Vibrational Response
A physical condition occurs when a printed circuit board assembly is subjected to periodic forces that match its natural frequency of vibration, causing large-amplitude oscillations. Under these conditions, mechanical resonance amplifies the acceleration forces experienced by board-mounted components. The resulting deflection can bend the board and damage electronic assemblies far more than random vibration does.
Structural Failure
When an assembly vibrates at its natural frequency, the displacement of the board reaches a peak at the anti-nodes, which are the points of maximum deflection. This flexing creates intense bending stresses in solder joints and the copper traces on the circuit board. Solder joints of heavy components like capacitors and inductors are particularly vulnerable because their mass increases the inertial forces during oscillation.
High-cycle fatigue under these resonance conditions can cause wire bonds to snap and solder joints to fracture in a matter of minutes. Test labs use sweep sine tests to identify these resonant frequencies and measure the amplification factor of the board.
Damping Strategy
Mitigation of this failure mode is achieved by shifting the natural frequency of the board away from the expected excitation frequency of the operating environment. Designers achieve this shift by adding structural supports, increasing the number of mounting holes or choosing thicker laminate materials. Adding damping materials to the housing or the board can also absorb the vibrational energy to limit the peak displacement during resonant events.
