A method for preparing a special coating for a spring probe

Abstract

This invention belongs to the field of test probe fabrication technology, specifically a method for preparing a special coating for spring probes. The method includes: depositing a Si gradient transition layer on the surface of a spring substrate, followed by oxygen plasma activation treatment to form a specific active pinning layer of 3 to 5 nanometers; then depositing a DLC coating using a specific process, employing a specific peak voltage and a specific duty cycle pulse bias mode to pre-position dispersed carbon clusters. The SixOy pinning layer provides dual anchoring of chemical bonding and mechanical interlocking for the DLC coating during cyclic stress-induced graphitization transformation, preventing microcracks from propagating to the interface and ensuring the safe operation of the adaptive lubrication process. This invention overcomes the technical bottleneck of fatigue spalling of DLC coatings on elastic components, significantly improving the service life of spring probes.

Description

Technical Field

[0001] This invention relates to the field of test probe fabrication technology, and in particular to a method for preparing a special coating for a spring probe. Background Technology

[0002] Spring-loaded test probes are key consumables in automated test equipment (ATE) for semiconductor chips. Their internal compression helical springs provide a stable elastic contact force between the probe tip and the chip's pads. As integrated circuit manufacturing processes evolve towards advanced nodes such as 7nm and 5nm, the spacing between chip pads continues to shrink, placing extremely high demands on the miniaturization and long lifespan of probes. Currently, the design lifespan of mainstream spring-loaded probes is limited to approximately 100,000 cycles, which is insufficient to meet the ever-increasing demand for high-reliability testing.

[0003] To improve the wear resistance and service life of spring probes, the industry has explored depositing diamond-like carbon (DLC) coatings on the spring surface. DLC coatings possess high hardness, a low coefficient of friction, and good chemical inertness, making them ideal wear-resistant protective coatings. However, applying DLC ​​coatings to spring elastic components faces an inherent contradiction: springs undergo tens of thousands of compression-release cycles during service, requiring the coating to possess sufficient toughness to elastically deform synchronously with the substrate without cracking or peeling; while traditional DLC coatings, especially those with high... Although tetrahedral amorphous carbon (ta-C) coatings with high bond content have extremely high hardness, they also have high internal stress and brittleness. Under cyclic strain, they are prone to the initiation and propagation of microcracks, which eventually lead to fatigue spalling of the coating.

[0004] To resolve the aforementioned contradictions, existing technologies typically employ the following two approaches: One approach is to reduce the internal stress of the DLC coating by increasing the deposition temperature or performing high-temperature post-treatment. For example, hot-wire chemical vapor deposition (HFCVD) can be used to deposit the DLC coating at temperatures above 500°C, utilizing the thermal relaxation effect at high temperatures to release the film stress. However, the tempering temperature of spring steel is typically 350-500°C. Exceeding this temperature range will cause the spring to soften during annealing and lose its elastic properties. Therefore, high-temperature process routes are not suitable for spring substrates.

[0005] Secondly, DLC can be controlled by adjusting the type of carbon source gas. / Bond ratio. For example, using methane (CH4) as a carbon source allows for deposition. High-hardness DLC films with high content can be deposited using acetylene (C2H2). Low-stress DLC films with high content. However, balancing hardness and toughness solely through the selection of carbon source type offers only a single dimension of control. Under long-term cyclic loading, even... High-content hydrogen-containing amorphous carbon films (aC:H) have an inherent coefficient of friction (typically in the range of 0.1-0.2) that can still cause significant energy dissipation and surface micro-damage accumulation during hundreds of thousands of friction cycles, ultimately leading to insufficient fatigue life of the coating.

[0006] Moreover, a deeper technical challenge lies in the fact that the tribological behavior of traditional DLC coatings during service is "passive"—once the coating is prepared, its coefficient of friction is fixed, and it typically increases with wear, accelerating coating degradation. If DLC coatings could be endowed with an "adaptive" capability, enabling them to actively reduce the coefficient of friction in areas with high local stress or high wear risk, transforming the "passive wear" of traditional coatings into "active self-optimization," it is hoped that the fatigue life bottleneck of DLC coatings on elastic components can be fundamentally overcome.

