Two solder pastes, used in an electronic card assembly process, were investigated under both oscillating and continuous shear fields, in order to characterize their viscoelastic and plastic properties. A further study on the vehicle used for the formulation of a paste was carried out in order to isolate the contribution of the disperse phase to the rheological properties of the corresponding system. The stress conditions for the departure from linear viscoelasticity and the transition from the solid- to liquid-like behavior, respectively, were defined on the basis of creep and oscillatory data. Appreciable elastic components were exhibited by the pastes examined, particularly at low stress conditions and, hence, can affect their screening performance. The contribution of the disperse phase is almost negligible at low shear or frequency, despite the high content of the disperse phase, and increases with increasing strain rate or frequency, essentially concerning only the viscous properties of the paste. This means that the rheological properties of the paste can be properly modulated by adjusting the formulation of the vehicle.