The choice of heat sink is obviously important as some have large fins and therefore a large surface area to dissipate the heat. Equally it is important not to mount them directly to a component as this will trap air in any air gaps or voids. Air is a very poor conductor of heat which will in turn make the heat sink inefficient. The use of a Thermal Insulation Material between the component and heat sink will help remove any voids and allow optimum thermal conductivity.