Integrated bidirectional pogo pin and applications thereof

Abstract

This invention discloses an integrated bidirectional spring needle, its manufacturing method, and its application. The spring needle is integrally wound from a single high-strength alloy wire, completely eliminating the need for an external needle tube. It comprises a helical spring body and two contact heads extending perpendicularly along its axis. Key design features include: the effective number of coils of the helical spring is limited to 8-18 turns, and the wire diameter (d) is limited to 0.05 mm to 0.12 mm; the outer diameter (D) of the helical spring in its free state is 0.20 mm to 0.60 mm; the alloy wire is an age-hardened high-strength copper alloy, and the overall Vickers hardness (HV) of the resulting spring needle is not less than 380. This invention, through integrated molding and parameter optimization, solves the problem of balancing probe stroke and stiffness in needle-less probes, offering advantages such as simple structure, complete signal transmission, and long lifespan. It is suitable for precision testing of double-sided multilayer HD high-frequency PCBs, chip packaging, and high-performance substrates.

Description

Technical Field

[0001] This invention relates to the field of microelectronics technology, and in particular to an integrated bidirectional spring pin and its applications. Background Technology

[0002] In the field of microelectronics testing, spring probes are the core component connecting test equipment and the device under test (DUT). Traditional bidirectional (dual-headed) probes typically employ an assembled structure of "sleeve-spring-two independent contact heads".

[0003] For example, in complex interconnect testing of high-performance packaged board (PAB) boards, the wiring density of PAB boards is extremely high and the structure is complex. They typically employ multi-layer structures (including a combination of rigid and flexible layers) to achieve high-bandwidth signal transmission and power integrity. Traditional testing methods face significant challenges when performing electrical performance testing or aging tests on these multi-contact, multi-layered circuit boards. To connect the testing equipment to the test points distributed across multiple layers on the PAB board, dedicated multi-layer test adapter boards are usually required. These adapter boards themselves are complex and costly. Interlayer electrical connections are typically achieved by laser-drilling blind vias and filling them with conductive materials (such as conductive adhesive or copper pillars). This process is difficult, reliability is limited by the quality of the via filling, and once fabricated, it is difficult to modify.

[0004] For example, in semiconductor chip wafer testing (CP Test) and final packaging testing (FT Test), with the increase in the number of chip pins, the reduction in pitch (fine-pitch), and the development of 3D packaging technology, the complexity and accuracy requirements of testing are increasing day by day.

[0005] Wafer testing: For complex chips with pads distributed at the chip edge or requiring simultaneous testing of power / ground / signal networks, traditional vertical probe cards may require multi-level spatial routing, resulting in a complex structure. When testing ultra-thin wafers or wafers with micro-bumps, the probe travel and contact stability requirements are extremely high.

[0006] Package testing: For ball grid array (BGA) and chip-scale package (CSP), testing requires contacting the solder balls from the bottom of the package. For packages with side pads or fan-out, contact needs to be made from the side. Traditional single-head probes are difficult to achieve efficient and stable multi-faceted contact.

[0007] To address these issues, attempts have been made to simplify the structure, but existing technologies often sacrifice mechanical strength or stability. For example, some designs attempt to eliminate the external needle tube, but when using a spring directly as the conductor and load-bearing component, improper design of spring coils, dimensions, and other parameters presents a dilemma: insufficient stroke leads to ineffective compensation for test alignment errors; insufficient radial stiffness causes the probe to bend and shift under lateral forces, resulting in loss of accuracy; and insufficient overall rigidity can cause permanent deformation. Ensuring that the probe possesses a large stroke, high radial stiffness, high overall rigidity, and stable spatial orientation without relying on external needle tube constraints remains a technical challenge that existing technologies have failed to systematically solve. Summary of the Invention

[0008] The main objective of this invention is to overcome the shortcomings of existing technologies and provide an integrated bidirectional spring pin with optimized parameters and superior performance. This invention achieves long stroke, high bending stiffness, excellent deformation resistance, and flexible spatial wiring capabilities by combining a set of synergistically optimized structural parameters with specific high-hardness material processing.

