Experimental and FEM simulation study of compressive deformation of solder microballs and particle chains

Beaded microstructures, formed by side-by-side alignment of spherical microparticles, offer a promising approach for creating micropaths with pre-determined electrical and thermal conductivity. Post-processing through mechanical compression effectively modulates the structural and conductive properties, enabling precise control over conductivity by applying defined compressive forces and calibrating strain levels. To investigate the mechanical properties of these beaded structures, this study begins with an in-depth analysis of the compressive response of unconstrained individual solder microballs, representative of malleable soft materials. The study examines the influence of particle size, engineering strain rate, and temperature on compressive force and deformation characteristics. Results from single-particle experiments are then systematically compared with those from beaded structures, revealing distinct mechanical responses. In particular, particle chains require higher compressive forces due to lateral constraints introduced by neighbouring particles, with differences in force values dependent on strain level and also on the number of microballs in the chain. FEM simulations were employed to model stress distributions, contact pressures, and deformation profiles, extending the analysis to deformation scenarios beyond experimental limits. The Johnson-Cook (J-C) model proved to be a robust predictor of compressive behaviour under varying strain rates and elevated temperatures, with temperature exerting a more significant influence than strain rate. Parameterization of the model allowed for accurate replication of empirical scaling behaviours, with strain rate and temperature dependencies from the J-C model closely matching experimental observations. These results expand our understanding of single solder microparticle deformation and offer valuable insights into the deformation of beaded structures, which could be beneficial for practical applications such as the fabrication of electronic components.