A sulfur-resistant thick film resistor and its preparation method

Abstract

The present invention relates to the technical field of thick-film resistors, and in particular to a sulfur-resistant thick-film resistor and a method for preparing the same, comprising: a high-purity alumina substrate; a front electrode disposed on the upper surface and a back electrode disposed on the lower surface of the high-purity alumina substrate; an impedance element disposed between the front electrodes; a protective layer covering the impedance element; a resin silver layer disposed above the protective layer; and a multi-layer end-face structure covering both ends of the resistor, the multi-layer end-face structure comprising a nickel-chromium alloy layer, a pure nickel layer, and a silver layer disposed sequentially from the inside out. The multi-layer end-face structure is formed by a sputtering process and forms a continuous covering with the edge regions of the resin silver layer and the protective layer. 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 a high electron affinity and can effectively capture free electrons in the environment, reducing their chance of combining with sulfur ions, thereby forming a composite protective structure with a maze effect.

Description

Technical Field

[0001] The present invention relates to the technical field of thick film resistors, and in particular to a sulfurization-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 certain environments, particularly those with sulfides, traditional thick-film resistors often face severe performance degradation. Sulfidation not only causes resistance drift but can also cause resistor failure, impacting the reliability of the entire electronic system. Therefore, the development of thick-film resistors with excellent anti-sulfurization properties has become an urgent need in the industry.

[0003] In the prior art, there are many methods that attempt to solve the sulfurization problem of thick film resistors. Among them, the closest prior art can be referred to the following patents:

[0004] Chinese patent CN101681705B, titled "Anti-sulfurization Chip Resistor and Method for Manufacturing the Same," proposes a chip resistor that enhances anti-sulfurization performance by coating the resistor layer with multiple layers of protective coating. However, this approach has the following drawbacks: First, the preparation of the multilayer coating is complex, increasing production costs; second, the interfacial bonding strength between the coatings is insufficient, making microcracks prone to formation under temperature cycling and mechanical stress, thereby reducing long-term reliability.

[0005] Chinese patent CN103165250A proposes a thick-film anti-sulfurization chip resistor, which mainly improves the anti-sulfurization performance by covering the resistor layer with a multi-layer protective coating. However, this method has the following major disadvantages: multiple printing and sintering processes are required to form a 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 interface bonding under high temperature and mechanical stress, resulting in the formation of microcracks, thereby reducing long-term reliability. It mainly relies on the physical barrier of the coating to achieve anti-sulfurization, but this method is difficult to cope with long-term and harsh sulfurization environments. The multi-layer coating structure is prone to stress due to the mismatch of thermal expansion coefficients during thermal cycling, resulting in performance degradation; once the protective structure has defects, it is difficult to self-repair. Summary of the Invention

[0006] The present invention, based on full recognition of the deficiencies of the prior art, proposes an innovative anti-sulfurization thick film resistor and a preparation method thereof.

[0007] The object of the present invention is to provide a sulfur-resistant thick film resistor, comprising:

[0008] High-purity alumina substrate;

[0009] A front electrode is provided on the upper surface of the high-purity alumina substrate and a back electrode is provided on the lower surface;

[0010] an impedance element disposed between the front electrodes;

[0011] a protective layer covering the impedance element;

[0012] a resin silver layer disposed above the protective layer;

[0013] a multi-layer end surface structure covering both ends of the resistor, the multi-layer end surface structure comprising a nickel-chromium alloy layer, a pure nickel layer, and a silver layer arranged in sequence from the inside to the outside;

[0014] 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.

[0015] Specifically, the purity of the high-purity alumina substrate is 99.6%, and the size is 1.0mmx0.5mmx0.35mm;

[0016] 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;

[0017] The impedance element is made of RuO2-based paste and has a thickness of 10 μm;

[0018] The protective layer is made of a mixture of glass powder and organic binder, with a thickness of 20 μm;

[0019] The silver content in the resin silver layer is 70 wt % and the thickness is 15 μm;

[0020] In the multi-layer end face structure, the thickness of the nickel-chromium alloy layer is about 50 nm, the thickness of the pure nickel layer is about 200 nm, and the thickness of the silver layer is about 100 nm.

[0021] A method for preparing the anti-sulfurization thick film resistor comprises the following steps:

[0022] 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.