[0009] To achieve the above objectives, this invention proposes an integrated bidirectional spring needle, the core of which lies in abandoning the external needle tube that traditional probes rely on for support and guidance, and innovatively adopting the manufacturing concept of "one wire, one-piece molding". Specifically, the spring needle is formed from a single continuous high-strength alloy wire through precision winding and subsequent processing, creating a fully functional integral structure in one go, fundamentally eliminating all mechanical assembly interfaces.

[0010] The specific structure of this spring pin is as follows: A helical spring that serves as both the main body and the conductive circuit; A first contact head is formed by extending one end of the alloy wire, extending axially along the axis of the helical spring, and extending at a 90-degree angle to the cross-section of the helical spring. A second contact head, formed by extending from the other end of the alloy wire, extends axially along the axis of the helical spring; and its axial direction extends at a 90-degree angle to the cross-section of the helical spring. Both the first contact head and the second contact head have contact tips at their ends; The effective number of coils of the helical spring is 8 to 18.

[0011] Furthermore, the spring has the following dimensional parameter system: a) The diameter (d) of the alloy wire constituting the spring needle is 0.05 mm to 0.12 mm; b) The outer diameter (D) of the helical spring in its free state is 0.20 mm to 0.60 mm; c) The alloy wire is a high-strength copper alloy that has been hardened by age, and the overall Vickers hardness (HV) of the spring needle is not less than 380.

[0012] Furthermore, the dimensional parameter system is specifically the first optimization scheme: The wire diameter (d) is 0.10 mm to 0.12 mm; The outer diameter (D) is 0.50 mm to 0.60 mm; The height (H) of the coil spring in its free state is 3.00 mm to 3.50 mm; The effective number of coils of the helical spring is 15 to 18. The maximum elastic travel (S) of a single contact head is 0.85 mm to 0.90 mm.

[0013] Furthermore, the dimensional parameter system is specifically the second optimization scheme: The wire diameter (d) is 0.05 mm to 0.09 mm; The outer diameter (D) is 0.20 mm to 0.35 mm; The effective number of coils of the helical spring is 8 to 14. The height (H) of the coil spring in its free state is 1.5 mm to 2.5 mm.

[0014] Furthermore, the helical spring is a variable pitch spring, wherein the pitch of its middle section is smaller than the pitch of its two ends.

[0015] Another aspect of the present invention provides a method for manufacturing an integral bidirectional spring pin, comprising the steps of: S1: Select high-strength alloy wire; S2: Integrated winding: On a spring forming machine, wire is wound to form a helical spring body and first and second contact head blanks extending at a specific angle, wherein the effective number of turns of the helical spring is controlled to be between 8 and 18 turns; S3: Contact head machining and heat treatment: The end of the contact head blank is machined to form a contact tip; the workpiece is subjected to solution treatment and age hardening treatment to obtain the required mechanical properties; S4: Surface treatment: After cleaning, a wear-resistant conductive metal layer is electroplated in at least the contact tip area.

[0016] Furthermore, when manufacturing the spring needle according to claim 3, the winding parameters in step S2 satisfy: wire diameter of 0.10-0.12 mm, outer diameter of 0.50-0.60 mm, and free height of 3.00-3.50 mm; The aging hardening treatment in step S3 makes the hardness of the finished product reach HV 450 or higher.

[0017] The third aspect of this invention provides the application of an integrated bidirectional spring pin in electrical performance testing. The bidirectional spring pin is mounted in a test fixture, such that its first contact head and second contact head respectively contact two test points located in its axial direction, for the purpose of achieving double-sided testing or vertical interconnection.

[0018] Furthermore, the test is a multilayer interconnect test of a high-performance packaging substrate, a semiconductor wafer test, or a chip packaging test.

[0019] Furthermore, when using the spring pin described in claim 3, it is suitable for test scenarios where there is coplanarity deviation or long stroke compensation is required; when using the spring pin described in claim 4, it is suitable for ultra-high density test scenarios where the pad spacing is less than 100 micrometers. The beneficial effects of this invention are: 1. Revolutionary simplification of structure and leap in reliability: The external needle tube is completely eliminated, and the entire function is integrated into one piece. This eliminates the unstable contact resistance, impedance discontinuity and potential failure points caused by assembly, and significantly improves the integrity of electrical signals and long-term reliability.

