Method of manufacturing a high air tightness connector terminal with enhanced glue adhesion and terminal assembly

Abstract

The application relates to a high-airtightness connector terminal manufacturing method and a terminal assembly, which comprises the following steps: obtaining a terminal base material and stamping a V-shaped groove microstructure in a sealing operation area; performing overall electroplating on the base material containing the microstructure to form an anticorrosion plating layer continuously covering the inner wall and the groove bottom of the microstructure; assembling the terminal to an insulating body; performing plasma cleaning on the microstructure surface before glue injection; and injecting sealing glue to fill the microstructure and solidifying in a negative pressure environment. The application has the advantages that the plating layer integrity is guaranteed by the stamping and then electroplating process to prevent the base material from being corroded, micro air holes are eliminated by using the plasma and vacuum processes, and the mechanical interlocking strength and the air-tightness reliability of the terminal and the glue are significantly improved.

Description

Technical Field

[0001] This application relates to the field of connector manufacturing, and in particular to a method for manufacturing high-airtight connector terminals and terminal assemblies that enhance adhesive adhesion. Background Technology

[0002] In modern industrial automation and new energy vehicle electronics, high-airtightness connectors are crucial basic components, and their sealing performance directly affects the long-term stability and safety of the entire control system. The core function of these connectors is to prevent external moisture, oil, or corrosive gases from seeping into the device through the interface between the terminals and the insulating body. To ensure good conductivity, the metal terminals of the connectors typically use a copper alloy substrate, with a layer of precious metal such as silver or gold plated on its surface through an electroplating process. However, the silver plating layer has high chemical inertness and relatively low surface energy, resulting in weak chemical bonding between it and epoxy resin or silicone-based sealant adhesives. Under conditions such as thermal shock or mechanical vibration, the adhesive is prone to microscopic peeling from the smooth plating surface, forming leakage channels and leading to airtightness failure.

[0003] To address this issue, existing technologies often attempt to increase the surface roughness of terminals through physical methods, such as sandblasting or mechanical indentation, hoping to enhance physical adhesion using the principle of mechanical interlocking. However, conventional manufacturing processes typically involve pre-plating the metal strip before stamping. This pre-plating followed by stamping process damages the plating layer in the stamped area, particularly in the micro-grooves or the bottom of the indentation, exposing the underlying copper alloy substrate. During subsequent adhesive curing or long-term use, the exposed copper substrate is prone to oxidative corrosion from residual moisture or chemicals in the adhesive. This interfacial corrosion not only weakens the adhesive's bonding strength, but the resulting porous oxide layer can even directly lead to sealing interface failure, turning the microstructure intended to enhance adhesion into a source of corrosion.

[0004] Furthermore, even if the issue of coating integrity is resolved, significant technical challenges remain in the encapsulation and filling of microstructures. When the terminal surface has micro-grooves with large depth-to-width ratios, traditional atmospheric pressure dispensing processes struggle to ensure that the adhesive can overcome surface tension and displace air from the bottom of the groove. Especially when the adhesive viscosity is high or the dispensing speed is fast, the adhesive can easily form bridging at the groove opening, trapping air at the bottom of the microstructure and creating cavitation. These residual cavities expand during high-temperature reflow soldering or equipment operation, and the resulting internal pressure may force the adhesive apart or cause internal cracking, thereby compromising the sealing structure. Simultaneously, organic contaminants adsorbed on the metal surface further reduce the adhesive's wetting and spreading ability, hindering its penetration into the depths of the microstructure. Summary of the Invention

[0005] To address the issues of insufficient physical adhesion between the plated terminals and the sealant leading to airtightness failure, and the easy damage to the plating during microstructure processing on the terminal surface resulting in substrate corrosion, this application provides a high-airtightness connector terminal manufacturing method and terminal assembly that enhances adhesive adhesion.

[0006] In a first aspect, this application provides a method for manufacturing a high-airtightness connector terminal that enhances adhesive adhesion, employing the following technical solution: A method for manufacturing a high-airtight connector terminal that enhances adhesive adhesion includes the following steps: S1. Obtain a metal terminal substrate, and form an array of V-shaped groove microstructures within a predefined sealing working area on the metal terminal substrate by cold stamping process; S2. The metal terminal substrate with the V-groove microstructure is subjected to overall electroplating to form an anti-corrosion coating that continuously covers the inner wall, bottom and edge of the V-groove microstructure. S3. Assemble the processed metal terminal substrate into the insulating body, and position the sealing operation area within the injection cavity defined by the insulating body; S4. Perform plasma cleaning on the surface of the metal terminal substrate and the V-groove microstructure located in the injection cavity to remove organic contaminants and increase surface energy; S5. Under negative pressure, the sealant is injected into the injection cavity, and the pressure difference drives the sealant to fill the internal space of the V-groove microstructure. S6. The sealant located in the injection cavity is subjected to multi-stage heating and curing to form a mechanically interlocked sealing structure.

[0007] Optionally, S1 includes the following sub-steps: S11. On the metal terminal substrate, a sealing operation area for contact with the sealant adhesive and a preset bending deformation area are defined; between the sealing operation area and the preset bending deformation area, a stress buffer band with a length not less than twice the thickness of the metal terminal substrate is retained, and the stress buffer band maintains a flat surface and is not grooved. S12. Apply a stamping load to the upper and lower surfaces of the sealing operation area to form the V-groove microstructure; wherein, the projection position of the V-groove microstructure on the upper surface in the direction perpendicular to the surface of the metal terminal substrate and the projection position of the V-groove microstructure on the lower surface in the direction perpendicular to the surface of the metal terminal substrate are axially staggered to form an interleaved distribution structure. S13. During cold stamping, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, while the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle. S14. The groove edge of the V-groove microstructure after cold stamping is subjected to tumbling or electrochemical polishing to remove the flash height of the groove edge to below 0.01mm; S15. Under the protection of the stress buffer strip, a bending moment is applied to the preset bending deformation zone to bend the metal terminal substrate to a predetermined angle; the solid flat structure of the stress buffer strip is used to block the transmission of bending stress to the sealing operation area, preventing the V-groove microstructure from undergoing tensile deformation due to stress transmission.

