Differential transmission line wiring design method and wiring structure of circuit board

Abstract

The invention relates to a differential transmission line wiring design method and wiring structure of a circuit board, and the design method comprises the steps: calculating the basic finished product control line width, basic finished product control line distance and basic wiring space value of a differential transmission line according to the impedance design requirement of the differential transmission line; according to the through hole distance value between the two through holes and the hole line distance threshold value from the through holes to the differential transmission line, the actual wiring space value of the wire clamping area is calculated; if the actual wiring space value is smaller than the basic wiring space value, the differential transmission line is shrunk in a line clamping area to form narrow lines, and the design line width of the narrow lines and the design line distance between the two narrow lines are determined; and performing line width compensation in the non-line-clamping area to form wide lines, and confirming the design line width of the wide lines and the design line distance between the two wide lines. The problem that the impedance of the differential transmission line in the BGA area of the circuit board cannot meet the requirement and high-speed signal transmission is affected can be effectively solved.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit boards, and in particular to a differential transmission line wiring design method and wiring structure of a circuit board. Background Art

[0002] BGA (Ball Grid Assay) technology is increasingly being used in chip packaging. Due to its excellent electrical performance, high I / O pin count, and compact size, it has gradually become the mainstream packaging format for high-end devices and high-density packaging. With the rapid development of the electronic communications industry, high-speed circuit boards are moving towards greater integration and higher speeds. This places higher demands on the signal integrity performance of high-speed signals, and thus on transmission lines. High-speed circuit boards often use differential transmission lines for signal transmission to improve their anti-interference capabilities. In the prior art, differential transmission lines on high-speed circuit boards typically use the same line width in both the BGA and non-BGA areas. However, the smaller spacing between the through-holes in the BGA pin array makes it impossible to achieve the same line width for the differential transmission lines in the BGA and non-BGA areas. Therefore, the line width of the differential transmission lines in the BGA area needs to be reduced. This reduction in the line width of the differential transmission lines in the BGA area significantly increases impedance, resulting in impedance failure in the BGA area, which affects high-speed signal transmission. Summary of the Invention

[0003] In response to the above-mentioned problems, the purpose of the present invention is to provide a differential transmission line wiring design method and wiring structure for a circuit board, which can effectively avoid the problem that the differential transmission line impedance in the BGA area of ​​the circuit board cannot meet the requirements and affects high-speed signal transmission.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] A method for designing differential transmission line routing for a circuit board, the circuit board comprising a circuit layer, the circuit layer comprising a BGA area, a non-BGA area, and two differential transmission lines arranged opposite each other and extending from the BGA area to the non-BGA area, the BGA area comprising a plurality of through holes, a clamping area formed between two adjacent through holes, and a non-clamping area formed between two adjacent clamping areas, the differential transmission lines comprising a first differential transmission line located in the BGA area and a second differential transmission line located in the non-BGA area, the two first differential transmission lines being located between the same two through holes, the two first differential transmission lines being axially symmetric about a line of symmetry of the two through holes, the first differential transmission lines comprising a narrow line located in the clamping area and a wide line located in the non-clamping area; the design method comprising the following steps:

[0006] Calculate the basic finished product control line width, basic finished product control line spacing, and basic wiring space value of the differential transmission line according to the impedance design requirements of the differential transmission line;

[0007] Calculating an actual wiring space value of the clamping area according to a through-hole spacing value between two through-holes and a hole-line spacing threshold from the through-hole to the differential transmission line;

[0008] If the actual wiring space value is less than the basic wiring space value, the differential transmission line is shrunk in the clamping area to form the narrow line, and the design line width of the narrow line and the design line spacing between the two narrow lines are confirmed; line width compensation is performed in the non-clamping area to form the wide line, and the design line width of the wide line and the design line spacing between the two wide lines are confirmed.

[0009] This solution's differential transmission line routing design method achieves signal integrity optimization in high-density BGA areas through structural innovation and dynamic impedance adjustment technology. The actual routing space value is calculated based on a joint calculation model of via spacing and via safety thresholds. When the actual routing space value is less than the basic routing space value, a line width shrinkage algorithm is used in the clamping area. Precision narrow lines are designed in the clamping area to offset the high-density layout between vias. Narrow line widths can reduce parasitic capacitance effects between vias and avoid impedance mutations caused by excessive line width, thereby maintaining the impedance continuity of differential pairs. In non-clamping areas, a gradient line width compensation structure is used to form wide lines through line width compensation to compensate for the impedance impact caused by the narrow line design in the clamping area.

