Mechanical stress is when the body is deformed byexternal causes (force, load, temperature change, etc.), internal forces thatinteract with each other between the parts of the body are generated in orderto resist the effect of such external causes and try to make the body recoverfrom the position after deformation to the position before deformation.
The mechanical stress in the assembly andmanufacturing process mainly includes the following aspects:
1. The force exerted on PCBA during the operation oftooling and equipment.
For example, when the PCBA is removed from a tightfixture, the chip capacitor will crack. Improper adjustment of the second sidesupport of double-sided printing leads to cracks or damage of the topmount-mounted components; The manual board appears the board is broken or thecomponent is damaged.
2. The force exerted on PCBA by the rapidly changingtemperature difference during welding.
In the process of reflow welding, wave peak weldingand manual WELDING of PCBA, the temperature difference is too large, which maycause warping of THE PCB. The solidification of the solder will causemechanical stress on the components of the PCB, leading to stress cracks in theceramic and glass parts of the components. Stress cracks are an adverse factoraffecting the long-term reliability of the solder joints.
3. The tolerance of mechanical impact caused bycollision and drop due to improper PCBA use.
Solder joints are generally not damaged by mechanicalshock. However, other parts of the welding structure will fail. For example,the large inertial force generated by large and heavy lead components subjectedto mechanical impact will cause the peeling of copper covering on the PCB boardor the board fracture, and then the components themselves will be damaged.