PCB structure based on reduction of BGA fan-out wiring via hole crosstalk

Abstract

The utility model relates to a PCB structure based on reduction of BGA fan-out wiring via hole crosstalk, a surface layer board is provided with a signal bonding pad and a ground bonding pad, the bottom of the signal bonding pad is connected with a signal via hole, the bottom of the ground bonding pad is connected with a ground via hole, the central axis of the signal via hole is arranged to deviate from the central point of the signal bonding pad; and the direction in which the central axis of the signal via hole deviates from the signal bonding pad is opposite to the fan-out direction of the fan-out wire on the signal via hole. According to the design of the signal via hole offset disc, the direction in which the central axis of the signal via hole deviates from the signal bonding pad is opposite to the fan-out direction of the fan-out wire, so that the space between the signal via hole and the ground via hole on the side is increased, the wiring space of the fan-out wire is increased, and the fan-out wire can still keep the original wire width even if the fan-out wire keeps the original wire width. According to the fan-out routing structure, the ground via holes can be avoided in the dense array bonding pad area, the line widths of the fan-out routing lines are equal everywhere, line width abrupt change of narrow line segments and width limit segments does not exist, and therefore crosstalk of high-frequency signals on the fan-out routing lines can be effectively improved.

Description

Technical Field

[0001] The utility model relates to the field of circuit boards, and in particular to a PCB structure based on reducing BGA fan-out routing via crosstalk. Background Art

[0002] Printed Circuit Board (PCB) is an important component of the physical support and signal transmission of electronic products. As the signal transmission rate becomes higher and higher, the industry pays more attention to the via crosstalk of the fan-out routing in the BGA chip area. From the fan-out routing on the surface of the circuit board to the fan-out routing on the plate, the integrated electronic technology has made rapid progress.

[0003] Among them, the BGA chip is a ball grid array chip. The area corresponding to the BGA chip on the circuit board is provided with dense array pads, including signal pads and ground pads. The bottom of the pad is provided with vias that pass through the inner layer of the circuit board, which are signal vias and ground vias, and the central axis of the via overlaps with the center point of the pad. The surface fan-out routing refers to the routing set on the surface board of the PCB and connected to the signal pad, and the plate-in-hole fan-out routing refers to the routing set on the inner board and connected to the signal via.

[0004] Some inner layers of the circuit board are also provided with fan-out traces with holes in the disk (hereinafter referred to as fan-out traces). One end of the fan-out trace is connected to the signal via, and the other end fans out of the area of ​​the BGA chip from the dense array pad. If the trace is a pair of differential lines, one end of the two fan-out traces is connected to an adjacent pair of signal vias, and the two fan-out traces fan out in parallel from the gaps between the dense ground vias. In order to avoid the ground vias, the trace segments in the BGA chip area need to have a small line width, and then restore the original line width when reaching outside the BGA chip area. Therefore, the fan-out traces have different line widths. Although they can effectively avoid the ground vias, they will cause impedance mutations at the point where the line width suddenly changes. There is obvious crosstalk when high-frequency signals are transmitted on the above fan-out traces.

[0005] The above problems are worth solving. Utility Model Content

[0006] In order to solve the problem of crosstalk in high-frequency signal transmission of existing BGA fan-out routing, the utility model provides a PCB structure based on reducing the crosstalk of BGA fan-out routing vias.

[0007] The technical solution of the utility model is as follows:

[0008] A PCB structure based on reducing BGA fan-out trace via crosstalk, comprising a multilayer circuit board having a surface layer board, an inner layer board and a bottom layer board, the surface layer board being provided with a signal pad and a ground pad, the bottom of the signal pad being connected to a signal via, the bottom of the ground pad being connected to a ground via, the signal via being connected to a fan-out trace in one of the inner layer boards, the central axis of the signal via being arranged to deviate from the central point of the signal pad, and the direction in which the central axis of the signal via deviates from the signal pad is opposite to the fan-out direction of the fan-out trace on the signal via; the line width of the fan-out trace is a constant value.

[0009] The utility model according to the above solution is characterized in that there is a first distance between the center point of the signal pad and the center axis of the signal via, and the first distance is greater than zero and less than the radius of the signal pad.

