High-accuracy three-dimensional shape measurement of micro solder paste and printed circuits based on digital image correlation

There is an urgent demand for high-accuracy, real-time three-dimensional (3-D) shape measurements in industrial production as an ideal tool for quality control. Based on 3-D digital image correlation (3D-DIC), in this study, we measured micro-stair-steps of solder paste and printed circuits on circuit boards. The 3-D shapes of the circuit boards were successfully reconstructed, and the shapes of both solder paste and printed circuits were identified with high accuracy. To evaluate the performance of the 3D-DIC method, a stylus profiler was used to conduct shape measurements for printed circuit boards (PCBs), and comparisons were made between the results of 3D-DIC and the stylus profiler. The experimental results demonstrate that: (1) printed circuits with a length of several tens of microns can be measured with an accuracy of 3 mu m using 3D-DIC in a field of view of 14 x 12 mm(2); (2) the time required for 3-D reconstruction was less than 1 s for a 500 x 500 image with a grid step of 3 and a subset size of 19 on a consumer-grade computer (i7 4790k CPU, 16 GB of memory), thus meeting the requirements of online and real-time shape measurements of PCBs; and (3) for printed circuit measurements, the subset size chosen should be close to or slightly larger than the width of the printed circuit. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)