Anti-vulcanization thick-film resistor and preparation method thereof

Abstract

The invention relates to the technical field of thick-film resistors, in particular to an anti-vulcanization thick-film resistor and a preparation method thereof. The front electrode and the back electrode are arranged on the upper surface and the lower surface of the high-purity aluminum oxide substrate; an impedance element disposed between the front electrodes; a protective layer covering the impedance element; the resin silver layer is arranged above the protective layer; the multi-layer end face structure comprises a nickel-chromium alloy layer, a pure nickel layer and a silver layer which are sequentially arranged from inside to outside; wherein the multi-layer end face structure is formed through a sputtering process and continuously covers the edge areas of the resin silver layer and the protective layer, and the nickel-chromium alloy layer, the pure nickel layer and the silver layer in the multi-layer sputtering structure form a gradient electronic structure. The nickel-chromium alloy layer has high electron affinity, free electrons in the environment can be effectively captured, the opportunity that the free electrons are combined with sulfur ions is reduced, and a composite protection structure with the labyrinth effect is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of thick film resistors, and particularly to a sulfur-resistant thick film resistor and a preparation method thereof. Background Art

[0002] Thick film resistors are widely used in the electronics industry due to their excellent electrical performance, reliability, and cost-effectiveness. However, in some special environments, especially in the presence of sulfides, traditional thick film resistors often face serious performance degradation problems. The sulfidation phenomenon not only causes the resistance value to drift but also may lead to the failure of the resistor, thus affecting the reliability of the entire electronic system. Therefore, developing thick film resistors with excellent sulfur resistance has become an urgent need in the industry.

[0003] In the prior art, there have been various methods to attempt to solve the sulfidation problem of thick film resistors. Among them, the closest prior art can refer to the following patents: Chinese Patent CN101681705B, titled Sulfur-resistant chip resistor and manufacturing method thereof. This patent proposes a chip resistor, which improves the sulfur resistance by covering a multi-layer protective coating on the resistor layer. However, this method has the following defects: Firstly, the preparation process of the multi-layer coating is complex, increasing the production cost; Secondly, the interfacial bonding strength between the coatings is insufficient, and micro-cracks are likely to occur under temperature cycling and mechanical stress, thus reducing the long-term reliability.

[0004] Chinese Patent CN103165250A proposes a thick film sulfur-resistant surface mount resistor, mainly improving the sulfur resistance by covering a multi-layer protective coating on the resistor layer. However, this method has the following main drawbacks: Multiple printing and sintering processes are required to form the multi-layer protective coating, which not only increases the production time but also significantly increases the manufacturing cost. The multi-layer coating structure is prone to poor interfacial bonding under high temperature and mechanical stress, resulting in the formation of micro-cracks, thus reducing the long-term reliability. It mainly relies on the physical barrier of the coating to achieve sulfur resistance, but this method is difficult to cope with long-term and harsh sulfidation environments. The multi-layer coating structure is prone to generate stress due to the mismatch of thermal expansion coefficients during the thermal cycling process, resulting in performance degradation; once the protection structure has defects, it is difficult to self-repair. Summary of the Invention

[0005] Based on a full understanding of the deficiencies of the prior art, the present invention proposes an innovative sulfur-resistant thick film resistor and a preparation method thereof.

[0006] The object of the present invention is to provide a sulfur-resistant thick film resistor, including: A high-purity alumina substrate; A front electrode disposed on the upper surface of the high-purity alumina substrate and a back electrode disposed on the lower surface; An impedance element disposed between the positive electrodes; A protective layer covering the impedance element; A resin silver layer disposed above the protective layer; A multi-layer end face structure covering both ends of the resistor, the multi-layer end face structure including a nickel-chromium alloy layer, a pure nickel layer, and a silver layer sequentially arranged from the inside to the outside; Wherein, the multi-layer end face structure is formed by a sputtering process and forms a continuous coverage with the edge regions of the resin silver layer and the protective layer.

[0007] Specifically, the high-purity alumina substrate has a purity of 99.6% and dimensions of 1.0 mm x 0.5 mm x 0.35 mm; The positive electrode and the negative electrode are made of a silver-palladium alloy paste, wherein the weight ratio of silver to palladium is 95:5; The impedance element is made of a RuO 2 base paste and has a thickness of 10 μm; The protective layer is made of a mixed paste of glass powder and an organic binder and has a thickness of 20 μm; The silver content in the resin silver layer is 70 wt% and the thickness is 15 μm; In the multi-layer end face structure, the nickel-chromium alloy layer has a thickness of about 50 nm, the pure nickel layer has a thickness of about 200 nm, and the silver layer has a thickness of about 100 nm.

[0008] A preparation method of the anti-sulfuration thick film resistor includes the following steps: High-purity alumina substrate preparation, electrode preparation, impedance element preparation, protective layer preparation, resin silver layer preparation, preliminary end face electrode preparation, innovative sputtering enhancement process, pelletizing, cleaning, laser trimming, final end face treatment, and high-temperature aging and testing.

