Full-field 3-D measurement of solder pastes using LCD-based phase shifting techniques

Quality inspection of deposited solder pastes is critical in surface mounting processes. As surface-mount technology (SMT) component pitches decrease, three-dimensional (3-D) measurement of solder pastes has become more and more important in ensuring solder joint reliability. Currently, the 3-D measurements for solder pastes are mainly performed by laser-based systems. However, they suffer from low inspection speed due to the physical line-scanning process. In this paper, a fast and cost-effective 3-D measurement system for deposited solder pastes is proposed. The proposed system uses a liquid crystal display (LCD)-based phase shifting technique to perform full-field 3-D measurement of solder pastes with high accuracy. Experiments have shown that the 3-D profiling and volume measurement of solder pastes are very efficient and effective with the proposed system. The volume measurement repeatability is in the micrometer range. The processing time of the proposed 3-D measurement system for an image of 640 x 480 pixels is less than 1 s on a typical personal computer.