Measurement of thermally induced warpage of BGA packages/substrates using phase-stepping shadow moire

A phase-stepping technique is applied to the analysis of fringe pattern images of BGAs (ball grid arrays) obtained by shadow moire interferometry. The sensitivity of the fringe pattern analysis is shown to be significantly increased. Thermally induced warpage of BGAs is successfully measured in real-time as the sample is driven through a simulated reflow process. The paper discusses the technique of phase stepping and its application to the shadow moire method. Applications of the technology are presented.