[0007] Therefore, there is an urgent need to develop a process that can prepare a DLC coating with high toughness, high adhesion and adaptive lubrication function on the surface of spring elastic components under low temperature conditions (≤200℃) to solve the fatigue peeling problem of DLC coating under cyclic strain conditions in the existing technology and meet the application requirements of long-life spring probes with higher cycles (currently up to 100,000 cycles). Summary of the Invention

[0008] The purpose of this invention is to provide a method for preparing a special coating for a spring probe, so as to solve the problems mentioned in the background art.

[0009] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a special coating for a spring probe, comprising the following steps: A Si gradient transition layer is deposited on the surface of the spring substrate; The surface of the Si gradient transition layer is subjected to oxygen plasma activation treatment to form a SixOy active pinning layer with a thickness of 3nm to 5nm; A diamond-like carbon (DLC) coating is deposited on the surface of the SixOy active pinning layer using a plasma-enhanced chemical vapor deposition process. During the deposition of the DLC coating, a pulsed bias mode is employed, with a peak voltage of -250V to -350V and a duty cycle of 15% to 25%. This aims to pre-place dispersed graphitization elements within the DLC coating that are capable of undergoing nanoscale graphitization transformation under cyclic stress. Carbon clusters; The SixOy active pinning layer provides dual anchoring of chemical bonding and mechanical interlocking for the DLC coating during the graphitization transformation process, thereby preventing microcracks from propagating to the interface.

[0010] The method for preparing a special coating for a spring probe according to the present invention wherein the surface nanoroughness Ra of the SixOy active pinning layer is 1 nm to 3 nm, so as to significantly improve the nucleation density of the subsequent DLC coating.

[0011] The method for preparing a special coating for a spring probe according to the present invention wherein the initial nucleation density of the DLC coating on the surface of the SixOy active pinning layer is increased by at least one order of magnitude compared with that without a pinning layer, so as to form a denser initial film structure, enhance the cohesive strength of the DLC coating, and prepare for subsequent stress-induced graphitization. The stable evolution of clusters provides a structural basis.

[0012] The method for preparing a special coating for a spring probe according to the present invention includes a pulse bias voltage with a frequency of 80 kHz to 120 kHz, a pulse waveform of an asymmetric rectangular wave or trapezoidal wave, and a rising edge slope of 0.1 μs to 1 μs, to form a curved graphene fragment morphology. Cluster.

[0013] The method for preparing a special coating for a spring probe according to the present invention includes the following steps: During the deposition of the DLC coating, acetylene is used as the carbon source gas at a flow rate of 18 sccm to 25 sccm; argon is used as the auxiliary gas at a flow rate of 5 sccm to 8 sccm; the flow ratio of acetylene to argon is 3:1 to 4:1, which is beneficial for the formation of dispersion. The cluster structure provides sufficient and appropriately shaped cluster precursors for stress-induced graphitization.

[0014] The method for preparing a special coating for a spring probe according to the present invention includes a DLC coating deposition temperature controlled within the range of 150°C to 200°C. The low duty cycle of the pulse bias reduces the average input power, ensuring that the deposition temperature remains within this range even under high peak bias conditions, thus preventing the spring substrate from annealing and softening. This range also ensures the... The clusters remain in a diffuse metastable state without premature graphitization.

[0015] The method for preparing a special coating for a spring probe according to the present invention includes the following process parameters for the oxygen plasma activation treatment: Introduce oxygen with a purity of ≥99.999%, at a flow rate of 3 sccm to 5 sccm, at a working pressure of 3 Pa to 5 Pa, at a radio frequency power of 150 W to 200 W, at a substrate bias of -50 V to -100 V, and at a processing time of 30 s to 60 s. The parameter range ensures that the oxidation reaction only acts on the surface of the Si gradient transition layer at a depth of 3nm to 5nm, avoiding excessive oxidation that would cause the SixOy layer to thicken and affect the conductive path between the spring substrate and the DLC coating.

