PCB quasi-coaxial differential via hole structure

Abstract

The utility model discloses a PCB (Printed Circuit Board) quasi-coaxial differential via hole structure, which relates to the technical field of PCB design and comprises a first signal layer exchange hole and a second signal layer exchange hole arranged in parallel with the first signal layer exchange hole at an interval, the first signal layer change hole is located in the first ground wall hole and is coaxial with the first ground wall hole, and an insulating medium is filled between the inner wall of the first ground wall hole and the outer wall of the first signal layer change hole; the second signal layer changing hole is located in the second ground wall hole and is coaxial with the second ground wall hole, and an insulating medium is filled between the inner wall of the second ground wall hole and the outer wall of the second signal layer changing hole; and the outer walls of the first ground wall hole and the second ground wall hole are connected with a ground plane in the PCB. The structure can effectively reduce crosstalk and noise of the signal layer change hole, and effectively alleviate the problem of discontinuous impedance at the via hole.

Description

TECHNICAL FIELD

[0001] The utility model relates to PCB design technical field especially a kind of PCB coaxial differential via hole structure. BACKGROUND

[0002] Printed circuit board (PCB) is important electronic component manufactured with copper foil substrate as raw material, and is the support body and the carrier of electrical connection of electronic component. Since it is made by electronic printing, it is called "printed" circuit board. PCB can be divided into single-sided board, double-sided board, four-layer board, six-layer board and other multi-layer circuit board according to the number of circuit board layers. In double-sided board and multi-layer board, in order to connect the printed conductors between layers, a common hole is drilled at the intersection of conductors needing to be connected in each layer, and then copper is plated on the hole wall to form a conductive channel, i.e. via hole. Via hole can be generally divided into three categories: through hole, blind hole and buried hole.

[0003] As shown in Figure 1 Blind hole refers to a hole located on the top layer or bottom layer surface of the printed circuit board, having a certain depth, and used for connecting surface layer circuit and inner layer circuit. The depth of the hole is usually not more than a certain ratio of the hole diameter. Buried hole refers to a connecting hole located in the inner layer of the printed circuit board, which does not extend to the surface of the circuit board. Through hole is a hole that penetrates through the entire circuit board, which can be used for internal interconnection or as a mounting positioning hole for components. Since through hole is easier to implement in process and has lower cost, through hole design is generally used in printed circuit board.

[0004] When the transmission signal rate is lower than Gpbs (gigabit per second), the via hole can play a good signal connection role, and its parasitic capacitance and inductance can be ignored. When the transmission signal rate reaches Gpbs, the parasitic effect of the via hole on signal integrity cannot be ignored. At this time, the via hole behaves as an impedance discontinuity breakpoint in the transmission path, which can cause signal reflection, delay, attenuation and other signal integrity problems. When the signal rate reaches 5Gpbs or above, it is necessary to consider adding a ground hole near the signal via hole, commonly known as a companion ground hole. The ground hole can provide a better current return path for signal transmission, reduce signal interference, and thus improve signal quality. Under high-frequency signals, the ground hole can help to disperse the same-direction current, reduce mutual inductance, and thus reduce impedance, reducing the problem of impedance mismatch in signal transmission. Therefore, in high-speed PCB board, the practitioner must consider the optimization of the via hole to solve the problem of signal integrity caused by impedance discontinuity at the via hole.

[0005] The prior art uses means such as removing non-functional pads, reducing pads, increasing anti-pads, back drilling, adding companion ground holes to solve the problem of impedance discontinuity of high-speed via hole. However, these technical means often cannot be effectively implemented.

[0006] Specifically, removing non-functional pads can alleviate the impact of via impedance discontinuity to some extent, but cannot accurately compensate for impedance deviation; the size and shape of the pads have a direct impact on the welding quality and reliability, and reducing the size of the pads may cause various problems during welding, such as insufficient solder coverage of the pads, insufficient solder joint strength, poor welding, etc., thereby affecting the overall performance and stability of the circuit board.