[0020] 2. Optimized mechanical properties to resolve core contradictions: By strictly limiting the effective number of coils of the helical spring to 8-18 turns and matching it with optimized wire diameter, outer diameter, and height, the technical contradiction of "long stroke" and "high radial stiffness" in needle-free probe design has been successfully resolved. The long stroke ensures excellent tolerance compensation capabilities, while the compact spring structure provides superior resistance to bending and displacement.

[0021] 3. Materials and processes ensure long-term stability: High-strength alloys and specific age-hardening processes are used to ensure that the product has high hardness and can resist plastic deformation under repeated compression and lateral force during long strokes, thereby greatly extending the service life and ensuring the consistency of test results.

[0022] 4. Wide range of applications and suitability for high-end testing needs: Its coaxial bidirectional contact, large stroke and high reliability make it perfectly suited for a range of high-end and precision electronic testing applications, from complex PCB interconnect testing to advanced semiconductor chip testing and packaging testing, and it has significant industrial value. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0024] Figure 1 A schematic diagram of an integrated bidirectional spring pin structure provided in an embodiment of the present invention; Figure 2 A flowchart illustrating the manufacturing method of an integrated bidirectional spring pin provided in an embodiment of the present invention; Figure 3 This is a schematic diagram provided for Embodiment 2 of the present invention; The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0027] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0028] The present invention provides an integrated bidirectional spring pin, as shown in the reference. Figure 1 A spring needle is a spring needle that is integrally wound from a single high-strength alloy wire, has no external needle tube, and has two contact heads extending along the spring axis (perpendicular to the spring cross-section).

[0029] Traditional bidirectional probes typically consist of a probe tube, an internal spring, and two independent contact heads, assembled through methods such as crimping and riveting. This structure presents multiple electrical and mechanical contact interfaces, leading to signal reflection and loss during high-frequency testing. Over long-term use, these interfaces are prone to wear and oxidation, resulting in increased contact resistance and instability. This invention utilizes a "one-piece molding" technique, directly forming the spring body and two contact heads from a single continuous metal wire, eliminating all internal mechanical connections. This means the current path is continuous and integrated, ensuring extremely low and stable contact resistance and excellent signal integrity (especially in GHz-level high-frequency testing). Simultaneously, the absence of an external probe tube significantly simplifies the number of parts, reduces manufacturing costs and assembly errors, and improves product consistency.

[0030] The technical concept of this invention is not limited to the specific dimensional parameters disclosed in the following embodiments. By scaling proportionally or following the same design principles (i.e., adjusting parameters such as wire diameter, outer diameter, and height in a coordinated manner while maintaining the balance between effective number of turns and stroke and stiffness), the needle-free integrated structure of this invention can be applied to applications requiring miniaturization (e.g., wire diameter down to 0.05 mm, outer diameter down to 0.20 mm) or larger sizes. These variations based on the same inventive concept should all fall within the protection scope of this invention.

[0031] In this embodiment, the effective number of coils of the helical spring is 15 to 18. The effective number of coils (n) is one of the most critical parameters determining the mechanical properties (stiffness K, stroke S) of the helical spring. For probes without external needle tube constraints, the spring itself is both an elastic element and the main support structure. The coil number design must achieve a delicate balance between "stroke" and "stiffness".

[0032] 1. Stroke Considerations: The compression stroke (S) of a spring is related to the effective number of turns (n), wire diameter (d), mean diameter (Dm), and the shear modulus (G) of the material. According to the spring mechanics formula, under the same load, the stroke S is approximately proportional to n. To ensure that the probe can effectively compensate for the coplanarity error of the PCB board, chip, or fixture during testing (typically requiring a compensation capability >0.5mm), a sufficient number of turns is needed to provide a long stroke.

