In this paper, we show analytically how to optimize the spacing between heat generating boards in a stack cooled by single-phase laminar forced convection. The thickness of each board is not negligible. The theoretical results for optimal spacing and maximum overall thermal conductance between stack and coolant are validated by means of numerical simulations of the complete flow and temperature fields. Results are reported for three different situations, which are dictated by the way in which the stack is attached to the rest of the cooling network of the electronics package : (1) fixed pressure drop, (2) fixed mass flowrate, and (3) fixed pumping power. © 1993.