[0007] Due to the limitation of layout space, the via anti-pad at the FPGA pad cannot be too large, and the anti-pad at this place is too large, which has the risk of signal cross partition, which will further exacerbate the impedance discontinuity of the signal. Using the back drilling technology will greatly increase the cost of manufacturing the board. Secondly, back drilling requires a certain drilling depth requirement, and the pin length limit at the connector also needs to be considered, and due to the existence of objective errors, in order to ensure that the signal line will not be drilled off, back drilling will control a certain safety distance, which actually cannot completely eliminate the stub; under normal circumstances, the higher the signal rate, the more ground holes are beneficial to signal quality. However, due to space limitations and manufacturing processing capabilities, the number of ground holes is limited. Practical new type content

[0008] The applicant proposes a PCB coaxial differential via structure in view of the above problems and technical needs. The technical scheme of the present application is as follows:

[0009] A PCB coaxial differential via structure, comprising a first signal layer-changing hole and a second signal layer-changing hole arranged in parallel and spaced apart from the first signal layer-changing hole;

[0010] The first signal layer-changing hole is located in the first ground wall hole and is coaxially arranged with the first ground wall hole, and the inner wall of the first ground wall hole and the outer wall of the first signal layer-changing hole are filled with an insulating medium;

[0011] The second signal layer-changing hole is located in the second ground wall hole and is coaxially arranged with the second ground wall hole, and the inner wall of the second ground wall hole and the outer wall of the second signal layer-changing hole are filled with an insulating medium;

[0012] The outer walls of the first ground wall hole and the second ground wall hole are connected with the ground plane in the PCB.

[0013] A further technical scheme is that the upper end of the first signal layer-changing hole is connected with a first transmission signal line through a first signal pad, and the lower end of the first signal layer-changing hole is connected with a second transmission signal line through a second signal pad.

[0014] A further technical scheme is that the upper end of the second signal layer-changing hole is connected with a third transmission signal line through a third signal pad, and the lower end of the second signal layer-changing hole is connected with a fourth transmission signal line through a fourth signal pad.

[0015] Further, the interval between the first signal layer change hole and the second signal layer change hole is 0.65mm-1.27mm.

[0016] Further, the first ground wall hole and the second ground wall hole have the same diameter, and the first signal layer change hole and the second signal layer change hole have the same diameter.

[0017] Further, the length of the first ground wall hole is less than the length of the first signal layer change hole, and the length of the second ground wall hole is less than the length of the second signal layer change hole.

[0018] Further, the impedance Z0 of the coaxial-like differential via hole structure can be expressed as:

[0019]

[0020] Wherein, ε r represents the relative dielectric constant of the insulating medium, D represents the diameter of the first ground wall hole and the second ground wall hole, and d represents the diameter of the first signal layer change hole and the second signal layer change hole.

[0021] The beneficial technical effects of the utility model are:

[0022] The utility model provides a kind of PCB coaxial-like differential via hole structure, compared with ordinary PCB via hole, the via hole structure is correspondingly set with coaxial ground wall hole outside each signal layer change hole, ground wall hole is similar to the outer metal wall of coaxial cable, ground wall hole outer wall is connected to the ground plane that provides excellent return path, can shield signal interference well, to reduce crosstalk, noise.And the impedance of the differential via hole structure is more easily accurate calculation, by controlling the diameter size of ground wall hole and signal layer change hole, the desired target impedance value can be more conveniently reached, effectively alleviate the impedance discontinuity problem of via hole.Eliminate the need to increase additional ground via basically, and space efficiency is higher, and anti-interference ability is strong. DRAWINGS

[0023] Figure 1 It is the schematic diagram of via hole, blind hole and buried hole provided by the utility model.

[0024] Figure 2 It is the three-dimensional schematic diagram of one embodiment of PCB coaxial-like differential via hole structure provided by the utility model.

[0025] Figure 3 It is the cross-sectional schematic diagram of one embodiment of first signal layer change hole and first ground wall hole provided by the utility model.

[0026] Figure 4 It is the overhead schematic diagram of one embodiment of first signal layer change hole and first ground wall hole provided by the utility model.

[0027] Figure 5 The simulation comparison result of the TDR impedance curve is provided by the utility model.

[0028] Figure 6 The simulation comparison result of the return loss is provided by the utility model.

[0029] Figure 7 The simulation comparison result of the insertion loss is provided by the utility model.

[0030] Reference signs:

[0031] 1-first signal layer hole, 2-second signal layer hole, 3-ground plane, 10-first ground wall hole, 20-second ground wall hole, 11-first signal pad, 12-second signal pad, 13-third signal pad, 14-fourth signal pad, 21-first transmission signal line, 22-second transmission signal line, 23-third transmission signal line, 24-fourth transmission signal line. DETAILED DESCRIPTION

[0032] The specific embodiment of the utility model is further explained in combination with the drawings.

