Warpage analysis of 144-pin TQFP during reflow using image processing

A Moire Fringe Analysis software was developed to assist the experimental Study of a 144-pin 20/spl times/20/spl times/1.4 mm Thin Quad Flat Pack package warpage during reflow. Twyman Green with sensitivity of 0.3165 /spl mu/m/fringe and shadow Moire with sensitivity of 16.93 /spl mu/m/fringe were used to measure the out-of-plane displacement of the package from 20/spl deg/C to 180/spl deg/C with a 20/spl deg/C step. It happened to be that this warpage fell into the well-known technology gap of Twyman-Green and Shadow Moire. Instead of giving conclusive results, this paper intends to show how very simple image processing concepts can help to guarantee high quality Moire image and illuminate the potential of bridging the technology gap between Shadow Moire and Twyman Green with the help of image processing. The Moire Fringe Analysis software was designed to optimize the experimental setup and procedure, and do semiautomatic fringe pattern analysis afterwards. A noise tolerant fringe pattern recognition algorithm was coded to give relative displacement along a line between arbitrary two points on the pattern. The result of Twyman Green gave a minimum warpage at 80-100/spl deg/C. The module expansion was linear below 120/spl deg/C and highly non-linear local warpage peaks showed up above this temperature. With Shadow Moire, only qualitative results could be given. At this stage, it is shown that Shadow Moire does not show warpage details as Twyman Green interferometer. The comparison between the two is not conclusive.