PCB Blog - Frequently Asked Questions about PCB board Layout Design

Question 1: What is a part package and how is it different from a part?
Answer: (1) Part package refers to the appearance and solder joint position indicated when the actual part is soldered to the printed circuit boards.
(2) The part package is only the appearance of the part and the position of the solder joints. The pure part package is only the concept of space, so different parts can share the same part package; on the other hand, the same part can also have different packages, such as RES2 stands for resistance, and its package forms are AXAIL0.4, AXAIL0.3, AXAIL0.6, etc., so when taking welding parts, not only the name of the part but also the package of the part must be known.
(3) The package of parts can be specified when designing the circuit diagram or when importing the netlist. When designing a circuit diagram, it can be specified in the Footprint setting item in the part properties dialog box, or it can be specified when the netlist is imported.

Question 2: What is the difference between wires, flying leads and nets?
Answer: The wire is also called copper film trace, referred to as wire. It is used to connect each solder joint and is an important part of the printed circuit boards. The design of the printed circuit board is based on how to arrange the wires. Another kind of wire related to the wire, often called flying wire, also called pre-pulled wire. The flying wire is a kind of connection that is generated by the system according to the rules and used to guide the wiring after the introduction of the netlist. There are essential differences between flying leads and wires. The flying lead is only a form of connection, it only formally expresses the connection relationship between the various solder joints, and has no electrical connection meaning. The wires are arranged according to the connection relationship between the solder joints indicated by the flying leads, and are connection lines with electrical connection significance. Nets are different from wires, and nets also include solder joints, so when referring to nets, not only the wires but also the solder joints connected to the wires.

Question 3: What is the difference between inner layer and middle layer?
A: The middle layer and the inner layer are two easily confused concepts. The middle layer refers to the middle board layer used for wiring, in which the wires are distributed; the inner layer refers to the power layer or the ground layer, which is generally not wired. It is composed of a whole piece of copper film, which is negative. phase displayed.

Question 4: What is an internal netlist and an external netlist and what is the difference between the two?
Answer: The network table is divided into external network table and internal network table. The external netlist refers to the imported netlist, that is, the schematic netlist generated by Sch or other schematic design software; the internal netlist is the netlist used for wiring inside the PCB board system after modification based on the imported external netlist. Strictly speaking, these two network lists are completely different concepts, but readers do not need to strictly distinguish.

Question 5: What does the netlist manager do?
Answer: 1) Introducing the netlist, the introduction process of this netlist is actually the process of loading the data of the schematic design to the PCB board of the printed circuit board design system. All changes in the data in the PCB board design system can be completed through the Netlist Macro. The system automatically generates network macros by comparing and analyzing the netlist file and the internal data of the PCB board system.
2) You can use the netlist manager to edit the connection relationship between the components of the circuit board directly in the PCB board system to form a netlist.

Question 6: What is a class and what are the benefits of introducing the concept of a class?
Answer: The so-called class refers to a collection of units with the same meaning. The class definition in the PCB board is open to the user, and the user can define the meaning of the class and the composition of the class. The introduction of classes in the PCB board has two main functions:
(1) Ease of wiring During the wiring process of the circuit board, some networks need special treatment, such as some important data lines, in order to avoid the interference of other components on the circuit board, it is often necessary to increase these data lines and other components during wiring. safe distance between them. These data lines can be grouped into a class, and this class can be added to the rule when setting the automatic routing safety spacing rule, and the safety spacing can be appropriately increased, then during automatic routing, the safety spacing of all data lines in this class will be the same. It is enlarged; in the process of circuit board wiring, 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 routing wire width (Width Constraint) rule , you can add this class to the rule, and appropriately increase the width of the wire, then the power and ground wires in this class will be wider during automatic routing.
(2) Easy to manage circuit board components For a large-scale circuit board, there are many parts and packages on it, and there are thousands of networks, which is very messy, and it is very convenient to manage the circuit board by using classes. For example, to classify all input networks in the circuit board, when looking for a certain input network, just search in this input network class; you can also classify all the limiting resistors in the circuit board, when looking for a certain input network When using a voltage limiting resistor, just look it up in this voltage limiting resistor category.

Question 7: How to add extra solder joints to the network?
Answer: You can add solder joints to the circuit board first, then double-click the solder joint to open the solder joint property 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 function 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 the printed circuit boards. If you want to wrap wires or fill teardrops on the circuit, then copper coating should be done.