CN113033140B - Simulation method for accurately obtaining dielectric constant difference of upper and lower layers of PCB wiring - Google Patents
Simulation method for accurately obtaining dielectric constant difference of upper and lower layers of PCB wiring Download PDFInfo
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- CN113033140B CN113033140B CN202110228658.8A CN202110228658A CN113033140B CN 113033140 B CN113033140 B CN 113033140B CN 202110228658 A CN202110228658 A CN 202110228658A CN 113033140 B CN113033140 B CN 113033140B
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- 238000004088 simulation Methods 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 23
- 238000003475 lamination Methods 0.000 claims abstract description 58
- 238000012360 testing method Methods 0.000 claims description 14
- 238000001228 spectrum Methods 0.000 claims description 3
- 238000010586 diagram Methods 0.000 description 5
- 239000011347 resin Substances 0.000 description 3
- 229920005989 resin Polymers 0.000 description 3
- 239000004744 fabric Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000010030 laminating Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008054 signal transmission Effects 0.000 description 1
Classifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/30—Circuit design
- G06F30/39—Circuit design at the physical level
- G06F30/394—Routing
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/30—Circuit design
- G06F30/39—Circuit design at the physical level
- G06F30/398—Design verification or optimisation, e.g. using design rule check [DRC], layout versus schematics [LVS] or finite element methods [FEM]
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- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
- H05K3/00—Apparatus or processes for manufacturing printed circuits
- H05K3/0005—Apparatus or processes for manufacturing printed circuits for designing circuits by computer
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- Engineering & Computer Science (AREA)
- Computer Hardware Design (AREA)
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- Theoretical Computer Science (AREA)
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- Geometry (AREA)
- General Engineering & Computer Science (AREA)
- General Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
- Manufacturing & Machinery (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Production Of Multi-Layered Print Wiring Board (AREA)
Abstract
The invention discloses a simulation method for accurately obtaining dielectric constant differences of upper and lower layers of a PCB wiring, which comprises the steps of firstly obtaining far-end signal crosstalk characteristics of prepregs in a circuit board after lamination, secondly obtaining far-end signal crosstalk characteristics of the prepregs in the circuit board before lamination, thirdly simulating the dielectric constant of the prepregs before lamination in simulation software, obtaining the dielectric constant of the prepregs after lamination, and finally obtaining actual dielectric constant difference values of the upper and lower layers of the PCB wiring. By the simulation method, the dielectric constant of the prepreg after lamination is accurately obtained, and the prepreg with the dielectric constant closer to that of the core board can be selected when the PCB wiring design is carried out, so that the dielectric constant difference between the prepreg and the core board is reduced, and the PCB wiring design is optimized.
Description
Technical Field
The invention relates to the technical field of circuit board design, in particular to a simulation method for accurately obtaining dielectric constant differences of upper and lower layers of a PCB wiring.
Background
The printed circuit board (Printed Circuit Board, PCB) is also called as printed circuit board, is an important component of electronic product physical support and signal transmission, and the multilayer board is formed by laminating a plurality of different core boards and prepregs (PP sheets).
Because the core plate is a structure which is cured before lamination, the dielectric constant of the core plate is relatively fixed, but the prepreg is not cured before lamination and can be slowly cured after being melted at high temperature in the lamination process, so that the dielectric constants of the prepregs before and after lamination have small difference. When the PCB is designed to run on the inner layer, the dielectric constants of the upper layer and the lower layer are the same in theory, so that far-end signal crosstalk does not exist in the running line in the same direction, but in practice, the dielectric constants of the upper layer and the lower layer of the running line are different due to the fact that core boards and prepregs of different types are selected, and the far-end signal crosstalk is generated.
Therefore, how to obtain the dielectric constant of the prepreg after lamination, and further optimize the PCB trace design by using the dielectric constant difference between the upper and lower layers of the trace, the above-mentioned problems are to be solved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a simulation method for accurately obtaining the dielectric constant difference of the upper layer and the lower layer of a PCB wiring.
