A differential via structure, design method and printed circuit board

Abstract

The application discloses a differential via structure, a design method and a printed circuit board, relates to the field of circuit design, and is used for solving the problem that the differential via occupies a large space of the printed circuit board. The scheme is characterized in that two reflow vias are tangent to each other, and the two reflow vias are tangent to two signal vias respectively, symmetry is maintained between the signal vias and the reflow vias, the layout of the differential signal vias is optimized, the spacing between the differential signal vias is reduced, the wiring space on the printed circuit board is effectively saved, the structure is divided into three parts by adding a milled groove on the printed circuit board, the differential signal can be well isolated and reflowed between different parts, the isolation and reflow effect of the GND signal are enhanced, the integrity of the high-speed signal is improved, signal crosstalk in high-density design is reduced, high-density and miniaturization design are supported without increasing production difficulty, and the flexibility and replicability of the design are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of circuit design, in particular to a differential via structure, a design method and a printed circuit board. BACKGROUND

[0002] With the development of electronic information technology and the improvement of signal transmission rate, the requirements for signal performance and quality are also increasing, and the margin of link design is gradually reduced, which requires designers to handle various optimization problems more carefully in printed circuit board design to achieve performance optimization, cost minimization, shorten the design cycle and improve production efficiency.

[0003] In related printed circuit board and signal integrity design, differential via design is usually used, that is, a pair of differential signal lines (DP and DN respectively) correspond to a pair of GND signal reflow vias (as shown in Figure 1 However, with the increase in the number of high-speed signal pins of chips and connectors, the density of signal layer change vias in the fan-out area also increases, and the layout and wiring space required increases. With the improvement of signal rate, the optimization requirement for high-speed signal layer change via is higher, and the number of GND signal reflow via increases from one pair to two pairs or even three pairs, which occupies more space and is not conducive to high-density design of printed circuit board. SUMMARY

[0004] The purpose of the present application is to provide a differential via structure, a design method and a printed circuit board, which effectively saves the wiring space on the printed circuit board, and enables the differential signal to be well isolated and refluxed between different parts, not only enhancing the isolation and reflux effect of the GND signal, improving the integrity of the high-speed signal, but also reducing signal crosstalk in high-density design, thereby supporting high-density and miniaturization design without increasing production difficulty, improving design flexibility and replicability.

[0005] In a first aspect, the present application provides a differential via structure, comprising at least one via unit, the via unit comprising:

[0006] a first reflow via and a second reflow via, the first reflow via and the second reflow via being tangent;

[0007] a first signal via and a second signal via, the first signal via and the first reflow via being tangent, and the second signal via and the second reflow via being tangent;

[0008] The first signal via and the second signal via are symmetrical about a first tangent plane, the first tangent plane being a plane tangent to the two reflow vias, a first distance between a central axis of the first signal via and a central axis of the second signal via being not greater than a second distance between a central axis of the first reflow via and a central axis of the second reflow via;

[0009] At least two milling grooves, a first milling groove being used to separate the two reflow vias and the two signal vias, and a second milling groove being used to separate the two signal vias;

[0010] The first signal via is connected with a first signal line of a differential line, the second signal via is connected with a second signal line of the differential line, and the two reflow vias are signal reflow holes.

[0011] Optionally, a second tangent plane at which the first signal via and the first reflow via are tangent coincides with a third tangent plane at which the second signal via and the second reflow via are tangent, and the second tangent plane or the third tangent plane is perpendicular to the first tangent plane.

[0012] Optionally, the number of the milling grooves is 2.

[0013] A first milling groove is arranged along the second tangent plane or the third tangent plane, penetrates the two reflow vias and the two signal vias, and a length of the first milling groove is greater than or equal to 2 times a diameter of the reflow via plus 2 times a width of a pad outside the reflow via, the first milling groove being used to separate the two reflow vias and the two signal vias.

[0014] A second milling groove is arranged along the first tangent plane, penetrates the two reflow vias and the two signal vias, and a diameter of the signal via plus a width of a pad outside the signal via plus half of a diameter of the reflow via is less than or equal to a length of the second milling groove, which is less than or equal to the diameter of the signal via plus the width of the pad outside the signal via plus the diameter of the reflow via, the second milling groove being located between the two signal vias.

[0015] Optionally, there are a plurality of the via units, and in the plurality of the via units, central axes of all the reflow vias are on a first plane, and central axes of all the signal vias are on a second plane, the first plane being parallel to the second plane.

[0016] The plurality of the first milling grooves are integrally formed.

[0017] Optionally, the via units are multiple, the first tangent planes of all the via units coincide, the middle axis of the reflow via of the ith via unit and the middle axis of the reflow via of the i+2th via unit are on the same plane, the middle axis of the signal via of the ith via unit and the middle axis of the signal via of the i+2th via unit are on the same plane, i≥1, i is an integer;

[0018] The first milling grooves are integrally formed.

[0019] Optionally, the via units are multiple, the first milling grooves in every two adjacent via units are arranged in a staggered manner, so that the distance between the second milling grooves in the two adjacent via units is less than the width of the via unit.

