PCB circuit board design should pay attention to the seven steps

First, PCB circuit board preset for the previous stage of office

1. Use the schematic preset tool to draw the schematic diagram and generate the corresponding network table. If the circuit board is relatively simple and there is a network table, you can also enter the PCB preset system directly without the implementation of the schematic diagram. In the PCB circuit board preset system, you can directly take parts packaging and manually generate the network table.

2, manually change the network table, will be a bit of components fixed with the feet on the diagram without the welding pad defined to connect with it on the network, no matter what physical cosign can be defined to take care of the area. Change the pin names of parts that are not exactly the same in schematic diagram and PCB circuit board package library to be exactly the same as those in circuit board package library, especially the pipes with three electrodes, etc.

Two, draw their own definition of the non-standard parts of the package library. It is proposed to put all the parts drawn by oneself into a dedicated preset file of PCB library built by oneself.

Three, set the preset background of the PCB circuit board and draw the frame of the printed circuit

1. The first step of entering the PCB circuit board system is to set the PCB preset background, including setting the grid volume and type, cursor type, version layer reference, wiring reference, etc. Most of the parameters can use the system acquiescence value, and these parameters can be set in the future, according to private habits, there is no way to correct later.

2. Plan the circuit board, mainly to confirm the frame of the circuit board, including the size and volume of the circuit board. Place a proper volume of pad where the fixing holes are required. For 3mm screws, 6.5~8mm OD and 3.2~3.5mm OD pads are available, for standard plates from other plates or PCBizard. Note that before drawing the board frame, the current layer must be set to KeepOut layer, that is, no wiring layer.

Four, open all the need to use the PCB board library file, call into the network table file and correct parts packaging this step is a very close link. Network table is the soul of PCB circuit board semi-automatic wiring, and is also the interface between schematic presets and printed board presets. Only after loading the network table, the ability to implement circuit board wiring. ERC search does not involve the packaging of parts during schematic presets. Because of this, schematic preset, parts packaging may be forgotten, in the introduction of the network table can be based on the preset situation to correct or supplement parts packaging. Of course, you can directly generate the network table on the PCB circuit board, and also specify the parts package.

Five, the location of the parts packaging, also known as the parts layout. Protel99 can implement semi-automatic layout, can also implement manual layout. For a semi-automatic layout, run AutoPlace under Tools. The key to wiring is layout, and most presetters use manual layout as appropriate. Select a component with the mouse, hold down the left mouse button, contain the component to the target, release the left button, the component fixed. The Protel99 adds a little more technique to the layout. New interactive layout options include semi-automatic selection and semi-automatic alignment. With semi-automatic selection, components can be quickly brought together in a similar package, which can then be rotated, unfolded and packed into groups to move to the desired position on the board. When the simple layout is complete, a group of components in the package phase is unrolled or compacted using semi-automatic alignment.

Reminder: in semi-automatic selection, use ShiftX or Y and CtrlX or Y to expand and tighten the X and Y directions of the selected components.

Note: parts layout should be from the mechanical structure of heat dissipation, electromagnetic interference, future wiring convenience and other aspects of comprehensive consideration. Place and lock the parts related to the mechanical dimensions, then the larger parts and the central components of the circuit, and then the smaller peripheral components.

Six, according to the situation of the matter to make appropriate debugging, and then lock all parts. If the space above the board permits, a wiring area roughly similar to that of the test board can be placed on the board. For large wrenches, more screw holes should be fixed in the mid-waist. There are heavy parts on the plate or larger connectors and other force parts should also be added to the side of the fixing screw hole, if there is demand, you can put a little test in the appropriate position to try to use the welding pad, it is best to add in the schematic diagram. The too small welding pad through the hole to enlarge, all fixed screw hole welding pad network defined to the ground or try to take care of the ground. Put good use VIEW3D function to see a real effect, save to disk.

Seven, wiring rules set. Wiring rules are specifications for setting up wiring. If the local rules such as layer, group line width, hole spacing and topology structure of wiring are used, they can be exported from other boards through the Menu of Design-Rules and then imported into this board. This step doesn't need to be set every time. Just set it once according to your personal habits.

1. Circuit Schematic presets: The presets of circuit schematic are mainly the Advanced Schematic system of PROTEL99 to draw a circuit schematic. In this process, to make full use of PROTEL99 provided by a variety of schematic drawing tools, a variety of editing functions, to obtain an accurate, exquisite circuit schematic.

2, Initiation of the network table: the network table is a bridge between the circuit schematic preset (SCH) and printed circuit board preset (PCB), it is the semi-automatic circuit board soul. The network table can be obtained from the circuit schematic, also can be obtained from the printed circuit board.

3, printed circuit board preset: with PROTEL99 supply of strong and abundant functions to successfully achieve the layout of the circuit board preset.