Circuit board structure

Abstract

The utility model discloses a circuit board structure, it includes a substrate and a ground plane. The substrate is equipped with signal transmission line, and signal transmission line contains lead and pad. The ground plane is connected to the substrate and is equipped with the hollow region, and the hollow region is located below the pad.

Description

Technical Field

[0001] This utility model relates to a circuit board structure, and more particularly to a circuit board structure for improving impedance matching. Background Technology

[0002] In modern electronic devices, the amount of data that needs to be transmitted is increasing, leading to a greater number of signal transmission lines and higher signal transmission frequencies. Time Domain Reflectometry (TDR) is a technique that measures the time-domain reflection of high-frequency signals on a signal transmission line to determine impedance changes. TDR curves can reflect the impedance discontinuities caused by parasitic capacitance and inductance in the signal transmission line.

[0003] When a high-frequency signal is transmitted from the lead to the pad, the impedance drops significantly, causing impedance mismatch. Current solutions typically involve changing the shape of the pad to reduce impedance variation; however, this approach is not always applicable, and sometimes the modified pad shape is difficult to manufacture. Utility Model Content

[0004] One embodiment of this utility model discloses a circuit board structure, which includes:

[0005] A substrate is provided with a signal transmission line, the signal transmission line including a lead and a pad; a ground plane is connected to the substrate and has a cutout area, the cutout area being located below the pad.

[0006] Optionally, the substrate includes a first surface and a second surface, the first surface and the second surface being located on opposite sides of the substrate, the signal transmission line being disposed on the first surface, and the second surface being connected to the ground plane.

[0007] Optionally, the cutout area is circular in shape, and the area of ​​the cutout area is equal to the area of ​​the pad.

[0008] Optionally, the cutout area is D-shaped, and the area ratio of the cutout area to the pad is between 0.72 and 0.78.

[0009] Optionally, the cutout area is D-shaped, and the area ratio of the cutout area to the pad is between 0.3 and 0.55.

[0010] Optionally, the hollowed-out area includes a first annular area and a second annular area, the second annular area surrounding the first annular area, and the width of the first annular area being equal to the width of the second annular area.

[0011] Optionally, the hollowed-out area includes a first annular area and a second annular area, the second annular area surrounding the first annular area, and the width of the first annular area being greater than the width of the second annular area.

[0012] Optionally, the hollowed-out area includes a first annular area and a second annular area, the second annular area surrounding the first annular area, and the width of the first annular area being smaller than the width of the second annular area.

[0013] Optionally, the cutout area comprises two rectangular areas, which have the same area and are parallel to each other.

[0014] Alternatively, the cutout area may be located on the side away from the lead wire.

[0015] In summary, the circuit board structure of this utility model reduces the capacitance between the pads and the ground plane by removing the ground plane below the pads, thereby reducing the impedance drop. Compared to changing the shape of the pads, removing the ground plane below the pads is easier to achieve.

[0016] To further understand the features and technical content of this utility model, please refer to the following detailed description and drawings of this utility model. However, these descriptions and drawings are only used to illustrate this utility model and are not intended to limit the scope of protection of this utility model in any way. Attached Figure Description

[0017] Figure 1 This is a perspective view of a circuit board structure according to an embodiment of the present invention;

[0018] Figure 2 for Figure 1 A sectional view of section II-II;

[0019] Figure 3 for Figure 2 A schematic diagram of the hollowed-out area of ​​the grounding plane;

[0020] Figure 4 This is a schematic diagram of a second embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0021] Figure 5 This is a schematic diagram of the third embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0022] Figure 6 This is a schematic diagram of the fourth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0023] Figure 7 This is a graph showing the impedance variation of a signal transmission line with a standard impedance of 50 ohms.

[0024] Figure 8This is a graph showing the impedance variation of a signal transmission line with a standard impedance of 100 ohms.

