Mechanical stress is the internal force that produces interaction between various parts of an object when the object is deformed due to external factors ( stress, load, temperature change, etc. ) in order to resist the action of such external factors and try to return the object from the deformed position to the position before deformation.
The mechanical stress in the assembly and manufacturing process mainly includes the following aspects:
1. acting force on PCBA during operation of tooling and equipment.
For example, when PCBA is removed from a tight clamp, cracks will occur in the chip capacitor. Improper adjustment of the second side support of double-sided printing resulted in cracks or damages to the components on the top surface of the patch. Manual separation of boards may result in board failure or damage to components.
2. the acting force of the rapidly changing temperature difference between cold and heat on PCBA during welding.
In the process of reflow soldering, wave soldering and manual soldering of PCBA, when the temperature difference is too large, it may cause the PCB to warp. the solidification of solder causes the components on the PCB to generate mechanical stress, causing stress cracks in the ceramic and glass parts of the components. stress cracks are unfavorable factors affecting the long-term reliability of solder joints.
3. the endurance of PCBA to mechanical impacts such as collision and falling due to improper handling.
When subjected to mechanical impact, solder joints will generally not be damaged. However, other parts of the welding structure will fail. for example, the large inertia force generated by the mechanical impact of large and heavy leaded components will cause the peeling of copper-clad on the PCB or the fracture of the board, and the components themselves will also be damaged.
4. PCBA packaging is not properly protected and bears the vibration during transportation.
For PCBA packaging protection, it should be considered from the design of packaging materials. for PCBA transportation, it is ok to use a special anti-static box supplemented by a built-in knife card.