Consider the PCB deformation when the device layout requirements

Assembled in SMT, In the process of testing, transportation and use, corresponding mechanical stress will inevitably be generated. When the mechanical stress exceeds the stress limit of some components and traces, it will cause cracks in components, and even lead to component cracking and failure in severe cases. , which seriously affects the reliability of the product. Common stress-sensitive components multilayer ceramic capacitors (MLCCs), especially large-sized multilayer ceramic capacitors, are more sensitive to stress.

Common occasions where mechanical stress occurs are:

1. Mechanical stress generated during the placement process

3. The mechanical stress of the panel pcb during division< /span>

4. Mechanical stress during ICT test

5. Mechanical stress during screw tightening

From a reliability design perspective Look, the reliability problem caused by mechanical stress can be improved from the aspect of layout. The basic principle is: stress-sensitive components, such as MLCC, etc., should be considered in the stress-prohibited area and avoid high-stress areas. For example, in the case of splitting, the stress generated in the devices in different layout directions is different. The stress generated in the device parallel to the auxiliary edge will be smaller than that of the device perpendicular to the auxiliary edge. In addition to the layout of the device, there are also requirements for the layout direction, as shown in Figure 1. Similarly, the deformation direction of the PCB is different, and the impact on the physical examination is also different. When the PCB has the deformation direction as shown in the figure, the long side of the layout component is consistent with the deformation direction, the internal stress of the component is larger, and the stress in the opposite direction is larger. is small, so the recommended layout direction is shown in Figure 2.