[0009] Specifically, the substrate preparation step includes: Performing ultrasonic cleaning on an alumina substrate with a purity of 99.6% and dimensions of 1.0 mm x 0.5 mm x 0.35 mm for 5 minutes each using deionized water and isopropyl alcohol, and then performing plasma treatment with a power of 100 W for 30 seconds.

[0010] Specifically, the electrode preparation step includes: Using a silver-palladium alloy paste (silver:palladium = 95:5 wt%), printing a 15-μm-thick back electrode and a front electrode through a 325-mesh stainless steel wire screen, drying at 150 °C for 10 minutes, and then sintering in an air atmosphere at 850 °C for 10 minutes.

[0011] Specifically, the impedance element preparation step includes: Using RuO 2The base paste is used to screen-print a 10-μm thick impedance element through a 400-mesh stainless steel wire screen, dried at 150°C for 15 minutes, and then sintered in an air atmosphere at 850°C for 30 minutes.

[0012] Specifically, the preparation steps of the protective layer include: A paste is prepared by mixing glass powder and an organic binder, and a 20-μm thick protective layer is screen-printed through a 325-mesh screen, dried at 150°C for 10 minutes, and then sintered in an air atmosphere at 850°C for 20 minutes.

[0013] Specifically, the preparation steps of the resin silver layer include: A paste is prepared by mixing silver powder and epoxy resin (silver content 70 wt%), and a 15-μm thick resin silver layer is screen-printed through a 400-mesh screen and cured at 180°C for 30 minutes. The preliminary preparation of the end electrodes includes: using silver glass paste to screen-print end electrodes at both ends of the component through a 200-mesh screen, drying at 150°C for 10 minutes, and then sintering in an air atmosphere at 600°C for 15 minutes.

[0014] Specifically, the innovative sputtering enhancement process steps include: Use a 0.1-mm thick stainless steel mask to precisely cover the middle area, leaving 0.2 mm exposed at both ends; In a multi-target magnetron sputtering system, at a substrate temperature of 200°C and a working pressure of 0.5 Pa (Ar atmosphere), multi-layer sputtering is carried out: The first layer (nickel-chromium alloy): Use a Ni80Cr20 alloy target, with a power of 100 W RF, sputter for 5 minutes, and the thickness is about 50 nm; The second layer (pure nickel): Use a 99.99% pure nickel target, with a power of 150 W DC, sputter for 10 minutes, and the thickness is about 200 nm; The third layer (silver): Use a 99.99% pure silver target, with a power of 80 W DC, sputter for 3 minutes, and the thickness is about 100 nm; Angle-variable sputtering is adopted: The initial inclination angle of the sample stage is 45°, it changes 10° every 2 minutes, the range is 45° - 90°, and the rotation speed of the sample stage is 10 rpm; Pulse sputtering is carried out on the silver layer: The frequency is 50 kHz and the duty cycle is 70%; In-situ plasma treatment is carried out before and after each layer of sputtering: Use a mixture of Ar and O 2 mixed gas (9:1), with a power of 50 W RF, and the time for each is 30 seconds.

[0015] Specifically, the step of splitting grains includes: dividing the continuous strip structure into individual resistor elements; the cleaning step uses an ultrasonic cleaning device to clean the resistor elements after splitting grains successively with deionized water and isopropyl alcohol, and each solvent is used for cleaning for 5 minutes. The laser fine-tuning step includes: Using a Nd:YAG laser with a wavelength of 1064 nm, a pulse width of 100 ns, a frequency of 20 kHz, and a power range of 0.1 - 2 W, dynamically adjusted according to the required adjustment amount; the final end face treatment step includes: Electroplating a nickel layer: Using a nickel sulfate solution (250 g / L NiSO 4 ·6H 2 O, 45 g / L NiCl 2 ·6H 2 O, 40 g / L H 3 BO 3 ), with a current density of 2 A / dm², electroplating for 15 minutes at 50°C to form a nickel layer about 5 μm thick; Electroplating a lead-free tin layer: Using a tin methylsulfonate solution (50 g / L Sn²⁺, 130 g / L methylsulfonic acid), with a current density of 1 A / dm², electroplating for 10 minutes at 25°C to form a tin layer about 3 μm thick; The high-temperature aging and testing step includes: Aging at 125°C for 168 hours, and then performing a 1000-hour anti-sulfidation test under an 85°C, 85% relative humidity, 10 ppm H 2 S atmosphere, testing the resistance value by the four-wire method, and the test current does not exceed 1 / 10 of the rated power.

[0016] The innovation points and technical effects of the present invention are mainly reflected in the following aspects: The core innovation point of the present invention lies in the adoption of a unique multi-layer sputtering process, combined with a carefully designed material combination, to form a composite protection structure with a labyrinth effect. This structure can not only effectively prevent the penetration of sulfides but also maintain good stability in harsh environments.

[0017] From the perspective of chemical mechanism, the innovation of the present invention is mainly reflected in the following aspects: Firstly, the nickel-chromium alloy layer, pure nickel layer, and silver layer in the multi-layer sputtering structure form a gradient electron structure. The nickel-chromium alloy layer has a high electron affinity and can effectively capture free electrons in the environment, reducing the chance of their combination with sulfide ions. The pure nickel layer acts as an electron barrier, further hindering the migration of sulfide ions. The outermost silver layer not only provides good conductivity but also forms a dense silver oxide film on the surface, which can block the entry of sulfides at the molecular level.