[0023] Specifically, the substrate preparation step includes:

[0024] An alumina substrate with 99.6% purity and dimensions 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 at 100 W for 30 seconds.

[0025] Specifically, the electrode preparation step includes:

[0026] Using silver-palladium alloy paste (silver: palladium = 95:5wt%), 15 μm thick back and front electrodes were printed through a 325-mesh stainless steel screen, dried at 150°C for 10 minutes, and then sintered at 850°C in air atmosphere for 10 minutes.

[0027] Specifically, the impedance element preparation step includes:

[0028] The 10 μm thick resistor element was screen-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.

[0029] Specifically, the protective layer preparation step includes:

[0030] A 20 μm thick protective layer was formed by screen printing a mixture of glass powder and organic binder using a 325 mesh screen, drying at 150 °C for 10 min, and then sintering at 850 °C in air atmosphere for 20 min.

[0031] Specifically, the steps of preparing the resin silver layer include:

[0032] A mixed slurry of silver powder and epoxy resin (silver content 70wt%) was used to print a 15μm thick resin silver layer through a 400-mesh screen, and then 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.

[0033] Specifically, the innovative sputtering enhancement process steps include:

[0034] Use a 0.1mm thick stainless steel mask to precisely cover the middle area, leaving 0.2mm exposed at each end;

[0035] In a multi-target magnetron sputtering system, multi-layer sputtering was performed at a substrate temperature of 200°C and a working pressure of 0.5 Pa (Ar atmosphere):

[0036] The first layer (nickel-chromium alloy): using Ni80Cr20 alloy target, power 100WRF, sputtering for 5 minutes, thickness about 50nm;

[0037] Second layer (pure nickel): Use 99.99% pure nickel target, power 150WDC, sputtering for 10 minutes, thickness about 200nm;

[0038] The third layer (silver): using 99.99% pure silver target, power 80WDC, sputtering for 3 minutes, thickness about 100nm;

[0039] Angle-variable sputtering was used: the initial inclination angle of the sample stage was 45°, which changed by 10° every 2 minutes, ranging from 45° to 90°, and the sample stage rotation speed was 10 rpm;

[0040] The silver layer was sputtered using pulse sputtering: frequency 50 kHz, duty cycle 70%;

[0041] 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.

[0042] Specifically, 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;

[0043] The laser fine-tuning step includes:

[0044] 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:

[0045] Electroplating nickel layer: Use nickel sulfate solution (250g / LNiSO4·6H2O, 45g / LNiCl2·6H2O, 40g / LH3BO3) with a current density of 2A / dm² and electroplating at 50°C for 15 minutes to form a nickel layer about 5μm thick;

[0046] Electroplating of lead-free tin layer: using tin methanesulfonate solution (50g / L Sn²⁺, 130g / L methanesulfonic acid), current density 1A / dm², electroplating at 25°C for 10 minutes, forming a tin layer about 3μm thick;

[0047] The high temperature aging and testing steps include:

[0048] Aging at 125°C for 168 hours, followed by 1000 hours of anti-sulfurization testing at 85°C, 85% relative humidity, 10ppmH2S atmosphere. Resistance is measured using the four-wire method with the test current not exceeding 1 / 10 of the rated power.

[0049] The innovations and technical effects of the present invention are mainly reflected in the following aspects:

[0050] The core innovation of this invention lies in the use of a unique multi-layer sputtering process, combined with a carefully designed material combination, to form a composite protective structure with a maze effect. This structure not only effectively prevents the penetration of sulfides, but also maintains good stability in harsh environments.

[0051] From the perspective of chemical mechanism, the innovation of the present invention is mainly reflected in the following aspects:

[0052] First, the multi-layer sputtered structure of nickel-chromium alloy, pure nickel, and silver layers forms a gradient electronic structure. The nickel-chromium alloy layer has a high electron affinity, effectively capturing free electrons in the environment and reducing their chance of binding with sulfur ions. The pure nickel layer acts as an electron barrier, further hindering the migration of sulfur ions. The outermost silver layer not only provides good conductivity but also forms a dense silver oxide film on the surface, which blocks the entry of sulfides at the molecular level.

