Collaborative design method of tin connection prevention PCB (Printed Circuit Board)

Abstract

The invention discloses a collaborative design method of a tin connection prevention PCB (Printed Circuit Board), which belongs to the technical field of printed circuit board design and manufacture, and comprises the following steps: firstly, mechanically guiding and segmenting a soldering tin flow by adopting an asymmetric special-shaped bonding pad with center offset and carrying out differential direction layout; secondly, functional composite solder resist ink is creatively assigned to be applied between bonding pads, and a microscopic isolation barrier is constructed by utilizing the super-hydrophobic tin characteristic of the functional composite solder resist ink; then, a wave-soldering process window matched with the design is defined, and it is ensured that the design intention is stably achieved; and finally, carrying out manufacturability verification. According to the method, the wave-soldering tin connection problem is systematically solved from the source through multi-dimensional cooperation in the design stage, the tin connection reject ratio can be stably controlled to be 0.3% or below, and the manufacturing first pass yield and reliability of the high-density PCB are remarkably improved.

Description

Technical Field

[0001] This invention relates to the technical field of printed circuit board design and manufacturing, and in particular to a design method for systematically suppressing solder bridging defects in the wave soldering process of high-density printed circuit boards through four-dimensional collaboration of innovative pad structure design, process parameter optimization, material science selection, and real-time monitoring system. Background Technology

[0002] Wave soldering is an automated soldering technology widely used in electronics manufacturing, primarily for the mass production of printed circuit boards containing through-hole components. Its core principle is to allow the bottom surface of a circuit board, pre-coated with flux and pre-inserted with components, to smoothly pass through a continuous, upward-flowing "wave" surface formed by molten solder at a specific angle and speed. The molten solder, through capillary action, wets and fills the gap between the component leads and the PCB pad holes, thereby achieving a one-time, efficient, and reliable electrical connection and mechanical fixation for all through-hole component solder joints.

[0003] Currently, the USB components with simplified packaging technology on the market have a simple design and save PCB space. However, they generally have the problem of solder bridging between the pins. When there are multiple USBs on the same PCB that are not on the same straight line, the probability of solder bridging is low in only one direction, but high in other directions.

[0004] Based on this, Chinese patent document CN211184419U discloses a low-cost anti-bridging PCB board. The PCB board has at least one row or column of solder holes for inserting component leads and pads surrounding the solder holes. The pads have an irregular shape, and adjacent pads have different orientations. This technical solution can avoid bridging caused by adjacent pads being too close together during wave soldering, and the probability of bridging between component leads can be greatly reduced regardless of the direction of the wave soldering.

[0005] However, as electronic products become increasingly miniaturized and feature-rich, the density of through-hole components per unit area on PCBs has significantly increased, leading to a sharp reduction in the spacing between pads and leads. During wave soldering, molten solder is highly susceptible to forming unintended conductive bridges between adjacent pads due to capillary action, thermodynamic imbalances, and process fluctuations. These bridges, known as "solder bridging" or "bridging" defects, cause short circuits and severely reduce product yield and reliability.

[0006] However, existing solutions often address only one dimension, which has limitations: 1. Design Dimension: Simply increasing the pad spacing goes against the trend of high density; or using standard rectangular pads results in a single direction of solder flow and a high risk of solder bridging.

[0007] 2. Process dimension: Although parameters such as peak height and temperature can be adjusted, there is a lack of linkage with PCB design characteristics, resulting in a narrow optimization window and poor universality.

[0008] 3. Material dimension: The selection of solder resist ink is mostly based on cost and appearance, without fully considering its compatibility with the soldering process and its contribution to preventing bridging.

[0009] 4. Inspection dimensions: Mostly offline inspections after welding, which cannot achieve process intervention, resulting in delayed defect detection and high rework costs. Summary of the Invention

[0010] Therefore, it is necessary to provide a collaborative design method for PCB boards that prevents solder bridging, in order to address the technical problem of solder bridging on PCBs during wave soldering.

[0011] A collaborative design method for preventing solder bridging on a PCB board includes the following steps: S1: Implement asymmetric irregular pad design and differentiated orientation layout to make the solder contraction force of adjacent pads have different directions; S2: In the PCB solder mask design file, it is specified that functionalized composite solder mask ink is applied to high-risk areas between pads. The ink is configured to enable the contact angle between the cured solder mask surface and the molten solder to be greater than 110°. S3: Based on the designs of S1 and S2, define a wave soldering process parameter window that works in conjunction with them, and include this parameter window as part of the design output; S4: Perform a manufacturability check on the completed layout design to ensure there are no potential electrical short circuit hazards.