[0008] Optionally, S12 includes the following sub-steps: S121. Set the axial projection distance d between the V-groove microstructure on the upper surface and the V-groove microstructure on the lower surface, and limit the projection distance d to 0.5 to 0.8 times the original thickness T of the metal terminal substrate; S122. According to the set projection spacing d, a stamping load is applied to the sealing operation area to form a solid metal strip that extends continuously in a wave-like shape between the upper surface V-groove microstructure and the lower surface V-groove microstructure. The solid metal strip includes a geometrically neutral layer of the metal terminal substrate to provide a continuous shear stress transmission path.

[0009] Optionally, S13 includes the following sub-steps: S131. When performing the cold stamping process, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, and the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle to form a cross section suitable for fluid wetting. S132. At the end of the V-groove microstructure along the flow direction of the sealant adhesive, a gradually shallowing and disappearing climbing slope is formed by pressing the end shape of the die punch; the elevation angle β of the climbing slope is set to less than 30 degrees to guide the residual gas at the bottom of the groove to be discharged along the climbing slope, and to prevent the formation of air pockets at the end of the V-groove microstructure.

[0010] Optionally, in S13, the specific geometric parameters of the V-groove microstructure satisfy the following conditions: The ratio of the radius of curvature R of the bottom arc surface of the V-groove microstructure to the groove depth h of the V-groove microstructure is in the range of 0.15≤R / h≤0.25; the range of the opening angle θ of the V-groove microstructure is 90°<θ<120°.

[0011] Optionally, step S5 includes the following sub-steps: S51. Reduce the absolute pressure in the injection cavity to less than 1000 Pa, and inject the sealant until the liquid surface covers the main area of ​​the V-shaped groove microstructure, but does not completely wet the edge of the groove. S52. During the injection process, a periodic pulse with frequency f and amplitude ΔP is applied to the injection pressure, wherein the amplitude ΔP is set to 5% to 15% of the current injection pressure; the periodic pulse is used to drive the sealant to reciprocate along the slope direction on the climbing slope, thereby discharging the air bubbles located at the bottom of the groove along the climbing slope. S53. After the glue injection is completed, a graded re-pressure operation is performed; after restoring the pressure of the glue injection cavity to normal pressure, positive pressure is applied and maintained for a predetermined time t; the positive pressure is used to drive the sealant to bypass the solid metal strip formed by the interlacing of the upper surface V-groove microstructure and the lower surface V-groove microstructure, and fill the fluid shadow area located on the back of the interlaced structure, wherein the fluid shadow area is the area located on the side of the solid metal strip opposite to the flow direction of the sealant.

[0012] Optionally, in step S4, an atmospheric plasma cleaning process is used, and the dyne value of the metal terminal substrate and the surface of the V-groove microstructure after the atmospheric plasma cleaning process is not less than 50 mN / m.

[0013] Optionally, step S6 includes the following sub-steps: S61. While maintaining the applied positive pressure, the injection cavity is heated to a first temperature T1 and maintained for a first predetermined time to allow the sealant to undergo a preliminary crosslinking reaction; the positive pressure is used to suppress the sealant from flowing out of the fluid shadow area to the back of the solid metal strip; S62. Remove the positive pressure, raise the temperature of the injection cavity to a second temperature T2 and maintain it for a second predetermined time; use the molecular chain relaxation effect to reduce the interfacial stress between the sealant and the solid metal strip and the climbing slope to prevent the mechanical interlocking sealing structure from peeling off. S63. Raise the temperature of the injection cavity to a third temperature T3 and maintain it for a third predetermined time to allow the sealant to fully cure and form the mechanical interlocking sealing structure.

[0014] Secondly, this application also discloses a high-airtightness connector terminal assembly, which adopts the following technical solution: A high-tightness connector terminal assembly, comprising: The metal terminal has a sealed working area, the surface of which is provided with an array of V-shaped groove microstructures, and the inner wall, bottom and edge of the V-shaped groove microstructures are continuously covered with an anti-corrosion coating. An insulating body is attached to the outside of the metal terminal and defines a filling cavity surrounding the sealing operation area; A sealing adhesive is filled into the injection cavity and penetrates into the V-groove microstructure of the metal terminal; The sealant is cured within the V-groove microstructure to form a solid mechanically interlocked seal structure, and there is no cavitation residue between the mechanically interlocked seal structure and the V-groove microstructure.

[0015] In summary, this application includes at least one of the following beneficial technical effects: 1. This application employs a process sequence of microstructure stamping followed by overall electroplating, ensuring that the interior and edges of the V-groove microstructure are completely covered by an anti-corrosion coating. This design effectively avoids the problem of exposed copper at the bottom of the groove caused by electroplating followed by stamping in existing technologies, prevents peeling of the sealing interface due to substrate oxidation and corrosion, and significantly improves the corrosion resistance and adhesion durability of the terminals.

[0016] 2. This application combines plasma cleaning with negative pressure injection molding, solving the problem that micro-grooves are difficult to wet and fill with high-viscosity adhesives. Plasma cleaning improves the surface activity of the microstructure, and combined with the pressure difference drive under vacuum, it enables the sealant to climb through capillary action and fill the depths of the V-groove, eliminating micro-cavitation and thus constructing a dense and defect-free mechanical interlocking structure, significantly enhancing the airtight reliability of the connector. Attached Figure Description

[0017] Figure 1 A flowchart illustrating a method for manufacturing a high-airtight connector terminal that enhances adhesive adhesion according to an embodiment of the present invention is shown.

[0018] Figure 2 Illustration of an embodiment of the present invention Figure 1 The specific flowchart of S1-S4.

[0019] Figure 3 Illustration of an embodiment of the present invention Figure 1 The specific flowchart of S4-S6.

[0020] Figure 4 A schematic diagram of a high-airtightness connector terminal assembly is shown in one embodiment of the present invention.

[0021] Figure 5 A schematic diagram of the metal terminal in one embodiment of the present invention is shown.

[0022] Explanation of reference numerals in the attached figures: 1. Insulating body; 2. Metal terminal; 3. Sealing adhesive; 4. V-groove microstructure. Detailed Implementation

[0023] The present application will be further described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the application and are not intended to limit the scope of the application.

