A study on dimensional variation in flexible printed circuits during post-lamination baking

The dimensional shrinkage for single-layer flexible printed circuit (FPC) panels measured after post-lamination baking has been evaluated experimentally and using a finite element model. Experiments and modelling for dot hatch flexible printed circuit panels show a linearly decreasing dimensional change with increasing copper fill percentage. Across three material suppliers, there is a strong variation in dimensional change for a given FPC design. A finite element model has been developed to simulate the shrinkage due to the volumetric contraction of the epoxy adhesive. The model fits well with the experimental data for low to medium copper fill percentages, but further work to incorporate the dimensional variation in the copper is required to improve accuracy at high copper fill percentages. The model indicates that adhesive shrinkage plays an important role in the overall dimensional change in FPCs.