PCB pad structure and printed circuit board

Abstract

This utility model relates to a PCB pad structure and a printed circuit board. The PCB pad structure is disposed on a printed circuit board for mounting surface mount diodes. The surface mount diode has a body and solder terminals located at both ends of the body, including a pair of pads corresponding to the two solder terminals respectively. The ratio of the width of the pad to the width of the solder terminal is 0.8 to 1.2. This utility model provides a PCB pad structure and a printed circuit board, aiming to improve the phenomenon of surface mount diodes tilting after reflow soldering and reduce their short circuit risk in high-density, fine-pitch applications.

Description

Technical Field

[0001] This utility model relates to the field of electronic circuit manufacturing technology, specifically to a PCB pad structure and a printed circuit board including the structure. Background Technology

[0002] In surface mount technology (SMT) for electronic assembly, surface mount diodes (SMD) are typically fixed to corresponding pads on a printed circuit board (PCB) via solder terminals on their bottom. A common pad design approach is to determine the width of the pad based on the width of the diode itself. However, with this design, during reflow soldering, the center of gravity of the solder joint formed by the molten solder tends to deviate from the component's center. This shift in center of gravity can make it difficult to balance the torque exerted on the component by the liquid solder, resulting in the component sometimes tilting at a certain angle after the solder solidifies. Significant tilting can affect component performance and even lead to functional defects.

[0003] In applications with dense component layouts, the impact of this tilting phenomenon becomes particularly pronounced. Tilted components may have reduced electrical clearance between their conductive parts and adjacent circuitry, posing a challenge to the circuit's insulation performance and long-term reliability. Therefore, the industry needs an improved pad structure design to improve component soldering posture. Utility Model Content

[0004] In view of this, the present invention provides a PCB pad structure, which aims to improve the phenomenon that surface mount diodes tend to tilt after reflow soldering and reduce their short circuit risk in high-density fine-pitch applications.

[0005] The objective of this utility model is achieved through the following technical solution: A PCB pad structure is disposed on a printed circuit board for mounting a surface mount diode. The surface mount diode has a body and solder terminals located at both ends of the body, including a pair of pads corresponding to the two solder terminals respectively. The ratio of the width of the pad to the width of the solder terminal is 0.8 to 1.2.

[0006] This core width ratio matches the pad and solder tip dimensions, guiding the formation of symmetrical solder joint menisci during reflow soldering and controlling the solder joint's center of gravity within the component's projection. This significantly enhances component self-alignment and torque balance, directly suppressing tilting caused by uneven solder tension. In high-density layouts, this tilt suppression reduces the risk of short circuits caused by solder tips contacting adjacent conductors, improving connection reliability and production yield. This design provides sufficient solder area to ensure strength and electrical performance while promoting stable return force, simplifying manufacturing, and improving consistency.

[0007] Preferably, the width of the pad is equal to the width of the solder end.

[0008] Equal width configuration achieves ideal matching, promoting uniform solder wetting and forming a highly symmetrical meniscus. The symmetrical meniscus enables excellent balance of solder surface tension on both sides of the component, effectively suppressing torsion or tilting tendencies, providing direct support for optimal soldering uprightness, while reducing soldering defects and improving process stability.

[0009] Preferably, the length of the pad is greater than or equal to the length of the solder end.

[0010] The extended length provides additional solder reserve and climb-up space, ensuring sufficient solder body to envelop the solder tip and create a well-defined meniscus for the solder joint. This increases the contact area of ​​the solder joint, improving mechanical strength and electrical reliability. Combined with width control, it creates a more robust three-dimensional solder joint structure, enhancing stress resistance.

[0011] Preferably, the ratio of the length of the pad to the length of the solder end is 1.0 to 1.5.

[0012] This length ratio range provides clear design guidelines for optimizing solder joints, ensuring sufficient solder to form reliable joints while avoiding overspreading. Working in conjunction with the width ratio, it optimizes the pad-to-terminal fit in two dimensions, improving solder flow and shaping, and enhancing stress dispersion and long-term reliability.

[0013] Preferably, it further includes a solder mask layer disposed between the pair of pads, the solder mask layer having windows that expose the soldering area of ​​the pads.

