Automatic Segmentation Method for Segmenting PBGA Package and PWB Regions during Warpage Measurement of Unpainted PWB Assembly

摘要

Among the various warpage measurement techniques, the digital fringe projection (DFP) technique is recent trend because of its noncontact, full-field, and high-resolution measurement capabilities for measuring the warpage of chip packages, printed wiring boards (PWBs), and PWB assemblies (PWBAs). When using the DFP technique, reflective painting is generally sprayed on a sample surface to ensure uniform surface reflectance and to obtain better image contrast for the measurement process. However, because painted samples may no longer be re-used, and the spray-painting process is not suitable inline, warpage measurement of unpainted chip packages, PWBs, and PWBAs using the DFP technique is required. One of the important tasks for measuring unpainted PWBAs is segmentation of the chip package and PWB regions in unpainted PWBA images so that separate warpage of the chip package(s) and the PWB can be determined. In this paper, an automatic image segmentation method that is used to segment plastic ball grid array (PBGA) package and PWB regions in unpainted PWBA images is presented. Because the patterns such as the copper patterns and traces, and inscriptions on a PWBA can cause measurement errors, the patterns and inscriptions are automatically masked out during the segmentation. The method is experimentally tested by segmenting the PBGA package and PWB regions in three different PWBA samples and measuring the warpage of the PBGA packages and the PWB in an unpainted PWBA.