Steady state and transient thermal characterization for flip chip interconnection on flexible substrate

As flexible electronic applications gain more and more research interests, the thermal management issues related to these become more critical. This paper quantifies the thermal resistance of flip chip interconnection on flexible substrate by both simulation and experimental measurements. For the simulation, both finite element method (FEM) and computational fluid dynamics (CFD) are used. Measurements are employed in both steady state and transient state conditions. Results reveal that thinner flex substrate is a poor thermal conductor and one of the key factors in improving thermal performance is the amount of copper in the substrate, as this acts as a heat spreader to remove heat over a larger area. The module without backside metallization has a significant amount of heat conduction through the copper tracks, while for the module having backside metallization, the main portion of heat is spread over the backside metallization. Thermal resistance is also boundary-dependent: it is smaller in cold-plate condition, while 5-15 times higher at natural convection condition. The backside copper metallization plays an important role under natural convection condition, while this influence is not pronounced under cold-plate conditions.