Our drive power supply in, often appear patch capacitor failure. Especially for mass-produced power supplies. Here are some of your common causes of failure and ways to avoid them.
1. During the mounting process of the chip capacitor, if the suction nozzle head of the chip mounter is bent under excessive pressure, it is easy to deform and cause cracks. This kind of situation is actually relatively rare, but once there is a problem, it will be a large proportion of batch failure.
2. The patch capacitor is too close to the edge of the PCB, which causes the capacitor to break internally after being stressed when the board is divided.
Solution: improve the cloth board, the capacitor is parallel to the edge or as far away as possible; Using mechanical plate splitting; Deepen the micro-cutting depth to 1/3; Increase slotting to facilitate plate splitting.
In fact, increasing slotting is the most reliable method. When slotting, note that if the patch capacitor is too close to the edge and even the slotting space is not enough, then your slotting has the same effect on the other side. Note that the slot width cannot be too small, too small, and the supplier cannot process it, generally at least 1mm.
3. The patch capacitor pad is connected to the nearby large solder joint. When welding by thermal expansion thrust, curing contraction generated tension, easy to make the capacitor crack.
Sometimes, we put a patch capacitor to remove high frequency and a patch resistor to discharge in the big electrolysis.
In doing so, the chip capacitor has the possibility of failure, too close to the big electrolysis. This problem can be avoided by exchanging the position of the patch capacitor and the patch electricity.
4. The thermal shock in the welding process and the deformation of the substrate after welding are easy to cause cracks: in the wave welding process, the preheating temperature, insufficient time or too high welding temperature are easy to cause cracks.
5. In the process of manual repair welding. The soldering iron tip is in direct contact with the capacitor ceramic body, and the capacity causes cracks. The deformation of the substrate after the completion of welding (such as plate separation, installation, etc.) is also easy to cause cracks.
The above is the failure in the production process, and we also need to pay attention to when we choose the voltage and capacitance of the chip capacitor:
1. As VCC capacitors and other large capacitance values (uF level), try to choose foreign big names such as TDK capacitors or raise the withstand voltage value of domestic capacitors by one level.
2. Try not to use high-voltage and large-capacity chip capacitors, such as capacitors above 100V/100nF.
In general, as long as we pay attention to design and production, we can avoid most of the patch capacitor failure.