CN110516199B - Influence degree calculation method for influence factors of characteristic impedance and circuit board - Google Patents
Influence degree calculation method for influence factors of characteristic impedance and circuit board Download PDFInfo
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Abstract
The application discloses a method for calculating influence degree of influence factors on characteristic impedance and a circuit board. The influence degree calculation method for the influence factors of the characteristic impedance comprises the following steps: acquiring coefficient values corresponding to the influence factors; obtaining a deviation calculated value corresponding to the influence factors; calculating an influence value of the corresponding influence factor on the characteristic impedance according to the first equation and based on the coefficient value and the deviation calculated value; and calculating the influence degree of all influence factors on the characteristic impedance according to the second equation and based on the calculated influence values. According to the influence degree calculation method of the influence factors on the characteristic impedance, the influence value of the single influence factor on the characteristic impedance is calculated through a first equation, and then the influence degree of all influence factors on the characteristic impedance is calculated through a second equation, so that the calculation of the influence degree of all influence factors on the characteristic impedance is possible.
Description
Technical Field
The application relates to the technical field of circuit board processing, in particular to a method for calculating the influence degree of influence factors on characteristic impedance.
Background
With the continuous development of the electronic information industry, more and more high-speed signal PCBs have requirements for consistency of characteristic impedance, and tolerance control of the characteristic impedance is increasingly under test in the technical level of circuit board manufacturers.
The influence factors which can influence the characteristic impedance are more, however, the influence degree of the up-and-down fluctuation value of each influence factor on the characteristic impedance value is not calculated by a related model, so that each influence factor which influences the characteristic impedance value cannot be adjusted and controlled at the front end, and the quality control is plagued.
Disclosure of Invention
Based on this, it is necessary to provide a method for calculating the influence degree of influence factors on characteristic impedance, which can calculate the influence degree of each influence factor on characteristic impedance finally, and a circuit board; the influence degree calculation method of the influence factors on the characteristic impedance is adopted in the production process of the circuit board to calculate the influence degree of the influence factors on the characteristic impedance.
The technical scheme is as follows:
in one aspect, a method for calculating a degree of influence on influence factors of a characteristic impedance is provided, wherein at least one influence factor of the characteristic impedance is provided, and the method for calculating the degree of influence on the influence factors of the characteristic impedance comprises the following steps:
acquiring coefficient values corresponding to the influence factors;
obtaining a deviation calculated value corresponding to the influence factors;
calculating an influence value of the corresponding influence factor on the characteristic impedance according to the first equation and based on the coefficient value and the deviation calculated value;
calculating the influence degree of all influence factors on the characteristic impedance according to a second equation and based on the calculated influence values;
the first equation is:
Y i ＝k i *X i ；
the second equation is:
Z＝[∑(Y i 2 )] 0.5 ；
wherein i is the number of influencing factors, and takes a positive integer, k i For the coefficient value corresponding to the ith influencing factor, X i Calculate a value for the deviation corresponding to the ith influencing factor, Y i The i-th influence factor has an influence value on the characteristic impedance, and Z is the influence degree of all influence factors on the characteristic impedance.
According to the influence degree calculation method of the influence factors on the characteristic impedance, the influence value of the single influence factor on the characteristic impedance is calculated through the first equation, and then the influence degree of all influence factors on the characteristic impedance is calculated through the second equation, so that calculation of the influence degree of all influence factors on the characteristic impedance is possible.
The technical scheme is further described as follows:
in one embodiment, the coefficient value is retrieved from a preset database based on a first preset requirement.
In one embodiment, the coefficient values corresponding to the influencing factors in the preset database are determined by the following steps:
obtaining a deviation calculation value of an influence factor and obtaining a plurality of groups of deviation calculation values;
acquiring influence values of influence factors on characteristic impedance and acquiring a plurality of groups of influence values;
and processing the deviation calculated value and the influence value according to a first preset method, and obtaining a coefficient value which enables the influence value and the deviation calculated value to be in a linear relation.
In one embodiment, the first preset method is a linear regression method.
In one embodiment, the step of obtaining the coefficient value corresponding to the influencing factor includes:
obtaining the line type of the impedance line of the circuit board:
based on the line type, and obtaining a coefficient value corresponding to the line type.