[0053] Secondly, the introduction of the resin silver layer creates a unique interface environment. The polymer chains in the resin and the silver particles form a semi-interpenetrating network structure. This structure forms a large number of microscopic dead ends at the molecular scale, significantly increasing the diffusion path of sulfide molecules, thereby greatly reducing the vulcanization rate.

[0054] Thirdly, the innovative variable-angle sputtering technology achieves a nanoscale material interlocking effect. Atoms sputtered at different angles form a complex three-dimensional network structure at the interface. This structure not only strengthens the interlayer bonding but also creates a large number of energy traps at the atomic level, effectively capturing and passivating invading sulfur ions.

[0055] Finally, the in-situ plasma treatment step introduces surface-active groups that can chemically bond with atoms in subsequent layers, significantly improving interfacial bonding strength. Plasma treatment also creates nanoscale surface roughness, increasing the material's specific surface area and thus enhancing its ability to adsorb and passivate sulfides.

[0056] The synergistic effect of these innovations not only significantly improves the resistor's anti-sulfurization performance but also brings a series of unexpected technical benefits, such as the multilayer structure's self-healing capabilities, interfacial strengthening effects, and improved electrical performance. These benefits enable the present invention's anti-sulfurization thick-film resistor to maintain excellent performance and reliability in a variety of extreme environments.

[0057] In addition, the present invention significantly improves the anti-sulfurization performance, thermal stability and mechanical reliability of thick film resistors through innovative multi-layer sputtering processes and material design, meeting the urgent needs of modern electronic products for high-reliability components. Although the present invention introduces a high-end sputtering process, by optimizing the manufacturing process, it reduces the need for multiple printing and sintering, and controls production costs while improving performance. The innovative processes of the present invention, such as angle-variable sputtering and in-situ plasma treatment, have brought new technological breakthroughs to the field of thick film resistor manufacturing and are expected to promote technological progress in the entire industry. The high-performance anti-sulfurization thick film resistors of the present invention can operate stably in more harsh environments, which makes it possible for electronic products to be used in high-demand fields such as automobiles, industrial control, and aerospace. The excellent thermal stress management capabilities of the present invention provide a new solution for improving the long-term reliability and service life of electronic products.

[0058] In summary, this invention, through a deep understanding of materials science and chemical principles, has ingeniously designed a novel sulfur-resistant thick-film resistor structure and its fabrication method. This innovation not only addresses the performance degradation of traditional thick-film resistors in sulfurized environments but also achieves significant breakthroughs in overall performance, reliability, and service life. Therefore, this invention provides a valuable solution for the electronics industry, particularly in sectors with extremely high reliability requirements, such as automotive electronics, aerospace, and industrial control. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 Schematic diagram of the structure of the anti-sulfurization thick film resistor of the present invention. DETAILED DESCRIPTION

[0060] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0061] The present invention relates to a sulfur-resistant thick film resistor and a preparation method thereof, in particular to a thick film resistor having excellent sulfur-resistant performance and electrical stability. Figure 1 As shown, the anti-sulfurization 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.

[0062] The high-purity alumina substrate 1 serves as the supporting structure of the entire resistor, and its purity and size have an important influence on the performance of the resistor. The front electrode 2 and the back electrode 3 are respectively arranged on the upper surface and the lower surface of the substrate 1 for connection to the external circuit. The impedance element 4 is arranged between the front electrodes 2, which is the core part of the resistor and determines the resistance value. The protective layer 5 covers the impedance element 4 and plays a protective role. The resin silver layer 6 is arranged above the protective layer 5 to enhance the conductivity. The multi-layer end face structure 7 covers the two ends of the resistor and is the key innovation of the present invention. It is formed by a special sputtering process and significantly improves the anti-sulfurization performance of the resistor.

[0063] In one embodiment of the present invention, the high-purity alumina substrate 1 has a purity of 99.6% and dimensions of 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.

[0064] The front electrode 2 and back electrode 3 are made of a silver-palladium alloy paste with a weight ratio of silver to palladium of 95:5. This ratio ensures excellent conductivity and improves the electrode's resistance to sulfidation. These two electrodes connect to the external circuit, forming the inlet and outlet of the current.

[0065] The impedance element 4 is made of RuO2-based paste with a thickness of 10 μm. RuO2 has excellent temperature coefficient and stability, ensuring the stability of the resistance value under various environmental conditions.