[0033] 2. Stiffness and Stability Considerations: The radial (bending) stiffness of a spring differs from its axial stiffness, but both are affected by the number of coils. More coils increase the spring's susceptibility to instability and bending under axial force (similar to a slender rod under pressure). For needleless probes, excessive radial bending can cause the contact head to deviate from the target test pad, resulting in poor contact or even a short circuit. Fewer than 15 coils, while increasing radial stiffness, severely sacrifices travel, failing to meet the tolerance compensation requirements of actual testing. More than 18 coils increase travel, but the spring becomes overly "flexible," with a sharp decrease in radial stiffness. This makes it prone to bending and wobbling under lateral forces or slight installation errors, severely impacting test accuracy and reliability. Therefore, 15-18 coils is the core optimization range of this invention, determined after extensive simulation and physical testing. This range ensures sufficient travel (reaching 0.85-0.90 mm with subsequent dimensional parameters) while maintaining high radial stability against common lateral forces encountered in testing.

[0034] To verify the superiority of this lap range, we conducted a comparative experiment, and the test results are shown in the table below: Valid number of loops (n) Stroke test (40gf contact force) Radial stiffness test (apply a 0.5N lateral force to the second contact head of the spring needle and measure the tip offset). Fatigue test (elasticity decay rate after 100,000 compression cycles) This invention 16.5 0.88mm 25μm <8% Control group A 12 0.52mm 18μm A<5% Control group B 22 1.05mm 95μm 15% Data shows that n=16.5 revolutions (within the range of 15-18 revolutions) achieves the best overall performance in terms of stroke, anti-offset capability, and durability, perfectly resolving the triangular contradiction of "stroke-stiffness-life".

[0035] In this embodiment, the contact head extends along the axial direction (at a 90-degree angle to the cross-section), and the two contact heads extend from both ends of the spring along the same axis, resulting in a symmetrical structure and uniform force distribution. This design allows the probe, when vertically mounted on the test fixture, to act as an ideal "elastic conductor post," with its upper and lower tips able to reliably contact test points located simultaneously or separately on its upper and lower planes along its axis. This is the most direct and reliable structural form for achieving double-sided testing and vertical interconnection.

[0036] Furthermore, the helical spring features a "variable pitch" design, meaning the pitch in the middle section is smaller than the pitch at both ends. During spring compression, stress distribution is not entirely uniform. When the spring is compressed, the deformation and stress of the end coils are typically more concentrated. The variable pitch design (also known as a "tower-shaped" or "drum-shaped" spring) has the following advantages: 1. Optimized stress distribution: In the initial stage of compression, the end coils with larger pitch begin to contact and deform first. As compression continues, the middle coils gradually participate in the operation. This design allows for a more uniform distribution of stress along the entire length of the spring, avoiding excessive stress concentration in localized areas, thereby improving the fatigue life of the spring.

[0037] 2. Improved mechanical properties: The force-stroke curve of a variable pitch spring may be closer to linear or have more ideal progressive characteristics, which helps to provide more stable contact pressure.

[0038] 3. Enhanced stability: The denser coils in the middle can act as a "waistband," which helps to suppress the radial expansion or bending instability that may occur when the spring is compressed, further enhancing the radial stiffness emphasized in claims 1 and 2.

[0039] Furthermore, the high-strength alloy wire is a beryllium copper alloy, palladium copper alloy, or titanium copper alloy that has undergone peak aging treatment; the overall Vickers hardness (HV) of the made spring needle is not less than 450.

[0040] Hardness is an indicator of a material's resistance to plastic deformation. For the needleless probe described in this invention, its spring body and the root of the contact head need to withstand: 1. Repeated large strain cycles: To achieve a long stroke of 0.85-0.90mm, the spring material is subjected to a large strain amplitude. If the material hardness (strength) is insufficient, "permanent deformation" (i.e., "collapse") will occur after repeated compression, resulting in decreased elasticity, shortened stroke, and eventual failure.

[0041] 2. Effect of lateral force: During testing, the contact head may be subjected to lateral force when the device under test is uneven or misaligned. High hardness ensures that the root of the contact head will not undergo plastic bending due to lateral force.

[0042] 3. Abrasion resistance of contact tips: Although the surface coating is mainly responsible for abrasion resistance, the high hardness of the substrate provides a strong support for the coating, preventing the substrate from deforming under pressure, which could lead to cracking or peeling of the coating.

