Circuit board structure for optimizing AC coupling capacitor impedance in BGA area

Abstract

The utility model discloses a circuit board structure for optimizing AC coupling capacitor impedance in a BGA area, which comprises a circuit board, a BGA chip and an AC coupling capacitor, the BGA chip and the AC coupling capacitor are arranged on the circuit board, the BGA chip is positioned on the surface layer of the circuit board, the AC coupling capacitor is positioned on the bottom layer of the circuit board, and the BGA chip is positioned on the surface layer of the circuit board. A pin bonding pad of the AC coupling capacitor is aligned with a pin bonding pad of the BGA chip, the AC coupling capacitor is connected with a via hole in a BGA chip area through a wire, and the wire outlet direction of the AC coupling capacitor faces the outside of the AC coupling capacitor. According to the utility model, by adjusting the wire outlet direction of the AC coupling capacitor, the wire outlet direction of the AC coupling capacitor faces the outside of the AC coupling capacitor, so that the impedance can be effectively improved, the impedance continuity of a link is increased, and the wiring space of a BGA chip area is basically not influenced.

Description

TECHNICAL FIELD

[0001] The utility model relates to the PCB design technical field more specifically, is related to a kind of circuit board structure for optimizing the impedance of AC coupling capacitor in BGA area. BACKGROUND

[0002] Printed Circuit Board (PCB board) is also called printed circuit board, and it is an important component of physical support and signal transmission of electronic product.The ratio of voltage and current of signal at a point on transmission line represents the impedance that signal feels at this position, and for ideal uniform transmission line, the impedance of signal at each position on line is same, which is called impedance continuity.Impedance discontinuity can deteriorate signal quality.With the increasing of signal rate, the impedance continuity of interconnection wiring is increasingly influenced.

[0003] In high-speed serial link, AC coupling capacitor is often used for direct passage isolation, that is, removing DC bias component in signal, while allowing high-frequency component to pass smoothly, which is similar to the role of high-bandwidth filter.Because the pad of capacitor is usually larger than the line width of transmission line, and the body of capacitor has a certain height, the equivalent thickness of conductor is increased, so that a low impedance point is formed at capacitor.

[0004] At the same time, with the increasing complexity of circuit system and the increasing integration of digital chip, BGA (Ball Grid Array) packaged chip is more and more common, and the design density of PCB is also increasing, in order to save layout space, AC coupling capacitor is laid out under BGA device.

[0005] Because of the limited layout and wiring space in BGA area, the traditional method selects the punching out-line direction of AC coupling capacitor inside the capacitor in order to save wiring space, which leads to the increase of impedance deviation at this place.

[0006] How to optimize the impedance of AC coupling capacitor in BGA area is a problem to be solved. UTILITY MODEL CONTENT

[0007] In order to overcome the problem that the layout and wiring space in BGA area is limited, and in order to save wiring space, the punching out-line direction of AC coupling capacitor is selected inside the capacitor, which leads to the increase of impedance deviation at this place, the utility model provides a kind of circuit board structure for optimizing the impedance of AC coupling capacitor in BGA area.

[0008] The technical scheme of the utility model is as follows:

[0009] The utility model provides a kind of circuit board structure for optimizing the impedance of AC coupling capacitor in BGA area, including circuit board and the BGA chip and AC coupling capacitor of being located on the circuit board, the BGA chip is located in the surface layer of the circuit board, the AC coupling capacitor is located in the bottom layer of the circuit board, the pin pad of the AC coupling capacitor is aligned with the pin pad of the BGA chip, the AC coupling capacitor is connected with via hole in BGA chip area by wiring, and the wire direction of the AC coupling capacitor is towards the outside of the AC coupling capacitor.

[0010] According to the above-mentioned scheme, the via hole penetrates the circuit board.

[0011] According to the above-mentioned scheme, the via hole connects the surface layer pad of the circuit board and the bottom layer pad of the circuit board.

[0012] According to the above-mentioned scheme, the via hole includes a signal via hole, which connects the pin pad of the BGA chip signal pin and the pin pad of the AC coupling capacitor signal pin.

[0013] According to the above-mentioned scheme, the pin pad of the AC coupling capacitor is circular.