[0016] The method for preparing a special coating for a spring probe according to the present invention includes, after the oxygen plasma activation treatment is completed, in-situ removal of residual oxygen to a background vacuum within the same plasma-enhanced chemical vapor deposition chamber. After stabilizing for 5 to 10 minutes, the DLC coating is deposited to eliminate the impact of residual oxygen on the purity of the DLC coating components. Interference with the controllability of cluster structure.

[0017] The method for preparing a special coating for a spring probe according to the present invention, wherein the deposition process of the Si gradient transition layer is as follows: Using tetramethylsilane as the precursor gas, the flow rate decreased linearly from 10 sccm to 0 sccm; Simultaneously, carrier gas argon is introduced, with the flow rate linearly decreasing from 10 sccm to 5 sccm; The deposition time is 10 min, the RF power is 300 W, the substrate pulse bias voltage is -150 V, the duty cycle is 50%, the frequency is 100 kHz, and the working pressure is 5 Pa.

[0018] The method for preparing a special coating for a spring probe according to the present invention, wherein the spring substrate is a compression helical spring made of piano wire with a wire diameter of 0.08 mm to 0.3 mm, and the spring substrate has undergone stress annealing treatment before depositing the Si gradient transition layer, with an annealing temperature of 240°C to 280°C. The annealing temperature is higher than the deposition temperature of the subsequent PECVD process to ensure the final stability of the mechanical properties of the spring matrix and to prevent the subsequent PECVD process from generating additional heat treatment effects.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The Si gradient transition layer alleviates the thermal expansion coefficient and lattice mismatch between the DLC coating and the spring steel substrate, reducing residual stress at the interface. The key step, "oxygen plasma activation treatment," generates a 3-5 nm thick SixOy active pinning layer in situ on the Si transition layer surface. This pinning layer provides dual anchoring through chemical bonding (Me-O-Si) and nanoscale mechanical interlocking, improving adhesion by 30%-50%. Furthermore, it acts as a diffusion barrier, inhibiting the diffusion of carbon atoms into the metal substrate and ensuring long-term stability of the contact resistance.

[0020] During the deposition of the DLC layer, a pulsed bias voltage with a peak voltage of -250V to -350V and a duty cycle of 15% to 25% was used to pre-place dispersed [materials] within the coating. Carbon clusters. These clusters undergo nanoscale graphitization at localized high-stress points generated by hundreds of thousands of cycles of spring compression, generating solid lubricants in situ. This achieves adaptive lubrication that becomes smoother with use, actively reducing the coefficient of friction and preventing the propagation of microcracks. The SixOy pinning layer provides a safety boundary for this graphitization process, ensuring that even if microstructural evolution occurs within the film, macroscopic peeling will not occur at the interface. Attached Figure Description

[0021] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a flowchart of the method steps of the present invention.

[0023] Figure 2 The image shows an atomic force microscopy (AFM) image of the SixOy pinning layer of this invention, with a surface nanoroughness Ra of approximately 2.1 nm.

[0024] Figure 3 This is a high-resolution transmission electron microscope image of the DLC film deposited under a -300V pulsed bias voltage according to the present invention, revealing bent sp2 carbon (graphene-like fragments) distributed in the soft carbon network.

[0025] Figure 4 This is a top-view SEM image of the initial DLC nucleation on the SixOy pinned layer of the present invention, wherein the nucleation density is approximately 12 times that of the reference sample without a pinned layer.

[0026] Figure 5 The image shows a scanning electron microscope image of the cross-section of the initially deposited DLC film on the SixOy pinning layer of the present invention, revealing a dense microstructure and a uniform interface.

[0027] Figure 6 The Raman spectrum of the DLC film of the present invention shows a D band near 1350 cm⁻¹ and a G band at 1542 cm⁻¹ with a ratio of 1.35, indicating that it has a typical aC:H structure and contains abundant sp² clusters. Detailed Implementation

[0028] The terms "first," "second," "third," and "fourth," etc., used in the specification, claims, and accompanying drawings of this invention are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0029] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0030] "Multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0031] Furthermore, the terms indicating orientation, such as "up," "down," "left," "right," "upper end," "lower end," and "longitudinal," are all based on the posture and position of the device or equipment described in this solution during normal use.

