In this paper, a preconditioning technique based on the null field method is presented to accelerate the convergence of fast near-linear complexity iterative Method of Moments (MoM) solution. For large-scale package-board 3D full-wave parasitic extraction, the solution time is often prohibitive for use in a design-cycle which might necessitate several analysis stages. The bottleneck is often the slow-convergence of the Krylov subspace-based iterative solution. Since the null field method scales the near field interactions to a block-diagonal form it can be used as an efficient preconditioner as shown in the numerical experiments.