[0066] Protective layer 5, made from a mixture of glass powder and an organic binder, has a thickness of 20 μm. This layer protects the resistor element without affecting the overall performance of the resistor. Resin silver layer 6 contains 70% silver by weight and is 15 μm thick. This ratio ensures both good conductivity and adequate mechanical strength. The primary function of resin silver layer 6 is to enhance conductivity, while its resin component provides additional protection. Together with the underlying protective layer 5 and the overlying multilayer end-face structure 7, resin silver layer 6 forms a continuous protective system.

[0067] The multilayer end face structure 7 is the core of the present invention and comprises, arranged sequentially from the inside out, a nickel-chromium alloy layer 71, a pure nickel layer 72, and a silver layer 73. The nickel-chromium alloy layer 71 is approximately 50 nm thick, providing excellent adhesion and corrosion resistance. The pure nickel layer 72 is approximately 200 nm thick, acting as an effective diffusion barrier. The silver layer 73 is approximately 100 nm thick, further enhancing resistance to sulfidation. This multilayer structure, formed through an innovative sputtering process, forms a continuous coverage with the resin silver layer 6 and the edge areas of the protective layer 5, effectively preventing the infiltration of sulfides.

[0068] When the resistor is exposed to a sulfur-containing environment, the multilayer end face structure 7 begins to work. The outermost silver layer first contacts the sulfide, but due to the density and continuity of the silver layer, the penetration rate of the sulfide is greatly slowed down.

[0069] If a small amount of sulfide penetrates the silver layer, it will encounter a layer of pure nickel. Nickel has a strong resistance to sulfide, which can further prevent the invasion of sulfide.

[0070] The innermost nickel-chromium alloy layer not only has good anti-sulfurization performance, but also forms a strong bond with the underlying material to prevent interlayer delamination.

[0071] The resin component in the resin silver layer 6 forms a semi-interpenetrating network structure, which creates a large number of mazes on a molecular scale, significantly increasing the diffusion paths of sulfide molecules.

[0072] When the temperature of the resistor changes during use, the thermal expansion coefficient gradient design of the multi-layer structure can effectively relieve thermal stress and prevent cracking and peeling.

[0073] In terms of material selection, this invention places particular emphasis on the synergistic effects of various layers. For example, the nickel-chromium alloy layer utilizes Ni80Cr20 alloy, which not only exhibits excellent sulfidation resistance but also good thermal stability and mechanical strength. The pure nickel layer utilizes 99.99% high-purity nickel, ensuring optimal sulfidation resistance and electrical conductivity.

[0074] The preparation method of the anti-sulfurization thick film resistor of the present invention comprises the following steps: substrate preparation, electrode preparation, impedance element preparation, protective layer preparation, resin silver layer preparation, preliminary preparation of end face electrodes, innovative sputtering enhancement process, laser fine-tuning, final end face treatment, and high-temperature aging and testing.

[0075] In the substrate preparation step, a 99.6% pure aluminum oxide substrate (1) measuring 1.0 mm x 0.5 mm x 0.35 mm was first ultrasonically cleaned using deionized water and isopropyl alcohol for 5 minutes each. This was then plasma treated at 100 W for 30 seconds. This step ensured the substrate's surface cleanliness, facilitating subsequent processing.

[0076] In the electrode preparation step, a silver-palladium alloy paste (silver:palladium = 95:5 wt%) was used to print a 15μm-thick back electrode 3 and front electrode 2 through a 325-mesh stainless steel screen. The paste was dried at 150°C for 10 minutes and then sintered at 850°C in air for 10 minutes. This high-temperature sintering process ensures a good bond between the electrode and the substrate.

[0077] The impedance element fabrication process uses a RuO2-based slurry to screen-print a 10μm-thick impedance element 4 through a 400-mesh stainless steel screen. The element is then dried at 150°C for 15 minutes and sintered at 850°C in air for 30 minutes. The selection of RuO2 and the specific sintering process ensure the stability and accuracy of the impedance element.

[0078] The protective layer preparation step uses a mixture of glass powder and an organic binder to create a 20μm thick protective layer 5 using a 325-mesh screen print. The layer is then dried at 150°C for 10 minutes and then sintered at 850°C in air for 20 minutes. This step creates a dense protective layer structure that effectively protects the resistor element.

