An Optical Method for Measuring the Two-Dimensional Surface Curvatures of Electronic Packages During Thermal Cycling

Abstract

An optical method was developed to measure the two-dimensional (2D) surface curvatures of electronic packages by employing four laser beams. Each laser beam measures the slopes of the surface at the incident point along two perpendicular directions. By combining four pairs of slopes, the 2D surface curvatures of the package can be calculated. The surface warpage of an underfilled flip-chip package during thermal cycling was measured by this method and the result was verified by finite element analysis (FEA). Both experimental and FEA results show that the surface warpage is almost a linear function of temperature between 25°C and 150°C for the measured package.