Determination of Optimum Values of Control Parameters to Reduce Laser Speckle Noise for Projection Moire´ System

Projection moire´ technique using laser interferometry to generate grating patterns is one of the major techniques for out-of-plane displacement or warpage measurement of electronic packaging devices. Laser speckle is one of the most crucial sources of noise that increase measurement error and decrease repeatability of projection moire´ systems. The aim of this work is to reduce the laser speckle noise by optimizing the noise control parameters (laser power, camera exposure and camera gain) to minimize the measurement error and maximize the repeatability of the projection moire´ system. Taguchi’s design experimental method is used to formulate the experimental layout, to investigate the effect of the each control parameter on the measurement error and repeatability, and to determine the best possible parameter levels. Regression analysis is employed to precisely find the optimum values of the each control parameter. The validation test shows that the approach using Taguchi method and regression analysis is well established to optimize the noise control parameters of the projection moire´ system.