PCB design is the design of the pointer to the circuit board. Circuit board design is based on the circuit diagram, circuit designers need to achieve the functions. PCB design mainly refers to layout design, which needs to consider various factors such as the layout of external connections, the optimal layout of internal electronic components, the optimal layout of metal wiring and through-hole, and heat dissipation. Layout design requires the help of computer aided design (CAD). Excellent layout design can save production costs 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 conforms to the rules formulated by the designer. At the same time, it is also necessary to confirm whether the rules formulated conform to the requirements of the PCB production process. The general inspection includes the following aspects:
1. Whether the distance between wire and wire, wire and element welding pad, wire and through hole, element welding pad and through hole, through hole and through hole are reasonable and meet the production requirements.
2. Is the power cord and ground wire of appropriate width and tight coupling (low wave impedance) between the power cord and ground wire? Is there any area in the PCB where the ground wire can be widened?
3. Whether the best measures are taken for the key signal lines, such as the shortest length, adding protective lines, and the input line and output line are obviously separated.
4. Whether there are independent ground wires for analog circuit and digital circuit.
5. Whether the graphs added in the PCB will cause signal short-circuit.
6, some not ideal linear modification.
7. Are process lines added to the PCB? Whether the soldering resistance conforms to the requirements of production process, whether the size of soldering resistance is appropriate, and whether the character mark is pressed on the device soldering plate, so as not to affect the quality of electronic equipment.
8. Whether the edge of the outer frame of the power layer in the multilayer plate is narrowed, for example, the copper foil of the power layer is exposed outside the plate, which is likely to cause a short circuit.
The characteristic impedance of controllable impedance plates and circuits is one of the most important and common problems in high-speed design. First look at the definition of a transmission line, transmission line consists of two with a certain length of conductor, a conductor used to send signals, another is used to receive signals (remember “loop” to replace the concept of “land”) in a multilayer board, every line is part of the transmission line, adjacent to the reference plane can be used as a second line or loop, a route as “good performance” is the key to make it the characteristic impedance of a transmission line remained constant throughout the line.