Mechanical Strain
Physical bending concentrated within a small region of a printed board occurs during point-loading operations. When a force is exerted on a specific point during component insertion, localized substrate flexure is induced in the surrounding area. The stress concentrates at the nearest solder joints, forcing the solder ball to pull away from the copper pad.
Assembly Defect
Electrical failures often surface after board routing or secondary assembly steps due to micro-cracks formed during board bending. When localized substrate flexure is allowed to exceed critical thresholds, the copper trace or the resin beneath the pad may tear apart. Solder joints located near mounting holes are particularly susceptible to this damage because screw installation generates high torque and concentrated force.
Automated testing often misses these cracks if they remain closed during static electrical checks, allowing defective assemblies to pass undetected into subsequent stages. Thermal cycling in the field later opens these fractures, which results in intermittent open circuits and expensive warranty claims.
Mitigation Method
Mechanical support fixtures are required under the assembly line to prevent the board from bending under concentrated forces. By placing support pins directly beneath the connector being pressed, localized substrate flexure is restricted to safe limits. Modern assembly lines utilize rigid aluminum pallets or dedicated support blocks during connector press operations to ensure structural integrity is maintained.
This prevents trace fractures and pad cratering without requiring expensive design modifications.
