A 3-dimensional model of internal charging simulation

To break through the limitation of the traditional 1-dimensional (1-D) method of internal charging computation, a 3-D calculation model of internal electric field and potential for arbitrary configuration dielectric with complex boundary conditions is developed. It includes two steps: 3-D electron transport simulation and internal electric field computation. The transport simulation, which aims for obtaining electron deposition and dose rate distribution, is implemented by a self-developed software founded on GEANT4. And the calculation of 3-D internal electric field, which takes above transport results as input, is conducted through solving a set of electrostatic equations by the software COMSOL Multiphysics. In this paper, this 3-D simulation model applied to a typical printed circuit board grounded on a rectangular circuit and cylindrical pin will be presented. For purpose of comparison, a simpler 1-D planar dielectric wholly grounded on the back surface is simulated in the same method. Finally, the electric field computed by the 3-D algorithm is much larger than the 1-D simplified method widely used at present and hence the 1-D method may neglect crucial risk. Besides, the following conclusions are drawn: grounding has significant influence on electric field distribution, and the maximum field generally occurs at grounding edges or corners. Increasing the curvature radius of the circuit corner can reduce the field and the discharge risk.