[0010] Furthermore, the determining of the design line width of the narrow line and the design line distance between two narrow lines includes:

[0011] Calculating the finished product control line width of the narrow line and the finished product control line distance between two narrow lines according to the actual wiring space value;

[0012] Calculating an initial design line width of the narrow line and an initial design line distance between two narrow lines according to a line width compensation threshold, a finished product control line width of the narrow line, and a finished product control line distance between the narrow lines;

[0013] If the initial design line spacing between the two narrow lines is less than the minimum line spacing processing capability between the two differential transmission lines in the BGA area, determining the design line spacing between the two narrow lines according to the minimum line spacing processing capability between the two differential transmission lines in the BGA area;

[0014] The designed line width of the narrow line is calculated according to the designed line distance between the two narrow lines and the actual wiring space value.

[0015] Determining the design spacing between two narrow traces based on the minimum spacing capability of the BGA area ensures that the spacing between the two narrow traces remains above the etching precision limit, avoiding problems such as short circuits and high processing rejection rates caused by excessively small spacing. The design width of the narrow traces is optimized based on the spacing between the narrow traces and the actual routing space to meet the design impedance requirements of the differential transmission lines.

[0016] Furthermore, the determining of the design line distance between the two width lines includes:

[0017] The designed line distance between the two wide lines is determined according to the designed line distance between the two narrow lines.

[0018] The designed line spacing between two wide lines and the designed line spacing between two narrow lines can be designed to be equidistant, which can ensure the geometric consistency of the signal transmission path and meet the process requirements.

[0019] Furthermore, the determining of the design line width of the wide line includes:

[0020] Calculating an impedance impact value of the narrow line after shrinkage according to an initial design line width of the narrow line and a design line width of the narrow line;

[0021] The designed line width of the wide line is calculated according to the impedance impact value.

[0022] By evaluating the impedance impact of narrow trace reduction and dynamically assessing wide trace width compensation based on copper thickness, dielectric thickness, and dielectric constant, the designed width of the wide trace can be adjusted. By performing line width compensation on wide traces in non-clipped areas, the impedance impact of narrow trace design in the clipped areas can be offset, effectively resolving the issue of differential transmission line impedance not meeting requirements in the BGA area of ​​the PCB.

[0023] Furthermore, the determining of the design line width of the wide line and the design line distance between two wide lines includes:

[0024] Calculating an impedance impact value of the narrow line after shrinkage according to an initial design line width of the narrow line and a design line width of the narrow line;

[0025] Calculating the initial design line width of the wide line and the initial design line distance between two wide lines based on the basic finished product control line width and the basic finished product control line distance, and then calculating the impedance value corresponding to the initial design line width of the wide line;

[0026] The designed line width of the wide line and the initially designed line distance between two wide lines are calculated according to the impedance impact value and the impedance value corresponding to the initially designed line width of the wide line.

[0027] There is more space for wiring in the non-clamping area, so wide lines can be routed with wider line widths and line spacing. The designed line spacing between two wide lines is larger than the designed line spacing between two narrow lines, which reduces the process difficulty and improves the processing yield.

[0028] A differential transmission line wiring structure for a circuit board, the circuit board comprising a circuit layer, the circuit layer comprising a BGA area, a non-BGA area, and two differential transmission lines arranged opposite each other and extending from the BGA area to the non-BGA area, the BGA area comprising a plurality of through holes, a clamping area formed between two adjacent through holes, and a non-clamping area formed between two adjacent clamping areas, the differential transmission lines comprising a first differential transmission line located in the BGA area and a second differential transmission line located in the non-BGA area, the two first differential transmission lines being located between the same two through holes, the two first differential transmission lines being axially symmetric about a line of symmetry of the two through holes, and the first differential transmission lines comprising a narrow line located in the clamping area and a wide line located in the non-clamping area.