[0024] In the following description, numerous specific details are set forth for purposes of explanation in order to provide a thorough understanding of the inventive concept. As part of this specification, some of the accompanying drawings of this disclosure are block diagrams illustrating structures and devices to avoid complicating the disclosed principles. For clarity, not all features of the actual embodiment need to be described. Furthermore, the language used in this disclosure has been primarily chosen for readability and instructional purposes and may not have been chosen to define or limit the subject matter of the invention, thus requiring the necessary claims to determine such inventive subject matter. References to “an embodiment” or “an embodiment” in this disclosure mean that a particular feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment, and multiple references to “an embodiment” or “an embodiment” should not be construed as necessarily referring to the same embodiment.

[0025] Unless explicitly defined, the terms “a,” “an,” and “the” are not intended to refer to a singular entity, but rather to include a general category whose specific examples can be used for illustration. Therefore, the use of the terms “a” or “an” can mean any number of at least one, including “a,” “one or more,” “at least one,” and “one or more.” The term “or” means any of the options and any combination of the options, including all options unless explicitly indicated that the options are mutually exclusive. The phrase “at least one of” when combined with a list of items refers to a single item in the list or any combination of items in the list. The phrase does not require all items listed unless explicitly defined as such.

[0026] This application discloses a method for manufacturing high-airtight connector terminals that enhances adhesive adhesion, referring to... Figure 1-3 This includes the following steps S1-S6.

[0027] S1. Obtain a metal terminal substrate, and form an array of V-shaped groove microstructures within a predefined sealing working area on the metal terminal substrate by cold stamping.

[0028] The metal terminal substrate is made of copper alloy materials with high conductivity and good ductility, such as brass or phosphor bronze. The material's ductility supports plastic flow during cold stamping, preventing brittle fracture and serving as a stable carrier for microstructure forming. The sealing operation area is limited to specific areas that will subsequently come into contact with the sealant adhesive. This localized treatment enhances the physical roughness of the sealing interface while avoiding micro-deformation in the electrical contact or welding areas, thus maintaining the overall structural rigidity of the terminal.

[0029] Cold stamping applies instantaneous high-pressure loads at room temperature through the use of convex and concave dies. Compared to hot working, it avoids material softening due to annealing, and compared to chemical etching, it utilizes the metal work hardening effect to increase the microhardness of the V-groove surface. The arrayed V-groove microstructure increases the specific surface area of ​​the sealing working area through dense micro-undulations, extending the contact interface into three-dimensional space and providing a mechanical anchoring position.

[0030] This process employs a stamping-then-electroplation sequence, completing the microstructure formation in the bare copper state. This sequence avoids the problems of plating cracking and exposure of the substrate at the bottom of the V-groove due to severe deformation when processing pre-plated strips, ensuring that the substrate undergoes plastic deformation before surface protection.

[0031] Specifically, S1 includes the following sub-steps S11-S15.

[0032] S11. On the metal terminal substrate, a sealing operation area for contact with the sealant adhesive and a preset bending deformation area are defined; between the sealing operation area and the preset bending deformation area, a stress buffer band with a length not less than twice the thickness of the metal terminal substrate is retained, and the stress buffer band maintains a flat surface and is not grooved.

[0033] The sealing operation area utilizes microstructures to anchor the adhesive, and a pre-set bending deformation zone adapts to the connector's assembly shape through mechanical bending. During the plastic deformation of the metal, the tensile or compressive stress field generated by bending diffuses along the substrate lattice to the periphery. If the bending action is close to the sealing operation area, the transmitted stress causes geometric distortion or closure of the V-groove microstructure, compromising the anchoring function.

[0034] The stress buffer strip acts as a physical isolation barrier, utilizing the continuity of the solid metal to prevent stress from diffusing from the deformation zone to the microstructure region. The length of the buffer strip is set to be no less than twice the thickness of the metal terminal substrate, conforming to the Saint-Venant principle's distance requirement for local stress attenuation, ensuring that stress decays to a safe threshold before reaching the sealing operation area. This buffer strip maintains a flat surface and is not grooved, aiming to eliminate notch effects, prevent the formation of fracture sources along the stress transmission path, and ensure the structural integrity of the terminal during the molding process.

[0035] Furthermore, S12 includes the following sub-steps S121-S122.

[0036] S121. Set the axial projection distance d between the V-groove microstructure on the upper surface and the V-groove microstructure on the lower surface, and limit the projection distance d to 0.5 to 0.8 times the original thickness T of the metal terminal substrate.

[0037] S122. According to the set projection spacing d, a stamping load is applied to the sealing operation area to form a solid metal strip that extends continuously in a wave-like shape between the upper surface V-groove microstructure and the lower surface V-groove microstructure. The solid metal strip includes a geometrically neutral layer of the metal terminal substrate to provide a continuous shear stress transmission path.

[0038] The projection spacing d is defined as the misalignment distance between the bottom of the microstructure groove on the upper surface and the bottom of the microstructure groove on the lower surface in the axial extension direction of the substrate. This parameter determines the spatial distribution pattern of the forces between the upper and lower dies in the double-sided stamping process. Limiting d to 0.5T to 0.8T aims to avoid excessive necking of the substrate cross-section. If d=0 (i.e., top-to-bottom distribution), the cutting edges of the upper and lower dies are opposite each other in the vertical direction, which can easily cut the substrate fibers, forming weak fracture lines similar to the perforations of a stamp, resulting in a sharp drop in tensile strength. If d is too large, the distance between the upper and lower grooves is too far, making it impossible to form a compact wavy structure. The staggered distribution structure, through spatial misalignment, ensures that the substrate retains sufficient solid thickness on any vertical cross-section, thus avoiding the stress concentration risk caused by traditional top-to-bottom stamping from a mechanical structural perspective.

[0039] Under a set spacing of stamping load, the metal material undergoes plastic flow, flowing along the mold guide direction and retaining a continuous, wavy solid metal strip between the upper and lower V-grooves. This solid metal strip completely encompasses the geometrically neutral layer of the substrate, maintaining axial rigidity even when the overall thickness of the substrate is reduced due to the slotting. This continuous path serves as a shear stress transmission channel, ensuring that the terminals will not fracture or fail due to fatigue in the sealing area when subjected to insertion / extraction forces or thermal stress during subsequent assembly or use.