[0014] The solder mask and windows provide precise spatial control for soldering, confining the solder within a preset area to prevent bridging defects and ensure consistent solder joint shape. Clear window boundaries assist in automated placement and positioning, while the copper foil cover provides electrical insulation protection, enhancing the product's long-term environmental durability.

[0015] Preferably, the size of the window matches the size of the pad, and the distance between its boundary and the edge of the pad is 0.05-0.1mm, so as to precisely define the solder spreading range.

[0016] The precise window size and spacing design enables micro-management of solder spread, ensuring that solder is precisely confined, preventing overflow or underspending, and resulting in a consistent and reliable solder joint shape. This control reduces solder quality fluctuations, improves production stability, and helps maintain electrical safety clearances in high-density layouts.

[0017] Preferably, the shape of the pad is the same as the shape of the solder end.

[0018] Identical shapes ensure consistent geometric contours, allowing solder to wet evenly along the entire contour of the solder joint, forming a symmetrical meniscus. This generates balanced surface tension and enhances the anti-tilting effect. This design simplifies rules, increases application flexibility, and reduces localized stress concentrations.

[0019] Preferably, in a direction perpendicular to the printed circuit board, the projection of the pad on the printed circuit board substantially coincides with the projection outline of the solder end.

[0020] The projection contours basically overlap to achieve the most ideal spatial position correspondence, so that the solder force center is stable near the component central axis, minimizing the misalignment torsional torque, providing the best welding stability and posture balance, and optimizing heat transfer and solder joint metallurgical consistency.

[0021] Preferably, the ratio of the length of the pad to the length of the solder end is 0.9 to 1.1.

[0022] This close length-to-width ratio, combined with the equal-width design, achieves a tight two-dimensional fit, helping to create a solder joint shape that provides additional upright stability against tilting moments. It reduces over-reliance on solder volume, lowers process sensitivity, and facilitates reliable soldering in compact spaces.

[0023] Preferably, the center distance between the pair of pads is equal to the center distance between the two solder ends of the surface mount diode.

[0024] Matching the center-to-center distance is crucial for ensuring precise spatial alignment between pads and solder tips. If there is a deviation between the pad center-to-center distance and the component solder tip center-to-center distance, even if the width and length of each individual pad are in ideal proportion to the solder tip, the component will still experience overall positional shift during mounting. This shift directly leads to asymmetrical stress on the solder on both sides of the component during reflow, introducing a tilting torque that causes the component to twist. This torque weakens or even completely negates the anti-tilting effect provided by optimizing the size of individual pads. By strictly ensuring that the center-to-center distance of a pair of pads is equal to the center-to-center distance of the two solder tips of the component, the stability of the component's stress center can be ensured from the overall layout, making it completely coincident with the support center provided by the pads. This, combined with the optimization of individual pad sizes, constitutes a complete solution for suppressing tilting torque, significantly improving the stability and consistency of the component's upright posture after soldering, and is an essential guarantee for reliable mounting in high-density applications.

[0025] A printed circuit board integrating the PCB pad structure described above.

[0026] Circuit boards integrating this optimized pad structure achieve higher solder pass rates and process stability during manufacturing. Its effective tilt suppression helps maintain safe electrical clearances in high-density layouts, reducing short-circuit risks and providing greater design flexibility and reliability for compact designs, high integration, and product miniaturization.

[0027] The advantages of this utility model compared to the prior art are: This invention's PCB pad structure offers a unique solution for improving soldering posture by setting the pad width to match the solder tip width. This specific dimensional relationship ensures that the center of gravity of the solder joint formed during reflow tends to lie within the projected range of the component's body width. This adjustment of the center of gravity helps improve the torque balance of the component during soldering, thus positively impacting the suppression of its final tilt angle.

[0028] Because the component tilt angle is reduced, its upright position on the printed circuit board is improved. In cases of dense component placement, this translates to maintaining a relatively suitable electrical clearance between its conductive parts and surrounding conductors. Maintaining this clearance contributes to reducing the risk of electrical short circuits caused by component tilt, thereby supporting improved assembly yield and long-term circuit stability.

[0029] This structural design optimizes the dimensional fit between the pads and solder tips, enabling the solder to form a relatively symmetrical meniscus profile during reflow, resulting in a more balanced surface tension distribution. This balanced tension distribution helps components achieve self-centering during soldering and provides some correction for initial placement deviations. Simultaneously, the appropriate pad size design ensures solder strength while providing conditions for forming well-formed solder joints.

