State-of-the-art LC filter design of Buck DC-DC converter is based on the specifications of voltage and current ripples and constraints in power density and cost. Since lifetime is an important performance factor in reliability critical applications, this digest proposes a method to optimize the design of the LC filters from a reliability perspective among other considerations. It investigates the design freedom between the values of inductor and capacitors, the physical formation of the LC network, and the corresponding electro-thermal stresses of the selected capacitors. The outcome enables an optimized LC filter design to fulfill the required lifetime. The theoretical analysis and simulation study are presented which are verified by the experimental results from a Buck converter prototype.