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, a clear and complete description will be provided below in conjunction with the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the protection scope of the present invention.

[0033] This embodiment discloses a method for preparing a special coating for a spring probe, specifically for preparing a DLC coating with adaptive lubrication function on the compression helical spring of a test probe. The following is in conjunction with the appendix... Figure 1 The process shown is described in detail for this embodiment, but the implementation of the present invention is not limited thereto.

[0034] This embodiment uses SWP-B piano wire (compliant with JIS G3522 standard) as the spring base material. The piano wire is cold-rolled using a CNC automatic spring coiling machine to produce a compression coil spring with a wire diameter of 0.12 mm, an outer diameter of 0.85 mm, and a free length of 8.0 mm. The spring ends are closed-end ground flat, with the deviation of the ground surface perpendicular to the spring axis controlled within 3°. The formed spring is placed in a vacuum tempering furnace and held at 270°C for 15 minutes for stress-relief annealing to eliminate residual internal stress generated during cold rolling. It is then cooled to room temperature under an argon protective atmosphere. After annealing, the spring's microhardness is HV510, and its elastic modulus is 0.32 N / mm. The annealing temperature (270℃) is higher than the deposition temperature (150-200℃) of the subsequent PECVD process, thereby ensuring that the mechanical properties of the spring substrate are ultimately stabilized in the annealing process, so that the subsequent PECVD coating process does not produce additional heat treatment effects and does not cause degradation of the spring's elasticity and fatigue performance.

[0035] After annealing, the springs undergo surface pretreatment. They are placed in a multi-tank ultrasonic cleaning line and first ultrasonically cleaned for 12 minutes in an alkaline degreasing solution (a deionized aqueous solution containing 5% NaOH and 3% Na2CO3) at 65℃, alternating between ultrasonic frequencies of 40kHz and 80kHz to enhance the cleaning effect. Subsequently, they are rinsed twice with deionized water (resistivity ≥18MΩ·cm), 10 minutes each, to thoroughly remove residual degreasing agent. Finally, they are dried with high-purity nitrogen. The cleaned springs are inspected using the water film method; a continuous, unbroken water film on the surface indicates acceptable cleanliness.

[0036] The cleaned springs were mounted on a custom-made stainless steel fixture, with a minimum spacing of 8 mm between them to avoid mutual obstruction and plasma shadowing effects. The fixture was placed on the rotating sample stage of the PECVD equipment, which rotated planetarily at 6 rpm. After closing the chamber, a vacuum was evacuated to the background vacuum level. Then, high-purity argon gas (99.999% purity) was introduced at a flow rate of 40 sccm, and the working pressure was adjusted to 3 Pa. The RF power supply was turned on to 250 W (13.56 MHz), and a DC pulse bias voltage of -400 V (frequency 100 kHz, duty cycle 40%) was applied to the substrate for argon plasma cleaning and activation treatment for 15 minutes. This step utilizes the dual effects of physical bombardment and chemical activation of Ar plasma to remove residual oxides and adsorbates on the spring surface, while activating the surface to enhance the adhesion of subsequent coatings. During this process, the substrate temperature was monitored in real time using a K-type thermocouple and did not exceed 145 °C.

[0037] After argon plasma cleaning, the Si gradient transition layer was deposited under vacuum conditions. The precursor gas was switched to tetramethylsilane (TMS, purity ≥99.9%), with an initial flow rate of 10 sccm. Simultaneously, high-purity argon was introduced as the carrier gas at an initial flow rate of 10 sccm. The RF power was set to 300W (13.56MHz), the substrate pulse bias voltage to -150V, the pulse frequency to 100kHz, the duty cycle to 50%, and the working pressure to 5Pa.

