Electronic Design - Error Analysis of Loading Net List in Software PCB Design

Starting from the functions defined by the PCB design netlist and the method of loading netlists and components, five network macro errors that often occur during the loading of the netlist are summarized: undefined component package form, PCB package definition name does not exist, or not found Component, node not found, network already exists, analyze the possible cause of the error and give a solution.

I. Introduction

The ProteI design system is the world's first EDA development tool that introduces EDA technology into the Windows environment. It has powerful functions and a friendly interface. It is one of the most popular and best-selling EDA (Electronic Design Automation) software today. Generally speaking, the use of Protel software for circuit board design needs to go through the steps of schematic design (circuit simulation), generating net list, planning PCB board, loading net list, component layout, and component wiring. When loading the network table to generate network macros and editing network macros, some network macro errors often occur, which causes the loading failure. If these errors are not resolved, the corresponding macro operations will not proceed normally at all, which will bring many problems to the subsequent PCB design, resulting in the failure of the design work to proceed smoothly. This article mainly describes the two methods of loading the netlist and components, and the causes and solutions of various typical error messages that appear when the netlist is loaded.

Second, the definition and function of the network table

The netlist is a very important file needed in the process of designing PCB. It is the bridge between circuit schematic design and PCB board design, and it is the soul of PCB file generation. As the name suggests, the network table is the definition of the electrical connection between the components in the schematic diagram, and is a textual expression of the component network connection extracted from the graphical schematic diagram. Through the transfer of the network table, the connection definitions between the components that are exactly the same as those in the schematic diagram can be automatically obtained in the PCB diagram.

Protel software can generate netlists in several formats to adapt to different PCB design tools. Protel schematics are generated to. The netlist file with net as the suffix consists of two parts: The first part: component information, which describes the three attributes of the component in the schematic diagram. The description information of the component is in square brackets. The first line is the component label, usually of various types. Elements start with different letters. For example, the beginning of R indicates resistance, the beginning of C indicates capacitance; the second row is the package form of the component on the PCB; the third row is the model of the component. For the description of the properties of the component itself, different types of components are indicated in the component model in different ways. You can indicate the effective value or the chip type according to your needs.

The second part: component connection information, including all electrical connection networks in the schematic diagram. The network information is in parentheses. The first line is the network name. If a network label is defined on the connection in the schematic diagram, the network is named after the network label in the network table. If the network label is not defined, then When generating the network table, the software assigns the names in order; the second and subsequent lines are the node information in the network, and the node information includes the component label and the pin number. For example, U3-13 refers to the 13th quote of the U3 component. foot. All component pins in the same network are connected, that is, the network name can be defined for any pin in the network.

Three, load the network table and components

The process of loading the netlist and components is actually the process of loading the data of the schematic design into the PCB design system of the printed circuit board. This process can be implemented in two ways. Method 1: Use the synchronizer to directly load the netlist and components from the schematic file. You must first create a PEB file in the same design database where the schematic is located, and load all the required PCB component libraries in advance. Method 2: Use the netlist file to load the netlist and components. All changes in the data in the PCB design system can be done through network macros. The network macro list includes three columns of attributes: column N0 (used to display the step number of the conversion network table); Action column (used to display the content of the operation to be performed when the network table is converted); Error column (used to display the occurrences in the conversion network table) mistake).

When loading a netlist in PCB production, errors often occur due to various reasons, and the error information provided by the software itself is too simple, often just a simple English prompt, which makes people understand it. This brings to the subsequent PCB design. Many problems caused the design work to not proceed smoothly. The following will analyze the possible causes of the errors from various typical macro errors displayed, and give corresponding solutions.

Four, common network macro error messages, reasons and handling methods

1. The package form of the component is not defined in the schematic

Error description: Footprint not found in Library

The reason for the error: (1) In the circuit schematic diagram, the component does not specify the package form; (2) The component library containing the required package component is not added in the PCB editor;

Processing method: (1) Open the netlist file to check which components have not defined packages, and directly add packages to this component in the netlist, or find the corresponding component in the schematic diagram, double-click the component, and in the pop-up properties dialog box Fill in the corresponding component package in the Footprint column; (2) In the PCB editor, execute the menu command Design/Add/Remove Library..., in the pop-up dialog box, specify the required PCB component library, and add it to In the current PCB editor.

2. The name of the PCB package definition does not exist

Error description: Footprint**not found in Librarv

The reason for the error: (1) There is no package drawing of the corresponding component in the PCB component library. Such as PCB Footprint. There is no component package available for small light-emitting diode LED in Lib; (2) The package form of the component is wrong in the schematic diagram. For example, write "RB0.2/0.4" as the packaging form of the polar capacitor Electrol.

Processing method: (1) Edit PCB Footprint. Lib file, create the LED component package, and then execute the update PCB command; (2) Return to the schematic diagram and carefully check whether the component package name in the schematic diagram is consistent with the name in the PCB component library.

3. No component found

Error description: Component not found

The reason for the error: Advpcb. PCB Footprint in the ddb file package. The Lib file contains most of the component packages, but if a component in the schematic diagram has a special package form, PCB Footprint. The Lib file library cannot be found, and the package library of non-used components needs to be loaded.

Processing method: In the design file manager window, click the PCB file icon to enter the PCB editing state, and load the corresponding component package library through the "Add/Remove" command.

4. No node found

Error description: Node not found

Reasons for the error: (1) There are more nodes that do not exist in the specified network; (2) The component pin name is different from the package pin name in the PCB library; (3) The component package given in the schematic diagram and the corresponding PCB The package name is different.

5. The network already exists

Error description: Net already exists

The reason for the error: (1) The network name that a certain macro operation tried to add is the same as the existing network name in the PCB network table; (2) The hidden pin information network point in the schematic diagram and other network points have the same name.

Processing method: For (1) you can open the schematic file, and modify the duplicate network name or delete the redundant network name according to the schematic; for (2), you can open the schematic file, find the wrong network connection point, and then open the component properties In the dialog box, select Hidden Pin, then you can observe the hidden component pin information network point, and then adjust the same network connection point to make it belong to a different node.

Five, concluding remarks

Netlist loading errors often occur, mainly due to encapsulation errors. After finding an error, you should browse first, and then you can quickly find the problem after you understand the cause of its occurrence. The root cause of the error should be eliminated so that the problem can be solved quickly and effectively. At the same time, it is necessary to be standardized and careful when designing the schematic diagram and editing the PCB component library to reduce the occurrence of errors.