[0020] The width of the via unit = 2 x the diameter of the reflow via + 2 x the width of the pad outside the reflow via.

[0021] Optionally, the diameter of the first reflow via and the diameter of the second reflow via are the same, the diameter of the first signal via and the diameter of the second signal via are the same, and the diameter of each reflow via is greater than the diameter of each signal via.

[0022] Optionally, the width of each milling groove is not less than the width of the pad outside the reflow via or the pad outside the signal via.

[0023] In a third aspect, the present application provides a printed circuit board comprising the differential via structure as described above.

[0024] In a third aspect, the present application provides a design method of a differential via structure, applied to the differential via structure as described above, comprising:

[0025] According to the target requirement and the board space of the printed circuit board, the target size of the differential via is determined;

[0026] The first reflow via and the second reflow via are drilled by using a first drill needle, and the first reflow via and the second reflow via are tangent to each other;

[0027] The first signal via and the second signal via are drilled by using a second drill needle, the first signal via and the first reflow via are tangent to each other, the second signal via and the second reflow via are tangent to each other, the first signal via and the second signal via are symmetric about a first tangent plane, the first tangent plane is the plane where the two reflow vias are tangent to each other, the first distance between the middle axis of the first signal via and the middle axis of the second signal via is not greater than the second distance between the middle axis of the first reflow via and the middle axis of the second reflow via;

[0028] Electroplating is performed on the two reflow through holes and the two signal through holes respectively;

[0029] At least two milling grooves are drilled by using a third drill bit, a first milling groove is used to separate the two reflow through holes and the two signal through holes, and a second milling groove is used to separate the two signal through holes; wherein the first signal through hole is connected with a first signal line of a differential line, the second signal through hole is connected with a second signal line of the differential line, and the two reflow through holes are used as signal reflow holes;

[0030] The milling grooves, the reflow through holes and the signal through holes are filled with resin.

[0031] The application provides a differential through hole structure, a design method and a printed circuit board, and relates to the field of circuit design, and aims to solve the problem that a differential through hole occupies a large space of a printed circuit board. The scheme is characterized in that two reflow through holes are tangent to each other, and two reflow through holes are tangent to two signal through holes respectively, symmetry is maintained between the signal through holes and the reflow through holes, the layout of the differential signal through holes is optimized, the spacing between the differential signal through holes is reduced, the wiring space on the printed circuit board is effectively saved, the structure is divided into three parts by adding milling grooves on the printed circuit board, the differential signal can be well isolated and reflowed between different parts, the isolation and reflow effect of the GND signal are enhanced, the integrity of the high-speed signal is improved, signal crosstalk in high-density design is reduced, high-density and small-size design are supported without increasing production difficulty, and the flexibility and replicability of the design are improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the application, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0033] Figure 1 A schematic diagram of a differential through hole structure in the related art;

[0034] Figure 2 A schematic diagram of the positions of four through holes in a differential through hole structure provided by the application;

[0035] Figure 3 A schematic diagram of the positions of four through holes and surrounding pads in a differential through hole structure provided by the application;

[0036] Figure 4 A complete schematic diagram of a differential through hole structure provided by the application;

[0037] Figure 5A first embodiment of the differential via structure provided by the present application is shown in the following figure.

[0038] Figure 6 A second embodiment of the differential via structure provided by the present application is shown in the following figure.

[0039] Figure 7 A third embodiment of the differential via structure provided by the present application is shown in the following figure.

[0040] Figure 8 A flow chart of the design method of the differential via structure provided by the present application is shown in the following figure. DETAILED DESCRIPTION

[0041] The core of the present application is to provide a differential via structure, a design method and a printed circuit board, which effectively saves the wiring space on the printed circuit board, enables the differential signal to be well isolated and backflowed between different parts, enhances the isolation and backflow effect of the GND signal, improves the integrity of the high-speed signal, reduces the signal crosstalk in high-density design, supports high-density and miniaturization design without increasing the production difficulty, and improves the design flexibility and replicability.

[0042] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0043] In a first aspect, as shown in the following figures, Figure 2 、 Figure 3 and Figure 4 The present application provides a differential via structure, comprising at least one via unit, the via unit comprising:

[0044] a first backflow via 11 and a second backflow via 12, the first backflow via 11 and the second backflow via 12 being tangent to each other;

[0045] a first signal via 21 and a second signal via 22, the first signal via 21 and the first backflow via 11 being tangent to each other, and the second signal via 22 and the second backflow via 12 being tangent to each other;

[0046] The first signal via 21 and the second signal via 22 are symmetrical about a first tangent plane, the first tangent plane being a plane tangent to the two reflow vias, and a first distance between a central axis of the first signal via 21 and a central axis of the second signal via 22 is not greater than a second distance between a central axis of the first reflow via 11 and a central axis of the second reflow via 12;

[0047] At least two milled slots, a first milled slot for separating the two reflow vias and the two signal vias, and a second milled slot for separating the two signal vias;

[0048] The first signal via is connected to a first signal line of the differential line, the second signal via is connected to a second signal line of the differential line, and the two reflow vias serve as signal reflow holes.