[0038] During deposition, the TMS and argon flow rates were synchronously and linearly decreased using a mass flow controller (MFC): the TMS flow rate decreased linearly from 10 sccm to 0 sccm within 10 minutes, and the argon flow rate decreased linearly from 10 sccm to 5 sccm accordingly. This step formed a Si gradient transition layer with a thickness of approximately 120 nm on the spring surface, whose composition smoothly transitioned from a Si-rich state at the bottom to a near-pure carbon state at the surface. This gradient structure effectively alleviated the residual interfacial stress caused by the difference in thermal expansion coefficients and lattice constants between the metal substrate and the subsequent DLC coating, which is the basis for obtaining high adhesion. The substrate temperature was stabilized at around 165℃ during the process.

[0039] After the Si gradient transition layer was deposited, an in-situ oxygen plasma activation-pinning process was performed within the same PECVD chamber. The TMS gas supply was shut off, and high-purity oxygen (99.999% purity) was introduced through an independent mass flow controller, with the flow rate precisely controlled at 4 sccm (MFC accuracy ±0.1 sccm). Simultaneously, the argon flow rate was adjusted to 0 sccm, and the working pressure was adjusted to 4 Pa. The RF power was reduced to 180W, and the substrate pulse bias was adjusted to -80V (frequency 100kHz, duty cycle 50%), with the processing time strictly controlled to 45 seconds. In this step, the low-power, weakly biased oxygen plasma only acted on the outermost 3-5 nm depth of the Si gradient transition layer, forming a highly active pinning layer with a chemical composition of SixOy in situ on the surface (this pinning layer may also contain a small amount of SixNy, but for convenience, it is collectively referred to as the SixOy active pinning layer). Atomic force microscopy (AFM) analysis showed that the surface nanoroughness Ra of this SixOy pinning layer was approximately 2.1 nm. Figure 2 As shown.

[0040] The SixOy pinning layer has three key functions: First, it forms a Me-O-Si type chemical bond with the underlying metal matrix, the strength of which far exceeds that of simple physical adsorption. Second, its own nanoscale uneven structure provides a large number of mechanical interlocking anchor points for the subsequent DLC coating, increasing the adhesion area by about an order of magnitude. Third, the dense SixOy layer naturally acts as a diffusion barrier layer, which can effectively suppress the low-temperature diffusion of carbon atoms into the metal substrate during subsequent DLC deposition and long-term use, thereby ensuring the long-term stability of the probe contact resistance.

[0041] After processing, stop the oxygen supply, turn off the radio frequency and bias power supplies, and evacuate the chamber to a vacuum level. The system is then stabilized under this background vacuum for 8 minutes to ensure complete removal of residual oxygen. This "in-situ evacuation and removal" step is crucial because residual oxygen can contaminate the subsequently deposited DLC film, leading to impurities and the formation of unwanted oxygen-containing functional groups, thus making it impossible to precisely control the formation of the desired subsequent layers. The structure and content of clusters disrupt the adaptive lubrication function.

[0042] After the SixOy pinning layer was prepared and residual oxygen was removed, DLC functional layers were deposited continuously in the same chamber. High-purity acetylene (C2H2, 99.999% purity) was introduced as the carbon source gas at a flow rate of 22 sccm; simultaneously, high-purity argon was introduced as the auxiliary gas at a flow rate of 6 sccm, with an acetylene to argon flow ratio of approximately 3.7:1. This specific ratio range (3:1 to 4:1) proved beneficial for forming a diffuse distribution in the film. The cluster structure, rather than a uniform amorphous network, is a structural prerequisite for subsequent adaptive graphitization. The working gas pressure was adjusted to 3 Pa, the RF power supply was turned on to 380 W (13.56 MHz), and a pulse bias voltage with a peak voltage of -300 V was applied to the substrate.

[0043] The specific parameters of the pulsed bias voltage are as follows: frequency 100kHz, duty cycle 20%, waveform is an asymmetric trapezoidal wave with a rise slope of 0.3μs. During the deposition process, the temperature is monitored in real time by a K-type thermocouple installed near the sample stage, and the deposition temperature is strictly maintained at 178±2℃ using a PID control system. In this pulsed bias mode, the high peak bias voltage of -300V provides sufficient ion bombardment energy, enabling the deposited carbon atoms to have high migration and local reconstruction capabilities when reaching the substrate surface, thereby pre-setting a large number of diffusely distributed carbon atoms with a certain curvature in the amorphous carbon network. Carbon clusters (graphene-like fragment morphology), such as Figure 3 As shown; the low duty cycle of only 20% significantly reduces the average input power, ensuring that the deposition temperature can still be safely controlled below 200℃ under high peak bias conditions (far below the tempering temperature range of 350-500℃ for spring steel), thus fully preserving the elasticity and fatigue strength of the spring matrix.

