Mechanical stress is when the body is deformed by external causes (force, load, temperature change, etc.), internal forces that interact with each other between the parts of the body are generated in order to resist the effect of such external causes and try to make the body recover from the position after deformation to the position before deformation.
The mechanical stress in the assembly and manufacturing process mainly includes the following aspects:
1. The force exerted on PCBA during the operation of tooling and equipment.
For example, when the PCBA is removed from a tight fixture, the chip capacitor will crack. Improper adjustment of the second side support of double-sided printing leads to cracks or damage of the top mount-mounted components; The manual board appears the board is broken or the component is damaged.
2. The force exerted on PCBA by the rapidly changing temperature difference during welding.
In the process of reflow welding, wave peak welding and manual WELDING of PCBA, the temperature difference is too large, which may cause warping of THE PCB. The solidification of the solder will cause mechanical stress on the components of the PCB, leading to stress cracks in the ceramic and glass parts of the components. Stress cracks are an adverse factor affecting the long-term reliability of the solder joints.
3. The tolerance of mechanical impact caused by collision and drop due to improper PCBA use.
Solder joints are generally not damaged by mechanical shock. However, other parts of the welding structure will fail. For example, the large inertial force generated by large and heavy lead components subjected to mechanical impact will cause the peeling of copper covering on the PCB board or the board fracture, and then the components themselves will be damaged.