[0025] Figure 9 This is a schematic diagram of the fifth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0026] Figure 10 This is a schematic diagram of the sixth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0027] Figure 11 This is a schematic diagram of the sixth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0028] Figure 12 This is a schematic diagram of the seventh embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0029] Figure 13 This is a schematic diagram of the eighth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0030] Figure 14 This is a schematic diagram of the ninth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0031] Figure 15 This is a schematic diagram of the tenth embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0032] Figure 16 This is a cross-sectional view of the eleventh embodiment of the hollowed-out area of ​​the grounding plane of this utility model;

[0033] Figure 17 This is a cross-sectional view of the twelfth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. Detailed Implementation

[0034] In the following description, if a specific drawing is indicated or shown in a specific drawing, it is only to emphasize that most of the relevant content mentioned in the following description appears in that specific drawing, but does not limit the following description to refer only to that specific drawing.

[0035] Figure 1 This is a perspective view of a circuit board structure according to an embodiment of the present invention. (See reference...) Figure 1 The circuit board structure includes a substrate 1, a ground plane 2, and multiple signal transmission lines 3. The substrate 1 has a substrate thickness H1 and includes a first surface 11 and a second surface 12, which are located on the upper and lower sides of the substrate 1, respectively. The ground plane 2 is located below the substrate 1 and connected to the second surface 12 of the substrate 1. In some embodiments, the ground plane 2 may also be located within the substrate 1.

[0036] Multiple signal transmission lines 3 are disposed on the first surface 11 of the substrate 1. Each signal transmission line 3 includes a lead 31 and a pad 32, wherein the width of the pad 32 is greater than the width of the lead 31.

[0037] The substrate 1 is, for example, a printed circuit board, and the lead 31 is a pre-set conductive line on the printed circuit board and is made of copper foil. The lead 31 is responsible for transmitting current or signal from one area of ​​the printed circuit board to another area of ​​the printed circuit board.

[0038] The pad 32 is, for example, a solder mask defined (SMD) pad or a non-solder mask defined (NSMD) pad. The pad 32 is typically circular or square in shape and made of copper foil. To improve the conductivity, durability, and solderability of the pad 32, other protective layers may be added to the copper foil. The function of the pad 32 is to serve as the physical interface for electrical connection between electronic components and the printed circuit board. The leads of the electronic components can be placed on the corresponding pads 32, and then soldered to fix the leads of the electronic components to the pads 32.

[0039] The pad 32 is connected to the lead 31, thereby conducting electrical energy or signals to the electronic component. Through the combination of the lead 31 and the pad 32, the electronic component forms a complete and normally functioning circuit on the printed circuit board.

[0040] Figure 2 for Figure 1 Sectional view of section II-II. (See also...) Figure 2 The ground plane 2 has a ground plane thickness H2. The ground plane 2 is connected to the lower part of the substrate 1 and has multiple cutout areas R, which are located below multiple pads 32. The depth of each cutout area R is equal to the ground plane thickness H2. Each cutout area R is located on the side away from the lead 31.

[0041] Figure 3 for Figure 2 A schematic diagram of the hollowed-out area of ​​the grounding plane. See also... Figure 3 Each pad 32 is circular in shape, each cutout area R is circular in shape, and the area of ​​each cutout area R is equal to the area of ​​the pad H located above the cutout area R.

[0042] For example, the standard impedance of signal transmission line 3 is 50 ohms. When the pad 32 is below a complete ground plane 2, the highest impedance and lowest impedance of signal transmission line 3 are 54 ohms and 27 ohms, respectively. The error percentages of the highest impedance and lowest impedance of signal transmission line 3 compared to the standard impedance are 8% and 46%, respectively.

[0043] When the area of ​​the cutout region R below the pad 32 is equal to the area of ​​the pad 32, the highest impedance and the lowest impedance of the signal transmission line 3 are 60 ohms and 44 ohms, respectively, and the percentage errors of the highest impedance and the lowest impedance of the signal transmission line 3 compared to the standard impedance are 20% and 12%, respectively. Therefore, the cutout region R reduces the percentage error of the lowest impedance of the signal transmission line 3 compared to the standard impedance.

[0044] In other embodiments of this utility model, the hollow area R is D-shaped, the depth of the hollow area R is equal to the thickness H2 of the ground plane, and the ratio of the area of ​​the hollow area R to the area of ​​the pad 32 located above the hollow area R is between 0.7 and 0.9.

