Do not go wrong in the PCB board design

In general, the most basic process of designing a board can be divided into the following steps:

(1) The design of the circuit schematic: The design of the circuit schematic is mainly the PROTEL099 schematic design system (AdvancedSchematic) to draw a circuit schematic. In this process, we should make full use of the various schematic drawing tools and various editing functions provided by PROTEL99 to achieve our goal, that is, to obtain a correct and exquisite circuit schematic.

(2) Generate network table: The network table is a bridge between circuit schematic design (SCH) and printed circuit board design (PCB), which is the automatic soul of the circuit board. The netlist can be obtained from the schematic or extracted from the printed circuit board.

(3) Design of printed circuit board: The design of printed circuit board is mainly for another important part of PROTEL99 PCB. In this process, we use the powerful functions provided by PROTEL99 to realize the layout of the circuit board. Complete difficult tasks.

First, the preliminary work of the circuit board design 1, using the schematic design tool to draw the schematic, and generate the corresponding network table. Of course, in some special cases, such as the circuit version is relatively simple, if you have a network table, you can also not design the schematic, directly enter the PCB design system, in the PCB design system, you can directly access the parts package, manual Generate a network table. 2. Manually change the network table to define the pads that are not on the schematic diagram of the fixed feet of some components to the network connected to it. No physical connection can be defined to the ground or the protection ground. 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.

Second, draw a package library of non-standard devices defined by yourself. It is recommended to put the devices you have drawn into a dedicated PCB library design file.

Third, set the PCB design environment and draw the printed circuit board with the middle of the hollow, etc. 1, the first step after entering the PCB system is to set the PCB design environment, including setting the grid size and type, cursor type, layer 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. 2, planning circuit version, mainly to determine the layout of the circuit board, including the size of the circuit board and so on. 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 pads are available. For standard boards, they can be transferred from other boards or PCBizard. Note - Before drawing the circuit board grounding, be sure to set the current layer to the KeepOut layer, which disables the wiring layer.

Fourth, 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 table is the soul of PCB automatic routing, and also the schematic design and the impression circuit design. Interface, the circuit board can only be wired after the network table is 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.

Fifth, the location of the package parts, also known as the part layout Protel99 can be automatically layout, or manual layout. If you are doing automatic layout, run "AutoPlace" under "Tools". With this command, you need to have enough patience. 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 the parts should be considered in terms of heat dissipation from the mechanical structure, electromagnetic interference, and convenience of wiring in the future. 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 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.

VII. Wiring Rules Setting the wiring rules is to set the various specifications of the wiring (such as the use level, the line width of each group, the spacing of the vias, the topology of the wiring, etc.), which can be exported from other boards through the Menu of Design-Rules. Then import this board. This step does not have to be set every time. It can be set once according to personal habits.