Differential transmission line and printed circuit board

Abstract

The embodiments of the present disclosure provide a differential transmission line and a printed circuit board. The differential transmission line comprises: a first differential structure, a second differential structure and a connecting structure, the width of the first differential structure being greater than that of the second differential structure, the thickness of the first differential structure being less than that of the second differential structure, and the first differential structure and the second differential structure being connected by means of the connecting structure.

Description

Differential transmission line and printed circuit board

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This disclosure is based on Chinese patent application CN202310933845.5, filed on July 27, 2023, entitled “A Differential Transmission Line and Printed Circuit Board,” and claims the priority of the patent application. All of the disclosed contents are incorporated into this disclosure by reference. Technical Field

[0003] The present disclosure relates to the field of high-speed communications, and in particular to a differential transmission line and a printed circuit board. Background Art

[0004] With the rapid development of the electronic communications industry, communication equipment has become more complex and more integrated, and signal rates have gradually increased. This means that there are higher requirements for the signal integrity (SI) performance of high-speed signals, and the requirements for transmission lines have also increased.

[0005] In high-speed products, chips are essential components, and the chip pin area needs to be connected via transmission lines. However, if the differential signal spacing is small, the lead-out area is very narrow. Due to the combined influence of various factors, the impedance of differential transmission lines is high: on the one hand, differential transmission lines are required to ensure the quality of high-speed signal transmission. On the other hand, process limitations such as drilling and backdrilling result in very small differential line widths in narrow areas. To meet standard channel settings, high-speed materials with low dielectric constants are used. However, the high impedance of differential transmission lines affects the impedance continuity of the channel, which can lead to reduced channel performance.

[0006] As signal rates continue to increase, the dielectric constant of the material needs to be further reduced, resulting in higher differential impedance in narrow areas. As a result, the impedance of the differential transmission line becomes an important factor affecting the continuity of the impedance of the entire channel.

[0007] Summary of the Invention

[0008] The embodiments of the present disclosure provide a differential transmission line and a printed circuit board to at least solve the problems in the related art of excessively high differential impedance in narrow areas of the differential transmission line and poor channel impedance continuity.

[0009] According to one embodiment of the present disclosure, a differential transmission line is provided, comprising: a first differential structure, a second differential structure, and a connecting structure, wherein the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected by the connecting structure.

[0010] According to another embodiment of the present disclosure, a printed circuit board is provided, comprising one or more differential transmission lines as described in any one of the embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG1 is a schematic diagram of a differential transmission line structure according to an embodiment of the present disclosure;

[0012] FIG2 is a schematic diagram of a cross-sectional structure of a differential transmission line according to an embodiment of the present disclosure;

[0013] FIG3 is a schematic cross-sectional view of a differential transmission line according to an embodiment of the present disclosure;

[0014] FIG4 is an impedance comparison diagram of a differential transmission line according to an embodiment of the present disclosure;

[0015] FIG5 is a comparison diagram of insertion losses of differential transmission lines according to an embodiment of the present disclosure;

[0016] FIG6 is a comparison diagram of return losses of differential transmission lines according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0017] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings and in conjunction with embodiments.

[0018] It should be noted that the terms "first", "second", etc. in the specification and claims of the present disclosure and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0019] According to one embodiment of the present disclosure, a differential transmission line is provided.

[0020] FIG1 is a schematic diagram of a differential transmission line structure according to an embodiment of the present disclosure. As shown in FIG1 , the differential transmission line includes the following structures:

[0021] A first differential structure 10 , a second differential structure 20 and a connection structure 30 .

[0022] In this embodiment, the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected via the connecting structure.

[0023] In this embodiment, the first differential structure 10 can be arranged in an area with loose wiring, and the second differential structure 20 can be arranged in an area with narrow wiring, so as to save wiring space.