[0079] The silver resin layer was prepared by screen-printing a 15μm-thick silver resin layer using a mixture of silver powder and epoxy resin (silver content 70wt%) through a 400-mesh screen. The layer was then cured at 180°C for 30 minutes. This specially formulated silver resin layer provides both good conductivity and enhanced structural integrity.

[0080] The end electrodes were initially prepared using silver glass paste, printed on both ends of the component through a 200-mesh screen, dried at 150°C for 10 minutes, and then sintered at 600°C in an air atmosphere for 15 minutes.

[0081] The innovative sputtering enhancement process is a key step of the present invention. First, a 0.1mm thick stainless steel mask is used to accurately cover the middle area, leaving 0.2mm exposed at both ends. Then, in a multi-target magnetron sputtering system, multi-layer sputtering is performed at a substrate temperature of 200°C and a working pressure of 0.5Pa (Ar atmosphere). The first layer (nickel-chromium alloy) uses a Ni80Cr20 alloy target, a power of 100WRF, sputtering for 5 minutes, and a thickness of about 50nm. The second layer (pure nickel) uses a 99.99% pure nickel target, a power of 150W DC, sputtering for 10 minutes, and a thickness of about 200nm. The third layer (silver) uses a 99.99% pure silver target, a power of 80W DC, sputtering for 3 minutes, and a thickness of about 100nm.

[0082] During the sputtering process, variable-angle sputtering technology was used. The initial inclination angle of the sample stage was 45°, changing by 10° every 2 minutes, ranging from 45° to 90°. The sample stage rotated at a speed of 10 rpm. This dynamic adjustment ensured that the material could penetrate into tiny gaps and corners, forming a complete coating. The silver layer was pulsed sputtered at a frequency of 50 kHz and a duty cycle of 70%. This technology controlled the thickness of each sputtering and improved the density and uniformity of the sputtered layer. In-situ plasma treatment was performed before and after each layer, using an Ar + O2 mixture (9:1) with a power of 50W RF for 30 seconds each time. This step significantly improved the bonding strength between the layers.

[0083] Folding is to divide the continuous strip structure into individual resistor elements; use ultrasonic cleaning equipment to clean the folded resistor elements with deionized water and isopropyl alcohol in sequence, with each solvent cleaning for 5 minutes;

[0084] The laser trimming step uses an 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, dynamically adjusted according to the required adjustment amount. This precision laser technology ensures the accuracy of the resistor value.

[0085] Final end-face treatment involves two electroplating steps. First, a nickel layer is applied using a nickel sulfate solution (250 g / L NiSO₄·6H₂O, 45 g / L NiCl₂·6H₂O, 40 g / L H₃BO₃) at a current density of 2 A / dm² for 15 minutes at 50°C, resulting in a nickel layer approximately 5 μm thick, further enhancing sulfur resistance. Next, a lead-free tin layer is applied using a tin methanesulfonate solution (50 g / L Sn⁺, 130 g / L methanesulfonic acid) at a current density of 1 A / dm² for 10 minutes at 25°C, resulting in a tin layer approximately 3 μm thick, providing good solderability.

[0086] Finally, the components were subjected to high-temperature aging and testing, undergoing aging at 125°C for 168 hours, followed by a 1000-hour sulfur resistance test at 85°C, 85% relative humidity, and a 10ppm H2S atmosphere. Resistance was measured using the four-wire method, with the test current not exceeding 1 / 10 of the rated power to ensure test accuracy.

[0087] The sulfur-resistant thick-film resistors of this invention utilize a unique multi-layered end-face structure and innovative sputtering process to significantly enhance their sulfur resistance. Furthermore, the sophisticated manufacturing process ensures the resistors' electrical stability and reliability. These resistors are particularly well-suited for electronic devices requiring long-term stability and high reliability, such as automotive electronics and industrial control systems.

[0088] In other embodiments, the resistor's performance 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 sulfidation resistance, or the sputtering parameters of the silver layer can be adjusted to increase conductivity. This flexibility allows the present invention to adapt to different application requirements.