[0029] The differential transmission line wiring structure of this solution achieves a balance between high-density wiring and signal integrity in the BGA area of ​​the circuit board through partitioned line width adjustment. The wiring space in the clamping area of ​​adjacent through-holes in the BGA area is limited. By reducing the line width (narrow line), the high-density layout effect between through-holes is offset. The narrow line width can reduce the parasitic capacitance effect between through-holes and avoid impedance mutations caused by excessive line width, thereby maintaining the impedance continuity of the differential pair. At the same time, for the dense through-hole layout of the BGA solder ball array, the narrow line design in the clamping area can avoid the risk of short circuit between the line and the through-hole. The wiring space in the non-clamping area of ​​the BGA area is relatively ample, and a wider line width is restored to compensate for the loss of the narrow line segment. In the non-BGA area, the second differential transmission line can adopt a standard wide line width, which can reduce transmission loss and simplify impedance matching design, and is suitable for long-distance wiring. Furthermore, the two first differential transmission lines are located between the same two vias. A symmetrical design within the BGA area—that is, the two narrow and wide lines are completely mirrored—ensures geometric consistency in the signal transmission paths. Parasitic parameters between vias, such as inter-via capacitance, are shared. By synchronously adjusting line width and spacing, an equivalent LC resonant compensation structure is formed, reducing inter-via impedance variations. Compared to placing the two first differential transmission lines between two different vias, this effectively minimizes the impact of vias on signal transmission.

[0030] Furthermore, the distance between the two narrow lines is not less than a first distance threshold.

[0031] The first line spacing threshold is the minimum line spacing processing capability of the two differential transmission lines in the BGA area, which avoids problems such as line short circuit and high processing defect rate caused by the line spacing between the two narrow lines being too small.

[0032] Furthermore, the distance between two of the narrow lines is less than or equal to the distance between two of the wide lines.

[0033] In the non-clamping area of ​​the BGA region, there is ample wiring space. While increasing the line width, the line spacing between two wide lines can also be increased. By enhancing the coupling between differential pairs, the inductance increase caused by the line width reduction is compensated and the odd-mode impedance is maintained constant.

[0034] Furthermore, the distance between the two second differential transmission lines is not less than a second distance threshold, and the distance between the two second differential transmission lines is greater than the distance between the two narrow lines.

[0035] The second line spacing threshold is the optimal design line spacing of the two differential transmission lines in the non-BGA area. By adjusting the line width and line spacing of the two second differential transmission lines, the stability of high-speed signal transmission is guaranteed. At the same time, it can avoid problems such as line short circuit and high processing defect rate caused by the line spacing between the two second differential transmission lines being too small.

[0036] Furthermore, the differential transmission line further includes a connecting line that is arranged obliquely and connects the first differential transmission line and the second differential transmission line.

[0037] The line spacing of the two first differential transmission lines is smaller than the line spacing of the two second differential transmission lines. The two are connected by an inclined and gradually changing line width connecting line. The inclination angle of the connecting line is 125°-165°, forming a gradually changing impedance structure to reduce signal loss.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] The differential transmission line routing design method and routing structure of this solution achieves signal integrity optimization in high-density BGA areas through structural innovation and dynamic impedance adjustment technology. The actual routing space value is calculated based on a joint calculation model of via spacing and via safety threshold. When the actual routing space value is less than the basic routing space value, a line width shrinkage algorithm is used in the clamping area. Precision narrow lines are designed in the clamping area to offset the high-density layout impact between vias. Narrow line width can reduce the parasitic capacitance effect between vias and avoid impedance mutations caused by excessive line width, thereby maintaining the impedance continuity of the differential pair. In the non-clamping area, a gradient line width compensation structure is used to form wide lines through line width compensation to compensate for the impedance impact caused by the narrow line design in the clamping area. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a differential transmission line wiring design method for a circuit board according to an embodiment of the present invention.

[0041] Figure 2 Schematic diagram of a differential transmission line wiring structure according to an embodiment of the present invention Figure 1 .

[0042] Figure 3 Schematic diagram of a differential transmission line wiring structure according to an embodiment of the present invention Figure 2 .

[0043] Description of Figure Numbers:

[0044] Illustration: 1. Circuit layer; 2. BGA area; 21. Through hole; 22. Clamping area; 23. Non-clamping area; 3. Non-BGA area; 4. Differential transmission line; 41. First differential transmission line; 411. Narrow line; 412. Wide line; 42. Second differential transmission line; 43. Connecting line. DETAILED DESCRIPTION

[0045] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. The accompanying drawings illustrate preferred embodiments of the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein.

[0046] Embodiment 1: Provides a wiring design method for differential transmission lines 4 of a circuit board.

