A printed circuit board

Abstract

An embodiment of the present invention provides a printed circuit board, comprising: a plate-shaped main body having a plurality of core boards and a plurality of dielectric layers laid alternately and parallel to each other, wherein, among the plurality of core boards, there are a plurality of conductor layers, and the plurality of conductor layers include a differential signal transmission layer located on the surface layer of the plate-shaped main body and a differential signal output layer located on the inner layer of the plate-shaped main body; two differential signal holes oppositely arranged on the plate-shaped main body, and the two differential signal holes sequentially penetrate at least part of the core boards from the differential signal transmission layer to the differential signal output layer and connect the differential signal transmission layer and the differential signal output layer; two slotted conductive posts located between the two differential signal holes, the two slotted conductive posts are respectively adjacent to one of the two differential signal holes, and both of the two slotted conductive posts extend from the differential signal transmission layer to the differential signal output layer. The printed circuit board provided by the embodiment of the present invention improves the impedance continuity between the differential signal holes and the differential lines.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of circuit technologies, and in particular, to a printed circuit board. Background Art

[0002] With the rapid development of science and technology, the signal rate of high-speed systems has reached Gbps (Gbps: GigaBit Per Second), and at the same time, the research on G+ has also been launched. As the signal rate increases to Gbps and above, the performance of each passive component in the system link becomes crucial. The differential signal holes of the Ball Grid Array Package (BGA) are key passive components in the high-speed interconnection channel, and their performance can directly affect the passive performance of the entire link.

[0003] In order to reduce the loss of the printed circuit board and improve the capacity of the printed circuit board when the signal rate increases to Gbps and above, a board material with a dielectric constant less than 3.0 is selected for manufacturing the printed circuit board, and the package pitch (pitch: the center distance between two BGA pads) of the BGA chip also develops towards a small pitch. At this time, in order to ensure differential output, only differential signal holes with a small aperture can be used.

[0004] However, due to the small aperture of the differential signal holes, the impedance of the differential signal holes is much greater than the impedance of the differential lines connected thereto, resulting in impedance discontinuity between the differential signal holes and the differential lines, and further leading to deterioration of the insertion loss, return loss, and increased insertion loss fluctuation of the differential signal holes. Summary of the Invention

[0005] The main purpose of the embodiments of the present application is to propose a printed circuit board, which can make the impedance of the differential signal holes approach the impedance of the differential lines connected thereto, improve the impedance continuity between the differential signal holes and the differential lines, and further reduce the insertion loss, return loss deterioration, and insertion loss fluctuation of the differential signal holes.

[0006] To achieve the above object, the embodiments of the present application provide a printed circuit board, including: a plate-shaped main body having a plurality of core boards and a plurality of dielectric layers laid alternately and parallel to each other, wherein, among the plurality of core boards, there are a plurality of conductor layers, and the plurality of conductor layers include a differential signal transmission layer on the surface layer of the plate-shaped main body and a differential signal output layer on the inner layer of the plate-shaped main body; two differential signal holes oppositely arranged on the plate-shaped main body, the two differential signal holes sequentially penetrate at least part of the core boards from the differential signal transmission layer to the differential signal output layer and connect the differential signal transmission layer and the differential signal output layer; two slotted conductive columns located between the two differential signal holes, the two slotted conductive columns are respectively adjacent to one of the two differential signal holes, and both of the two slotted conductive columns extend from the differential signal transmission layer to the differential signal output layer.

[0007] A printed circuit board proposed in the present application, by arranging two slotted conductive posts between two differential signal holes, each of the two slotted conductive posts is adjacent to one of the two differential signal holes, and both of the two slotted conductive posts extend from the differential signal transmission layer to the differential signal outlet layer, so as to increase the aperture of the differential signal hole in the thickness direction perpendicular to the plate-like main body, reduce the inductance of the differential signal hole, and further reduce the impedance of the differential signal hole, making the impedance of the differential signal hole approach the impedance of the differential line connected thereto, improving the impedance continuity between the differential signal hole and the differential line, and further reducing the insertion loss, return loss deterioration and insertion loss fluctuation of the differential signal hole. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a three-dimensional structural schematic diagram of the printed circuit board provided in the first embodiment of the present invention;