[0045] Figure 4 This is a schematic diagram of a second embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 4 The shape of the pad 32 is circular, the shape of the cutout area R is D-shaped, the depth of the cutout area R is equal to the thickness H2 of the ground plane, and the ratio of the area of ​​the cutout area R to the area of ​​the pad 32 located above the cutout area R is 0.0.85.

[0046] Figure 5 This is a schematic diagram of a third embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 5 The shape of the pad 32 is circular, the shape of the hollow area R is D-shaped, the depth of the hollow area R is equal to the thickness H2 of the ground plane, and the ratio of the area of ​​the hollow area R to the area of ​​the pad 32 located above the hollow area R is 0.75, preferably in the range of 0.72-0.78.

[0047] In other embodiments of this utility model, the hollowed-out area R is D-shaped, and the depth of the hollowed-out area R is equal to the thickness H2 of the ground plane. Furthermore, the ratio of the area of ​​the hollowed-out area R to the area of ​​the pad 32 located above the hollowed-out area R is between 0.3 and 0.55.

[0048] Figure 6 This is a schematic diagram of the fourth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 6 The shape of the pad 32 is circular, the shape of the cutout area R is D-shaped, the depth of the cutout area R is equal to the thickness H2 of the ground plane, and the ratio of the area of ​​the cutout area R to the area of ​​the pad 32 located above the cutout area R is 0.5.

[0049] Figure 7 This is an impedance variation diagram for a signal transmission line with a standard impedance of 50 ohms. When the depth of the cutout region R is equal to the thickness H2 of the ground plane and the ratio of the area of ​​the cutout region R to the area of ​​the pad 32 located above the cutout region R is 0.9, see [reference needed]. Figure 7 The curve O1 shows that the highest impedance and the lowest impedance of signal transmission line 3 are 59 ohms and 46 ohms, respectively.

[0050] When the depth of the cutout region R is equal to the thickness H2 of the ground plane, and the ratio of the area of ​​the cutout region R to the area of ​​the pad 32 above the cutout region R is 0.75, see [reference needed]. Figure 7 The curve O2 shows that the highest impedance and the lowest impedance of signal transmission line 3 are 54 ohms and 46 ohms, respectively.

[0051] When the depth of the cutout region R is equal to the thickness H2 of the ground plane and the ratio of the area of ​​the cutout region R to the area of ​​the pad 32 located above the cutout region R is 0.5, see [reference needed]. Figure 7 The curve O3 shows that the highest impedance and the lowest impedance of signal transmission line 3 are 53 ohms and 31 ohms, respectively.

[0052] Therefore, when the depth of the cutout area R is equal to the thickness H2 of the ground plane, the cutout area R is D-shaped, and the ratio of the area of ​​the cutout area R to the area of ​​the pad 32 located above the cutout area R is 0.75, the error percentages of the highest and lowest impedances of the signal transmission line 3 compared to the standard impedance are 8%, which is the best way to reduce the impedance variation of the signal transmission line 3.

[0053] Figure 8 This is an impedance variation diagram for a signal transmission line with a standard impedance of 100 ohms. When the depth D of the cutout region R is equal to the thickness H2 of the ground plane and the area of ​​the cutout region R below pad 32 is equal to the area of ​​pad 32, see [reference needed]. Figure 8 The curve S1 shows that the highest and lowest impedances of signal transmission line 3 are 105.70 ohms and 82.75 ohms, respectively, and the percentage error of the lowest impedance of signal transmission line 3 compared with the standard impedance is 17.25%.

[0054] When the depth of the cutout region R is equal to the thickness H2 of the ground plane and the area below pad 32 is a complete ground plane 2, see [reference needed]. Figure 8 Curve S2 shows that the highest and lowest impedances of signal transmission line 3 are 103.33 ohms and 80.50 ohms, respectively, and the percentage error of the lowest impedance of signal transmission line 3 compared with the standard impedance is 19.5%.

[0055] When the depth D of the cutout region R is equal to the thickness H2 of the ground plane, the shape of the cutout region R is D-shaped, and the ratio of the area of ​​the cutout region R to the area of ​​the pad 32 located above the cutout region R is 0.75, see [reference needed]. Figure 8The curve S3 shows that the highest and lowest impedances of signal transmission line 3 are 99.71 ohms and 90.68 ohms, respectively, and the percentage error of the lowest impedance of signal transmission line 3 compared to the standard impedance is 9.32%.

