Laser Doppler vibrometry use in detecting faulty printed circuit boards

Laser Doppler vibrometry has been demonstrated to have significant potential to detect a wide range of faults in printed circuit boards and components. Large scale structural defects, such as loose or aging solder joints, will change the resonant frequency of the unit under test. The physical changes in components or PC board due to thermal overstress will also change the encapsulating material frequency response. Impulse stimulation excites a broad range of frequencies simultaneously and allows observation of ldquoring downrdquo behavior. Optical impulse generation is a completely non-contact test system with a high degree of spatial resolution. Laser vibrometry is applicable to passive and active mode testing. The information obtained from vibrometric inspection provides complimentary data suitable for integration into a large suite of automated test systems. Optimization of a number of hardware parameters must be tuned to achieve consistent results that correlate actual faults with statistically significant data.