[0049] In this embodiment, the differential via structure uses two tangent reflow vias to achieve more effective signal reflow and isolation. It should be noted that all the vias in this application penetrate the first signal layer and the second signal layer of the PCB. Specifically, the two reflow vias are tangent to each other. The purpose of this tangent design is to maximize the use of wiring space while ensuring the continuity and symmetry of the GND signal. By increasing the density of the reflow vias, the length of the reflow path can be effectively reduced in high-speed signal transmission, thereby reducing signal loss and interference caused by path lengthening and improving the integrity of high-speed signals.

[0050] The tangent design of the first signal via 21 and the second signal via 22 is similar to the reflow via, and the purpose is to ensure the transmission symmetry of the differential signal. In design, the differential signal line needs to maintain strict symmetry to reduce differential mode interference and common mode noise. By making the first signal via 21 tangent to the first reflow via 11 and the second signal via 22 tangent to the second reflow via 12, it is ensured that the differential signal can be tightly coupled with the corresponding reflow path when switching, providing good signal reflow path and electromagnetic shielding effect.

[0051] The first signal via 21 and the second signal via 22 are symmetrical about a first tangent plane, the first tangent plane being a plane tangent to the two reflow vias. The symmetry of the differential via is crucial to the transmission quality of the differential signal, because the asymmetry of the signal line can cause inconsistent signal delay, thereby introducing differential mode interference. By ensuring the symmetry of the signal via and the reflow via, the signal delay difference can be reduced during high-speed signal switching, and reflection and signal integrity problems can be reduced. In addition, the central axis distance of the first signal via 21 and the second signal via 22 is not greater than the central axis distance of the two reflow vias, to further avoid occupying the space of the PCB board. This design can reduce the impedance mismatch of the differential signal, thereby reducing reflection and improving signal quality.

[0052] The at least two milling grooves added in this embodiment, the first milling groove is used to separate the two return vias and the two signal vias, and the second milling groove is used to separate the two signal vias, so as to divide the entire differential via structure into three parts. This partition design helps to further improve signal isolation, because the milling groove can effectively suppress the coupling and crosstalk between adjacent signals. The design of the milling groove can also form a clear physical boundary, which can constrain the electromagnetic field of each part within a specified area, thereby reducing electromagnetic interference in high-speed signal transmission. In addition, the milling groove can also optimize the current distribution, so that the transmission path of the differential signal in each part remains consistent, effectively improving signal integrity.

[0053] In an optional embodiment, the diameter of the first return via 11 and the diameter of the second return via 12 are the same, the diameter of the first signal via 21 and the diameter of the second signal via 22 are the same, and the diameter of each return via is greater than the diameter of each signal via. This design aims to ensure that the electrical performance of the two return vias is consistent, thereby providing uniform current distribution in the signal return path. The same diameter helps to ensure the stability of the transmission of the return signal, avoiding the problem of signal asymmetry or reflection caused by inconsistent sizes. The main function of the return via is to provide a channel for signal return, so its size design should give priority to meeting the needs of signal return while ensuring the electrical performance of the hole. At the same time, the diameter of the first signal via 21 and the diameter of the second signal via 22 are also the same, and the design principle is to ensure that the transmission characteristics of the two signal vias are consistent, reducing the problem of signal delay, distortion or mismatch that may be caused by different hole diameters. The size of the signal via needs to be accurately controlled to ensure the integrity and reliability of the signal, especially in the case of high-speed signal transmission, and mismatched via size may cause signal loss or interference. In addition, the diameter of the return via is larger than the diameter of the signal via, and the core of this design idea is to ensure that the impedance and current capacity of the signal return path can carry the return current of the high-speed signal, avoiding the phenomenon of overheating or electrical instability caused by excessive current density due to too small return via. Larger return via diameter helps to reduce the resistance and inductance of the return path, thereby improving the flow of current and the stability of the signal. This design also helps to achieve better electromagnetic compatibility on the PCB, reducing interference during signal transmission.

[0054] In an optional embodiment, the width of each milling groove is not less than the width of the pad 3 outside the reflow via or the pad 3 outside the signal via. The design requires that the width of each milling groove is not less than the width of the pad 3 outside the reflow via or the pad 3 outside the signal via. The core of this design idea is to ensure that the size of the milling groove can effectively accommodate and support the size of the corresponding pad 3 outside the reflow via or the signal via, avoiding interference or influence on the area of these pads 3 during the milling process. The pad 3 is an important part of connecting the signal via and the reflow via, and its width is usually determined according to the electrical connection requirements and mechanical strength requirements to ensure that the pad 3 can stably bear the solder joint. The width of the milling groove is not less than the width of these pads 3, firstly to ensure the machining precision of the milling groove, avoiding too narrow milling groove limiting the space between the reflow via and the signal via, thereby affecting the soldering quality. Too narrow milling groove may cause the pad 3 and the via to fail to form a reliable connection during soldering, affecting the stability of signal transmission and electrical performance. Secondly, a milling groove with appropriate width helps to provide sufficient space for the transition of signal and reflow path, reducing signal loss or reflow current resistance.

