Steel mesh opening process for improving welding yield

Abstract

The invention discloses a steel mesh opening process for improving the welding yield, and belongs to the technical field of steel mesh processes, the steel mesh opening process comprises a steel mesh opening structure adopting gradient micropore array design, and the opening structure is composed of an outer ring guide structure and an inner micropore array; preparing a nano coating on the surface of the steel mesh; opening parameters are automatically calculated and adjusted through a dynamic compensation algorithm according to the PCB bonding pad size, the device pin height and the mounting precision data which are collected in real time. According to the steel mesh opening process, the release rate of the soldering paste can be remarkably increased, welding defects are reduced, the welding yield is increased to 99.5% or above, and the steel mesh opening process is particularly suitable for the welding requirements of micro-pitch devices and high-reliability electronic products.

Description

Technical Field

[0001] This invention relates to the technical field of steel mesh manufacturing, and in particular to a steel mesh opening process for improving welding yield. Background Technology

[0002] The stencil process is a crucial step in surface mount technology (SMT). It involves using a stainless steel stencil of a specific thickness with openings that precisely correspond to the PCB pads. Under the action of a printer squeegee, an appropriate amount of solder paste with a precise shape is deposited onto the PCB pads in a quantitative and precise manner. This provides accurate solder deposition for subsequent component placement and reflow soldering. Its core objective is to ensure the final soldering yield by controlling the printing quality of the solder paste.

[0003] For example, Chinese patent document CN109743852B discloses a stencil for SMT mounting that increases solder volume. It includes a stencil substrate with multiple solder holes. These solder holes fit over electronic components on a circuit board. Multiple solder guiding mechanisms are provided on the walls of the solder holes. Each solder guiding mechanism includes a mounting base fixedly mounted on the wall of the solder hole. A first guiding block and a second guiding block are elastically connected to opposite sides of the mounting base. The end of the first guiding block extends towards the top of the solder hole, and the end of the second guiding block extends towards the circuit board. Compared to existing technologies, this stencil can effectively increase solder volume, achieving 100% solder climb after reflow.

[0004] However, as electronic devices become increasingly miniaturized and denser, the soldering process in surface mount technology (SMT) faces increasingly severe challenges. Traditional stencil opening designs typically employ simple geometric shapes, such as rectangles, circles, or ellipses. These designs are prone to the following problems during solder paste release:

[0005] 1. Uneven solder paste distribution, resulting in insufficient or excessive solder content;

[0006] 2. Poor gas drainage creates cavities or air holes;

[0007] 3. Poor adaptability to micro-pitch components, such as BGA and QFN with a pitch of less than 0.4mm;

[0008] 4. The process window is narrow, and it is highly sensitive to equipment precision and process parameters.

[0009] Furthermore, while existing technologies have introduced some improved stencil opening designs, such as trapezoidal openings and nano-coatings, they have not fundamentally solved the problem of matching the rheological properties of solder paste with the opening structure. Especially in high-density interconnect / HDI boards and chip-scale packaging / CSP applications, the soldering defect rate of traditional processes remains relatively high. Summary of the Invention

[0010] Therefore, it is necessary to provide a gradient microporous array steel mesh opening process that can significantly improve welding yield, addressing the technical issue of how to improve welding yield.

[0011] A process for opening stencils to improve welding yield includes the following steps:

[0012] S1. A steel mesh opening structure with a gradient microporous array design, wherein the opening structure consists of an outer ring guide structure and an inner microporous array;

[0013] S2. Prepare a nano-coating on the surface of a steel mesh;

[0014] S3. The aperture parameters are automatically calculated and adjusted based on real-time data collected from PCB pad size, component pin height, and mounting accuracy using a dynamic compensation algorithm.