[0040] S12. Apply a stamping load to the upper and lower surfaces of the sealing operation area to form the V-groove microstructure; wherein the projection position of the V-groove microstructure on the upper surface in the direction perpendicular to the surface of the metal terminal substrate is axially offset from the projection position of the V-groove microstructure on the lower surface in the direction perpendicular to the surface of the metal terminal substrate, forming an interleaved distribution structure.

[0041] S13. During cold stamping, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, while the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle.

[0042] The staggered distribution structure with axially offset components avoids the fracture line effect of traditional top-to-top symmetrical structures in terms of mechanical cross-section. Top-to-top structures tend to cause drastic thinning of the substrate at the same cross-section, forming stress concentration points; while the staggered distribution, through spatial misalignment, prevents excessive necking of the substrate in the thickness direction, thus maintaining the effective stress-bearing cross-section and tensile strength of the terminal substrate without sacrificing the sealing surface area.

[0043] The design of the tank bottom as a curved surface with a radius of curvature R, rather than a V-shaped sharp corner, is primarily based on fluid dynamics and electrochemical considerations. From a fluid dynamics perspective, sharp corners easily become dead zones, preventing high-viscosity adhesives from reaching the bottom and leaving cavitation. The curved surface provides a continuous streamline boundary, facilitating the complete expulsion of air from the adhesive. From an electroplating process perspective, the curved surface eliminates the tip discharge effect, preventing scorching or nodulation of the plating at the tank bottom due to excessive current density, ensuring the integrity of the plating at deep holes. Simultaneously, controlling the opening angle θ to an obtuse angle reduces capillary resistance when the adhesive enters the tank, facilitating rapid spreading and wetting of the high-viscosity fluid on the tank walls.

[0044] In S13, the specific geometric parameters of the V-groove microstructure satisfy the following conditions: the ratio of the radius of curvature R of the bottom arc surface of the V-groove microstructure to the groove depth h of the V-groove microstructure is in the range of 0.15≤R / h≤0.25; the range of the opening angle θ of the V-groove microstructure is 90°<θ<120°.

[0045] The R / h ratio defines the roundness of the tank bottom. Setting R / h ≥ 0.15 aims to prevent the tank bottom from being too sharp, thereby avoiding plating defects caused by discharge at the electroplating tip and cavitation residue during glue injection; setting R / h ≤ 0.25 is to prevent the tank bottom from being too flat, ensuring that the microstructure has a sufficient depth-to-width ratio to form an effective mechanical interlocking gripping force.

[0046] The opening angle θ is limited to the range of 90° < θ < 120° to achieve a balance between filling and anchoring force. If θ ≤ 90° (acute angle or right angle), the deep and narrow groove will lead to difficulty in venting; if θ ≥ 120°, the groove opening is too wide, and the cured colloid lacks sufficient geometric resistance when subjected to normal tensile force, making it prone to slippage.

[0047] In S13, the specific geometric parameters of the V-groove microstructure satisfy the following conditions: The ratio of the radius of curvature R of the bottom arc surface of the V-groove microstructure to the groove depth h of the V-groove microstructure is in the range of 0.15≤R / h≤0.25; the range of the opening angle θ of the V-groove microstructure is 90°<θ<120°.

[0048] The R / h ratio defines the roundness of the tank bottom. Setting R / h ≥ 0.15 aims to prevent the tank bottom from being too sharp, thereby avoiding plating defects caused by electroplating tip discharge and cavitation residue during adhesive injection; setting R / h ≤ 0.25 is to prevent the tank bottom from being too flat, ensuring that the microstructure has a sufficient depth-to-width ratio to form an effective mechanical interlocking adhesion force. Regarding the opening angle θ, limiting it to the range of 90° < θ < 120° achieves a balance between filling performance and anchoring force. If θ ≤ 90°, a deep and narrow tank shape will lead to difficulty in venting; if θ ≥ 120°, the tank opening is too wide, and the cured adhesive lacks sufficient geometric resistance when subjected to normal tensile force, making it prone to slippage.

[0049] To be further refined, S13 includes the following sub-steps S131-S132.

[0050] S131. When performing the cold stamping process, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, and the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle to form a cross section suitable for fluid wetting.

[0051] S132. At the end of the V-groove microstructure along the flow direction of the sealant adhesive, a gradually shallowing and disappearing climbing slope is formed by pressing the end shape of the die punch; the elevation angle β of the climbing slope is set to less than 30 degrees to guide the residual gas at the bottom of the groove to be discharged along the climbing slope, and to prevent the formation of air pockets at the end of the V-groove microstructure.

[0052] The profile of the die punch directly determines the forming quality of the microstructure. The rounded bottom and obtuse angle features are replicated onto the metal surface through the precision grinding of the punch end shape. From the perspective of contact angle and surface tension, compared with the sharp V-shape, the U-shaped bottom + obtuse angle cross-section significantly reduces the flow resistance of high viscosity adhesive at the solid-liquid interface, allowing the adhesive front to wet the tank wall more smoothly.

[0053] For the ends of microstructures, traditional vertically truncated tank designs create fluid dead zones, where the glue flow front easily traps air, forming high-pressure cavitation. The ascending slope, with its gradually varying depth, eliminates this dead zone, establishing a continuous gas escape channel. Setting the elevation angle β < 30° based on bubble force analysis reveals that, at the microscale, bubbles are significantly pinned by surface tension. If the slope is too steep, the tangential component of bubble buoyancy or fluid thrust is insufficient to overcome the pinning force; a gentle slope of less than 30 degrees ensures that bubbles can smoothly slide out of the tank bottom under fluid drive, avoiding stagnation.

[0054] S14. The groove edge of the V-shaped groove microstructure after cold stamping is subjected to tumbling or electrochemical polishing to remove the flash height of the groove edge to below 0.01mm.

[0055] In cold stamping, the metal material undergoes intense plastic deformation at the edge of the V-groove. Due to the material's ductility limits and the compression from the die gap, microscopic protrusions or burrs inevitably form at the groove edge. Roll grinding removes these protrusions through the mechanical impact of abrasive particles, while electrochemical polishing utilizes the tip-preferential dissolution effect, concentrating the current density at the burr tip to rapidly dissolve and smooth the burr.