[0055] Through the above structural design, the differential via architecture reduces the differential via pitch without increasing the production complexity, thereby saving the PCB layout and wiring space, suitable for high-density and miniaturization design requirements. At the same time, this design can also enhance the GND signal isolation and reflow effect, improve the integrity of high-speed signals, and meet the strict requirements of modern high-speed circuits on signal quality and performance.

[0056] In an optional embodiment, the second tangent plane at the tangent of the first signal via 21 and the first reflow via 11 coincides with the third tangent plane at the tangent of the second signal via 22 and the second reflow via 12, and the second tangent plane or the third tangent plane is perpendicular to the first tangent plane.

[0057] In this embodiment, by making the second tangent plane at the tangent of the first signal via 21 and the first reflow via 11 coincide with the third tangent plane at the tangent of the second signal via 22 and the second reflow via 12, the symmetry of the differential signal on both sides is ensured. The coincident tangent plane design can accurately align the positions of the two pairs of signal and reflow vias, so that the differential signal via maintains strict mirror symmetry in structure, thereby reducing the offset or imbalance of the differential signal in the via area and improving the phase consistency of the signal. This symmetry can significantly reduce the common-mode noise in the differential signal, reduce the crosstalk between signals, and improve the signal integrity and anti-interference ability.

[0058] Furthermore, the design of a second or third tangent plane perpendicular to the first further enhances three-dimensional symmetry, ensuring a balanced arrangement of signal and return vias across different planes. This perpendicular plane layout not only reduces interference when differential signals are transmitted across a multilayer board, but also ensures the integrity and uniformity of the return path, providing a more stable return path for high-speed signals and better electromagnetic compatibility.

[0059] For example, Figure 2 As shown, the two reflow vias are equal in size and are horizontally tangent after electroplating. Their original diameter F is 12 mils, and the finished diameter E of the reflow vias after electroplating is 10 mils, i.e., E = F - 2 mils. The signal vias are equal in size, with an original diameter H of 8 mils. The finished diameter G of the signal vias after electroplating is 6 mils, i.e., G = H - 2 mils. The centers of the first reflow via 11 and the first signal via 21 are on the same centerline and are vertically tangent after electroplating. The centers of the second reflow via 12 and the second signal via 22 are on the same centerline and are vertically tangent after electroplating. The first signal via 21 and the second signal via 22 are on the same horizontal line.

[0060] like Figure 3 As shown, the width of pad 3 is 4 mils. The diameter P of pad 3 for the two reflow vias is 18 mils, i.e., P = E + 8 mils. The diameter Q of pad 3 for the two signal vias is 14 mils, i.e., Q = G + 8 mils.

[0061] As an optional embodiment, the number of milling slots is 2;

[0062] The first milling groove 41 is arranged along the second tangent plane or the third tangent plane, passes through the two reflow vias and the two signal vias, and the length of the first milling groove 41 is ≥ 2×the diameter of the reflow via+2×the width of the pad 3 outside the reflow via. The first milling groove 41 is used to separate the two reflow vias and the two signal vias;

[0063] The second milling groove 42 is arranged along the first cutting plane, passing through two reflow vias and two signal vias, and the diameter of the signal via + the width of the pad 3 outside the signal via + the diameter of the reflow via / 2 ≤ the length of the second milling groove 42 ≤ the diameter of the signal via + the width of the pad 3 outside the signal via + the diameter of the reflow via, and the second milling groove 42 is located between the two signal vias.

[0064] In this optional embodiment, two milling slots are designed to divide the differential via structure and enhance signal isolation and transmission quality. The first milling slot 41 is arranged along the second or third tangent plane, passing through the two return vias and the two signal vias, and its length satisfies the condition of being at least equal to twice the diameter of the return via plus twice the width of the return via external pad 3. This length is designed to ensure that the milling slot can cover the area of ​​the two return vias, provide sufficient electromagnetic isolation, and effectively block electromagnetic coupling between the return paths. Through this division, the two sides of the differential signal can be transmitted in independent parts, thereby reducing crosstalk between signals and improving signal integrity and stability.

[0065] The second milled slot 42 is arranged along the first tangent plane, extending through the two return vias and the two signal vias, and located between the two signal vias. The length of the second milled slot must meet a minimum range: the signal via diameter plus the width of its outer pad 3 plus half the return via length; the maximum length is the signal via diameter plus the pad 3 width plus the return via diameter. This design ensures that the second milled slot provides adequate isolation without excessively cutting into the return path. This limited range helps effectively partition the via structure while avoiding structural instability caused by slots that are too long or too short. The second milled slot, located between the signal vias, further reduces mutual interference between the differential signal pairs and achieves more efficient signal isolation without compromising signal integrity. This milled slot layout provides sufficient signal isolation in miniaturized PCB designs, ensuring electrical symmetry and a good return path for the signal and return vias within the via structure, thereby meeting the electromagnetic compatibility and signal integrity requirements of high-speed signal designs.

