PCB Technical - Several small steps for PCB design clearance

PCB design will not go wrong in a few small steps (1) Circuit schematic design: The circuit schematic design is mainly the PROTEL099 schematic design system (dvancedschematic) to draw the circuit schematic.

In the PCB design 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 netlist: netlist is the bridge between circuit schematic design (SCH) and printed circuit board design (PCB), and it is the automatic soul of the circuit board.

The netlist can be obtained from the schematic circuit diagram or extracted from the printed circuit board.

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

However, in practice, the main focus is mainly on the following subdivision steps: First, the advanced work of circuit board design 1. Use the schematic design tool to draw the schematic and generate the corresponding netlist. Of course, in some special cases, such as the circuit version is relatively simple, there is already a netlist, etc., you can directly enter the PCB design system without the schematic design. In the PCB design system, you can directly access some packages and manually generate the netlist.

2. Manually change the network table to define certain components of the fixed foot and other schematic diagrams on the mat to be connected on the network, and no physical connection can be defined to the ground or protected land, etc.

The pin names of some schematics and the device pins in the PCB package library are changed to be the same as the pin names in the PCB package library, especially the two transistors.

Second, draw a self-defined non-standard equipment packaging library. It is recommended to put the drawn equipment into the self-built PCB library special design file. Third, set the PCB design environment, and after setting the PCB design environment in the first step, draw the printed circuit version (such as 1) containing the hollow box in the PCB system, including setting the grid point size and type, and the cursor type. Layer parameters, wiring parameters, etc. Most of the parameters can use the system default values, and these parameters are set, in line with personal habits, there is no need to modify. 2. Planning the circuit version is mainly to determine the circuit version of the frame, including the size of the circuit version, etc. Place the appropriate size of the pad at the location where the fixing hole needs to be placed. For 3mm screws, the outer diameter of the pad is 6.5~8mm, and the inner diameter of the pad is 3.2~3.5mm, which can be transferred from other boards or PCBizard to standard boards.

Note-Before drawing the circuit version of the border, be sure to set the current layer to the Keepout layer, that is, the routing layer is disabled. Fourth, open all PCB library files to be used, enter the netlist file and modify part of the package. This step is a very important step. The netlist is the soul of PCB automatic routing, and it is also the interface for schematic design and printed circuit board design. Can install network table, wiring of circuit version. During the schematic design process, ERC inspection does not involve the packaging of components. Therefore, when designing the schematic, you may forget the packaging of the components, and when the netlist is introduced, the packaging of the components can be modified or supplemented according to the design situation.

Of course, you can manually generate the netlist and specify the component package directly in the PCB. Fifth, the position of the decorative component package, also known as the component layout, Protel99 can be laid out automatically or manually. If you do auto layout and run "autoplace" under "Tools", you need to be patient enough to use this command. The key to routing is layout, and most designers use manual layout. Use the mouse to select the component, hold down the left mouse button, drag the component to reach the target, release the left button, and then protect the component. Protel99 adds some new tricks to the layout. New interactive layout options include automatic selection and automatic alignment. Using automatic selection, you can quickly collect similar packaged components, and then rotate, unfold and organize them into groups so that you can move to the desired location on the board. After completing a simple layout, use automatic alignment to neatly expand or tighten a group of components with similar packages. Tip-For automatic selection, use Shiftx or Y and ctrlx or y to expand and tighten the X and y directions of the selected component. Pay attention to part of the layout, and comprehensive consideration should be given to the heat dissipation of the mechanical structure, electromagnetic interference, and the convenience of future wiring.

First arrange and lock the devices related to the mechanical size, then the core components of the large positioning device and circuit, and then the small peripheral components.

Sixth, make appropriate adjustments according to the situation, and then lock all equipment. If the space on the board allows, you can place some wiring areas similar to the experiment board on the board. For large circuit boards, a fixing screw hole should be added in the middle. There are heavy equipment or larger connectors and other force devices on the board should also be added to the edge of the screw hole, if necessary, some test pads can be placed in the appropriate position, it is best to add in the schematic diagram. If the via hole of the pad is too small, the network of all fixed screw hole pads is defined as ground or protected ground, etc.

After taking it away, use the VIEW3D function to view the actual effect, the disk.

Seven, PCB wiring rules setting Wiring rules are to set wiring of various specifications (such as using level, line width, hole spacing, topology wiring and other rules, you can use the design rule menu from other motherboards, and then import this motherboard). You don’t need to set it every time, you can set it once according to your personal habits.