to 10mm, the heating time is controlled between 5s and 15s, and heating is stopped after the low-temperature solder paste has completely melted and fully wetted the indium electrode and the metal wire. During the cooling process, the metal wire is kept without displacement to avoid the occurrence of cold solder joint defects.

9. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding according to claim 1, characterized in that: In step S6, the weld joint formed after cooling is a solid-bonded metallurgical structure. The molten solder and the indium electrode form an inter-fusion diffusion layer. The weld joint completely covers the end of the metal wire. The boundary of the weld joint does not exceed the range of the electrode welding window. There are no defects such as solder overflow or cold welding, thus achieving a low-resistance connection between the electrode and the wire.

10. The novel electrode fabrication and wiring process combining indium-pressed contact and hot air welding according to claim 1, characterized in that: After step S6 is completed, the contact resistance of each electrode is tested using the four-probe method. The contact resistance between a single electrode and the wire is no higher than 1Ω. After the contact resistance test is completed, the sample is subjected to more than 10 cold and hot cycle tests. After the cycle, the fluctuation range of the electrode contact resistance does not exceed 5%.

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