[0018] Secondly, the introduction of the resin silver layer creates a unique interfacial environment. The polymer chains in the resin form a semi-interpenetrating network structure with silver particles, which forms a large number of microscopic dead ends at the molecular scale, significantly increasing the diffusion path of sulfide molecules and thus greatly reducing the sulfidation rate.

[0019] Thirdly, the innovative angle-variable sputtering technology achieves a material interlocking effect at the nanoscale. Atoms sputtered at different angles form a complex three-dimensional network structure at the interface, which not only enhances the interlayer bonding force but also creates a large number of energy traps at the atomic level, capable of effectively capturing and passivating invading sulfur ions.

[0020] Finally, the in-situ plasma treatment step introduces surface-active groups that can form chemical bonds with the atoms of the subsequent layer, significantly improving the interfacial bonding strength. At the same time, the plasma treatment can also form nanoscale roughness on the surface, increasing the specific surface area of the material and thus enhancing its adsorption and passivation ability for sulfides.

[0021] The synergistic effect of these innovative points not only significantly improves the sulfidation resistance of the resistor but also brings a series of unexpected technical effects. For example, the self-healing ability of the multi-layer structure, the interface strengthening effect, and the optimization of electrical properties. These effects enable the sulfidation-resistant thick film resistor of the present invention to maintain excellent performance and reliability in various extreme environments.

[0022] In addition, through the innovative multi-layer sputtering process and material design, the present invention significantly improves the sulfidation resistance, thermal stability, and mechanical reliability of the thick film resistor, meeting the urgent needs of modern electronic products for highly reliable components. Although the present invention introduces high-end sputtering processes, by optimizing the manufacturing process, the need for multiple printing and sintering is reduced, controlling production costs while improving performance. The innovative processes such as angle-variable sputtering and in-situ plasma treatment of the present invention bring new technological breakthroughs to the field of thick film resistor manufacturing and are expected to promote the technological progress of the entire industry. The high-performance sulfidation-resistant thick film resistor of the present invention can operate stably in more stringent environments, which provides the possibility for the application of electronic products in high-demand fields such as automotive, industrial control, and aerospace. The excellent thermal stress management ability of the present invention provides a new solution for improving the long-term reliability and service life of electronic products.

[0023] In summary, by deeply understanding the principles of materials science and chemistry, the present invention ingeniously designs a novel anti-sulfuration thick film resistor structure and its preparation method. This innovation not only solves the problem of performance degradation of traditional thick film resistors in a sulfuration environment but also achieves remarkable breakthroughs in overall performance, reliability, and service life. Therefore, the present invention provides a highly valuable solution for the electronics industry, especially in fields with extremely high reliability requirements, such as automotive electronics, aerospace, and industrial control. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 FIG. is a schematic structural diagram of the anti-sulfuration thick film resistor of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention. Embodiment 1

[0026] The present invention relates to an anti-sulfuration thick film resistor and its preparation method, particularly a thick film resistor with excellent anti-sulfuration performance and electrical stability. As Figure 1 shown, the anti-sulfuration thick film resistor of the present invention includes a high-purity alumina substrate 1, a front electrode 2, a back electrode 3, an impedance element 4, a protective layer 5, a resin silver layer 6, and a multi-layer end face structure 7.

[0027] The high-purity alumina substrate 1 serves as the support structure of the entire resistor, and its purity and size have important effects on the performance of the resistor. The front electrode 2 and the back electrode 3 are respectively disposed on the upper surface and the lower surface of the substrate 1 for connecting to an external circuit. The impedance element 4 is disposed between the front electrodes 2 and is the core part of the resistor, determining the resistance value. The protective layer 5 covers the impedance element 4 to play a protective role. The resin silver layer 6 is disposed above the protective layer 5 to enhance conductivity. The multi-layer end face structure 7 covers both ends of the resistor and is a key innovation point of the present invention. It is formed by a special sputtering process, significantly improving the anti-sulfuration performance of the resistor.

[0028] In an embodiment of the present invention, the purity of the high-purity alumina substrate 1 is 99.6%, and the size is 1.0 mm x 0.5 mm x 0.35 mm. The high-purity alumina substrate 1 serves as the support structure of the entire resistor, ensuring the mechanical strength and dimensional stability of the resistor.

[0029] The front electrode 2 and the back electrode 3 are made of a silver-palladium alloy paste, in which the weight ratio of silver to palladium is 95:5. This ratio not only ensures good electrical conductivity but also improves the anti-sulfuration ability of the electrodes. It not only provides good electrical conductivity but also has a certain anti-sulfuration ability. These two electrodes are connected to the external circuit to form the inlet and outlet of the current.

[0030] The impedance element 4 is made of a RuO 2 base paste with a thickness of 10 μm. RuO 2 has excellent temperature coefficient and stability, ensuring the stability of the resistance value under various environmental conditions.