[0033] The utility model provides a kind of PCB coaxial differential via structure, including first signal layer hole 1 and the second signal layer hole 2 being arranged in parallel interval with first signal layer hole 1;

[0034] The first signal layer hole 1 is located in the first ground wall hole 10 and is coaxially arranged with the first ground wall hole 10, and the inner wall of the first ground wall hole 10 is filled with insulating medium between the outer wall of the first signal layer hole 1;

[0035] The second signal layer hole 2 is located in the second ground wall hole 20 and is coaxially arranged with the second ground wall hole 20, and the inner wall of the second ground wall hole 20 is filled with insulating medium between the outer wall of the second signal layer hole 2;

[0036] The outer wall of the first ground wall hole 10 and the second ground wall hole 20 is connected with the ground plane in PCB.

[0037] Figure 2 The utility model provides a kind of PCB coaxial differential via structure, including first signal layer hole 1 and the second signal layer hole 2 being arranged in parallel interval with first signal layer hole 1;

[0038] Similar to the positional relationship between the first signal transition hole 1 and the first ground wall hole 10, the second ground wall hole 20 is filled with an insulating medium, and the second signal transition hole 2 is coaxially arranged through the insulating medium filled in the second ground wall hole 20. The diameter of the second signal transition hole 2 is smaller than that of the second ground wall hole 20, so that the second ground wall hole 20 surrounds the second signal transition hole 2, and the inner wall of the second ground wall hole 20 and the outer wall of the second signal transition hole 2 are insulated and separated by the insulating medium.

[0039] The first ground wall hole 10 and the second ground wall hole 20 are mutually independent through holes. Optionally, the outer walls of the first ground wall hole 10 and the second ground wall hole 20 can be in contact or not in contact. The ground plane is a conductive layer in the PCB for providing a common reference point and a return path. Connecting the first ground wall hole 10 and the second ground wall hole 20 to the ground plane can shield signal interference, thereby reducing crosstalk and noise of the signal transition hole and effectively alleviating the impedance discontinuity problem at the through hole.

[0040] The upper end of the first signal transition hole 1 is connected to the first transmission signal line 21 through the first signal pad 11, and the lower end of the first signal transition hole 1 is connected to the second transmission signal line 22 through the second signal pad 21, so as to form a first signal transmission path. The first signal in the differential signal pair can be transmitted along the transmission path of the first transmission signal line 21-first signal pad 11-first signal transition hole 1-second signal pad 21-second transmission signal line 22. The upper end of the second signal transition hole 2 is connected to the third transmission signal line 23 through the third signal pad 13, and the lower end of the second signal transition hole 2 is connected to the fourth transmission signal line 24 through the fourth signal pad 14, so as to form a second signal transmission path. The second signal in the differential signal pair can be transmitted along the transmission path of the third transmission signal line 23-third signal pad 13-second signal transition hole 2-fourth signal pad 24-fourth transmission signal line 24.

[0041] To avoid the first ground wall hole 10 from being mistakenly contacted with the first signal pad 11 or the second signal pad 12, and to avoid the second ground wall hole 20 from being mistakenly contacted with the third signal pad 13 or the fourth signal pad 14, the length of the first ground wall hole 10 is slightly smaller than the length of the first signal transition hole 1, and the length of the second ground wall hole 20 is slightly smaller than the length of the second signal transition hole 2.

[0042] Figure 3 The cross-sectional schematic diagram of the through hole structure is illustrated by taking the first signal transition hole 1 and the first ground wall hole 10 as an example. In this embodiment, the first signal transition hole 1 is a via hole. Figure 3 Similarly, the second ground wall hole 20 can also be connected to multiple ground planes at the same time.

[0043] Further, the interval between the first signal via hole 1 and the second signal via hole 2 ranges from 0.65mm to 1.27mm. The interval between the first signal via hole 1 and the second signal via hole 2 refers to the distance between the center of the first signal via hole 1 and the center of the second signal via hole 2.

[0044] In order to facilitate the calculation of the impedance of the coaxial-like differential via structure, the diameter of the first ground wall hole 10 and the second ground wall hole 20 is the same, and the diameter of the first signal via hole 1 and the second signal via hole 2 is the same. The impedance Z0 of the coaxial-like differential via structure can be expressed as:

[0045]

[0046] Wherein, ε r represents the relative dielectric constant of the insulating medium, D represents the diameter of the first ground wall hole 10 and the second ground wall hole 20, and d represents the diameter of the first signal via hole 1 and the second signal via hole 2. Figure 4 The top view of the via structure is illustrated by taking the first signal via hole 1 and the first ground wall hole 10 as an example.