The technical scheme of the invention is as follows:
a simulation method for accurately obtaining dielectric constant differences of upper and lower layers of a PCB wiring is characterized by comprising the following steps:
step 1: obtaining far-end signal crosstalk characteristics after pressing prepregs adjacent to PCB wires in a circuit board;
step 2: obtaining far-end signal crosstalk characteristics before lamination of prepregs adjacent to PCB wires in a circuit board;
step 3: setting a prepreg dielectric constant scanning range in simulation software, gradually scanning the dielectric constant before prepreg lamination according to a set value until a simulation far-end signal crosstalk result is matched with an actual far-end signal crosstalk test result, stopping scanning, and determining the value as the dielectric constant after prepreg lamination;
step 4: and obtaining a real dielectric constant difference value of the upper layer and the lower layer of the PCB wiring, and designing the PCB wiring according to the difference value.
According to the scheme, the method is characterized in that in step 1, the lamination and wiring data of the existing circuit board are tested by utilizing a spectrum analyzer, and the far-end signal crosstalk characteristic of the circuit board after the prepregs adjacent to the PCB wiring are pressed is obtained.
According to the scheme, the method is characterized in that in step 2, a lamination model and a routing model are built in simulation software, lamination parameters of a circuit board are input in the lamination model, routing parameters of a routing layer are input in the routing model, then simulation test is carried out, and far-end signal crosstalk characteristics before lamination of prepregs adjacent to PCB routing in the circuit board are obtained.
The invention according to the above scheme is characterized in that the simulation software is ADS simulation software.
According to the above scheme, in the step 2, the input lamination parameters include a prepreg dielectric constant adjacent to the PCB trace, a core dielectric constant adjacent to the PCB trace, a height of the trace layer from the upper reference layer, and a height of the trace layer from the lower reference layer.
According to the above scheme, in step 2, the input routing parameters include the width of the routing, the center-to-center distance of the routing, and the length of the routing.
The invention according to the scheme is characterized by further comprising the step of looking up a table to obtain the dielectric constant of the prepreg before lamination and the dielectric constant of the core plate before the step 2 is carried out.
According to the scheme, the simulation method has the beneficial effects that the dielectric constant value of the prepreg after lamination is obtained, and when the PCB wiring design is carried out, the prepreg with the dielectric constant closer to that of the core plate can be selected, so that the dielectric constant difference between the prepreg and the core plate is reduced, and the manufactured differential line is further ensured to have better far-end signal crosstalk characteristics. The difference between the dielectric constant of the prepreg after lamination and the dielectric constant of the core board is obtained through a simulation method, and when the inner layer of the PCB is designed at high speed, the wiring interval of the same group of signals is required to be pulled to ensure a certain crosstalk margin, so that better data are provided.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments or the description of the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and that other drawings can be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a circuit board laminate structure according to one embodiment of the present invention;
fig. 3 is a schematic diagram of a test result of far-end signal crosstalk after lamination of the prepreg according to the present invention;
FIG. 4 is a schematic diagram showing a simulation of the crosstalk results of the far-end signals and a fitting of the actual crosstalk test results of the far-end signals;
FIG. 5 is a schematic diagram of a scan range setup interface in a simulation software scan model of the present invention;
FIG. 6 is a schematic diagram of an interface of optimal values obtained by scanning in a simulation software scanning model of the invention;
FIG. 7 is a second schematic fitting diagram of the simulated far-end signal crosstalk results and the actual far-end signal crosstalk test results according to the present invention;
fig. 8 is a graph showing a fitting of far-end signal crosstalk results with different dielectric constants according to the present invention.
Detailed Description
The invention is further described below with reference to the drawings and embodiments:
as shown in fig. 2, the invention provides a circuit board with 8 laminated layers, wherein the 8 laminated layers are formed by laminating a core board and prepregs, the types of the prepregs of all layers are the same, and the type 1078 (RC 70%) is selected; the core board has different types, namely, a model 1078 (RC 59%) and a model 2116 (RC 55%).
In this embodiment, two single-ended wires are designed in the fifth layer, i.e., L5, the wire width of the wires is 4.5mil, the wire pitch of the wires is 4mil, and the length of the wires is 5000mil. The upper reference layer of the fifth layer is a model 2116 (RC 55%) core plate, and the dielectric constant of the core plate obtained by table lookup is 3.63; the lower reference layer is a prepreg of model 1078 (RC 70%), and the dielectric constant of the prepreg is 3.18 obtained by looking up a table. In order to obtain the difference of dielectric constants of upper and lower layers of a PCB wiring, a simulation test is carried out, and the simulation method comprises the following steps:
as shown in fig. 1 and 3, step 1: and testing the lamination and wiring data of the 8 layers by using a spectrum analyzer to obtain the far-end signal crosstalk characteristic, namely the actual test result of dielectric loss and frequency, of the prepreg pressed close to the PCB wiring.