[0009] Figure 2 is from Figure 1 the remaining structural schematic diagram after removing the core board and the dielectric layer from the printed circuit board structure shown;

[0010] Figure 3 is from Figure 2 the remaining structural top view after removing two first signal hole pads, two connecting parts and two BGA pads from the printed circuit board structure shown;

[0011] Figure 4 is the test data diagram of the impedance change effect of the printed circuit board provided in the first embodiment of the present invention with slotted conductive posts set compared with that without slotted conductive posts;

[0012] Figure 5 is a partial schematic diagram of the surface layer of the plate-like main body provided in the second embodiment of the present invention;

[0013] Figure 6 is the test data diagram of the impedance change effect of the printed circuit board provided in the second embodiment of the present invention with slotted conductive posts set compared with that without slotted conductive posts. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0014] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the following will elaborate on each embodiment of the present application with reference to the drawings. However, those of ordinary skill in the art can understand that in each embodiment of the present application, many technical details are provided for the readers to better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented. The following division of each embodiment is for convenience of description and should not constitute any limitation to the specific implementation manner of the present application. Each embodiment can be combined and cross-referenced with each other on the premise of no contradiction.

[0015] Embodiment 1 of the present invention relates to a printed circuit board. By arranging two slotted conductive posts between two differential signal holes, the two slotted conductive posts are respectively adjacent to one of the two differential signal holes, and both of the two slotted conductive posts extend from the differential signal transmission layer to the differential signal output layer, so as to increase the aperture of the differential signal hole perpendicular to the thickness direction of the plate-shaped main body, reduce the inductance of the differential signal hole, and further reduce the impedance of the differential signal hole, making the impedance of the differential signal hole approach the impedance of the differential line connected thereto, improving the impedance continuity between the differential signal hole and the differential line, and further reducing the insertion loss, return loss deterioration and insertion loss fluctuation of the differential signal hole.

[0016] The implementation details of the printed circuit board of this embodiment will be specifically described below. The following content is only the implementation details provided for convenient understanding and is not necessary for implementing this solution.

[0017] See Figure 1 , the printed circuit board in this embodiment includes a plate-shaped main body 10. The plate-shaped main body 10 has a core board and a plurality of dielectric layers 12 that are parallel to each other and alternately laid. Among them, a plurality of core boards include a plurality of conductor layers, and the plurality of conductor layers include a differential signal transmission layer on the surface layer of the plate-shaped main body 10 and a differential signal output layer on the inner layer of the plate-shaped main body 10. Each of the plurality of dielectric layers 12 includes a dielectric filled inside thereof, and the dielectric constant of the dielectric is less than 3.0. In this embodiment, each core board includes two conductor layers and an intermediate dielectric layer located between the two conductor layers. The two conductor layers are respectively a signal layer and a plane layer 11, and both the differential signal transmission layer and the differential signal output layer are signal layers.

[0018] The above-mentioned printed circuit board is applied to high-speed products with Gbps and above, using BGA chip packaging, with a pitch less than 1.0 mm and requiring differential output. Further, in this embodiment, the printed circuit board is a rigid board with a thickness of 4 mm (mm: millimeter). The laminated structure composed of twelve core boards and thirteen dielectric layers 12 that are parallel to each other and alternately laid is a plate-shaped main body 10 with twenty-six conductor layers. The dielectric layer 12 is used to maintain the insulation between the printed circuit board lines and each core board. The differential signal transmission layer (i.e., the signal layer of the first core board, that is, the first conductor layer) is located on the surface layer of the plate-shaped main body 10, and the differential signal output layer (i.e., the signal layer of the twelfth core board) is the twenty-third conductor layer. The dielectric constant of the dielectric filled in the dielectric layer 12 is 2.5.

[0019] It should be noted that the plate-shaped main body is not limited to the plate-shaped main body with a laminated structure of twenty-six conductor layers mentioned above, and the dielectric constant of the dielectric filled in the dielectric layer can also be other values.