[0066] like Figure 4 As shown, the length of the first milling groove 41 is L and the width is K. The first milling groove 41 is centered on the symmetry center point of the four circles. The length L needs to ensure that the two reflow vias and the two signal vias are completely disconnected, so the minimum value of L is equal to the diameter of the two reflow vias plus the width of the pad 3, that is, Lmin=E+E+8mil. The width K needs to be larger than the ring width of the pad 3, that is, Kmin=4mil. The length of the second milling groove 42 is M and the width is N. The second milling groove 42 is centered on the symmetry axis of the two reflow vias. The pads 3 of the two reflow vias are not milled off at the top, and the pads 3 of the two signal vias need to be milled off at the bottom, so Mmin=1 / 2E+G+4mil. The width N needs to be larger than the ring width of the pad 3, that is, Nmin=4mil.

[0067] Through the arrangement of the two milling grooves, the differential via structure is divided into three parts in space, which are respectively used for transmitting DP, DN and GND signals, effectively improving the isolation between signals and ensuring higher signal integrity in high-frequency high-speed applications. Without increasing the area of the PCB, the design effectively suppresses various interference factors in the process of high-speed signal transmission and provides more reliable return flow path support for differential signals, which helps to improve the stability and reliability of the overall circuit performance.

[0068] As shown in Figure 5 , a distribution of two via units is shown. Figure 5 As shown in

[0069] As shown in Figure 6 , as an optional embodiment, the via unit has a plurality of via units, and the central axes of all the return flow vias in the plurality of via units are on the first plane, and the central axes of all the signal vias are on the second plane, and the first plane and the second plane are parallel;

[0070] The plurality of first milling grooves 41 are integrally formed.

[0071] In this embodiment, the via unit includes two return flow vias, two signal vias and two milling grooves, which realize a more complete high-speed signal differential via unit and have better isolation and symmetry. The design of the plurality of via units ensures that the central axes of the return flow vias and the signal vias of each via unit are on the first plane and the second plane, respectively, and the two planes are parallel to each other, which ensures the overall symmetry of the units when arranged longitudinally, reduces the phase difference and reflection problem in the process of signal transmission. The parallel plane arrangement helps to ensure the consistency of the signal path in the multi-layer board design and improve the integrity of the high-speed signal.

[0072] In the plurality of via units, the first milling grooves 41 can be made into through grooves by integral molding, thereby forming a continuous physical isolation channel in the whole row of via structures. This through groove design simplifies the processing flow and reduces the manufacturing complexity, which is helpful for arranging multiple high-speed signal differential via units, such as 4, 8 or 16, in a row, facilitating the layer change operation of a group of high-speed signals. The structure of the through groove also improves the isolation effect between signals, further plays the shielding role of the GND signal, reduces the electromagnetic interference between signals, and ensures the signal transmission quality. When multiple groups of layer change vias need to be distributed side by side, the through groove provides a unified isolation channel, so that multiple differential signals can be stably transmitted on the same plane, while effectively reducing the noise coupling and interference between layers. This design also meets the high-density and high-speed PCB design requirements, so that the high-speed signal transmission has better electromagnetic compatibility on the basis of maintaining signal integrity.

[0073] As an optional embodiment, there are multiple via units, the first tangent planes of all the via units coincide, the central axis of the reflow via of the i-th via unit and the central axis of the reflow via of the i+2-th via unit are on the same plane, the central axis of the signal via of the i-th via unit and the central axis of the signal via of the i+2-th via unit are on the same plane, i≥1, i is an integer;

[0074] The multiple first milling grooves 41 are integrally formed.

[0075] In this embodiment, the via unit is composed of two reflow vias, two signal vias and two milling grooves, forming a structured differential via design to improve the density and signal transmission quality of the PCB design. The design of multiple via units ensures that the same first tangent planes coincide, that is, the tangent planes of all these structures are on the same horizontal plane, thereby providing higher symmetry and consistency, ensuring that the layout of the signal vias and the reflow vias has uniformity on different parts of the PCB.

[0076] Specifically, the central axes of the reflow vias of the i-th via unit and the i+2-th via unit in the design are on the same plane, which ensures the consistency and stability of the reflow path between multiple structures, reducing signal reflection or reflow path interference caused by misalignment of vias. Similarly, the central axes of the signal vias of the i-th and i+2-th via units are also on the same plane, ensuring good symmetry of the signal path, thereby enhancing the transmission stability of the differential signal and reducing the risk of crosstalk.

[0077] The implementation of this design simplifies the manufacturing and layout process by keeping multiple via units sharing a common tangent plane. The multiple via units are further optimized for production efficiency through a unified milling groove design (i.e., the multiple first milling grooves 41 are integrally formed). By integrally forming the milling grooves, the precise position of each via unit can be ensured, and the electrical signals between the vias can be effectively isolated, reducing cross-interference while reducing the difficulty and time cost in the manufacturing process. This design not only improves electromagnetic compatibility, but also enables higher density wiring design on the PCB, adapting to the transmission needs of high-performance, high-speed signals.