[0030] This design provides an alternative technical approach to address the component tilting problem encountered in high-density electronic assembly, and has positive implications for improving the quality control level of surface mount technology. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a cross-sectional view of a PCB pad structure according to an embodiment of the present invention.

[0033] Figure 2 This is a schematic diagram showing the correspondence between the solder end and the solder pad in one embodiment of the present invention.

[0034] Figure 3 This is a schematic diagram illustrating the correspondence between the solder tip and the solder pad in a conventional solder pad design according to an embodiment of this utility model.

[0035] Figure 4 This is a schematic diagram showing the dimensions of a surface-mount diode according to an embodiment of the present invention.

[0036] Labeling explanation: 1 Printed circuit board, 2 Body, 3 Solder terminal, 4 Solder pad, 5 Solder resist, 6 Window, 7 Solder, 03 Solder terminal (traditional design), 04 Solder pad (traditional design). Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0038] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0039] It should be noted that similar reference numerals and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. In the description of the embodiments of this application, it should be understood that the terms "upper," "lower," "left," "right," "vertical," "horizontal," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the figures, or the orientation or positional relationship commonly used when the product of this application is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are only for the convenience of describing this application 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 application.

[0040] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0041] The technical solutions in this application will now be described with reference to the accompanying drawings. Example 1

[0042] This embodiment provides a PCB pad structure disposed on a printed circuit board 1 for mounting surface mount diodes. The surface mount diode has a body 2 and solder terminals 3 located at both ends of the body 2, including a pair of pads 4 corresponding to the two solder terminals 3 respectively. The ratio of the width of the pad 4 to the width of the solder terminal 3 is 0.8 to 1.2.

[0043] The specific ratio range between the width of pad 4 and the width of solder tip 3 forms the core of improving soldering posture. By setting the width of pad 4 to be close to the width of solder tip 3, rather than traditionally referencing the larger width of body 2, this design allows molten solder 7 to be more evenly wetted and spread along the entire width of solder tip 3 during reflow soldering. This uniform wetting behavior directly contributes to the formation of symmetrical solder joint menisci, and the resulting surface tension torque center of gravity is effectively controlled within the projection range of body 2 width. The internal control of the solder joint center of gravity significantly enhances the self-alignment capability and torque balance of the component on the liquid solder 7, thereby directly counteracting the torsional torque caused by uneven surface tension of solder 7. When the width of pad 4 matches the width of solder tip 3, the support surface formed by the solder 7 extending from solder tip 3 to pad 4 is more concentrated and stable, which avoids the tension imbalance caused by excessive spread of solder 7 on one side of the component due to an overly wide pad 4. Therefore, surface-mount diodes can maintain a near-vertical position after soldering and curing, greatly reducing the tilt angle. This effective suppression of tilt is particularly important in high-density, fine-pitch layouts, directly preventing the solder terminals 3 or the body 2 from contacting the electrical components of adjacent components due to excessive tilting. This reduces the risk of short circuits and improves circuit connection reliability and production yield. This ratio range achieves optimized matching between the pads 4 and the solder terminals 3, providing sufficient soldering area to ensure the mechanical strength and good electrical conductivity of the solder joint, while also promoting the formation of a full-shaped, well-defined meniscus of the solder joint by the molten solder 7, further consolidating the long-term stability of the soldered connection.

[0044] Solder 7 is formed by applying solder paste to the soldering area of ​​solder pad 4 and then performing a reflow soldering process. Its final form is a solder joint that wraps around solder end 3 and connects solder end 3 to solder pad 4.

[0045] In this embodiment, the width of the pad 4 is equal to the width of the solder tip 3.

[0046] This equal-width configuration represents an ideal balance in matching the widths of pad 4 and solder tip 3. In this configuration, the edges of pad 4 and solder tip 3 are ideally roughly aligned, allowing the molten solder 7 to achieve the most uniform wetting and spreading along the entire width of solder tip 3. This highly uniform wetting behavior results in a highly symmetrical meniscus formed by the solder 7 on both sides of the component. The symmetrical meniscus means that the surface tension of the solder 7 on both sides of the component is nearly perfectly consistent in magnitude and direction, resulting in a highly effective torque balance. This balance effectively suppresses the tendency of the component to twist or tilt to either side during reflow, providing the most direct and effective structural support for maintaining the component's perpendicular orientation to the surface of the printed circuit board 1 after soldering. It is the preferred solution for achieving optimal soldering uprightness while reducing soldering defects caused by dimensional mismatches.

