High-Precision Grating Projection 3-D Measurement Method Based on Multifrequency Phases for Printed Circuit Board Inspection

The grating projection 3-D measurement method based on multifrequency heterodyne (MFH) can achieve the measurement of complex objects by obtaining absolute phase through differential phase. However, in the application of printed circuit board (PCB) inspection, the differential process amplifies phase errors introduced by factors, such as materials and environment, consequently significantly diminishing the measurement accuracy and posing serious hardware safety hazards. To avoid the impact of phase errors, this article proposes a high-precision grating projection 3-D measurement method based on multifrequency phases for PCB inspection. In this method, the high-frequency phase synthesis phase patterns are directly project onto the object to bypass the phase differential process to eliminate the influence of heterodynes. Then, phase errors are compensated by using the relationship between phases and phase errors to minimize the impact of noises on measurement. The results from measurement experiments of components on PCB show that the measurement errors obtained by this method are reduced to less than 0.03 mm and improved accuracy by at least twice compared to other method (0.06–0.09 mm).