PCB Tech - PCB circuit board design skills and specifications

PCB design is one of the important tasks in the design of any power supply. Its design method determines the electromagnetic interference (EMI) and the stability of the power supply. Therefore, the importance is self-evident. This article will explain the PCB design techniques and specifications in the LED drive power supply.

(1) Establishing component parameters from schematic to PCB design flow-"input principle netlist-"design parameter setting-"manual layout -" manual wiring-"verification design -" review -" CAM output.

(2) Parameter setting The distance between adjacent wires must be able to meet electrical safety requirements, and in order to facilitate operation and production, the distance should be as wide as possible. The minimum spacing must be at least suitable for the voltage tolerated. When the wiring density is low, the spacing of the signal lines can be increased appropriately. For signal lines with a large gap between high and low levels,

the spacing should be as short as possible and the spacing should be increased. Generally, Set the trace spacing to 8mil. The distance between the edge of the inner hole of the pad and the edge of the printed board should be greater than 1mm, which can avoid the defects of the pad during processing. When the traces connected to the pads are thin, the connection between the pads and the traces should be designed into a drop shape. The advantage of this is that the pads are not easy to peel, but the traces and the pads are not easily disconnected.

(3) The component layout practice has proved that even if the circuit schematic is designed correctly and the printed circuit board is designed improperly, it will adversely affect the reliability of electronic equipment. For example, if the two thin parallel lines of the printed board are close together, it will cause the delay of the signal waveform, and the reflection noise will be formed at the terminal of the transmission line; the interference caused by the improper consideration of the power supply and ground will cause the product The performance drops, so when designing the printed circuit board, you should pay attention to adopting the correct method.

(4) The wiring switching power supply contains high-frequency signals. Any printed line on the PCB can function as an antenna. The length and width of the printed line will affect its impedance and inductance, thereby affecting the frequency response. Even printed lines that pass DC signals can couple to radio frequency signals from adjacent printed lines and cause circuit problems (and even radiate interfering signals again).

(5) After checking the wiring design, it is necessary to carefully check whether the wiring design conforms to the rules set by the designer. At the same time, it is also necessary to confirm whether the rules made meet the requirements of the printed board production process. Generally check the lines and lines, lines and components Whether the distances between pads, lines and through holes, component pads and through holes, and through holes and through holes are reasonable and whether they meet the production requirements. Whether the width of the power line and the ground line are appropriate, and whether there is a place to widen the ground line in the PCB. Note: Some errors can be ignored. For example, when a part of the outline of some connectors is placed outside the board frame, errors will occur when checking the spacing; in addition, each time the wiring and vias are modified, the copper must be re-coated.

(6) According to the "PCB checklist", the content includes design rules, layer definitions, line width, spacing, pads, and via settings, and also focus on reviewing the rationality of the device layout, the wiring of the power supply and the grounding network, The routing and shielding of high-speed clock networks, the placement and connection of decoupling capacitors, etc.