[0043] Peak aging treatment is a key process for achieving high hardness. Taking the most commonly used beryllium copper C17200 as an example, after solution treatment and rapid cooling (quenching), a supersaturated solid solution is obtained, at which point the material is relatively soft. Subsequently, an aging treatment is performed at approximately 320°C, causing tiny beryllium phase particles to disperse and precipitate from the matrix. These particles effectively hinder dislocation movement, thereby greatly improving the material's strength and hardness (up to HV 400 or higher), while maintaining good electrical conductivity. The requirement of HV ≥ 450 ensures that the probe maintains its shape and performance stability under harsh testing conditions (such as high-temperature aging tests).

[0044] Furthermore, the integrated bidirectional spring pin has the following synergistically optimized dimensional parameters: The diameter (d) of the alloy wire constituting the spring needle is 0.10 mm to 0.12 mm; b) The outer diameter (D) of the helical spring in its free state is 0.50 mm to 0.60 mm; c) The height (H) of the helical spring in its free state is 3.00 mm to 3.50 mm; d) The length (L1) of the first contact head from the end face of the helical spring to its contact tip is 1.10 mm to 1.20 mm; e) The length (L2) of the second contact head from the other end face of the helical spring to its contact tip is 1.10 mm to 1.20 mm.

[0045] These parameters (d, D, H, L, S) are not isolated; they together constitute a performance-optimized system.

[0046] 1. Wire diameter (d: 0.10-0.12mm): This determines the cross-sectional area of ​​the material, affecting current carrying capacity, spring stiffness, and manufacturing cost. Too thin and it lacks strength, making it prone to breakage; too thick and it becomes bulky, unsuitable for high-density test arrays. This range is the preferred range for precision probe applications.

[0047] 2. Spring outer diameter (D: 0.50-0.60mm) and free height (H: 3.00-3.50mm): These two dimensions, along with the effective number of turns (n: 15-18), determine the spring's spatial volume and basic shape. H / n ≈ single-turn pitch. In this invention, a height of 3.0-3.5mm provides reasonable winding space for 15-18 turns, resulting in a single-turn pitch of approximately 0.17mm-0.23mm. This is a reasonable range that ensures no interference between coils (at maximum compression) while maintaining structural stability. The outer diameter D and wire diameter d together determine the spring's "density," affecting its bending section modulus.

[0048] 3. Contact length (L1, L2: 1.10-1.20mm): This length needs to match the stroke S. When the spring is compressed to its maximum stroke S (0.85-0.90mm), a sufficient portion of the contact head must still protrude outside the spring body (at least 0.2-0.35mm) to ensure stable contact with the test point and prevent the tip from sinking into the spring, causing unstable contact. The 1.10-1.20mm length design provides this safety margin.

[0049] 4. Maximum elastic stroke (S: 0.85-0.90mm): This is the final performance result achieved through the combined effect of all structural parameters (d, D, H, n, material G value). This value is ensured through precise design and manufacturing processes. It is much larger than the stroke of many traditional micro probes (typically 0.2-0.5mm), giving this probe strong tolerance compensation capabilities and adaptability.

[0050] To demonstrate the practical benefits of the stroke parameters of this invention, we conducted a comparative test with two mainstream bidirectional probes of the same size (approximately φ0.6mm) on the market: Comparison objects: M company's assembled dual-head probe (claimed stroke 0.6mm), T company's simple tubeless probe (claimed stroke 0.7mm).

[0051] Test scenario: Simulate testing a PCB board with a warp of 0.15mm.

[0052] result: The probe of this invention (S=0.88mm): all contacts achieve stable contact, and the standard deviation of contact resistance is 3.2mΩ.

[0053] M Company probe: Multiple contacts in the edge-raised area have poor contact, with a contact failure rate of 18% and a standard deviation of contact resistance of 15.7mΩ.

[0054] Company T probes: Although all contacts are made, due to insufficient radial stiffness, some probes bend laterally at the warp points, resulting in uneven contact pressure and a standard deviation of 9.8mΩ for contact resistance.

[0055] Data demonstrates that the long stroke of 0.85-0.90 mm, combined with high radial stiffness, significantly improves the reliability and consistency in non-ideal planar test scenarios.

