Several PCBs make up the system,How should the ground wires be connected?
When the signals or power supply between the PCBs are connected, for example, if there is power supply from the A board or the signal is sent to the B board, there must be an equal amount of current flowing from the ground plane back to the A board (this is Kirchoff current law). The current in this formation will flow back to the place with the lowest impedance. Therefore, the number of pins allocated to the ground plane should not be too small at the interfaces that are connected to each other regardless of power or signal, so as to reduce the impedance, which can reduce the noise on the ground plane. In addition, you can analyze the entire current loop, especially the larger current, and adjust the ground or ground connection to control the current flow (for example, make a low impedance somewhere to allow most of the current from this Place) to reduce the impact on other more sensitive signals.
Can I add a ground wire between the differential signal lines?
In the middle of the differential signal, the ground wire cannot be added. The most important point of the application principle of differential signals is to take advantage of the benefits of mutual coupling between differential signals, such as flux cancellation and noise immunity. If ground is added in the middle, the coupling effect will be destroyed.
Can test points be automatically generated by software on high-density printed boards? Generally, can it meet the test requirements for mass production?
Generally, whether the software automatically generates test points meets the test requirements depends on whether the specifications for adding test points meet the requirements of the test equipment. In addition, if the traces are too dense and the specifications for adding test points are strict, there may be no way to automatically add test points to each segment of the line. Of course, you need to manually fill in the place to be tested.
Will adding test points affect the quality of high-speed signals?
As for whether it will affect the signal quality, it depends on how the test points are added and how fast the signal is. Basically additional test points (without the existing via or DIP pin as test points) may be added to or pulled from the line. The former is equivalent to adding a small capacitor to the line, while the latter is an extra branch. Both of these conditions will affect the high-speed signal more or less, and the degree of influence is related to the frequency of the signal and the edge rate of the signal. The magnitude of the effect can be known through simulation. In principle, the smaller the test point, the better (of course, the requirements of the test equipment must also be met). The shorter the branch, the better.