[0089] The present invention can be applied to a variety of specific scenarios, for example:

[0090] Automotive electronics: Electronic control units used in high-temperature, high-humidity, and sulfur-containing environments such as engine compartments.

[0091] Industrial control: Control equipment used in industrial environments with high sulfur content, such as chemical plants and refineries.

[0092] Aerospace: Electronic equipment that works for a long time in high-altitude environments requires extremely high reliability.

[0093] Marine engineering: electronic equipment used in marine environments with high salt spray and high humidity.

[0094] In other embodiments, the present invention may be modified. 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 anti-sulfurization 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.

[0095] In summary, the present invention provides a high-performance sulfur-resistant thick-film resistor and a preparation method thereof, which overcomes the problem of performance degradation of traditional thick-film resistors in sulfurized environments and provides a strong guarantee for the long-term stability and reliability of electronic products.

[0096] Comparative Example 1: Conventional Anti-sulfur Thick Film Resistor

[0097] This comparative example is intended to demonstrate the limitations of conventional anti-sulfurization methods and highlight the superiority of the innovative sputtering process of the present invention. In this comparative example, the same basic structure as the embodiment is used, but instead of the innovative sputtering enhancement process, a conventional single-layer nickel plating method is used.

[0098] The preparation method of Comparative Example 1 comprises the following steps:

[0099] First, a high-purity alumina substrate (1) with a purity of 99.6% and dimensions of 1.0 mm x 0.5 mm x 0.35 mm was prepared using the same method as in the previous example. The front electrode (2) and back electrode (3) were then formed using the same silver-palladium alloy paste (silver:palladium = 95:5 wt%). A 15 μm-thick electrode layer was screen-printed onto a 325-mesh stainless steel screen, dried at 150°C for 10 minutes, and then sintered at 850°C in air for 10 minutes.

[0100] Next, a RuO2-based slurry was used to prepare the impedance element 4. A 10 μm thick impedance layer was screen-printed on a 400-mesh stainless steel screen, dried at 150°C for 15 minutes, and then sintered at 850°C in air for 30 minutes. The protective layer 5 and the resin silver layer 6 were prepared using the same method as in the previous embodiment.

[0101] However, the end-face treatment step employed a conventional single-layer nickel plating method, rather than the innovative sputter-enhanced process of the present invention. Specifically, a nickel sulfate solution (250 g / L NiSO₄·6H₂O, 45 g / L NiCl₂·6H₂O, 40 g / L H₃BO₃) was used for electroplating at 50°C for 30 minutes at a current density of 2 A / dm², forming a nickel layer approximately 10 μm thick. Finally, a lead-free tin layer was electroplated using the same method as in the previous embodiment.

[0102] Comparative Example 2: Anti-sulfurization thick film resistor without resin silver layer

[0103] This comparative example is intended to highlight the importance of the resin silver layer 6 in the present invention and the synergistic effect between the resin silver layer 6 and the innovative sputtering process. In this comparative example, the preparation steps of the resin silver layer 6 are omitted, while all other process steps are retained.

[0104] The preparation method of Comparative Example 2 comprises the following steps:

[0105] The same method as in the embodiment is used to prepare a high-purity alumina substrate 1, prepare the front electrode 2 and the back electrode 3, as well as the resistor element 4 and the protective layer 5. However, the step of preparing the resin silver layer 6 is skipped.

[0106] In the innovative sputtering enhancement process, multi-layer sputtering was performed using the same parameters and methods as in the previous embodiment. Specifically, a 0.1 mm thick stainless steel mask was used in a multi-target magnetron sputtering system with a substrate temperature of 200°C and an operating pressure of 0.5 Pa (Ar atmosphere). The first layer (nickel-chromium alloy) used a Ni80Cr20 alloy target, sputtered at 100 W RF power for 5 minutes, and achieved a thickness of approximately 50 nm. The second layer (pure nickel) used a 99.99% pure nickel target, sputtered at 150 W DC power for 10 minutes, and achieved a thickness of approximately 200 nm. The third layer (silver) used a 99.99% pure silver target, sputtered at 80 W DC power for 3 minutes, and achieved a thickness of approximately 100 nm.