[0024] In the disclosed embodiments, the use of differential transmission lines ensures high-speed signal transmission quality. However, due to process limitations such as drilling and backdrilling, the width of the differential lines in narrow areas of the chip can be very small, resulting in high impedance. The disclosed embodiments achieve impedance matching by adjusting the thickness of the differential lines, reducing impedance fluctuations caused by overly narrow interconnect transmission lines. This addresses the issues of high differential impedance and poor channel impedance continuity in narrow areas of differential transmission lines in related technologies.

[0025] In some embodiments, the first differential structure 10 includes two mutually parallel first differential lines 11 and 12 ; the second differential structure 20 includes two mutually parallel second differential lines 21 and 22 .

[0026] In this embodiment, the width of the first differential line is greater than the width of the second differential line, and the distance between the two first differential lines is greater than the distance between the two second differential lines.

[0027] In some embodiments, the width of the first differential structure is the sum of the spacing between two first differential lines and the width of the two first differential lines, the width of the second differential structure is the sum of the spacing between two second differential lines and the width of the two second differential lines, the thickness of the first differential structure is the thickness of the first differential line, and the thickness of the second differential structure is the thickness of the second differential line.

[0028] In some embodiments, the connection structure 30 includes two connection components 31 and 32 , wherein each of the connection components connects one of the first differential lines and one of the second differential lines.

[0029] In some embodiments, the first differential line, the second differential line, and the connecting component are made of conductive materials, including but not limited to copper foil.

[0030] In some embodiments, the differential transmission line further includes: a first reference layer, a first dielectric layer, a second dielectric layer, and a second reference layer arranged in sequence from top to bottom, wherein the first differential structure, the second differential structure, and the connection structure are located between the first dielectric layer and the second dielectric layer.

[0031] In some embodiments, the thickness of the first dielectric layer between the second differential structure and the first reference layer is less than the thickness of the first dielectric layer between the first differential structure and the first reference layer; and / or the thickness of the second dielectric layer between the second differential structure and the second reference layer is less than the thickness of the second dielectric layer between the first differential structure and the second reference layer.

[0032] In some embodiments, the width and thickness of the connecting component close to the first differential line are the same as the width and thickness of the first differential line, and the width and thickness of the connecting component close to the second differential line are the same as the width and thickness of the second differential line.

[0033] In some embodiments, a width of the connection member transitions from a width of the first differential line to a width of the second differential line, and a thickness of the connection member transitions from a thickness of the first differential line to a thickness of the second differential line.

[0034] Through the embodiments of the present disclosure, differential transmission lines can be arranged in narrow areas, ensuring the transmission quality of high-speed signals. At the same time, impedance matching is achieved by adjusting the thickness of the differential transmission lines, reducing the impedance mutation problem caused by the transmission lines being too narrow, further improving the channel performance, and reducing the impact on the quality of high-speed signals.

[0035] FIG2 is a schematic diagram of a cross-sectional structure of a differential transmission line according to an embodiment of the present disclosure. As shown in FIG2 , the differential transmission line further includes the following structures:

[0036] Arranged from top to bottom are a first reference layer 41 , a first dielectric layer 42 , a second dielectric layer 43 and a second reference layer 44 .

[0037] In this embodiment, the first differential structure 10, the second differential structure 20 and the connection structure 30 are located between the first dielectric layer 42 and the second dielectric layer 43. The first differential structure 10, the connection structure 30 and the second differential structure 20 are arranged and connected in a horizontal direction.

[0038] In some embodiments, the first dielectric layer 42 and the second dielectric layer 43 may be substrates of a printed circuit board (PCB).

[0039] In some embodiments, the material of the first reference layer 41 and the second reference layer 44 can be copper foil, and its thickness is the copper thickness of the PCB stack. The material of the first differential structure 10, the second differential structure 20 and the connecting structure 30 can be copper foil or other conductive materials.

[0040] In some embodiments, the first differential structure 10 is applied in a space with ample routing, and the copper thickness t10 of the PCB stack can be used in the vertical direction. The second differential structure 20 is applied in a space with narrow routing, and a copper thickness t20 greater than the PCB stack is used in the vertical direction. The thickness of the connection structure 30 on one side of the first differential structure is t10, and the thickness on the side of the second differential structure is t20.

