Evaluating thermal packaging concepts using thermal impedance

The thermal performance of a new electronic system must usually be determined long before details of the design are available. However, an exact thermal analysis is not possible without a computer model of a dimensioned design. Therefore, during the early design stages, it is necessary to use basic equations for the verification of design concepts to obtain an answer to the question Can the system be designed within given limits to operate without overheating? During the early investigation, it is sufficient to represent the thermal characteristics of a system by a resistance model. The total thermal path can be divided in three parts and each part can be represented by a thermal impedance value. The three parts of the thermal path are related to temperature differentials occurring in three separate design areas 1. the internal temperature drop between the heat sources and the heat transfer surface, 2. the temperature drop between the heat transfer surface and the cooling medium and 3. the average temperature increase of the cooling medium. The paper presents an approach based on thermal impedances for the design of cooling concepts of electronic subsystems.