[0020] See Figure 2 And Figure 3, the printed circuit board further includes a first differential signal hole 131 and a second differential signal hole 132 that are oppositely disposed on the plate-shaped main body 10. The first differential signal hole 131 and the second differential signal hole 132 sequentially penetrate through ten core boards from the differential signal transmission layer to the differential signal output layer, and connect the differential signal transmission layer and the differential signal output layer. In this embodiment, the drilling aperture of the first differential signal hole 131 and the second differential signal hole 132 is 0.15 mm, and then copper is deposited in the 0.15-mm aperture to form the first differential signal hole 131 and the second differential signal hole 132 surrounded by copper walls. The center distance between the first differential signal hole 131 and the second differential signal hole 132 is 0.8 mm.

[0021] The printed circuit board further includes a first slotted conductive post 141 and a second slotted conductive post 142 located between the first differential signal hole 131 and the second differential signal hole 132. The first slotted conductive post 141 is adjacent to the first differential signal hole 131, and the second slotted conductive post 142 is adjacent to the second differential signal hole 132. Both the first slotted conductive post 141 and the second slotted conductive post 142 extend from the differential signal transmission layer to the differential signal output layer.

[0022] Specifically, the parasitic inductance L of the first differential signal hole 131 and the second differential signal hole 132 can be calculated by the following formula (1):

[0023] L = 5.08H[ln(4H / d) + 1]................................(1)

[0024] The impedance Z of the first differential signal hole 131 and the second differential signal hole 132 can be calculated by formula (2):

[0025]

[0026] In the above formulas (1) and (2), H is the via length of the first differential signal hole 131 and the second differential signal hole 132, d is the aperture of the first differential signal hole 131 and the second differential signal hole 132, and C is the parasitic capacitance of the first differential signal hole 131 and the second differential signal hole 132.

[0027] The printed circuit board provided in this embodiment makes the "d" value in the above formula (1) include the cross-sectional areas of the first slotted conductive post 141 adjacent to the first differential signal hole 131 and the second slotted conductive post 142 adjacent to the second differential signal hole 132 in the thickness direction of the plate-shaped main body 10 (i.e., the Z direction shown in the figure). As a result, the "d" value becomes larger, increasing the parasitic inductance "L" of the first differential signal hole 131 and the second differential signal hole 132. When the parasitic capacitance C of the first differential signal hole 131 and the second differential signal hole 132 remains unchanged, the impedance Z of the first differential signal hole 131 and the second differential signal hole 132 is reduced, making the impedance of the first differential signal hole 131 and the second differential signal hole 132 approach the impedance of the differential line connected thereto, and reducing the insertion loss, return loss deterioration, and insertion loss fluctuation of the first differential signal hole 131 and the second differential signal hole 132.

[0028] Preferably, in the thickness direction of the plate-shaped main body 10, the shapes and sizes of the cross-sections of the first slotted conductive post 141 and the second slotted conductive post 142 are the same everywhere. In this way, the impedances of the first differential signal hole 131 and the second differential signal hole 132 are the same everywhere in the hole body extension direction, improving the stability of the first differential signal hole 131 and the second differential signal hole 132 when transmitting data.

[0029] More preferably, both the first slotted conductive post 141 and the second slotted conductive post 142 are rectangular parallelepipeds; in the direction perpendicular to the thickness direction of the plate-like main body 10, the cross-sectional shapes of the first differential signal hole 131 and the second differential signal hole 132 are both circular holes. The direction from the first differential signal hole 131 to the second differential signal hole 132 is the first direction (i.e., the Y direction shown in the figure). In the thickness direction of the plate-like main body 10, the cross-sections of the first slotted conductive post 141 and the second slotted conductive post 142 are rectangles. That is to say, the cross-sections of the first slotted conductive post 141 and the second slotted conductive post 142 both include a long straight side 143 parallel to the first direction and a short straight side 144 perpendicular to the first direction. Among them, the length of the long straight side 143 is equal to half of the difference between the center distance of the first differential signal hole 131 and the second differential signal hole 132 and the distance between the first slotted conductive post 141 and the second slotted conductive post 142. The outer diameters of the first differential signal hole 131 and the second differential signal hole 132 are the same. The length dimension of the short straight side 144 is not greater than the outer diameter of the circular pad provided on the inner layer of the printed circuit board and surrounding the first differential signal hole 131 or the second differential signal hole 132; in this embodiment, the length of the short straight side 144 is equal to the diameter of the outer diameter of the first differential signal hole 131.