[0012] Furthermore, in step S1, the asymmetric irregular-shaped pad is an elliptical pad, and its geometric center is offset by 0.05mm~0.15mm relative to the center of the component mounting hole along the pad arrangement direction. Furthermore, in step S1, the minor axis of the elliptical pad is 45 to 70 mil, and the major axis is 50 to 120 mil.

[0013] Furthermore, in step S1, the differentiated orientation layout refers to making the long axis direction of adjacent pads in the same row form an angle of 15°~75° with the wave soldering over soldering direction, and these angles are different from each other.

[0014] Furthermore, step S1 also includes solder-stealing pads designed at the ends of the pad array to absorb excess solder.

[0015] Furthermore, in step S2, the functionalized composite solder resist ink is a green liquid optical imaging solder resist ink in which nano-sized silica particles are dispersed.

[0016] Furthermore, the nano-sized silica particles account for 1% to 5% of the total weight of the ink, and the particles are surface-modified with a silane coupling agent.

[0017] Furthermore, in step S3, the defined wave soldering process parameter window includes: wave height 0.5~1.0mm, conveyor speed 1.2~1.8m / min, chain tilt angle 5°~7°, and welding temperature 250℃~265℃.

[0018] Furthermore, in step S4, the manufacturability check includes performing an electrical network check using DFM tools to ensure there is no short-circuit risk due to design flaws.

[0019] Furthermore, the average particle size of the nanoscale silica particles is between 20 nm and 30 nm.

[0020] In summary, this invention discloses a collaborative design method for preventing solder bridging in PCB boards. First, it mechanically guides and segments the solder flow by employing asymmetrical, irregularly shaped pads with a center offset and differentiated directional layout. Second, it innovatively specifies the application of functionalized composite solder resist ink between the pads, utilizing its super-solder-repellent properties to construct a microscopic isolation barrier. Then, it defines a wave soldering process window matching the above design to ensure the stable realization of the design intent. Finally, it performs manufacturability verification. This invention, through multi-dimensional collaboration during the design phase, systematically solves the solder bridging problem in wave soldering from its source, consistently controlling the solder bridging defect rate below 0.3%, significantly improving the manufacturing pass rate and reliability of high-density PCBs. Attached Figure Description

[0021] Figure 1 This is a flowchart of a collaborative design method for preventing solder bridging on a PCB board according to the present invention. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] Please see Figure 1 The present invention discloses a collaborative design method for preventing solder bridging on a PCB board, which includes the following steps: S1: Design and Layout of Asymmetric Irregular Pads For the pads of through-hole components, an elliptical design is adopted, with its geometric center offset by 0.05mm to 0.15mm relative to the center of the component mounting hole along the pad arrangement direction. This is to disrupt the symmetrical balance of the solder surface tension, causing the solder contraction force to point towards itself rather than adjacent pads.

[0029] Define the pad dimensions as follows: short axis 45 to 70 mil, long axis 50 to 120 mil.

[0030] Differentiated orientation layout is adopted between adjacent pads in the same row, so that the long axis of each pad forms an angle of 15° to 75° with the preset wave soldering direction, so as to divide the continuous solder flow.

[0031] At the end of the pad array, a solder-stealing pad with a pre-designed structure is designed to absorb excess solder during manufacturing.

[0032] S2: Design and Application of Functionalized Composite Solder Resist Inks In the solder mask design document, functionalized composite solder mask ink is specified to be applied to high-risk areas between solder pads.

[0033] The functionalized composite solder resist ink consists of 1% to 5% by weight of nano-sized silica particles uniformly dispersed in a standard green liquid optical imaging solder resist ink. These nanoparticles are surface-modified with a silane coupling agent, resulting in a strong bond with the ink resin matrix.

[0034] This design creates a micro-rough structure on the surface of the cured solder resist layer, with a contact angle with the molten solder greater than 110°, exhibiting "super solder-repellent" properties, which can effectively prevent solder from spreading and bridging.

