PCB Technical - Common problems in PCB circuit layout design

Question 1: What is part packaging, and what is the difference between it and parts?

Answer: (1) Part package refers to the appearance and solder joint position indicated when the actual part is soldered to the printed circuit board.

(2) The part packaging is only the appearance of the part and the location of the solder joints. The pure part packaging is only the concept of space, so different parts can share the same part packaging; on the other hand, the same kind of parts can also have different packaging, such as RES2 stands for resistance, and its packaging forms are AXAIL0.4, AXAIL0.3, AXAIL0.6, etc., so when using welding parts, you must know not only the name of the part but also the package of the part.

(3) The package of parts can be specified when designing the circuit diagram, or when the netlist is introduced. When designing the circuit diagram, you can specify it in the Footprint setting item in the part properties dialog box, or you can specify the part package when importing the netlist.

Question 2: What is the difference between wire, fly line and network?

Answer: Wires are also called copper film traces, or wires for short. They are used to connect various solder joints. They are the most important part of a printed circuit board. The design of printed circuit boards revolves around how to arrange the wires.

Another kind of wire related to the wire, often called flying wire or pre-pull wire. The flying line is generated by the system according to the rules after the network table is introduced, and is used to guide the wiring of a kind of connection.

Flying wire and wire are essentially different. The flying line is just a form of connection, it only shows the connection relationship between the various solder joints in form, and has no electrical connection significance. The wire is arranged according to the connection relationship between the solder joints indicated by the flying lead, and it is a connection line with electrical connection significance.

The network and the wire are different. The network also includes solder joints. Therefore, when referring to the network, not only the guide wire but also the solder joints connected to the wire are included.

Question 3: What is the difference between the inner layer and the middle layer?

Answer: The middle layer and the inner layer are two concepts that are easy to confuse. The middle layer refers to the middle board layer used for wiring, and the wires are laid in this layer; the inner layer refers to the power layer or the ground layer. Generally, this layer is not wired. It is composed of a whole piece of copper film, which is negative. Phase display.

Question 4: What is an internal network table and an external network table, and what is the difference between the two?

Answer: The network table is divided into external network table and internal network table. The external network table refers to the imported network table, that is, the schematic network table generated by Sch or other schematic design software; the internal network table is the network table used for wiring inside the PCB system after modification based on the imported external network table. Strictly speaking, these two kinds of netlists are completely different concepts, but readers do not need to distinguish strictly.

Question 5: What is the role of the netlist manager?

Answer: First: Introduce a netlist. The introduction process of this netlist is actually a process of loading the data of the schematic design to the PCB of the printed circuit board design system. All changes of the data in the PCB design system can be completed through the Netlist Macro. The system automatically generates the Netlist Macro by comparing and analyzing the netlist file and the internal data of the PCB system.

Second: You can use the netlist manager to directly edit the connection relationship between the various components of the circuit board in the PCB system to form a netlist.

Question 6: What is a class, and what are the benefits of introducing the concept of class?

Answer: The so-called class refers to a collection of units with the same meaning. The class definition in PCB is open to users, and users can define the meaning and composition of classes by themselves. The introduction of classes in PCB has two main functions:

(1) Easy wiring

In the circuit board wiring process, some networks need special treatment. For example, some important data lines need to increase the safety distance between these data lines and other components in order to avoid interference from other components on the circuit board. These data lines can be classified into one category. This category can be added to the rules when setting the automatic wiring safety spacing rules, and the safety spacing should be increased appropriately. Then, when the automatic wiring is performed, the safety spacing of all data lines in this category is the same. Be enlarged; in the circuit board wiring process, the power and ground wires often need to be thickened to ensure the reliability of the connection. The power and ground wires can be classified into one category. When setting the automatic wiring wire width (Width Constraint) rule, You can add this class to the rule, and appropriately increase the wire width, then the power and ground wires in this class will become wider during automatic routing.

(2) Easy to manage circuit board components

For a large circuit board, there are many parts and packages on it, and there are thousands of networks, which is very messy, and the use of classes can easily manage the circuit board. For example, to classify all the input networks in the circuit board, when looking for a certain input network, you only need to search in this input network category; you can also classify all the finite voltage resistances in the circuit board, and you can search for a certain input network. When voltage-limiting resistors are used, you only need to find them in this category of voltage-limiting resistors.

Question 7: How to add additional solder joints to the network?

Answer: You can add the solder joints to the circuit board first, then double-click the solder joints to open the solder joint properties setting dialog box, and select the appropriate network in the Net item in Advaced to complete the solder joint placement.

Question 8: What is the use of inner segmentation?

Answer: The divided inner layer can be used to connect some important circuits, which can improve the anti-interference ability and protect important circuits.

Question 9: What is the effect of copper coating and what should be paid attention to?

Answer: The main function of copper coating is to improve the anti-interference ability of PCB circuits. If you want to wrap wires or make up teardrops on the circuit, then copper coating should be done last.