As shown in fig. 4, step 2: establishing a lamination model and a wiring model in ADS simulation software, and inputting lamination parameters of 8 layers in the lamination model, wherein the lamination parameters comprise a core board dielectric constant adjacent to a PCB wiring, namely a dielectric constant of an upper reference layer of an L5 layer is 3.63, a prepreg dielectric constant adjacent to the PCB wiring, namely a dielectric constant of a lower reference layer of the L5 layer is 3.18, a height of the L5 layer from the upper reference layer is 7.2mil, and a height of the L5 layer from the lower reference layer is 29.5mil; and inputting wiring parameters of a wiring layer in a wiring model, wherein the wiring parameters comprise the width of the wiring is 4.5mil, the center distance of the wiring is 4mil, the length of the wiring is 5000mil, then performing simulation to obtain the far-end signal crosstalk characteristic, namely the simulation result of dielectric loss and frequency, of the prepreg adjacent to the PCB wiring before lamination, and finding that the simulation result and the test result are not fit.
Step 3: setting a prepreg dielectric constant scanning range in ADS simulation software, scanning the dielectric constant of the prepreg adjacent to the PCB wiring before lamination, gradually scanning according to a set value, simulating until the simulation far-end signal crosstalk result is similar to the actual far-end signal crosstalk test result, and stopping scanning to obtain the dielectric constant value of the prepreg after lamination.
As shown in fig. 5 to 7, in the present invention, the dielectric constant of the lower reference layer prepreg of the L5 layer is scanned, at this time, the dielectric constant of the prepreg is 3.18 before lamination, a scanning range is set, the minimum value is set to 3, the maximum value is set to 3.5, in order to obtain a more accurate dielectric constant of the prepreg after lamination, the scanning set value is 0.02, and step-by-step scanning is performed, and simulation is performed until the simulation far-end signal crosstalk result and the actual far-end signal crosstalk test result are simulated, the scanning is stopped, and the dielectric constant value of the prepreg is 3.32, which is the dielectric constant of the prepreg after lamination.
In step 3, the acquisition of the simulation scan range: the prepreg is formed by combining two parts of glass cloth and resin, the glass cloth is relatively stable before and after lamination, but the resin is melted during lamination to cause gummosis, so that the dielectric constant of the final prepreg after lamination is influenced, the dielectric constant of the laminated prepreg can be increased according to the dielectric constant of the resin per se to about 2.5 to 3, and the scanning range can be obtained after the gummosis is combined with a certain proportion of gummosis.
In step 3, after the dielectric constant of the prepreg after lamination is obtained, the prepreg with the dielectric constant closer to that of the core plate can be selected when the circuit board is manufactured, so that the manufactured differential line can be ensured to have better far-end signal crosstalk characteristic.
Step 4: and obtaining a real dielectric constant difference value of the upper layer and the lower layer of the PCB wiring, and designing the PCB wiring according to the difference value.
The simulation method of the invention finds that the dielectric constant of the prepreg changes after lamination, and the dielectric constant is changed from 3.18 before lamination to 3.32 after lamination. The dielectric constant difference between the laminated prepreg and the core board is calculated, and the distance between the PCB wirings can be determined according to the difference.
In one embodiment, it is simulated that if the difference between the dielectric constant of the prepreg after lamination and the dielectric constant of the core board reaches 0.4, the PCB wiring design needs to be pulled apart by 3 times of line width spacing, and the far-end signal crosstalk characteristics are as shown in the dashed line image in FIG. 8. Through simulation, if the dielectric constant difference between the prepreg after lamination and the dielectric constant of the core board reaches 0.2, the PCB wiring design needs to be pulled by 2 times of line width spacing, and the obtained far-end signal crosstalk characteristic is shown as a solid line image in fig. 8. The far-end signal crosstalk characteristics of the two are compared, and the result shows that the result with small dielectric constant difference is basically similar to the result with large dielectric constant difference, and when the PCB is designed, the wiring and the wiring with the distance of 2 times can save a lot of space, and the PCB has the advantage when the design density of the PCB is large.
