This article presents a computational investigation on prediction of limiting conditions of temperatures that withstand on the substrate for the safe operation of electronic equipment. Conjugate laminar passive air cooling of fifteen idential aluminum heated blocks mounted in a vertical channel are studied. For passive cooling of isothermal heated blocks on substrates of different materials in a vertical channel subjected to uniform heat flux values of 1500, 5000, and 7500 W/m² are applied. The configuration that results in a minimum temperature was considered from the literature. It consists of fifteen square heated modules of size 15 × 15 × 5 mm arranged on a multilayer copper clad boards of thermal conductivities 13.5 and 59.5 W/m K, respectively. The commercially available software Comsol Multiphysics 5.4 is used for computational work. Results shows heat transfer enhanceent using multilayer copper clad board of 59.5 W/m K. The limiting conditions for both the substrates dissipating heat in the range between 10-55 W are presented. The heat flux values used to predict the maximum heat transfer for safe operation of electronic devices in all cases considered in this study.