  The exchange coupling between Fe layers separated by BCC Cu is calculated for
Fe/Cu/Fe (001) trilayers. It is shown that the coupling is basically regulated
by three extrema of the bulk BCC Cu Fermi surface. The contributions from those
extrema are all of the same order of magnitude, but that associated with the
``belly'' at the $\Gamma$-point dominates. The calculated temperature
dependence of the coupling varies considerably with spacer layer thickness.
Individually, the amplitudes of these extrema contribution decrease with
temperature, each according to a different rate. Such an effect may cause an
actual increase of coupling with temperature for some Cu thicknesses.
