PCB design refers to the design of the circuit board. The design of the circuit board is based on the circuit schematic diagram to realize the functions required by the circuit designer. The design of the printed circuit board mainly refers to the layout design, which needs to consider various factors such as the layout of external connections, the optimized layout of internal electronic components, the optimized layout of metal connections and through holes, and heat dissipation. Layout design needs to be realized with the help of computer-aided design (CAD). Excellent layout design can save production cost and achieve good circuit performance and heat dissipation performance.
After the wiring design is completed, it is necessary to carefully check whether the wiring design meets the rules set by the designer, and at the same time, it is also necessary to confirm whether the rules set meet the requirements of the printed board production process. The general inspection has the following aspects:
1. Whether the distance between the line and the line, the line and the component pad, the line and the through hole, the component pad and the through hole, the through hole and the through hole is reasonable, and whether it meets the production requirements.
2. Is the width of the power line and the ground line appropriate, and is there a tight coupling between the power line and the ground line (low wave impedance)? Is there any place in the PCB where the ground wire can be widened?
3. Whether the best measures have been taken for the key signal lines, such as the shortest length, the protection line is added, and the input line and output line are clearly separated.
4. Whether there are separate ground wires for the analog circuit and digital circuit part.
5. Whether the graphics added to the PCB will cause signal short circuit.
6. Modify some unsatisfactory linear shapes.
7. Is there a process line on the PCB? Whether the solder mask meets the requirements of the production process, whether the solder mask size is appropriate, and whether the character logo is pressed on the device pad, so as not to affect the quality of the electrical equipment.
8. Whether the outer frame edge of the power ground layer in the multilayer board is reduced, such as the copper foil of the power ground layer exposed outside the board, which may cause a short circuit.
In high-speed design, the characteristic impedance of controllable impedance boards and lines is one of the most important and common problems. First understand the definition of a transmission line: a transmission line is composed of two conductors with a certain length, one conductor is used to send signals, and the other is used to receive signals (remember the concept of “loop” instead of “ground”) in a multilayer board, Each line is an integral part of the transmission line, and the adjacent reference plane can be used as a second line or loop. The key to a line becoming a “good performance” transmission line is to keep its characteristic impedance constant throughout the line.