[0047] like Figure 4 Dimensions D and E are the length and width of the chip diode body 2, and dimensions b and L are the length and width of the solder terminal 3.

[0048] To better understand the fundamental difference between this embodiment and traditional designs, it is first necessary to clarify the size definition of the surface-mount diode. For example... Figure 4 As shown, surface mount diodes are usually sized by their body dimensions (length D and width E), but the key parts for soldering are the solder terminals at both ends, which have their own independent length L and width b, and the center distance between the two solder terminals is e.

[0049] On this basis Figure 3 This demonstrates a traditional pad design. In this design, the width of pad 04 is typically determined by referencing and exceeding the diode body width E, presumably to provide ample soldering area. However, this wide pad design results in pad 04 being significantly wider than the actual width b of the solder tip 03. During reflow soldering, molten solder wets the entire exposed pad area. Because the pad is much wider than the solder tip, the solder easily overspreads laterally at the solder tip, forming an asymmetrical meniscus. The center of surface tension resulting from this asymmetrical meniscus (i.e., the solder joint centroid) deviates from the component's central axis, creating a torsional torque that causes the component to tilt or even exhibit "tombstone" phenomena after soldering.

[0050] In contrast, the core design concept of this embodiment is as follows: Figure 2As shown. The design of pad 4 no longer depends on the body width E, but is directly based on the dimensions (length L and width b) of the solder tip 3 itself. By setting the width of pad 4 to be equal to or close to the solder tip width b (ratio 0.8-1.2), and ensuring its shape matches that of solder tip 3, the dimensions of pad 4 are designed based on the aforementioned width ratio, combined with the preferred ratio of pad length to solder tip length (e.g., 0.9 to 1.5). This allows pad 4 to provide precise support and alignment for solder tip 3. This matching relationship based on solder tip dimensions ensures that the solder can wet and climb evenly and symmetrically along the solder tip contour during reflow, forming a highly symmetrical solder meniscus. At this time, the resultant force of the solder surface tension can effectively pass through the component's center of gravity, generating a restoring torque that is much greater than the tilting torque, thereby forcing the component to self-correct to an upright posture on the liquid solder and maintain stability after the solder solidifies. This not only eliminates the tilting problem but also prevents the risk of short circuits caused by tilting.

[0051] like Figure 3 As shown, in the traditional design, the diagonal shading represents pad 04, and the orthogonal shading represents solder tip 03. The width of pad 04 is significantly larger than the width of the corresponding solder tip 03 above it. However, as... Figure 2 As shown, the diagonal shading represents pad 4, and the orthogonal shading represents solder tip 3. In the preferred embodiment of this utility model, the width of pad 4 is designed based on the width (dimension b) of solder tip 3 (the ratio is 0.8 to 1.2), rather than based on the body width E.

[0052] The center-to-center distance between a pair of pads is equal to the center-to-center distance between the two solder ends of the surface mount diode.

[0053] In this embodiment, the length of the pad 4 is greater than or equal to the length of the solder tip 3.

[0054] Pad 4 extends beyond solder tip 3 in the length direction, creating additional space and reserve for solder 7 to climb and anchor. This extended area serves as an effective solder reserve, ensuring sufficient solder body is formed during reflow soldering to fully cover the end of solder tip 3 and form a solder meniscus with good height. This meniscus not only significantly increases the actual contact area of ​​the solder joint, improving mechanical connection strength and resistance to vibration and thermal fatigue, but also enhances the conductivity and reliability of the electrical connection. More importantly, the ample solder 7 filling in the length direction, combined with precise control in the width direction, contributes to a more stable and robust solder joint structure in three-dimensional space. This further assists in the final positioning of components during the soldering process and strengthens the ability to resist displacement or loosening caused by external stress or thermal expansion stress after solder solidification, improving the overall assembly durability.

[0055] In this embodiment, the ratio of the length of the pad 4 to the length of the solder tip 3 is 1.0 to 1.5.

