Electro-Hydro-Dynamic-Force-Driven Filling Method for Through Polymer Substrates Via With Ag-Based Conductive Epoxy

Through polymer substrates via (TPSV) plays an important role in system integration for not only silicon-based devices but also emerging flexible electronics implemented with polymer substrates. Conventional electroplating approach for filling TPSVs encounters high cost and environmental issues such as complex preprocessing, long deposition time, heavy metal ions, and pollutant side-products from the electrolytes. To tackle these challenges, this work presents an electro-hydro-dynamic-force (EHDF) driven filling method for TPSVs with conductive polymers. A customized bench-top setup is implemented to demonstrate the feasibility of the filling method. The proposed EHDF-driven filling technique can fill TPSVs of various aspect ratios (ARs) completely within 1 min, utilizing electrostatic fields. We established an empirical model for the correlation of the driving voltage and filling depth for various substrate thicknesses and TPSVs ARs. The experimental results show that the resistance of filled TPSVs is proportional to their AR. The lowest resistance is about $1~\Omega $ for the TPSV with an AR of 1. The conductive property of EHDF-filled TPSVs is only limited by the intrinsic resistivity of the filler material, therefore, demonstrating promising application potentials in emerging devices integration.