To reduce the risk of welding cracks, it is necessary to adopt good process control and quality control measures in SMT processing, including correct selection of solder, optimization of welding temperature and cycle, consideration of component layout and material selection, and regular quality inspection and testing. This helps to improve the reliability of welding and reduce the occurrence of welding cracks.

1. Thermal stress: During SMT process, PCBs and components may undergo multiple heating and cooling processes, which may lead to the accumulation of thermal stress. This thermal stress may cause stress concentration in solder joints and welding materials, ultimately leading to the formation of welding cracks.
2. Temperature gradient: During SMT process, the temperature of components and PCBs may undergo rapid changes, especially during the soldering and cooling stages. The temperature gradient difference may lead to thermal stress inside the solder joint, increasing the risk of welding cracks.

3. Material mismatch: The material properties of different components and PCBs may not match, such as different coefficients of linear thermal expansion. This mismatch may lead to stress accumulation during temperature changes, resulting in the formation of welding cracks.
4. Excessive thermal cycling: PCBs and components may undergo multiple temperature cycles in practical applications. If the welding quality is poor, these cycles may lead to fatigue of the solder and solder joints, ultimately forming cracks.
5. High temperature welding: When using high-temperature welding processes such as wave soldering or reflow soldering, the solder joints and solder may be exposed to high temperature environments. If not operated correctly, this may cause the solder to overheat, leading to welding cracks.
6. Pre stress and mechanical stress: The weight, size, and placement of components may apply mechanical stress, which can lead to stress accumulation near welding points, resulting in welding cracks.

7. Ductility difference: The difference in ductility between the solder and substrate materials, as well as the insufficient ductility of the solder, may cause the solder to stretch and form welding cracks.
8. Environmental conditions: Environmental factors such as humidity, exposure to chemicals, and even vibration may have adverse effects on solder and solder joints, increasing the risk of welding cracks.