[0047] like Figure 2 and Figure 3 As shown, a circuit board structure design diagram, the circuit board includes a circuit layer 1, the circuit layer 1 includes a BGA area 2, a non-BGA area 3, and two differential transmission lines 4 relatively arranged and extending from the BGA area 2 to the non-BGA area 3, the BGA area 2 includes a plurality of through holes 21, a clamping area 22 is formed between two adjacent through holes, and a non-clamping area 23 is formed between two adjacent clamping areas 22, the differential transmission line 4 includes a first differential transmission line 41 located in the BGA area 2, and a second differential transmission line 42 located in the non-BGA area 3, the two first differential transmission lines 41 are located between the same two through holes 21, the two first differential transmission lines 41 are axially symmetrical with respect to the symmetry line of the two through holes 21, and the first differential transmission line 41 includes a narrow line 411 located in the clamping area 22 and a wide line 412 located in the non-clamping area 23.

[0048] like Figure 1 As shown, the differential transmission line 4 wiring design method includes the following steps:

[0049] S10: Calculate the basic finished product control line width, basic finished product control line spacing, and basic wiring space value of the differential transmission line 4 according to the impedance design requirements of the differential transmission line 4;

[0050] The impedance of the differential transmission line 4 satisfies the following formula (1):

[0051]

[0052] Z is the impedance of the differential transmission line 4. The actual impedance or the designed impedance during the calculation process meets the design requirements within the range of Z±10%; w is the line width of the differential transmission line 4; d is the line distance between the two differential transmission lines 4; ε r is the dielectric constant of the electrolyte layer. If the electrolyte layer is FR4, then ε r In the range of 4.2-4.5, the typical value is 4.3; h is the thickness of the electrolyte layer, generally in the range of 0.1-0.5mm; t is the copper thickness of the circuit layer, generally in the range of 12-35μm.

[0053] According to the impedance design requirements of the differential transmission line 4, the design impedance Z of the differential transmission line 4 is d Substituting formula (1) into the formula, we can calculate the basic finished product control line width w0 and the basic finished product control line spacing d0 of the differential transmission line 4. The values ​​of w0 and d0 are not unique. You can select appropriate values ​​as the basic finished product control line width and basic finished product control line spacing according to actual needs.

[0054] The basic wiring space value satisfies formula (2):

[0055] S0=2w0+d0

[0056] S0 is the basic wiring space value.

[0057] S20: Calculating an actual wiring space value of the clamping area 22 according to the through-hole spacing value between the two through-holes 21 and the hole-line spacing threshold from the through-hole 21 to the differential transmission line 4;

[0058] The actual wiring space value of the clamping area 22, the through-hole spacing value between the two through-holes 21, and the through-hole spacing threshold from the through-hole 21 to the differential transmission line 4 satisfy formula (3):

[0059] S1=D k -2d k

[0060] S1 is the actual wiring space value; D k is the through-hole spacing value between two through-holes 21; d k is the hole-line spacing threshold from the through hole 21 to the differential transmission line.

[0061] S30: If the actual wiring space value is less than the basic wiring space value, the differential transmission line 4 is shrunk in the clamping area 22 to form a narrow line 411, and the design line width of the narrow line 411 and the design line spacing between the two narrow lines 411 are confirmed; line width compensation is performed in the non-clamping area 23 to form a wide line 412, and the design line width of the wide line 412 and the design line spacing between the two wide lines 412 are confirmed.

[0062] If the actual wiring space value meets the basic wiring space value, the basic finished product control line width and basic finished product control line distance can be used as the basic finished product control line width and basic finished product control line distance of the first differential transmission line 41 in the BGA area 2 and the second differential transmission line 42 in the non-BGA area 3. The design line width and design line distance of the first differential transmission line 41 and the second differential transmission line 42 in the non-BGA area are calculated in combination with the line width compensation threshold. Specifically, the design line width is the basic finished product control line width plus the line width compensation threshold, and the design line distance is the basic finished product control line distance minus the line width compensation threshold.

[0063] In step S30, determining the design line width of the narrow line 411 and the design line distance between two narrow lines 411 includes the following steps:

[0064] S311: Calculate the finished product control line width of the narrow line and the finished product control line distance between two narrow lines based on the actual wiring space value;

[0065] The actual wiring space value, the finished product control line width of the narrow line 411, and the finished product control line distance between two narrow lines 411 satisfy formula (4):

[0066] 2w a0 +d a0 ≤S1

[0067] w a0 The finished product control line width of narrow line 411; d a0 is the finished product control line distance between the two narrow lines 411; at the same time, w a0 and d a0 The design impedance requirement of the differential transmission line 4 needs to meet the formula (1). a0 and d a0 The value of is not unique, and a set of appropriate values ​​can be selected based on the actual process capability.

