A computational macro and micro thermal model of a printed circuit board dielectric breakdown due to local and global heating of the laminate material is presented in this paper. On a macro level, under certain conditions, the circuit board temperature can approach the glass transition temperature (Tg) due to electronic surface mounted components dissipating heat to the board surface. Under these conditions interfacial micro cracks or dielectric inhomogeneities can be aggravated to an extent where localized voltage breakdown can occur across copper planes within the board. The micro thermal modeling results demonstrate that even under relatively high defect resistance levels the localized temperature at the defect site can greatly exceed the Tg of the dielectric material resulting in carbonization and eventually catastrophic failure. A temperature profile at the defect site clearly shows the spike in the local temperature due to the low thermal conductivity properties of the dielectric material and the localized high current density. The thermal modeling was performed using Flotherm (trademark of Flomerics Limited) code.