[0056] Removing burrs is crucial for subsequent processes. Sharp burrs can trigger a "point discharge effect" during electroplating, leading to excessively high current density in certain areas, causing scorching, nodules, or uneven thickness of the edge plating. During the application and dispensing stages, tall burrs not only hinder the smooth flow of high-viscosity adhesives but also become stress concentration points after the adhesive cures, potentially puncturing the adhesive or inducing interfacial microcracks during thermal expansion and contraction. Strictly limiting burr height to below 0.01 mm is the critical engineering threshold for eliminating the point discharge effect during electroplating and ensuring that the rheological behavior of the sealant remains undisturbed.

[0057] S15. Under the protection of the stress buffer strip, a bending moment is applied to the preset bending deformation zone to bend the metal terminal substrate to a predetermined angle; the solid flat structure of the stress buffer strip is used to block the transmission of bending stress to the sealing operation area, preventing the V-groove microstructure from undergoing tensile deformation due to stress transmission.

[0058] S15 applies a bending moment to a preset bending deformation zone, bending the substrate to a predetermined angle (such as a 90-degree right angle or a specific arc) required to fit the connector housing or PCB layout. Due to the elastoplastic characteristics of metallic materials, the bending process is essentially a strong lattice slip and stress redistribution process. Without protective measures, this high-intensity stress field will be transmitted very quickly along the metal fibers to adjacent areas.

[0059] At this point, the stress buffer zone reserved in S11, as a solid metal area without grooves and of uniform thickness, has a significantly higher cross-sectional modulus than the microstructure areas or bending areas on both sides. According to the principle of mechanical transmission, when the bending stress wave is transmitted to this buffer zone, it will attenuate and dissipate due to the abrupt change in cross-sectional stiffness, and will not be able to continue to cross the buffer zone and reach the sealing operation area. Therefore, even if the bending area undergoes severe plastic deformation, the V-groove microstructure in the sealing operation area can still maintain its original geometric accuracy, and there will be no problems such as the groove opening being widened, the groove bottom being torn, or overall warping deformation, so as to facilitate subsequent mechanical interlocking with the adhesive.

[0060] After completing the microstructure processing and deburring of the substrate, proceed to step S2.

[0061] S2. The metal terminal substrate with the V-groove microstructure is subjected to overall electroplating to form an anti-corrosion coating that continuously covers the inner wall, bottom and edge of the V-groove microstructure.

[0062] The overall electroplating process utilizes the principle of electrolysis to reduce corrosion-resistant metal ions such as nickel, silver, or gold under the influence of an electric field, and then uniformly deposit them on the surface of the metal terminal, which serves as the cathode. Since the substrate has already completed its microstructure formation at this point, the electroplating solution can fully contact and wet the complex surface of the V-shaped groove, thereby constructing a dense metal protective layer in terms of microstructure.

[0063] The process of stamping before electroplating differs fundamentally from the traditional process of electroplating before stamping. Traditional processes often involve directly stamping pre-plated strip, where intense plastic deformation causes brittle fracture of the original plating at the cut surface and the bottom of the V-groove, exposing the easily oxidized copper substrate underneath. This embodiment, by adjusting the process sequence, ensures continuous plating formation on the surface of the formed microstructure, completely eliminating exposed copper defects.

[0064] The continuous anti-corrosion coating covering the inner wall and bottom of the microstructure plays a crucial physical barrier role, cutting off the contact path between the external environmental medium and the copper substrate. At the chemical level, this coating prevents the formation of porous oxides (such as copper oxide) on the substrate surface, avoiding the delamination failure of the sealant at the interface due to substrate corrosion. Particularly for the groove edges, where curvature is typically high and residual stress exists, the complete coating coverage eliminates potential corrosion initiation points, ensuring the interfacial bonding strength of the sealing structure during long-term use.

[0065] S3. Assemble the processed metal terminal substrate into the insulating body, and position the sealing operation area within the injection cavity defined by the insulating body.

[0066] The assembly of metal terminals and the insulating body typically employs insert injection molding or mechanical assembly processes to achieve a secure connection. The insulating body is made of high-performance engineering plastics such as PBT and PA66, providing electrical isolation while constructing the physical support framework of the connector. The injection cavity is a closed or semi-closed space formed by the inner wall of the insulating body and the outer surface of the metal terminal.

[0067] Precise positioning of the sealing area is crucial in this process. It is essential to ensure that the area with the V-groove microstructure falls completely within the geometry of the injection cavity, exposing the microstructure surface entirely to the cavity interior. Positioning deviations, such as the microstructure area being obscured by the injection molding material of the insulating body, or the microstructure being exposed outside the cavity, will prevent the sealant from contacting the V-groove or allow it to adhere only to the smooth substrate surface. This will prevent the formation of the desired mechanical anchoring effect, ultimately leading to a loss of airtightness.

[0068] S4. Perform plasma cleaning on the surface of the metal terminal substrate and the V-groove microstructure located in the injection cavity to remove organic contaminants and increase surface energy.

[0069] In step S4, an atmospheric plasma cleaning process is used, and the dyne value of the metal terminal substrate and the surface of the V-groove microstructure after the atmospheric plasma cleaning process is not less than 50 mN / m.

[0070] In S4, an atmospheric plasma cleaning process is used, and the dyne value of the metal terminal substrate and the surface of the V-groove microstructure after atmospheric plasma cleaning is not less than 50mN / m.

[0071] Atmospheric plasma cleaning technology utilizes high-voltage discharge to generate a low-temperature plasma jet containing high-energy electrons, ions, and free radicals. In the preceding stages such as stamping, electroplating, transportation, and assembly, the surface of metal terminals inevitably adsorbs organic hydrocarbons, grease, or mold release agent residues. These contaminants form a "weak boundary layer" at the microscopic interface, physically isolating the adhesive from direct contact with the substrate and severely hindering bonding performance.