[0031] The protective layer 5 is made of a mixed paste of glass powder and organic binder with a thickness of 20 μm, which can protect the impedance element without affecting the overall performance of the resistor. The silver content in the resin silver layer 6 is 70 wt% and the thickness is 15 μm. This ratio not only ensures good electrical conductivity but also provides appropriate mechanical strength. The main function of the resin silver layer 6 is to enhance electrical conductivity, and at the same time its resin component provides additional protection. The resin silver layer 6 forms a continuous protection system with the underlying protective layer 5 and the overlying multi-layer end face structure 7.

[0032] The multi-layer end face structure 7 is the core of the present invention, including a nickel-chromium alloy layer 71, a pure nickel layer 72, and a silver layer 73 arranged in sequence from the inside to the outside. The nickel-chromium alloy layer 71 has a thickness of about 50 nm, providing good adhesion and corrosion resistance. The pure nickel layer 72 has a thickness of about 200 nm and serves as an effective diffusion barrier layer. The silver layer 73 has a thickness of about 100 nm, further enhancing the anti-sulfuration ability. This multi-layer structure is formed by an innovative sputtering process and forms continuous coverage with the edge regions of the resin silver layer 6 and the protective layer 5, effectively preventing the infiltration of sulfides.

[0033] When the resistor is exposed to a sulfur-containing environment, the multi-layer end face structure 7 begins to function. The outermost silver layer first contacts the sulfides, but due to the denseness and continuity of the silver layer, the penetration rate of the sulfides is greatly slowed down.

[0034] If a small amount of sulfides penetrate through the silver layer, they will encounter the pure nickel layer. Nickel has a strong anti-sulfuration ability and can further prevent the intrusion of sulfides.

[0035] The innermost nickel-chromium alloy layer not only has good anti-sulfuration performance but also can form a strong bond with the underlying material to prevent interlayer delamination.

[0036] The resin component in the resin silver layer 6 forms a semi-interpenetrating network structure, which creates a large number of mazes at the molecular scale, significantly increasing the diffusion path of sulfide molecules.

[0037] When the temperature of the resistor changes during use, the design of the thermal expansion coefficient gradient of the multi-layer structure can effectively relieve thermal stress and prevent cracking and peeling.

[0038] In terms of material selection, the present invention pays particular attention to the synergistic effect of each layer of materials. For example, the nickel-chromium alloy layer uses Ni80Cr20 alloy, which not only has excellent anti-sulfidation performance, but also good thermal stability and mechanical strength. The pure nickel layer selects 99.99% high-purity nickel to ensure the best anti-sulfidation performance and conductivity.

[0039] The preparation method of the anti-sulfidation thick film resistor of the present invention includes the following steps: substrate preparation, electrode preparation, impedance element preparation, protective layer preparation, resin silver layer preparation, preliminary end electrode preparation, innovative sputtering enhancement process, laser trimming, final end treatment, and high-temperature aging and testing.

[0040] In the substrate preparation step, first, the alumina substrate 1 with a purity of 99.6% and dimensions of 1.0 mm x 0.5 mm x 0.35 mm is ultrasonically cleaned with deionized water and isopropyl alcohol for 5 minutes each, and then plasma treatment is carried out with a power of 100 W and a time of 30 seconds. This step ensures the cleanliness of the substrate surface and is conducive to the subsequent processes.

[0041] In the electrode preparation step, a silver-palladium alloy paste (silver: palladium = 95:5 wt%) is used to screen-print a 15-μm-thick back electrode 3 and a front electrode 2 through a 325-mesh stainless steel screen, dried at 150°C for 10 minutes, and then sintered in an air atmosphere at 850°C for 10 minutes. This high-temperature sintering process ensures good bonding between the electrode and the substrate.

[0042] The impedance element preparation step uses RuO 2 -based paste to screen-print a 10-μm-thick impedance element 4 through a 400-mesh stainless steel screen, dried at 150°C for 15 minutes, and then sintered in an air atmosphere at 850°C for 30 minutes. The selection of RuO 2 and the specific sintering process ensure the stability and accuracy of the impedance element.

[0043] In the protective layer preparation step, a mixed paste of glass powder and organic binder is used to screen-print a 20-μm-thick protective layer 5 through a 325-mesh screen, dried at 150°C for 10 minutes, and then sintered in an air atmosphere at 850°C for 20 minutes. This step forms a dense protective layer structure and effectively protects the impedance element.

[0044] The preparation steps of the resin silver layer use silver powder and epoxy resin mixed slurry (silver content 70wt%), screen-print a 15μm thick resin silver layer 6 through a 400-mesh screen, and cure it at 180°C for 30 minutes. This resin silver layer with a special formula provides both good electrical conductivity and enhanced structural integrity.

[0045] The preliminary preparation of the end electrodes uses silver glass slurry, screen-print the end electrodes at both ends of the component through a 200-mesh screen, dry them at 150°C for 10 minutes, and then sinter them in an air atmosphere at 600°C for 15 minutes.

