Orthotropic thermal conductivity and Joule heating effects on the temperature distribution of printed circuit boards

A printed circuit board (PCB) comprises alternating layers of dielectric material and current carrying traces and vias. As performing system-level simulations of PCB's with detailed trace and via geometries is very costly, the present approach considers the effects of the trace and via geometry in the physical model by importing ECAD data consisting of the trace and via layout of the board and determines locally varying orthotropic conductivity (k_x, k_y and k_z) on the printed circuit board based on the ECAD data. In addition, the present approach considers the effects of Joule heating in the current carrying traces by utilizing multiple 2-D sources where the powermap is determined by solving the governing electric field equations on the trace. In this paper, the effects of both trace layer orthotropic thermal conductivity and Joule heating are studied on a sample PCB. Comparisons are made with earlier studies and conventional models when possible. It is shown that location of the hot spots and temperature values differ substantially if different methods are used.

NOMENCLATURE

e

specific thermal internal energy, JIkg

E

electrical field, Vim

j

electric current density, A/m^L

k

thermal conductivity, W Im.K

P

pressure, Pa

T

temperature, K

u

velocity, m/s

x,y,z

coordinate, m