Warpage and curvature determination of PCB with DIMM socket during reflow process by strain gage measurement

Abstract

The purpose of this study is to in-situ measure the warpage of the PCB with surface-mount dual in-line memory module (DIMM) sockets during reflow process by using strain gages. In the experiments, a full-field shadow moire is used for measuring real-time out-of-plane deformations (or warpage) of the PCB with DIMM sockets under heating condition. A finite element method (FEM) is used to analyze the thermally-induced deformation of the PCB with DIMM sockets in order to ensure the validity of the measurement. The conventional strain gages and rosette are employed to in-situ measure the strains (even though they are in-plane strain data) in this PCB specimen during the solder reflow process. The results indicate that the strain gage measurement can be used to determine the bending strains of the PCB occurring during the solder reflow. These bending strains can be transferred to curvature data and global warpage. Therefore, it provides a real-time and easy-to-use method for monitoring the PCB warpage under temperature variation during the reflow process. In addition, the strain gage rosette has been successfully proved to be an enabling measurement of the local and full-field deformation of the PCB with DIMM socket during reflow process.