[0041] In some embodiments, the thickness of the connection structure 30 may transition uniformly between t10 and t20, but the present disclosure is not limited thereto.

[0042] In this embodiment, the two second differential lines in the second differential structure 20 can form a parallel plate capacitor structure with the first reference layer 41 or the second reference layer 44, respectively. The capacitance of the second differential line satisfies the following capacitance formula:

[0043] Wherein, C is the capacitance, A is the area facing the capacitor plates, h is the distance between the capacitor plates, that is, the distance between the second differential line and the first reference layer or the second reference layer, and ε0 is the dielectric constant of the medium between the plates.

[0044] It can be seen from this that the dielectric thickness h at the second differential structure 20 in FIG. 2 is smaller, so the capacitance is larger and the impedance is smaller.

[0045] Through the embodiments of the present disclosure, it is possible to use differential lines in narrow spatial areas, and also to ensure a smoother impedance curve, thereby improving the quality of high-speed signal transmission.

[0046] FIG3 is a schematic cross-sectional view of a differential transmission line according to an embodiment of the present disclosure. As shown in FIG3 , the differential transmission line includes the following structures:

[0047] Two first differential lines 11 and 12 are parallel to each other, and two second differential lines 21 and 22 are parallel to each other.

[0048] In this embodiment, the line width of the first differential lines 11 and 12 is greater than the line width of the second differential lines 21 and 22, and the spacing between the first differential lines 11 and 12 is greater than the spacing between the second differential lines 21 and 22. Therefore, the first differential lines can be used in locations with ample wiring space, and the second differential lines can be used in locations with limited wiring space, such as between two rows of through holes.

[0049] In this embodiment, the thickness of the first differential lines 11 and 12 is smaller than the thickness of the second differential lines 21 and 22 .

[0050] In this embodiment, FIG3 does not show the connecting components 31 and 32. The connecting components are used for transition connection between the first differential line and the second differential line. The width of the connecting components transitions from the width of the first differential line to the width of the second differential line, and the thickness of the connecting components also transitions from the thickness of the first differential line to the thickness of the second differential line.

[0051] Through the embodiments of the present disclosure, the impedance consistency of the traditional differential transmission line can be improved, thereby increasing the bandwidth of the differential signal.

[0052] In one embodiment, in a BGA ball grid array package with a differential signal pitch of 0.8 mm, the fan-out part adopts a line width of 3 mil and a spacing of 3 mil, and the impedance, insertion loss and return loss of the traditional structure differential transmission line and the differential transmission line in the embodiment of the present disclosure are tested respectively.

[0053] FIG4 is an impedance comparison diagram of differential transmission lines according to an embodiment of the present disclosure. As shown in FIG4 , the solid line represents the impedance of the differential transmission line in the present disclosure, and the dotted line represents the impedance of the differential transmission line in a traditional structure.

[0054] In this embodiment, the impedance of the differential transmission line in the present disclosure is significantly lower than that of the differential transmission line in the traditional structure, thereby improving impedance continuity.

[0055] FIG5 is a comparison diagram of insertion losses of differential transmission lines according to an embodiment of the present disclosure. As shown in FIG5 , the solid line represents the insertion loss of the differential transmission line in the present disclosure, and the dotted line represents the insertion loss of the differential transmission line with a traditional structure.

[0056] In this embodiment, the insertion loss of the differential transmission line in the present disclosure is slightly smaller than the insertion loss of the differential transmission line with a traditional structure, that is, the insertion loss of the differential transmission line is improved.

[0057] FIG6 is a comparison diagram of the return loss of the differential transmission line according to an embodiment of the present disclosure. As shown in FIG5 , the solid line is the return loss of the differential transmission line in the present disclosure, and the dotted line is the return loss of the differential transmission line with a traditional structure.

