An automated on-line warpage measurement system for printed wiring board assemblies (PWBAs) has been developed. The system is capable of simulating an infrared reflow soldering process and performing real-time PWBA warpage measurements using the shadow moire´ technique. The system can be used to characterize the warpage behavior of virtually any PWBA during infrared soldering processes as well as during operational conditions. Using this system, warpage of PWB test vehicles was measured during simulated infrared reflow soldering. The measurement results and the measurement system will be presented. The measured warpage varied significantly during reflow soldering from that observed both before and after reflow. These results help us to understand how the board deforms at every stage of the reflow process.