New Equivalent Approach and Optimized Strategy for Evaluating Warpage Characteristics in PCB Milling Process

In the production of large-scale multi-layer Printed Circuit Boards (PCBs), warpage is a common phenomenon that can lead to various reliability issues during assembly and packaging, ultimately affecting the quality and yield of the final products. This study aims to provide a comprehensive assessment of PCB warpage during the milling process by examining the underlying stress and strain mechanisms. A novel equivalent method of the milling process was developed, and the impact of milling process on PCBs under static conditions were analyzed using finite element analysis (FEA). The research concentrated on the warpage evolution and the forces exerted at the milling boundaries. Both the Rectangular Plate (RP) model and the Notched Rectangular Plate (NRP) model were employed to simulate the lamination and milling processes. The high level of morphological agreement between the simulation results and the measurements from shadow moiré analysis substantiates the validity of this approach. The average error in warpage values was found to be 3.4%, verifying the reliability and accuracy of the simulation. Additionally, the impact of differences in stiffness between the milled and residual areas on PCB warpage was discussed.