Re: 3D MOM problem
For non-singular integrations (non-overlapping triangles) you should use a N-point gaussian quadrature rule. 1, 4 and 7 point rules are very common.
For overlapping triangles (EFIE formulation) you should use singularity extraction. For the analytic part you can use the relationships in the following paper:
T. F. Eibert and V. Hansen, "On the Calculation of Potential Integrals for Linear Source Distributions on Triangular Domains," IEEE Trans. Antennas Propag., vol. 43, pp. 1499-1502, Dec. 1995.
Best of luck.