[0030] In this embodiment, the center distance between the first differential signal hole 131 and the second differential signal hole 132 is 0.8 mm, and the distance between the first slotted conductive post 141 and the second slotted conductive post 142 is 17 mils (mil: mil, one thousandth of an inch); the length of the short straight side 144 (i.e., the outer diameter of the first differential signal hole 131 or the outer diameter of the second differential signal hole 132) is 6 mils.

[0031] It should be noted that since the impedance differences between the differential signal holes of different printed circuit boards and the differential lines connected thereto are different, therefore, by adjusting the distance between the two second slotted conductive posts and the length dimension of the short straight side 144, the impedance difference between the BGA fan-out differential signal holes and the differential lines can be reduced to a preset range, thereby reducing the insertion loss, return loss, and insertion loss fluctuation of the differential signal holes and improving the stability of the entire printed circuit board during signal transmission.

[0032] Specifically, the above-mentioned printed circuit board in this embodiment further includes: two first signal hole pads 15 provided on the surface layer of the plate-like main body 10 (i.e., the differential signal transmission layer) and respectively connected to the first differential signal hole 131 and the second differential signal hole 132, and two BGA pads 16 respectively connected to the two first signal hole pads 15.

[0033] Further, each first signal via pad 15 includes a main body portion 15a connected to the BGA pad 16 and an extension portion 15b connected to the main body portion 15a. One end of the first differential signal via 131 penetrates through a main body portion 15a and is connected to the penetrated main body portion 15a. One end of the second differential signal via 132 penetrates through another main body portion 15a and is connected to the penetrated main body portion 15a. The first slotted conductive post 141 and the second slotted conductive post 142 are respectively connected to an extension portion 15b at the ends adjacent to the differential signal transmission layer. In this embodiment, there are also two connecting portions 161, and each first signal via pad 15 is connected to the BGA pad 16 through a connecting portion 161.

[0034] In another changeable embodiment, both the first differential signal via 131 and the second differential signal via 132 include a hole 13a formed in the plate-shaped main body portion 10 and a conductive copper plating layer 13b provided on the hole wall of the hole 13a. The first slotted conductive post 141 and the second slotted conductive post 142 are respectively connected to a conductive copper plating layer 13b. In this embodiment, the first slotted conductive post 141 and the second slotted conductive post 142 are respectively electroplated and connected to a conductive copper plating layer 13b, so that the first slotted conductive post 141 and the first differential signal via 131 are connected as a whole, and the second slotted conductive post 142 and the second differential signal via 132 are connected as a whole.

[0035] More specifically, the above printed circuit board in this embodiment further includes: two oppositely arranged first differential lines 171 and second differential lines 172 provided on the differential signal output layer, first impedance transition portions 181 and second impedance transition portions 182 provided oppositely on the differential signal output layer, and two oppositely arranged third pads 19 provided on the differential signal output layer; the first differential line 171 and the first impedance transition portion 181 are connected to the first differential signal via 131 and the first slotted conductive post 141 through a third pad 19; the second differential line 172 and the second impedance transition portion 182 are connected to the second differential signal via 132 and the second slotted conductive post 142 through another third pad 19.

[0036] Further, the thicknesses of the first differential line 171, the second differential line 172, the first impedance transition portion 181, and the second impedance transition portion 182 are the same; the width (i.e., the illustrated W) of the first impedance transition portion 181 gradually increases in the direction close to the first differential signal via 131 (i.e., the illustrated Z direction), and the width (i.e., the illustrated W) of the second impedance transition portion 182 gradually increases in the direction close to the second differential signal via 132 (i.e., the illustrated X direction). In this way, the first impedance transition portion 181 and the second impedance transition portion 182 reduce the impedance of the two third pads 19, ensuring impedance continuity while enhancing their structural strength.

