Structure light measurement for a BGA packaged chip with high-precision and large field-of-view

Ball grid Array (BGA) packaging is one of the mainstream chip packaging modes. The deviation of solder ball height can significantly affect the safety and reliability of packaged chips and may even lead to chip failure. To efficiently and accurately measure the height of solder balls on large-sized square BGA chips, a large field-of-view (FOV) and high-precision structured light measurement system is constructed in this paper. The influence of fringes with different contrast and gamma nonlinearity on three-dimensional (3D) reconstruction height is simulated to determine the boundary conditions of fringe quality. Based on these boundary conditions, the projection clarity and spot shape of the oblique projection lens are optimized according to the Scheimpflug principle. This effectively solves the problems of unbiased axis and low utilization of projection in traditional structured light projection lenses and enables high-precision fringe projection on large-sized square BGA chips. Aiming at the abnormal height measurement problems caused by the high reflectivity and occlusion of the solder ball, an improved fusion algorithm is proposed, which can accurately fuse height data from multi-directional 3D reconstruction data. The measurement system has an FOV of 95mm×95mm, a measurement accuracy of 1.4 µm for a standard plane, and 4.7 µm for BGA solder balls. The results show that this system can perform high-precision detection of the height of solder balls on BGA chips, especially large-sized square chips.