Reduced thermal stress in composites via negative thermal expansion particulate fillers

The use of negative thermal expansivity (NTE) particles as composite fillers is relatively new and the particle–matrix interface is not well studied. This lack of understanding of the particle–matrix interface is further complicated as in many engineering applications, such as microchip packaging, the composite is constrained by its surroundings and is not free to expand upon heating; an important consideration that is often not taken into account. This paper presents a systematic theoretical study of the behaviour at the particle–matrix interface under varying particle coefficient of thermal expansivity (CTE), Poisson’s ratios (including negative Poisson’s ratios), Young’s moduli, boundary conditions and particle separation distances via finite element modelling, and describes how to optimise composite formulation for problems of thermal mismatch through tailoring of particle–matrix interaction. The effects of reduced CTE are explored via models of electronic chip package assembly.