Warpage measurement using projection speckle correlation method and microscopic interferometry

Abstract

Recent advances in the electronics industries are drove by the rapid development of LCD technology. However, warpage is one of the major reliability and quality concerns in chip-on-glass (COG) packaging. Optical technique combined with microscopes is an obvious candidate for the non-contact measurement of warpage of LCD chips whose profiles vary from nanometers to micrometers. In this paper, projection speckle correlation method and Newton's ring interferometry are employed to obtain the warpage of a LCD chip. With respect to projection speckle correlation method, the technique of image merging is necessary in registration of 3D shape of entire object. Continuous wavelet transform is employed to extract 3D profile of the electronic chip by analyzing its fringe patterns. Phase retrieval is performed by computing the phase at a wavelet ridge. In addition, the points which introduce phase ambiguity are identified by tracking the inflexion points on the unwrapped phase map and detected by Savitzky-Golay differential operator. The feasibility of the proposed method is also validated by simulations. Experimental results from both techniques are compared, and excellent agreement is found. Above conclusions demonstrate that the techniques proposed in this study are powerful inspection tools for measuring warpage of LCD chips. © 2009 SPIE.