[0010] Furthermore, the first distance ranges from 0 to 5 mil.

[0011] The utility model according to the above solution is characterized in that the circuit board is provided with an anti-pad hollowing area, and the signal via is located in the anti-pad hollowing area.

[0012] Further, in the width direction of the anti-pad hollowing area, the distance from one side of the signal via to the anti-pad hollowing area is equal to the distance from the other side of the signal via to the anti-pad hollowing area.

[0013] The utility model according to the above solution is characterized in that the routing is a pair of differential lines, and the line width of a single differential line is 4.5 mil.

[0014] The utility model according to the above scheme is characterized in that the center axis of the ground via is set away from the center point of the ground pad, and the center axis of the ground via adjacent to the fan-out trace deviates in a direction away from the fan-out trace.

[0015] Furthermore, the anti-pad hollowing area of ​​the circuit board is away from the ground via on one side of the fan-out trace, and its central axis deviates toward a direction close to the anti-pad hollowing area.

[0016] Furthermore, it is characterized in that there is a second distance between the center point of the ground pad and the center axis of the ground via, and the second distance is greater than zero and less than the radius of the ground pad.

[0017] Furthermore, the second distance ranges from 0 to 4 mil.

[0018] The utility model according to the above scheme has the following beneficial effects:

[0019] The utility model sets the central axis of the signal via hole away from the central point of the signal pad, and the direction in which the central axis of the signal via hole deviates from the signal pad is opposite to the fan-out direction of the fan-out trace on the signal via hole, thereby increasing the space between the signal via hole and the ground via hole next to it, thereby increasing the wiring space of the fan-out trace, and achieving that even if the fan-out trace maintains the original line width, it can avoid the ground via hole in the dense array pad area, the line width of the fan-out trace is equal everywhere, and there is no sudden change in the line width of the narrow line segment and the wide limit segment, so that the crosstalk of the high-frequency signal on the fan-out trace can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of the utility model;

[0021] Figure 2 It is a structural schematic diagram of the prior art;

[0022] Figure 3 A crosstalk comparison diagram of the utility model and the prior art;

[0023] Figure 4 This is a comparison diagram of the return loss of the utility model and the prior art.

[0024] In the figure,

[0025] 1. Signal via; 10. Signal pad; 2. Ground via; 20. Ground pad; 201. First ground via; 202. Second ground via; 3. Fan-out trace; 4. Anti-pad hollowing area. DETAILED DESCRIPTION

[0026] In order to better understand the purpose, technical solution and technical effect of the utility model, the utility model is further explained in conjunction with the drawings and embodiments below. It should be noted that similar numbers and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. At the same time, it is stated that the embodiments described below are only used to explain the utility model and are not used to limit the utility model.

[0027] It should be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may also be a central element, and when an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time.

[0028] The indicated orientation or position relationship is based on the orientation or position relationship shown in the drawings, or the orientation or position relationship in which the product of the application is usually placed when used, or the orientation or position relationship commonly understood by technical personnel in this field, or the orientation or position relationship in which the product of the application is usually placed when used. It is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0029] The terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Several" means two or more, unless otherwise clearly and specifically defined.

[0030] like Figure 1 As shown, in the traditional via-in-pad fan-out routing circuit board structure, the central axis of the signal via 1 overlaps with the center point of the signal pad 10, and the central axis of the ground via 2 overlaps with the center point of the ground pad 20. When the projection diagram is observed from the top view of the circuit board, it is reflected as concentric circles. The fan-out routing of the signal via 1 is a narrow line segment in the dense array pad area, and returns to a wide line segment after fanning out of the area. Therefore, the fan-out routing line width varies inside and outside the BGA chip area, and the impedance mutation will result at the point where the line width suddenly changes.

