With the increasing requirement to analyse structures with great complexity and significant size, existing electromagnetic analysis tools are showing their limitations. For instance, an integrated circuit together with its interconnects and package presents a considerable challenge. Methods which can be used include the finite difference time domain (FDTD) method which is versatile and general but which has impracticable computational requirements for structures with fine detail. In this contribution, an existing thin wire formalism is generalised in order to allow complete microstrip and printed circuits to be modelled in an efficient and rigorous manner.