Except in specific activities in electronic equipment, thermal management is not the most exciting subject for those involved in design. With micro-assembly (surface mounting of components) the cooling of components and PCB is now being seen in a new light. This paper, very rapidly, highlights the problems every designer has to take into account today. Solutions are checked and the importance of simulation, an economical and powerful tool for evaluation, is enhanced. An example of the method is mentioned, followed by a calculation. Components and basic materials manufacturers may also find some ideas as to the development of new and/or improved products.