Some simple and common rules for PCB layout

btty038

Some simple and common rules for PCB layout [Copy link]

Abstract : 1. We should pay attention to the minimum distance between SMD components (resistors and capacitors) and chips and other components. Chip: Generally, we define the distance between discrete components and IC chips as 0.5-0.7mm. Special places may change due to different fixture configurations. 2. For discrete plug-in components, the general resistor is more accurate than the SMD component if it is a discrete plug-in...

1. We need to pay attention to the minimum distance between SMD components (resistors and capacitors) and chips and other components. Chip: Generally, we define the distance between discrete components and IC chips as 0.5-0.7mm. Special places may change due to different fixture configurations. 2. For discrete plug-in devices, the distance between discrete plug-in resistors is slightly larger than that between SMD resistors, usually between 1 and 3 mm. Pay attention to maintaining sufficient spacing (because of the trouble of processing, plug-in resistors are basically not used) 3. For the placement of IC decoupling capacitors, decoupling capacitors need to be placed near the power port of each IC, and the position should be as close to the power port of the IC as possible. When a chip has multiple power ports, decoupling capacitors must be placed at each port. 4. Since discrete devices near the edge are generally made of jigsaw boards to make PCBs, the devices near the edge need to meet two conditions. The first is to be 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 (to prevent damage to the components when the board is cut) 5. If adjacent pads need to be connected, first make sure to connect them on the outside to prevent them from being connected together and causing bridges. At the same time, pay attention to the width of the copper wire at this time. 6. If the pad is in the through area, a thermal pad needs to be considered (it must be able to carry enough current). If the lead is smaller than the pad of the through-hole device, a teardrop needs to be added (angle less than 45 degrees). The same applies to the pins of the through-hole connector. 7. The lead widths on both sides of the component pads should be consistent. If there is a difference in size between the pad and the electrode, pay attention to whether a short circuit will occur. Finally, pay attention to retaining the pads of unused pins and properly grounding or connecting to the power supply. 8. Note that it is best not to drill through holes on pads. 9. Another thing to note is that the lead cannot be too close to the edge of the board, and copper is not allowed to be placed on the edge of the board (including the area near the positioning hole) 10. Large capacitors: First, consider whether the ambient temperature of the capacitor meets the requirements. Second, keep the capacitor as far away from the heating area as possible. Regarding the last point, I would like to add a tragic incident. We used chip capacitors and placed them near a heat source. Due to jitter and the hot conditions nearby, the solder joints of the capacitors were not sticky enough during operation, resulting in the capacitors falling off. Please be careful!

宋元浩

When I was drawing the board before, I punched the through hole on the pad, which was criticized by my leader. Later, I changed it. The main reason was that it was easy to leak tin and cause cold soldering when the chip was put into the furnace.

btty038

Song Yuanhao posted on 2020-7-6 21:36 When I was drawing the board before, the through hole was punched on the pad, which was criticized by the leader. Later, it was changed. The main reason was that it was easy to leak tin and cause cold soldering when the patch was passed through the furnace

The author of the post is an experienced person. Only when you have experienced it yourself can you feel this way. However, some special processes require special considerations. The general operation is basically like this.