BGA STIM package architecture for high performance systems

Embodiments include semiconductor packages and methods of forming such packages. A semiconductor package includes a die on a package substrate, an integrated heat spreader (IHS) on the package substrate and above the die, and a solder thermal interface material (STIM) coupling the die to the IHS. The semiconductor package includes a low-temperature solder (LTS) paste comprising an alloy of tin and bismuth (Bi), and the LTS paste on a bottom surface of the package substrate having a ball grid array. The LTS paste may have a weight percentage of Bi greater than 35% and a melting point less than or equal to a melting point of the STIM, where the STIM includes indium. The weight percentage of Bi may be between approximately 35% to 58%. The semiconductor package may include a solder ball coupling the LTS paste on the package substrate to the LTS paste on a second package substrate.