[0046] The innovative sputtering enhancement process is the key step of the present invention. First, use a 0.1mm thick stainless steel mask to precisely cover the middle area, exposing 0.2mm at each end. Then, in a multi-target magnetron sputtering system, at a substrate temperature of 200°C and a working pressure of 0.5Pa (Ar atmosphere), perform multi-layer sputtering. The first layer (nickel-chromium alloy) uses a Ni80Cr20 alloy target, with a power of 100WRF, sputter for 5 minutes, and the thickness is about 50nm. The second layer (pure nickel) uses a 99.99% pure nickel target, with a power of 150W DC, sputter for 10 minutes, and the thickness is about 200nm. The third layer (silver) uses a 99.99% pure silver target, with a power of 80W DC, sputter for 3 minutes, and the thickness is about 100nm.

[0047] During the sputtering process, the angle-variable sputtering technique is adopted. The initial inclination angle of the sample stage is 45°, it changes 10° every 2 minutes, the range is 45° - 90°, and the rotation speed of the sample stage is 10 rpm. This dynamic adjustment ensures that the material can penetrate into tiny gaps and corners to form a complete coating. Pulse sputtering is used for the silver layer, with a frequency of 50 kHz and a duty cycle of 70%. This technique controls the thickness of each sputtering, improving the density and uniformity of the sputtered layer. In-situ plasma treatment is carried out before and after each layer of sputtering, using an Ar + O 2 mixed gas (9:1), with a power of 50W RF and a time of 30 seconds each. This step significantly improves the bonding force between layers.

[0048] Die breaking is to divide the continuous strip structure into individual resistor elements; for cleaning, use an ultrasonic cleaning device to clean the resistor elements after die breaking with deionized water and isopropanol in sequence, and each solvent is cleaned for 5 minutes; The laser trimming step uses a Nd:YAG laser, with a wavelength of 1064nm, a pulse width of 100ns, a frequency of 20kHz, and a power range of 0.1 - 2W, which is dynamically adjusted according to the required adjustment amount. This precise laser technology ensures the accuracy of the resistance value.

[0049] The final end face treatment includes two electroplating steps. First, electroplate a nickel layer, using a nickel sulfate solution (250 g / L NiSO 4 ·6H2 O, 45 g / L NiCl 2 ·6H 2 O, 40 g / L H 3 BO 3 (), the current density is 2 A / dm², electroplate for 15 minutes at 50 °C to form a nickel layer about 5 μm thick, further enhancing the anti-sulfuration ability. Then electroplate a lead-free tin layer, using a stannous methanesulfonate solution (50 g / L Sn²⁺, 130 g / L methanesulfonic acid), the current density is 1 A / dm², electroplate for 10 minutes at 25 °C to form a tin layer about 3 μm thick, providing good solderability.

[0050] Finally, perform high-temperature aging and testing. Age at 125 °C for 168 hours, and then conduct a 1000-hour anti-sulfuration test under an 85 °C, 85% relative humidity, 10 ppm H 2 S atmosphere. Test the resistance value by the four-wire method, and the test current does not exceed 1 / 10 of the rated power to ensure the accuracy of the test.

[0051] The anti-sulfuration thick film resistor of the present invention significantly improves the anti-sulfuration performance of the resistor through a unique multi-layer end face structure and an innovative sputtering process. At the same time, the precise preparation process ensures the electrical stability and reliability of the resistor. This kind of resistor is particularly suitable for electronic devices that require long-term stability and high reliability, such as automotive electronics, industrial control systems and other fields.

[0052] In other embodiments, the performance of the resistor can be further optimized by adjusting the thickness of each layer, sputtering parameters or electroplating conditions. For example, the thickness of the nickel layer can be increased to further improve the anti-sulfuration ability, or the sputtering parameters of the silver layer can be adjusted to improve the conductivity. This flexibility enables the present invention to adapt to different application requirements.

[0053] The present invention can be applied to a variety of specific scenarios, such as: Automotive electronics: Electronic control units used in high-temperature, high-humidity, sulfur-containing environments such as the engine compartment.

[0054] Industrial control: Control equipment used in industrial environments with more sulfur-containing gases such as chemical plants and refineries.

[0055] Aerospace: Electronic devices that work in the high-altitude environment for a long time and require extremely high reliability.

[0056] Marine engineering: Electronic devices used in high-salt fog and high-humidity marine environments.

[0057] In other embodiments, some modifications can be made to the present invention. For example, the silver layer in the multi-layer end face structure 7 can be replaced with a tin layer, a gold layer or a palladium layer to further improve the anti-sulfuration performance. The resin silver layer 6 can be replaced with other conductive polymer materials to meet different application requirements. In addition, a nano-scale ceramic coating can be added to the outermost layer to further enhance the overall corrosion resistance.

[0058] In summary, the present invention provides a high-performance anti-sulfuration thick film resistor and its preparation method, which overcomes the problem of performance degradation of traditional thick film resistors in a sulfuration environment and provides a strong guarantee for the long-term stability and reliability of electronic products.

[0059] Comparative Example 1: Conventional anti-sulfuration thick film resistor This comparative example aims to demonstrate the limitations of traditional anti-sulfuration methods and highlight the superiority of the innovative sputtering process of the present invention. In this comparative example, the same basic structure as in the embodiment is used, but instead of using the innovative sputtering enhancement process, a traditional single-layer nickel plating method is adopted.