In one embodiment, the deviation calculation is a deviation percentage or/and a deviation value.
In one embodiment, the influencing factors include at least one of a line width, a line thickness, a dielectric thickness, and a solder resist thickness.
In one embodiment, the calculated deviation value corresponding to the line width is a deviation percentage;
the calculated deviation value corresponding to the line thickness adopts a deviation value;
the deviation calculated value corresponding to the thickness of the medium adopts deviation percentage;
the deviation calculated value corresponding to the solder resist thickness adopts the deviation percentage.
In one embodiment, the line width has a line width in the range of 3.0mil to 15mil;
the thickness of the circuit is in the range of 0.5mil to 2.0mil;
the thickness of the medium ranges from 3.0mil to 10mil;
the thickness of the solder resist is 0.5mil-3.0mil.
On the other hand, the circuit board is also provided, and the influence degree calculation method for the influence factors of the characteristic impedance is adopted to calculate the influence degree of the influence factors of the characteristic impedance.
According to the circuit board, the influence degree of the influence factors of the characteristic impedance is calculated, so that the influence factors can be adjusted and controlled in production, and the processing quality of the processed circuit board is better.
Drawings
FIG. 1 is a flowchart of a method for calculating the influence degree of influence factors on characteristic impedance according to an embodiment;
fig. 2 is a graph of coefficient values of line widths and a processed line graph in the embodiment.
Detailed Description
Embodiments of the present application will be described in detail below with reference to the attached drawings:
it will be understood that when an element is referred to herein as being "fixed" with respect to another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, there are no intervening elements present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only and are not meant to be the only embodiment.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the description of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
Referring to fig. 1, a method for calculating a degree of influence on influence factors of a characteristic impedance, at least one of the influence factors of the characteristic impedance, includes the steps of:
acquiring coefficient values corresponding to the influence factors;
obtaining a deviation calculated value corresponding to the influence factors;
calculating an influence value of the corresponding influence factor on the characteristic impedance according to the first equation and based on the coefficient value and the deviation calculated value;
calculating the influence degree of all influence factors on the characteristic impedance according to a second equation and based on the calculated influence values;
the first equation is:
Y i ＝k i *X i ；
the second equation is:
Z＝[∑(Y i 2 )] 0.5 ；
wherein i is the number of influencing factors, and takes a positive integer, k i For the coefficient value corresponding to the ith influencing factor, X i Calculate a value for the deviation corresponding to the ith influencing factor, Y i The i-th influence factor has an influence value on the characteristic impedance, and Z is the influence degree of all influence factors on the characteristic impedance.
According to the influence degree calculation method of the influence factors on the characteristic impedance, the influence value of the single influence factor on the characteristic impedance is calculated through a first equation, and then the influence degree of all influence factors on the characteristic impedance is calculated through a second equation, so that the calculation of the influence degree of all influence factors on the characteristic impedance is possible.
Characteristic impedance: also known as "characteristic impedance", in the high frequency range, an instantaneous current is generated between the signal line and the reference plane (power or ground) where the signal edge arrives during signal transmission, due to the establishment of an electric field, if the transmission line is isotropic, a current I always exists as long as the signal is being transmitted, and if the output level of the signal is V, the transmission line is equivalent to a resistance of V/I during signal transmission, and this equivalent resistance is referred to as the characteristic impedance Z of the transmission line. During transmission of the signal, if the characteristic impedance of the transmission path changes, the signal will reflect at the junction where the impedance is discontinuous. Therefore, the characteristic impedance has a large influence on the performance of the wiring board.
The factors influencing the characteristic impedance are more, the influence degrees of different influence factors on the characteristic impedance are different, and under different conditions, the influence of some influence factors is large, the influence of some influence factors is small, and the judgment is needed according to specific conditions. Therefore, in the specific calculation, it can be determined empirically which influencing factors have a large effect and which influencing factors have a small effect, and for the factors which can be ignored or have a relatively small effect, the factors can be directly not calculated or classified as a certain influencing value according to experience, while other influencing factors which can have more influence are calculated according to the method provided in the embodiment, that is: firstly, obtaining coefficient values and deviation calculated values corresponding to all influence factors; then, calculating influence values corresponding to the influence factors respectively according to the first equation; and then, carrying out square sum calculation on the influence values corresponding to the influence factors through a second equation, and carrying out root number processing, so as to obtain the integral influence of all the influence factors on the characteristic impedance.
