Reflow soldering as an important part of SMT chip processing, welding quality directly affects the quality of PCBA products, in the reflow soldering process may occur some welding defects, Anhui Interli sorted out some welding defects, causes and solutions, let's learn together.
1. Poor reflow welding phenomenon and causes.
1. SMD parts offset and rotate. This phenomenon may be caused by uneven heating at both ends of the part or poor tin eating at one end of the part;
2. BGA solder ball short circuit. The reasons that may cause short circuit are the amount of solder paste, solder paste printing offset, solder paste collapse, the scraper pressure is too small, and the gap between the steel plate and the PCB board is too large
3. BGA solder ball air welding. Solder paste has a great impact on BGA soldering, and the possible reasons for BGA solder ball air soldering are small amount of solder paste, solder balls do not stick to tin, high temperature leads to PCB board deformation and inconsistent solder ball size
4. There is air welding of SMD parts without feet. This situation can be divided into two categories, on the one hand, the reasons for the empty welding of SMD parts with feet are uneven parts feet, parts feet do not eat tin and PCB board soldering pads do not eat tin, etc.;On the other hand, the reasons for the empty soldering of smD parts without feet may be the small amount of solder paste, the unreasonable design of the solder pad, and the uneven heating of both ends of the solder pad.
5. Erect a tombstone. The reasons for the appearance of the monument are: the two ends of the solder pad are heated unevenly, so the tin eating is different;
6. Cold welding. The reflow temperature is the main cause of cold soldering, and reflow soldering temperature is too low or too short can lead to cold soldering
7. Cracking of solder joints. The solder paste melting temperature is too low and the PCB board warps to generate pressure, etc.
3. Solutions for poor reflow soldering.
1. Appropriately increase the thermal resistance to ensure that there is no oxidation of parts and PCB solder joints
2. Reduce the amount of solder paste printing, adjust the squeegee pressure, and ensure that the accuracy of PCB board imposition meets the requirements
3. Increase the thickness of the steel plate or increase the opening, check the solder ball pentoxide in time, slow down the heating rate and increase the amount of tin
4. Adjust the heating rate of reflow to ensure that the flatness of the part foot meets the relevant regulations
5. Slow down the heating rate of the temperature curve, and control the preheating temperature before reflow soldering, generally speaking, the preheating temperature is 170;
6. Increase the reflow soldering temperature to 245 -255 and extend the reflow soldering time appropriately
7. Avoid bending the PCB board, increase the amount of solder paste, and reduce the cooling rate.
For more information about EMS intelligent manufacturing (PCBA OEM material processing, SMT chip processing), please enter Anhui Interli**www.aitpbca.com view.