This study investigates the effects of sintering pressure and joint thickness on the microstructure, shear strength, and fracture behavior of nanosilver joints for high-power electronic applications. Lap-shear specimens with difference joint thicknesses of 50, 70, and 90 µm were fabricated via pressure-assisted sintering under two applied pressures of 1.0 and 1.5 MPa. Mechanical testing revealed that increased sintering pressure and reduced joint thickness significantly enhanced shear strength. Fractographic and microstructural analyses showed that higher pressure improved densification, reduced porosity, and promoted the formation of continuous metallurgical bonds at the Ag/Cu interface. Despite improved bonding, interfacial delamination remained the dominant fracture mode across all conditions. Thinner joints demonstrated more uniform microstructures and higher resistance to crack initiation and propagation, whereas thicker joints exhibited incomplete sintering and stress concentrations that promoted premature failure.