[0068] S312: Calculating the initial design line width of the narrow line 411 and the initial design line distance between two narrow lines 411 according to the line width compensation threshold, the finished product control line width of the narrow line 411, and the finished product control line distance between the narrow lines 411;

[0069] The initial design line width of the narrow line satisfies formula (5):

[0070] w a1 =w a0 +w l

[0071] w a1 is the initial design line width of the narrow line 411; w l is the line width compensation threshold, w lWhen compensating the narrow line 411 , since the narrow line 411 close to the through hole 21 cannot be compensated, only one-side compensation can be performed on the opposite side of the two narrow lines 411 .

[0072] The initial design line spacing between the two narrow lines 411 satisfies formula (6):

[0073] d a1 =S1-2w a1

[0074] d a1 is the initial designed line distance between the two narrow lines 411 .

[0075] S313: If the initial design line spacing between the two narrow lines 411 is less than the minimum line spacing processing capability between the two differential transmission lines 4 in the BGA area 2, then the design line spacing between the two narrow lines 411 is determined based on the minimum line spacing processing capability between the two differential transmission lines 4 in the BGA area 2;

[0076] Among them, the minimum line distance processing capability between the two differential transmission lines 4 in the BGA area 2 is related to the process. When the process is determined, the minimum line distance processing capability is a fixed value d min1 ; then the design line distance d between the two narrow lines 411 a2 Equal to d min1 .

[0077] S314 : Calculating the designed line width of the narrow line according to the designed line distance between the two narrow lines 411 and the actual wiring space value.

[0078] The designed line width of the narrow line 411, the designed line distance between two narrow lines 411, and the actual wiring space value satisfy formula (7):

[0079]

[0080] w a2 is the designed line width of the narrow line 411.

[0081] In addition, if the initial design line spacing between the two narrow lines 411 meets the minimum line spacing processing capability between the two differential transmission lines 4 in the BGA area 2, then the initial design line width of the narrow line 411 is the design line width of the narrow line 411, and the initial design line spacing between the two narrow lines 411 is the design line spacing between the two narrow lines 411.

[0082] The designed spacing between the two narrow lines 411 is determined based on the minimum spacing capability of BGA area 2. This ensures that the spacing between the two narrow lines 411 remains above the etching precision limit, avoiding problems such as short circuit defects and high processing rejection rates caused by excessively small spacing. The designed width of narrow lines 411 is optimized based on the designed spacing between narrow lines 411 and the actual routing space to meet the designed impedance requirements of the differential transmission lines.

[0083] In step S30 , the design line width of the wide lines 412 in the non-clip area 23 and the design line distance between two wide lines 412 can be designed in the following two different ways according to actual conditions.

[0084] Method 1:

[0085] Design line distance d between two width lines 412 b2 The design line distance d between the two narrow lines 411 a2 The use of an equidistant design can ensure the geometric consistency of the signal transmission path and meet process requirements. The specific steps for calculating the design line width of wide line 412 are as follows:

[0086] S321: Calculating an impedance impact value of the narrow line after shrinkage based on the initial design line width of the narrow line 411 and the design line width of the narrow line 411;

[0087] The impedance impact value is calculated according to formula (8):

[0088]

[0089] and Satisfying the above formula (1), is the impedance impact value of the narrow line 411 after shrinking, The design line width w of the narrow line 411 a2 The corresponding impedance value; is the initial design line width w of the narrow line 411 a1 The corresponding impedance value.

[0090] S322: Calculate the design line width of the wide line 412 according to the impedance impact value;

[0091] Among them, the design line width w of the width line 412 is b2 Satisfying formula (9):

[0092]

[0093] The design line width w is 412 b2 The corresponding impedance value, Satisfying the above formula (1), w b1is the initial design line width of width line 412, w b1 With w a1 equal, is the initial design line width w of width line 412 b1 The corresponding impedance value, Satisfying the above formula (1), since w b1 With w a1 If they are equal, and equal.

[0094] When the copper thickness of the wide line 412 is different from that of the narrow line 411, the design line width of the wide line 412 is calculated according to the above formula (9). When the copper thickness of the wide line 412 is the same as that of the narrow line 411, the design line width of the wide line 412 can be simplified, that is, the line width compensation value of the wide line 412 is the same as the line width reduction value of the narrow line 411, so the design line width w of the wide line 412 is b2 The calculation of is based on formula (10):

[0095] w b2 =2w a1 -w a2

[0096] By evaluating the impedance impact of the reduced narrow line 411 and dynamically assessing the line width compensation value for wide line 412 in combination with copper thickness, dielectric thickness, and dielectric constant, the designed line width of wide line 412 can be adjusted. By performing line width compensation on wide line 412 in the non-clip area 23, the impedance impact of the narrow line 411 design in the clip area 22 is offset, effectively resolving the issue of differential transmission line 4 failing to meet impedance requirements in BGA area 2 of the circuit board.