[0035] S3: Manufacturing process window definition that matches the design Based on the pad design of S1 and the ink characteristics of S2, a wave soldering process parameter window is defined to work in conjunction with these parameters and provided to the manufacturing end as part of the design output: Crest height: 0.5 to 1.0 mm; Conveying speed: 1.2 to 1.8 m / min; Chain tilt angle: 5° to 7°; Welding temperature: 250℃ to 265℃.

[0036] S4: Co-design of Manufacturability and Testability Use DFM tools to check the electrical network of the completed PCB design files to ensure there is no risk of short circuits.

[0037] The design provides clear inspection channels and contrast for the automated optical inspection system, ensuring a distinct boundary between the solder pads and the solder mask.

[0038] By implementing the collaborative design method for preventing solder bridging on a PCB board according to the present invention, the following technical effects can be achieved: Prevention at the source: Starting from the source of PCB design, internalize anti-solder bridging measures into product design, and transform passive remediation into proactive prevention.

[0039] Synergistic effect: Asymmetric pads guide solder through mechanical means, while functional inks repel solder through interfacial properties. The two work together to form a synergistic effect of macroscopic guidance and microscopic isolation, which is far more effective in preventing solder bridging than the simple superposition of single methods.

[0040] High stability: By defining a process window that matches the design, it ensures that the design intent can be executed stably and accurately in actual production, reducing the reliance on extreme adjustments to process parameters during production and improving the stability of yield.

[0041] Super-solder-repellent properties: The application of functionalized composite solder resist ink can introduce the concept of super-solder-repellent to the field of anti-bridging, which changes the interaction between solder and substrate from a physical and chemical perspective, greatly improving the reliability of anti-bridging, especially suitable for ultra-dense pitch designs.

[0042] High versatility: The method disclosed in this invention forms a complete set of design rules and material specifications, which can be seamlessly integrated into existing electronic design automation processes and is easy to promote and implement in various PCB design projects.

[0043] Quantitative benefits: The PCB board designed by this invention can stably control the solder bridging defect rate of wave soldering to below 0.3%, which is more than an order of magnitude better than traditional design methods (usually >1%).

[0044] Furthermore, the implementation of the method of the present invention will be described in detail below through a specific embodiment: Example: Anti-solder bridging collaborative design for a high-density PCB board for a communication module.

[0045] 1. Design Input: Receive board block diagram and schematic diagram, and confirm that there are two sets of 20-pin connectors with a spacing of 0.8mm on the board.

[0046] 2.S1: Pad Design and Layout In EDA software, such as Altium Designer's PCB library, create a new elliptical pad. Set the minor axis to 60 mil and the major axis to 90 mil.

[0047] In component package design, the through-hole is placed 0.1 mm to the left of the geometric center of the pad.

[0048] When laying out the PCB, the long axis of the odd-numbered pads of the first group of pins is set to be at a 45° angle to the transmission direction, i.e., the X-axis, and the even-numbered pads are at a 135° angle; while the second group of pins is set alternately to 30° and 60° angles.

[0049] At the end of each group of pins, place a rectangular solder pad measuring 80mil x 120mil.

[0050] 3.S2: Designation of Functionalized Inks In the solder mask settings, create a separate "anti-tin bridging zone" rule for the areas where the two sets of pins are located.

[0051] The rule specifies the use of functionalized composite solder resist inks of type LPI to Green-Nano-SiO2, and this requirement is clearly indicated in the processing drawings.

[0052] With this design, the solder mask layer in this area will have super tin-repellent properties.

[0053] 4.S3: Process Window Definition The "PCB Manufacturing and Assembly Technical Requirements" document issued to the manufacturer clearly states that the wave soldering process parameters must be controlled within the following range: wave height 0.8mm, conveyor speed 1.5m / min, chain tilt angle 6°, and soldering temperature 260℃±5℃.

[0054] 5.S4: DFM / DFA Inspection Run DFM verification to confirm that there are no potential short circuit risks such as silkscreen pads or copper foil debris.

[0055] Generate Gerber files and all the aforementioned technical requirements documents, and deliver them to production.

[0056] 6. Verification of technical effectiveness: After the communication module board was mass-produced, statistics showed that its solder bridging defect rate decreased from about 1.5% when using the traditional design method to 0.22%, and the production process was stable without the need for repeated debugging of process parameters, which fully proves the effectiveness and superiority of the method disclosed in this invention.

[0057] Furthermore, to specifically illustrate the composition, preparation, and technical effects of the functionalized composite solder resist ink described in this invention, the following three typical embodiments and comparative experiments will be provided; and all the embodiments below are in parts by weight.

