10 important rules for PCB layout
1. We should pay attention to the minimum distance between the chip device (resistance and capacitance) and the chip and the rest of the device. Generally, we define the distance between the discrete device and the IC chip from 0.5 to 0.7 mm. Special places may change due to different fixture configurations.
2. For discrete in-line devices
The general resistance is generally between 1 and 3 mm if the distance is slightly larger than the patch. Pay attention to keep enough spacing (because of the trouble of processing, the basic insertion will not be used).
3. For the placement of IC decoupling capacitors
Decoupling capacitors should be placed near the power port of each IC, and the position should be as close as possible to the power port of the IC. When a chip has multiple power ports, decoupling capacitors should be placed at each port.
4. Discrete devices near the edge
Since the PCB is generally used for the PCB, the device near the edge needs to meet two conditions, the first is parallel to the cutting direction (to make the stress of the device uniform), and the second is that the device cannot be arranged within a certain distance ( Prevent damage to components when the board is cut)
5. If adjacent pads need to be connected, first make sure to connect them outside to prevent bridging, and pay attention to the width of the copper wire at this time.
6. If the pad needs to consider the thermal pad in the paving area (must be able to carry enough current), if the lead is smaller than the pad of the in-line device, it needs to add teardrop (angle less than 45 degrees), the same applies to straight Plug the connector pins.
7. The lead width on both sides of the component pad should be the same. If there is a gap between the time pad and the electrode size, pay attention to whether there will be a short circuit. Finally, pay attention to the pad that retains the unused pin and ground it properly or connect it to the power supply.
8. Note that the vias are best not to be placed on the pads.
9. In addition, it should be noted that the lead wire cannot be too close to the edge of the board, and it is not allowed to lay copper on the edge of the board (including the area near the positioning hole).
10. Large capacitance: First, consider whether the ambient temperature of the capacitor meets the requirements, and secondly, make the capacitor as far away as possible from the heating area.
To add a tragedy to the last point, we use the capacitor of the chip, and it is placed close to the heat source. Due to the jitter and the hot situation in the vicinity during work, the solder joint adhesion force of the capacitor is insufficient during operation, resulting in the capacitor falling off. The tragedy happens, everyone must be careful!