[0056] When the depth D of the cutout region R is equal to the thickness H2 of the ground plane, the shape of the cutout region R is D-shaped, and the ratio of the area of ​​the cutout region R to the area of ​​the pad 32 above the cutout region R is 0.79, see [reference needed]. Figure 8 The impedance timing line S4, the highest impedance of signal transmission line 3 and the lowest impedance are 95.06 ohms and 88.51 ohms respectively. The percentage error of the lowest impedance of signal transmission line 3 compared with the standard impedance is 11.49%.

[0057] Therefore, it can be seen that the cutout area R can indeed reduce the impedance change of the signal transmission line 3. The effect of reducing the impedance change of the signal transmission line 3 is best when the depth of the cutout area R is equal to the thickness H2 of the ground plane, the cutout area R is D-shaped, and the ratio of the area of ​​the cutout area R to the area of ​​the pad 32 located above the cutout area R is 0.75.

[0058] Figure 9 This is a schematic diagram of the fifth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 9 The depth of the cutout region R is equal to the thickness H2 of the ground plane and the shape of the pad 32 is circular. The cutout region R includes a first annular region R11 and a second annular region R12. The first annular region R11 has a first outer radius and a first inner radius. The second annular region R12 has a second outer radius and a second inner radius. Since the second inner radius of the second annular region R12 is greater than the first outer radius of the first annular region R11, the second annular region R12 is located outside the first annular region R11 and surrounds the first annular region R11.

[0059] The width of the first annular region R11 is equal to the difference between the radius of the first outer circle and the radius of the first inner circle. The width of the second annular region R12 is equal to the difference between the radius of the second outer circle and the radius of the second inner circle. The width of the first annular region R11 is equal to the width of the second annular region R12.

[0060] Figure 10 This is a schematic diagram of the sixth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 10The depth of the cutout region R is equal to the thickness H2 of the ground plane and the shape of the pad 32 is circular. The cutout region R includes a first annular region R13 and a second annular region R14. The first annular region R13 has a first outer radius and a first inner radius. The second annular region R14 has a second outer radius and a second inner radius. Since the second inner radius of the second annular region R14 is greater than the first outer radius of the first annular region R13, the second annular region R14 is located outside the first annular region R13 and surrounds the first annular region R13.

[0061] The width of the first annular region R13 is equal to the difference between the radius of the first outer circle and the radius of the first inner circle, and the width of the second annular region R14 is equal to the difference between the radius of the second outer circle and the radius of the second inner circle. However, the width of the first annular region R13 is greater than the width of the second annular region R14.

[0062] Figure 11 This is a schematic diagram of the sixth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 11 The depth of the cutout region R is equal to the thickness H2 of the ground plane and the shape of the pad 32 is circular. The cutout region R includes a first annular region R15 and a second annular region R16. The first annular region R15 has a first outer radius and a first inner radius. The second annular region R16 has a second outer radius and a second inner radius. Since the second inner radius of the second annular region R16 is greater than the first outer radius of the first annular region R15, the second annular region R16 is located outside the first annular region R15 and surrounds the first annular region R15.

[0063] The width of the first annular region R15 is equal to the difference between the radius of the first outer circle and the radius of the first inner circle, and the width of the second annular region R16 is equal to the difference between the radius of the second outer circle and the radius of the second inner circle, and the width of the first annular region R15 is less than the width of the second annular region R16.

[0064] Figure 12 This is a schematic diagram of the seventh embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 12 The depth of the cutout region R is equal to the thickness H2 of the ground plane, and the shape of the pad 32 is circular. The cutout region R includes a first rectangular area T1 and a second rectangular area T2. The first rectangular area T1 and the second rectangular area T2 have the same area and are parallel to each other. The projection of the center of the pad 32 onto the ground plane 2 is between the first rectangular area T1 and the second rectangular area T2. The lengths of the first rectangular area T1 and the second rectangular area T2 are greater than the radius of the pad 32 and close to the diameter of the pad 32.