[0058] Ink Example 1 Base ink: Green liquid photolithography solder resist ink, i.e., epoxy acrylate system, 100 parts; Functional filler: Nano-silica with an average particle size of 20 nm, modified by silane coupling agent KH-570, in 3 parts; Dispersing agent: Polymer dispersant (BYK-163), 0.5 parts; Preparation method: 1. Premix the 3 parts of modified nano-silica with 0.5 parts of dispersant; In a high-speed shear disperser, at a speed of 3000 rpm, the premix is ​​slowly added to 100 parts of base ink.

[0059] 2. After continuous shearing and dispersion for 60 minutes, the mixture is then transferred to a three-roll mill for grinding until the fineness is ≤15μm, thus obtaining the functionalized composite solder resist ink. Example 2

[0060] Base ink: Green liquid photolithography solder resist ink, i.e., epoxy acrylate system, 100 parts; Functional filler: Nano-silica with an average particle size of 30 nm, modified by silane coupling agent KH-560, 1 part; Dispersing agent: Polymer dispersant (BYK-163), 0.2 parts; Preparation method: Same as in Example 1 Example 3

[0061] Base ink: Green liquid photolithography solder resist ink, i.e., epoxy acrylate system, 100 parts; Functional filler: Nano-silica with an average particle size of 20 nm, modified by silane coupling agent KH-570, in 5 parts; Dispersing agent: Polymer dispersant (BYK-163), 0.8 parts.

[0062] Preparation method: Same as in Example 1.

[0063] Comparative Example 1: 100 parts of the same base ink as in Example 1 were used, without the addition of any nano-silica. This comparative example represents conventional ordinary ink.

[0064] Comparative Example 2 Base ink: Same as in Example 1, 100 parts; Functional filler: Nano-silica without silane coupling agent surface modification, with an average particle size of 20nm, 3 parts; Dispersing agent: Polymer dispersant (BYK-163), 0.5 parts.

[0065] Preparation method: Same as in Example 1. This comparative example is used to verify the necessity of surface modification of nanoparticles.

[0066] Furthermore, performance tests and results analysis were conducted on the aforementioned comparative and exemplary examples. Specifically, the inks prepared in the examples and comparative examples were screen-printed onto standard FR-4 test pieces. After standard LPI processes including pre-baking, exposure, development, and post-curing, a solder resist layer was formed. The following key performance tests were then performed: Test 1, Contact Angle Measurement. Test Method: Using a contact angle meter, drop a drop of standard Sn63 / Pb37 molten solder (250℃) onto the surface of the cured solder mask and measure its static contact angle.

[0067] Table 1: Experimental Results of Test 1

[0068] Results Analysis: Comparative Example 1, i.e., the contact angle of ordinary ink is much less than 90°, indicating a solder-friendly surface that facilitates solder spread. Comparative Example 2, i.e., the addition of unmodified nano-... The contact angle of the sample was improved, but it did not reach the superhydrophobic state, i.e., >110°. This is because unmodified nanoparticles tend to agglomerate in the ink, resulting in uneven dispersion and weak bonding with the resin matrix, making it impossible to form a stable and uniform micro-rough structure.

[0069] The contact angles of Examples 1 and 3 were significantly greater than 110°, reaching the level of "super-tin-repellent". This proves that nano-silica modified with silane coupling agent can be effectively dispersed in ink and form a stable composite structure with resin, thereby constructing an ideal microstructure on the cured surface and greatly improving the solder wetting resistance.

[0070] Test 2, Verification of Anti-Bridging Effect: The test method involves fabricating a test board with comb-shaped pads with a 0.8mm pitch and applying the aforementioned inks. After wave soldering, the number of bridging connections between 1000 solder joints is counted under a microscope, and the bridging rate is calculated.

[0071] Table 2: Experimental Results of Test 2

[0072] Analysis of the experimental results in Table 2 shows a strong positive correlation between the anti-tin bridging effect and the contact angle data. Examples 1 and 3, with their super-tin-repellent properties, reduced the tin bridging rate to below 0.2%, demonstrating extremely significant effects and fully reflecting the practical value of the ink disclosed in this invention.

[0073] Test 3: Adhesion and Reliability Test Test method: Perform a 100-cross adhesion test according to the IPC-TM-650 standard to evaluate the adhesion between the solder mask and the PCB substrate.