[0015] Specifically, the gradient micropore array design includes:

[0016] Outer ring guide structure: It consists of a rectangular frame formed by four 1 / 4 ring openings, with an area accounting for 50-70% of the opening on one side;

[0017] Internal micropore array: composed of multiple uniformly distributed concentric fan-shaped rings, each ring with a width of 0.03-0.08 mm and a spacing of 0.02-0.05 mm;

[0018] Exhaust passage: A micro-air passage with a width of 0.005-0.015mm is designed between the fan-shaped rings.

[0019] Specifically, the nano-coating is a diamond-like carbon-based coating with a thickness of 50-200 nm and a surface energy of 18-25 mN / m. This coating is prepared using ion beam assisted deposition technology.

[0020] Specifically, the dynamic compensation algorithm integrates the following models:

[0021] A thermal expansion coefficient compensation model is used to compensate for the high-temperature reflow region.

[0022] Solder paste viscosity-shear rate relationship model;

[0023] Simulation model of tension distribution at micro-gap.

[0024] Specifically, in the aforementioned process, the steel mesh adopts a composite stepped structure, with a thickness of 0.06-0.10 mm in the grounding pad area and a thickness of 0.12-0.18 mm in the chip pin area.

[0025] Specifically, the aforementioned process also includes a steel mesh processing step:

[0026] Initial cutting is performed using ultraviolet laser with a pulse frequency of 70-90kHz;

[0027] Electroplating and polishing processes are used to control the roughness of the hole walls to Ra≤0.8μm.

[0028] Specifically, the aforementioned process also includes online monitoring and adaptive adjustment steps:

[0029] By integrating a visual positioning system with a CCD image processing algorithm, the alignment accuracy of the steel mesh reaches ±10μm.

[0030] The tension data is monitored in real time by a piezoelectric sensor, and the tensioning force is dynamically adjusted.

[0031] 3D-X-ray tomography was used to provide real-time feedback on deposition volume deviation.

[0032] Furthermore, a type of steel mesh using the aforementioned steel mesh opening process to improve welding yield has a base material of 316L stainless steel, an elastic modulus of 210 GPa, and a tension control of 35-50 N / cm. 2 .

[0033] Furthermore, a system for applying the aforementioned stencil opening process to improve welding yield includes:

[0034] Data acquisition module: used to acquire PCB pad size accuracy, component pin height, and coplanarity data;

[0035] Dynamic compensation algorithm module: used to generate steel mesh opening scheme based on the collected data;

[0036] Processing control module: used to control the laser cutting and nano-coating deposition process;

[0037] Online monitoring module: Used to monitor the printing process in real time and provide feedback for adjustments.

[0038] In summary, this invention discloses a gradient micro-via array stencil opening process for improving soldering yield. The process includes: a stencil opening structure designed with a gradient micro-via array, the opening structure consisting of an outer ring guide structure and an inner micro-via array; preparation of a nano-coating on the stencil surface; and automatic calculation and adjustment of opening parameters based on real-time collected data on PCB pad size, device pin height, and mounting accuracy using a dynamic compensation algorithm. This stencil opening process significantly improves solder paste release rate, reduces soldering defects, and increases soldering yield to over 99.5%, making it particularly suitable for the soldering requirements of micro-pitch devices and high-reliability electronic products. Attached Figure Description

[0039] Figure 1 This is a process flow diagram of a steel mesh opening process for improving welding yield according to the present invention.

[0040] Figure 2 This is a conceptual block diagram of the gradient micropore array design used in the stencil opening process for improving welding yield according to the present invention.

[0041] Figure 3 This is a flowchart illustrating the dynamic compensation algorithm system used in the stencil opening process for improving welding yield according to the present invention. Detailed Implementation

[0042] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0044] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0045] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0046] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0047] It should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on the other element or there may be an intervening element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there may be an intervening element. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only possible implementation.

[0048] Please refer to the following: Figures 1 to 3 This invention discloses a stencil opening process to improve soldering yield, comprising the following steps: a stencil opening structure designed with a gradient micropore array, the opening structure consisting of an outer ring guide structure and an inner micropore array; preparation of a nano-coating on the stencil surface; and automatic calculation and adjustment of opening parameters based on real-time collected data of PCB pad size, device pin height, and mounting accuracy using a dynamic compensation algorithm.

