Thermal management for stackable packages with stacked ICs

In mobile electronic devices an increasing number of functions have to be placed on a limited space. The stacking of ICs and packages becomes more and more common. A rising number of contacts on the same foot print leads to higher current densities and may conduct to electromigration induced reliability problems. Migration processes are strongly temperature depended. Therefore the thermal management within IC packages becomes more important to ensure an appropriate lifetime. The existence of heat sources in a package changes the temperature distribution and the values of the correlated mass flux and mass flux divergences due to electromigration. For this work the electromigration induced mass flux divergences in SAC305 solder joints for stackable packages were investigated by using the finite element software ANSYS® and a user routine. For the finite element simulation a structure of two stacked packages including a top package with two, four, six or eight stacked ICs were modelled. Two different scenarios were considered: firstly the total power loss of 2W was independent of the number of ICs. Secondly every single IC had a power loss of 222mW.