It should be noted that: i can be 1,2,3 and …, which refers to the number of influencing factors;
sigma is a sum symbol in a mathematical sense, and those skilled in the art should be aware of the sum symbol and will not be described in detail.
The deviation calculated value refers to a difference value or a fluctuation percentage of the influence factor relative to the normal condition, so that the conversion is performed through a coefficient value between the influence value and the deviation calculated value, and the description is omitted.
In one embodiment, the coefficient value is retrieved from a preset database based on a first preset requirement.
For the coefficient value of each influence factor, the system directly invokes the value during specific calculation, without temporary calculation, and improves the processing efficiency during calculation.
Further, the coefficient value corresponding to the influence factor in the preset database is determined by the following steps:
obtaining a deviation calculation value of an influence factor and obtaining a plurality of groups of deviation calculation values;
acquiring influence values of influence factors on characteristic impedance and acquiring a plurality of groups of influence values;
and processing the deviation calculated value and the influence value according to a first preset method, and obtaining a coefficient value which enables the influence value and the deviation calculated value to be in a linear relation.
Namely: firstly, acquiring a plurality of groups of deviation calculated values of one influence factor; then, obtaining an influence value corresponding to the deviation calculation value of the same influence factor; and then, the deviation calculated value corresponding to the influence factor is corresponding to the influence value, and the linear relation between the influence factor and the deviation calculated value is obtained through processing, namely, the coefficient value corresponding to the influence factor is obtained.
For the case of two or more influencing factors, the coefficient value corresponding to each influencing factor is obtained by adopting the method.
Further, the first preset method is a linear regression method. The linear regression method can fit the curve relationship between the deviation calculated values and the influence values into a linear relationship, so that the coefficient value corresponding to the influence factor is finally obtained, the linear regression method is an existing statistical processing method, and a person skilled in the art can obtain the coefficient value by searching related existing books such as a statistical theory and the like, and the description is omitted here.
In one embodiment, the step of obtaining the coefficient value corresponding to the influencing factor includes:
obtaining the line type of the impedance line of the circuit board:
based on the line type, and obtaining a coefficient value corresponding to the line type.
The impedance lines of the circuit board are divided into two types, i.e., single-ended and differential, and the distribution of the impedance lines on the circuit board is also divided into an outer layer and an inner layer, so there are four cases, namely: four cases of inner single-ended, inner differential, outer single-ended and outer differential are explained as follows:
single-ended inner layer: the impedance line is subjected to single-line wiring and is arranged on an inner circuit layer;
inner layer differential: the impedance line is used for carrying out double-line wiring and is in the case of an inner layer circuit layer;
single-ended outer layer: the impedance line is subjected to single-line wiring and is arranged on an outer layer circuit layer;
outer layer differential: the impedance line is used for double-line wiring and is arranged on the outer layer of the circuit layer.
The line types of different types of impedance lines have an influence on the influence degree of the influence factors on the characteristic impedance, so that the different coefficient values correspond to the line types of the impedance lines under different conditions and are required to be distinguished.
In one embodiment, the deviation calculation is a deviation percentage or/and a deviation value.
In one embodiment, the influencing factors include at least one of a line width, a line thickness, a dielectric thickness, and a solder resist thickness.
The factors which mainly affect the characteristic impedance are mainly the line width, the line thickness, the medium thickness and the solder resist thickness, and under the conditions of different processing flows, line designs and the like, the sizes of different influencing factors can be different, so that the influencing factors with larger influence can be calculated according to the actual conditions, and of course, various factors can be considered.
In fact, the influencing factors mainly influencing the characteristic impedance also comprise dielectric constant of the insulating matrix and dielectric constant of the solder resist ink, however, under the condition of determining the dielectric thickness, the dielectric constant of the insulating matrix is also determined, the dielectric constant of the insulating matrix is the self characteristic of the substrate, and the influence of the dielectric constant is also fixed, so that the dielectric thickness and the dielectric constant of the insulating matrix only need to be considered; the solder resist thickness and the dielectric constant of the solder resist ink are the same and will not be described in detail here.