[0056] This length ratio range provides a clear and optimized design guideline for the extension of pad 4 in the length direction. This range ensures that pad 4 has sufficient additional length to accommodate ample solder 7 to form a full and reliable solder joint, while avoiding excessive solder 7 spreading or material waste due to excessive pad 4 length. Solder joints formed under this ratio can better absorb and disperse stress caused by mismatched coefficients of thermal expansion or mechanical vibration, thereby improving the long-term reliability of the solder joint. Its synergistic design with the width ratio ensures that pad 4 and solder tip 3 form an optimal fit in both length and width dimensions, jointly optimizing the flow, shaping, and final solidification morphology of solder 7 during reflow, providing two-dimensional dimensional assurance for achieving high-strength, high-reliability solder joints.

[0057] In this embodiment, a solder mask layer 5 is also provided between a pair of solder pads 4, and the solder mask layer 5 has a window 6 for exposing the soldering area of ​​the solder pads 4.

[0058] The solder mask layer 5 and its window 6 structure provide precise spatial control and area limitation for the soldering process. The solder mask layer 5 strictly confines the solder 7 within the pre-defined window 6 area, effectively preventing the molten solder 7 from flowing randomly into non-soldering areas during reflow, thus fundamentally avoiding soldering defects such as bridging adjacent pads 4 or wires. This precise area limitation ensures that each solder joint is formed consistently according to the predetermined size and shape, significantly improving the repeatability and production yield of the soldering process. The clear window 6 boundary also provides a reliable reference for optical recognition and precise positioning by automated placement equipment, contributing to improved placement accuracy. Furthermore, the solder mask layer 5 covers the copper foil traces in non-soldering areas, providing durable electrical insulation protection to prevent accidental electrical leakage or short circuits in humid or contaminated environments, improving the long-term operational stability and safety of the product under complex conditions.

[0059] In this embodiment, the size of window 6 matches the size of pad 4, and the distance between its boundary and the edge of pad 4 is 0.05-0.1mm, so as to precisely define the spreading range of solder 7.

[0060] This precise control over the size and spacing of window 6 enables micro-management of the solder 7 spreading behavior. Window 6 matches the size of pad 4 and maintains a small, consistent spacing from the edge of pad 4, together forming a precise physical barrier. This barrier ensures that the solder 7 is perfectly confined within the intended soldering area, preventing bridging risks that could result from solder overflow and ensuring sufficient solder 7 to form full solder joints. This control results in highly consistent solder joint morphology, reducing intra-batch and inter-batch soldering quality fluctuations, thereby significantly improving production process stability and product yield. Precise solder 7 control also helps maintain minimum electrical safety clearances between components, which is crucial for achieving high-density, fine-pitch circuit layouts, enhancing design feasibility and reliability.

[0061] In this embodiment, the shape of the pad 4 is the same as the shape of the solder tip 3.

[0062] The identical shape of pad 4 and solder tip 3 ensures a high degree of geometric consistency between them. This shape matching allows the solder 7 to achieve uniform wetting and spreading along the entire contour of solder tip 3 during reflow, regardless of whether solder tip 3 is rectangular, circular, or any other specific shape. This all-around uniform wetting contributes to the symmetry of the solder joint meniscus in three-dimensional space, thereby generating balanced surface tension in all directions of the component. Balanced tension further enhances the effect of preventing component tilting and displacement, improving the accuracy of soldering position. In addition, the identical shape design principle simplifies the design rules of pad 4, making it flexible to adapt to surface mount diodes of different package sizes, improving the standardization and applicability of the design, while reducing local stress concentration caused by shape mismatch.

[0063] In this embodiment, in the direction perpendicular to the printed circuit board 1, the projection of the pad 4 on the printed circuit board 1 basically coincides with the projection outline of the solder terminal 3.

[0064] The configuration of essentially overlapping projected contours establishes the ideal spatial correspondence between pad 4 and solder tip 3. This relationship ensures precise vertical alignment between the soldering support surface provided by pad 4 and the solder tip 3, allowing the center of force of the molten solder 7 to be stably located near the central axis of the component body 2. This alignment minimizes harmful torsional moments caused by misalignment of pad 4 and solder tip 3, providing optimal positioning stability and attitude balance for the component throughout the reflow soldering process. Projected overlap also optimizes the heat transfer path, resulting in more uniform thermal bonding between solder tip 3 and pad 4, contributing to the formation of solder joints with consistent metallurgical properties. This design provides an ideal spatial basis for achieving the highest quality solder joints, especially in applications requiring extremely high component positioning accuracy.