[0044] Meanwhile, the deposition temperature range of 150-200℃ ensures the preset... The clusters exist in a "dispersed metastable state" and do not undergo premature and uncontrollable graphitization during the deposition process. The deposition lasted for 50 minutes, and a hydrogen-containing amorphous carbon (aC:H) type DLC coating with a total thickness of about 0.9 μm was finally obtained on the spring surface.

[0045] After deposition, the samples were naturally cooled to below 80°C in a vacuum before being removed. Randomly selected coated springs from the same batch were then subjected to performance testing. The morphology of the initially deposited DLC film on the SixOy pinning layer was observed using scanning electron microscopy (SEM). Compared to the control sample without a pinning layer, the initial nucleation density of the DLC film after the pinning layer was introduced increased by approximately 12 times (i.e., more than an order of magnitude). Figure 4 As shown), the cross-section of the membrane exhibits an extremely dense tissue structure, such as... Figure 5 This lays the foundation for subsequent stress-induced graphitization processes. The stable evolution of clusters provides a solid foundation for cohesive strength.

[0046] Nanoindentation testing (referencing ISO 14577) showed that the DLC coating had a hardness of 19.3 GPa and an elastic modulus of 145 GPa. Scratch testing (referencing ISO 20502) determined the coating's critical load Lc² to be 48 N, approximately 71% higher than the control sample without a pinning layer (Lc² = 28 N), indicating a significant improvement in adhesion. Ball-disc friction testing showed that the coating's initial coefficient of friction was 0.12. Raman spectroscopy analysis showed that... Figure 6 The ID / IG ratio of the DLC film is 1.35, and the G peak position is at... This indicates that the film has a typical aC:H structure and contains a large amount of... Clusters. The film thickness measured by the step profiler was 0.92 μm. The spring constant changed by 1.8% before and after coating, meeting the requirement of a change rate ≤3%, indicating that the mechanical properties of the spring substrate were not affected by the process temperature. After 120 hours of continuous salt spray testing (referring to ISO 9227 Neutral Salt Spray Test NSS), no red rust appeared on the spring surface, which is better than the original target of 96 hours.

[0047] The coated springs were assembled into probes in a Class 10,000 cleanroom (ISO Class 7, temperature 23±2℃, relative humidity 50%±10%RH). Using precision tweezers with a Teflon coating, the springs were carefully inserted into the beryllium copper needle tube, being handled gently to avoid scratching the coating. A precision press-fitting machine (including displacement and force sensors) was then used to press the needle tip and tail into both ends of the needle tube sequentially, with the pressing depth tolerance controlled within ±0.02mm. The closing force at both ends of the needle tube was 30N. The assembled probe, measured using the four-wire method, showed a contact resistance of 35mΩ (meeting the requirement of ≤50mΩ).