[0078] As shown in Figure 7 As an optional embodiment, there are multiple via units, the first milling grooves 41 of every two adjacent via units are misaligned to make the distance between the second milling grooves 42 of the two adjacent via units < the width of the via unit.

[0079] The width of the via unit = 2 x diameter of the reflow via + 2 x width of the pad 3 outside the reflow via.

[0080] In this embodiment, the via unit includes two return vias, two signal vias, and two milling slots. This design aims to optimize PCB space utilization and design density while ensuring signal transmission quality. The first milling slots 41 in the multiple via units are staggered to reduce the close arrangement of the via units, thereby maintaining a small spacing between adjacent milling slots (less than the overall width of the via unit). This staggered arrangement optimizes the distance between the second milling slots 42 in the via units, avoiding overcrowding between the via units, providing more isolation space for signal transmission, and also helping to reduce interference and reflection between signals.

[0081] The width of a via unit is defined as twice the diameter of the reflow via plus twice the width of the reflow via outer pad 3. This ensures sufficient layout space and avoids space constraints during dense signal routing. This design allows for wider spacing between via units during routing, while also improving PCB manufacturing accuracy and workability.

[0082] When designing multiple vias side-by-side, the design isn't limited to simply arranging them on the same horizontal line. To further optimize signal integrity, a staggered placement can be employed, such as one high and one low, or staggered with equal spacing. This design helps reduce unnecessary crosstalk and electromagnetic interference at the electrical level. This is especially true for differential signal transmission, where the side-by-side placement of DP (positive differential signal) and DN (negative differential signal) signal vias can cause significant crosstalk.

[0083] To further reduce crosstalk and improve signal integrity, the design also proposes a rotational layout: the DP and DN signal vias rotate 180 degrees for every other via unit. This layout ensures increased distance between adjacent differential signal pairs while effectively isolating the signals through the spaced GND signal vias. Because adjacent differential signal pairs are shielded by the GND signal, mutual interference (crosstalk) between the signals is significantly reduced, thereby improving the integrity and stability of high-speed signals. This optimized design effectively reduces unnecessary interference and loss during high-frequency signal transmission of differential signal pairs, enhancing the signal transmission performance of the overall PCB design.

[0084] In a third aspect, the present application provides a printed circuit board comprising the differential via structure as described above.

[0085] Thirdly, as Figure 8 As shown, the present application provides a design method for a differential via structure, including:

[0086] S11: Determine the target size of the differential via according to target requirements and the board space of the printed circuit board;

[0087] In this step, the size of the differential via is determined according to the functional requirements and available space of the circuit board before the design begins. The designer needs to consider multiple factors, including the frequency of the signal, the space limitation of the board, the electrical performance requirements, and the manufacturing process, etc. The determination of the target size ensures that the differential signal can be effectively transmitted in the specified space without compromising the integrity of the signal and the overall performance of the board. At this stage, the designer needs to comprehensively analyze the length of the signal line, the transmission speed, the signal strength, and the number of layers of the PCB, so as to determine the size of the via to meet the design requirements.

[0088] S12: drilling the first and second reflow vias with the first drill bit;

[0089] The first and second reflow vias are tangent to each other;

[0090] This step completes the processing of the reflow via by using the first drill bit. These reflow vias are used to provide a signal return path to ensure the integrity of the differential signal between the two layers. The two reflow vias pass through the two layers of the printed circuit board (the first signal layer and the second signal layer), and are tangent to each other. The tangent design of the reflow via helps to improve the stability of the signal return path, reduce electrical noise, and avoid signal interference. This design can ensure that the signal return path closely cooperates with the signal transmission path, further improving the electrical performance of the PCB.

[0091] S13: drilling the first and second signal vias with the second drill bit;

[0092] The first signal via is tangent to the first reflow via, and the second signal via is tangent to the second reflow via; the first signal via and the second signal via are symmetric about the first tangent plane, which is the plane where the two reflow vias are tangent to each other; the first distance between the central axis of the first signal via and the central axis of the second signal via is not greater than the second distance between the central axis of the first reflow via and the central axis of the second reflow via;

[0093] This step uses the second drill bit to drill the signal via and ensures that the signal via is tangent to the reflow via to ensure that the signal transmission path and the return path are coordinated. The design of the signal via is the key to the layer change of the differential signal line, and the symmetry design is achieved through the layout of the signal via to reduce signal crosstalk and optimize signal integrity. The key design idea here is to precisely control the relative position between the signal via and the reflow via to ensure that the distance difference between them is within an acceptable range (i.e., not greater than a preset value). By precisely controlling these dimensions, the design can ensure that signal loss and interference are minimized during high-speed signal transmission.

[0094] S14: electroplating the two reflow vias and the two signal vias, respectively;

[0095] In this step, the electroplating process is to enhance the conductivity of the via. During the electroplating process, metal material (such as copper) will be deposited on the inner wall of the via, forming a conductive layer to ensure reliable signal transmission and electrical connection. Both reflow vias and signal vias require electroplating treatment, as these vias need to connect different layers of the printed circuit board and maintain signal integrity and transmission stability. The thickness and uniformity of the electroplated layer directly affect the quality of signal transmission, so this step is crucial to ensure the stability and reliability of the signal transmission path.