For the line width, that is, the line width of the line layer, when calculating the influence degree of the influence factor on the characteristic impedance, the line types of four different impedance lines need to be considered, which are respectively: the inner layer single end, the inner layer differential, the outer layer single end and the outer layer differential are four, and each corresponds to a corresponding coefficient value of the line width under the corresponding condition.
For the line thickness, that is, the thickness of the line layer, that is, the thickness of the copper foil on the substrate, is the same as the line width, and the line types of four different impedance lines need to be considered, which are respectively: the inner layer single end, the inner layer differential, the outer layer single end and the outer layer differential are four, and each corresponds to a corresponding coefficient value of the line thickness under the corresponding condition.
For the medium thickness, i.e. the plate thickness, two cases of single end of the outer layer and difference of the outer layer need to be considered, each corresponding to the corresponding coefficient value of the medium thickness in the corresponding case.
For the solder resist thickness, namely the thickness of the solder resist green oil layer, because the solder resist only exists on the outer layer of the circuit board, only the circuit types of two different impedance lines need to be considered, and the circuit types are respectively: the single end of the outer layer and the difference of the outer layer are respectively corresponding to the corresponding coefficient value of the solder resist thickness under corresponding conditions.
In one embodiment, the calculated deviation value for the line width is a percentage deviation.
In one embodiment, the calculated deviation value corresponding to the line thickness is a deviation value;
in one embodiment, the calculated deviation value for the thickness of the medium is a percentage deviation;
in one embodiment, the calculated deviation value for the solder resist thickness is a deviation percentage.
Here, the deviation value refers to a deviation between actual data and set target data; the deviation percentage refers to the deviation between the actual data and the set target data, and the deviation percentage or the deviation value can be selected by those skilled in the art according to the actual calculation requirement to calculate the influence data on the final characteristic impedance, which is not described herein.
In one embodiment, the method for calculating the influence degree of the influence factors on the characteristic impedance provided by the application is especially suitable for the following situations:
line widths in the range of 3.0mil to 15mil;
the thickness of the circuit is in the range of 0.5mil to 2.0mil;
the thickness of the medium ranges from 3.0mil to 10mil;
the thickness of the solder resist is 0.5mil-3.0mil.
The present embodiment also provides a circuit board, which performs the influence degree calculation of the influence factor of the characteristic impedance by using the influence degree calculation method of the influence factor of the characteristic impedance as described in any one of the embodiments.
According to the circuit board, the influence degree of the influence factors of the characteristic impedance is calculated, so that the influence factors can be adjusted and controlled in production, and the processing quality of the processed circuit board is better.
Referring to fig. 2 and table 1, a specific example of calculating the coefficient value of the line width in the case of the outer layer difference is given.
TABLE 1 influence value of line width when the impedance line type is the outer layer difference
The table 1 shows the actual values of the widths of 30 groups of lines and the corresponding line width difference percentages in the case that the impedance lines are of the outer layer differential type, and shows the influence values of the corresponding line width differences on the characteristic impedance; fig. 2 is a graph prepared from the data of table 1, and a linear straight line graph obtained after fitting by a linear regression method. As can be seen from fig. 2, in this case, the coefficient value of the line width in the case of the outer layer difference is-0.4454, and the process is specifically the following steps, which are set as the outer layer difference case:
obtaining a target line width and an actual line width of a line width, and obtaining 30 groups of data;
obtaining deviation calculated values (the difference percentage in the embodiment) corresponding to the widths of 30 groups of lines respectively;
acquiring influence values of 30 groups of line widths on characteristic impedance;
the deviation calculated value and the influence value are processed according to a linear regression method, and coefficient values are obtained which make the influence value and the deviation calculated value in a linear relation.
To achieve the tolerance requirement (e.g., typically ±10% or ±5%) of the characteristic impedance, the tolerance can be allocated to the corresponding influencing factors, so as to control the tolerance requirement of the final characteristic impedance by controlling the influence degree of the influencing factors, and finally achieve the tolerance requirement by controlling the process standard of each process (e.g., acid etching, alkaline etching, pressing, electroplating, solder resist).