[0049] Furthermore, the gradient micropore array design includes: an outer ring guide structure consisting of four quarter-annular openings forming a rectangular frame, with an area accounting for 50-70% of the opening on one side; an inner micropore array consisting of multiple evenly distributed concentric fan-shaped rings, each ring with a width of 0.03-0.08 mm and a spacing of 0.02-0.05 mm; and exhaust channels with a width of 0.005-0.015 mm designed between the fan-shaped rings.

[0050] Furthermore, the nano-coating is a diamond-like carbon-based coating with a thickness of 50-200 nm and a surface energy of 18-25 mN / m, prepared by ion beam assisted deposition technology.

[0051] Furthermore, the dynamic compensation algorithm integrates the following models: a thermal expansion coefficient compensation model for compensating the high-temperature reflow zone; a solder paste viscosity-shear rate relationship model; and a micro-pitch tension distribution simulation model.

[0052] Furthermore, the steel mesh adopts a composite stepped structure, with a thickness of 0.06-0.10 mm in the grounding pad area and a thickness of 0.12-0.18 mm in the chip pin area.

[0053] Specifically, the steel mesh opening process of the present invention to improve welding yield also includes steel mesh processing steps, such as: using ultraviolet laser for initial cutting with a pulse frequency of 70-90kHz; electroplating and polishing treatment to control the roughness of the hole wall to Ra≤0.8μm.

[0054] Specifically, the steel mesh opening process of the present invention for improving welding yield also includes online monitoring and adaptive adjustment steps: integrating a visual positioning system and a CCD image processing algorithm to achieve steel mesh alignment accuracy of ±10μm; monitoring tension data in real time through piezoelectric sensors to dynamically adjust the mesh tensioning force; and using 3D-X-ray tomography to provide real-time feedback on deposition volume deviation.

[0055] Compared with the prior art, the present invention has the following significant advantages:

[0056] 1. Solder paste release rate increased from 80-85% in traditional processes to over 92%;

[0057] 2. The welding defect rate is reduced by more than 70%, making it particularly suitable for micro-pitch devices with a pitch of less than 0.4mm;

[0058] 3. The process window has been expanded from ±0.3mm to ±0.8mm;

[0059] 4. The nano-coating extends the service life of the steel mesh by 3 times.

[0060] Furthermore, several specific embodiments are disclosed below:

[0061] Example 1: Application of smartphone motherboard soldering

[0062] Stencil specifications: Made of 316L stainless steel base material, elastic modulus 210GPa. Adopts a composite stepped structure: 0.08mm thickness in the grounding pad area and 0.15mm thickness in the chip pin area.

[0063] Implementation of the opening structure: The outer ring guide structure consists of a rectangular frame formed by four 1 / 4 annular openings, accounting for 60% of the area of ​​one-sided openings. The internal micropore array consists of five concentric fan-shaped rings, each ring being 0.05 mm wide and 0.03 mm apart; the exhaust channel is 0.01 mm wide.

[0064] Nanocoating implementation: A diamond-like carbon-based coating with a thickness of 100 nm and a surface energy of 20 mN / m was prepared using ion beam assisted deposition. Deposition process parameters: vacuum degree 5 × 10⁻³ Pa, deposition temperature 150 °C, and deposition time 120 minutes.

[0065] Processing procedure: Ultraviolet laser cutting with a pulse frequency of 80kHz was used. After electroplating and polishing, the hole wall roughness Ra = 0.6μm.

[0066] Implementation of dynamic compensation algorithm: Integrated thermal expansion coefficient compensation model: based on the thermal expansion coefficient of stainless steel of 16.5×10⁻⁶. -6 / ℃ and the coefficient of thermal expansion of the PCB substrate is 12.8×10. -6 The difference in temperature was compensated for. Solder paste viscosity-shear rate relationship model: The Herschel-Bulkley model was adopted, with fitting parameters n = 0.35 and K = 225 Pa·s. n .