[0037] Preferably, the spacing (i.e., the illustrated D) between the first impedance transition portion 181 and the second impedance transition portion 182 gradually increases in the direction close to the first differential signal via 131 and the second differential signal via 132 (i.e., the illustrated Z direction). In this way, while reducing the spacing between the first differential line 171 and the second differential line 172 and preventing the line widths of the first differential line 171 and the second differential line 172 from being too narrow, it is ensured that the first differential line 171 and the second differential line 172 can bypass the unilateral back-drilled vias in the BGA via array, thereby increasing the routing density of the printed circuit board. In this embodiment, the spacing between the first differential line 171 and the second differential line 172 is 3 mil, and the line widths of the first differential line 171 and the second differential line 172 are 3 mil.

[0038] See further Figure 4 , the dashed line in the figure is the impedance change curve over time when the printed circuit board without the slotted conductive posts transmits data. At time 2.005 ns (ns: nanosecond), the impedance of the differential signal via starts to increase, and the maximum impedance reaches 135 ohm (ohm: ohm), with a maximum difference of up to 35 ohm from the impedance values before time 2.005 ns and after time 2.1 ns; the solid line in the figure is the impedance change curve over time when the printed circuit board with the first slotted conductive post 141 and the second slotted conductive post 142 transmits data. At time 2.005 ns, the impedance of the first differential signal via 131 and the second differential signal via 132 starts to fluctuate slightly, and the minimum impedance reaches 90 ohm, with a difference of only 10 ohm from the impedance values before time 2.005 ns and after time 2.1 ns. Moreover, when data is transmitted through the first differential signal via 131 and the second differential signal via 132, the impedance value fluctuates less, especially with a difference of less than 4 ohm between 2.35 ns and 2.55 ns.

[0039] See Figure 5 , in the second embodiment of the present invention, the board-like main body portion 20 of the printed circuit board is substantially the same as that in the first embodiment above, except that the first slotted conductive post 241 and the second slotted conductive post 242 are cylindrical; in the direction perpendicular to the thickness direction of the board-like main body portion 20, the cross-sectional shapes of the first differential signal via 231 and the second differential signal via 232 are circular holes.

[0040] Preferably, the above printed circuit board further includes: two first signal hole pads 25 disposed on the surface layer of the plate-shaped main body and respectively connected to the first differential signal hole 231 and the second differential signal hole 232; the cross-sectional shape of the first signal hole pad 25 in the direction perpendicular to the thickness direction of the plate-shaped main body is a circular hole, and the diameters of the first slotted conductive post 241 and the second slotted conductive post 242 are not greater than the outer diameter of the first signal hole pad 25. In this embodiment, the diameters of the first slotted conductive post 241 and the second slotted conductive post 242 are the same as the outer diameters of the first differential signal hole 231 and the second differential signal hole 232.

[0041] Further referring to Figure 6 , the dotted line in the figure is the impedance change curve of the printed circuit board without the slotted conductive post during data transmission over time. It can be obtained that at the time of 2.005 ns, the impedance of the differential signal hole starts to increase, and the maximum impedance reaches 135 ohm, with the maximum difference in impedance values before 2.005 ns and after 2.1 ns reaching 35 ohm; the solid line in the figure is the impedance change curve of the printed circuit board with the first slotted conductive post 241 and the second slotted conductive post 242 during data transmission over time. It can be obtained that at the time of 2.005 ns, the impedances of the first differential signal hole 231 and the second differential signal hole 232 start to increase, and the maximum impedance reaches 121 ohm, with the difference in impedance values before 2.005 ns and after 2.1 ns being only 21 ohm.

[0042] Those of ordinary skill in the art can understand that the above slotted conductive posts are not limited to the cuboid mentioned in Embodiment 1 and the cylinder with the volume in Embodiment 2 of the present invention. For example, the slotted conductive post is a semi-cylinder, etc. In addition, the above embodiments are specific embodiments for implementing the present invention, and in practical applications, various changes can be made in form and details without departing from the spirit and scope of the present invention.

