Reasons for component deviation during reflow soldering process

Deviation of SMT components after reflow soldering is a common process defect, sometimes resulting in slight deviation, and in severe cases, even deviation from the solder pad. To analyze the causes of component displacement after reflow soldering and find solutions, we can investigate the following aspects one by one:

1. When investigating the cause of component deviation after reflow soldering, we can check whether there is any deviation after SMT solder paste printing. If an offset occurs, the component may be pushed towards the direction with less solder paste during reflow soldering.

2. Next, we can open the upper cover of the reflow soldering equipment, check whether the transportation guide rail is horizontal, whether the chain is vibrating, and observe whether the action of the SMT machine is too large when transporting heavy components. These factors may also cause component displacement after reflow soldering.

3. Next, we need to observe the pattern of component offsets to see if they are moving in the same direction or if only certain components are offsetting. If all components are offset in the same direction, it may be due to excessive airflow during reflow soldering. In this case, we can try adjusting the air volume to 10-20Hz or the minimum air volume to see if the deviation problem can be resolved.

4. We also need to confirm the mounting height of the components to ensure that the depth of the components being pressed into the solder paste reaches half. If the height of the component is set higher than the actual height, it will cause the actual installation height to be higher, making the component easy to be blown off. Therefore, to avoid this situation, we need to ensure that the installation height of the components is set accurately.

5. The lack of overlap between the component and the solder pad after placement may be due to asymmetric solder pad design or excessive distance. In this case, the stability of the component may be affected, thereby increasing the risk of component deviation. Therefore, we need to ensure that the pad design is symmetrical and the distance is appropriate to increase the overlap area between the component and the pad, thereby improving the stability of the component.

6. If the preheating temperature set during reflow soldering is too high, it will cause the heating rate to be too fast. In this way, the viscosity of the solder paste will instantly decrease and its morphology will undergo rapid changes. When the temperature reaches its peak, the gas in the flux will vaporize, producing an impact force, which in turn leads to component displacement. Therefore, we need to pay attention to setting the preheating temperature reasonably during the reflow soldering process to avoid the problem of component deviation caused by rapid temperature changes.

7. In addition, there are other factors that may cause component offset, such as the large thickness of the PCB board, which leads to asynchronous heating rates between the PCB and the component; The preheating temperature is set too low or the insulation time is too short; The component has oxidation issues or foreign objects inside the solder paste. Among these factors, too short insulation time is often the main reason, leading to component displacement. Therefore, we need to pay attention to adjusting the insulation time to ensure that the components can fully conduct heat and stabilize, in order to avoid the occurrence of displacement problems.

In addition to the reasons mentioned earlier, there are also some small probability factors that may cause component offset. For example, after reflow soldering, there may be a collision phenomenon, the coordinates of the mounting machine may be offset, and there may be problems with the suction nozzle, resulting in uneven pressure during the mounting process, causing the components to move on the melted solder paste. In addition, if the component experiences unilateral tin eating during reflow soldering, it may also cause the component to pull. All of these factors may lead to component offset. By carefully investigating the causes of these issues, we can correspondingly solve the problem of component displacement after reflow soldering.