Thermal characterization of multichip structures

The advances in electronic packaging made it possible to encapsulate several independent semiconductor dice into a single package. In the last decade many packaging configurations are realized which range from the multichip modules to the 3D stack-die structures. Thermal aware design of such structures become complex, though. To understand the thermal behavior of multichip structure containing multiple dissipating elements placed on different dice, the couplings between individual dice have to be characterized. To determine their thermal transfer impedance matrix (TTIM) is a practical way to describe the thermal relations. In this paper we demonstrate the method utilized for TTIM measurements and also show how thermal surroundings (e.g. the PCB the chip is mounted on) affect the thermal relations inside the package. In addition, the temperature dependent non-linearity of the TTIMs is also described.