The most common examples of PCB Copy control impedance components that may be most common are the feeders that connect the wireless device or the TV receiving antenna. Antenna feeders are typically in the form of a "flat cable" (typically supplied with a VHF broadcast receiver) or a low attenuation coaxial cable. Regardless of the form, the impedance of the feeder is controlled by the physical size and the cable material.

You can think of PCB traces as shorter cables that are precisely laid out on the board to the various devices installed on the board, where the PCB traces resemble the conductors inside the coaxial cable, carrying the signal and its return line In this case the ground plane) is insulated by the board laminate. In the case of a microstrip configuration, this is shown in the cross-section in Fig.

The trace widths W and W1, the thickness T and the laminate height H and the insulation constant Er must be strictly controlled. The solder joints on the surface will slightly reduce the impedance, so a more predictable stripline configuration as shown in Figure 2 is often used.

Why PCB Copy Engineering Control Impedance?

Receiving antennas have natural or characteristic impedances. Electronic theory suggests that the impedance of the feeder and the receiver should match the antenna in order to transmit the maximum power to the receiver (ensuring the integrity of the electrical signal) using the antenna. In other words, the signal impedance should ideally behave as a constant during the transmission of the signal from its source to the target. If a mismatch occurs, only part of the signal will be sent, and the remaining signals will be reflected back to the source (weakening the signal). The cable designer must therefore ensure, in particular, the accuracy and consistency of cable length and material properties. With higher signal switching speeds, the electronic properties of the cable, such as capacitance and inductance, must be taken into account, and the cable can not be considered a simple wire. The corresponding cable that takes these factors into account when designing a cable for high-speed signals should be called a transmission line.

 Impedance Control on PCB Copy Engineering

Also, as the signal switching speed on the PCB continues to grow, the electronic properties of the traces carrying the signals become more important. The impedance of the PCB trace is controlled by the following factors

● Configuration

● Dimensions (trace width and thickness, the height of the board material)

● The insulation constant of the circuit board material

When using a cable, when the signal encounters an impedance change caused by a change in material or geometry, a portion of the signal is reflected back and a portion of the signal is delivered to the target. These reflections can cause signal artifacts, which can degrade circuit performance (such as low gain, noise, and random errors.) The board designer will in practice specify the impedance and error of the board traces and rely on the PCB manufacturer to follow the appropriate Of the specification.

Test the PCB

Most PCBs that control the impedance go through 100% of the tests. However, it is more difficult to detect PCB traces that are not easily detectable. In addition, the trace may be very short, and may include many branches, it is very difficult to accurately test the impedance. Adding additional lines for test purposes will affect performance and take up board space. PCB testing is therefore usually performed on one or two test coupons integrated into the PCB panel, rather than on the PCB itself. The sample has the same layered and trace construction as the main PCB, and is identical to the PCB's impedance, which is very accurate. And then test the sample is sufficient to determine the impedance of the circuit board is correct.

Measure the control impedance

Impedance measurements are usually done using a time-domain reflectometer (TDR). The TDR applies a fast voltage step to the sample by controlling the impedance cables and probes. Any reflections in the pulsed microwaves will be shown on the TDR and will represent a change in the impedance value (called a discontinuity.) TDR can indicate the position and magnitude of the discontinuity. Using the appropriate software, the TDR can plot the impedance plot over the length of the test trace of the specimen. The resulting graphical representation of the characteristic impedance of the trace will allow for the implementation of the complex measurements described earlier in a production environment.