The characteristic impedance of the inner layer impedance line includes two cases: the inner layer does not need to be electroplated with copper; the inner layer needs to be electroplated with copper, namely, the blind holes containing metal.
In the first case, the line thickness (i.e., copper thickness) is very small without electroplating copper on the inner layer, so that the etched line width is relatively uniform, and table 2 shows a specific example:
TABLE 2 case where copper plating is not required for the inner layer
Table 2 above, taking the case of the inner layer single-ended type as an example, the copper thickness tolerance of.+ -. 3 μm was obtained from the actual production experience, and Y i ＝k i *X i Calculating the influence degree of the copper thickness on the impedance to be +/-3%; line width tolerance + -8% is obtained from practical production experience, according to Y i ＝k i *X i Calculating the influence degree +/-4% of the line width on the impedance; other factorsThe influence on the impedance is obtained from practical experience, and other factors are that the Y cannot be used i ＝k i *X i The calculated impedance influence can be obtained according to practical production experience data, and can be set to be +/-3%, and finally the influence of copper thickness on impedance, line width on impedance and other factors on impedance are brought into Z= [ Σ (Y) i 2 )] 0.5 The equation calculates the impedance tolerance (theoretical) to be + -5.8%.
The specific numerical value of the impedance tolerance (theory) is obtained, so that a PCB manufacturer is facilitated to judge whether the processing capacity of each process meets the tolerance requirement (such as +/-10% or +/-5% in general) of impedance, if the calculated impedance tolerance (theory) exceeds the required numerical value, the fact that the existing processing capacity cannot meet the impedance requirement is indicated, measures are taken to improve the processing capacity of one or more processes, for example, the control of the tight line width tolerance can be adopted, the line width deviation is reduced, the influence of the line width on the impedance is reduced, and therefore the smaller impedance tolerance is obtained; otherwise, if the calculated impedance tolerance is within the required range, the control can be performed according to the existing process capability.
In the second case, the inner layer needs copper plating, i.e. in the case of blind vias containing metallization, the copper thickness uniformity is degraded due to the thickened copper plating, and the copper thickness tolerance is larger, so the line width tolerance is also larger, and table 3 is a specific example:
TABLE 3 copper electroplating of the inner layer, i.e., containing metallized blind vias
Table 3 above shows that, taking the case of single-ended type of inner layer as an example, copper plating is required for the inner layer, the copper thickness difference is large and the line width difference is also large as compared with the case of no copper plating for the inner layer, and in this case, the copper thickness tolerance of.+ -. 8 μm is obtained from the actual production experience, and Y i ＝k i *X i Calculating the influence degree of the copper thickness on the impedance to be +/-8%; the line width tolerance of + -10% is obtained from practical production experience, according to Y i ＝k i *X i Equation calculates the influence of line width on impedance as5%; the influence of other factors on the impedance is obtained from practical experience, and the other factors are that the Y cannot be used i ＝k i *X i The calculated impedance influence degree can be set to be +/-3% according to actual production experience data; finally, the influence of the copper thickness on the impedance, the influence of the line width on the impedance and the influence of other factors on the impedance are brought into Z = [ Σ (Y i 2 )] 0.5 The equation calculates the impedance tolerance (theoretical) to be + -9.9%.
The specific value of the impedance tolerance (theory) is obtained, so that a PCB manufacturer can judge whether the processing capacity of each process meets the tolerance requirement (such as +/-10% or +/-5% in general) of impedance, if the calculated impedance tolerance (theory) exceeds the required value, the existing processing capacity cannot meet the impedance requirement, measures are taken to improve the processing capacity of one or more processes, for example, the control of the line width tolerance can be tightly received, the line width deviation is reduced, the influence degree of the line width on the impedance is reduced, and the smaller impedance tolerance is obtained; otherwise, if the calculated impedance tolerance is within the required range, the control can be performed according to the existing process capability.
For the characteristic impedance of the outer layer impedance line, there are two cases: primary electroplating; and (5) electroplating for multiple times.