[0031] like Figure 2 As shown, in order to solve the problem of crosstalk in the high-frequency signal transmission of the fan-out routing of the via in the disk of the above-mentioned structure, the utility model proposes a PCB structure based on reducing the crosstalk of the BGA fan-out routing via. Similarly, the circuit board is a multi-layer circuit board, including a surface board, a plurality of inner boards and a bottom board. The signal pad 10 and the ground pad 20 are located on the surface board for soldering the pins of the electronic components. The bottom of the signal pad 10 is connected to the signal via 1, and the bottom of the ground pad 20 is connected to the ground via 2. The signal via 1 and the ground via 2 both pass through a plurality of inner boards. The number of inner board layers that the via passes through is designed according to actual needs, and can be 2 layers, 3 layers or through all the inner boards. The signal via 1 leads out the fan-out routing at the position of one of the inner board layers. The specific inner board layer from which the fan-out routing is led out is designed according to actual needs.

[0032] The key improvement of the utility model is that the center axis of the signal via 1 deviates from the center point of the signal pad 10, that is, the signal via 1 and the signal pad 10 are no longer "aligned", but deviate from the structure of the signal pad. When observing the projection diagram from a top-down angle, the projection center of the signal pad 10 and the projection center of the signal via 1 do not overlap. And the direction in which the center axis of the signal via 1 deviates from the signal pad 10 is opposite to the fan-out direction of the fan-out trace on the signal via 1. For example, the fan-out trace of the signal via 1 fans out from the left side in the figure, and the center axis of the signal via 1 deviates to the right side in the figure relative to the signal pad 10. The space between the signal via 1 deviating to the right and the ground via 2 on the left side becomes larger, which increases the wiring space of the fan-out trace. Therefore, the fan-out trace can maintain the original line width even in the dense array pad area, and the line width is maintained at a fixed value. Therefore, the line width of the fan-out trace of the utility model is equal everywhere, and there is no sudden change in the line width of the narrow line segment and the wide limit segment.

[0033] It should be noted that, for easy identification, the signal pads and ground pads of the surface board are represented by dotted lines, and the signal vias and ground vias of the inner board are represented by solid lines. Therefore, the fan-out traces represented by solid lines in the figure should pass under the pads represented by dotted lines.

[0034] In this embodiment, there is a first distance between the center point of the signal pad 10 and the center axis of the signal via 1, and the first distance is greater than zero and less than the radius of the signal pad 10, for example, 0 to 5 mil. The center axis of the signal via 1 is always located within the projection area of ​​the signal pad 10, and a large intersection area is still retained between the cross sections of the signal pad 10 and the signal via 1, thereby ensuring the electrical connection stability of the signal pad 10 and the signal via 1.

[0035] In this embodiment, the circuit board is provided with an anti-pad hollowing area 4, and the signal via 1 is located in the anti-pad hollowing area 4. The anti-pad hollowing area 4 forms a shielding insulation area around the signal via 1, and the electrical signal on the signal via 1 is stably transmitted, and the fan-out routing and the signal pad 10 obtain stable electrical signals through the signal via 1. The anti-pad hollowing area 4 is an oblong, and the two signal vias 1 of a pair of differential lines are arranged along the length direction of the anti-pad hollowing area 4, and in the width direction of the anti-pad hollowing area 4, the distance from one side of the signal via 1 to the anti-pad hollowing area 4 is equal to the distance from the other side of the signal via 1 to the anti-pad hollowing area 4, for example, the distance from the left side of the signal via 1 to the anti-pad hollowing area 4 is equal to the distance from the right side of the signal via 1 to the anti-pad hollowing area 4, so that the signal via 1 is located in the middle position of the width direction of the anti-pad hollowing area 4.

[0036] In this embodiment, the routing line is a pair of differential lines, and the line width of a single differential line is 4.5 mil, 4 mil, or 5 mil.

[0037] Embodiment 2

[0038] A PCB structure based on reducing the crosstalk of BGA fan-out routing vias, similar to the first embodiment, the center axis of the signal via 1 is set to deviate from the center point of the signal pad 10, and on this basis, the center axis of the ground via 2 is set to deviate from the center point of the ground pad 20, and the center axis of the ground via 2 adjacent to the fan-out routing deviates in the direction away from the fan-out routing. For example, the fan-out routing of the signal via 1 fans out from the left side of the figure, and the first ground via 201 on the left side of the fan-out routing deviates to the left relative to its corresponding ground pad 20, so that the distance between the first ground via 201 on the left side of the fan-out routing and the signal via 1 on the right side is further increased, thereby further increasing the wiring space of the fan-out routing, ensuring that the fan-out routing still has sufficient insulation space with the vias on the side while maintaining the line width unchanged.