[0067] Online monitoring implementation: The visual positioning system employs a CCD image processing algorithm, achieving a positioning accuracy of ±8μm. Piezoelectric sensors monitor tension data, with a control accuracy of ±2N / cm. 2 3D-X-ray tomography has a resolution of 5 μm and provides real-time feedback on deposition volume deviation.

[0068] Experimental results:

[0069] The following are the results of testing 5000 mobile phone motherboards:

[0070] Solder paste release rate: 93.5% (82.3% for conventional processes);

[0071] Welding defect rate: 0.45% (5.2% for traditional processes);

[0072] BGA bridging defects: 0.2% (4.8% in conventional processes);

[0073] Process capability index Cp: 2.1 (1.2 for traditional processes).

[0074] Example 2: Welding Application of Automotive Electronic Control Units

[0075] Special steel mesh design: For the composite stepped structure, a thickness of 0.12mm is used in the QFN area and a thickness of 0.18mm is used in the through-hole area; the area ratio of the outer ring guide structure is increased to 65%.

[0076] Nanocoating optimization: The thickness of the diamond-like carbon-based coating was increased to 150 nm, and the surface energy was reduced to 18 mN / m. Multi-arc ion plating technology was used to improve the coating density and wear resistance.

[0077] Enhanced dynamic compensation algorithm: The thermal expansion coefficient compensation model has been optimized for the operating temperature range of automotive electronics, from -40℃ to 150℃. A temperature gradient compensation algorithm has been added, with a compensation coefficient α = 1.25 × 10⁻⁶. -5 / ℃.

[0078] Experimental results:

[0079] Testing was conducted on 3,000 automotive electronic control units:

[0080] Solder paste release rate: 94.2% (80.1% for conventional processes);

[0081] Through-hole filling rate: 98.5% (85.3% with conventional process);

[0082] QFN solder joint defects: 0.15% (5.2% with traditional processes);

[0083] All environmental tests are certified by AEC-Q100.

[0084] Example 3: Application of electronic component welding in medical devices

[0085] Data acquisition module implementation: A 3D optical scanner is used to acquire PCB pad dimensions with an accuracy of ±3μm. A laser confocal sensor measures device pin height with a resolution of 0.1μm.

[0086] Implementation of the dynamic compensation algorithm module: The compensation algorithm is developed based on MATLAB / Simulink, with a processing time of <50ms. Output parameters include: opening compensation coefficient, doctor blade pressure correction amount, and optimized printing speed value.

[0087] Processing control module implementation: Ultraviolet laser cutting system: wavelength 355nm, pulse energy 0.8mJ, repetition frequency 80kHz. Nano-coating deposition system: vacuum degree <5×10-3Pa, substrate temperature 150±5℃.

[0088] Online monitoring module implementation: High-resolution CCD camera: 5 megapixels, acquisition speed 30fps. X-ray inspection system: 5μm resolution, inspection speed 15s / plate.

[0089] System performance: Response time: <100ms; Control accuracy: ±2μm; Data processing capacity: 1000 boards / hour; System stability: MTBF>5000 hours.

[0090] Furthermore, to verify the effectiveness of the present invention, a series of comparative experiments were conducted, and the results are shown in Table 1 below:

[0091] Table 1: Comparison Test of Welding Quality

[0092] Test Project Traditional crafts This invention Improvement range Solder paste release rate 81.5％ 93.8％ +12.3％ Welding defect rate 5.8％ 0.42％ -5.38％ BGA bridging defect 4.5％ 0.18％ -4.32％ Process window ±0.3mm ±0.8mm +167％

[0093] Furthermore, the reliability test data after implementing the present invention are as follows: temperature cycling test, such as -40℃ to 125℃: failure rate of conventional process is 12.5%, failure rate of the present invention is 0.8%; mechanical vibration test, such as 20G, 100h: failure rate of conventional process is 8.3%, failure rate of the present invention is 0.4%; high temperature and high humidity test, such as 85℃ / 85%RH: failure rate of conventional process is 15.2%, failure rate of the present invention is 1.1%.