[0072] Plasma cleaning works through a dual mechanism: at the physical level, high-energy particle beams bombard the surface, breaking down and vaporizing organic contaminant molecules; at the chemical level, active particles in the plasma react with the metal coating surface, introducing polar functional groups such as hydroxyl and carboxyl groups, thereby significantly activating the surface. Compared to vacuum plasma cleaning, atmospheric plasma technology eliminates the need for expensive vacuum chambers, allowing for seamless integration into automated production lines for continuous online production. It is particularly suitable for localized, targeted treatment of specific areas within the confined space of a dispensing mold cavity.

[0073] The dyne value is a physical quantity characterizing the wetting ability of a solid surface and is negatively correlated with the contact angle. Setting the treated surface energy threshold to no less than 50 mN / m is primarily based on fluid dynamics considerations. High-viscosity sealants typically have significant flow resistance. Only when the solid surface energy is significantly higher than the liquid surface tension can sufficient capillary driving force be generated to allow the adhesive to overcome viscous resistance and achieve spontaneous wetting within the fine V-groove structure, ensuring that the adhesive can actively penetrate deep into the microstructure.

[0074] The subsequent glue injection operation is carried out. The specific implementation of step S5 and its sub-steps S51-S53 is as follows.

[0075] S5. Under negative pressure, the sealant is injected into the injection cavity, and the pressure difference drives the sealant to fill the internal space of the V-groove microstructure.

[0076] Negative pressure environments are typically created by placing the injection mold inside a vacuum chamber or by directly evacuating the sealed cavity, aiming to establish a rarefied gas environment far below standard atmospheric pressure. If injection is performed at normal pressure, high-viscosity sealant, due to surface tension, easily forms liquid bridges at the narrow opening of the V-groove, preventing air from escaping from the bottom and creating high-pressure air pockets that hinder the sealant's penetration. By utilizing pressure difference—the significant pressure gradient between the external injection pump pressure and the vacuum level within the cavity—the viscous and capillary resistance of the sealant within the microchannels is overcome. Only when the sealant completely occupies the geometric volume of the V-groove can an effective barbed effect be formed after curing, transforming the bonding interface from a fragile two-dimensional planar bond to a high-strength three-dimensional volume anchoring.

[0077] Specifically, S5 includes the following sub-steps S51-S53.

[0078] S51. Reduce the absolute pressure in the injection cavity to less than 1000 Pa, and inject the sealant until the liquid surface covers the main area of ​​the V-shaped groove microstructure, but does not completely wet the edge of the groove.

[0079] Setting the absolute pressure threshold to less than 1000 Pa is to ensure that the partial pressure of residual air in the cavity is extremely low. According to the ideal gas law, even if trace amounts of gas remain in the dead corners of the microstructure, during the subsequent restoration to normal pressure, the volume of these bubbles will be compressed to less than one percent of their original volume, thus becoming negligible on a macroscopic scale.

[0080] S52. During the injection process, a periodic pulse with a frequency of f and an amplitude of ΔP is applied to the injection pressure, wherein the amplitude ΔP is set to 5% to 15% of the current injection pressure; the periodic pulse is used to drive the sealant to reciprocate along the slope direction on the climbing slope, thereby discharging air bubbles located at the bottom of the groove along the climbing slope.

[0081] High-viscosity adhesives exhibit significant "contact hysteresis" when flowing on microstructured surfaces. Static friction at the solid-liquid interface often causes the adhesive flow to stagnate, making it difficult to spontaneously fill all microscopic gaps even in a vacuum environment. A pressure pulse with frequency f introduces oscillatory energy, disrupting the static equilibrium of the adhesive's surface tension and causing microscopic forward and backward motion along the gas-liquid-solid three-phase contact line, thus overcoming the contact hysteresis. An amplitude ΔP set between 5% and 15% provides sufficient driving force to induce liquid surface displacement while maintaining laminar flow, preventing excessive amplitude from causing turbulence and entraining new air bubbles. This oscillatory force, in conjunction with the ramp formed in S132, creates a ratchet-like unidirectional conveying mechanism, gradually pushing air bubbles from the bottom of the tank to the liquid surface for discharge.

[0082] S53. After the glue injection is completed, a graded re-pressure operation is performed; after restoring the pressure of the glue injection cavity to normal pressure, positive pressure is applied and maintained for a predetermined time t; the positive pressure is used to drive the sealant to bypass the solid metal strip formed by the interlacing of the upper surface V-groove microstructure and the lower surface V-groove microstructure, and fill the fluid shadow area located on the back of the interlaced structure, wherein the fluid shadow area is the area located on the side of the solid metal strip opposite to the flow direction of the sealant.

[0083] The wavy solid metal strip formed in S121 acts as an obstacle in the fluid path, blocking the straight flow of the adhesive and easily creating low-pressure cavities on its leeward side that are difficult to fill, i.e., fluid shadow zones. Since the sealant is a non-Newtonian fluid with shear-thinning or creep properties, simply restoring normal pressure is insufficient to fill these complex areas. The staged repressurization operation applies continuous positive pressure and maintains it for time t, keeping a constant shear stress. This forces the high-viscosity fluid to bypass the obstacle through slow creep flow, completely displacing the remaining space within the shadow zones.

[0084] Finally, step S6 and its sub-steps S61-S63 are executed to complete the curing and shaping of the sealing structure.

[0085] S6. The sealant located in the injection cavity is subjected to multi-stage heating and curing to form a mechanically interlocked sealing structure.

[0086] Multi-stage temperature-curing process aims to avoid the thermodynamic defects of traditional single-stage rapid curing. Single-stage curing often triggers violent cross-linking reactions, resulting in excessively high exothermic peaks, causing bubbles to form inside the colloid due to boiling or skin formation on the surface before the interior. By controlling the cross-linking kinetics of polymer chains through step-by-step temperature increase, the morphological changes of the colloid near the gel point are made more gradual, ensuring uniform curing.

[0087] While the volume shrinkage that accompanies the transition of adhesive from liquid to solid often leads to peeling at smooth interfaces, this method utilizes a V-groove microstructure to achieve mechanical interlocking. The cured adhesive embeds itself like a wedge within the V-groove, creating a physical geometric locking effect. This three-dimensional volume anchoring no longer relies solely on chemical bonding forces, thus exhibiting significant mechanical stability in addressing the mismatch in thermal expansion coefficients caused by thermal shock and in resisting external mechanical vibration and shear forces.