[0048] Accelerated life testing was conducted on the assembled probe. Under normal temperature conditions, the probe was repeatedly compressed at its rated working stroke (1.0 mm) at a frequency of 15 Hz for 200,000 cycles. The spring force was recorded every 10,000 cycles. Results showed that in the first 50,000 cycles, the spring force decreased by approximately 2.1%, and the compression-release curve was smooth and without jamming. Between 100,000 and 200,000 cycles, the force decay rate not only did not increase but gradually slowed down, with a cumulative force decay of only 6.8% at 200,000 cycles, far below the acceptable threshold of 10%. More significantly, in the latter half of the life test, the probe's compression-release friction showed a significant decreasing trend—the average friction during the cycle period from 100,000 to 200,000 cycles was reduced by approximately 16% compared to the average friction during the initial 10,000 cycles. This phenomenon strongly confirms the occurrence of the "adaptive lubrication" mechanism described in this invention (i.e., the localized high stress points generated by the spring coating during cyclic compression induce a pre-set...). The clusters undergo nanoscale graphitization, generating in-situ graphite solid lubricating media, actively reducing the local friction coefficient and exhibiting a "slipperier with use" effect, transforming the "passive wear" of traditional coatings into "active self-optimization." After the life test, the probe was disassembled, and the spring coating was examined using a scanning electron microscope. No macroscopic peeling or penetrating cracks were found; only a few microcracks were observed in local high-stress areas. However, these microcracks all terminated at the SixOy pinning layer interface and did not extend into the spring matrix, proving that the ultra-strong adhesion provided by the SixOy pinning layer provides a "safety boundary" for adaptive graphitization. Even if the microstructure of the DLC film evolves, the high-bonding interface ensures that the coating does not undergo macroscopic peeling. In contrast, the probe without the SixOy pinning layer and using only the same DLC deposition parameters showed flaky peeling of the coating after approximately 130,000 cycles, resulting in a sharp decrease in spring force.

[0049] Intermittent life tests were conducted in a corrosive atmosphere containing H2S (10 ppm): after every 10,000 compressions, the cells were allowed to stand for 24 hours, and this cycle was repeated. After 5 cycles (a total of 50,000 compressions and 5 long-term corrosion exposures), the spring force fluctuation of the probe was less than 2%, and the spring extension and contraction movements remained smooth without any corrosion or adhesion. Upon disassembly, no corrosion product accumulation or interface peeling was observed at the interface between the SixOy pinning layer and the DLC coating. This confirms that the dense SixOy pinning layer effectively blocks the penetration path of corrosive gases along the interface into the spring matrix, fundamentally solving the failure problem caused by corrosive gases eroding the internal spring in existing technologies.

[0050] In addition, comparative experiments were conducted to verify the linkage effect of the key parameters of the present invention: With other parameters remaining the same, increasing the duty cycle of the pulse bias to 50% (i.e., outside the 15%-25% range of this invention) causes the substrate temperature to rise rapidly to 235°C due to the increased average input power in order to maintain the same peak bias of -300V, exceeding the upper limit of 200°C. Furthermore, the spring constant decreases by 7.2% after coating, indicating that the spring has undergone partial annealing. However, when the duty cycle is maintained at the 20% limit specified in this invention, the temperature stabilizes at 178°C, and the spring constant remains almost unchanged.

[0051] Furthermore, Raman spectroscopy analysis was performed on the DLC coatings prepared under two conditions: 20% and 50% duty cycles. The sample with a 50% duty cycle showed sharp G and 2D peaks even in the deposited state, indicating that... The clusters had overgrown and even prematurely graphitized, losing their potential for subsequent stress-induced graphitization; while the sample with a 20% duty cycle remained diffuse. Cluster-characteristic peak shape. This fully demonstrates the effectiveness of a low duty cycle in maintaining low temperature while protecting the environment under high peak bias. The metastable state of the clusters plays a key role, and this parameter linkage provides an indispensable structural prerequisite for the adaptive lubrication function of the coating of this invention.

[0052] The above embodiments fully demonstrate the entire process of this invention, from spring fabrication, surface pretreatment, construction of gradient transition and pinning layers, pulsed bias DLC deposition to probe assembly and lifetime verification. In summary, this embodiment successfully fabricates a high-lifetime test probe using PECVD to deposit a DLC coating, increasing the probe's lifespan from approximately 100,000 cycles to over 200,000 cycles, and fundamentally solving the failure problem caused by corrosive gases eroding the internal spring.

