indium solder TIM as a function of integrated heat spreader metallization thickness, TIM bond line thickness, and die size. Also studeied were the steps taken to improve its temperature cycle performance. Analyses were performed using thermal resistance measurements, scanning-electron microscopy, scanning-acoustic microscopy, and transmission-electron microscopy to characterize the solder TIM thermal performance, interfacial microstructure, and failure mechanisms.

In the present study, the thermal performance of flip chip electronics packages was evaluated by characterizing the amount of voiding present in the Solder Thermal Interface Material (STIM) which is placed between the die and Integrated Heat Spreader (IHS). The study found that the thermal resistance, Rjc (resistance between the Si die and IHS), is dependent upon the amount of voiding present as well as the location of the voiding in the STIM. The study also described the techniques to reduce the STIM voids in flip chip packages and identified the key process parameters to improve the thermal performance. The process parameters varied in this study consisted of STIM thickness, dwell time and temperature, flux weight, and many others. A detailed DOE and statistical analysis were carried out to determine the impact of the parameters mentioned above toward reducing the quantity of voids in the STIM. The analysis showed that for the packages under consideration, the primary process parameters that affect the STIM voiding are cure time, flux weight and TIM thickness.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.