[0056] The manufacturing method of the aforementioned integrated bidirectional spring pin is as follows, please refer to... Figure 2 The steps include: S1: Select high-strength alloy wire; S2: Integrated Winding: On a spring forming machine, wire is wound to form the main body of a helical spring and first and second contact head blanks extending at a specific angle, wherein the effective number of turns of the helical spring is controlled between 15 and 18 turns; using a high-precision CNC spring machine, inputting the parameters d, D, H, L, etc., as specified in claim 5, and strictly controlling the number of turns and pitch (including the variable pitch of claim 3), is the first step in obtaining a product that conforms to the designed geometry. This is the physical basis for achieving the "integrated molding" structure and precise dimensions.

[0057] S3: Contact Head Machining and Heat Treatment: The end of the contact head blank is machined to form a contact tip; the workpiece undergoes solution treatment and age hardening treatment, wherein the age hardening treatment must achieve a finished product hardness of HV 450 or higher. "Solution treatment + age hardening" is an indispensable core step. Solution treatment ensures uniform dissolution of alloying elements, preparing for subsequent strengthening. Age hardening, especially for the material specified in claim 4, is the only way to obtain a high hardness of HV ≥ 450. The process parameters (e.g., aging temperature 310-330°C, time 2-3 hours) are the optimal window determined based on materials science principles and extensive experiments, aiming to maximize the precipitation strengthening effect, thereby ensuring the product possesses the high deformation resistance and long service life required by claim 4.

[0058] To verify the necessity of high hardness (HV≥450), we compared the product performance under different heat treatment processes: Experimental group (standard process): The above-mentioned 320°C / 180-minute peak aging process was used, and the finished product hardness was HV470.

[0059] Control group C (under-aged): aged only at 280°C for 60 minutes, finished product hardness HV 380.

[0060] Control group D (over-aged / non-aged): The material is in a solid solution state (soft state) with a hardness of HV 180.

[0061] Test results (after 50,000 cycles at a stroke of 0.8mm): 1. Permanent deformation (free height shortening): 0.03 mm in the experimental group, 0.12 mm in control group C, and 0.45 mm in control group D (which has failed). The deformation of control group C is 4 times that of the experimental group.

[0062] 2. Condition of the contact head root: Microscopic examination showed that no visible bending or deformation was observed in experimental group 2; slight plastic bending was observed in part of the probe in control group C; and severe bending was observed in all probes in control group D.

[0063] 3. Elasticity attenuation rate: Experimental group 2 attenuated by 7%, control group C attenuated by 22%, and control group D attenuated by more than 60%.

[0064] Experimental data fully demonstrates that achieving a high hardness of HV≥450 is the key threshold for ensuring that the needle-free structure of this invention does not undergo plastic deformation and maintains stable performance during long-stroke, long-cycle operation. Below this hardness, probe life and reliability will decrease sharply.

[0065] S4: Surface treatment: After cleaning, a wear-resistant conductive metal layer is electroplated in at least the contact tip area.

[0066] In step S2, the winding parameters are: wire diameter is 0.10-0.12mm, outer diameter of helical spring is 0.50-0.60mm, free height is 3.00-3.50mm, and contact head blank length is 1.10-1.20mm. Example 1: Manufacturing a typical specification needleless integrated bidirectional spring needle 1. Material selection: C17200 beryllium copper alloy wire conforming to ASTM B197 standard is selected, with a wire diameter d = 0.11 mm.

[0067] 2. Integrated winding: Parameters are set on an imported precision CNC spring forming machine: Spring mean diameter (Dm): 0.50 mm (corresponding to outer diameter D≈0.61 mm) Free height (H): 3.30 mm Total laps: 18.5 laps, of which the number of valid laps (n) is set to 16.5 laps.

[0068] Pitch: Variable pitch design. 4 turns at each end with a pitch of 0.22mm; 8.5 turns in the middle with a pitch of 0.18mm.

[0069] Contact head reserved length: A 1.15mm long straight wire section is reserved at each end as the contact head blank.

[0070] The machine automatically completes the winding and 90-degree bending (so that the straight wire sections at both ends coincide with the spring axis), resulting in a one-piece blank.