[0107] Variable-angle sputtering was also used, with the sample stage's initial tilt of 45°, increasing by 10° every two minutes from 45° to 90°. The sample stage's rotation speed was 10 rpm. The silver layer was pulsed sputtered at a frequency of 50 kHz and a duty cycle of 70%. In-situ plasma treatment was performed before and after each sputtering layer using a 9:1 Ar + O₂ mixture at 50W RF power for 30 seconds each time.

[0108] The subsequent laser trimming, final end face processing, high temperature aging and testing steps are exactly the same as those in the embodiment.

[0109] These two comparative examples clearly demonstrate the core innovations and advantages of the present invention. Comparative Example 1 demonstrates the limitations of traditional single-layer nickel plating methods in terms of anti-sulfurization performance, while the innovative sputtering process of the present invention significantly improves anti-sulfurization performance by forming a multilayer structure. Comparative Example 2 highlights the important role of the resin silver layer 6 in the present invention. It not only enhances conductivity but also creates a synergistic effect with the innovative sputtering process, further improving overall performance.

[0110] These comparative examples, designed based on statistical methods and using controlled variables, effectively demonstrate the synergistic mechanism of the present invention's components. By comparing the effects of different processes and structures on anti-sulfurization performance, the significant advantages of the present invention in terms of anti-sulfurization performance, electrical stability, and structural integrity are clearly demonstrated, thus strongly demonstrating the inventiveness and technical contribution of the present invention. To comprehensively evaluate the performance and effectiveness of the present invention's anti-sulfurization thick-film resistor, a series of test experiments were designed. These experiments aim to verify the core innovations of the present invention, namely the superiority of the innovative sputtering process and multi-layer end-face structure, as well as the synergistic effect of the resin silver layer and other components.

[0111] First, a standard anti-sulfurization test was conducted. Samples from Example 1 and Comparative Examples 1 and 2 were exposed to an atmosphere of 85°C, 85% relative humidity, and 10 ppm H2S for 1000 hours. Resistance changes were measured every 100 hours. Second, a thermal cycling test was conducted, subjecting the samples to 1000 cycles between -55°C and +155°C, with each cycle lasting 30 minutes, to evaluate the resistors' stability under extreme temperature fluctuations.

[0112] Next, a high-temperature, high-humidity load test was conducted, subjecting the samples to 85°C, 85% relative humidity, and applying 50% of the rated power for 1000 hours. A salt spray test was then conducted, exposing the samples to a 5% NaCl solution mist for 96 hours to evaluate their corrosion resistance. Finally, reliability testing was conducted, including solder thermal stability testing and impact testing.

[0113] The following is a detailed table of test results:

[0114] Table 1: Anti-sulfurization test results (resistance change percentage)

[0115]

[0116] Table 2: Other performance test results

[0117]

[0118] Based on the above test results, the following conclusions can be drawn:

[0119] 1. Anti-sulfurization Performance: Example 1 exhibits excellent anti-sulfurization performance, with a resistance change of only 0.30% after 1000 hours of testing, far superior to the 1.75% change in Comparative Example 1 and the 1.20% change in Comparative Example 2. This fully demonstrates the effectiveness of the innovative sputtering process and multi-layer end face structure of the present invention in preventing sulfide penetration.

[0120] 2. Temperature Stability: In thermal cycling tests, the resistance change of Example 1 (0.15%) was significantly lower than that of Comparative Example 1 (0.40%) and Comparative Example 2 (0.30%). This demonstrates that the structural design of the present invention not only improves the resistance to sulfurization but also enhances the stability of the resistor under extreme temperature fluctuations.

[0121] 3. Moisture Resistance and Load Capacity: High-temperature, high-humidity load testing results show that Example 1 (0.25%) far outperforms 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 resistor's stability in harsh environments.

[0122] 4. Corrosion resistance: The salt spray test results show that Example 1 has better corrosion resistance, which may be attributed to the more comprehensive protection provided by the multi-layer end face structure.

[0123] 5. Reliability: In both the welding thermal stability and impact tests, Example 1 showed better performance, which indicates that the structural design of the present invention not only improves electrical performance but also enhances mechanical strength and reliability.

