FMI applied to the study of the temperature distribution in flip chips

The use of the fluorescent microthermal imaging (FMI) as a tool to study the temperature distribution in flip chip packages was investigated. Backgrinding of the die was required to minimize heat diffusion and maximize the spatial resolution. A test structure was created in order to evaluate the spatial resolution of FMI from the backside of flip chips as a function of the die thickness and of the power dissipation. A lateral resolution of 50 mu m is obtained after polishing the die to a thickness of 5 mu m. At this thickness, the centre of a hot spot can be located with a precision of +/- 5 mu m. For a 5 mu m thick die, the FMI temperature map revealed the heat-sinking effect of the flip chip's solder bumps.