PCB impedance calculator is usually used in the design of multi-layer PCB, high-frequency PCB, antenna PCB. In these high-frequency PCB signals,
We need to perform PCB impedance calculator and PCB impedance control to ensure the stability of PCB and the pass rate of various index tests.

With the development of science and technology, especially with the progress of integrated circuit materials, the operation speed has been significantly improved,
And integrated circuits have developed towards high density, small volume, and single component. These have led to the high-frequency response of printed circuit boards in the present and future,
And the use of high-speed digital circuits, that is, the impedance of the line must be controlled, low distortion, low interference, low crosstalk, and EMI must be eliminated.
Impedance design is becoming more and more important in PCB design. ZBPCB engineers are the front-end department of PCB manufacturing,
Responsible for impedance simulation and impedance strip design. Customers have higher and higher requirements for impedance control, and the number of impedance controls is also increasing.
How to design impedance quickly and accurately is a very important issue for prenatal CAM engineers.

What is the PCB impedance calculator control in PCB?

1. Introduction to the concept of PCB impedance control

In order to distinguish it from the resistance of direct current (DC), the resistance encountered by alternating current is called impedance (Z0), including resistance (R),
Inductive reactance (XC), and capacitive reactance (XL).

PCB characteristic impedance, also known as “characteristic impedance”, refers to the resistance encountered by PCB high-frequency signals or electromagnetic waves in the transmission signal line
(i.e., the copper wire of the PCB we make) relative to a certain reference layer (i.e., shielding layer, projection layer or reference layer) during propagation.
It is actually the sum of vectors such as resistance, inductance, and capacitance.

2. The significance of controlling the PCB impedance calculator

PCB not only plays the role of current conduction in electronic products, but also plays the role of signal transmission.

The high-frequency and high-speed PCB of electronic products requires that the circuit performance provided by the
PCB must ensure that the signal does not reflect during transmission and keep the signal intact and undistorted.

The characteristic impedance of the PCB is the core of solving the signal integrity problem.

When electronic equipment (such as computers, communication switches, etc.) is running, the signal sent by the driver must reach the receiver through the PCB signal line.
To ensure signal integrity, the characteristic impedance (Z0) of the PCB signal line must match the “electronic impedance” of the head and tail components.

When the transmission line exceeds 1/3 of the rise time, the signal will be reflected, so the PCB characteristic impedance must be considered.

3. Factors affecting the PCB impedance calculator, the characteristic impedance of the PCB trace.

The dielectric constant of PCB is inversely proportional to the characteristic impedance (ER) of PCB

The dielectric thickness between the PCB circuit layer and the ground plane (or outer layer) is proportional to the characteristic impedance value (H)

The width of the bottom of the PCB impedance line (lower W1); the width of the line surface (upper W2) is inversely proportional to the characteristic impedance

The copper thickness of PCB is inversely proportional to the characteristic impedance (T) of PCB

The distance between adjacent lines of PCB is proportional to the characteristic impedance value (differential impedance) (s)

The thickness of the solder mask layer of the PCB substrate is inversely proportional to the impedance value (c)

4. Process factors affecting PCB impedance

Due to etching, when the copper thickness exceeds 2oz, the impedance of the PCB cannot be controlled.

There is no blank space for copper and line layers in the design, and it needs to be filled with curing film during production.
When calculating impedance, the dielectric thickness provided by the board supplier cannot be directly used instead, but the thickness of the blank space filled with curing film needs to be subtracted.
This is also one of the main reasons why the impedance calculated by ourselves is inconsistent with the manufacturer’s results.

5. PCB impedance calculator

PCB impedance calculation is more cumbersome, but we can summarize some experience values to help improve calculation efficiency.
For the commonly used FR4, 50ohm microstrip line, the line width is generally equal to twice the thickness of the dielectric;
For 50ohm stripline, the line width is equal to half of the total thickness of the dielectric between the two planes.
This can help us quickly lock the line width range, and note that the calculated line width should be less than this value.

In addition to improving calculation efficiency, we also need to improve calculation accuracy.
Do you often encounter situations where the PCB impedance you calculated is inconsistent with that of the PCB factory? Some people will say that it doesn’t matter, just let the PCB factory adjust it directly.
But will there be a situation where the PCB factory cannot adjust it and let you relax the PCB impedance control? It is better to make a good product or to have everything under your control.

How do we control the impedance of PCB in design?

1. Use experience values to record the impedance routing done before, such as PCB line width, board thickness, etc., and apply it directly next time you use it.

