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Out-of-plane displacement (warpage) causes mis-registration, delamination, possibly solder joint opening(s), and other printed wiring board assembly (PWBA) failures during surface-mount assembly processes and life-span operations. Many material, geometry, and process related parameters contribute to the warpage of a PWBA. The objective of this paper is to investigate these parametric effects on PWBA warpage. Based on the parametric study, the identified material, geometry, and process parameters can then be optimized to achieve the most reliable product. In this paper, a PWBA test vehicle consisting of a four-layer PWB and a surface-mount ball grid array package is studied. Its warpage during infrared reflow is measured by the shadow moire´ method to validate finite-element results. The validated modeling results are used for parametric study. In the parametric study, Taguchi and full-factorial design of experiments (DOE) are adopted to systematically vary parameters that are of interest. After running experiments based on DOE, analysis of variance is employed to identify the influential parameters. Thereafter, the warpage data is regressed with respect to the identified influential parameters. According to the regression model, the influential parameters can be optimized within practical range to achieve the least warped design.