[0097] Method 2:

[0098] In the non-clamping area 23 of the BGA region 2, there is ample wiring space, and a wider line spacing can be used. While increasing the line spacing between the two wide lines 412, the line width can also be increased. By enhancing the coupling between the differential pairs, the inductance increase caused by the line width reduction is compensated, and the odd-mode impedance is maintained constant. At the same time, the designed line spacing between the two wide lines 412 is greater than the designed line spacing between the two narrow lines 411, which reduces the process difficulty and improves the processing yield.

[0099] The wiring design of the wide line 412 is performed based on the basic finished product control line width and basic finished product control line spacing of the differential transmission line 4. The specific steps for calculating the design line width of the wide line 412 and the initial design line spacing between two wide lines 412 are as follows:

[0100] S321: Calculate the impedance impact value of the narrow line 411 after shrinkage based on the initial design line width of the narrow line 411 and the design line width of the narrow line 411; wherein the impedance impact value is calculated according to the above formula (8);

[0101] S322: Calculate the initial design line width of the wide line 412 and the initial design line distance between two wide lines 412 based on the basic finished product control line width and the basic finished product control line distance, and then calculate the impedance value corresponding to the initial design line width of the wide line 412;

[0102] The initial design line width of the wide line 412 satisfies formula (11):

[0103] w b1 =w0+w l

[0104] w b1 is the initial design line width of the wide line 412 .

[0105] The initial design line spacing between the two width lines 412 satisfies formula (12):

[0106] d b1 =d0-w b1

[0107] d b1 is the initial design line distance between the two wide lines 412.

[0108] The impedance value corresponding to the initial design line width of the wide line 412 The above formula (1) is satisfied.

[0109] S323: Calculate the design line width of the wide line 412 and the initial design line distance between two wide lines 412 according to the impedance impact value and the impedance value corresponding to the initial design line width of the wide line 412; wherein the design line width w of the wide line 412 is b2 and the design line distance d between the two width lines 412 b2 Satisfying formula (13):

[0110]

[0111] The design line width w is 412 b2 The corresponding impedance value, Satisfies the above formula (1). b2 and d b2 The value of is not a unique solution. Just choose an appropriate value based on the actual process capability.

[0112] It should be noted that the length of the wide line 412 is equal to the length of the narrow line 411 and is half the via pitch between the two vias 21. Furthermore, the design line width of the second differential transmission line 42 in the non-BGA area 3 can be calculated by adding the line width compensation threshold to the basic finished product control line width, and the design line spacing between the two second differential transmission lines can be calculated by subtracting the line width compensation threshold from the basic finished product control line spacing.

[0113] Embodiment 2: Based on the above-mentioned method for designing the wiring of the differential transmission line 4 of the circuit board, a wiring structure of the differential transmission line 4 of the circuit board is designed.

[0114] like Figure 2 and Figure 3 As shown, this embodiment provides a differential transmission line wiring structure of a circuit board. The circuit board includes a circuit layer 1, the circuit layer 1 includes a BGA area 2, a non-BGA area 3, and two differential transmission lines 4 arranged opposite to each other and extending from the BGA area 2 to the non-BGA area 3. The BGA area 2 includes a plurality of through holes 21, a clamping area 22 is formed between two adjacent through holes, and a non-clamping area 23 is formed between two adjacent clamping areas 22. The differential transmission line 4 includes a first differential transmission line 41 located in the BGA area 2 and a second differential transmission line 42 located in the non-BGA area 3. The first differential transmission line 41 includes a narrow line 411 located in the clamping area 22 and a wide line 412 located in the non-clamping area 23. The line width of the narrow line 411 is smaller than the line width of the wide line 412, and the line width of the narrow line 411 is also smaller than the line width of the second differential transmission line 42.

[0115] In this embodiment, the two first differential transmission lines 41 are located between the same two through-holes 21, sharing parasitic parameters between the through-holes 21, such as inter-hole capacitance. By synchronously adjusting the line width and line spacing, an equivalent LC resonant compensation structure is formed, reducing the impedance jump between the through-holes 21. Compared to the case where the two first differential transmission lines 41 are located between two different through-holes 21, the impact of the through-holes 21 on signal transmission can be effectively avoided. The two first differential transmission lines 41 are axially symmetrical about the symmetry line of the two through-holes 21. Through the symmetrical design in the BGA area 2, that is, the two narrow lines 411 and the wide line 412 are completely mirrored, the geometric consistency of the signal transmission path is ensured.