[0058] In this embodiment, the absolute value of the return loss of the differential transmission line in the present disclosure is greater than the absolute value of the return loss of the differential transmission line with a traditional structure, that is, the return loss of the differential transmission line can also be improved.

[0059] According to another embodiment of the present disclosure, a printed circuit board is provided, comprising one or more differential transmission lines as described in any one of the above embodiments.

[0060] The embodiments of the present disclosure can be applied to multi-layer PCB structures with narrow lead-out areas, such as ball grid array (BGA) packages, and especially PCB structures in high-speed backplane systems with speeds of 112 Gbps and above.

[0061] For specific examples in this embodiment, reference may be made to the examples described in the above embodiments and exemplary implementation modes, and this embodiment will not be described in detail here.

[0062] Obviously, those skilled in the art should understand that the modules or steps of the present disclosure described above can be implemented using a general-purpose computing device, they can be concentrated on a single computing device, or distributed across a network composed of multiple computing devices, they can be implemented using program code executable by the computing device, and thus, they can be stored in a storage device and executed by the computing device, and in some cases, the steps shown or described can be performed in a different order than herein, or they can be fabricated into separate integrated circuit modules, or multiple modules or steps can be fabricated into a single integrated circuit module for implementation. Thus, the present disclosure is not limited to any particular combination of hardware and software.

[0063] The foregoing is merely an exemplary embodiment of the present disclosure and is not intended to limit the present disclosure. Those skilled in the art will readily appreciate that the present disclosure is susceptible to various modifications and variations. Any modifications, equivalent substitutions, improvements, and the like made within the principles of the present disclosure shall be included within the scope of protection of the present disclosure.

Claims

1. A differential transmission line, comprising: A first differential structure, a second differential structure and a connecting structure, wherein the width of the first differential structure is greater than the width of the second differential structure, the thickness of the first differential structure is less than the thickness of the second differential structure, and the first differential structure and the second differential structure are connected via the connecting structure.

2. The differential transmission line according to claim 1, wherein: The first differential structure comprises two first differential lines parallel to each other; The second differential structure comprises two second differential lines parallel to each other; The width of the first differential line is greater than the width of the second differential line, and the spacing between the two first differential lines is greater than the spacing between the two second differential lines.

3. The differential transmission line according to claim 2, wherein: The width of the first differential structure is the sum of the spacing between two first differential lines and the width of the two first differential lines, the width of the second differential structure is the sum of the spacing between two second differential lines and the width of the two second differential lines, the thickness of the first differential structure is the thickness of the first differential line, and the thickness of the second differential structure is the thickness of the second differential line.

4. The differential transmission line according to claim 3, wherein: The connection structure includes two connection components, wherein each of the connection components connects one of the first differential lines and one of the second differential lines.

5. The differential transmission line according to claim 4, wherein: The first differential line, the second differential line and the connecting component are made of conductive materials.

6. The differential transmission line according to claim 1, wherein: The differential transmission line further includes: a first reference layer, a first dielectric layer, a second dielectric layer and a second reference layer arranged in sequence from top to bottom, wherein the first differential structure, the second differential structure and the connection structure are located between the first dielectric layer and the second dielectric layer.

7. The differential transmission line according to claim 6, wherein: The thickness of the first dielectric layer between the second differential structure and the first reference layer is less than the thickness of the first dielectric layer between the first differential structure and the first reference layer; and / or, The thickness of the second dielectric layer between the second differential structure and the second reference layer is smaller than the thickness of the second dielectric layer between the first differential structure and the second reference layer.

8. The differential transmission line according to claim 4, wherein: The width and thickness of the connecting component on the side close to the first differential line are the same as those of the first differential line, and the width and thickness of the connecting component on the side close to the second differential line are the same as those of the second differential line.

9. The differential transmission line according to claim 8, wherein: The width of the connection member transitions from the width of the first differential line to the width of the second differential line, and the thickness of the connection member transitions from the thickness of the first differential line to the thickness of the second differential line.

10. A printed circuit board comprising one or more differential transmission lines as claimed in any one of claims 1 to 9.

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