Low Flux Residue No-Clean Solder Paste for System-in-Package (SiP) Application

With the development of electronic packaging heading toward miniaturization, high-density system-in-package (SiP) assembly processes frequently face challenges with flux cleaning when cleanable paste is employed. Given the regularly-occurring issues with cleanable paste, another solution is required. Both ultra-low residue solder paste for die-attach applications and ultra-low residue flux for flip-chip attach have been employed in high-volume production, both of which do not require cleaning after reflow. With this in mind, low-residue no-clean solder paste could be another solution for SiP applications. In this paper, a new solder paste “A” (flux A with fine powder SAC305, Sn96.5Ag3.0Cu0.5, T6SGS) has been designed and applied to SiP. The advantage of using this paste would be the minimal, completely benign flux residue, which could be compatible with molding or underfill material and eliminate the cleaning procedure of the package process. The evaluation for solderability, slump behavior, and printing performance also provides evidence that solder paste A will be an appropriate solder material in the high-density SiP assembly processes.