[0065] In this embodiment, the ratio of the length of the pad 4 to the length of the solder tip 3 is 0.9 to 1.1.

[0066] This length ratio range defines a near-uniform matching strategy between pad 4 and solder tip 3 in the length direction. Within this range, the length of pad 4 is very close to the length of solder tip 3, which helps to create a solder joint shape after reflow soldering where the solder 7 is mainly concentrated on the sidewalls of solder tip 3 rather than extending extensively to the end of solder tip 3. This shape generates a more vertical tensile component, thus providing additional upright stability to the component and effectively counteracting tilting moments. Combined with the equal-width pad 4 design, this ensures that pad 4 closely matches solder tip 3 in both length and width dimensions, working together to form a stress-balanced, contour-controlled solder joint. This close dimensional matching reduces over-reliance on solder 7 usage, lowers process sensitivity, and helps achieve a clean and reliable solder appearance in a compact space. Example 2

[0067] A printed circuit board having a PCB pad structure as described in Embodiment 1 above integrated on its board body.

[0068] This printed circuit board significantly improves process stability and product yield during the soldering process, especially when surface-mounting SMD diodes. Its fundamental advantage lies in the integrated optimized pad structure, which, through precise size matching and spatial positioning, effectively guides the molten solder to form a symmetrical meniscus, thereby fundamentally suppressing the tilting defect of SMD diodes after reflow soldering.

[0069] This precise control over component soldering posture provides crucial assurance for high-density, fine-pitch designs of printed circuit boards. When components can maintain a near-ideal upright position, the minimum electrical clearance between their bodies and solder tips and adjacent wiring and components can be reliably maintained. This directly reduces the potential risk of reduced electrical clearance or even bridging short circuits caused by component tilting, making it particularly suitable for modern electronic products with extremely high requirements for reliability and space utilization, such as communication equipment and portable consumer electronics.

[0070] Therefore, printed circuit boards using this pad structure not only improve the production yield and consistency of single-board assembly, but also lay a solid hardware foundation for the miniaturization, high integration and long-term stable operation of end products due to their excellent interconnect reliability.

[0071] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A PCB pad structure, characterized in that, The surface mount diode is mounted on a printed circuit board (1) and has a body (2) and solder terminals (3) located at both ends of the body (2). It includes a pair of pads (4) corresponding to the two solder terminals (3) respectively. The ratio of the width of the pads (4) to the width of the solder terminals (3) is 0.8 to 1.

2.

2. The PCB pad structure according to claim 1, characterized in that, The width of the pad (4) is equal to the width of the solder end (3).

3. The PCB pad structure according to claim 1 or 2, characterized in that, The length of the pad (4) is greater than or equal to the length of the solder end (3).

4. The PCB pad structure according to claim 3, characterized in that, The ratio of the length of the pad (4) to the length of the solder end (3) is 1.0 to 1.

5.

5. The PCB pad structure according to claim 1, characterized in that, It also includes a solder mask layer (5) disposed between the pair of pads (4), the solder mask layer (5) having a window (6) for exposing the soldering area of ​​the pads (4).

6. The PCB pad structure according to claim 5, characterized in that, The size of the window (6) matches the size of the pad (4), and the distance between its boundary and the edge of the pad (4) is 0.05-0.1 mm, so as to precisely define the spread range of the solder (7).

7. The PCB pad structure according to claim 1 or 2, characterized in that, The shape of the pad (4) is the same as that of the solder end (3). In the direction perpendicular to the printed circuit board (1), the projection of the pad (4) on the printed circuit board (1) basically coincides with the projection outline of the solder end (3).

8. The PCB pad structure according to claim 1 or 2, characterized in that, The ratio of the length of the pad (4) to the length of the solder end (3) is 0.9 to 1.

1.

9. The PCB pad structure according to claim 1 or 2, characterized in that, The center-to-center distance between the pair of pads is equal to the center-to-center distance between the two terminals of the surface mount diode.

10. A printed circuit board, characterized in that, It integrates the PCB pad structure as described in any one of claims 1 to 9.

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