Three-illumination-beam phase-shifted holographic interferometry study of thermally induced displacements on a printed wiring board

Spatially resolved measurement of thermally induced surface displacements of printed wiring boards using phase-shifted holographic interferometry is discussed. Three separate holograms with three linearly independent illumination beams were recorded. The interferograms were viewed in real time from a fixed detector location, and phase maps corresponding to each illumination direction were generated with the phase-shifting interferometer. The phase maps are then used to compute the displacements on a point by point basis. The measurement accuracy is estimated to be +/-0.004 microm out-of-plane and +/-0.02 microm in-plane over a temperature range of 40 degrees C. The system was tested on a through hole in a printed wiring board; the results of this test are discussed. Phase computation and unwrapping, data reduCtion, experimental geometry, surface preparation, and displacement computation are discussed.