Claims

1. A printed circuit board, characterized in that, Comprising: A plate-shaped main body having a plurality of core plates and a plurality of dielectric layers laid alternately and parallel to each other. Among them, the plurality of core plates include a plurality of conductor layers, and the plurality of conductor layers include a differential signal transmission layer located on the surface layer of the plate-shaped main body and a differential signal outgoing layer located on the inner layer of the plate-shaped main body; wherein, the differential signal outgoing layer and the differential signal transmission layer are spaced apart by at least one intermediate dielectric layer; Two differential signal holes oppositely arranged on the plate-shaped main body, and the two differential signal holes sequentially penetrate at least part of the core plates from the differential signal transmission layer to the differential signal outgoing layer and connect the differential signal transmission layer and the differential signal outgoing layer; Two slotted conductive posts located between the two differential signal holes, the two slotted conductive posts are respectively adjacent to one of the two differential signal holes, and the two slotted conductive posts both extend from the differential signal transmission layer to the differential signal outgoing layer; Two first signal hole pads provided on the surface layer of the plate-shaped main body and respectively connected to the two differential signal holes, and two BGA pads respectively connected to the two first signal hole pads. Each of the first signal hole pads includes a main body connected to the BGA pad and an extension connected to the main body. One end of the differential signal hole penetrates through the main body and is connected to the main body, and the end of the slotted conductive post adjacent to the differential signal transmission layer is connected to the extension.

2. The printed circuit board according to claim 1, characterized in that In the thickness direction perpendicular to the plate-shaped main body, the cross-sectional shapes and sizes of the two slotted conductive posts are the same everywhere.

3. The printed circuit board according to claim 1, wherein The slotted conductive post is a cuboid; in the thickness direction perpendicular to the plate-shaped main body, the cross-sectional shape of the differential signal hole is a round hole.

4. The printed circuit board according to claim 3, wherein The direction of one of the two differential signal holes pointing to the other is the first direction. In the thickness direction perpendicular to the plate-shaped main body, the cross-section of the slotted conductive post includes a long straight side parallel to the first direction and a short straight side perpendicular to the first direction; the length of the long straight side is equal to half of the difference between the center distance of the two differential signal holes and the distance between the two slotted conductive posts, and the length of the short straight side is equal to the diameter of the outer diameter of the differential signal hole.

5. The printed circuit board according to claim 1, wherein The slotted conductive post is a cylinder; in the thickness direction perpendicular to the plate-shaped main body, the cross-sectional shape of the differential signal hole is a round hole.

6. The printed circuit board according to claim 5, wherein, The cross-sectional shape of the first signal hole pad in the thickness direction perpendicular to the plate-shaped main body is a round hole, and the diameter of the slotted conductive post is not greater than the outer diameter of the first signal hole pad.

7. The printed circuit board according to any one of claims 1 to 6, characterized in that Further comprising: The differential signal hole includes a hole opened on the plate-shaped main body and a conductive copper plating layer provided on the hole wall of the hole, and the slotted conductive post is in contact with the conductive copper plating layer.

8. The printed circuit board according to any one of claims 1-6, characterized in that Further comprising: Two differentially - arranged differential lines disposed on the differential - signal output layer, two differentially - arranged impedance transition portions disposed on the differential - signal output layer, and two differentially - arranged third pads disposed on the differential - signal output layer; each of the differential lines is connected to one of the third pads through one of the impedance transition portions; each of the third pads is connected to one of the differential - signal holes and one of the slotted conductive posts.

9. The printed circuit board according to claim 8, characterized in that The thickness of the impedance transition portion is the same as the thickness of the differential line; the width of the impedance transition portion gradually increases in the direction approaching the differential - signal hole connected thereto.

10. The printed circuit board according to claim 9, characterized in that, The distance between the two impedance transition portions gradually increases in the direction approaching the two differential - signal holes.

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