2. First, according to the conventional design, mark the lines that need to be impedance on the PCB, and then take a screenshot to the PCB factory.
If the PCB factory wants to control it, the PCB factory will modify the data according to the PCB impedance we require, such as adjusting the PCB line width, line spacing, etc. to achieve the required impedance.

3. At the beginning of the design: According to the lamination parameters of the PCB and the relevant data provided by the PCB manufacturer (PCB board type, dielectric constant, green oil, PP thickness, etc.),
Use the si9000 software to calculate the impedance, and then use the calculated parameters to draw the impedance line, and finally get the PCB data. At the same time,
The PCB factory needs the PCB factory to control the impedance of the PCB. The advantage of this is that under normal circumstances, the PCB factory will not change our data, and it is also a very small adjustment.

As can be seen from the above,

Points 1 and 2 are not safe. If the stacking parameters of the PCB are changed in point 1, the impedance of the PCB will also change. I don’t know if it was applied continuously on the same day.

Click the screenshot at point 2 and hand it over to the PCB factory for control. However, engineers from PCB factories often call and say that your PCB impedance cannot be made.
The reason is that the line width and line spacing of the PCB you designed are too different, and there is not enough space on the PCB to widen the line width and line spacing.

Obviously, the third solution is the safest, and the PCB factory will not be able to control the impedance of the PCB.

The most commonly used impedance calculation tool in our industry is the Si8000 Field Solver provided by Polar.
Si8000 Field Solver is a new boundary element method field effect solver software,
Which is based on the simple and easy-to-use user interface of the early Polar impedance design system that we are familiar with.
The software contains various impedance modules. By selecting a specific module, the personnel can calculate the impedance result by inputting relevant data such as line width,
line spacing, dielectric thickness, copper thickness, er value, etc. The number of impedance controls for a PCB ranges from 4 or 5 groups to dozens of groups.
The control line width, dielectric thickness, and copper thickness of each group are different. If the data is checked one by one and then the relevant parameters are manually entered for calculation,
It is very time-consuming and prone to errors.

Opal’s inplan software can automatically design PCB impedance and greatly improve prefabrication efficiency.
Opal’s inplan system can be connected to si8000 and automatically calculate impedance based on the establishment of the following database:
First, a complete material warehouse is established in inplan, classified according to different PCB manufacturers and models, and the data such as pressing thickness, substrate copper thickness,
And PP glue content obtained according to the actual process parameters of the PCB factory are built in.

Then, inplan, rules for calculating impedance are established, such as green oil thickness, undercut value, etc.,
And rules are set according to different copper thickness, impedance modules or inner and outer layers.
The dielectric constant is mainly written into the formula according to the material type and different impedance modules,
And the impedance value and impedance line width tolerance are also written into the rules through inplan rules.
When calculating impedance, inplan automatically brings out the relevant impedance influencing parameter values according to the rules and calculates the optimal impedance result.
And no matter how many groups of impedance there are, you can get all the results in a few seconds by clicking a button.

If the customer does not design the PCB impedance bar by himself,
We need to design the PCB impedance bar by ourselves and put it on the edge of the board or the broken edge (generally,
The placement of the impedance bar on the broken edge requires the consent of the customer), and the circuit board manufacturer will design
The PCB impedance bar on the edge of the circuit board that meets all the characteristics and parameters of the customer’s PCB impedance control. By testing the PCB
Impedance value of the impedance bar, it reflects whether the circuit board impedance meets the customer’s requirements.
In order to correctly test the impedance value in the board, the key lies in the design of the impedance bar.

The competition in PCB is becoming more and more fierce, and the delivery time of PCB samples is getting shorter and shorter,
And PCB impedance design accounts for a large proportion of the work before PCB manufacturing.
How to shorten the PCB impedance manufacturing time and make the impedance matching meet customer requirements is a problem that must be considered before PCB manufacturing.

How to specify PCB impedance? You can also use this PCB impedance calculator to calculate PCB impedance.

This is Rogers’ PCB impedance calculator. Download PCB impedance calculator

ZBPCB’s PCB impedance calculator method is: MI engineers fill in the impedance attachment table according to the calculated impedance results,
Such as impedance value, reference layer, control line width, test hole, reference layer attribute (positive and negative film), etc.,
And then CAM engineers manually make impedance bars according to the impedance table provided by Mi,
Or input relevant impedance data through scripts and run impedance bars through programs. Generally, for a PCB impedance value, we design a PCB impedance bar and make a PCB impedance calculator.