[0060] The preparation method of Comparative Example 1 includes the following steps: First, a high-purity alumina substrate 1 with a purity of 99.6% and a size of 1.0 mm x 0.5 mm x 0.35 mm is prepared in the same manner as in the embodiment. Subsequently, the front electrode 2 and the back electrode 3 are prepared using the same silver-palladium alloy paste (silver: palladium = 95:5 wt%). An electrode layer with a thickness of 15 μm is screen-printed through a 325-mesh stainless steel wire mesh, dried at 150°C for 10 minutes, and then sintered in an air atmosphere at 850°C for 10 minutes.

[0061] Next, the impedance element 4 is prepared using a RuO 2 -based paste. An impedance layer with a thickness of 10 μm is screen-printed through a 400-mesh stainless steel wire mesh, dried at 150°C for 15 minutes, and then sintered in an air atmosphere at 850°C for 30 minutes. The preparation methods of the protective layer 5 and the resin silver layer 6 are the same as those in the embodiment.

[0062] However, in the end face treatment step, a traditional single-layer nickel plating method is adopted instead of the innovative sputtering enhancement process of the present invention. Specifically, a nickel sulfate solution (250 g / L NiSO 4 ·6H 2 O, 45 g / L NiCl 2 ·6H 2 O, 40 g / L H 3 BO 3 ) is used, with a current density of 2 A / dm², and electroplated at 50°C for 30 minutes to form a nickel layer with a thickness of about 10 μm. Finally, an unleaded tin layer is electroplated in the same manner as in the embodiment.

[0063] Comparative Example 2: Sulfur-resistant thick film resistor without resin silver layer This comparative example aims to highlight the importance of the resin silver layer 6 in the present invention and its synergistic effect with the innovative sputtering process. In this comparative example, the preparation step of the resin silver layer 6 will be omitted while retaining all other process steps.

[0064] The preparation method of Comparative Example 2 includes the following steps: Prepare the high-purity alumina substrate 1 using exactly the same method as in the embodiment, prepare the front electrode 2 and the back electrode 3, as well as the impedance element 4 and the protective layer 5. However, the preparation step of the resin silver layer 6 is skipped.

[0065] In the innovative sputtering enhancement process step, multi-layer sputtering is carried out using the same parameters and method as in the embodiment. Specifically, a 0.1 mm thick stainless steel mask is used, and in a multi-target magnetron sputtering system, multi-layer sputtering is carried out at a substrate temperature of 200 °C and a working pressure of 0.5 Pa (Ar atmosphere). The first layer (nickel-chromium alloy) uses a Ni80Cr20 alloy target, with a power of 100 W RF, sputtered for 5 minutes, and a thickness of about 50 nm. The second layer (pure nickel) uses a 99.99% pure nickel target, with a power of 150 W DC, sputtered for 10 minutes, and a thickness of about 200 nm. The third layer (silver) uses a 99.99% pure silver target, with a power of 80 W DC, sputtered for 3 minutes, and a thickness of about 100 nm.

[0066] The angle-variable sputtering technology is also adopted, with the initial inclination angle of the sample stage being 45°, changing by 10° every 2 minutes, in the range of 45° to 90°, and the rotation speed of the sample stage being 10 rpm. Pulse sputtering is used for the silver layer, with a frequency of 50 kHz and a duty cycle of 70%. In-situ plasma treatment is carried out before and after each layer of sputtering, using an Ar + O 2 mixed gas (9:1), with a power of 50 W RF and a time of 30 seconds each.

[0067] The subsequent laser trimming, final end face treatment, and high-temperature aging and testing steps are exactly the same as in the embodiment.

[0068] Through these two comparative examples, the core innovation points and their superiority of the present invention can be clearly seen. Comparative Example 1 shows the limitations of the traditional single-layer nickel plating method in sulfur resistance, while the innovative sputtering process of the present invention significantly improves the sulfur resistance by forming a multi-layer structure. Comparative Example 2 highlights the important role of the resin silver layer 6 in the present invention. It not only enhances the conductivity but also forms a synergistic effect with the innovative sputtering process, further improving the overall performance.

[0069] The designs of these comparative examples are based on statistical methods, and the synergistic mechanism of each component of the present invention is effectively verified through the method of controlling variables. By comparing the effects of different processes and structures on the anti-sulfuration performance, the significant advantages of the present invention in terms of anti-sulfuration performance, electrical stability, and structural integrity can be clearly seen, thus strongly proving the creativity and technical contribution of the present invention. To comprehensively evaluate the performance and effectiveness of the anti-sulfuration thick film resistor of the present invention, a series of test experiments were designed. These experiments aim to verify the core innovation points of the present invention, namely the superiority of the innovative sputtering process and the multi-layer end face structure, as well as the synergistic effect between the resin silver layer and other components.

[0070] First, a standard anti-sulfuration test was carried out. In this test, the samples of Example 1 and Comparative Examples 1 and 2 were placed in an atmosphere of 85°C, 85% relative humidity, and 10 ppm H 2 2S for 1000 hours. During the test, the change in the resistance value was measured every 100 hours. Secondly, a thermal cycle test was carried out, and the samples were cycled 1000 times between -55°C and +155°C, with each cycle lasting 30 minutes, to evaluate the stability of the resistor under extreme temperature changes.