For the case of primary electroplating, the electroplating times are less, the copper thickness is better uniform, and the copper thickness tolerance and the line width tolerance are smaller. Factors affecting the outer layer impedance tolerance include dielectric thickness tolerance, solder resist thickness tolerance, and other factors, table 4 being a specific example:
TABLE 4 external impedance, primary plating case
Table 4 above, taking the case of the outer layer single-ended type as an example, the copper thickness tolerance of.+ -. 10. Mu.m, obtained from the practical production experience, is defined by Y i ＝k i *X i Calculating the influence degree of the copper thickness on the impedance to be +/-2%; line width tolerance of + -10% is obtained from practical production experience, according to Y i ＝k i *X i Calculating the linewidth resistanceThe influence degree of the resistance is +/-5%; the thickness tolerance of + -10% is obtained from practical production experience and is based on Y i ＝k i *X i Calculating the influence degree of the dielectric thickness on the impedance to be +/-6%; the tolerance of the solder resist thickness is +/-30 percent, which is obtained from practical production experience and is based on Y i ＝k i *X i Calculating the influence degree of the solder resist thickness on the impedance to be +/-1%; the influence of other factors on the impedance is obtained from practical experience, and the other factors are that the Y cannot be used i ＝k i *X i The calculated impedance influence degree can be set to +/-2% according to actual production experience data; finally, the influence of copper thickness on impedance, line width on impedance, thickness on impedance, tolerance of solder resist thickness on impedance and influence of other factors on impedance are brought into Z = [ -sigma (Y) i 2 )] 0.5 The equation calculates the impedance tolerance (theoretical) to be + -8.4%.
The specific value of the impedance tolerance (theory) is obtained, so that a PCB manufacturer can judge whether the processing capacity of each process meets the tolerance requirement (such as +/-10% or +/-5% in general) of impedance, if the calculated impedance tolerance (theory) exceeds the required value, the existing processing capacity cannot meet the impedance requirement, and measures are taken to improve the processing capacity of one or more processes, for example, the control of the narrow line width tolerance can be adopted, the line width deviation is reduced, the influence degree of the line width on the impedance is reduced, and the smaller impedance tolerance is obtained; otherwise, if the calculated impedance tolerance is within the required range, the control can be performed according to the existing process capability.
For the case of multiple plating (two or more plating cases), copper thickness uniformity is poor, copper thickness tolerance is large, and line width tolerance is also large, table 5 is an example:
TABLE 5 external impedance, multiple plating case
Table 5 above shows that, taking the case of single-ended type of the outer layer as an example, the outer layer is plated a plurality of times, the copper thickness difference is larger than that of the outer layer by one-time plating, and the wireThe wide margin is also increased, and under the condition, the tolerance of copper thickness is + -15 mu m according to practical production experience, and Y is used for i ＝k i *X i The influence degree of the copper thickness on the impedance is calculated as +/-3% according to the equation; line width tolerance of + -15% is obtained from practical production experience, according to Y i ＝k i *X i Calculating the influence degree of the line width on the impedance to be +/-7.5%; the thickness tolerance of + -10% is obtained from practical production experience and is based on Y i ＝k i *X i Calculating the influence degree of the dielectric thickness on the impedance to be +/-6%; the tolerance of the solder resist thickness is +/-30 percent, which is obtained from practical production experience and is based on Y i ＝k i *X i Calculating the influence degree of the solder resist thickness on the impedance to be +/-1%; the influence of other factors on the impedance is obtained from practical experience, and the other factors are that the Y cannot be used i ＝k i *X i The calculated impedance influence degree can be set to +/-2% according to actual production experience data; finally, the influence of copper thickness on impedance, line width on impedance, thickness on impedance, tolerance of solder resist thickness on impedance and influence of other factors on impedance are brought into Z = [ -sigma (Y) i 2 )] 0.5 The equation calculates the impedance tolerance (theoretical) to be + -10.3%.