[0094] In summary, the stencil opening process for improving soldering yield according to the present invention includes: a stencil opening structure designed with a gradient micropore array, wherein the opening structure consists of an outer ring guide structure and an inner micropore array; a nano-coating is prepared on the stencil surface; and the opening parameters are automatically calculated and adjusted based on real-time collected data on PCB pad size, device pin height, and mounting accuracy using a dynamic compensation algorithm. The stencil opening process of the present invention can significantly improve solder paste release rate, reduce soldering defects, and increase soldering yield to over 99.5%, making it particularly suitable for the soldering requirements of micro-pitch devices and high-reliability electronic products.

[0095] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0096] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A process for opening steel mesh to improve welding yield, characterized in that, It includes the following steps: S1. A steel mesh opening structure with a gradient microporous array design, wherein the opening structure consists of an outer ring guide structure and an inner microporous array; S2. Prepare a nano-coating on the surface of a steel mesh; S3. Based on real-time data collected from PCB pad size, component pin height, and mounting accuracy, the dynamic compensation algorithm automatically calculates and adjusts the opening parameters.

2. The stencil opening process for improving welding yield according to claim 1, characterized in that... The gradient micropore array design includes: Outer ring guide structure: It consists of a rectangular frame formed by four 1 / 4 ring openings, with an area accounting for 50-70% of the opening on one side; Internal micropore array: composed of multiple uniformly distributed concentric fan-shaped rings, each ring with a width of 0.03-0.08 mm and a spacing of 0.02-0.05 mm; Exhaust passage: A micro-air passage with a width of 0.005-0.015mm is designed between the fan-shaped rings.

3. The stencil opening process for improving welding yield according to claim 1, characterized in that: The nano-coating is a diamond-like carbon-based coating with a thickness of 50-200 nm and a surface energy of 18-25 mN / m. This coating is prepared by ion beam assisted deposition technology.

4. The stencil opening process for improving welding yield according to claim 1, characterized in that, The dynamic compensation algorithm integrates the following models: A thermal expansion coefficient compensation model is used to compensate for the high-temperature reflow region. Solder paste viscosity-shear rate relationship model; Simulation model of tension distribution at micro-gap.

5. The stencil opening process for improving welding yield according to claim 1, characterized in that: The steel mesh adopts a composite stepped structure, with a thickness of 0.06-0.10 mm in the grounding pad area and 0.12-0.18 mm in the chip pin area.

6. The stencil opening process for improving welding yield according to claim 1, characterized in that... It also includes the steel mesh processing steps: Initial cutting is performed using ultraviolet laser with a pulse frequency of 70-90kHz; Electroplating and polishing processes are used to control the roughness of the hole walls to Ra≤0.8μm.

7. The stencil opening process for improving welding yield according to claim 1, characterized in that, It also includes online monitoring and adaptive adjustment steps: By integrating a visual positioning system with a CCD image processing algorithm, the alignment accuracy of the steel mesh reaches ±10μm. The tension data is monitored in real time by a piezoelectric sensor, and the tensioning force is dynamically adjusted. 3D-X-ray tomography was used to provide real-time feedback on deposition volume deviation.

8. A steel mesh employing a steel mesh opening process for improving welding yield as described in any one of claims 1-7, characterized in that: The base material of this type of steel mesh is 316L stainless steel, with an elastic modulus of 210 GPa and a tension control of 35-50 N / cm. 2 .

9. A system for applying a stencil opening process to improve welding yield as described in any one of claims 1-7, characterized in that, It includes: Data acquisition module: used to acquire PCB pad size accuracy, component pin height, and coplanarity data; Dynamic compensation algorithm module: used to generate steel mesh opening scheme based on the collected data; Processing control module: used to control the laser cutting and nano-coating deposition process; Online monitoring module: Used to monitor the printing process in real time and provide feedback for adjustments.

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