[0116] In this embodiment, the line distance between the two narrow lines 411 is not less than the first line distance threshold, such as Figure 2 As shown, the line distance between the two narrow lines 411 is equal to the line distance between the two wide lines 412; Figure 3 As shown, the spacing between the two narrow lines 411 is smaller than the spacing between the two wide lines 412. The first spacing threshold represents the minimum spacing capability of the two differential transmission lines 4 in BGA area 2. This prevents problems such as short circuits and high processing failure rates caused by the spacing between the two narrow lines 411 being too small. In the non-clip region 23 of BGA area 2, there is ample wiring space. While increasing the line width, the spacing between the two wide lines 412 can also be increased. This enhances coupling between differential pairs, compensating for the increased inductance caused by the reduced line width, and maintaining a constant odd-mode impedance.

[0117] In this embodiment, the line spacing between the two second differential transmission lines 42 is not less than the second line spacing threshold, and the line spacing between the two second differential transmission lines 42 is greater than the line spacing between the two narrow lines 411. In the non-BGA area 3, under the condition that the differential impedance requirements of the circuit board are met, the line width and line spacing of the two differential transmission lines are as large as possible, thereby improving the signal transmission performance of the circuit board. The second line spacing threshold is the optimal design line spacing of the two differential transmission lines in the non-BGA area 3. By adjusting the line width and line spacing of the two second differential transmission lines 42, the stability of high-speed signal transmission is guaranteed, and at the same time, it can avoid problems such as line short circuit and high processing defect rate caused by the line spacing between the two second differential transmission lines 42 being too small. Furthermore, the differential transmission line 4 also includes a connecting line 43 that is arranged obliquely and connects the first differential transmission line 41 and the second differential transmission line 42. The line spacing of the two first differential transmission lines 41 is smaller than the line spacing of the two second differential transmission lines 42. The two are connected by an inclined and gradually width connecting line 43. The inclination angle of the connecting line 43 is 125°-165°, forming a gradually changing impedance structure to reduce signal loss.

[0118] Specifically, when designing the working draft, the design impedance Z of the differential transmission line 4 is d is 85Ω, which can fluctuate within the range of ±10%. According to formula (1), the basic finished product control line width w0 of the differential transmission line 4 is 4 mil, the basic finished product control line distance d0 of the differential transmission line is 7 mil, and the through-hole spacing value D between the two through-holes 21 in the BGA area 2 is k The line width compensation threshold w is 31.5 mil, the aperture of the through hole 21 is 8 mil, the hole-line spacing threshold from the through hole 21 to the first differential transmission line 41 is 7 mil, and the wiring space of the clamping area 22 is 9.5 mil. l The minimum line spacing processing capability is 1.6mil, the fixed value d min1 The design line distance d between the two narrow lines 411 can be determined based on the design method of the narrow line 411 in the clipping area 22 of the wiring design method. a2 The design line width w of the narrow line 411 is 2mil a2 is 3.75mil. Figure 2 As shown, the wiring structure of the wide lines 412 in the non-clamping area 23 is designed according to the first method of the wiring design method described above, and the design line spacing d between the two wide lines 412 is b2 The design line width w is 2mil and the width of the line is 412 b2 In the non-BGA area 3, the design line width of the second differential transmission line 42 is 5.6 mil, and the design line distance between the two second differential transmission lines 42 is 5.4 mil. Figure 3As shown, the wiring structure of the wide line 412 in the non-clamping area 23 is designed according to the second method in the above wiring design method. The design line width of the wide line 412 is w b2 The design line distance d between the two width lines 412 is 6.6mil. b2 In the non-BGA area 3, the line width of the second differential transmission line 42 is 5.6 mil, and the line spacing between the two second differential transmission lines 42 is 5.4 mil. The above line width and line spacing design may have other designs in other possible embodiments and are not specifically limited here.

[0119] In the description of the present invention, it should be understood that terms such as "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying 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 limiting the present invention.