[0014] According to the above-mentioned scheme, the pin pad of the AC coupling capacitor is octagonal.

[0015] According to the above-mentioned scheme, the circuit board is provided with a silk screen outside the pin pad of the AC coupling capacitor.

[0016] According to the above-mentioned scheme, the silk screen includes a contour mark arranged at the edge of the pin pad of the AC coupling capacitor.

[0017] According to the above-mentioned scheme, the contour mark is rectangular, and the long side is provided with an interruption.

[0018] According to the above-mentioned scheme, it has the beneficial effects that a kind of circuit board structure for optimizing the impedance of AC coupling capacitor in BGA area, by adjusting the wire direction of AC coupling capacitor, the wire direction of AC coupling capacitor is towards the outside of the AC coupling capacitor, can effectively improve impedance, thereby increase the impedance continuity of link, and there is basically no influence to the wiring space of BGA chip area. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical scheme in the embodiments of the present application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without any creative effort on the premise of not paying creative effort.

[0020] Figure 1 The present application is a structural schematic diagram.

[0021] Figure 2 The present application is an impedance curve simulation comparison diagram

[0022] In the drawings, various reference signs are as follows:

[0023] 100, circuit board; 10, pin pad of AC coupling capacitor; 20, via hole; 30, trace; 40, contour mark. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical schemes and beneficial effects to be solved by the present application more clearly understood, the present application will be further described in detail below with reference to the drawings and embodiments.

[0025] It should be noted that the terms "comprising" and "having" and any variations thereof in the specification and claims of the present application are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device including a series of steps or units is not limited to the listed steps or units, but can optionally include steps or units not listed, or can optionally include other steps or units inherent to the process, method, product or device. The terms "provided" and the like should be broadly understood, for example, it can be fixedly connected, or can be detachably connected, or can be integrated; it can be mechanically connected, or can be electrically connected; it can be directly connected, or can be indirectly connected through an intermediate medium; it can be the internal communication or interaction relationship of two elements, unless otherwise specified. The terms "up", "down", "left", "right", "front", "back", "bottom" and the like indicate the orientation or position based on the orientation or position shown in the drawings, and are only for convenience of description, and cannot be understood as a limitation on the technical scheme.

[0026] It should be noted that, due to the increasing complexity of circuit system and the increasing integration of digital chips, BGA packaged chips are becoming more and more common, and the design density of circuit board is also increasing. In order to save layout space, the AC coupling capacitor is arranged directly below the BGA device.

[0027] Because the layout wiring space of the BGA area is limited, the traditional method saves the wiring space by selecting the punching out-line direction of the AC coupling capacitor inside the capacitor, thereby causing the impedance deviation of the place to increase.

[0028] As shown in Figure 1 The embodiment provides a circuit board structure for optimizing the impedance of an AC coupling capacitor in a BGA area. By adjusting the out-line direction of the AC coupling capacitor, the out-line direction of the AC coupling capacitor is directed towards the outside of the AC coupling capacitor, which can effectively improve the impedance and increase the impedance continuity of the link, without affecting the wiring space of the BGA chip area.

[0029] Specifically, the circuit board 100, the BGA chip and the AC coupling capacitor arranged on the circuit board 100 are included. The BGA chip is located on the surface layer of the circuit board 100, and the AC coupling capacitor is located on the bottom layer of the circuit board 100. The pin pad 10 of the AC coupling capacitor is aligned with the pin pad of the BGA chip. The AC coupling capacitor and the via 20 in the BGA chip area are connected through the trace 30, and the out-line direction of the AC coupling capacitor is directed towards the outside of the AC coupling capacitor.

[0030] As shown in Figure 2 The impedance of the high-speed differential trace 30 on a certain single board on the control PCB is 100 ohms. When the traditional AC coupling capacitor punching out-line is selected inside the AC coupling capacitor, the impedance of the AC coupling capacitor of the traditional method is only 83.6 ohms. By adjusting the punching out-line direction of the AC coupling capacitor and selecting the outside of the AC coupling capacitor, the impedance of the AC coupling capacitor is increased to 95.6 ohms, which is closer to the characteristic impedance of 100 ohms. Compared with the traditional method, it is increased by 12 ohms, which is equivalent to an increase of 12% of the system margin.