[0071] Then, a high-temperature and high-humidity load test was carried out. The samples were placed in an environment of 85°C and 85% relative humidity, and a load of 50% of the rated power was applied for 1000 hours. Again, a salt spray test was carried out, and the samples were exposed to an environment atomized with 5% NaCl solution for 96 hours to evaluate their corrosion resistance. Finally, reliability tests were carried out, including welding thermal stability tests and impact tests.

[0072] The following is a detailed table of the test results: Table 1: Anti-sulfuration test results (percentage change in resistance value)

[0073] Table 2: Other performance test results

[0074] Based on the above test results, the following conclusions can be drawn: 1. Anti-sulfuration performance: Example 1 exhibits excellent anti-sulfuration performance. After 1000 hours of testing, the change in the resistance value is only 0.30%, far superior to 1.75% of Comparative Example 1 and 1.20% of Comparative Example 2. This fully proves the effectiveness of the innovative sputtering process and the multi-layer end face structure of the present invention in preventing the penetration of sulfides.

[0075] 2. Temperature stability: In the thermal cycling test, the change in resistance value of Example 1 (0.15%) was significantly lower than that of Comparative Example 1 (0.40%) and Comparative Example 2 (0.30%). This indicates that the structural design of the present invention not only improves the anti-sulfuration ability but also enhances the stability of the resistor under extreme temperature changes.

[0076] 3. Moisture resistance and load capacity: The results of the high-temperature and high-humidity load test showed that the performance of Example 1 (0.25%) was far superior to that of Comparative Example 1 (0.90%) and Comparative Example 2 (0.70%). This result highlights the synergistic effect of the resin silver layer and the innovative sputtering process, effectively improving the stability of the resistor in harsh environments.

[0077] 4. Corrosion resistance: The results of the salt spray test showed that Example 1 had better corrosion resistance. This may be attributed to the more comprehensive protection provided by the multi-layer end face structure.

[0078] 5. Reliability: In the welding thermal stability and shock tests, Example 1 showed better performance. This shows that the structural design of the present invention not only improves the electrical performance but also enhances the mechanical strength and reliability.

[0079] By analyzing these results in depth, some unexpected technical effects of the present invention were found: 1. Synergistic enhancement effect: There is a significant synergistic effect between the multi-layer end face structure formed by the innovative sputtering process and the resin silver layer. This effect not only improves the anti-sulfuration performance but also enhances the overall stability of the resistor in various harsh environments. This synergistic effect may stem from the maze effect provided by the multi-layer structure, effectively preventing the penetration of corrosive substances, while the resin silver layer further seals possible micro-defects.

[0080] 2. Self-healing ability: In the long-term test, it was observed that the performance decay rate of Example 1 gradually slowed down over time. This may indicate that the structure of the present invention has a certain degree of self-healing ability. It is speculated that the micro-defects or cracks that may form initially may be filled by subsequent oxidation processes or material migration, thus forming a more stable protective layer.

[0081] 3. Interface strengthening: The test results showed that the performance of the present invention in terms of mechanical strength and thermal stability far exceeded expectations. This may be because the innovative sputtering process not only forms a multi-layer protection structure but also enhances the interfacial bonding strength between the layers. This strengthened interface may be achieved through in-situ plasma treatment and variable-angle sputtering technology during the sputtering process.

[0082] 4. Electrical performance optimization: In addition to the improvement in anti-sulfuration performance, an improvement in the temperature coefficient of resistance (TCR) and voltage coefficient of resistance (VCR) of the resistor was also observed. This may be due to the multi-layer structure and the presence of the resin silver layer, which optimize the current distribution in the resistor and reduce the formation of local hot spots.

[0083] In summary, through the innovative sputtering process and the carefully designed multi-layer structure, the present invention not only significantly improves the anti-sulfuration performance of the thick film resistor, but also makes breakthrough progress in terms of overall stability, reliability and electrical performance. These excellent properties and unexpected technical effects enable the anti-sulfuration thick film resistor of the present invention to have broad application prospects in demanding application fields such as automotive electronics, industrial control and aerospace.

[0084] The above are only the embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the scope of the claims of the present invention.

Claims

1. A sulfur-resistant thick film resistor, characterized in that: include: High purity alumina substrate; A front electrode disposed on the upper surface of the high-purity alumina substrate and a back electrode disposed on the lower surface; An impedance element disposed between the front electrodes; a protective layer covering the impedance element; a resin silver layer disposed above the protective layer; A multi-layer end surface structure covering both ends of the resistor, wherein the multi-layer end surface structure comprises a nickel-chromium alloy layer, a pure nickel layer and a silver layer arranged in sequence from the inside to the outside; The multi-layer end face structure is formed by a sputtering process and forms a continuous coverage with the edge areas of the resin silver layer and the protective layer.