[0047] The impedance of the differential via structure is easier to calculate accurately, and the desired target impedance value can be more conveniently achieved by controlling the diameter of the ground wall hole and the signal via hole. As an application example, the impedance control is performed on a certain high-speed 12-layer PCB, the overall thickness of the PCB is 2mm, the substrate uses Panasonic R-5775G, the differential signal impedance is required to be 100 ohms, and the impedance control deviation is 10%. Under the premise of meeting the via thickness-diameter ratio, the interval between the first signal via hole 1 and the second signal via hole 2 is 1mm, the first signal via hole 1 and the second signal via hole 2 adopt type 8-18, that is, the diameter of the first signal via hole 1 and the second signal via hole 2 is 8mil, and the diameter of the first signal pad 11, the second signal pad 12, the third signal pad 13 and the fourth signal pad 14 is 18mil. Using the above formula, Z0 is taken as 100 and the relative dielectric constant ε r of the insulating medium, D can be calculated as 34mil.

[0048] In order to verify the improvement effect of the coaxial-like differential via structure on the differential signal transmission, the first ground wall hole 10 and the second ground wall hole 20 are replaced with a traditional ground hole structure under the condition that other design parameters remain unchanged, and a 3D simulation model of the coaxial-like differential via structure and a 3D simulation model of the traditional differential via structure are created by using a 3D HFSS modeling method, and the TDR (Time Domain Reflectometry) impedance curve, return loss and insertion loss of the two simulation models are simulated and compared.

[0049] Figure 5 The simulation comparison results of the TDR impedance curve are shown, the dotted line represents the TDR impedance curve of the traditional differential via structure, and the solid line represents the TDR impedance curve of the coaxial-like differential via structure. Figure 5 It can be known that the impedance fluctuation of the traditional differential via structure is 10.96%, which does not meet the design requirements. The impedance fluctuation of the coaxial-like differential via structure is 1.68%, the impedance fluctuation is smaller and meets the design requirements.

[0050] Figure 6 The simulation comparison results of the return loss are shown, the dotted line represents the return loss curve of the traditional differential via structure, and the solid line represents the return loss curve of the coaxial-like differential via structure. Figure 6 It can be known that the return loss of the coaxial-like differential via structure is optimized by 31.05-17.33=13.72dB at 10GHz compared with the return loss of the traditional differential via structure. Figure 7 The simulation comparison results of the insertion loss are shown, the dotted line represents the insertion loss curve of the traditional differential via structure, and the solid line represents the insertion loss curve of the coaxial-like differential via structure. Figure 7 It can be known that the insertion loss of the coaxial-like differential via structure is optimized by 0.805-0.042=0.763dB at 10GHz compared with the insertion loss of the traditional differential via structure. In summary, the coaxial-like differential via structure can effectively solve the impedance discontinuity problem at the via.

[0051] The above-mentioned is only the preferred embodiment of the present application, and the present application is not limited to the above-mentioned embodiments. It can be understood that other improvements and changes directly derived or thought by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A PCB-type coaxial differential via structure, characterized in that, The first signal transition hole and the second signal transition hole are arranged in parallel and spaced apart; The first signal transition hole is arranged coaxially in the first ground wall hole, and the inner wall of the first ground wall hole and the outer wall of the first signal transition hole are filled with an insulating medium; The second signal transition hole is arranged coaxially in the second ground wall hole, and the inner wall of the second ground wall hole and the outer wall of the second signal transition hole are filled with an insulating medium; The outer walls of the first ground wall hole and the second ground wall hole are connected with the ground plane in the PCB.

2. The PCB-type coaxial differential via structure of claim 1, wherein, The upper end of the first signal transition hole is connected with the first transmission signal line through a first signal pad, and the lower end of the first signal transition hole is connected with the second transmission signal line through a second signal pad.

3. The PCB-type coaxial differential via structure of claim 1, wherein, The upper end of the second signal transition hole is connected with the third transmission signal line through a third signal pad, and the lower end of the second signal transition hole is connected with the fourth transmission signal line through a fourth signal pad.

4. The PCB-type coaxial differential via structure of claim 1, wherein, The spacing between the first signal transition hole and the second signal transition hole ranges from 0.65mm to 1.27mm.

5. The PCB-type coaxial differential via structure of claim 1, wherein, The diameters of the first ground wall hole and the second ground wall hole are the same, and the diameters of the first signal transition hole and the second signal transition hole are the same.

6. The PCB-type coaxial differential via structure of claim 1, wherein, The length of the first ground wall hole is less than the length of the first signal transition hole, and the length of the second ground wall hole is less than the length of the second signal transition hole.

7. The PCB-type coaxial differential via structure of claim 5, wherein, The impedance Z0 of the coaxial-like differential via structure can be expressed as: where ε r represents the relative dielectric constant of the insulating medium, D represents the diameter of the first ground-wall hole and the second ground-wall hole, and d represents the diameter of the first signal-layer hole and the second signal-layer hole.

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