What is a thermal contact resistance?
The general definition of a thermal resistance is very simple. It is the ratio of a temperature difference and a heat flow. This is not a problem for well conditioned laboratory cases but as shown above, it is often problematic in applications. The main dilemma is the temperature difference definition. It is easy to make all kinds of definitions, (a definition is by definition always correct), but it is very difficult to make them purposeful. Figure 7 The sandwich method. The truth of the matter is that the thermal contact resistance concept rarely can be used for applications. An alternative approach is the sandwich method, figure 7. It consists of including parts of the surrounding structures in a thermal resistance definition. For a package it typically results in a Rj-s value, (junction-to-heat sink). The basic idea is to push the temperature definitions away form the contact surface, where the temperature gradients are high, onto surfaces with more uniform temperatures. Such surfa