[0096] S15: Drill at least two milling grooves with a third drill bit;

[0097] The first milling groove is used to separate the two reflow vias and the two signal vias, and the second milling groove is used to separate the two signal vias; wherein the first signal via is connected to the first signal line of the differential line, the second signal via is connected to the second signal line of the differential line, and the two reflow vias are used as signal reflow holes;

[0098] In this step, by using a third drill bit, the PCB is divided into three main parts through milling, ensuring that each part is connected to different signal channels and reflow paths. The design of the milling groove ensures that the reflow via and the signal via are located in different parts, ensuring effective isolation of the signal and reflow paths, and improving the integrity of the signal. By reasonably dividing the structure of the PCB, the milling groove design can effectively optimize the layout of the signal transmission path and the reflow path, thereby improving the overall performance.

[0099] S16: Fill the milling grooves, reflow vias and signal vias with resin.

[0100] In this step, after the milling groove and via processing is completed, the resin filling is used to fix and seal the via area, enhance the structural stability, and prevent the signal path from being disturbed. Resin filling can also provide additional mechanical support to ensure that the milling groove and via area will not be damaged due to vibration or external force during use. In addition, the use of resin can also reduce signal crosstalk and effectively isolate different signal channels, ensuring that the electrical performance of the PCB is effectively guaranteed. This step is necessary to ensure the long-term stability and high reliability of the entire differential via structure.

[0101] The embodiment connects four via holes together by electroplating copper on the inner wall of the via holes. Then, the via hole unit for high-speed signals is divided into three parts by the milling groove process, which respectively transmits DP, DN and GND signals. Finally, the drilling and milling groove parts are filled with resin to reduce the loss and crosstalk of high-speed signals at the via holes, optimize the electrical performance of the PCB, and improve the transmission quality of the signals. In summary, the differential via hole structure obtained by using the design method of the differential via hole structure provided in the application effectively saves the wiring space on the printed circuit board, can make the differential signals get good isolation and reflux channel between different parts, not only enhances the isolation and reflux effect of the GND signal, improves the integrity of the high-speed signal, but also reduces the signal crosstalk in high-density design, thereby supporting high-density and miniaturization design without increasing the production difficulty, and improving the flexibility and replicability of the design.

[0102] As an optional embodiment, the method further includes testing the differential via hole structure to determine whether the differential via hole structure meets a preset test result.

[0103] If the preset test result is met, the differential via hole structure is determined as the final differential via hole structure. Specifically, testing the differential via hole structure to determine whether the differential via hole structure meets a preset test result includes: determining whether the electroplated copper of the first signal via hole for transmitting the first signal line and the second signal via hole for transmitting the second signal line is damaged; respectively performing open circuit tests on the first signal line of the first signal layer and the first signal line of the second signal layer, and performing open circuit tests on the second signal line of the first signal layer and the second signal line of the second signal layer, to determine whether there is an electrical connection between the signal lines corresponding to the first signal layer and the second signal layer; respectively performing short circuit tests on the first signal line and the second signal line of the first signal layer, and the first signal line and the second signal line of the second signal layer, to determine whether there is an electrical connection between the two signal lines of the first signal layer and the two signal lines of the second signal layer; if the electroplated copper of the first signal via hole for transmitting the first signal line and the second signal via hole for transmitting the second signal line is not damaged, there is an electrical connection between the signal lines corresponding to the first signal layer and the second signal layer, and there is no electrical connection between the two signal lines of the first signal layer and the two signal lines of the second signal layer, it is determined that the differential via hole structure meets the preset test result.

[0104] Check the damage of electroplated copper: the purpose is to ensure that the copper layer of the electroplated via hole is not mechanically or chemically damaged during production, and maintains its good electrical conductivity. If the electroplated copper layer is damaged, it may cause unstable signal transmission or poor electrical connection.

[0105] Open circuit test on signal lines: test the first signal line of the first signal layer and the first signal line of the second signal layer, and the second signal line of the first signal layer and the second signal line of the second signal layer respectively. The purpose of these tests is to verify whether there is a correct electrical connection between the signal lines of the vias, that is, to ensure that the signals between the first signal layer and the second signal layer can be normally transmitted through the first signal via without being cut off. That is, the open circuit test aims to confirm whether the signal lines are normally connected, and if there is an electrical connection between the signal lines, it means that the first via correctly completes the signal transmission path.

[0106] Short circuit test on signal lines: test the first signal line and the second signal line of the first signal layer, and the first signal line and the second signal line of the second signal layer respectively. The purpose of this step is to ensure that there is no unwanted electrical short circuit in the design of the first via, that is, to confirm that there is no unexpected electrical connection between the signal lines. That is, the short circuit test is used to verify whether there is an unexpected electrical connection between the signal lines. If the test result shows that there is a short circuit connection between the signal lines, it may mean that the design has defects and needs to be adjusted.

