A Novel Frequency-Shift Moiré Fringe Method for 3D Inspection of BGA Packaging

BGA (ball-grid array) is an advanced electronic packaging technology that has increasingly become more important and demanding in microelectronic industry. However, no effective technique is available to inspect the performances of the welding points and its co-planarity. The moire fringe method is often employed to measure the three-dimensional (3D) shape of the welding spot on BGA, and a high-resolution CCD camera is utilised to capture the deformation stripe image. In order to gain high measuring accuracy, a frequency-shift moire fringe technique is proposed in this paper, in which three light-sources are deployed to create the fringe. The system parameters are designed to ensure the BGA ball height within exactly one grade moire fringe. By using zero-maximum equation transformation, the measuring range can be segregated into eight subsets. Equal-step interpolation and indexed table approaches are also introduced to greatly improve the measurement speed, so it may be useful for industrial on-line application. Finally, the predicted results based on the simulated images are presented, demonstrating that its measuring accuracy can be achieved to 5 micron.