Analyzing thermo-mechanical reliability of an interconnect based on metal coated polymer spheres (MPS)

In this study, we explore the thermo-mechanical stress distribution of a chip/substrate BGA interconnect based on metal coated polymer spheres (MPS) of 30 μm diameter. The bonding of the chip to a glass substrate with MPS is obtained by deposition and sintering of a silver nanoparticle suspension that forms a menisci needed for necking and metallic bonding of the MPS towards pads. The stand-off height is determined by the ball diameter, thus the necks and the MPS coating are considered to be the critical parameters of the system. The simulation study is focused on varying the shape and the size of the neck and the MPS coating thickness. The polymer core is modeled as a viscoelastic material using generalized Maxwell model with Prony series. The distribution of the relaxed thermal stress and strain within the MPS coating and necks is analyzed as a function of temperature and the identified critical parameters. Moreover, shear test measurements of single MPS and SEM images of the structures are presented and discussed, in order to expose the feasibility of this new interconnect technology.