[0120] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0121] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for designing differential transmission line wiring of a circuit board, wherein the circuit board includes a circuit layer, characterized in that: The circuit layer includes a BGA area, a non-BGA area, and two differential transmission lines arranged opposite to each other and extending from the BGA area to the non-BGA area. The BGA area includes a plurality of through holes, a line clamping area is formed between two adjacent through holes, and a non-line clamping area is formed between two adjacent line clamping areas. The differential transmission lines include a first differential transmission line located in the BGA area and a second differential transmission line located in the non-BGA area. The first differential transmission line includes a narrow line located in the line clamping area and a wide line located in the non-line clamping area. The design method includes the following steps: Calculate the basic finished product control line width, basic finished product control line spacing, and basic wiring space value of the differential transmission line according to the impedance design requirements of the differential transmission line; Calculating an actual wiring space value of the clamping area according to a through-hole spacing value between two through-holes and a hole-line spacing threshold from the through-hole to the differential transmission line; If the actual wiring space value is less than the basic wiring space value, the differential transmission line is shrunk in the clamping area to form the narrow line, and the design line width of the narrow line and the design line spacing between the two narrow lines are confirmed; line width compensation is performed in the non-clamping area to form the wide line, and the design line width of the wide line and the design line spacing between the two wide lines are confirmed.

2. The differential transmission line layout design method for a circuit board according to claim 1, wherein: The determining of the design line width of the narrow line and the design line distance between two narrow lines includes: Calculating the finished product control line width of the narrow line and the finished product control line distance between two narrow lines according to the actual wiring space value; Calculating an initial design line width of the narrow line and an initial design line distance between two narrow lines according to a line width compensation threshold, a finished product control line width of the narrow line, and a finished product control line distance between the narrow lines; If the initial design line spacing between the two narrow lines is less than the minimum line spacing processing capability between the two differential transmission lines in the BGA area, determining the design line spacing between the two narrow lines according to the minimum line spacing processing capability between the two differential transmission lines in the BGA area; The designed line width of the narrow line is calculated according to the designed line distance between the two narrow lines and the actual wiring space value.

3. The differential transmission line layout design method for a circuit board according to claim 2, wherein: Determining the design line distance between the two width lines includes: The designed line distance between the two wide lines is determined according to the designed line distance between the two narrow lines.

4. The differential transmission line layout design method for a circuit board according to claim 3, wherein: The determining of the design line width of the wide line includes: Calculating an impedance impact value of the narrow line after shrinkage according to an initial design line width of the narrow line and a design line width of the narrow line; The designed line width of the wide line is calculated according to the impedance impact value.

5. The differential transmission line layout design method for a circuit board according to claim 2, wherein: The determining of the design line width of the wide line and the design line distance between two wide lines includes: Calculating an impedance impact value of the narrow line after shrinkage according to an initial design line width of the narrow line and a design line width of the narrow line; Calculating the initial design line width of the wide line and the initial design line distance between two wide lines based on the basic finished product control line width and the basic finished product control line distance, and then calculating the impedance value corresponding to the initial design line width of the wide line; The designed line width of the wide line and the initially designed line distance between two wide lines are calculated according to the impedance impact value and the impedance value corresponding to the initially designed line width of the wide line.

6. A differential transmission line wiring structure of a circuit board, the circuit board comprising a circuit layer, characterized in that: The circuit layer includes a BGA area, a non-BGA area, and two differential transmission lines relatively arranged and extending from the BGA area to the non-BGA area. The BGA area includes a plurality of through holes, a clamping area is formed between two adjacent through holes, and a non-clamping area is formed between two adjacent clamping areas. The differential transmission lines include a first differential transmission line located in the BGA area and a second differential transmission line located in the non-BGA area. The two first differential transmission lines are located between the same two through holes, and the two first differential transmission lines are axially symmetrical about the symmetry line of the two through holes. The first differential transmission lines include a narrow line located in the clamping area and a wide line located in the non-clamping area.

7. The differential transmission line wiring structure of a circuit board according to claim 6, wherein: The distance between the two narrow lines is not less than a first distance threshold.

8. The differential transmission line wiring structure of a circuit board according to claim 7, wherein: The distance between the two narrow lines is less than or equal to the distance between the two wide lines.

9. The differential transmission line wiring structure of a circuit board according to claim 8, wherein: The distance between the two second differential transmission lines is not less than a second distance threshold, and the distance between the two second differential transmission lines is greater than the distance between the two narrow lines.

10. The differential transmission line wiring structure of a circuit board according to claim 6, wherein: The differential transmission line further includes a connecting line that is arranged obliquely and connects the first differential transmission line and the second differential transmission line.

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