Warpage Measurement of Board Assemblies Using Projection Moire System with Improved Automatic Image Segmentation Algorithm

Abstract

Out-of-plane displacement (warpage) has been a major reliability concern for board-level electronic packaging. Printed wiring board (PWB) and component warpage results from CTE mismatch among the materials that make up the PWB assembly (PWBA). Warpage occurring during surface-mount reflow process and normal operations may lead to serious reliability problems. PWB/PWBA warpage can be measured by many different optical techniques, among which moire methods have emerged as real-time, non-contact, full-field, and superior techniques with high resolutions. In this paper, a warpage measurement system based on the projection moire technique and improved automatic image segmentation algorithm is presented. In order to use the projection moire system to accurately and separately determine the warpage of a PWB and assembled chip packages in a PWBA, a novel automatic image segmentation algorithm is discussed in this research. The algorithm uses mask image models to detect and segment assembled packages from the PWB, and defines their warpage respectively. The approach achieved much higher resolution and higher processing rate compared with the original algorithm based on snakes. The warpage of the PWB and chip packages in a PWBA can be determined individually despite the package locations and orientations. Real-time continuous and composite Hermite surface models were generated to evaluate the PWB warpage values underneath packages. The improved segmentation algorithm was integrated with the projection moire system to evaluate the warpage of PWBs and populated chip packages respectively and accurately.