[0031] In one embodiment, the via 20 penetrates through the circuit board 100 to realize electrical connection between different layers. The via 20 connects the surface layer pad of the circuit board 100 and the bottom layer pad of the circuit board 100.

[0032] The via 20 includes a signal via which connects the pin pad of the signal pin of the BGA chip and the pin pad of the signal pin of the AC coupling capacitor. The AC coupling capacitor is connected in series on the high-speed serial link through the two-end vias 20, and the signal path is: BGA chip-via-AC coupling capacitor-via-inner layer trace. The other vias except the signal via are set as ground vias to optimize the signal return flow.

[0033] In one embodiment, the pin pad 10 of the AC coupling capacitor is circular or octagonal. The specific shape of the pin pad 10 of the AC coupling capacitor can be selected according to the actual design requirements to meet the wiring needs of the circuit board 100 while ensuring the soldering performance of the pad. The circular pad has better symmetry and uniformity, which is beneficial to heat distribution and solder flow during soldering. The octagonal pad provides a larger contact area or more stable soldering effect in some cases, especially in applications that require to withstand larger mechanical stress or current.

[0034] The selection of the pad shape is also affected by other factors, such as the size of the device, the pin pitch, the space limitation of the circuit board 100, and the consideration of the production process. According to the actual design requirements, the above factors are considered comprehensively to select the appropriate pad shape.

[0035] In one embodiment, the circuit board 100 is provided with a silk screen outside the pin pad 10 of the AC coupling capacitor. The silk screen is used to provide information such as component position, polarity, number, and to help identification and positioning during assembly and maintenance. The silk screen provided outside the pin pad 10 of the AC coupling capacitor can further improve the readability and maintainability of the circuit board 100.

[0036] The silk screen includes a contour mark 40 provided at the edge of the pin pad 10 of the AC coupling capacitor. The contour mark 40 is rectangular with an interrupted long side. It helps to visually distinguish the installation positions of different components, and helps the assembler to quickly identify the installation position of the AC coupling capacitor, especially in the case of dense arrangement of components. At the same time, the interrupted long side can also be used as a positioning reference to help the assembler quickly and accurately find the installation direction of the AC coupling capacitor during installation.

[0037] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all such improvements and changes shall fall within the scope of the appended claims of the present application.

[0038] The above description of the present application is exemplary in conjunction with the accompanying drawings. Obviously, the implementation of the present application is not limited by the above manner. Any improvement or change using the method concept and technical solution of the present application, or directly applying the concept and technical solution of the present application to other occasions without improvement, is within the protection scope of the present application.

Claims

1. A circuit board structure for optimizing the AC coupling capacitor impedance in a BGA region, comprising a circuit board and a BGA chip and an AC coupling capacitor disposed on the circuit board, wherein the BGA chip is located on the surface layer of the circuit board and the AC coupling capacitor is located on the bottom layer of the circuit board, characterized in that, The pin pad of the AC coupling capacitor is aligned with the pin pad of the BGA chip, the AC coupling capacitor is connected with the via in the BGA chip area through a trace, and the wire-out direction of the AC coupling capacitor is towards the outside of the AC coupling capacitor.

2. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 1, wherein, The via penetrates the circuit board.

3. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 2, wherein, The via connects the surface layer pad of the circuit board and the bottom layer pad of the circuit board.

4. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 3, wherein, The via includes a signal via, which connects the pin pad of the BGA chip signal pin and the pin pad of the AC coupling capacitor signal pin.

5. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 1, wherein, The pin pad of the AC coupling capacitor is circular.

6. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 1, wherein, The pin pad of the AC coupling capacitor is octagonal.

7. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 1, wherein, The circuit board is provided with a silk screen outside the pin pad of the AC coupling capacitor.

8. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 7, wherein, The silk screen includes a contour mark arranged at the edge of the pin pad of the AC coupling capacitor.

9. The circuit board structure for optimizing impedance of AC coupling capacitors in a BGA area according to claim 8, wherein, The contour mark is rectangular, and the long side is provided with an interruption.

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