[0107] By checking whether the electroplated copper is damaged and performing open circuit test, it can be ensured that the electroplated via will not have signal transmission problems in actual use; short circuit test can confirm whether the design of two signal vias effectively avoids unwanted signal interference, thereby ensuring the purity of the signal and the electrical performance; the design condition that meets all the preset test results indicates that the design architecture of the differential via can stably run in actual application, thereby meeting the design requirements and ensuring the performance and reliability of the circuit board.

[0108] Overall, this design method, through the fine control of each step, not only ensures the integrity of the signal and the electrical performance, but also effectively improves the space utilization efficiency of the PCB design, reduces the production complexity and cost, and provides a solid foundation for the realization of high-density and high-performance electronic equipment. For other introductions of the design method of the differential via structure, please refer to the above examples, and the present application will not be repeated here.

[0109] It is also noted that, in this disclosure, relational terms such as first and second, and the like, can be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0110] The above description of disclosed embodiments provides enabling concepts for practicing or using the application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A differential via structure, characterized in that: The method comprises at least one via unit, wherein the via unit comprises: a first return via and a second return via, wherein the first return via and the second return via are tangent to each other; a first signal via and a second signal via, wherein the first signal via and the first return via are tangent to each other, and the second signal via and the second return via are tangent to each other; The first signal via and the second signal via are symmetrical about a first tangent plane, the first tangent plane being a plane where the two return vias are tangent to each other, and a first distance between a central axis of the first signal via and a central axis of the second signal via is not greater than a second distance between a central axis of the first return via and a central axis of the second return via; at least two milling grooves, a first milling groove is used to separate the two return vias and the two signal vias, and a second milling groove is used to separate the two signal vias; The first signal via is connected to the first signal line of the differential line, the second signal via is connected to the second signal line of the differential line, and the two return vias serve as signal return holes.

2. The differential via structure according to claim 1, wherein: A second tangent plane where the first signal via and the first return via are tangent coincides with a third tangent plane where the second signal via and the second return via are tangent, and the second tangent plane or the third tangent plane is perpendicular to the first tangent plane.

3. The differential via structure according to claim 2, wherein: The number of the milling slots is 2; The first milling groove is arranged along the second tangent plane or the third tangent plane, passes through the two return vias and the two signal vias, and the length of the first milling groove is ≥ 2×the diameter of the return via+2×the width of the pad outside the return via, and the first milling groove is used to separate the two return vias and the two signal vias; The second milling groove is arranged along the first cutting plane, passing through the two return vias and the two signal vias, and the diameter of the signal via + the width of the pad outside the signal via + the diameter of the return via / 2 ≤ the length of the second milling groove ≤ the diameter of the signal via + the width of the pad outside the signal via + the diameter of the return via, and the second milling groove is located between the two signal vias.

4. The differential via structure according to claim 3, wherein: There are a plurality of via units, and in the plurality of via units, central axes of all the return vias are on a first plane, and central axes of all the signal vias are on a second plane, and the first plane and the second plane are parallel; The plurality of first milling grooves are integrally formed.

5. The differential via structure according to claim 3, wherein: There are a plurality of via units, and the first milling grooves in every two adjacent via units are staggered so that the distance between the second milling grooves in the two adjacent via units is less than the width of the via unit; The width of the via unit=2×the diameter of the reflow via+2×the width of the pad outside the reflow via.

6. The differential via structure according to any one of claims 1 to 5, wherein: The diameter of the first return via is the same as that of the second return via, the diameter of the first signal via is the same as that of the second signal via, and the diameter of each return via is larger than the diameter of each signal via.

7. The differential via structure according to any one of claims 1 to 5, wherein: The width of each of the milling grooves is not less than the width of the pad outside the reflow via or the pad outside the signal via.

8. A printed circuit board, characterized in that: The method comprises the differential via structure according to any one of claims 1 to 7.

9. A design method for a differential via structure, characterized in that: The differential via structure according to any one of claims 1 to 7 comprises: Determine the target size of the differential vias based on target requirements and printed circuit board space; Drilling a first return via hole and a second return via hole using a first drill needle, wherein the first return via hole and the second return via hole are tangent to each other; Drilling a first signal via and a second signal via using a second drill bit, wherein the first signal via and the first return via are tangent to each other, and the second signal via and the second return via are tangent to each other; the first signal via and the second signal via are symmetrical about a first tangent plane, which is a plane where the two return vias are tangent to each other, and a first distance between a central axis of the first signal via and a central axis of the second signal via is no greater than a second distance between a central axis of the first return via and a central axis of the second return via; performing electroplating treatment on the two reflow vias and the two signal vias respectively; Drilling at least two milling grooves using a third drill bit, wherein the first milling groove is used to separate the two return vias and the two signal vias, and the second milling groove is used to separate the two signal vias; wherein the first signal via is connected to the first signal line of the differential line, the second signal via is connected to the second signal line of the differential line, and the two return vias serve as signal return holes; The milling groove, the reflow via and the signal via are filled with resin.

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