[0039] In this embodiment, there is a second distance between the center point of the ground pad 20 and the center axis of the ground via 2, and the second distance is greater than zero and less than the radius of the ground pad 20. For example, the second distance ranges from 0 to 4 mil. The center axis of the ground via 2 is always located within the projection area of ​​the signal pad 10, and a large intersection area is still retained between the cross section of the ground pad 20 and the ground via 2, thereby ensuring the electrical connection stability between the ground pad 20 and the ground via 2.

[0040] Embodiment 3

[0041] A PCB structure based on reducing the crosstalk of BGA fan-out routing vias, similar to the second embodiment, the center axis of the signal via 1 is set away from the center point of the signal pad 10, and the center axis of the ground via 2 is set away from the center point of the ground pad 20, and on this basis, the circuit board anti-pad hollow area 4 is away from the ground via 2 on one side of the fan-out routing, and its center axis deviates in the direction close to the anti-pad hollow area 4. For example, the fan-out routing of the signal via 1 fans out toward the left side in the figure, that is, fans out from the left side of the anti-pad hollow area 4, then the second ground via 202 on the right side of the anti-pad hollow area 4 deviates toward the left side to get closer to the anti-pad hollow area 4, so that the second ground via 202 and the signal via 1 are closer, and a plurality of second ground vias 202 have better wrapping properties for the signal via 1.

[0042] like Figure 3 As shown, a comparison of the crosstalk between the existing circuit board structure and the circuit board structure of the utility model is shown. Curve A in the figure is the utility model, and curve B is the prior art. It can be seen from the figure that the PCB structure of the utility model has obvious improvement on the crosstalk of high-frequency signals.

[0043] like Figure 4As shown, a comparison of return loss between the existing circuit board structure and the circuit board structure of the utility model is shown. Curve C in the figure is the utility model, and curve D is the prior art. It can be seen from the figure that the PCB structure of the utility model has a significant improvement in the return loss of high-frequency signals.

[0044] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0045] The above embodiments only express several implementation methods of the utility model, and the descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A PCB structure based on reducing BGA fan-out trace via crosstalk, comprising a multilayer circuit board having a surface layer, an inner layer, and a bottom layer, wherein the surface layer is provided with a signal pad and a ground pad, the bottom of the signal pad is connected to a signal via, the bottom of the ground pad is connected to a ground via, and the signal via is connected to a fan-out trace in one of the inner layers, characterized in that: The central axis of the signal via is set away from the central point of the signal pad, and the direction in which the central axis of the signal via deviates from the signal pad is opposite to the fan-out direction of the fan-out line on the signal via; the line width of the fan-out line is a constant value.

2. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 1, characterized in that: There is a first distance between the center point of the signal pad and the center axis of the signal via, and the first distance is greater than zero and less than the radius of the signal pad.

3. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 2, characterized in that: The first distance ranges from 0 to 5 mil.

4. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 1, characterized in that: The circuit board is provided with an anti-pad hollowing area, and the signal via is located in the anti-pad hollowing area.

5. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 4, characterized in that: In the width direction of the anti-pad hollowing area, the distance from one side of the signal via to the anti-pad hollowing area is equal to the distance from the other side of the signal via to the anti-pad hollowing area.

6. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 1, characterized in that: The routing lines are a pair of differential lines, and the line width of a single differential line is 4.5 mil.

7. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 1, characterized in that: The center axis of the ground via is offset from the center point of the ground pad, and the center axis of the ground via adjacent to the fan-out trace deviates in a direction away from the fan-out trace.

8. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 7, characterized in that: The anti-pad hollowing area of ​​the circuit board is away from the ground via on one side of the fan-out wiring, and its central axis deviates toward a direction close to the anti-pad hollowing area.

9. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 7 or 8, characterized in that: There is a second distance between the center point of the ground pad and the center axis of the ground via hole, and the second distance is greater than zero and less than the radius of the ground pad.

10. The PCB structure based on reducing BGA fan-out routing via crosstalk according to claim 9, characterized in that: The second distance ranges from 0 to 4 mil.

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