2. The anti-sulfurization thick film resistor according to claim 1, characterized in that: The purity of the high-purity alumina substrate is 99.6%, and the size is 1.0mmx0.5mmx0.35mm; The front electrode and the back electrode are made of silver-palladium alloy paste, wherein the weight ratio of silver to palladium is 95:5; The impedance element is made of RuO2-based slurry and has a thickness of 10 μm; The protective layer is made of a mixture of glass powder and an organic binder and has a thickness of 20 μm; The silver content in the resin silver layer is 70wt% and the thickness is 15μm; In the multi-layer end face structure, the thickness of the nickel-chromium alloy layer is 50 nm, the thickness of the pure nickel layer is 200 nm, and the thickness of the silver layer is 100 nm.

3. A method for preparing the anti-sulfurization thick film resistor according to claim 1 or 2, characterized in that: The following steps are involved: Preparation of high-purity alumina substrate, electrode preparation, impedance element preparation, protective layer preparation, resin silver layer preparation, preliminary preparation of end face electrode, innovative sputtering enhancement process, particle folding, cleaning, laser fine-tuning, final end face processing, and high temperature aging and testing.

4. The method according to claim 3, characterized in that The high-purity alumina substrate preparation step comprises: An alumina substrate with 99.6% purity and size of 1.0 mm x 0.5 mm x 0.35 mm was ultrasonically cleaned using deionized water and isopropyl alcohol for 5 minutes each, and then plasma treated with a power of 100 W for 30 seconds.

5. The method according to claim 3, characterized in that: The electrode preparation step comprises: Using silver-palladium alloy paste, silver: palladium = 95:5wt%, 15μm thick back electrode and front electrode were printed through 325 mesh stainless steel screen, dried at 150°C for 10 minutes, and then sintered at 850°C in air atmosphere for 10 minutes.

6. The method according to claim 3, characterized in that The impedance element preparation step comprises: The 10 μm thick resistor element was printed using a RuO2-based paste through a 400 mesh stainless steel screen, dried at 150 °C for 15 min, and then sintered at 850 °C in air atmosphere for 30 min.

7. The method according to claim 3, characterized in that The protective layer preparation step comprises: A 20 μm thick protective layer was screen printed using a slurry of glass powder and organic binder through a 325 mesh screen, dried at 150 °C for 10 min, and then sintered at 850 °C in an air atmosphere for 20 min.

8. The method according to claim 3, characterized in that The steps of preparing the resin silver layer include: A silver powder and epoxy resin mixed slurry with a silver content of 70wt% was used, and a 15μm thick resin silver layer was printed through a 400-mesh screen, which was cured at 180°C for 30 minutes. The preliminary preparation of the end face electrode included: using silver glass slurry, printing the end face electrodes at both ends of the component through a 200-mesh screen, drying at 150°C for 10 minutes, and then sintering at 600°C in an air atmosphere for 15 minutes.

9. The method according to claim 3, characterized in that: The innovative sputtering enhancement process steps include: Use a 0.1mm thick stainless steel mask to accurately cover the middle area, leaving 0.2mm exposed at each end; In a multi-target magnetron sputtering system, multi-layer sputtering was performed at a substrate temperature of 200°C and an Ar atmosphere working pressure of 0.5Pa: The first layer is nickel-chromium alloy: using Ni80Cr20 alloy target, power 100WRF, sputtering for 5 minutes, thickness 50nm; The second layer is pure nickel: using 99.99% pure nickel target, power 150WDC, sputtering for 10 minutes, thickness 200nm; The third layer is pure silver: using 99.99% pure silver target, power 80WDC, sputtering for 3 minutes, thickness 100nm; Adopting variable angle sputtering: the initial inclination angle of the sample stage is 45°, which changes by 10° every 2 minutes, ranging from 45° to 90°, and the rotation speed of the sample stage is 10rpm; The silver layer was sputtered by pulse: frequency 50kHz, duty cycle 70%; In-situ plasma treatment was performed before and after each layer was sputtered: using a mixture of Ar and O2 (9:1), a power of 50WRF, and a time of 30 seconds each.

10. The method according to claim 3, characterized in that The folding step includes: dividing the continuous strip structure into individual resistor elements; the cleaning step uses an ultrasonic cleaning device to clean the folded resistor elements with deionized water and isopropyl alcohol in sequence, with each solvent cleaning for 5 minutes; The laser fine-tuning step comprises: Using Nd:YAG laser, wavelength 1064nm, pulse width 100ns, frequency 20kHz, power range 0.1-2W, dynamically adjusted according to the required adjustment amount; the final end face processing steps include: Electroplating nickel layer: using nickel sulfate solution, including 250g / LNiSO4·6H2O, 45g / LNiCl2·6H2O, 40g / LH3BO3, current density 2A / dm², electroplating at 50°C for 15 minutes, forming a 5μm thick nickel layer; Electroplating of lead-free tin layer: using tin methanesulfonate solution, including 50g / L Sn²⁺, 130g / L methanesulfonic acid, current density 1A / dm², electroplating at 25°C for 10 minutes, forming a 3μm thick tin layer; The high temperature aging and testing steps include: Aging at 125°C for 168 hours, then anti-sulfurization test at 85°C, 85% relative humidity, 10ppmH2S atmosphere for 1000 hours, resistance value tested by four-wire method, test current does not exceed 1 / 10 of rated power.

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