[0071] 3. Processing and heat treatment: a. Use a precision grinding machine to grind the blanks at both ends into dome-shaped tips with a radius of curvature R = 0.03 mm; b. Place the blank in a vacuum heat treatment furnace for solution treatment: hold at 785°C for 15 minutes, then cool with nitrogen (quenching). c. Next, perform age hardening treatment: hold at 320°C for 180 minutes (3 hours), then cool in the furnace; d. After treatment, the hardness of the matrix is ​​measured and reaches HV 460-480, which meets the requirements of claim 4 (≥450).

[0072] 4. Surface treatment a. Perform ultrasonic cleaning on the heat-treated probe; b. First, electroless nickel plating is applied to a thickness of approximately 1.5 μm; c. Then, selective electroplating is used to electroplat a cobalt-gold alloy (hard gold) with a thickness of about 1.2 μm over a length of about 0.4 mm at both contact tips.

[0073] size Mechanical properties Electrical performance Durability Measured using an optical projector, the outer diameter D = 0.61 mm, the free height H = 3.28 mm, and the contact head length L = 1.13 mm. On a probe tester, one end was fixed while pressure was applied to the other. When the elastic force was measured to be 35 gf, the stroke S = 0.88 mm. Pressure was continued until the coil was fully tightened; the maximum stroke was 0.92 mm, confirming that the maximum elastic stroke S of a single head was 0.88 mm. Contact resistance <30mΩ After undergoing 100,000 compression cycles (0.8mm stroke), the elasticity decay was <10%, the stroke change was <0.02mm, and there was no permanent bending. Example 2: Application of integrated bidirectional spring pin in PAB plate testing (refer to...) Figure 3 ) The challenge in testing multilayer interconnects on PAB boards lies in how to contact the signals of each layer in a low-cost and flexible manner. The probes of this invention can serve as standard "vertical interconnect units." They are mounted in rows on a fixture, with one end connected to the testing machine and the other end contacting the test pads of each layer extending from the surface of the PAB board. Their integrated structure ensures consistent electrical performance for each channel; high rigidity ensures minimal damage when contacting board edges; and the long stroke compensates for board thickness and installation tolerances. This is far more economical and flexible than fabricating dedicated multilayer test boards.

[0074] For example, when testing circuit boards with a large number of test points, we need to make a multi-layer test board. The number of layers depends on the number of test points on the customer's product. For example, we can make a 5-layer rigid-flex test board, including a first substrate and a second substrate as the front and back of the substrate, as well as a calibration board, a first flexible board and a second flexible board. Holes are drilled through the middle of each layer (the outer ring is for connecting to the equipment), and then an integrated bidirectional spring pin is installed in the hole to conduct electricity and connect to the circuit board under test.

[0075] Example 3: Application of integrated bidirectional spring pins in chip test sockets 1000 spring pins manufactured in Example 1 above were implanted in a 20x50 array into a test socket for testing 0.4mm pitch BGA chips. The socket design is such that the first contact head (upper) of the spring pin contacts the PCB board inside the socket, and the second contact head (lower) is ready to contact the solder balls of the BGA chip.

[0076] Testing Procedure: The BGA chip is placed in the socket, and pressure is applied. Since the chip's coplanarity tolerance is approximately 0.08mm, the 0.88mm long stroke of the probe in this invention easily absorbs this error, ensuring that each solder ball receives stable and consistent pressure. Comparative advantages: Compared to sockets using traditional dual-point probes with needles, this solution yields superior signal integrity (eye diagram) and a more concentrated contact resistance distribution. After 50,000 consecutive chip insertion and removal tests, the socket performance showed no significant degradation, demonstrating the high reliability and long lifespan of the probes in this invention.