[0074] Test results: The adhesion of all examples and comparative examples reached the highest level of 5B.

[0075] Results Analysis: These results demonstrate that, with a reasonable formulation and preparation process, especially the use of silane coupling agents, the addition of nano-silica does not sacrifice the key adhesion performance between the solder resist layer and the substrate, thus ensuring product reliability.

[0076] The above examples and comparative experiments demonstrate that the functionalized composite solder resist ink formulation proposed in this invention is effective and feasible. The addition of nano-silica in the range of 1% to 5% effectively improves tin repellency, with an addition of 3% to 5% achieving the best super-tin repellency effect. Surface modification of nano-silica is a key step in achieving uniform dispersion and obtaining stable super-tin repellency performance; the effect of unmodified nanoparticles is significantly reduced. This functionalized ink achieves excellent anti-tin bridging effect (tin bridging rate <0.2%) while maintaining the excellent physical reliability (adhesion 5B) of traditional inks.

[0077] In summary, this invention discloses a collaborative design method for preventing solder bridging in PCB boards. First, it mechanically guides and segments the solder flow by employing asymmetrical, irregularly shaped pads with a center offset and differentiated directional layout. Second, it innovatively specifies the application of functionalized composite solder resist ink between the pads, utilizing its super-solder-repellent properties to construct a microscopic isolation barrier. Then, it defines a wave soldering process window matching the above design to ensure the stable realization of the design intent. Finally, it performs manufacturability verification. This invention, through multi-dimensional collaboration during the design phase, systematically solves the solder bridging problem in wave soldering from its source, consistently controlling the solder bridging defect rate below 0.3%, significantly improving the manufacturing pass rate and reliability of high-density PCBs.

[0078] 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.

[0079] 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 collaborative design method for preventing solder bridging on a PCB board, characterized in that, Includes the following steps: S1: Implement asymmetric irregular pad design and differentiated orientation layout to make the solder contraction force of adjacent pads have different directions; S2: In the PCB solder mask design file, it is specified that functionalized composite solder mask ink is applied to high-risk areas between pads. The ink is configured to enable the contact angle between the cured solder mask surface and the molten solder to be greater than 110°. S3: Based on the designs of S1 and S2, define a wave soldering process parameter window that works in conjunction with them, and include this parameter window as part of the design output; S4: Perform a manufacturability check on the completed layout design to ensure there are no potential electrical short circuit hazards.

2. The collaborative design method for preventing solder bridging on a PCB board according to claim 1, characterized in that: In step S1, the asymmetric irregular pad is an elliptical pad, whose geometric center is offset from the center of the component mounting hole along the pad arrangement direction by 0.05mm to 0.15mm.

3. The collaborative design method for preventing solder bridging on a PCB board according to claim 2, characterized in that: In step S1, the minor axis of the elliptical pad is 45 to 70 mil, and the major axis is 50 to 120 mil.

4. The collaborative design method for preventing solder bridging on a PCB board according to claim 1, characterized in that: In step S1, the differentiated orientation layout refers to making the long axis direction of adjacent pads in the same row form an angle of 15°~75° with the wave soldering over soldering direction, and these angles are different from each other.

5. The collaborative design method for an anti-tin bridging PCB board according to claim 1, characterized in that: Step S1 also includes solder-stealing pads designed at the ends of the pad array to absorb excess solder.

6. The collaborative design method for an anti-tin bridging PCB board according to claim 1, characterized in that: In step S2, the functionalized composite solder resist ink is a green liquid optical imaging solder resist ink in which nano-sized silica particles are dispersed.

7. The collaborative design method for an anti-tin bridging PCB board according to claim 6, characterized in that: The nano-sized silica particles account for 1% to 5% of the total weight of the ink, and the particles are surface-modified with a silane coupling agent, with an average particle size between 20 nm and 30 nm.

8. The collaborative design method for an anti-tin bridging PCB board according to claim 1, characterized in that: In step S3, the defined wave soldering process parameter window includes: wave height 0.5 to 1.0 mm, conveyor speed 1.2 to 1.8 m / min, chain tilt angle 5° to 7°, and soldering temperature 250° to 265°.

9. The collaborative design method for an anti-tin bridging PCB board according to claim 1, characterized in that: In step S4, the manufacturability check includes performing an electrical network check using DFM tools to ensure there is no short-circuit risk due to design flaws.

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