Multiscale Micromechanical Study of Polymer Core Solder Ball for BGA Interconnections Reliability

Polymer core solder balls (PCSB) are among the most promising lead-free solder solutions for the optimization of assembly reliability. This type of solder ball is produced through electroless plating processes, which result in specific deposit microstructures as well as unique mechanical properties. However, the properties of bulk materials are often attributed to them, leading to inaccurate predictive modeling of interconnection lifespan. This study focuses on the mechanical characterization of PCSB across representative scales. First, at the microscopic scale, the characterization of the mechanical properties (Young's modulus (E) and yield strength (σ)) of two coatings (Cu, Ni-P) is conducted by in-situ micro-mechanical tests (micropillar compression and nanoindentation). Then, at the mesoscopic scale, the aforementioned properties are validated by applying a compressive load to a PCSB solder ball. All these mechanical data were then used to feed predictive models of assembly service life. Finally, a comparison was made between PCSBs and standard SAC balls in terms of interconnection fatigue life.