Measurement of continuous bending deformation for circuit boards by digital holographic interferometry

The measurement of continuous bending deformation for a circuit board surface was achieved by using digital off-axis Fresnel holographic interferometry. 1501 holograms were recorded by applying a displacement load to both ends of the circuit board from 0 to 15 mm by the step of 0.01 mm. The interference phase difference was obtained by subtracting the complex amplitude phase distributions of two adjacent holograms with numerical reconstruction. Then, the out-of-plane displacement of the lighting measurement area was obtained according to the relationship between the phase difference and the out-of-plane displacement, and the measurement results were obtained by accumulating the bending deformation of the displacement load from 1 mm to 15 mm. By calculating the out-of-plane displacements of the same capacitor center in the lighting measurement area from five pieces of circuit boards with the same specifications, it indicates that the measurement results are no more than 0.008 mm for the type A uncertainty, no more than 0.0035 mm for the type B uncertainty from a loading clamp and no more than 0.0087 mm for the combined uncertainty. The results show that the method based on digital off-axis Fresnel holographic interferometry for measuring the continuous bending deformation of the object with a large displacement load has good repeatability and stability.