An optical method for measuring the two-dimensional surface curvatures of electronic packages during thermal cycling

An optical method was developed to measure the two-dimensional (2D) surface curvatures of electronic packages by employing four laser beams. Each lase r beam measures the slopes of the surface at the incident point along two p erpendicular directions. By combining four pairs of slopes, the 2D surface curvatures of the package can be calculated. The surface warpage of an unde rfilled flip-chip package during thermal cycling was measured by this metho d and the result was verified by finite element analysis (FEA). Both experi mental and FEA results show that the surface warpage is almost a linear fun ction of temperature between 25 degreesC and 150 degreesC for the measured package.