The specific value of the impedance tolerance (theory) is obtained, so that a PCB manufacturer can judge whether the processing capacity of each process meets the tolerance requirement (such as +/-10% or +/-5% in general) of impedance, if the calculated impedance tolerance (theory) exceeds the required value, the existing processing capacity cannot meet the impedance requirement, measures are taken to improve the processing capacity of one or more processes, for example, the control of the line width tolerance can be tightly received, the line width deviation is reduced, the influence degree of the line width on the impedance is reduced, and the smaller impedance tolerance is obtained; otherwise, if the calculated impedance tolerance is within the required range, the control can be performed according to the existing process capability.
According to tables 2-5, the tolerance standards of the line width, copper thickness (i.e. line thickness), dielectric thickness and solder resist thickness, which are required to be controlled for each process to meet the impedance tolerance required by the customer, can be determined based on the influence on the characteristic impedance, so that the indexes of each process can be controlled conveniently in the manufacturing process of the circuit board. Meanwhile, whether the capability of the existing working procedure can meet the tolerance requirement of the characteristic impedance of the customer can be intuitively reflected.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the application, which are described in detail and are not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (10)
1. A method for calculating the influence degree of influence factors on characteristic impedance, wherein at least one influence factor on characteristic impedance is included, the influence factor includes at least one of line width, line thickness, dielectric thickness and solder resist thickness, the influence degree calculation method for influence factors on characteristic impedance includes the steps of:
acquiring coefficient values corresponding to the influence factors, wherein the coefficient values are obtained by calling from a preset database based on a first preset requirement; the step of obtaining the coefficient value corresponding to the influence factor comprises the following steps: acquiring a line type of an impedance line of a circuit board, and acquiring the coefficient value corresponding to the line type based on the line type;
obtaining a deviation calculated value corresponding to the influence factor, wherein the deviation calculated value is a deviation percentage or/and a deviation value;
calculating an influence value of the influence factor on the characteristic impedance according to a first equation and based on the coefficient value and the deviation calculated value;
calculating the influence degree of all the influence factors on the characteristic impedance according to a second equation and based on the calculated influence values;
the first equation is:
Y i =k i *X i ；
the second equation is:
Z=[∑（Y i 2 ）] 0.5 ；
wherein i is the number of influencing factors, and takes a positive integer, k i For the coefficient value corresponding to the ith influencing factor, X i Calculate a value for the deviation corresponding to the ith influencing factor, Y i Z is the influence degree of all influence factors on the characteristic impedance;
the coefficient value corresponding to the influence factor in the preset database is determined by the following steps:
obtaining a deviation calculated value of the influence factors and obtaining a plurality of groups of deviation calculated values;
acquiring an influence value of the influence factors on characteristic impedance and acquiring a plurality of groups of influence values;
and processing the deviation calculated value and the influence value according to a first preset method, and obtaining the coefficient value which enables the influence value and the deviation calculated value to be in a linear relation.
2. The method for calculating the influence degree of influence factors on characteristic impedance according to claim 1, wherein the first preset method is a linear regression method.
3. The method for calculating the influence degree of influence factors on characteristic impedance according to claim 1, wherein the types of the impedance lines of the circuit board are divided into single-ended and differential, and the distribution manner of the impedance lines on the circuit board is further divided into an outer layer and an inner layer.
4. The method according to claim 1, wherein the deviation calculated value corresponding to the line width is a deviation percentage.
5. The method according to claim 1, wherein the deviation calculated value corresponding to the line thickness is a deviation value.
6. The method according to claim 1, wherein the deviation calculated value corresponding to the medium thickness is a deviation percentage.
7. The method according to claim 1, wherein the deviation calculated value corresponding to the solder resist thickness is a deviation percentage.
8. The method for calculating the degree of influence of the influence factor on the characteristic impedance according to claim 1, wherein the line width is in a line width range of 3.0mil to 15mil; the line thickness ranges from 0.5mil to 2.0mil.
9. The method for calculating the degree of influence of the influence factor on the characteristic impedance according to claim 1, wherein the thickness of the medium is in a range of 3.0mil to 10mil; the thickness of the solder resist is in the range of 0.5mil to 3.0mil.
10. A wiring board, characterized in that the influence degree calculation of the influence factor on the characteristic impedance is performed by using the influence degree calculation method of the influence factor on the characteristic impedance according to any one of claims 1 to 9.
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