[0077] Example 4: Miniaturized variant example Based on the design principles of this invention, a miniaturized variant suitable for micro-pitch testing can also be manufactured. A palladium-copper alloy wire with a diameter d = 0.08 mm is selected, and a helical spring body with an outer diameter D = 0.30 mm, a free height H = 2.0 mm, and an effective number of turns n = 12 is wound, with a contact head length L = 0.8 mm. After similar heat treatment, a miniature spring needle with a single-head stroke S ≈ 0.45 mm can be obtained. This variant is suitable for wafer testing with a pitch less than 80 μm. The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. An integrated bidirectional spring needle, integrally wound and machined from a single continuous high-strength alloy wire, with no external needle tube structure, characterized in that... include: A helical spring that serves as both the main body and the conductive circuit; A first contact head is formed by extending one end of the alloy wire, extending axially along the axis of the helical spring, and extending at a 90-degree angle to the cross-section of the helical spring. A second contact head, formed by extending from the other end of the alloy wire, extends axially along the axis of the helical spring; and its axial direction extends at a 90-degree angle to the cross-section of the helical spring. Both the first contact head and the second contact head have contact tips at their ends; The effective number of coils of the helical spring is 8 to 18.

2. The integrated bidirectional spring pin as described in claim 1, characterized in that, It has the following dimensional parameter system: a) The diameter (d) of the alloy wire constituting the spring needle is 0.05 mm to 0.12 mm; b) The outer diameter (D) of the helical spring in its free state is 0.20 mm to 0.60 mm; c) The alloy wire is a high-strength copper alloy that has been hardened by age, and the overall Vickers hardness (HV) of the spring needle is not less than 380.

3. The integrated bidirectional spring pin as described in claim 2, characterized in that, The aforementioned size parameter system is specifically the first optimization scheme: The wire diameter (d) is 0.10 mm to 0.12 mm; The outer diameter (D) is 0.50 mm to 0.60 mm; The height (H) of the helical spring in its free state is 3.00 mm to 3.50 mm; The effective number of coils of the helical spring is 15 to 18. The maximum elastic travel (S) of a single contact head is 0.85 mm to 0.90 mm.

4. The integrated bidirectional spring pin as described in claim 2, characterized in that, The aforementioned size parameter system is specifically the second optimization scheme: The wire diameter (d) is 0.05 mm to 0.09 mm; The outer diameter (D) is 0.20 mm to 0.35 mm; The effective number of coils of the helical spring is 8 to 14. The height (H) of the coil spring in its free state is 1.5 mm to 2.5 mm.

5. The integral bidirectional spring pin as described in any one of claims 1 to 4, characterized in that, The helical spring is a variable pitch spring, where the pitch of the middle section is smaller than the pitch of the two ends.

6. A method for manufacturing an integral bidirectional spring pin as described in any one of claims 1-5, characterized in that, Including the following steps: S1: High-strength alloy wire is selected; S2: Integrated winding: On a spring forming machine, wire is wound to form a helical spring body and first and second contact head blanks extending at a specific angle, wherein the effective number of turns of the helical spring is controlled to be between 8 and 18 turns; S3: Contact head machining and heat treatment: The end of the contact head blank is machined to form a contact tip; the workpiece is subjected to solution treatment and age hardening treatment to obtain the required mechanical properties; S4: Surface treatment: After cleaning, a wear-resistant conductive metal layer is electroplated in at least the contact tip area.

7. The manufacturing method of the integrated bidirectional spring pin as described in claim 6, characterized in that, When manufacturing the spring needle according to claim 3, the winding parameters in step S2 satisfy: wire diameter of 0.10-0.12mm, outer diameter of 0.50-0.60mm, and free height of 3.00-3.50mm; The aging hardening treatment in step S3 makes the hardness of the finished product reach HV 450 or higher.

8. The application of the integrated bidirectional spring pin as described in any one of claims 1-5 in electrical performance testing, characterized in that, The bidirectional spring pin is installed in the test fixture, so that its first contact head and second contact head respectively contact two test points located in its axial direction, for the purpose of realizing double-sided testing or vertical interconnection.

9. The application of the integrated bidirectional spring pin as described in claim 8, characterized in that, The tests are multilayer interconnect tests of high-performance packaging substrates, semiconductor wafer tests, or chip packaging tests.

10. The application of the integrated bidirectional spring pin as described in claim 9, characterized in that, When using the spring pin as described in claim 3, it is suitable for test scenarios where there is coplanarity deviation or long stroke compensation is required; when using the spring pin as described in claim 4, it is suitable for ultra-high density test scenarios where the pad spacing is less than 100 micrometers.

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