[0088] Optionally, S6 includes the following sub-steps S61-S63.

[0089] S61. While maintaining the applied positive pressure, the injection cavity is heated to a first temperature T1 and maintained for a first predetermined time to allow the sealant to undergo a preliminary crosslinking reaction; the positive pressure is used to suppress the sealant from flowing out of the fluid shadow area to the back of the solid metal strip.

[0090] Thermosetting adhesives follow specific viscosity-temperature rheological properties. In the initial stage of heating, the viscosity of the adhesive decreases significantly before increasing as the cross-linking reaction proceeds. At this point, without external force, the adhesive in its low-viscosity state is easily affected by gravity or capillary forces, flowing out from the filled micropores (such as the fluid shadow area). Applying positive pressure continuously before reaching the gel point can counteract the flowability caused by the viscosity reduction, physically locking the densely filled state obtained in S53 until the adhesive loses its flowability.

[0091] S62. Remove the positive pressure, raise the temperature of the injection cavity to a second temperature T2 and maintain it for a second predetermined time; utilize the molecular chain relaxation effect to reduce the interfacial stress between the sealant and the solid metal strip and the climbing slope, and prevent the mechanical interlocking sealing structure from peeling off.

[0092] When the volume shrinkage of polymer materials during crosslinking is geometrically constrained by rigid microstructures such as the wavy solid metal bands formed in S121, it generates huge tangential tensile stress at the interface. By maintaining a constant temperature at the intermediate temperature T2, the local movement of polymer chain segments in the rubber state dissipates the internal stress. This stress relaxation mechanism effectively prevents excessive shrinkage force from causing the colloid to peel off from the climbing slope or the bottom of the trough.

[0093] S63. Raise the temperature of the injection cavity to a third temperature T3 and maintain it for a third predetermined time to allow the sealant to fully cure and form the mechanical interlocking sealing structure.

[0094] The final high-temperature T3 curing stage is used to ensure that the colloid reaches the highest crosslinking density, so that the material properties reach the designed glass transition temperature Tg and final mechanical strength. After curing, there is no cavitation residue between the sealed structure and the V-groove microstructure, achieving a highly airtight connection.

[0095] This application also discloses a high-airtightness connector terminal assembly, which mainly consists of a metal terminal 2, an insulating body 1, and a cured sealant 3. The metal terminal 2 is fixed to the insulating body 1 by insert injection molding or mechanical assembly, and the sealant 3 fills the cavity space defined by the insulating body 1 and the metal terminal 2.

[0096] The metal terminal 2 includes a substrate body, a sealing operation area located in the middle of the substrate body, and a stress buffer zone and a pre-set bending deformation area connecting the sealing operation area. The substrate body is made of a high-conductivity copper alloy such as brass or phosphor bronze, and its surface is covered with an anti-corrosion coating. This coating continuously covers the inner wall, bottom, and edge of the V-groove microstructure 4 at the microscopic level, and the edge of the groove has no flash exceeding 0.01 mm in height. The V-groove microstructure 4 in the sealing operation area is not a simple surface mark, but a deep groove structure distributed in an array. The V-grooves on the upper surface and the lower surface are staggered axially, forming a continuous, wavy solid metal strip between the upper and lower grooves. This solid metal strip retains the geometric neutral layer of the substrate, maintaining the axial tensile strength of the terminal while ensuring the depth of the microstructure. In addition, each V-groove microstructure 4 has a ramp with an elevation angle of less than 30 degrees at its end to guide air bubbles out during the glue injection process.

[0097] The insulating body 1 is made of high-temperature resistant engineering plastics such as PBT or PA66. Its structure includes a body frame and a dam extending inward from the inner wall of the body frame. This dam cooperates with the sealing working area of ​​the metal terminal 2 to jointly enclose a closed or semi-closed injection cavity. The insulating body 1 and the metal terminal 2 are mechanically fixed by interference fit or plastic encapsulation, and the geometry of the injection cavity is designed to completely encompass the sealing working area, ensuring that all V-groove microstructures 4 are within the injection range of the cavity.

[0098] The sealant 3, a thermosetting polymer cured through multiple stages, fills the injection cavity. Microstructurally, the sealant 3 not only covers the surface of the metal terminal 2 but also completely fills the internal space of the V-groove microstructure 4, including the arcuate area at the bottom of the V-groove microstructure and the fluid shadow area on the back of the solid metal strip. The cured adhesive forms a solid mechanical interlocking structure with the metal terminal 2, free of cavitation residue, and the adhesive and metal surface have a high-bonding-energy chemical bonding interface due to plasma activation treatment. This dual effect of mechanical interlocking and chemical bonding ensures that the sealing interface will not peel off when the component is subjected to thermal shock or mechanical vibration, thus guaranteeing the long-term airtightness of the connector.

[0099] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0100] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A method for manufacturing a high-airtightness connector terminal that enhances adhesive adhesion, characterized in that, Includes the following steps: S1. Obtain a metal terminal substrate, and form an array of V-shaped groove microstructures in a predefined sealing working area on the metal terminal substrate by cold stamping process, and mechanically bend the metal terminal substrate to form it. S2. The metal terminal substrate with the V-groove microstructure is subjected to overall electroplating to form an anti-corrosion coating that continuously covers the inner wall, bottom and edge of the V-groove microstructure. S3. Assemble the processed metal terminal substrate into the insulating body, and position the sealing operation area within the injection cavity defined by the insulating body; S4. Perform plasma cleaning on the surface of the metal terminal substrate and the V-groove microstructure located in the injection cavity to remove organic contaminants and increase surface energy; S5. Under negative pressure, the sealant is injected into the injection cavity, and the pressure difference drives the sealant to fill the internal space of the V-groove microstructure. S6. The sealant located in the injection cavity is subjected to multi-stage heating and curing to form a mechanically interlocked sealing structure.