The simulation method of the invention can accurately obtain the dielectric constant of the prepreg after lamination, and optimize the PCB wiring design by utilizing the difference between the dielectric constant of the prepreg after lamination and the dielectric constant of the core board, and has the following technical effects:
(1) When the PCB is designed, the prepreg with the dielectric constant closer to that of the core board can be selected, the dielectric constant difference between the prepreg and the core board is reduced, and the manufactured differential line is further ensured to have better far-end signal crosstalk characteristics.
(2) The difference between the dielectric constant of the prepreg after lamination and the dielectric constant of the core board is accurately obtained, and when the inner layer of the PCB is designed at high speed, the wiring interval of the same group of signals is required to be pulled to ensure a certain crosstalk margin, so that better data are provided.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
While the invention has been described above with reference to the accompanying drawings, it will be apparent that the implementation of the invention is not limited by the above manner, and it is within the scope of the invention to apply the inventive concept and technical solution to other situations as long as various improvements made by the inventive concept and technical solution are adopted, or without any improvement.
Claims (7)
1. A simulation method for accurately obtaining dielectric constant differences of upper and lower layers of a PCB wiring is characterized by comprising the following steps:
step 1: obtaining far-end signal crosstalk characteristics after pressing prepregs adjacent to PCB wires in a circuit board;
step 2: obtaining far-end signal crosstalk characteristics before lamination of prepregs adjacent to PCB wires in a circuit board;
step 3: setting a prepreg dielectric constant scanning range in simulation software, gradually scanning the dielectric constant before prepreg lamination according to a set value, performing simulation test until a simulation far-end signal crosstalk result is matched with a far-end signal crosstalk test result after prepreg lamination, stopping scanning, wherein the scanned dielectric constant is the dielectric constant after prepreg lamination;
step 4: and obtaining a real dielectric constant difference value of the upper layer and the lower layer of the PCB wiring, and designing the PCB wiring according to the difference value.
2. The simulation method for precisely obtaining the dielectric constant difference between the upper layer and the lower layer of the PCB trace according to claim 1, wherein in step 1, the lamination and trace data of the existing circuit board are tested by utilizing a spectrum analyzer to obtain the far-end signal crosstalk characteristic after lamination of prepregs adjacent to the PCB trace in the circuit board.
3. The simulation method for precisely obtaining the dielectric constant difference between the upper layer and the lower layer of the PCB wiring according to claim 1, wherein in step 2, a lamination model and a wiring model are built in simulation software, lamination parameters of a circuit board are input in the lamination model, wiring parameters of a wiring layer are input in the wiring model, and then simulation test is performed to obtain far-end signal crosstalk characteristics before lamination of prepregs adjacent to the PCB wiring in the circuit board.
4. A simulation method for accurately obtaining the dielectric constant difference between the upper layer and the lower layer of a PCB trace according to claim 3, wherein the simulation software is ADS simulation software.
5. A simulation method for accurately obtaining the difference between the dielectric constants of the upper and lower layers of the PCB trace according to claim 3, wherein in step 2, the inputted lamination parameters include the dielectric constant of the prepreg adjacent to the PCB trace, the dielectric constant of the core board adjacent to the PCB trace, the height of the trace layer from the upper reference layer, and the height of the trace layer from the lower reference layer.
6. The simulation method for precisely obtaining the dielectric constant difference between the upper layer and the lower layer of the PCB trace according to claim 3, wherein in the step 2, the inputted trace parameters include the width of the trace, the center-to-center distance of the trace and the length of the trace.
7. The simulation method for precisely obtaining the dielectric constant difference between the upper layer and the lower layer of the PCB trace according to claim 1, wherein the simulation method further comprises the step of looking up a table to obtain the dielectric constant before lamination of the prepreg and the dielectric constant of the core board before the step 2 is performed.
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| CN115361787B (en) * | 2022-09-16 | 2024-01-23 | 苏州浪潮智能科技有限公司 | PCB wiring design method, PCB wiring design processing method and PCB |
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