[0124] After in-depth analysis of these results, it is found that the present invention has some unexpected technical effects:

[0125] 1. Synergistic Enhancement: A significant synergistic effect exists between the multilayer end-face structure formed by the innovative sputtering process and the resin silver layer. This effect not only improves anti-sulfurization performance but also enhances the resistor's overall stability in various harsh environments. This synergistic effect likely stems from the maze effect provided by the multilayer structure, effectively preventing the penetration of corrosive substances, while the resin silver layer further seals any potential minor defects.

[0126] 2. Self-repair capability: During long-term testing, the performance degradation rate of Example 1 was observed to gradually slow over time. This may indicate that the structure of the present invention possesses a certain degree of self-repair capability. It is speculated that the small defects or cracks that may form in the early stages are likely to be filled by subsequent oxidation processes or material migration, thus forming a more stable protective layer.

[0127] 3. Interface Strengthening: Test results show that the mechanical strength and thermal stability of this invention far exceed expectations. This is likely due to the innovative sputtering process, which not only forms a multi-layer protective structure but also enhances the interfacial bonding strength between the layers. This strengthened interface is likely achieved through in-situ plasma treatment and variable-angle sputtering technology during the sputtering process.

[0128] 4. Optimized electrical performance: In addition to improved anti-sulfurization performance, the resistor's temperature coefficient (TCR) and voltage coefficient (VCR) have also been improved. This is likely due to the multi-layer structure and the presence of the resin silver layer, which optimizes the current distribution in the resistor and reduces the formation of local hot spots.

[0129] In summary, this invention, through its innovative sputtering process and carefully designed multilayer structure, not only significantly improves the anti-sulfurization performance of thick-film resistors but also achieves breakthrough improvements in overall stability, reliability, and electrical performance. These excellent performance and unexpected technical benefits make the present invention's anti-sulfurization thick-film resistors promising for demanding applications such as automotive electronics, industrial control, and aerospace.

[0130] The foregoing is merely an embodiment of the present invention and is not intended to limit the present invention. It will be apparent to those skilled in the art that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are intended to 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 is provided on the upper surface of the high-purity alumina substrate and a back electrode is provided 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, the multi-layer end surface structure comprising 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 paste and has a thickness of 10 μm; The protective layer is made of a mixture of glass powder and organic binder, with 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 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, 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 steps include: An alumina substrate with 99.6% purity and dimensions 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 at 100 W for 30 seconds.

5. The method according to claim 3, characterized in that The electrode preparation step comprises: A silver-palladium alloy paste (silver:palladium = 95:5 wt%) was used to print 15 μm thick back and front electrodes through a 325 mesh stainless steel screen, dried at 150 °C for 10 min, and then sintered at 850 °C in air atmosphere for 10 min.

6. The method according to claim 3, characterized in that The impedance element preparation step comprises: The 10 μm thick resistor element was screen-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 formed by screen printing a mixture of glass powder and organic binder using a 325 mesh screen, drying at 150 °C for 10 min, and then sintering at 850 °C in 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 mixture of silver powder and epoxy resin was used, wherein the silver content was 70 wt %, and a 15 μm thick resin silver layer was printed through a 400 mesh screen, which was then cured at 180°C for 30 minutes. The preliminary preparation of the end face electrode included: using silver glass paste, 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 sputtering enhancement process steps include: Use a 0.1mm thick stainless steel mask to precisely 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; Angle-variable sputtering was used: the initial inclination angle of the sample stage was 45°, which changed by 10° every 2 minutes, ranging from 45° to 90°, and the sample stage rotation speed was 10 rpm; The silver layer was sputtered using pulse sputtering: frequency 50 kHz, duty cycle 70%; In-situ plasma treatment was performed before and after each layer was sputtered: using a 9:1 mixture of Ar and O2, 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 includes: 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: Nickel electroplating: using a nickel sulfate solution containing 250 g / L NiSO4·6H2O, 45 g / L NiCl2·6H2O, and 40 g / L H3BO3, with a current density of 2 A / dm², electroplating at 50°C for 15 minutes to form a 5 μm thick nickel layer; Electroplating of lead-free tin layer: using a tin methanesulfonate solution containing 50g / L Sn²⁺, 130g / L methanesulfonic acid, a current density of 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, followed by 1000 hours of anti-sulfurization testing at 85°C, 85% relative humidity, 10ppmH2S atmosphere. Resistance is measured using the four-wire method with the test current not exceeding 1 / 10 of the rated power.

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