2. The method for manufacturing high-airtight connector terminals with enhanced adhesive adhesion according to claim 1, characterized in that, S1 includes the following sub-steps: S11. On the metal terminal substrate, a sealing operation area for contact with the sealant adhesive and a preset bending deformation area are defined; between the sealing operation area and the preset bending deformation area, a stress buffer band with a length not less than twice the thickness of the metal terminal substrate is retained, and the stress buffer band maintains a flat surface and is not grooved. S12. Apply a stamping load to the upper and lower surfaces of the sealing operation area to form the V-groove microstructure; wherein, the projection position of the V-groove microstructure on the upper surface in the direction perpendicular to the surface of the metal terminal substrate and the projection position of the V-groove microstructure on the lower surface in the direction perpendicular to the surface of the metal terminal substrate are axially staggered to form an interleaved distribution structure. S13. During cold stamping, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, while the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle. S14. The groove edge of the V-groove microstructure after cold stamping is subjected to tumbling or electrochemical polishing to remove the flash height of the groove edge to below 0.01mm; S15. Under the protection of the stress buffer strip, a bending moment is applied to the preset bending deformation zone to bend the metal terminal substrate to a predetermined angle; the solid flat structure of the stress buffer strip is used to block the transmission of bending stress to the sealing operation area, preventing the V-groove microstructure from undergoing tensile deformation due to stress transmission.

3. The method for manufacturing high-airtight connector terminals with enhanced adhesive adhesion according to claim 2, characterized in that, S12 includes the following sub-steps: S121. Set the axial projection distance d between the V-groove microstructure on the upper surface and the V-groove microstructure on the lower surface, and limit the projection distance d to 0.5 to 0.8 times the original thickness T of the metal terminal substrate; S122. According to the set projection spacing d, a stamping load is applied to the sealing operation area to form a solid metal strip that extends continuously in a wave-like shape between the upper surface V-groove microstructure and the lower surface V-groove microstructure. The solid metal strip includes a geometrically neutral layer of the metal terminal substrate to provide a continuous shear stress transmission path.

4. The method for manufacturing high-airtight connector terminals with enhanced adhesive adhesion according to claim 3, characterized in that, S13 includes the following sub-steps: S131. When performing the cold stamping process, the die punch is controlled to extrude the bottom of the V-groove microstructure into an arc surface with a radius of curvature R, and the opening angle θ of the V-groove microstructure is controlled to be an obtuse angle to form a cross section suitable for fluid wetting. S132. At the end of the V-groove microstructure along the flow direction of the sealant adhesive, a gradually shallowing and disappearing climbing slope is formed by pressing the end shape of the die punch; the elevation angle β of the climbing slope is set to less than 30 degrees to guide the residual gas at the bottom of the groove to be discharged along the climbing slope, and to prevent the formation of air pockets at the end of the V-groove microstructure.

5. The method for manufacturing a high-airtight connector terminal with enhanced adhesive adhesion according to claim 4, characterized in that, In step S13, the specific geometric parameters of the V-groove microstructure satisfy the following conditions: The ratio of the radius of curvature R of the bottom arc surface of the V-groove microstructure to the groove depth h of the V-groove microstructure is in the range of 0.15≤R / h≤0.25; the range of the opening angle θ of the V-groove microstructure is 90°<θ<120°.

6. The method for manufacturing a high-airtight connector terminal with enhanced adhesive adhesion according to claim 1, characterized in that, In step S4, an atmospheric plasma cleaning process is used, and the dyne value of the metal terminal substrate and the surface of the V-groove microstructure after the atmospheric plasma cleaning process is not less than 50 mN / m.

7. The method for manufacturing a high-airtight connector terminal with enhanced adhesive adhesion according to claim 5, characterized in that, S5 includes the following sub-steps: S51. Reduce the absolute pressure in the injection cavity to less than 1000 Pa, and inject the sealant until the liquid surface covers the main area of ​​the V-shaped groove microstructure, but does not completely wet the edge of the groove. S52. During the injection process, a periodic pulse with frequency f and amplitude ΔP is applied to the injection pressure, wherein the amplitude ΔP is set to 5% to 15% of the current injection pressure; the periodic pulse is used to drive the sealant to reciprocate along the slope direction on the climbing slope, thereby discharging the air bubbles located at the bottom of the groove along the climbing slope. S53. After the glue injection is completed, a graded re-pressure operation is performed; after restoring the pressure of the glue injection cavity to normal pressure, positive pressure is applied and maintained for a predetermined time t; the positive pressure is used to drive the sealant to bypass the solid metal strip formed by the interlacing of the upper surface V-groove microstructure and the lower surface V-groove microstructure, and fill the fluid shadow area located on the back of the interlaced structure, wherein the fluid shadow area is the area located on the side of the solid metal strip opposite to the flow direction of the sealant.

8. The method for manufacturing a high-airtight connector terminal with enhanced adhesive adhesion according to claim 7, characterized in that, S6 includes the following sub-steps: S61. While maintaining the applied positive pressure, the injection cavity is heated to a first temperature T1 and maintained for a first predetermined time to allow the sealant to undergo a preliminary crosslinking reaction; the positive pressure is used to suppress the sealant from flowing out of the fluid shadow area to the back of the solid metal strip; S62. Remove the positive pressure, raise the temperature of the injection cavity to a second temperature T2 and maintain it for a second predetermined time; use the molecular chain relaxation effect to reduce the interfacial stress between the sealant and the solid metal strip and the climbing slope to prevent the mechanical interlocking sealing structure from peeling off. S63. Raise the temperature of the injection cavity to a third temperature T3 and maintain it for a third predetermined time to allow the sealant to fully cure and form the mechanical interlocking sealing structure.

9. A high-airtightness connector terminal assembly, characterized in that, include: Metal terminal (2), the metal terminal (2) has a sealed working area, the surface of the sealed working area is provided with an array of V-shaped groove microstructures (4), and the inner wall, bottom and edge of the V-shaped groove microstructures (4) are continuously covered with an anti-corrosion coating. An insulating body (1) is attached to the outside of the metal terminal (2) and defines a filling cavity surrounding the sealing operation area; The sealant (3) fills the injection cavity and penetrates into the V-groove microstructure (4) of the metal terminal (2); The sealing adhesive (3) is cured in the V-groove microstructure (4) to form a solid mechanical interlocking sealing structure, and there is no cavitation residue between the mechanical interlocking sealing structure and the V-groove microstructure (4).

Images