[0065] Figure 13 This is a schematic diagram of the eighth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 13The depth of the cutout region R is equal to the thickness H2 of the ground plane, and the shape of the pad 32 is circular. The shape of the cutout region R is rectangular, and the projection of the center of the pad 32 onto the ground plane 2 lies within the cutout region R. The length of the cutout region R is approximately equal to the radius of the pad 32.

[0066] Figure 14 This is a schematic diagram of the ninth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 14 The depth of the cutout region R is equal to the thickness H2 of the ground plane, and the shape of the pad 32 is circular. The shape of the cutout region R is cross-shaped, and the projection of the center of the pad 32 onto the ground plane 2 is located in the cutout region R. The length of the cutout region R is close to the diameter of the pad 32.

[0067] Figure 15 This is a schematic diagram of the tenth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. See also... Figure 15 The depth of the cutout area R is equal to the thickness H2 of the ground plane, and the shape of the pad 32 is circular. The shape of the edge of the cutout area R is stepped.

[0068] In other embodiments of the present invention, the ratio between the depth of the hollow region R and the thickness H2 of the ground plane 2 is greater than 0 and less than 1.

[0069] Figure 16 This is a cross-sectional view of the eleventh embodiment of the hollowed-out area of ​​the grounding plane of this utility model. (See also...) Figure 16 The ratio between the depth of the cutout region R and the thickness H2 of the ground plane is 0.5, and the area of ​​the cutout region R is equal to the area of ​​the pad 32 located above the cutout region R2.

[0070] Figure 17 This is a cross-sectional view of the twelfth embodiment of the hollowed-out area of ​​the grounding plane of this utility model. (See also...) Figure 17 The ratio between the depth of the cutout region R and the thickness H2 of the ground plane is 0.3, and the area of ​​the cutout region R is equal to the area of ​​the pad 32 located above the cutout region R2.

[0071] In summary, the circuit board structure of this utility model reduces the capacitance between the pads and the ground plane by removing the ground plane under the pads, thereby reducing the impedance drop. Compared to changing the shape of the pads, removing the ground plane under each pad is easier to achieve.

[0072] The above description is only a preferred embodiment of the present utility model and does not limit the patent scope of the present utility model. Therefore, all equivalent technical changes made based on the contents of the present utility model specification and drawings are included within the protection scope of the present utility model.

Claims

1. A circuit board structure, characterized in that, The circuit board structure includes: A substrate is provided with a signal transmission line, the signal transmission line including a lead and a pad; and A ground plane is connected to the substrate and has a cutout area, which is located below the pad.

2. The circuit board structure according to claim 1, characterized in that, The substrate includes a first surface and a second surface, the first surface and the second surface being located on opposite sides of the substrate, the signal transmission line being disposed on the first surface, and the second surface being connected to the ground plane.

3. The circuit board structure according to claim 1, characterized in that, The hollowed-out area is circular in shape, and the area of ​​the hollowed-out area is equal to the area of ​​the solder pad.

4. The circuit board structure according to claim 1, characterized in that, The hollowed-out area is D-shaped, and the area ratio of the hollowed-out area to the pad is between 0.72 and 0.

78.

5. The circuit board structure according to claim 1, characterized in that, The hollowed-out area is D-shaped, and the area ratio of the hollowed-out area to the pad is between 0.3 and 0.

55.

6. The circuit board structure according to claim 1, characterized in that, The hollowed-out area includes a first annular area and a second annular area, the second annular area surrounds the first annular area, and the width of the first annular area is equal to the width of the second annular area.

7. The circuit board structure according to claim 1, characterized in that, The hollowed-out area includes a first annular area and a second annular area, the second annular area surrounds the first annular area, and the width of the first annular area is greater than the width of the second annular area.

8. The circuit board structure according to claim 1, characterized in that, The hollowed-out area includes a first annular area and a second annular area, the second annular area surrounds the first annular area, and the width of the first annular area is smaller than the width of the second annular area.

9. The circuit board structure according to claim 1, characterized in that, The hollowed-out area comprises two rectangular areas, which have the same area and are parallel to each other.

10. The circuit board structure according to claim 1, characterized in that, The hollowed-out area is located on the side away from the lead wire.

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