[0053] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a special coating for a spring probe, characterized in that, Includes the following steps: A Si gradient transition layer is deposited on the surface of the spring substrate; The deposition process of the Si gradient transition layer is as follows: Using tetramethylsilane as the precursor gas, the flow rate decreased linearly from 10 sccm to 0 sccm; Simultaneously, carrier gas argon is introduced, with the flow rate linearly decreasing from 10 sccm to 5 sccm; The deposition time is 10 min, the RF power is 300 W, the substrate pulse bias voltage is -150 V, the duty cycle is 50%, the frequency is 100 kHz, and the working gas pressure is 5 Pa. The surface of the Si gradient transition layer is subjected to oxygen plasma activation treatment to form a SixOy active pinning layer with a thickness of 3nm to 5nm; A diamond-like carbon (DLC) coating is deposited on the surface of the SixOy active pinning layer using a plasma-enhanced chemical vapor deposition process. During the deposition of the DLC coating, a pulsed bias mode is employed, with a peak voltage of -250V to -350V and a duty cycle of 15% to 25%. This aims to pre-place dispersed graphitization elements within the DLC coating that are capable of undergoing nanoscale graphitization transformation under cyclic stress. Carbon clusters; The SixOy active pinning layer provides dual anchoring of chemical bonding and mechanical interlocking for the DLC coating during the graphitization transformation process, thereby preventing microcracks from propagating to the interface.

2. The method for preparing a special coating for a spring probe according to claim 1, characterized in that, The surface nanoroughness Ra of the SixOy active pinning layer is 1 nm to 3 nm, which significantly improves the nucleation density of the subsequent DLC coating.

3. The method for preparing a special coating for a spring probe according to claim 2, characterized in that, The frequency of the pulse bias voltage is from 80 kHz to 120 kHz, and the pulse waveform is an asymmetric rectangular wave or trapezoidal wave with a rising slope of 0.1 μs to 1 μs to form sp² clusters of curved graphene fragments.

4. The method for preparing a special coating for a spring probe according to claim 3, characterized in that, When depositing the DLC coating, acetylene is used as the carbon source gas with a flow rate of 18 sccm to 25 sccm; argon is used as the auxiliary gas with a flow rate of 5 sccm to 8 sccm; the flow rate ratio of acetylene to argon is 3:1 to 4:1, which is conducive to the formation of a diffuse sp² cluster structure, providing sufficient and appropriately shaped cluster precursors for stress-induced graphitization.

5. The method for preparing a special coating for a spring probe according to claim 1, characterized in that, The deposition temperature of the DLC coating is controlled within the range of 150°C to 200°C; the low duty cycle of the pulse bias reduces the average input power, ensuring that the deposition temperature remains within this range even under high peak bias conditions, thus preventing the spring substrate from softening during annealing; this range also ensures that the... The clusters remain in a diffuse metastable state without premature graphitization.

6. The method for preparing a special coating for a spring probe according to claim 1, characterized in that, The process parameters for the oxygen plasma activation treatment are as follows: Introduce oxygen with a purity of ≥99.999%, at a flow rate of 3 sccm to 5 sccm, at a working pressure of 3 Pa to 5 Pa, at a radio frequency power of 150 W to 200 W, at a substrate bias of -50 V to -100 V, and at a processing time of 30 s to 60 s. The parameter range ensures that the oxidation reaction only acts on the surface of the Si gradient transition layer at a depth of 3nm to 5nm, avoiding excessive oxidation that would cause the SixOy layer to thicken and affect the conductive path between the spring substrate and the DLC coating.

7. The method for preparing a special coating for a spring probe according to any one of claims 1 to 6, characterized in that, After the oxygen plasma activation treatment is completed, residual oxygen is evacuated to a background vacuum in situ within the same plasma-enhanced chemical vapor deposition chamber. After stabilizing for 5 to 10 minutes, the DLC coating is deposited to eliminate the impact of residual oxygen on the purity of the DLC coating components. Interference with the controllability of cluster structure.

8. The method for preparing a special coating for a spring probe according to claim 5, characterized in that, The spring substrate is a compression helical spring made of piano wire with a wire diameter of 0.08 mm to 0.3 mm. Before depositing the Si gradient transition layer, the spring substrate has undergone stress annealing treatment at a temperature of 240°C to 280°C. The annealing temperature is higher than the deposition temperature of the subsequent PECVD process to ensure the final stability of the mechanical properties of the spring matrix and to prevent the subsequent PECVD process from generating additional heat treatment effects.

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