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Doing these things, PCB board design is not easy to make mistakes

Posted:05:07 PM February 11, 2019 writer: G

1. Preliminary work of circuit board design

1.1. Use the schematic design tool to draw the schematic and generate the corresponding network table. If the circuit board is relatively simple, there is already a network table, and it is also possible to directly enter the PCB design system without performing the schematic design. In the PCB design system, the parts package is directly taken, and the network table is manually generated.

1.2. Manually change the network table, and define the pads that are not on the schematic diagram of the fixed feet of some components to the network connected to it. Any physical connection can be defined to the geographical protection area. Change the pin names of the device names in the schematic and PCB package libraries to be consistent with those in the PCB package library, especially the diodes and transistors.

2. Draw a package library of your own defined non-standard devices. 

It is recommended to put the devices you have drawn into a dedicated PCB library design file.

3. Set the PCB design environment and draw the border of the printed circuit

3.1. The first step into the PCB system is to set up the PCB design environment, including setting the grid size and type, cursor type, layout parameters, wiring parameters, and so on. Most of the parameters can use the system defaults, and after these parameters are set, it is in line with personal habits, and there is no need to modify them later.

3.2. Planning the circuit board, mainly to determine the border of the circuit board, including the size of the circuit board. Place the appropriate size pad where you need to place the mounting holes. For 3mm screws, 6.5~8mm outer diameter and 3.2~3.5mm inner diameter pad can be used. For standard board, it can be transferred from other boards or PCBizard. Note that before drawing the board border, be sure to set the current layer to the KeepOut layer, which disables the wiring layer.

4. After opening all the PCB library files to be used, it is very important to transfer the network table file and modify the part package. 

The network watch is the soul of PCB automatic routing, and also the interface between schematic design and printed circuit board design. The board layout can only be performed after the network table has been loaded. In the process of schematic design, the ERC inspection does not involve the packaging of the part. Therefore, when the schematic design, the package of the part may be forgotten, and the package of the part may be modified or supplemented according to the design situation when the network table is introduced. Of course, you can manually generate a netlist directly in the PCB and specify the part package.

5. Arrange the position of the part package, also called the part layout. Protel99 can be used for automatic layout or manual layout. 

If you are doing automatic layout, run "AutoPlace" under "Tools". The key to wiring is layout, and most designers use manual layout. Select a component with the mouse, hold down the left mouse button, drag the component to the destination, release the left button, and fix the component. Protel99 adds some new tricks in layout. New interactive layout options include automatic selection and automatic alignment. Using the automatic selection method, components of similar packages can be quickly collected, then rotated, expanded, and organized into groups, which can be moved to the desired position on the board. When the simple layout is complete, use automatic alignment to neatly unfold or tighten a set of similar components.

    Tip: When auto-selecting, use ShiftX or Y and CtrlX or Y to expand and contract the X, Y directions of the selected component.

    Note: The layout of parts should be considered from the aspects of mechanical structure heat dissipation, electromagnetic interference, and convenience of future wiring. The devices associated with the mechanical dimensions are placed first, and these devices are locked, then the core components of the large positional devices and circuits, and then the small components of the periphery.

6. Make the appropriate adjustments according to the situation and then lock all the devices. 

If the board space allows, you can put some wiring areas similar to the experiment board on the board. For large boards, add more screw holes in the middle. Screw holes should be added to the side of the device with heavy components or larger connectors. If necessary, put some test pads in place, preferably in the schematic. Change too small pad vias to define the network of all fixed screw pad pads to ground or protective ground. After putting it in, use the VIEW3D function to check the actual effect and save it.

7. Wiring rules settings. 

The wiring rules are the specifications for setting up wiring. If you use partial rules such as layer, line width, via spacing, and routing topology, you can export it from other boards through the Menu of Design-Rules. This step does not have to be set every time, according to personal habits, set it once.

7.1. Circuit schematic design: The schematic design of the circuit diagram is mainly the PROTEL99 schematic design system (Advanced Schematic) to draw a circuit schematic. In this process, you should make full use of the various schematic drawing tools and various editing functions provided by PROTEL99 to get a correct and beautiful circuit schematic.

7.2. Generating a Network Table: A network table is a bridge between Circuit Schematic Design (SCH) and Printed Circuit Board Design (PCB). It is the automatic soul of the board. The netlist can be obtained from the schematic or extracted from the printed circuit board.

7.3. Printed circuit board design: The layout of the board is realized by the powerful functions provided by PROTEL99.

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